Polarization system and method

Abstract

An example polarization splitter and rotator device is described. In one example, an optical device includes: a splitter configured to split an optical signal into a first signal having a first polarization and a second signal having a second polarization; a polarization rotator configured to rotate the second polarization of the second signal to a third polarization; and a polarization mode converter configured to convert the third polarization of the second signal to the first polarization. In some aspects of the embodiments, the splitter can be a curved multimode interference (MMI) polarization splitter, and the polarization rotator includes an input port and an output port, where the output port is wider than the input port. The polarization mode converter can be an asymmetric waveguide tapered mode converter. The devices described herein can overcome the deficiencies of conventional devices and provide low insertion loss, flat and / or wide wavelength response, high manufacturing tolerances, and compact size.

Description

Technical Field

[0001] The present invention generally relates to optical waveguide devices, and more particularly to optical waveguide devices that change the polarization of optical signals. Background Art

[0002] Polarization splitters and rotators (PSRs) can be passive devices used in integrated optics, such as data transmitters or receivers (e.g., transceivers). For example, a PSR can use dual-polarization division multiplexing (DPDM) to double the bandwidth of a transceiver. A PSR can also be used to construct a polarization-insensitive receiver that can detect signals transmitted in an optical single-mode fiber.

[0003] When an optical signal is input into a waveguide of a photonic integrated circuit (PIC), the polarization of the optical signal can be known based on the input circuit. However, when an optical signal is received by a receiver, the polarization of the optical signal can be unknown. In fact, the polarization can be randomly polarized or an unknown transverse electric (TE), transverse magnetic (TM), or TE / TM polarization. Thus, a PSR can use a directional coupler to separate the optical signal into TE and TM polarizations and rotate the light to a known TE state so that data can be retrieved from the optical signal.

[0004] However, conventional PSRs can suffer from narrow wavelength response, high insertion loss, sensitivity to manufacturing errors, and large size. The coupling ratio of a directional coupler can be wavelength-sensitive, and it can be difficult to obtain a flat wavelength response. In addition, the sizes of the associated polarization rotator and mode converter can be relatively large and exhibit optical attenuation.

[0005] FIG. 1 shows a conventional PSR 100. The PSR 100 can include a directional-coupler-based polarization splitter 110, a bilayer-taper-based TM0 to TE1 polarization rotator 120, and an asymmetric Mach-Zehnder interferometer (MZI)-based TE1 to TE0 mode converter 130. An optical signal having both TE0 (i.e., zero-order TE mode) and TM0 (i.e., zero-order TM mode) polarizations can be input via an input port 101. For a TE0 input, the TE0-polarized light can directly propagate to a through port 111. For a TM0 input, the TM0-polarized light can be coupled to a cross port 112 and then gradually converted into a TE1 (i.e., first-order TE mode) polarization mode when propagating through the polarization rotator 120, which can provide a bilayer taper. The output TE1 polarization mode can then be separated into two TE0 mode beams by the converter 130, which can also introduce an additional π phase difference between the two beams and then phase-align the beams so that they can be converted into a TE0 polarization mode output from the converter 130.

[0006] FIG. 2 shows another example of a conventional PSR 200. The order of operations in this example is polarization rotation, separation, and mode conversion. TE0 / TM0 hybrid polarized light can be input at input port 201. As the input light propagates through the tapered waveguide polarization rotator 210, the TM0 mode light can be converted into TE1 mode light, while the TE0 mode light remains unchanged. Then, the TE1 and TE0 modes can be input into the mode separator and rotator 220 at input 211 and then separated into two light beams by the mode separator and rotator 220. For example, the mode separator and rotator 220 can be a directional coupler of a Y-junction or an MZI interferometer. The TE0 mode light can be output at the through port 221. Using mode conversion or mode interference in the mode separator and rotator 220, the TE1 mode light can be converted into TE0 mode and output at the cross port 222. SUMMARY OF THE INVENTION

[0007] In an exemplary embodiment of the present disclosure, a method of transmitting multiple optical modulation signals for output to an optical fiber system is provided. The method includes the steps of: providing a first laser source configured to emit light of a first wavelength having a first polarization and a second laser source configured to emit light of a second wavelength having the first polarization, the second wavelength being different from the first wavelength; receiving a first portion of the light emitted by the first laser source with a first modulator and receiving a second portion of the light emitted by the first laser source with a second modulator; receiving a first portion of the light emitted by the second laser source with a third modulator and receiving a second portion of the light emitted by the second laser source with a fourth modulator; outputting a first modulated optical signal from the first modulator, the first modulated optical signal having the first polarization; outputting a second modulated optical signal from the second modulator, the second modulated optical signal having the first polarization; outputting a third modulated optical signal from the third modulator, the third modulated optical signal having the first polarization; outputting a fourth modulated optical signal from the fourth modulator, the fourth modulated optical signal having the first polarization; multiplexing the first modulated optical signal and the third modulated optical signal to provide a first multiplexed optical signal having the first polarization; multiplexing the second modulated optical signal and the fourth modulated optical signal to provide a second multiplexed optical signal having the first polarization; changing the second multiplexed optical signal to have a second polarization, the second polarization being different from the first polarization; and combining the first multiplexed optical signal having the first polarization and the second multiplexed optical signal having the second polarization into a third optical signal.

