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.
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 1-9
Claims 1-9 are rejected under 35 U.S.C. 103 as being unpatentable over Chen et al. (Broadband Silicon-On-Insulator directional couplers using a combination of straight and curved waveguide sections, Scientific Reports, 7: 7246; “Chen”) in view of Popovic et al. (2010/0209038; “Popovic”).
Regarding claim 1, embodiments of directional couplers (including wavelength filtering embodiments) and related design and modeling methods and fabrications, comprising curved waveguides, disparately sized coupled waveguides, and asymmetrically arranged directional couplers. Chen, figures 1 and 4, and related figures and text, for example, Selected Text below. Chen, abstract (“Broadband Silicon-On-Insulator (SOI) directional couplers are designed based on a combination of curved and straight coupled waveguide sections. A design methodology based on the transfer matrix method (TMM) is used to determine the required coupler section lengths, radii, and waveguide crosssections. A 50/50 power splitter with a measured bandwidth of 88 nm is designed and fabricated, with a device footprint of 20 μm × 3 μm. In addition, a balanced Mach-Zehnder interferometer is fabricated showing an extinction ratio of >16 dB over 100 nm of bandwidth .”).
Chen – Figures 1 and 4, and Selected Text
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The use of directional couplers as 2 × 2 power splitters /combiners is ubiquitous in photonic integrated circuits. Due to its simplicity and ease of design, it is commonly used in multiplexing circuits1, …, optical switches …., …, polarisation splitters …., and wavelength filters …. However the directional coupler splitting ratio is known to be very sensitive to the operating wavelength, as can be seen in high index contrast platforms like SOI.
In this paper, we study in detail the design of curved asymmetric directional couplers, where the asymmetry arises due to different bending radii between the two constituent waveguides of the coupler. We note that coupler waveguides may or may not necessarily have the same core size, which is a further asymmetry.
In this paper, we study in detail the design of curved asymmetric directional couplers, where the asymmetry arises due to different bending radii between the two constituent waveguides of the coupler. We note that coupler waveguides may or may not necessarily have the same core size, which is a further asymmetry
Further regarding claim 1, Popovic discloses in figures 17-22 and 31-32, and related figures and text, ring resonators participating in directional couplers, including heaters and coupled waveguides having different heater configurations. Popovic, paragraph [0140] (“FIGS. 20 and 21 depict heater 163, 164 configurations that permit switching and tuning of the filter 160 to each be performed by one independent heater element, simplifying the control of the filter 160 at the expense of additional required power and temperature.”).
Popovic – Figures 17-22 and 31-32, and Selected Text
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[0052] FIG. 12 illustrates a hitless tunable ring/racetrack resonator coupled to an input waveguide, via a variable Mach-Zehnder coupler having equal arm lengths, and to an output waveguide having a fixed coupler in accordance with an embodiment of the invention;
[0100] In various embodiments, the hitless tunable device designs described herein include a variable input coupling to an input waveguide, which may be achieved by control of the waveguide-ring coupling field configurations and phase relationships. The designs may also include a variable loss mechanism on at least one cavity, and may further include a variable output coupling to an output (drop-port) waveguide. The variable input coupling, variable output coupling, and variable cavity loss mechanism may each be implemented with, for example, a Mach-Zehnder interferometer having: i) 50% or less coupling per coupler; ii) a difference in arm lengths that provides an FSR substantially equal to the FSR of the cavity to which it is attached divided by any non-negative integer, L=0, 1, 2, 3 . . . ; and iii) a phase shift that may be 0.degree. or 180.degree. to place the cavity to which the Mach-Zehnder interferometer is coupled in an off-state or on-state, respectively, by default when phase shifters are not actuated. In many embodiments, the Mach-Zehnder variable couplers use orders L=0 or L=1. In one embodiment, the hitless tuning relies on the substantially simultaneous control of at least two phase shifters. Higher-order filters may be switched with a loss mechanism placed according to Mach-Zehnder FSR and supermode amplitude in the various cavities.
