DETAILED 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 .
Response to Amendments
Applicant's amendment filed on December 31st, 2025 has been fully considered and entered.
Response to Arguments
Applicant’s arguments filed December 31st, 2025 have been fully considered but they are not persuasive.
Applicant states: “Independent claims 1, 13, and 16 each recite first and second optical fiber lengths/first and second lengths of optical fiber. The Office Action alleges that Abedin discloses the claimed lengths of optical fiber, relying on Figure 9. See Office Action at 9. However, Abedin states that Figures 9 and 10 show a length of fiber which seems to be a single length, not first and second lengths. See, e.g., paragraph [0050].”
The examiner respectfully disagrees. The claims recite “a first length of optical fiber” and “a second length of optical fiber” without requiring these lengths to be separate, distinct, or individually labeled components. Any continuous optical fiber can be conceptually divided into segments, as annotated in the previous office action with respect to Figure 9 of Abedin. LPG1 constitutes a first length, the length following LPG1 constitutes a second length, and so on. The structure of a first and second segment are present, and therefore taught. MPEP 2125, “Drawings and pictures can anticipate claims if they clearly show the structure which is claimed,” In re Mraz, 455 F.2d 1069, 173 USPQ 25 (CCPA 1972).
Applicant argues that the claims require a “wavelength-sensitive propagation mode coupler” with specific characteristics – receiving light in a first length, passing light in a second, the light comprising a signal and Raman component, and having different mode coupling efficiency over each respective spectrum. This is not taught in Abedin.
The examiner respectfully disagrees, LPGs are wavelength dependent mode coupling components, as detailed in the phase matching condition/equation in the examiner’s rejection (
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L
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G
~
λ
r
a
m
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n
). This meets the ‘wavelength-sensitive’ limitation.
Coupling the guided mode to a cladding mode is necessarily a wavelength dependent operation – it’s unclear to the examiner how one could couple a guided mode to a cladding mode in a manner that is agnostic to wavelength. Is there a mechanism or physics that permits wavelength independent coupling between guided modes and cladding modes?
The examiner emphasizes that a Raman spectrum is necessarily/by definition at a different, usually longer wavelength than any corresponding signal spectrum.
Importantly, applicant’s claims do not require the mode coupler to be designed for signal/Raman discrimination, merely that the coupler has a “mode coupling efficiency over the Raman spectrum that is different from that over the signal spectrum.” This is an intrinsic property of any wavelength-dependent mode coupler involving Raman and signal spectra, including Abedin’s LPGs.
Applicant states: “Applicant submits that Abedin does not disclose the claimed propagation mode coupler. The Office Action alleges that LPG 1 in Abedin is the claimed propagation mode coupler. See Office Action at 9. However, the Office Action also alleges that LPGl functions as the claimed propagation mode filter. Id at 10. Applicant respectfully submits that LPG 1 cannot be both the claimed propagation mode coupler and the claimed propagation mode filter, especially as Applicant has specified that the propagation mode filter is distinct from the propagation mode coupler. See, e.g., Applicant's Specification paragraph [0045].”
The examiner appreciates the distinction between the propagation mode coupler and the mode filter. Since the LPGs are capable of fulfilling the functions of both propagation mode couplers and mode filters, LPG1 may be designated as the mode coupler OR mode filter, and LPG2, which is separate, may be designated as the other, and still meet the claim language.
The key benefits are at least that:
a skilled artisan recognizes that spatial separation of the coupling and filtering components allows the Raman signal to accumulate propagation losses prior to suppression, leading to better attenuation of the unwanted signal. This is explicitly taught in Brochu et al. (US 20180217322), which was made of record but not used in the rejection. Brochu uses chirped/slanted fiber gratings to couple Raman light to counter-propagating cladding modes, which is separate from the mode filtration (Figures 9a and 9b). The periods of these gratings are different throughout the fiber, and thus designate at least a first and second grating region. Brochu illustrates how a skilled artisan recognizes the benefit of using separate components as a part of optical physics, and Abedin teaches multiple LPGs anyways.
Multiple components allow for greater bandwidth selectivity and optimization. Attempting to accomplish both in one component places constraints on component design, whereas two LPGs can be separately configured to accommodate the signal versus Raman spectrum.
The examiner’s previous rejection includes “LPGs 1 and 2 function as propagation mode filters that discriminate between the guided modes”, and already accounts for the use of more than one component. The rejection has been further clarified to designate the first LPG as performing one of the mode filtration or coupling, and the second LPG as performing the remaining of the two.
