Photonic bandpass filter with polarization diversity

Abstract

A photonic integrated circuit ("PIC") bandpass filter with polarization diversity comprising: a polarization management stage operable to receive a polarization diverse optical input and output an intermediate beam having uniform polarization; and a filter stage operable to receive the intermediate beam from the polarization management stage, filter the intermediate beam, and output a filter output beam, whereby energy from both in-plane and out-of-plane polarizations of the polarization diverse optical input can be transferred to the filter stage.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 285,751, filed December 3, 2021, which is incorporated by reference herein in its entirety. [Background technology]

[0002] A typical photonic integrated circuit ("PIC") bandpass filter (or photonic bandpass filter) is sensitive to the polarization of the input signal due to its strong refractive index contrast. Thus, a typical PIC bandpass filter generally requires a linearly polarized input to achieve optimal performance. In practice, optical fiber networks often transmit randomly polarized light. Although there has been much progress in PIC bandpass filters, most efforts have demonstrated filters for a specific linear polarization. Thus, there remains a demand for PIC bandpass filters (such as silicon PIC bandpass filters or other PIC bandpass filters) that can achieve high performance with optical inputs having random polarizations.

[0003] Features and advantages of the technology will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the technology. [Brief description of the drawings]

[0004] [Figure 1] FIG. 1 shows a schematic diagram of a PIC bandpass filter with polarization diversity according to an example of the present disclosure. [Diagram 2] FIG. 1 shows a schematic diagram of a PIC bandpass filter with polarization diversity according to an example of the present disclosure. [Diagram 3] FIG. 1 shows a schematic diagram of a PIC bandpass filter with polarization diversity according to an example of the present disclosure. [Figure 4]1A and 1B show examples of measured spectral responses of filter structures comparing a PIC bandpass filter with polarization diversity as shown in FIGS. 1-3 with a PIC bandpass filter without polarization diversity. [Diagram 5] 1 illustrates a method for filtering polarization-diverse optical input on a photonic integrated circuit ("PIC") bandpass filter according to an example of the present disclosure. [Figure 6] 1 illustrates a method for filtering polarization-diverse optical input on a photonic integrated circuit ("PIC") bandpass filter according to an example of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] Reference will now be made to the illustrated embodiments and specific language will be used to describe them, nevertheless it will be understood that no limitation of scope is intended thereby.

[0006] An initial overview of the inventive concepts is provided below, followed by a more detailed description of specific embodiments. This initial overview is intended to aid the reader in understanding the embodiments more quickly, but is not intended to identify key features or essential features of the embodiments, nor is it intended to limit the scope of the claimed subject matter.

[0007] In view of the above, there is a need to implement a PIC bandpass filter that is polarization insensitive (i.e., compatible with polarization-diverse optical inputs). Such a PIC bandpass filter may be beneficial for a wide range of signal processing applications in classical and quantum photonics. According to one example of the present disclosure, a photonic integrated circuit ("PIC") bandpass filter with polarization diversity may include a polarization management stage operable to receive a polarization-diverse optical input and output an intermediate beam having uniform polarization, and a filter stage operable to receive the intermediate beam from the polarization management stage, filter the intermediate beam, and output a filter output beam. Energy from both the in-plane and out-of-plane polarizations of the polarization-diverse optical input may thereby be transferred to the filter stage.

[0008] In some examples, the polarization management stage may comprise an optical splitter. The optical splitter may be operable to split the polarization diverse optical input into a first beam having a first polarization and a second beam having a second polarization different from the first polarization. The polarization management stage may further comprise a polarization rotator. The polarization rotator may be operable to rotate a first polarization of the first beam such that the first beam comprises a rotated polarization that coincides with the second polarization.

[0009] In some examples, the polarization management stage can include a beam coupler that can combine or splice a first beam having a circular polarization and a second beam having a second polarization into an intermediate beam. The polarization management stage can also include a phase shifter operable to shift a phase of the second beam to match a phase of the first beam before the first and second beams are received by the beam coupler.

[0010] In some examples, the intermediate beam can comprise a first intermediate beam and a second intermediate beam. The filter stage can comprise a first filter to receive the first intermediate beam and a second filter to receive the second intermediate beam. The first filter can output a first filtered intermediate output and the second filter can output a second filtered intermediate output.