[0116] FIG. 31 depicts one embodiment of an actual silicon-core device design 290 that may be used to show the simulated switching curves depicted in FIG. 13b. The device 290 may be realized in silica-cladded, Si-core ring 291 and variable coupler 292 waveguides of approximately 600.times.100 nm cross-section and bus waveguides 293 of approximately 500.times.100 nm cross-section. The ring 291 outer radius may be 7 microns. The two input directional couplers 294, 295 of the variable Mach-Zehnder coupler 292 may have a power coupling coefficient of approximately 2%, and the output coupler 293 may have a coupling coefficient of approximately 7%. This may be achieved by having all three wall-to-wall coupling gaps at approximately 300 nm.
[0164] FIGS. 31 and 32 depict two complete realizations of hitless tunable filters 290, 300 in silicon-core microphotonic waveguides. The dimensions and parameters of the single-ring filter 290 depicted in FIG. 31 have already been described. The 4.sup.th-order hitless tunable filter 300 depicted in FIG. 32 comprises four ring resonators 301, 302, 303, 304 coupled in a series configuration, but laid out in a folded arrangement, such that the first resonator 301 is coupled to an input waveguide via a variable Mach-Zehnder input coupler 305, and to the second resonator 302. The second resonator 302 is further coupled to a variable Mach-Zehnder loss coupler 306 and to the third resonator 303. The third resonator 303 is further coupled to the fourth resonator 304, and the fourth resonator 304 is further is coupled to an output bus waveguide 307. This filter 300 may be realized in silica-cladded, Si-core ring 301, 302, 303, 304 and variable coupler 305, 306 waveguides of 600.times.100 nm cross-section and output bus waveguides 307 of about 500.times.100 nm cross-section. The outer ring 301, 302, 303, 304 radii may be approximately 7 microns. The two input directional couplers of the variable Mach-Zehnder input coupler 305 and variable Mach-Zehnder loss coupler 306 may have a power coupling coefficient of approximately 5%, or waveguide coupling gaps of about 200 nm in each of the two directional couplers and in each Mach-Zehnder coupler. The output coupler 307 on the fourth ring 304 may have a coupling coefficient of approximately 7%, or about a 175 nm waveguide-ring coupling gap. The rings 301, 302, 303, 304 may have couplings of approximately 0.65% or a gap of approximately 400 nm between the first ring 301 and the second ring 302 and also between the third ring 303 and the fourth ring 304, and a coupling coefficient of approximately 0.35% or a gap of approximately 460 nm between the second ring 302 and the third ring 303. In one embodiment, the closest spacing between the first ring 301 and the fourth ring 304 is at least 1.5 microns, ensuring no substantial coupling.
[0136] In FIG. 17, a schematic of the single-ring hitless tunable filter 160 of FIG. 16 is shown, with an additional arrangement of phase shifters 163.sup.2, 163.sup.3 in the shared ring-waveguide section 167 and in the Mach-Zehnder switching arm 162. As illustrated in FIG. 19, which depicts a physical embodiment of a filter 160, combining the phase shifter 163.sup.2 in the shared ring-waveguide section 167 and the phase shifter 163.sup.1 in the resonator ring-waveguide section 168 into a single phase shifter 163 permits the tuning of the ring resonator 161 with a maximally distributed temperature, i.e., minimized maximum temperature on the ring waveguide 161. On the other hand, when the ring resonance is tuned to a longer wavelength by actuating the ring heater element 163, the actuation of the shared ring-waveguide section 167 also shifts the Mach-Zehnder input coupling spectrum to shorter wavelength. The latter needs to be compensated either by actuation of the Mach-Zehnder switching arm heater 164 or another heater.