Applicant states: “Also, there is no disclosure in the applied references of a wavelength-sensitive propagation mode coupler that receives light in the first length of optical fiber and passes light propagating in the second length of optical fiber, and the light comprises a signal component and a Raman component spanning longer wavelengths than those in the signal component and having a wider band than the signal component.”
The examiner respectfully disagrees. Hemenway discloses a fiber system structurally identical to that claimed: first and second lengths of optical fiber with multiple confinement regions (216, 218, 220), wherein beam power is divided among confinement regions. The light being both signal spectrum and Raman spectrum describes an input to the claimed device, not a structural limitation of the device itself.
The applied references teach a device that structurally meets the claims, as an input signal spectrum would naturally lead to a Raman spectrum as a result of the physics of optical fibers, gratings, and confinement regions. The taught device does not need to explicitly mention an input signal spectrum (a signal spectrum just refers to input light that can be found in any natural environment that would be considered illuminated to the human eye). This input contains a signal spectrum that would pass into the fiber and naturally generate Raman light, which by definition is of a longer wavelength and having a wider band than the signal component. The interplay between the signal spectrum and a Raman spectrum is a direct consequence of the structural design of the fiber and the grating/coupling components, leveraging the fundamental physics of these components instead of intended input. The only way for the claimed device and the taught device to not generate Raman signal spectra which meet the limitations would be to not have any signal spectrum input, defeating the purpose of all devices discussed.
Applicant argues that the claimed device recites “filtering the light in a manner that discriminates between the first and second guided modes and increases propagation losses for the Raman spectrum,” and that Abedin does not disclose filtering that discriminates between modes and increases Raman losses.
The examiner respectfully disagrees. Abedin do not use the term ‘filter’, but the act of filtration is still performed by the disclosed LPGs, whose function is to selectively filter light of a specific wavelength or wavelength range. This is why LPGs are generally understood to be a discriminating/filtering component in the art – they function as what a skilled artisan would refer to as a filter. Absent a specific definition of filter in the present application, the examiner interprets the filter to be a component which receives light and selectively passes light of a specific wavelength/wavelength range as a result of its structure, which is consistent with the filtering components of the present application.
Drawings
Eight (8) sheets of drawings were filed on June 22nd, 2021, and have been accepted by the examiner.
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, 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.
Claim(s) 1-4, 16, 17 is/are rejected under 35 U.S.C. 103 as being unpatentable over Abedin et al. (US 2015/0192733 A1).
Regarding claim 1;
Abedin et al discloses a fiber optic device (see Figure 9, annotated below), comprising:
a first length of optical fiber (first length, Figure 9 and/or 10) comprising a core and one or more cladding layers (Figure 1, Element 101 depicts a core in cladding, the fiber inherently includes a core and a cladding), wherein the first length of optical fiber supports at least a first guided mode for light (LP01, ‘01’ in Figure 9) comprising both signal spectrum and Raman spectrum (the disclosed fiber is inherently capable of supporting both a signal and a Raman spectrum);
a second length of optical fiber (second length of fiber, Figure 9 and/or 10) comprising a core and one or more cladding layers (this is inherent to the fiber), wherein the second length of optical fiber supports the first guide mode and other guided modes (LP01, LP11, LP02, abbreviated 01, 11, 02 respectively in Figure 9), wherein the signal spectrum is propagated predominantly in the first guided mode through the second optical fiber length (Abedin’s mode converters are configured sequences which restore desired modes after conversion; it is a design choice whether a given signal remains in a given mode, as the periodicity of the LPG determines the coupling efficiency of various wavelengths of light) and the Raman spectrum is propagated through the second optical fiber length predominantly in the other guided modes other than the first guided mode and the Raman spectrum experiences lower gain from the signal spectrum as a result of lower overlap between the modes (Figure 1 depicts different modes and their E-field distributions, which inform us as to why LP01 is minimally interactive with LP11, as the E-fields overlap little; Figure 14 depicts the LPG periodicity versus resonance wavelength, which determines coupling efficiencies across bands); and
a wavelength-sensitive propagation mode coupler (LPG1) receiving light in the first length of optical fiber (LPG1) and passing light propagating in the second length of optical fiber (LPG2), the light comprising a signal component and a Raman component spanning longer wavelengths than those in the signal component and having a wider band than the signal component (a Raman spectrum generates as the result of signal interaction with fiber components, a Raman spectrum by definition spans longer wavelengths and wider band than the signal component – this is a consequence of optical physics)
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Figure reference 1: Figure 9 from Abedin et al.