[0011] In some examples, the filter stage may further comprise a power combiner operable to receive and combine the first filtered intermediate output and the second filtered intermediate output to output a filtered output beam. The filter stage may also comprise a bias tee operable to receive the first filtered intermediate output and the second filtered intermediate output and output a first biased intermediate output and a second biased intermediate output to the power combiner.

[0012] In another example of the present disclosure, a photonic integrated circuit ("PIC") bandpass filter with polarization diversity can include a polarization management stage. The polarization management stage can include an optical splitter. The optical splitter can be operable to split a polarization-diverse optical input into a first beam having a first polarization and a second beam having a second polarization different from the first polarization.

[0013] The polarization management stage may also comprise a polarization rotator operable to rotate a first polarization of the first beam such that the first beam comprises a rotated polarization that coincides with the second polarization. The PIC may also comprise a filter stage operable to receive and filter the first and second beams received from the polarization management stage and output a filtered output beam. In this manner, energy from both the in-plane and out-of-plane polarizations of the polarization diverse optical input may be transferred to the filter stage.

[0014] In some examples, the polarization management stage can include a beam coupler that combines a first beam having a circular polarization and a second beam having a second polarization into an intermediate beam. The filter stage can be operable to receive and filter the intermediate beam and output a filtered output beam.

[0015] In some examples, the polarization management stage can include a phase shifter that can be operable to shift the phase of the second beam to match the phase of the first beam before the first and second beams are received by the beam coupler.

[0016] In some examples, the filter stage can include a first filter that receives the first beam and a second filter that receives the second beam. The first filter can output a first filtered intermediate output, and the second filter can output a second filtered intermediate output. The filter stage can further include a power combiner operable to receive and combine the first filtered intermediate output and the second filtered intermediate output to output the filter output beam. The filter stage can also include a bias tee operable to receive the first filtered intermediate output and the second filtered intermediate output and output a first biased intermediate output and a second biased intermediate output to the power combiner.

[0017] In another example of the present disclosure, a method is provided for filtering a polarization-diverse optical input on a photonic integrated circuit ("PIC") bandpass filter. The method can include splitting the polarization-diverse optical input into a first beam having a first polarization and a second beam having a second polarization different from the first polarization, rotating the first polarization of the first beam such that the first beam includes a circular polarization that matches the second polarization, filtering the first beam including the circular polarization and the second beam including the second polarization, and outputting a filter output beam.

[0018] In some examples, the method can also include combining the first beam and the second beam into an intermediate beam prior to filtering. In some examples, the method can include phase shifting the second beam prior to combining such that a phase of the second beam matches a phase of the first beam.

[0019] In some examples, a first beam may be filtered by a first filter to output a first filtered intermediate output, a second beam may be filtered by a second filter to output a second filtered intermediate output, and the first filtered intermediate output may be combined with the second filtered intermediate output to output a filtered output beam.

[0020] In another example of the present disclosure, a polarization management device for a photonic bandpass filter is provided. The polarization management device may comprise an optical splitter. The optical splitter may be operable to split a polarization diverse optical input into a first beam having a first polarization and a second beam having a second polarization different from the first polarization. The polarization management device may further comprise a polarization rotator. The polarization rotator may be operable to rotate a first polarization of the first beam such that the first beam comprises a rotated polarization that matches the second polarization. The polarization management device may further comprise a beam coupler. The beam coupler may be operable to combine or couple the first beam and the second beam into an intermediate beam that may be output to a polarization sensitive filter input.

[0021] To further explain the present technology, examples are now presented with reference to the drawings. FIG. 1 shows a schematic diagram of a PIC bandpass filter with polarization diversity according to an example of the present disclosure. As shown in FIG. 1, the PIC bandpass filter 10 may include a polarization management stage 102 and a filter stage 104. It should be noted that the word "stage" is intended to be a structural term that includes or refers to one or more components or elements of a PIC bandpass filter as described herein. Each of the polarization management stage 102 and the filter stage 104 may be formed as at least a part of an on-chip architecture of a photonic integrated circuit. In some examples, each of the polarization management stage 102 and the filter stage 104 may be incorporated into a single integrated chip. In other examples, the polarization management stage 102 and the filter stage 104 may be formed on separate chips.