[0137] In order to maintain independent control of the tuning of the Mach-Zehnder coupling spectrum and the ring resonance components of the filter 160, an additional phase shifter 163.sup.3 may be added, as illustrated in FIG. 17, in the Mach-Zehnder switching arm 162. By actuating substantially simultaneously the two ring phase shifters 163.sup.1, 163.sup.2 and the added balancing phase shifter 163.sup.3 in the Mach-Zehnder switching arm 162, the ring resonance may be tuned, with lower maximum temperature, while not affecting the wavelength spectrum of the Mach-Zehnder input coupler 162 substantially, because the phase shifts added to both arms 162, 167 of the Mach-Zehnder input coupler are equal at all times. This operation may be done without requiring actuation of the main phase shifter 164 of the Mach-Zehnder switching arm 162 and, as such, the independent operation of the two functions is maintained.
[0138] FIG. 19 depicts a physical embodiment of the filter 160 depicted in FIG. 17. The phase shifter of the Mach-Zehnder switching arm 162 is accomplished by one heater 164, while the two ring phase shifters 163.sup.1, 163.sup.2 and the additional Mach-Zehnder switching arm 162 balancing phase shifter 163.sup.3 are combined into a single ring heater 163. In one embodiment, the ring heater 163 is designed to heat (i.e., cover) a length of waveguide in the Mach-Zehnder switching arm 162 that is approximately equal to the length of ring 161 waveguide in the shared ring-waveguide section 167. This embodiment of tuning permits reduced maximum temperature for a given ring resonance wavelength tuning range, at the cost of slightly greater overall tuning power used to compensate for the wavelength shifting of the Mach-Zehnder spectrum to shorter wavelengths by the ring heater 163. This embodiment also permits independent tuning of the ring 161 spectrum by heater element 163 and independent tuning of the Mach-Zehnder coupler spectrum by heater element 164
[0139] It is noted that in both tuning arrangements described thus far (the first arrangement depicted in FIGS. 16 and 18, and the second arrangement depicted in FIGS. 17 and 19), the switching is performed by changing the switching arm 162 phase by 180.degree., i.e., by actuating the Mach-Zehnder switching arm heater 164. However, the passband tuning requires the substantially simultaneous tuning of both the Mach-Zehnder switching arm 162 spectrum and the ring 161 resonance spectrum in order to shift both the input coupling coefficient and the resonance to the new target wavelength. Therefore, for tuning, a substantially simultaneous actuation of the Mach-Zehnder switching arm heater 164 and the resonator heater 163 are required.
[0140] FIGS. 20 and 21 depict heater 163, 164 configurations that permit switching and tuning of the filter 160 to each be performed by one independent heater element, simplifying the control of the filter 160 at the expense of additional required power and temperature.
[0141] In the first embodiment depicted in FIG. 20, the filter 160 is shown with an arrangement of two heater elements 163, 164. The first heater element 163 covers both the ring resonator 161 and a part of the Mach-Zehnder switching arm 162 of approximately equal length thereto, and the second heater element 164 covers a part of the Mach-Zehnder switching arm 162. The first heater element 163 is schematically shown to exclude coverage of the shared ring-waveguide section 167 of the ring 161, since heating that part of the ring 161 requires a greater amount of power to be expended in the Mach-Zehnder switching arm 162 to compensate for the (undesired) wavelength shift caused to the Mach-Zehnder coupling response by the ring 161 tuning, and this calls for greater overall switching and tuning power. The second heater element 164 is disposed so as to cover a remaining part of the Mach-Zehnder switching arm 162. In this embodiment, the ring resonance and Mach-Zehnder coupling spectrum are tuned substantially simultaneously by actuating the first heater 163, which requires about twice the power required to tune a ring resonator 161 alone. The second heater 164 is actuated to add a 180.degree. phase shift to the Mach-Zehnder switching arm 162 to turn on the filter response. This embodiment simplifies control at the expense of about a 50% increase in maximum power used.