Abedin et al. does not specifically disclose that a mode coupling efficiency over the Raman spectrum differs from that over a signal spectrum.
Long period gratings mode couplers (LPGs) are frequency/wavelength dependent and therefore will inherently couple a spectrum of a first frequency/wavelength associated with the period of the grating with more coupling efficiency than a signal of a second frequency/wavelength. Raman scattered/back-reflected light experiences a wavelength shift resulting from the interactions between the signal light photons and the fiber molecules that generate the Raman scattered/back-reflected light, and therefore the Raman scattered/back-reflected light will be at a different wavelength than the signal light from which the Raman light is generated. Abedin teaches that the gain fibers may be separated by isolators to suppress back-reflections and amplified spontaneous emission noise (see paragraph 37).
Before the effective filing date of the present invention, one of ordinary skill in the art would have found it obvious to form the LPGs to couple at least some of the light propagated into a first guided mode of signal light into a second guided mode, including Raman scattered/back-scattered light, for the purpose of providing higher order Raman scattered light that may be selectively suppressed as suggested by the teachings of Abedin. This would eliminate back-reflections and noise, thereby improving signal quality.
Regarding claim 2;
Abedin et al. discloses the fiber optic device of claim 1 (see discussion for claim 1 above):
Abedin et al. further discloses a filter coupled to receive the light from the first or second lengths of optical fiber, and to discriminate between the first and second guided modes (Figure 9, LPGs 1 and 2 function as propagation mode filters that discriminate between the guided modes).
Abedin et al. does not explicitly disclose that this filter is a propagation mode filter.
Long period gratings operate as propagation mode filters, selectively coupling at least a portion of the signal in the core to propagating cladding modes and functioning as band-rejection filters.
Abedin therefore discloses a propagation mode filter (LPG1 or LPG2), distinct from the propagation mode coupler (LPG1 or LPG2, whichever the filter is not), coupled to receive the light from the first or second lengths of optical fiber.
Therefore, before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to construct the LPGs of claim 1 disclosed by Abedin et al. (see discussion for claim 1) using methods known to the art, to discriminate between the first and second guided modes and performing mode filtration with the purpose of propagating the signal spectrum in the core while separating the undesired Raman signal such that it may be filtered/attenuated. This could be accomplished using methods disclosed in the art, by designating the first LPG as a coupler and the second LPG as a filter (or vice versa), without altering the function of the claimed invention. This would predictably provide spatial separation of functions, which lends itself to more efficient suppression of Raman signal beyond what a single element can achieve.
Regarding claim 3;
Abedin et al discloses the fiber optic device of claim 2, wherein:
the second guided mode is of a higher-order (Figure 9, LP11, LP02) than the first guided mode (Figure 9, LP01);
Abedin et al does not specifically disclose that the Raman spectrum comprises one or more first wavelengths that are longer than one or more second wavelengths of the signal spectrum, or specify the coupling efficiency of the Raman spectrum, or describe if the mode filter attenuates the second guided mode more than the first.
However, the Raman spectrum generated by the signal spectrum input of the optical device of Abedin et al. will inherently comprise one or more first wavelengths that are longer than one or more second wavelengths of the signal spectrum due to the process they are created with (see discussion for Claim 1 above), and further satisfy at least one of:
the coupling efficiency over the Raman spectrum is higher than over the signal spectrum (this is inherently true based on the properties of the Raman spectrum and its mode coupling); or
the propagation mode filter is to attenuate the second guided mode more than a first guided mode (mode filters that attenuate specific modes are known to the art).
As the Raman spectrum is generated due to scattering of the signal spectrum in the fibers of the optical cable, it is necessarily longer than the wavelengths of the signal spectrum. Coupling undesired modes to cladding layers of the fiber optic for the purpose of attenuation/different treatment to the core mode is also known to the art. Abedin also teaches that converting light into specific modes can be used to reduce the accidental coupling of signals (paragraph 41), and that the Raman signal will naturally be attenuated in higher order modes unless otherwise amplified (paragraph 47). Therefore, before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to design the fiber optic device of Abedin et al. such that it propagates a Raman spectrum that is longer in wavelength than the signal spectrum, and is efficiently coupled/attenuated by the mode filtration, ensuring that the first guided mode is propagated further while reducing undesired signal from the Raman spectrum in the core.