[0022] Each of the polarization management stage 102 and the filter stage 104 may be formed as at least a part of an on-chip architecture that may include any number of suitable materials. For example, such materials may include silicon, silicon nitride, III / V (e.g., gallium arsenide, InP), III-nitrides (e.g., aluminum nitride, gallium nitride), and the like. In some examples, the polarization management stage 102 and the filter stage 104 may benefit from heterogeneous integration of different materials to provide more optimal performance. In one example, the polarization management stage 102 may comprise silicon waveguide circuitry and the filter stage 104 may comprise silicon nitride waveguide circuitry. In this example, the low loss of silicon nitride allows for ultra-low loss, narrow bandwidth filters to be realized. When heterogeneous integration of materials is utilized between the polarization management stage 102 and the filter stage 104, there may be an adiabatic transition stage from the polarization management stage 102 (e.g., silicon waveguide layer) at the output of the polarization management stage 102 to the input of the filter stage 104 (e.g., silicon nitride waveguide layer).

[0023] The polarization-managed stage 102 may be operable to receive a diversely polarized light input 106 and output an intermediate beam 126 having a uniform polarization. In one example, the polarization-diverse light input 106 may comprise a broadband LED light source that is sent to an on-chip polarization stage input 108 of the polarization-managed stage 102. The polarization-diverse light input 106 may comprise light having mixed polarizations. For example, the polarization-diverse light input 106 may comprise a transverse electric polarization (in-plane polarization) and a transverse magnetic polarization (out-of-plane polarization) that is received at the polarization stage input 108.

[0024] In this example, the polarization management stage 102 may include an optical splitter 110. The optical splitter 110 may receive a polarization diverse optical input 106 and split the polarization diverse optical input 106 into a first beam 112 having a first polarization and a second beam 114 having a second polarization. For example, the optical splitter 110 may split the polarization diverse optical input 106 such that the first beam 112 includes a transverse magnetic polarization (or out-of-plane polarization) and the second beam 114 includes a transverse electric polarization (or in-plane polarization). The optical splitter 110 may be any suitable on-chip optical splitter that is incorporated into the architecture of the polarization management stage 102. It should be noted that the paths of the various optical beams shown in the figures may be any suitable on-chip optical waveguides that form optical paths on the PIC bandpass filters.

[0025] The first beam 112 (a beam having a transverse magnetic polarization or an out-of-plane polarization) may travel from the optical splitter 110 to a polarization rotator 116 of the polarization management stage 102. The polarization rotator 116 may rotate the polarization of the first beam 112 received at the polarization rotator 116 and output a first beam having a rotated polarization 118. The first beam with the rotated polarization 118 may have a rotated polarization (i.e., a transverse electric polarization or an in-plane polarization) that matches the polarization of the second beam 114. The polarization rotator 118 may be any suitable on-chip polarization rotator incorporated into the architecture of the polarization management stage 102.

[0026] The polarization management stage 102 may also comprise a phase shifter 120. The phase shifter 120 may be operable to receive the second beam 114 and shift the phase of the second beam 114 to match the phase of the first beam with the rotated polarization 118. Thus, the phase shifter 120 may output the second beam 114 as a phase-shifted beam 122, such that the phase-shifted beam 122 has a phase that does not interfere with the first beam with the rotated polarization 118. In other words, the phase shifter 120 is operable to ensure that the phase-shifted beam 112 and the first beam with the rotated polarization 118 combine coherently and constructively. The phase shifter 120 may comprise any suitable on-chip phase shifter incorporated into the architecture of the polarization management stage 102.

[0027] The first beam 112 rotated by the polarization rotator 116 into a first beam having a rotated polarization 118 and the second beam 114 phase shifted by the phase shifter 120 into a phase shifted beam 122 can be combined by a beam coupler 124 of the polarization management stage 102. The beam coupler 124 can output an intermediate beam 126. The intermediate beam 126 can include a uniform polarization. In this example, the intermediate beam 126 can include a transverse electric polarization (or in-plane polarization). The intermediate beam 126 can be output from the polarization management stage 102 to a filter input 128 of the filter stage 104. In this manner, the polarization management stage 102 can facilitate the transfer of energy of both the in-plane and out-of-plane polarizations of the polarization diverse optical input 106 to the filter stage 104 of the PIC bandpass filter 10.

[0028] The filter stage 104 can be operable to receive the intermediate beam 126 from the polarization management stage 102, filter the intermediate beam 126, and output a filter output beam. The filter stage 104 can include an on-chip filter 130. As described above, a typical on-chip filter is sensitive to the input signal polarization due to its strong refractive index contrast. However, in this example, the intermediate beam 126 received at the filter input 128 includes a uniform polarization (e.g., transverse electric polarization or in-plane polarization). Thus, the entire energy of the polarization diverse optical input 106 received at the PIC bandpass filter 10 can be filtered by the filter 130 of the filter stage 104 (without the expected loss caused by the polarization management stage 102).

