Detailed Office Action
Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status.
Examiner’s Comment
Claim 2 recites: “the first electrical impedance value is between a portion of the first electrode corresponding to the optical input of the first waveguide and a portion of the second electrode corresponding to the optical input of the second waveguide.” This appears to describe an electrical ‘characteristic’ as a physical location ‘between’ two electrode portions. For the purposes of this Office action, claim 2 will be read as comprising ‘the first electrical impedance value corresponds to impedance characteristics of the region connecting (a) a portion of the first electrode corresponding to the optical input of the first waveguide and (b) a portion of the second electrode corresponding to the optical input of the second waveguide.’
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102 of this title, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
The factual inquiries set forth in Graham v. John Deere Co., 383 U.S. 1, 148 USPQ 459 (1966), that are applied for establishing a background for determining obviousness under 35 U.S.C. 103 are summarized as follows:
1. Determining the scope and contents of the prior art.
2. Ascertaining the differences between the prior art and the claims at issue.
3. Resolving the level of ordinary skill in the pertinent art.
4. Considering objective evidence present in the application indicating obviousness or nonobviousness.
This application currently names joint inventors. In considering patentability of the claims the examiner presumes that the subject matter of the various claims was commonly owned as of the effective filing date of the claimed invention(s) absent any evidence to the contrary. Applicant is advised of the obligation under 37 CFR 1.56 to point out the inventor and effective filing dates of each claim that was not commonly owned as of the effective filing date of the later invention in order for the examiner to consider the applicability of 35 U.S.C. 102(b)(2)(C) for any potential 35 U.S.C. 102(a)(2) prior art against the later invention.
Claims 1-14
Claims 1-14 are rejected under 35 U.S.C. 103 as being unpatentable over Meighan et al. (Microwave model for optimizing electro-optical modulation response of the Mach-Zehnder modulator, Session Poster 3 Optoelectronic devices and Integrated photonic circuits, ECIO 2020, 22 June 2020; “Meighan”), as evidenced by Pascher et al. ( Design and integration of MZI modulators and AWG-based multiwavelength lasers in InP, URSI General Assembly 2005, 23-29 October, New Delhi; “Pascher”) and Sadiq et al. (Efficient modelling approach for an InP based Mach-Zehnder modulator, 25th IET Irish Signals & Systems Conference, 2014, pp. 123-128; “Sadiq”), in view of Aimone, Alessandro (InP Segmented Mach-Zehnder Modulators with Advanced EO Functionalities, Doctoral Dissertation, Technischen Universität Berlin, 2016; “Aimone”), further in view of and further in view of Eghlidi et al. (Analytical Approach for Analysis of Nonuniform Lossy/Lossless Transmission Lines and Tapered Microstrips. IEEE Transactions on Microwave Theory and Techniques. 2007; “Eghlidi”), and further in view of Stiles, Jim (Tapered Lines, Dept. of EECS, University of Kansas, 2010; “Stiles”).
Regarding claim 1, Meighan discloses in figure 1, and related figures and text, for example, Selected Text, .optical waveguide embodiments characterized by p-i-n structures configured such that one axis is defined by the light guiding path (called Beam Axis, for the purposes of this Office action) while a second axis is defined by a vertical line through and normal to the p-i-n structure (called Vertical Axis, for the purposes of this Office action). See below, Meighan, figure 1 and Selected Text (“The optical waveguide includes a p-i-n structure with an intrinsic core layer and p-cladding and n-cladding layers above and below. A highly doped InGaAs ternary-layer (p-contact) is between the p-metal and p-cladding to minimize the contact resistance. The signal p-metal line is located above the optical waveguide, and the two n-metal ground lines are offset from the waveguide on the n-bottom layer. The length of the reference design is 1mm, and the gap between ground and signal is 11μm.”). And Meaghan discloses embodiments of models related to the optical waveguide embodiments. See below, Meighan, figure 1 and Selected Text (“The frequency response is assessed in terms of the electrical transmission along the transmission line from the source to termination, the characteristic impedance, and the modulation index 𝑀(𝜔)…. The model is created to study the role of impedance matching in indium phosphide modulators. The frequency-dependent characteristic impedance and propagation constant of the electrical transmission line structure is calculated from the cross-section of the phase modulator, electrode geometry, and p-i-n junction.”).
Regarding Meighan’s waveguide embodiments, Pascher evinces in figures 2 and 3, and related figures and text, for example, Selected Text: the p-i-n’s electric field distribution aligns with the Vertical Axis. ). See below, Pascher, Selected Text (“The microwave electrical field distribution for the optimized design, namely in the region of the signal electrode is presented in Fig. 3. Due to the pin-structure of the optical waveguide, the microwave field is mainly across the depleted region, which consists of the upper part of the film layer and the intrinsic layer. The mode observed is nearly a microstrip mode because of the comparatively high conductivity of the n-doped buffer layer, which behaves like a ground plane.”).
Regarding Meighan’s waveguide embodiments, Sadiq evinces in figure 2, and related figures and text, for example, Selected Text: “Increasing the signal electrode width (Wmetal) decreases the inductance which in turn reduces Z0. In order to maintain the value of inductance, the gap between electrodes has to be increased as well at the cost of a slight increase in microwave loss. The best optimised solution is to microwave loss. The best optimised solution is to keep the signal metal width same as the ridge width. However, for the ease of fabrication process it is better to keep the signal electrode slightly wider than ridge…” and “Ridge width has effects on all the resistive, capacitive and inductive elements of the CPW transmission line. Reducing the ridge width will decrease the capacitance due to intrinsic region but at the same time will increase the CPW line inductance and impedance. The most prevailing effect here is the reduction in capacitance due to intrinsic region which results in low microwave loss, low index and high impedance.” See below, Sadiq, Selected Text
The p-i-n’s lateral dimension (width) defines a third axis (called Lateral Axis, for the purposes of this Office action) that is simultaneously orthogonal to the Beam Axis and to the Vertical Axis.
Further regarding claim 1, Aimone discloses in figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text, p-i-n waveguide embodiments:
A second p-i-n waveguide aligns with Beam Axis (hence, perpendicular to Vertical Axis and Lateral Axis) while lying in a plane defined by Beam Axis and Lateral Axis. See below, Aimone, figure 2-3.
Each p-i-n waveguide’s junction’s capacitance is proportional to the ratio (waveguide width):(depletion region thickness). Aimone, Selected Text (“Due to the strong doping of the junction p- and n-layers in the employed InP technology, the depletion region does not extend significantly into these areas and is thus approximated by the physical intrinsic region thickness IRT.”) See below, Aimone, equation 3-3. Here, the examiner notes that waveguide width is ‘measured’ along the Lateral Axis while depletion region thickness is ‘measured’ along the Vertical Axis.
Electrode width and waveguide width are related parameters when designing phase-shifting p-i-n waveguide embodiments.