Regarding claim 4;
Abedin et al. discloses the fiber optic device of claim 2,
Abedin et al. further discloses that the first and second guided modes comprise linearly polarized (LP) modes (Figures 1 and/or 2); the first guided mode is a fundamental LP mode (LP01, Figures 9 and/or 10); and the second guided mode is an odd-ordered LP mode (LP11, Figures 9 and/or 10).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to design the fiber optic device disclosed by Abedin et al. such that it could propagate a signal spectrum with a first and second guided mode where the first mode is fundamental, while the second guided mode is odd-ordered. This could be accomplished by intentionally choosing a signal spectrum that propagates through multimode fibers, mode filtration, and other methods known to the art; it would predictably ensure that the Raman spectrum can be separated from the signal spectrum for further attenuation downstream without changing the function of the claimed invention.
Regarding claim 16;
Abedin et al. disclose a method of filtering Raman spectrum from a fiber system, the method comprising:
Propagating a first guided mode of light in a first optical fiber length (see Figure 9, annotated above), the first optical fiber length comprising a core and one or more cladding layers (core in cladding 101), and the light comprising both signal spectrum and Raman spectrum (the disclosed fiber is inherently capable of supporting both a signal and a Raman spectrum);
using a wavelength-sensitive mode coupler, receiving light in the first optical length and passing light propagating in a second length of optical fiber, the light comprising a signal component and a Raman component spanning longer wavelength than those in the signal component and having a wider band that the signal component (LP11, LP02),
Propagating the first and second guided modes in a second optical fiber length (LP01, LP11/LP02 seen in Figures 9 and 10) of the system, the second optical fiber length of fiber comprising a core and one or more cladding layers (core in cladding 101), wherein the signal spectrum is propagated predominantly in the first guided mode through the second optical fiber length (Abedin’s mode converters are configured sequences which restore desired modes after conversion; it is a design choice whether a given signal remains in a given mode, as the periodicity of the LPG determines the coupling efficiency of various wavelengths of light) and the Raman spectrum is propagated through the second optical fiber length predominantly in the other guided modes other than the first guided mode and the Raman spectrum experiences lower gain from the signal spectrum as a result of lower overlap between the modes (Figure 1 depicts different modes and their E-field distributions, which inform us as to why LP01 is minimally interactive with LP11, as the E-fields overlap little; Figure 14 depicts the LPG periodicity versus resonance wavelength, which determines coupling efficiencies across bands);
Using a mode filter that is distinct from the wavelength-sensitive mode coupler (LPG2), and filtering the light in a manner that discriminates between the first and second guided modes (Figure 9, LPG1-3) and increases propagation losses for the Raman spectrum (a long period grating is a mode-discriminating filter, which would couple the Raman spectrum to a higher order mode, like LP11, which is prone to greater loss due to its distance from the fiber core and natural propagation losses passing through a distance of fiber).
Abedin et al. does not specifically disclose that a mode coupling efficiency over the Raman spectrum is different
Mode couplers are frequency/wavelength dependent and therefore will inherently couple a spectrum of a first frequency/wavelength associated with the period of the grating with more coupling efficiency than a signal of a second frequency/wavelength. Raman scattered light will naturally be of a different wavelength, and therefore couple with a different efficiency than the signal spectrum (see claim 1 rejection for more details).
Before the effective filing date of the present invention, one of ordinary skill in the art would have found it obvious to utilize the method of Abedin et al. to filter some of the light propagated into a first guided mode of signal light into a second guided mode including Raman scattered/back-scattered light, for the purpose of providing higher order Raman scattered light that may be selectively suppressed as suggested by the teachings of Abedin to eliminate back-reflections and noise, thereby improving signal quality.
Regarding claim 17;
Abedin et al. discloses the method of claim 16, wherein:
Abedin et al. does not explicitly disclose that coupling at least some of the light comprises coupling the Raman spectrum more efficiently than the signal spectrum. However, the first mode (LP01) is guided in a core (Figure 1, element 101) of the second fiber length (the second segment containing LPG2) more efficiently than the second mode (the second mode in the teachings of Abedin naturally has less gain than the signal spectrum, thus, the first mode is guided more efficiently than the second mode; see paragraph 49).
The Raman spectrum will carry a longer wavelength that is more efficiently coupled than the signal spectrum in cladding layers of the optical fiber (the longer Raman wavelengths will naturally couple with the cladding modes more efficiently).