[0142] A related embodiment of the filter 160 is depicted in FIG. 21. As illustrated, the first heater element 163 is designed to also heat (i.e., cover) the shared ring-waveguide section 167. In this way, a lower maximum temperature is needed to tune the resonance, by permitting the tuning phase shift to be distributed over the entire length of the ring resonator 161, rather than about 3/4 of its length, as depicted in FIG. 20. This maximum temperature reduction comes at the expense of greater power required to compensate the undesired tuning of the Mach-Zehnder switching arm 162, by requiring the first heater element 163 to cover the entire length of the ring resonator 161 and the entire length of the Mach-Zehnder switching arm 162. A second heater element 164 may be disposed on a second lithographic layer (as illustrated in FIG. 21), or side by side with the first heater 163 near the Mach-Zehnder switching arm 162 in order to permit an independent control to switch on the filter 160 at the wavelength channel of interest.
Consequently, in light of Popovic’s disclosure of optical filter embodiments distinguished by different dimensions and different heater configurations, it would have been obvious to one of ordinary skill in the art to modify Chen’s design and modeling embodiments to comprise: an optical filter comprising: a ring resonator; an optical waveguide configured to be optically coupled to the ring resonator; and a heater provided at the ring resonator, wherein the ring resonator includes a first curved portion, wherein the optical waveguide includes a second curved portion, wherein the first curved portion and the second curved portion are configured to form a directional coupler, and wherein the heater is disposed above the directional coupler; Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text; because the resulting configuration would facilitate designing, fabricating, and deploying curved directional couplers suitable for ‘widespread use in multiplexers, splitters, filters and switches in photonic integrated circuits.’ Chen, Results; Popovic, paragraph [0022] (“In general, in one aspect, the invention features a hitless tunable filter. The filter includes a ring resonator, a Mach-Zehnder coupler, and first and second phase shifters. The Mach-Zehnder coupler includes a switching arm that is coupled to the ring resonator at first and second coupling points. The first phase shifter may be used to introduce a first phase shift to light propagating through the ring resonator, while the second phase shifter may be used to introduce a second phase shift to light propagating through the Mach-Zehnder coupler. The Mach-Zehnder coupler may have a free spectral range substantially equal to a free spectral range of the ring resonator divided by a non-negative integer.”).
Regarding dependent claims 2-9, it would have been obvious to one of ordinary skill in the art to modify Chen in view of Popovic’s embodiments to disclose:
2. The optical filter according to claim 1, wherein the heater is provided at a portion of the ring resonator, the portion forming the directional coupler, and at a portion of the ring resonator except for the directional coupler. Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
3. The optical filter according to claim 1, wherein the heater is provided above a portion of the ring resonator, the portion being 70% or more of the ring resonator. Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
4. The optical filter according to claim 1, wherein the first curved portion and the second curved portion are each curved toward outside the ring resonator. Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
5. The optical filter according to claim 1, wherein a radius of curvature of the first curved portion and a radius of curvature of the second curved portion are each 5 μm to 350 μm. Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
6. The optical filter according to claim 1, wherein a distance between the ring resonator and the optical waveguide is shortest in the directional coupler.Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
7. The optical filter according to claim 1, comprising: a silicon layer, wherein the silicon layer includes waveguide cores, wherein one of the waveguide cores is the ring resonator, wherein another one of the waveguide cores is the optical waveguide, and wherein the one of the waveguide cores and the another one of the waveguide cores are adjacent to each other in the directional coupler. Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
8. The optical filter according to claim 1, comprising: two optical waveguides each of which is the optical waveguide, wherein each of the two optical waveguides includes the second curved portion, and wherein the second curved portions are each configured to form the directional coupler together with the first curved portion. Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
9. The optical filter according to claim 8, wherein, in a direction around the ring resonator, a length of the ring resonator from one of two directional couplers each of which is the directional coupler to another one of the two directional couplers is equal to a length of the ring resonator from the another one of the two directional couplers to the one of the two directional couplers. Popovic, figures 17-22 and 31-32, and related figures and text; Chen, figures 1 and 4, and related figures and text.
because the resulting configurations would facilitate designing, fabricating, and deploying curved directional couplers suitable for ‘widespread use in multiplexers, splitters, filters and switches in photonic integrated circuits.’ Chen, Results; Popovic, paragraph [0022].
Conclusion
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/PETER RADKOWSKI/Primary Examiner, Art Unit 2874
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