Tapered waveguide structures facilitate having different waveguide widths (measured along the Lateral Axis) at different points along the Beam Axis. Aimone, figure 3-17 and Selected Text (“The integration of different waveguide widths in the same modulator entails the need for tapering structures in between consequent active sections and along the individual interferometer arms. An abrupt transition in the propagation layer not only causes optical power losses and reflections, but also causes energy to be transferred to different guided modes.”).
Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text.
Consequently, it would have been obvious to one of ordinary skill in the art to modify Meaghan’s p-i-n waveguide embodiments, as evidenced by Pascher and Sadiq, to disclose tapered ridge waveguides (intrinsic regions tapered laterally and/or vertically); See below, Aimone, figure 3-17; and the related tapered electrodes (including potential changes in the gaps between signal electrodes (top electrodes of adjacent p-i-n waveguides) and between signal and ground electrodes; see below, Aimone, figures 3-4 and 3-5; because the resultant device and method embodiments would facilitate designing, fabricating and deploying indium phosphide modulators. Meaghan, abstract (“A model is created to study the role of impedance matching in indium phosphide modulators. The frequency-dependent characteristic impedance and propagation constant of the electrical transmission line structure is calculated from the cross-section of the phase modulator, electrode geometry, and p-i-n junction.”)
Further regarding claim 1, Eghlidi discloses in figure 8 and table 1, and related figures and text, for example, Selected Text, device (and related method) embodiments of nonuniform transmission lines (widening and/or narrowing (Lateral Axis) tapers along the Beam Axis propagation direction. See below, Eghlidi, Selected Text (“[The], distribution of voltage along a general nonuniform transmission line is expanded in an appropriate form, and by employing an approach similar to conventional and modified differential transfer matrix methods already proposed for optical structures, analytical expressions are obtained for voltage/current distributions and reflection/transmission coefficients.”) and (“Tapered microstrip lines have been extensively used in many applications and play an important role in microwave engineering. These lines can be characterized by simple circuit models, whenever the fringing fields are negligible and only the dominant or quasi-TEM modes propagate along the line. In this section, the model … is employed to obtain the variation of the microstrip effective dielectric constant and characteristic impedance as a function of the width-to-height ratio …It should be noted that this model also takes the nonzero strip thickness and dispersion into account.”).
Consequently, in light of Eghlidi’s disclosure of tapered microwave transmission line’s ‘variations of … characteristic impedance as a function of the width-to-height ratio,’ it would have been obvious to one of ordinary skill in the art to modify Meaghan, as evidenced by Pascher and Sadiq, in view of Aimone’s p-i-n waveguide embodiments (and related methods) to disclose an electro-optical modulator for a photonic integrated circuit, comprising: a substrate; a first waveguide on a first portion of the substrate; a first electrode; a second waveguide on a second portion of the substrate; and a second electrode, wherein a first electrical impedance value between the first electrode and the second electrode is different from a second electrical impedance value between the first electrode and the second electrode, the first electrical impedance value along a first axis perpendicular a light propagation axis of the first waveguide, and the second electrical impedance value along a second axis perpendicular the light propagation axis of the first waveguide, the first axis spaced from the second axis along the light propagation axis of the first waveguide; Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; because the resultant device and method embodiments would facilitate predictably tailoring electrode widths, tapers, impedance, and bandwidth; Stiles, selected figures and text; while designing, fabricating and deploying indium phosphide modulators. Meaghan, abstract.
Meighan, Figure 1 and Selected Text
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ABSTRACT. A model is created to study the role of impedance matching in indium phosphide modulators. The frequency-dependent characteristic impedance and propagation constant of the electrical transmission line structure is calculated from the cross-section of the phase modulator, electrode geometry, and p-i-n junction. The impedance and propagation constant are used in combination with a closed-form approximation for the traveling wave electrode and electrical circuit to create the non-iterative compact model. It yields good agreement with the experiment in a 50 Ohm measurement environment and the effect of changing source and termination impedance has been modeled. The 3dB optical modulation bandwidth is predicted to increase from 30GHz to 60GHz with optimized impedance matching and the associated suppression of electrical reflections
2. MZM MODEL
The reference modulator used for validating the model is a hybrid co-planar waveguide (HCPW) MZM design, where the electrodes are in two different planes above and below the p-i-n junction. The MZM is connected to the source and termination with electrical coplanar waveguide probes. Figure 1.a is the schematic of the single drive HCPW-MZM. A source is applied to the central (signal) electrode with respect to the two ground lines of the HCPW structure. 𝑍𝑠 is the source impedance of the electrical driver, and 𝑍𝑡 is the termination impedance at the output of the MZM traveling wave electrode. The reference design has the cross-sectional parameters shown in Table 1 and Figure 1b. The model does not include bond-pads and tapers for electronic connections because it is intended to explore the ultimate technology limits of the inherent modulator itself. The model input consists only of parameters that can be directly controlled and specified in fabrication.
The optical waveguide includes a p-i-n structure with an intrinsic core layer and p-cladding and n-cladding layers above and below. A highly doped InGaAs ternary-layer (p-contact) is between the p-metal and p-cladding to minimize the contact resistance. The signal p-metal line is located above the optical waveguide, and the two n-metal ground lines are offset from the waveguide on the n-bottom layer. The length of the reference design is 1mm, and the gap between ground and signal is 11μm.
The frequency response is assessed in terms of the electrical transmission along the transmission line from the source to termination, the characteristic impedance, and the modulation index 𝑀(𝜔).
3. CODESIGN FOR REFLECTION SUPPRESSION
The modulation bandwidth is believed to be compromised by electrical reflections from the impedance mismatch, and so a study has been performed with the model to evaluate the effect of source and termination impedance mismatch on the electro-optic modulation response. The electro-optic frequency response is calculated for impedances from 20 to 55 Ω for our reference modulator.
When we match the termination impedance (𝑍𝑡~25Ω), the effect of source impedance mismatch when comparing Fig. 3a) and b) is not significant. When the termination is not matched to the modulator impedance (𝑍𝑡=50Ω), the source impedance matching plays a role, increasing the 3dB bandwidth from 30 GHz to 38 GHz. Comparison of these two figures shows that the load impedance has a higher impact on the electro-optical bandwidth than the source impedance. Matching the termination side also enables a flatter modulation response. This motivates the use of lower than 50Ω terminations, and also the use of low impedance co-designed electrical drivers. Such an approach will, however, be highly sensitive to the interconnection between the electrical components and the Mach-Zehnder modulator, motivating the intimate integration of electronics and photonics.
Pascher, Figures 2 and 3, and Selected Text
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The first Mach-Zehnder interferometer (MZI modulator integrated with an arrayed-waveguide grating (AWG) based laser shall be demonstrated. A novel 4-channel device as small as 4x8 mm 2 is realized, employing only one AWG instead of three needed conventionally. Integration of two required epitaxial layerstacks was realized by growing one waveguide layer, locally removing it and regrowing a second layer in the etched region. The modulator design is optimized using rigorous field simulation of the complex semiconductor layer stack. Almost perfect velocity match and low microwave loss are obtained by 1 µm-narrow waveguides with a 2 µm signal electrode on top.