[0029] The on-chip filter 130 can be any desired suitable filter based on the particular application. In the example shown in FIG. 1, the filter 130 can be a bandpass filter designed for transverse electric polarization and can be based on a ring-assisted Mach-Zehnder interferometer (RAMZI) architecture. The filter 130 can be a fourth-order filter with two ring resonators that can be tuned to a desired frequency in each arm of the Mach-Zehnder interferometer. Of course, this filter is merely exemplary and it is contemplated that other desired filters can be used. The filter stage 104 can filter the intermediate beam 126 and can output a first filter output 132 and a second filter output 134. The first filter output 132 and the second filter output 134 can be collected, for example, by a lensed fiber and can be sent to an output device depending on the desired application.

[0030] In some examples, the phase shifter 120 can be adjusted based on the first filter output 132 and the second filter output 134. To ensure that the phase shifted beam 112 and the first beam 118 with circular polarization have matched or coincident phases so that they can be coherently and constructively combined, at least one of the first filter output 132 and the second filter output 134 can be monitored to determine whether an expected amount of energy is output by the PIC bandpass filter 10. If the determined amount of energy is less than the expected output, the phase shifter 120 can be adjusted to reduce any interference between the phase shifted beam 112 and the first beam 118 with circular polarization. In some examples, this can be done manually via an operator measuring at least one of the first filter output 132 and the second filter output 134 and adjusting the phase shifter 120. In another example, the phase shifter may be adjusted autonomously, such as via a microcontroller operable to monitor at least one of the first filter output 132 and the second filter output 134 and adjust the phase shifter 120 to ensure coherent and constructive combination of the phase shifted beam 112 and the first beam having circular polarization 118.

[0031] As mentioned above, the PIC bandpass filter with polarization diversity is not limited to a single filter type. FIG. 2 shows a schematic diagram of a PIC bandpass filter with polarization diversity according to an example of the present disclosure. In FIG. 2, the PIC bandpass filter 20 includes a polarization management stage 102 similar to the polarization management stage 102 shown in FIG. 1. In this example, the polarization management stage 102 outputs the intermediate beam 126 to a filter input 228 of a filter stage 204. The filter stage 204 in this example can include a filter 230 made of a cascaded coupled resonator filter. The filter stage 204 can include a first filter output 232 and a second filter output 234. The first filter output 232 and the second filter output 234 can be collected, for example, by a lensed fiber and can be sent to an output device depending on the desired application. It should again be noted that the filter stage 204 may comprise any suitable filter based on the desired application, and the filters 130, 230 shown in FIGS. 1 and 2 are exemplary and are not intended to be limiting in any way.

[0032] 3 shows a schematic diagram of a PIC bandpass filter with polarization diversity according to an example of the present disclosure. In FIG. 3, a PIC bandpass filter 30 is provided. Similar to the PIC bandpass filters 10, 20, the PIC bandpass filter 30 can be configured and operable to transfer energy from in-plane and out-of-plane polarizations of a polarization-diverse optical input 306 to a filter stage 304 of the bandpass filter 30. The PIC bandpass filter 30 can include a polarization management stage 302 and a filter stage 304. Each of the polarization management stage 302 and the filter stage 304 can be formed as at least a part of an on-chip architecture of a photonic integrated circuit.

[0033] The polarization-managed stage 302 may be configured and operable to receive a polarization-diverse optical input 306 and output intermediate beams having similar polarizations. In one example, the polarization-diverse optical input 306 may comprise a broadband LED light source that is sent to an on-chip polarization stage input 308 of the polarization-managed stage 302. The polarization-diverse optical input 306 may comprise light having mixed polarizations. For example, the polarization-diverse optical input 306 may comprise a transverse electric polarization (in-plane polarization) and a transverse magnetic polarization (out-of-plane polarization) that is received at the polarization stage input 308.