Therefore, before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to utilize the method of Abedin et al to create a fiber that efficiency couples the second (Raman) mode more efficiently in cladding layers, while the first mode (signal) is most efficiently propagated through the core. This could be accomplished using fiber optic arrangements known to the art, and would predictably isolate the Raman and signal spectra to the cladding and core layers, respectively.
Claim(s) 13 & 15 is/are rejected under 35 U.S.C. 103 as being unpatentable over Hemenway et al. (WO 2018217284 A1) in view of Abedin (US 2015/0192733 A1).
Regarding claim 13;
Hemenway et al. discloses a fiber system (Figure 1), comprising:
a laser (i.e., LHS of Figure 22 & 23) to generate an optical beam when energized;
a first length of optical fiber (LHS of Figure 17, Figure 22A&B, Figure 23, element 2212) coupled to the laser to receive the optical beam, the first length of optical fiber comprising a core and one or more cladding layers (paragraph 10 discloses a cladding structure for the optical fiber), wherein the first length of fiber supports a first guided mode for light comprising both signal spectrum and Raman spectrum (2212 is capable of supporting both spectra);
a second length of optical fiber comprising a core and one or more cladding layers, wherein the second length of optical fiber supports the first guide mode and other guided modes (Figure 17, Figures 22, 23 and 24) wherein the signal spectrum is propagated predominantly in the first guided mode (second fiber has multiple confinement regions (216) and discloses that “…it may be desirable to have the beam 226 power divided among the confinement regions 216, 218, and 220, rather than concentrated in a single region,”) through the second optical fiber length (paragraph 90 discloses that, in the first length of wire, the power is predominantly in region 216, as depicted in Figure 5) and the Raman spectrum is propagated through the second optical fiber length predominantly in the other guided modes other than the first guided mode and the Raman spectrum experiences lower gain from the signal spectrum as a result of lower overlap between the modes (paragraph 90 discloses that, in the first length of wire, the power is predominantly in regions 218 and 220, as seen in Figure 6, which make them part of a different mode; visually, we can see that there is a lack of overlap between the power distributions for the signal light confined to different regions of the fiber cross section, and thus a Raman spectrum confined to another mode will necessarily have less overlap with the signal spectrum); and
a wavelength-sensitive mode coupler receiving light in the first length of optical fiber and passing light propagating in the second length of optical fiber, the light comprising a signal component and a Raman component spanning longer wavelengths than those in the signal component and having a wider band than the signal component (Figure 24, perturbation device 110 contains microbend 2404 to perform mode coupling, and the structural design of the microbend will couple light more or less efficiently depending on the wavelength of the light as a result of fundamental optical physics; this will naturally lead to Raman signal generation, wherein the Raman signal, by definition and as a consequence of fundamental optical physics, will span longer wavelengths and have a wider band than the signal component); and;
a mode filter distinct from the mode coupler, the mode filter coupled to receive the light form the first or second length of optical fiber, to discriminate between the first and second guides modes, (paragraph 138, Figure 25; “process 2500 moves to block 2508, ‘maintaining at least a portion of the one or more adjusted beam characteristic of the optical beam within one or more confinement regions of the second length of fiber’, where at least a portion of the one or more beam characteristic of the optical beam are maintained within one or more confinement regions of the second length of fiber”. This necessarily requires filtration of optical modes into separate components/regions to achieve).
Hemenway et al. does not specifically disclose that
The mode filtration is between the signal spectrum and Raman spectrum, and to increase propagation losses for the Raman spectrum.
the wavelength-sensitive propagation mode coupler has a mode coupling efficiency over the Raman spectrum that is different from that over the signal spectrum
Mode couplers will couple a spectrum of a first frequency/wavelength associated with the period of the grating with more coupling efficiency than a signal of a second frequency/wavelength. Hemenway further discloses that the fibers may contain fiber Bragg gratings or long-period gratings (paragraph 98), which are known to the art to filter/decouple signal light at a desired frequency, with an efficiency that depends on the wavelength. Raman scattered light will naturally be of a different wavelength, and therefore couple with a different efficiency than the signal spectrum (see claim 1 rejection rationale for more details).
Stimulated Raman scattering is a known problem in the art, and a decoupled-and-confined Raman signal spectrum would obviously be further attenuated as to prevent crosstalk with the signal spectrum. This may also be accomplished using methods known in the art, such as varying the refractive index of the cladding or changing its material to preferentially scatter the Raman spectrum.