To have a high modulation efficiency and a low microwave attenuation at the same time, the p-doped cladding should be as narrow and highly doped as possible. With respect to the modulator investigated in [4], we changed the phase shifters from a 4 μm-wide shallowly etched waveguide into a 1 μm-wide deeply etched waveguide. This causes a reduction of the microwave index and a slight increase in the optical group index. An almost perfect velocity match is achieved.
The microwave electrical field distribution for the optimized design, namely in the region of the signal electrode is presented in Fig. 3. Due to the pin-structure of the optical waveguide, the microwave field is mainly across the depleted region, which consists of the upper part of the film layer and the intrinsic layer. The mode observed is nearly a microstrip mode because of the comparitively high conductivity of the n-doped buffer layer, which behaves like a ground plane.
Any microwave attenuation in the CPW feed lines will decrease the measured bandwidth of the modulator. This is because the higher frequencies will be more attenuated by the CPW feed line than the lower frequencies. Any attenuation in the CPWs from the phase shifters to the loads does not affect the modulation bandwidth as the microwave signal has already been modulated onto the optical carrier.
Sadiq, Figure 2 and Selected Text
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In the vertical direction, light is mostly confined in the intrinsic region which consists of multiple quantum wells (MQWs) and undoped InP spacer layers. Spacer layers have been added above and below the MQWs to keep the optical mode away from the p and n doped region. Any overlap of the optical mode with doped layers can increase optical absorption. Optical absorption from a p-doped semiconductor layer is almost 10 times as high as a comparably doped n-doped semiconductor layer. To minimize the absorption losses due to doping, the doping profile of the p-doped layer above the InP spacer is increased gradually from 1017cm-3 to1019cm-3. However, low p-doping can increase the RF microwave loss so a compromise has to be made. Lateral confinement is achieved by the deep etched optical waveguide ridge.
a) Electrode ridge width (Wridge) optimisation
The maximum electro-optical overlap depends on the interaction of the electric field with the region of light confinement. Ideally, signal and ground electrodes can be placed on top and bottom of the ridge waveguide to ensure maximum overlap of both the RF and optical fields. However, practically it is not possible due to complex growth and fabrication process and requirement of low optical absorption loss as explained above. Ground electrodes have to be placed at a certain minimum distance from the signal electrode in a G-S-G configuration. This gap between signal and ground electrodes can be optimised for minimum microwave attenuation (αm), characteristic impedance (Z0) and microwave index (Nm).
Increasing the signal electrode width (Wmetal) decreases the inductance which in turn reduces Z0. In order to maintain the value of inductance, the gap between electrodes has to be increased as well at the cost of a slight increase in microwave loss. The best optimised solution is to microwave loss. The best optimised solution is to keep the signal metal width same as the ridge width. However, for the ease of fabrication process it is better to keep the signal electrode slightly wider than ridge…
Ridge width has effects on all the resistive, capacitive and inductive elements of the CPW transmission line. Reducing the ridge width will decrease the capacitance due to intrinsic region but at the same time will increase the CPW line inductance and impedance. The most prevailing effect here is the reduction in capacitance due to intrinsic region which results in low microwave loss, low index and high impedance.
Aimone, Figures 2-3, 3-4, 3-5, and 3-17, Equation 3-3, and Selected Text
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3.2.4. Optical Design
The need for segment’s capacitances of different values translates to electrodes of different lengths and widths. As the electrode lengths are directly connected to the phase-shift induced in each section, the waveguide width ww becomes an important degree of freedom for the design. Although wider waveguides correspond to larger capacitance values, the employed InP deeply-etched ridge waveguide allows for the propagation of high-order modes above the critical width of 1.8 μm. The integration of different waveguide widths in the same modulator entails the need for tapering structures in between consequent active sections and along the individual interferometer arms. An abrupt transition in the propagation layer not only causes optical power losses and reflections, but also causes energy to be transferred to different guided modes … The energy of non-fundamental modes is later lost in the recombining MMIs and should for this reason be minimized …
The segment’s capacitors CMZ take into account the junction capacitance of the reversely biased pin diodes. Because of their geometry, these capacitors can be thought of as parallel plates, where the doped InP layers represent the capacitor plates and the junction depletion regions constitute the dielectric. The capacitance CMZ is thus evaluated as: where 𝜖0 and 𝜖𝑟 are the permittivity of free space and the InP dielectric constant, respectively, le is the electrode length, ww the waveguide width, and xd the depletion region thickness. Due to the strong doping of the junction p- and n-layers in the employed InP technology, the depletion region does not extend significantly into these areas and is thus approximated by the physical intrinsic region thickness IRT.
Eghlidi, Figure 8, Table 1, and Selected Text
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ABSTRACT
In this paper, distribution of voltage along a general nonuniform transmission line is expanded in an appropriate form, and by employing an approach similar to conventional and modified differential transfer matrix methods already proposed for optical structures, analytical expressions are obtained for voltage/current distributions and reflection/transmission coefficients. This method shows great accuracy in different test cases and has been found to be superior to the well-known analytical method of small reflections. Notwithstanding, the overall accuracy of proposed approach is further improved by introducing the technique of multiple divisions. In particular, lossy/lossless tapered microstrip lines are examined, and excellent results are obtained. In deriving the formulation, a rigorous approach is followed and no simplifying assumptions are made; however, thanks to the analytical nature of the proposed method, high computational resources are not needed, and the results can be obtained extremely fast. This feature makes it suitable for optimization and synthesis of nonuniform transmission lines
II. ANALYSIS OF NONUNIFORM TRANSMISSION LINES
The voltage wave in each point of a transmission line is com posed of a right traveling wave and a left traveling wave. In a tapered transmission line, which is shown schematically in Fig. 1, the amplitudes of these waves are dependent on the coordinate …
V. TAPERED MICROSTRIP LINES
Tapered microstrip lines have been extensively used in many applications and play an important role in microwave engineering. These lines can be characterized by simple circuit models, whenever the fringing fields are negligible and only the dominant or quasi-TEM modes propagate along the line. In this section, the model derived by Hammerstad and Jensen [26] is employed to obtain the variation of the microstrip effective dielectric constant and characteristic impedance as a function of the width-to-height ratio , and then different microstrip circuits are analyzed. It should be noted that this model also takes the nonzero strip thickness and dispersion into account.
VI. CONCLUSION.
A new analytical method has been introduced for analyzing tapered transmission lines. This method is based on a suitable expansion of voltage distribution with unknown coefficients obtained by following a method similar to conventional and modified differential transfer matrix methods already employed for the analysis of optical structures, where no simplifying assumption is made and a rigorous approach is followed. Reflection and transmission coefficients were derived, the method of analyzing cascaded structures was presented, and the techniques of multiple divisions for improving the accuracy of the proposed method were also introduced. The applicability of the proposed method and its superiority to the well-known small reflections method was shown via several numerical examples. In particular, nonuniform lossy/lossless microstrip lines were investigated by following our proposed method.