[0034] In this example, the polarization management stage 302 may include an optical splitter 310. The optical splitter 310 may receive a polarization diverse optical input 306 and split the polarization diverse optical input 306 into a first beam 312 having a first polarization and a second beam 314 having a second polarization. For example, the optical splitter 310 may split the polarization diverse optical input 306 such that the first beam 312 includes a transverse magnetic polarization (or out-of-plane polarization) and the second beam 314 includes a transverse electric polarization (or in-plane polarization). The optical splitter 310 may be any suitable on-chip optical splitter incorporated into the architecture of the polarization management stage 302.

[0035] The first beam 312 (a beam having a transverse magnetic polarization or an out-of-plane polarization) may travel from the optical splitter 310 to a polarization rotator 316 of the polarization management stage 302. The polarization rotator 316 may rotate the polarization of the first beam 312 received at the polarization rotator 316 and output the first beam with a rotated polarization 318. The first beam with rotated polarization 318 may have a rotated polarization (i.e., a transverse electric polarization or an in-plane polarization) that matches the polarization of the second beam 314. The polarization rotator 318 may be any suitable on-chip polarization rotator incorporated into the architecture of the polarization management stage 302.

[0036] The first beam 318 and the second beam 314 having circular polarization may be output from the polarization management stage 302 as first and second intermediate beams that may be received by the filter stage 304. For example, the filter stage 304 may include a first filter input 328a at a first filter 330a that receives and filters the first beam 318 having circular polarization and a second filter input 328b at a second filter 330b that receives and filters the second beam 314. The first filter 330a and the second filter 330b may be any suitable on-chip filters based on a given application.

[0037] In one example, the first filter 330a and the second filter 330b may be operable with a photodiode or photodetector 335. The photodetector 335 may be integrated in the same chip as the first filter 330a and the second filter 330b, or the photodetector 335 may be on a separate chip or an off-chip component. The photodetector 335 may convert the optical output from the first and second filters into an RF signal or a clock signal. In this manner, the first filter 330a and its respective photodetector 335 may be operable to output a first filtered intermediate output 336a and a first intermediate clock signal 338a. Similarly, the second filter 330b and its respective photodetector 335 may be operable to output a second filtered intermediate output 336b and a second intermediate clock signal 338b.

[0038] In some examples, each of these outputs 336a, 336b and the clock signals 338a, 338b may be sent to a bias tee 339. The bias tee 339 may be configured and operable to add a desired voltage to each of the outputs 336a, 336b and the clock signals 338a, 338b. The bias tee 339 may output a first biased intermediate output 340a and a second biased intermediate output 340b to a first power combiner 344a. Similarly, the bias tee 339 may output a first biased clock output 342a and a second biased clock output 342b to a second power combiner 344b. Similar to the photodetector 335, the bias tee 339 may be integrated on the same chip as the first filter 330a and the second filter 330b, or may be formed on a separate chip, or may be formed as an off-chip component.

[0039] The power combiner 344a can be configured to combine the first biased intermediate output 340a and the second biased intermediate output 340b (if the bias tee 339 is not incorporated, the power combiner 344a can be configured to combine the first filtered intermediate output 336a and the second filtered intermediate output 336b). The power combiner 344b can be configured to combine the first biased clock output 342a and the second biased clock output 342b (if the bias tee 339 is not incorporated, the power combiner 344b can be configured to combine the first intermediate clock output 338a and the second intermediate clock output 338b). The first power combiner 344a can output the first filter output 332, and the second power combiner 344b can output the second filter output 334. The first filter output 332 and the second filter output 334 can be collected, for example, by a lensed fiber, and can be sent to an output device depending on the desired application.

[0040] In each of the above examples, the PIC bandpass filter 10, 20, 30 can transfer energy from the in-plane and out-of-plane polarizations of the polarization-diverse optical input to the filter stages of the bandpass filter 10, 20, 30. This allows the bandpass filter 10, 20, 30 to be polarization insensitive.