Abedin et al discloses a fiber optic device (Figure 9) with a first and second length of fiber (LPG1, LPG2), containing a wavelength sensitive mode coupler (LPG1 or LPG2) and a mode filter (the other of LPG1 or LPG2) in another length of fiber. Importantly, the separation between LPG1 and LPG2 permits the modification of the individual devices such that one is optimized for coupling within the optical fiber and the other takes advantage of natural propagation losses from the ensuing Raman spectrum and maximizes the attenuation of the unwanted Raman signal.
This teaching would make it obvious to use a component like LPG2 in the invention of Hemenway to ensure that the Raman signal is properly attenuated, while meeting the rest of the claim limitations. These limitations were addressed in further detail for identical claim language in Claims 1 and 2.
Therefore, before the effective filing date of the present invention, one of ordinary skill in the art would have found it obvious to form the mode couplers to couple at least some of the light propagated into a first guided mode of signal light into a second guided mode including Raman scattered/back-scattered light, via the perturbation (bend) separating the first and second lengths of fiber as taught in Hemenway, and to ensure maximal attenuation of Raman signal using the teachings of the LPG2 in Abedin. This would predictably move the Raman light to a higher order, such that it may be confined and attenuated downstream, preserving and propagating the signal component with minimal loss.
Regarding claim 15;
Hemenway et al. discloses the fiber system of claim 13, wherein:
The mode coupler comprises a Fiber Bragg Grating (FBG) having a refractive index that varies (paragraph 0098 states that the fiber may contain a grating, and applying a coating or changing the axial geometry as described would change the effective refractive index) over the third length of the fiber (the placement of the grating can be applied to any length of the fiber).
The mode filter is a fiber mode filter that guides a fundamental mode more efficiently than one or more higher-order modes (Figures 1 & 2, the mode filter can be a fiber more filter, and will necessarily guide the fundamental mode more efficiently due to a transitional coupling).
Hemenway et al do not disclose that the first and second guided modes comprise linearly polarized (LP) modes; the first guided mode is a fundamental LP mode; the second guided mode is an odd-ordered LP mode; or that the Raman spectrum comprises one or more first wavelength that are longer than one or more second wavelengths of the signal spectrum;
Abedin et al teaches a fiber system, wherein the first and second guided modes comprise linearly polarized (LP) modes (First page, Figures 1 and 2);
the first guided mode is a fundamental LP mode (LP01); and
the second guided mode is an odd-ordered LP mode (LP11, LP02);
the Raman spectrum comprises one or more first wavelengths that are longer than one or more second wavelengths of the signal spectrum (this is necessarily true based on how the Raman portion of the spectrum is generated).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to modify the fiber system of Hemenway et al. to have the first and second guided modes be fundamental and odd-ordered, respectively, such that the Raman spectrum wavelengths are longer than the signal spectrum wavelengths. This could be accomplished using methods known to the art (tweaks to the core in cladding of the fiber optics, specific bend radii for the mode couplers, changes to the input laser signal, etc.) and would have the predictable effect of ensuring low loss in the desired signal from the fundamental mode, while reducing the signal of higher ordered, undesired modes.
Claim(s) 5, 6, 11, 12, and 18-20 is/are rejected under 35 U.S.C. 103 as being unpatentable over Abedin et al. (US 2015/0192733 A1) in view of Hemenway et al. (WO 2018/217284 A1).
Regarding claim 5;
Abedin et al. disclose the fiber optic device of claim 1, wherein:
the mode coupler comprises a third length of optical fiber comprising a core and one or more cladding layers (Figure 7)
Abedin et al. does not disclose that a fiber grating (FG) within the core, the FG having a refractive index that varies over the third length of the optical fiber.
Hemenway et al. discloses a fiber optic device, wherein the fiber grating within the core may have a refractive index that varies (paragraph 98 states that the fiber may contain a grating, and applying a coating or changing the axial geometry as described would change the effective refractive index) along the third length of the fiber (the placement of the grating can be applied to any length of the fiber).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to alter the fiber cables of Abedin et al. by adding a fiber grating to the core, and coating the core with materials known to the art to vary the refractive index as detailed in Hemenway et al. This would predictably allow the device to selectively mode couple the input signal.
Regarding claim 6;
Abedin et al. in view of Hemenway et al. discloses the fiber optic device of claim 5;
Abedin et al does not disclose that the FG has a refractive index that varies azimuthally within the core.
Hemenway et al. discloses that the FG may have a refractive index that varies azimuthally within the core (paragraph 0098 discloses that the fibers, which would contain the FG, do not have to be azimuthally symmetric; their refractive indices would not be either).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to alter the fiber optic cable of Abedin et al. with an azimuthally asymmetric fiber grating as suggested in Hemenway et al. This would have the predictable effect of ensuring selective filtration of specific wavelength ranges.