Stiles, Selected Figures and Text
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Recall the bandwidth of a multi-section matching transformer increases with the number of sections. Similarly, the bandwidth of a tapered line will typically increase as the length L is increased.
Q: But how can we physically taper the characteristic impedance of a transmission line?
A: Most tapered lines are implemented in stripline or microstrip. As a result, we can modify the characteristic impedance of the transmission line by simply tapering the width W of the conductor …In other words, we can continuously increase or decrease the width of the microstrip or stripline to create the desired impedance taper …
Regarding claims 2-14, as dependent upon claim 1, it would have been obvious to one of ordinary skill in the art to modify Meaghan, as evidenced by Pascher and Sadiq, in view of Aimone, further in view of Eghlidi, and further in view of Stiles’ p-i-n waveguide embodiments (and related methods), as applied in the rejection of claim 1, to disclose:
2. The electro-optical modulator of claim 1, wherein the first waveguide comprises: an optical input; and an optical output, and the second waveguide comprises: an optical input; and an optical output, wherein the first electrical impedance value is between a portion of the first electrode corresponding to the optical input of the first waveguide and a portion of the second electrode corresponding to the optical input of the second waveguide, and the second electrical impedance value is between a portion of the first electrode corresponding to the optical output of the first waveguide and a portion of the second electrode corresponding to the optical output of the second waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
3. The electro-optical modulator of claim 2, wherein: i) the portion of the first electrode corresponding to the optical input of the first waveguide and the portion of the second electrode corresponding to the optical input of the second waveguide are opposed electrode surfaces; or ii) the portion of the first electrode corresponding to the optical output of the first waveguide and the portion of the second electrode corresponding to the optical output of the second waveguide are opposed electrode surfaces. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
4. The electro-optical modulator of claim 1, wherein at least one of: i) the magnitude of the first electrical impedance value is different to the magnitude of the second electrical impedance value; ii) the first electrical impedance value is greater than or less than the second electrical impedance value; iii) the first waveguide is tapered; iv) the second waveguide is tapered; v) the first electrode is tapered; vi) the second electrode is tapered; vii) a first separation, along the first axis, between the first electrode and the second electrode is different from, less than, or greater than a second separation, along the second axis, between the first electrode and the second electrode; viii) the first waveguide comprises a first portion of intrinsic semiconductor, and the first portion of intrinsic semiconductor is tapered; ix) the second waveguide comprises a second portion of intrinsic semiconductor, and the second portion of intrinsic semiconductor is tapered; x) the substrate comprises a semi-insulator layer, and an n-type semiconductor layer on the semi-insulator layer; xi) the first electrode is on at least one of the first waveguide or the substrate; xii) the first electrode is in contact with at least one of the first waveguide or the substrate; xiii) the second electrode is on at least one of the second waveguide or the substrate; xiv) the second electrode is in contact with at least one of the second waveguide or the substrate; or xv) the electro-optical modulator comprises a third electrode. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
5. The electro-optical modulator of claim 1, wherein the first waveguide is tapered, and at least one of: i) the size of a first portion of the first waveguide along a third axis is less than the size of a second portion of the first waveguide along a fourth axis parallel the third axis, the third axis and the fourth axis each perpendicular to the light propagation axis of the first waveguide, and the third axis spaced from the fourth axis along the light propagation axis of the first waveguide; ii) the third axis and the fourth axis are each parallel to a surface of the substrate closest to the first waveguide; iii) the third axis and the fourth axis each perpendicular to the surface of the substrate closest to the first waveguide; or iv) the size of the first portion of the first waveguide along a fifth axis is less than the size of the second portion of the first waveguide along a sixth axis parallel to the fifth axis, the fifth axis and the sixth axis each perpendicular to the light propagation axis of the first waveguide, the fifth axis and the sixth axis each perpendicular to the third axis, and the fifth axis spaced from the sixth axis along the light propagation axis of the first waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.6. The electro-optical modulator of claim 1, wherein the second waveguide is tapered and at least one of: i) the size of a first portion of the second waveguide along a seventh axis is less than the size of a second portion of the second waveguide along an eighth axis parallel to the eighth axis, the seventh axis and the eighth axis each perpendicular to a light propagation axis of the second waveguide, and the seventh axis spaced from the eighth axis along the light propagation axis of the second waveguide; ii) the seventh axis and the eighth axis are each parallel to a surface of the substrate closest to the second waveguide; iii) the seventh axis and the eighth axis are each perpendicular to the surface of the substrate closest to the second waveguide; or iv) the size of the first portion of the second waveguide along a ninth axis is less than the size of the second portion of the second waveguide along a tenth axis parallel to the ninth axis, the ninth and tenth axis each perpendicular to the light propagation axis of the second waveguide, the ninth and tenth axis perpendicular to the seventh axis and eighth axis, and the ninth axis spaced from the tenth axis along the light propagation axis of the second waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
7. The electro-optical modulator of claim 1, wherein the first electrode is tapered, and at least one of: i) the size of a first portion of the first electrode along an eleventh axis is less than the size of a second portion of the first electrode along a twelfth axis parallel to the eleventh axis, the eleventh axis and the twelfth axis each perpendicular to the light propagation axis of the first waveguide, and the eleventh axis spaced from the twelfth axis along the light propagation axis of the first waveguide; ii) the eleventh axis and the twelfth axis are each parallel to a surface of the substrate closest to the first waveguide; iii) the eleventh axis and the twelfth axis are each perpendicular to the surface of the substrate closest to the first waveguide; or iv) the size of the first portion of the first electrode along a thirteenth axis is less than the size of the second portion of the first electrode along a fourteenth axis, the thirteenth axis parallel to the fourteenth axis, the thirteenth axis and the fourteenth axis each perpendicular to the light propagation axis of the first waveguide, the thirteenth axis and the fourteenth axis each perpendicular to the eleventh axis, and the fourteenth axis spaced from the thirteenth axis along the light propagation axis of the first waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
8. The electro-optical modulator of claim 1, wherein the second electrode is tapered, and at least one of: i) the size of a first portion of the second electrode along a fifteenth axis is less than the size of a second portion of the second electrode along a sixteenth axis, the fifteenth axis and the sixteenth axis each perpendicular to the light propagation axis of the second waveguide, and the fifteenth axis spaced from the sixteenth axis along the light propagation axis of the second waveguide; ii) the fifteenth axis and the sixteenth axis are each parallel to a surface of the substrate closest to the second waveguide; iii) the fifteenth axis and the sixteenth axis are each perpendicular to the surface of the substrate closest to the second waveguide; or iv) the size of the first portion of the second electrode along a seventeenth axis is less than the size of the second portion of the second electrode along an eighteenth axis, the seventeenth axis and the eighteenth axis each perpendicular to the light propagation axis of the second waveguide, the seventeenth axis and the eighteenth axis each perpendicular to the fifteenth axis, and the eighteenth axis spaced from the seventeenth axis along the light propagation axis of the second waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