[0041] 4A and 4B show examples of measured spectral responses of filter structures comparing a PIC bandpass filter with polarization diversity as shown in FIGS. 1-3 with a PIC bandpass filter without polarization diversity. FIG. 4A shows a baseline measured spectral response for a PIC bandpass filter with polarization diversity (see, e.g., any one of bandpass filters 10, 20, or 30 described above). In FIG. 4A, linearly polarized transverse electric light was input to the PIC bandpass filter at both the polarization stage input (see, e.g., any one of polarization stage inputs 108, 308 described herein) (mixed port) and the filter input of the filter stage (see, e.g., any one of filter inputs 128, 228, 328a, 328b described herein) (TE port). As shown in FIG. 4A, similar performance was observed with an out-of-band rejection of about 35-50 dB. This also verifies that the on-chip polarization management stage does not involve any significant extra loss or distortion. In FIG. 4B, a polarization-diverse optical input is input to a PIC bandpass filter (e.g., see any one of the bandpass filters 10, 20, 30 described herein) at both the polarization stage input (e.g., see any one of the polarization stage inputs 108, 308 described herein) (mixed port) and the filter input (e.g., see any one of the filter inputs 128, 228, 328a, 328b described herein) (TE port). As shown in FIG. 4B, the mixed port exhibits an out-of-band rejection of over 40 dB, while the TE port exhibits an out-of-band rejection of about 25 dB. Based on this, it is shown that the PIC bandpass filter 10, 20, 30 can be proven to be polarization insensitive.

[0042] 5 illustrates a method of filtering a polarization-diverse optical input on a photonic integrated circuit ("PIC") bandpass filter according to an example of the present disclosure. As shown in FIG. 5, in step 552, the polarization-diverse optical input is split into a first beam and a second beam. As described above with reference to the PIC bandpass filter 10, 20, 30 (see FIGS. 1-3), the polarization-diverse optical input 106, 306 can be input to the polarization stage input 108, 308 and split by the optical splitter 110, 310 into a first beam 112, 312 having a first polarization (e.g., transverse electric polarization or in-plane polarization) and a second beam 114, 314.

[0043] In step 554, the polarization of the first beam may be rotated to match the polarization of the second beam. As described above, the polarization rotator 116, 316 may rotate the polarization of the first beam 112, 312 to output the first beam having a rotated polarization 118, 318 that matches the polarization of the second beam 114. If the first beam and the second beam have the same polarization, the energy of both the first beam and the second beam may be transmitted to a filter stage (e.g., the filter stage 104, 204, 304 described above).

[0044] In step 556, the second beam may be phase shifted to match the phase of the first beam. For example, the second beam 114 may be received by a phase shifter 120 to shift the phase of the second beam 114 so that the phase of the second beam 114 can match the phase of the first beam having a circular polarization 118 before combing the second beam 114. The phase shifter 120 may output the second beam 114 as a phase shifted beam 122 such that the phase shifted beam 122 has a phase that does not interfere with the first beam 118 having a circular polarization.

[0045] In step 558, the first beam and the second beam can be combined into an intermediate beam. For example, the first beam 118 having a circular polarization and the phase-shifted beam 122 can be combined by the beam coupler 124 of the polarization management stage 102. The beam coupler 124 can output an intermediate beam 126. The intermediate beam 126 can include a uniform polarization. In this example, the intermediate beam 126 can include a transverse electric polarization (or an in-plane polarization).

[0046] In step 560, the intermediate beam (which is a combination of the first beam and the second beam) can be filtered to output a filtered output beam. For example, the filter stage 104, 204 can include an on-chip filter 130, 230 configured and operable to filter the intermediate beam to output a filtered output beam, such as a first filter output 132, 232 and a second filter output 134, 234. As described above, a typical on-chip filter is sensitive to the input signal polarization due to its strong refractive index contrast. However, in this example, the intermediate beam can include a uniform polarization (e.g., transverse electric polarization or in-plane polarization). Thus, the entire energy of the polarization diverse optical input received at the PIC bandpass filter can be filtered (without the expected losses that may occur in steps 552, 554, 556, and 558).

[0047] 6 illustrates a method of filtering a polarization-diverse optical input on a photonic integrated circuit ("PIC") bandpass filter according to an example of the present disclosure. As shown in FIG. 6, in step 652, the polarization-diverse optical input is split into a first beam and a second beam. As described above with reference to the PIC bandpass filter 10, 20, 30 (see FIGS. 1-3), the polarization-diverse optical input 106, 306 can be input to the polarization stage input 108, 308 and split by the optical splitter 110, 310 into a first beam 112, 312 having a first polarization (e.g., transverse electric polarization or in-plane polarization) and a second beam 114, 314.

[0048] In step 654, the polarization of the first beam may be rotated to match the polarization of the second beam. As described above, the polarization rotator 116, 316 may rotate the polarization of the first beam 112, 312 to output the first beam having a rotated polarization 118, 318 that matches the polarization of the second beam 114. If the first beam and the second beam have the same polarization, the energy of both the first beam and the second beam may be transmitted to a filter stage (e.g., the filter stage 104, 204, 304 described above).