Regarding claim 11;
Abedin et al. discloses the fiber optic device of claim 1, wherein:
Abedin et al. does not disclose that the mode filter comprises a transition between a multi-mode fiber and a single-mode fiber.
Hemenway et al. discloses a fiber optic device, wherein the mode filter comprises a transition between a multi-mode fiber and a single-mode fiber (Figures 1 and 2).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to alter the fiber cables of Abedin et al. by coupling a multi-mode fiber and a single-mode fiber using methods known to the art. This would have the predictable effect of forcing higher order modes to be become lossy, preserving the low order mode signal.
Regarding claim 12;
Abedin et al. in view of Hemenway et al. discloses the fiber optic device of claim 11, wherein:
Abedin et al. does not disclose that the transition comprises a differential core splice.
Hemenway et al. discloses a fiber optic device, wherein the transition comprises a differential core splice (paragraphs 0008-0009, Figures 1 and 2).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to alter the fiber cables of Abedin et al. by transitioning a single mode fiber to a multi-mode fiber via a differential core splice, using methods known to the art. This would have the predictable effect of forcing higher order modes to be become lossy, preserving the low order mode signal and reducing the back reflection of light.
Regarding claim 18;
Abedin et al discloses the method of claim 16, wherein
The first guided mode is a fundamental LP mode (Figures 1 & 2, LP01);
The second guided mode is an odd-ordered LP mode (LP11);
Coupling at least some of the light comprises:
Propagating the light in a third length of optical fiber (LPG3, Figures 9 & 10) comprising a core and one or more cladding layers (core in cladding 101), the third length of optical fiber comprising fiber grating (FG; LPG3) within the core.
Abedin et al. does not disclose FG having a refractive index that varies over the third length of fiber.
Hemenway et al. disclose a method for utilizing a FG having a refractive index that varies over the third length of optical fiber (paragraph 98 discloses periodic index variation along the length of fiber using the LPG).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to modify the method of Abedin et al. to include the varying refractive index of Hemenway et al. in an optical device. This could be accomplished by altering core sizes and shapes which complement different beam characteristics, and would predictably allow one to design a fiber optic cable which varies its refractive index profile over any length of fiber, such that it may preferentially attenuate and/or propagate specific modes of a signal.
Regarding claim 19;
Abedin et al. in view of Hemenway et al. discloses the method of claim 18, and discloses that the FG is a long period grating (paragraph 98).
Abedin et al. does not specifically disclose a grating having a period greater than half of one or more wavelengths in the Raman spectrum; and coupling at least some of the light comprises co-propagating the second guided mode.
Long period gratings have periods
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a
d
When a multimode signal passes through an LPG, the longer-wavelength Raman portion will necessarily couple the light from the fundamental mode to a forward-propagating cladding mode. The difference in
n
c
o
r
e
-
n
c
l
a
d
must be smaller than 1 (typically on the order of ~0.01). As a result, the value of
Λ
L
P
G
will be greater than
λ
R
a
m
a
n
, and greater than half of the wavelength in the Raman spectrum. Such an LPG is necessarily forward propagating, which means the second guided-mode would co-propagate with the first.
Therefore, before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to use an LPG in the method of claim 18 as disclosed by Abedin et al. and Hemenway et al., with the period of the LPG being fixed such that it is much greater than the stimulated Raman spectrum. This could be accomplished using methods known to the art, and would predictably couple the Raman signal into a second mode which co-propagates with the signal spectrum mode in a cladding layer, ensuring that the two modes can be separated and treated individually without changing the function of the claimed invention.
Regarding claim 20;
Abedin et al. in view of Hemenway et al. discloses the method of claim 18, and discloses that the FG is a short period grating (paragraph 98, Bragg grating).
Hemenway et al. does not specifically disclose that a grating having a period no longer than half of one or more wavelengths in the Raman spectrum; and coupling at least some of the light comprises back propagating the second guided mode.
Short period (Bragg) gratings typically have periods
(
Λ
B
)
lesser than half of the wavelength in the input signal, based on the effective refractive index of the core fiber
(
n
e
f
f
)
and the wavelength of light
λ
R
a
m
a
n
.