9. The electro-optical modulator of claim 1, wherein the first waveguide comprises a first portion of intrinsic semiconductor, and: i) a first portion of n-type semiconductor in contact with the substrate, the first portion of intrinsic semiconductor on the first portion of n-type semiconductor, a first portion of a first p-type semiconductor on the first portion of intrinsic semiconductor, and a first portion of a second p-type semiconductor on the first portion of the first p-type semiconductor; ii) a first portion of n-type semiconductor in contact with the substrate, the first portion of intrinsic semiconductor on the first portion of n-type semiconductor, a second portion of n-type semiconductor on the first portion of intrinsic semiconductor, and a first portion of p-type semiconductor on the second portion of the first n-type semiconductor or of a second n-type semiconductor; or iii) the first waveguide comprises a portion of n-type semiconductor in contact with the substrate, and a portion of p-type semiconductor on the portion of n-type semiconductor. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
10. The electro-optical modulator of claim 9, wherein the first portion of intrinsic semiconductor is tapered, and at least one of: i) the size of a first portion of the first portion of intrinsic semiconductor along a nineteenth axis is different to the size of a second portion of the first portion of intrinsic semiconductor along a twentieth axis parallel the nineteenth axis, the nineteenth axis and the twentieth axis each perpendicular to the light propagation axis of the first waveguide, and the nineteenth axis spaced from the twentieth axis along the light propagation axis of the first waveguide. ii) the nineteenth axis and the twentieth axis are each parallel to a surface of the substrate closest to the first waveguide; iii) the nineteenth axis and the twentieth axis are each perpendicular to the surface of the substrate closest to the first waveguide; or iv) the size of the first portion of the first portion of intrinsic semiconductor along a twenty-first axis is less than the size of the second portion of the first portion of intrinsic semiconductor along a twenty-second axis parallel to the twenty-first axis, the twenty-first axis and twenty-second axis each perpendicular to the light propagation axis of the first waveguide, the twenty-first axis and twenty-second axis each perpendicular to the twentieth axis, and the twenty-first axis spaced from the twenty-second axis along the light propagation axis of the first waveguide.11. The electro-optical modulator of claim 1, wherein the second waveguide comprises a second portion of intrinsic semiconductor, and i) a third portion of n-type semiconductor in contact with the substrate, the second portion of intrinsic semiconductor on the third portion of n-type semiconductor, a second portion of the first p-type semiconductor on the second portion of intrinsic semiconductor, and a second portion of the second p-type semiconductor on the second portion of the first p-type semiconductor; ii) a third portion of n-type semiconductor in contact with the substrate, the second portion of intrinsic semiconductor on the third portion of n-type semiconductor, a fourth portion of n-type semiconductor on the second portion of intrinsic semiconductor, and a second portion of p-type semiconductor on the second portion of the n-type semiconductor; or iii) a portion of n-type semiconductor in contact with the substrate; and a portion of p-type semiconductor on the portion of n-type semiconductor. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
12. The electro-optical modulator of claim 11, wherein the second layer of intrinsic semiconductor is tapered, and at least one of: i) the size of a first portion of the second portion of intrinsic semiconductor along a twenty-third axis is less than the size of a second portion of the second portion of intrinsic semiconductor along a twenty-fourth axis parallel to the twenty-third axis, the twenty-third axis and the twenty-fourth axis each perpendicular to the light propagation axis of the second waveguide, and the twenty-third axis spaced from the twenty-fourth axis along the light propagation axis of the second waveguide; ii) the twenty-third axis and the twenty-fourth axis are each parallel to a surface of the substrate closest to the second waveguide; iii) the twenty-third axis and the twenty-fourth are each perpendicular to the surface of the substrate closest to the second waveguide; or iv) the size of the first portion of the second portion of intrinsic semiconductor along a twenty-fifth axis is less than the size of the second portion of the second portion of intrinsic semiconductor along a twenty-sixth axis parallel to the twenty-fifth axis, the twenty-fifth axis and the twenty-sixth axis each perpendicular to the light propagation axis of the second waveguide, the twenty-fifth axis and the twenty-sixth axis each perpendicular to the twenty-fourth axis, and the twenty-fifth axis spaced from the twenty-sixth axis along the light propagation axis of the second waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
13. The electro-optical modulator of claim 1, comprising a third electrode, and wherein at least one of: i) the third electrode is on at least one of the first waveguide, the second waveguide or the substrate; ii) the third electrode is in contact with at least one of the first waveguide, the second waveguide or the substrate; iii) at least one of the first electrode, second electrode or third electrode is in contact with the first waveguide and the second waveguide; or iv) the third electrode is tapered. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
14. The electro-optical modulator of claim 1, wherein at least one of: i) a surface of the first waveguide in contact with the first electrode is substantially coplanar with a surface of the second waveguide in contact with the second electrode; ii) the first waveguide is between the first electrode and the first portion of the substrate; iii) the second waveguide is between the second electrode and the second portion of the substrate; iv) a first distance between the first electrode and the first portion of the substrate is substantially the same as a second distance between the second electrode and the second portion of the substrate, the first distance and the second distance each perpendicular a light propagation axis of the first waveguide; v) the electro-optical modulator comprises an electrical insulator between the first waveguide and the second waveguide; vi) the electro-optical modulator comprises at least one of a fluid, a gas or air between the first waveguide and the second waveguide; vii) the first waveguide is spaced from the second waveguide by between 1 μm and 50 μm; viii) a length of at least one of the first waveguide and the second waveguide is between 0.5 mm and 5 mm along the light propagation axis of the first waveguide and the second waveguide respectively; ix) the first waveguide is between 0.5 μm and 5 μm in width taken perpendicular to the light propagation axis and perpendicular to a distance between the first electrode and the first portion of the substrate; x) at least one of the first waveguide or the second waveguide comprises InP; xi) at least one of the first electrode or the second electrode comprises gold; or xii) the electro-optical modulator comprises a dielectric material between the first electrode and the second electrode. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text.
because the resultant device and method embodiments would facilitate predictably tailoring electrode widths, tapers, impedance, and bandwidth; Stiles, selected figures and text; while designing, fabricating and deploying indium phosphide modulators. Meaghan, abstract.
Claims 15-18
Claims 15-18 are rejected under 35 U.S.C. 103 as being unpatentable over Meighan et al. (Microwave model for optimizing electro-optical modulation response of the Mach-Zehnder modulator, Session Poster 3 Optoelectronic devices and Integrated photonic circuits, ECIO 2020, 22 June 2020; “Meighan”), as evidenced by Pascher et al. ( Design and integration of MZI modulators and AWG-based multiwavelength lasers in InP, URSI General Assembly 2005, 23-29 October, New Delhi; “Pascher”) and Sadiq et al. (Efficient modelling approach for an InP based Mach-Zehnder modulator, 25th IET Irish Signals & Systems Conference, 2014, pp. 123-128; “Sadiq”), in view of Aimone, Alessandro (InP Segmented Mach-Zehnder Modulators with Advanced EO Functionalities, Doctoral Dissertation, Technischen Universität Berlin, 2016; “Aimone”), further in view of and further in view of Eghlidi et al. (Analytical Approach for Analysis of Nonuniform Lossy/Lossless Transmission Lines and Tapered Microstrips. IEEE Transactions on Microwave Theory and Techniques. 2007; “Eghlidi”), and further in view of Stiles, Jim (Tapered Lines, Dept. of EECS, University of Kansas, 2010; “Stiles”), as applied in the rejection of claims 1-14, further in view of Prosyk, Kelvin (2014/0153860; “Prosyk”) and further in view of Li et al. (Analysis of segmented traveling-wave optical modulators, in Journal of Lightwave Technology, vol. 22, no. 7, pp. 1789-1796, July 2004; “Li”).