[0049] In step 656, the first beam and the second beam may be filtered by an on-chip filter. For example, as described above with reference to FIG. 3, the first beam 318 and the second beam 314 having circular polarization may be output from the polarization management stage 302 as first and second intermediate beams that may be received by the filter stage 304. For example, the filter stage 304 may include a first filter input 328a at a first filter 330a that receives and filters the first beam having circular polarization 318 and a second filter input 328b at a second filter 330b that receives and filters the second beam 314. The first filter 330a and the second filter 330b may be any suitable on-chip filters based on a given application.

[0050] In step 658, the first beam and the second beam can be combined into a filter output beam. For example, the first filter 330a can be operable to output a first filtered intermediate output 336a, and the second filter 330b can be operable to output a second filtered intermediate output 336b. The first filtered intermediate output 336a and the second filtered intermediate output 336b can be sent to a bias tee 339. The bias tee 339 is configured and operable to apply a desired voltage to each of the outputs 336a, 336b. The bias tee 339 can output a first biased intermediate output 340a and a second biased intermediate output 340b to a first power combiner 344a. The power combiner 344a can combine the first biased intermediate output 340a and the second biased intermediate output 340b into the first filter output 332. Thus, the entire energy of the polarization diverse optical input received at the PIC bandpass filter can be filtered (without the anticipated losses that may occur in steps 652, 654, and 658).

[0051] Thus, as described herein, a polarization-insensitive PIC bandpass filter is provided. Additionally, a method for filtering polarization-diverse light inputs in a PIC bandpass filter is provided. Compared to typical PIC filters that are polarization-sensitive and may require uniformly polarized light inputs, the above-described filters and methods can accommodate polarization-diverse light inputs (i.e., light inputs that do not have uniform polarization or light inputs with random polarization). Thus, the entire energy of the polarization-diverse light inputs can be transferred to the filter (naturally, without expected loss). In one example, this facilitates the use of standard optical fibers, which in effect transmit random polarizations of light. Thus, light can be transmitted over long distances using standard optical fibers, reducing manufacturing and material costs in many applications.

[0052] Reference has been made to the examples illustrated in the drawings, and specific language has been used herein to describe these. It will be understood, however, that no limitation of the scope of the technology is intended thereby. Modifications and further variations of the features illustrated herein, as well as additional uses of the examples illustrated herein, should be considered within the scope of the description.

[0053] Although the present disclosure may not explicitly disclose that some embodiments or features described herein may be combined with other embodiments or features described herein, the present disclosure should be read to describe any such combinations that may be performed by one of ordinary skill in the art. The use of "or" in this disclosure should be understood to mean a non-exclusive or, i.e., "and / or," unless otherwise indicated herein.

[0054] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the foregoing description, numerous specific details, such as examples of various configurations, have been provided to provide a thorough understanding of examples of the described technology. However, it will be understood that the technology may be practiced without one or more of the specific details, or with other methods, components, devices, etc. In other instances, well-known structures or operations have not been shown or described in detail to avoid obscuring aspects of the technology.

[0055] Although the subject matter has been described in language specific to structural features and / or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described. Rather, the specific features and operations described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements may be devised without departing from the spirit and scope of the described technology.

Claims

1. a polarization management stage operable to receive a polarization diverse optical input and to output an intermediate beam having uniform polarization; a filter stage operable to receive the intermediate beam from the polarization management stage, filter the intermediate beam, and output a filtered output beam; A photonic integrated circuit ("PIC") bandpass filter with polarization diversity, where energy from in-plane and out-of-plane polarizations of the polarization-diverse optical input is transferred to the filter stage.

2. 2. The PIC bandpass filter of claim 1, wherein the polarization management stage comprises an optical splitter operable to split the polarization diverse optical input into a first beam having a first polarization and a second beam having a second polarization different from the first polarization.

3. 3. The PIC bandpass filter of claim 2, wherein the polarization management stage comprises a polarization rotator operable to rotate the first polarization of the first beam such that the first beam comprises a rotated polarization that coincides with the second polarization.

4. 4. The PIC bandpass filter of claim 3, wherein the polarization management stage comprises a beam coupler that combines the first beam having the circular polarization and the second beam having the second polarization into an intermediate beam.