This relationship can be expressed at a high level as:
Λ
L
P
G
~
λ
R
a
m
a
n
2
*
n
e
f
f
Bragg gratings are designed to facilitate the back-propagation of light in this wavelength regime by inducing periodic variation in the refractive index in the core of the optical fiber. As long as the period of the grating is an appropriate wavelength, this process will occur efficiently. Hemenway et al. teach that the Bragg gratings may be used as optical filters or reflectors for co-propagating fiber modes (paragraph 98), and in order to function properly they would have to have a period which is no longer than half of one or more wavelengths in the Raman spectrum.
Therefore, before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to use a Bragg grating in the method of claim 18 as disclosed by Abedin et al. and Hemenway et al., with the period of the Bragg grating being fixed such that it is no longer than half the wavelength of the Raman spectrum. This can be accomplished by inscribing periodic variations into the refractive index of the core. Such a grating would inherently back propagate at least some of the light in the second guided mode, and this would predictably reduce the noise from the Raman signal without altering the function of the claimed invention.
Claim(s) 7-10 is/are rejected under 35 U.S.C. 103 as being unpatentable over Abedin et al. (US 2015/0192733 A1) in view of Hemenway et al. (WO 2018/217284 A1) as applied to claim 5 above, and further in view of Nicholson et al. (US 2010/0284061 A1).
Regarding claim 7;
Abedin et al. in view of Hemenway et al. discloses the fiber optic device of claim 5, wherein:
the FG is a long-period grating (paragraph 0098) having a period greater than half of a center wavelength of the Raman spectrum (grating periods of LPGs for an Ir near the micron wavelengths will be on the order of 100 microns or more);
Abedin et al. and Hemenway et al do not disclose that the FG is optically coupled between the mode filter and an optical resonator, the optical resonator to excite at least the signal spectrum.
Nicholson et al. discloses a fiber optic device (100, 200), wherein the FG (240, LPG2) is optically coupled between the mode filter (pump source 220 utilizes mode filtration preceding the FG) and an optical resonator (260), the optical resonator to excite at least the signal spectrum.
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to couple the FG disclosed by Abedin et al. and Hemenway et al. between a mode filter and an optical resonator as described in Nicholson et al., deliberately placing it between those two components using methods known to the art. This would have the predictable effect of exciting the desired signal with low loss as it propagates.
Regarding claim 8;
Abedin et al. in view of Hemenway et al. discloses the fiber optic device of claim 5, wherein:
the FG is a short-period grating (paragraph 0098, Bragg grating) having a period no longer than half of a center wavelength of the Raman spectrum (grating periods of Bragg gratings for an Ir near a micron in wavelength will be on the order of a micron);
Abedin et al. and Hemenway et al do not disclose that the FG is optically coupled between the mode filter and an optical resonator, the optical resonator to excite at least the signal spectrum.
Nicholson et al. discloses a fiber optic device (100), wherein the mode filter (paragraph 0031, laser cavities 164) is optically coupled between the FG (140, LPG1) and an optical resonator (160), the optical resonator to excite at least the signal spectrum.
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to couple the mode filter disclosed by Abedin et al. and Hemenway et al. between an FG and an optical resonator as described in Nicholson et al., deliberately placing it between those two components using methods known to the art. This would have the predictable effect of filtering the undesired signal with high loss.
Regarding claim 9;
Abedin et al., Hemenway et al., and Nicholson et al. disclose the fiber optic device of claim 7 wherein:
Hemenway et al. and Nicholson et al. do not disclose that the optical resonator comprises the first length of optical fiber and supports only the first guided mode.
Abedin et al. discloses that the optical resonator comprises the first length of fiber (Abedin et al, Figures 10, 22, 23) and supports only the first guided mode (mode 11 goes into the resonator and comes out as 11 before being converted).
Before the effective filing date of the claimed invention, one of ordinary skill in the art would have found it obvious to place the optical resonator of Abedin et al. in the first length of fiber using methods known to the art, such that it supports the first guided mode. This would have the predictable effect of increasing the gain of the desired signal.
Regarding claim 10;
Abedin et al., Hemenway et al., and Nicholson et al. disclose the fiber optic device of claim 9 wherein:
Hemenway et al. and Nicholson et al. do not disclose that the second length of fiber comprises a gain medium to excite at least the signal spectrum.
Abedin et al. discloses a fiber optic device, wherein the second length of fiber comprises a gain medium to excite at least the signal spectrum (Figure 20, second length of fiber contains a gain medium).
Conclusion
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/PREET B PATEL/Examiner, Art Unit 2874
/THOMAS A HOLLWEG/Supervisory Patent Examiner, Art Unit 2874