Regarding claims 15-18, Prosyk discloses in figure 2B, and related figures and text, for example, Selected Text, embodiments of optical modulators having adjacent and parallel p-i-n waveguides (disposed along Beam Axes) topped by t-shaped electrode sections extending (along the Lateral Axis) from traveling wave electrodes (disposed along Beam Axes). Prosyk, paragraph [0040] (“FIG. 2B is an elevation view of a section of the optical modulator of FIG. 2A, showing two pairs of waveguide electrodes 32A, 32B. Each waveguide electrode 32A, 32B extends over a p-i-n junction 36A, 36B, formed within the corresponding waveguide branch. The p-layer 38A, 38B is in contact with the corresponding waveguide electrode 32A, 32B and the n-layer 40A, 40B is in contact with a common conducting backplane 42. The i-layer 39A, 39B contains a series of layers of InGaAsP of varying composition that acts as the waveguiding core. The entire structure extends on an insulating substrate 43. When an instantaneous change is applied in the voltage difference between the signal transmission line conductor S and the first ground transmission line conductor G1, a RF current 44 flows from the highly p-doped contact material 38A beneath waveguide electrode 32A, through the corresponding p-i-n junction 36A and the common conducting n-backplane 42, and up through the opposite p-i-n junction 36B.”).
Prosyk, Figure 2B and Selected Text
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[0027] With reference to FIG. 2A, there is shown a schematic top view of a Mach-Zehnder optical modulator 20 according to one embodiment. The optical modulator includes an optical structure 23 receiving the input optical beam 25 and dividing this input optical beam 25 into two optical beam components 27A, 27B propagating in two optical waveguide branches 28A, 28B, respectively. The optical structure 23 then recombines the optical beam components 27A, 27B downstream the optical waveguide branches 28A, 28B, resulting in an output optical beam 29. In some applications dual optical output beams can be provided, such as for example shown with respect to prior art configurations in FIG. 1B. In the illustrated configuration of FIG. 2A, the input optical beam is carried by an input waveguide 24, and a beam splitter 22 divides the input optical beam into the two optical beam components. The two optical beam components are recombined after propagation through the optical waveguide branches 28A, 28B by an output optical combiner 26.
[0028] In some embodiments, the optical structure 23 is defined by a semiconductor structure comprising a plurality of layers patterned to provide the desired light guiding characteristics. In one example, the optical structure may be defined by superposed layers of varying composition, such as the compound semiconductor indium gallium arsenide phosphide (InGaAsP) in different proportions of the constituent elements; such compositional differences resulting in differences in the index of refraction between the layers. The differences in index of refraction serve to confine the light in a given direction. In some embodiments, light confinement may be additionally achieved by etching away material in some regions creating a semiconductor-to-air or dielectric-to-air interface, again resulting in an index contrast. Etched interfaces can also be covered with the application of a different material, for example etching away a portion to create a semiconductor-to-air interface, and then replacing the material that was etched away with a dielectric, to form a semiconductor-to-dielectric interface. In other implementations superposed doped and undoped layers or differently doped layers of a same material such as lithium niobate may be provided and patterned to form ridge waveguiding constructions. As one skilled in the art will readily understand, optical structures appropriate for optical modulators may be made of a variety of materials and may be designed according to various patterns.
[0029] Typically, the beamsplitter may be embodied by multimode interference device (MMI), a directional coupler, a Y-junction splitter, or the like. Preferably, the beamsplitter divides the input light beam such that the two resulting optical beam components have a same optical power. Furthermore, the optical beam components are coherent, that is, they have a constant relative phase.
[0030] The combiner 26 may be embodied by a multimode interference (MMI) device or the like. A MMI relies on a transition from a narrow single mode guiding structure to a wider, multi-mode guiding structure. The multimode section is judiciously designed so that various modes excited by the inputs 28A and 28B combine together in the desired fashion at the output 29.
[0031] Of course, it will be readily understood that the optical structure 23 may include additional components guiding, shaping or otherwise acting on the light traveling therein without departing from the scope of the invention.
[0032] The optical mode of light travelling in each optical waveguide branch 28A, 28B has an optical group index which is determined by the geometry and materials of the optical waveguide branches 28A, 28B. As is well known to those skilled in the art, the refractive index of an optical medium can be modified through the application of an electrical field. In a Mach-Zehnder configuration, this principle is used to adjust the relative phase of the optical beam components guided along the optical waveguide branches, thereby determining whether these optical beam components will interfere constructively or destructively once recombined.
[0033] Still referring to FIG. 2A, the Mach-Zehnder modulator therefore includes a travelling wave electrode 21 modulating the relative phase of the optical beam components as they propagate along the optical waveguide branches 28A, 28B.
[0034] The travelling wave electrode 21 includes only one signal transmission line conductor S, coupled to one 28A of the optical waveguide branches and conveying the input electrical signal. The signal transmission line conductor S preferably extends longitudinally parallel to the optical waveguide 28A it is coupled to, along a substantial portion of the length thereof. The travelling-wave electrode 21 further includes a first ground transmission line conductor G1 coupled to the other one of the optical waveguide branches 28B. The first ground transmission line conductor 01 provides a first return path for the input electrical signal. The first ground transmission line conductor G1 preferably extends longitudinally parallel to the optical waveguide branch 28B it is coupled to, along a substantial portion of the length thereof. The travelling wave electrode 21 further includes a second ground line G2, providing a second return path for the input electrical signal.
[0035] In the illustrated embodiment, the RF signal circulating in the transmission line electrodes is provided by an RF voltage source 50 having a single signal output.
[0036] The signal transmission line conductor S and first and second ground transmission line conductors G1 and G2 may be embodied by any electrode structures of suitable shape and construction. In typical embodiments, a metallic layer is deposited over the semiconductor structure embodying the optical structure 23, and patterned to define the transmission lines S, G1 and G2. The metallic layer may for example be made of gold, aluminum, copper, a multilayer stack comprising titanium, platinum and gold, or the like.
[0037] By "coupled" it is understood that the signal transmission line conductor S and the first ground transmission line conductor G1 are disposed relative to the corresponding optical waveguide branch 28A, 28B such that the propagation of the electrical signal therealong generates a local electrical field within one or both of the optical waveguide branches 28A, 28B suitable to affect its refractive index, thereby changing the light transmission properties of the corresponding waveguide in accordance with the input electrical signal. As mentioned above, this allows a change in the relative phase of the optical beam components directly related to the electrical signal.