5. 5. The PIC bandpass filter of claim 4, wherein the polarization management stage comprises a phase shifter operable to shift the phase of the second beam to match the phase of the first beam before the first and second beams are received by the beam coupler for coherent and constructive combining of the first and second beams.

6. 2. The PIC bandpass filter of claim 1, wherein the intermediate beam includes a first intermediate beam and a second intermediate beam, and the filter stage comprises a first filter that receives the first intermediate beam and a second filter that receives the second intermediate beam.

7. 7. The PIC bandpass filter of claim 6, wherein the first filter outputs a first intermediate filtered output and the second filter outputs a second intermediate filtered output.

8. 8. The PIC bandpass filter of claim 7, wherein the filter stage further comprises a power combiner operable to receive and combine the first filtered intermediate output and the second filtered intermediate output to output the filtered output beam.

9. 9. The PIC bandpass filter of claim 8, wherein the filter stage further comprises a photodetector associated with the first filter and the second filter, respectively, the photodetector operable to convert an optical signal to an RF signal, and outputting the first filtered intermediate output and the second filtered intermediate output from the first filter and the second filter, respectively.

10. 9. The PIC bandpass filter of claim 8, wherein the filter stage further comprises a bias tee operable to receive the first filtered intermediate output and the second filtered intermediate output and to output a first biased intermediate output and a second biased intermediate output to the power combiner.

11. a polarization management stage comprising an optical splitter operable to split a polarization diverse optical input into a first beam having a first polarization and a second beam having a second polarization different from the first polarization, and a polarization rotator operable to rotate the first polarization of the first beam such that the first beam comprises a rotated polarization that coincides with the second polarization; a filter stage operable to receive and filter the first and second beams received from the polarization management stage and output a filtered output beam; A photonic integrated circuit ("PIC") bandpass filter with polarization diversity, where energy from in-plane and out-of-plane polarizations of the polarization-diverse optical input is transferred to the filter stage.

12. 12. The PIC bandpass filter of claim 11, wherein the polarization management stage comprises a beam coupler that combines the first beam having the circular polarization and the second beam having the second polarization into an intermediate beam, and the filter stage is operable to receive and filter the intermediate beam and output the filter output beam.

13. 13. The PIC bandpass filter of claim 12, wherein the polarization management stage comprises a phase shifter operable to shift the phase of the second beam to match the phase of the first beam before the first and second beams are received by the beam coupler for coherent and constructive combining of the first and second beams.

14. 12. The PIC bandpass filter of claim 11, wherein the filter stage comprises a first filter receiving the first beam and a second filter receiving the second beam.

15. 15. The PIC bandpass filter of claim 14, wherein the first filter outputs a first intermediate filtered output and the second filter outputs a second intermediate filtered output.

16. 16. The PIC bandpass filter of claim 15, wherein the filter stage further comprises a power combiner operable to receive and combine the first filtered intermediate output and the second filtered intermediate output to output the filtered output beam.

17. 17. The PIC bandpass filter of claim 16, wherein the filter stage further comprises a photodetector associated with the first filter and the second filter, respectively, the photodetector operative to convert an optical signal to an RF signal and output the first filtered intermediate output and the second filtered intermediate output from the first filter and the second filter, respectively.

18. 17. The PIC bandpass filter of claim 16, wherein the filter stage further comprises a bias tee operable to receive the first filtered intermediate output and the second filtered intermediate output and to output a first biased intermediate output and a second biased intermediate output to the power combiner.

19. 1. A method for filtering a polarization-diverse optical input on a photonic integrated circuit ("PIC") bandpass filter, comprising: splitting an input polarization diverse light into a first beam having a first polarization and a second beam having a second polarization different from the first polarization; rotating the first polarization of the first beam such that the first beam comprises a circular polarization that coincides with the second polarization of the second beam; filtering the first beam having the circular polarization and the second beam having the second polarization; outputting the filtered output beam; The method comprising:

20. 20. The method of claim 19, further comprising combining the first beam and the second beam into an intermediate beam prior to the filtering.

21. 21. The method of claim 20, further comprising phase shifting the second beam prior to said combining such that the phase of the second beam matches the phase of the first beam.

22. 20. The method of claim 19, wherein the first beam is filtered by a first filter to output a first filtered intermediate output, the second beam is filtered by a second filter to output a second filtered intermediate output, and the first filtered intermediate output is combined with the second filtered intermediate output to output the filtered output beam.

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