[0038] In the illustrated embodiment, the signal transmission line conductor S and first ground transmission line conductor G1 are coupled to the respectively associated optical waveguide branches 28A, 28B through a plurality of pairs of waveguide electrodes 32. The waveguide electrodes 32A, 32B of each pair are positioned adjacent the corresponding optical waveguide branch 28A or 28B. In the illustrated design, the waveguide electrodes 32A, 32B extend over the corresponding waveguide branch. Each waveguide electrode 32A, 32B is electrically connected to either the signal transmission line conductor S or to the first transmission ground line G1. In the illustrated embodiment, these connections are provided by bridge conductors 34, preferably embodied by a metallic segment linking the corresponding electrodes.
[0039] In the illustrated configuration, the Mach-Zehnder modulator 20 operates in "push-pull" mode, where a single voltage signal or field is used to phase modulate the optical beam components in the two waveguide branches in anti-phase. In a series push-pull configuration, each pair of waveguide electrodes 32A, 32B also act as a pair of capacitors in series and as a load on the corresponding transmission lines S and G.
[0040] FIG. 2B is an elevation view of a section of the optical modulator of FIG. 2A, showing two pairs of waveguide electrodes 32A, 32B. Each waveguide electrode 32A, 32B extends over a p-i-n junction 36A, 36B, formed within the corresponding waveguide branch. The p-layer 38A, 38B is in contact with the corresponding waveguide electrode 32A, 32B and the n-layer 40A, 40B is in contact with a common conducting backplane 42. The i-layer 39A, 39B contains a series of layers of InGaAsP of varying composition that acts as the waveguiding core. The entire structure extends on an insulating substrate 43. When an instantaneous change is applied in the voltage difference between the signal transmission line conductor S and the first ground transmission line conductor G1, a RF current 44 flows from the highly p-doped contact material 38A beneath waveguide electrode 32A, through the corresponding p-i-n junction 36A and the common conducting n-backplane 42, and up through the opposite p-i-n junction 36B. The direct current (DC) bias voltage of the backplane 42 is typically fixed by an external DC voltage source (not shown).
[0041] The present invention is however not limited to periodically loaded series push-pull configurations such as shown in the previously discussed embodiments. Referring to FIGS. 6 and 6A, there is shown an alternative embodiment where the signal transmission line conductor S and first ground transmission line conductor G1 are elongated electrode structures having an edge extending contiguous to the corresponding waveguide branch 28A, 28B in the X-Y plane. Such an embodiment operates similar to the embodiment of FIG. 2B, except that the index modulation and the RF current flow are continuous along the length of the optical waveguide branches 28A, 28B, rather than being confined to periodic waveguide electrodes.
[0042] Referring back to FIG. 2A, it will be apparent that the signal transmission line conductor S is positioned between the first and second ground transmission line conductors G1 and G2, whereas the first and second optical waveguide branches 28A, 28B are positioned between the signal transmission line conductor S and the first ground transmission line conductor G1. The modulator therefore has a GSG structure providing an asymmetrically-loaded configuration, as the loading capacitance of the travelling-wave electrode 21 is asymmetrically placed in only one of the S-G gaps of the GSG structure
Consequently, it would have been obvious to one of ordinary skill in the art to modify Meaghan, as evidenced by Pascher and Sadiq, in view of Aimone, further in view of Eghlidi, and further in view of Stiles’ p-i-n waveguide embodiments (and related methods), as applied in the rejection of claims 1-14, to disclose:
15. A photonic integrated circuit comprising an electro-optical modulator comprising: a substrate; a first waveguide on a first portion of the substrate; a first electrode; a second waveguide on a second portion of the substrate; and a second electrode, wherein a first electrical impedance value between the first electrode and the second electrode is different from a second electrical impedance value between the first electrode and the second electrode, the first electrical impedance value along a first axis perpendicular a light propagation axis of the first waveguide, and the second electrical impedance value along a second axis perpendicular the light propagation axis of the first waveguide, the first axis spaced from the second axis along the light propagation axis of the first waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text; Prosyk, figure 2B, and related figures and text, for example, Selected Text.
16. The photonic integrated circuit of claim 15, wherein at least one of: i) the photonic integrated circuit is configured to apply a potential difference between the substrate and at least one of the first electrode or the second electrode; ii) the photonic integrated circuit is configured to apply a first potential difference or a second potential difference between the first electrode and the second electrode; or iii) the photonic integrated circuit comprises electrical insulator between the first electrode and the optical source. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text; Prosyk, figure 2B, and related figures and text, for example, Selected Text.
17. The photonic integrated circuit of claim 15, comprising: an optical source; an optical splitter for splitting light from the optical source and directing the light after splitting to the first waveguide and the second waveguide; and an optical combiner for combining light from the first waveguide and the second waveguide. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text; Prosyk, figure 2B, and related figures and text, for example, Selected Text.
18. The photonic integrated circuit of claim 17, wherein the optical source is a semiconductor laser. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text; Prosyk, figure 2B, and related figures and text, for example, Selected Text.
because the resultant device and method embodiments would facilitate predictably tailoring electrode widths, tapers, impedance, and bandwidth; Stiles, selected figures and text; to match velocities and impedances at high frequencies; Li, III. SEGMENTED TRAVELING-WAVE GAAS MZM; while designing, fabricating and deploying indium phosphide modulators. Meaghan, abstract.
Claims 19 and 20
Claims 19 and 20 are rejected under 35 U.S.C. 103 as being unpatentable over Meighan et al. (Microwave model for optimizing electro-optical modulation response of the Mach-Zehnder modulator, Session Poster 3 Optoelectronic devices and Integrated photonic circuits, ECIO 2020, 22 June 2020; “Meighan”), as evidenced by Pascher et al. ( Design and integration of MZI modulators and AWG-based multiwavelength lasers in InP, URSI General Assembly 2005, 23-29 October, New Delhi; “Pascher”) and Sadiq et al. (Efficient modelling approach for an InP based Mach-Zehnder modulator, 25th IET Irish Signals & Systems Conference, 2014, pp. 123-128; “Sadiq”), in view of Aimone, Alessandro (InP Segmented Mach-Zehnder Modulators with Advanced EO Functionalities, Doctoral Dissertation, Technischen Universität Berlin, 2016; “Aimone”), further in view of and further in view of Eghlidi et al. (Analytical Approach for Analysis of Nonuniform Lossy/Lossless Transmission Lines and Tapered Microstrips. IEEE Transactions on Microwave Theory and Techniques. 2007; “Eghlidi”), and further in view of Stiles, Jim (Tapered Lines, Dept. of EECS, University of Kansas, 2010; “Stiles”), as applied in the rejection of claims 1-14, further in view of Prosyk, Kelvin (2014/0153860; “Prosyk”) and further in view of Li et al. (Analysis of segmented traveling-wave optical modulators, in Journal of Lightwave Technology, vol. 22, no. 7, pp. 1789-1796, July 2004; “Li”), as applied in the rejection of claims 15-18, further in view of Vanhoecke et al. (Design of a segmented modulator driver for advanced modulation formats, Proceedings Symposium IEEE Photonics Society Benelux, 2015, Brussels, Belgium; “Vanhoecke”) and further in view of Rakowski et al. (Low-Power, 10-Gbps 1.5-Vpp differential CMOS driver for a silicon electro-optic ring modulator, Proceedings of the IEEE 2012 Custom Integrated Circuits Conference, San Jose, CA, USA, 2012, pp. 1-6; “Rakowski”).
Regarding claims 19 and 20, Vanhoecke discloses in Table 1, and related figures and text, for example, Selected Text, embodiments of drivers for segmented modulators: “a current mode logic (CML) driver consisting of a differential pair and a CMOS inverter chain;” “The key difference between both drive schemes is that the drive voltages are not symmetric around zero for the inverter drivers since it is a pseudodifferential solution. When considering the transfer function of an MZM, in which 𝑉1 and 𝑉2 are the sum of the different segment voltage contributions applied to the two arms of the MZM (shown in Figure 2), one can see that the difference between the voltages controls the amplitude of the optical signal, while the sum of the voltages determines the phase of the output …” Vanhoecke, Selected Text.
Further regarding claims 19 and 20, Rakowski discloses in figure 6, and related figures and text, for example, Selected Text, modulator embodiments where applied voltages are determined, in part, by “the state of the switches.” Rakowski, Selected Text.
Consequently, in light of Vanhoecke’s disclosure of modulator driver embodiments with different ‘voltage outcomes’ and Rakowski’s disclosure of modulator driver circuit embodiments controlled by combinations of switches, it would have been obvious to one of ordinary skill in the art to modify Meaghan, as evidenced by Pascher and Sadiq, in view of Aimone, further in view of Eghlidi, and further in view of Stiles’ p-i-n waveguide embodiments (and related methods), as applied in the rejection of claims 1-14, further in view of Prosyk, and further in view of Li, as applied in the rejection of claims 15-18, to disclose:
19. A system for electro-optical modulation comprising: a photonic integrated circuit comprising an electro-optical modulator comprising a substrate, a first waveguide on a first portion of the substrate, a first electrode, a second waveguide on a second portion of the substrate, and a second electrode, wherein a first electrical impedance value between the first electrode and the second electrode is different from a second electrical impedance value between the first electrode and the second electrode, the first electrical impedance value along a first axis perpendicular a light propagation axis of the first waveguide, and the second electrical impedance value along a second axis perpendicular the light propagation axis of the first waveguide, the first axis spaced from the second axis along the light propagation axis of the first waveguide; and a controller configured to: apply a potential difference between the substrate and at least one of the first electrode or the second electrode, and switch between applying the first potential difference and applying the second potential difference between the first electrode and the second electrode. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text; Prosyk, figure 2B, and related figures and text, for example, Selected Text; Li, III. SEGMENTED TRAVELING-WAVE GAAS MZM; Vanhoecke, Table 1, and related figures and text, for example, Selected Text; Rakowski, figure 6, and related figures and text, for example, Selected Text.
20. The system for electro-optical modulation of claim 19, a difference in volts between the first potential difference and the second potential difference such that light propagating through the first waveguide is shifted in phase from light propagating through the second waveguide by 180°. Meighan, figure 1, and related figures and text, for example, Selected Text; Pascher, figures 2 and 3, and related figures and text, for example, Selected Text; Aimone, figures 2-3, 3-4, 3-5, and 3-17, equation 3-3, and related figures and text, for example, Selected Text; Sadiq, figure 2 and related figures and text, for example, Selected Text; Eghlidi, figure 8, table 1, and related figures and text, for example, Selected Text; Stiles, selected figures and text; Prosyk, figure 2B, and related figures and text, for example, Selected Text; Li, III. SEGMENTED TRAVELING-WAVE GAAS MZM; Vanhoecke, Table 1, and related figures and text, for example, Selected Text; Rakowski, figure 6, and related figures and text, for example, Selected Text.
because the resultant device and method embodiments would facilitate predictably tailoring electrode widths, tapers, impedance, and bandwidth; Stiles, selected figures and text; to match velocities and impedances at high frequencies; Li, III. SEGMENTED TRAVELING-WAVE GAAS MZM; while designing, fabricating and deploying indium phosphide modulators. Meaghan, abstract; capable of generating multi-level optical signals. Aimone, figure 4.1and related text (“The optical-DAC generates quantized optical intensity levels at the output of the SEMZM, but requires only binary signals as inputs. This is possible due to the discretization of the induced phase shifts into as many levels as the number of implemented segments (Figure 4-2). In the SEMZM, each of the modulator’s segments can individually be switched on and off. On the contrary, this is impossible in a traditional TWE-MZM, where all the active sections are connected. Depending on the number of switched on segments, a specific phase difference is induced in the interferometer arms and a precise optical intensity level is measured at the SEMZM output. Thus, the generation of a multi-level optical signal employing an IC driver whose output stages deliver only OOK stimuli becomes possible. Moreover, the driving IC is no longer required to be linear, opening the way for new energy-efficient driver topologies.”).
Vanhoecke, Table 1 and Selected Text
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Design choices and challenges. Because there is no need for a 50 Ω interface, nor for a linear driver, there is additional freedom in choosing a proper driver topology. Table 1 depicts the basic schemes of two possible driver topologies: a current mode logic (CML) driver consisting of a differential pair and a CMOS inverter chain, to be used in a pseudo-differential chain. Since a segment can be considered to be a lumped capacitive load, the static power consumption of an inverter chain is negligible in contrast to the CML topology. Within a technology node, the CMOS inverter delivers the highest swing as it switches from ground to supply. Though this swing is fixed, it can be matched to the modulator by choosing a proper interaction length. As the segmented configuration can reduce the effective 𝑉𝜋 voltage down to 1 𝑉, a CMOS inverter topology in a deep-submicron technology appears to be an ideal candidate to implement a power-efficient solution.
The key difference between both drive schemes is that the drive voltages are not symmetric around zero for the inverter drivers since it is a pseudodifferential solution. When considering the transfer function of an MZM, in which 𝑉1 and 𝑉2 are the sum of the different segment voltage contributions applied to the two arms of the MZM (shown in Figure 2), one can see that the difference between the voltages controls the amplitude of the optical signal, while the sum of the voltages determines the phase of the output …
Rakowski, Figure 6 and Selected Text
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The forward bias voltage is programmable via 3 switches as shown in Fig. 6, which allow controlling the anode drive strength according to the load capacitance. The obtained anode voltage depends on the state of the switches and on the load capacitance. Transistor MN2 works as a switch closing the charging path while MP1 is active. The width ratio of the transistors MN2 and MN3 determines how fast the gate voltage of MN2 decreases.
Conclusion
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/PETER RADKOWSKI/Primary Examiner, Art Unit 2874
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