[0008] In an example thereof, the method further includes the step of providing the third optical signal to the optical fiber system.

[0009] In another example thereof, each of the first laser source and the second laser source is a laser diode.

[0010] In yet another example thereof, the step of changing the second multiplexed optical signal to have the second polarization includes the step of passing the second multiplexed optical signal having the first polarization through a waveguide polarization rotator.

[0011] In yet another example thereof, the first polarization is TE mode polarization.

[0012] In yet another example thereof, the first polarization is TE mode polarization and the second polarization is TM mode polarization.

[0013] In another exemplary embodiment of the present disclosure, a method for detecting multiple optical signals of multiple wavelengths is provided. The method includes the following steps: receiving an optical signal including multiple polarization-mixed optical signals, each of the polarization-mixed optical signals being at a respective wavelength; separating the multiple polarization-mixed optical signals into a first partial optical signal having a first polarization and a second partial optical signal having a second polarization; demultiplexing the first partial optical signal into a first wavelength optical signal having the first polarization at a first wavelength and a second wavelength optical signal having the first polarization at a second wavelength; routing the first wavelength optical signal to a first photodetector and routing the second wavelength optical signal to a second photodetector; converting the second partial optical signal having the second polarization into a third partial optical signal having the first polarization; demultiplexing the third partial optical signal into a third wavelength optical signal having the first polarization at the first wavelength and a fourth wavelength optical signal having the first polarization at the second wavelength; and routing the third wavelength optical signal to the first photodetector and routing the fourth wavelength optical signal to the second photodetector.

[0014] In an example thereof, the step of converting the second partial optical signal having the second polarization into a third partial optical signal having the first polarization includes the following steps: passing the second partial optical signal through a waveguide polarization rotator to generate a fourth partial optical signal having a third polarization; and changing the polarization of the fourth partial optical signal to the first polarization to generate the third optical signal having the first polarization.

[0015] In another example thereof, the first polarization is TE mode polarization.

[0016] In another example thereof, the first polarization is TE mode polarization and the second polarization is TM mode polarization.

[0017] In yet another example, the first polarization is TE0 mode polarization, the second polarization is TM mode polarization, and the third polarization is TE1 mode polarization.

[0018] In another exemplary embodiment of the present disclosure, an optical device is provided. The optical device includes: a separator configured to separate an optical signal into a first signal having a first polarization and a second signal having a second polarization; a waveguide polarization rotator configured to rotate the second polarization of the second signal into a third polarization; and a polarization mode converter configured to convert the third polarization of the second signal into the first polarization.

[0019] In an example thereof, the separator is a multimode interference (MMI) polarization separator. In a variant thereof, the separator is curved.

[0020] In another example thereof, the polarization rotator includes an input port and an output port, wherein the output port is wider than the input port. In a variant thereof, the width of the input port is 420 nm or about 420 nm, and the width of the output port is 1000 nm or about 1000 nm.

[0021] In a further example thereof, the polarization rotator includes a rib layer and a ridge layer. In a variant thereof, the thickness of the rib layer is 90 nm or about 90 nm. In a further variant thereof, the thickness of the ridge layer is 220 nm or about 220 nm. In yet another variant thereof, the width of the rib layer is 1000 nm or about 1000 nm.

[0022] In yet another example thereof, the polarization mode converter is an asymmetric waveguide taper mode converter.

[0023] In yet another example, the first polarization is zero-order transverse electric (TE) mode polarization, and the second polarization is zero-order transverse magnetic (TM) mode polarization.

[0024] In yet another example, the third polarization is first-order transverse electric (TE) mode polarization.

[0025] In yet another example, the first signal having the first polarization and the second signal having the first polarization are output to one or more receivers.

[0026] In yet another exemplary embodiment of the present disclosure, an optical transmission method is provided. The optical transmission method includes: separating an optical signal into a first signal having a first polarization and a second signal having a second polarization; rotating the second polarization of the second signal into a third polarization using a waveguide polarization rotator; and converting the third polarization of the second signal into the first polarization.

[0027] In its example, the first polarization is a zero-order transverse electric (TE) mode polarization, and the second polarization is a zero-order transverse magnetic (TM) mode polarization.

[0028] In another example thereof, the third polarization is a first-order transverse electric (TE) mode polarization.

[0029] In a further example thereof, the first signal having the first polarization and the second signal having the first polarization are output to one or more receivers.

[0030] In yet another exemplary embodiment of the present disclosure, an optical device is provided. The optical device includes: a polarization mode converter configured to convert a first polarization of a first optical signal into a second polarization; a waveguide polarization rotator configured to rotate the second polarization of the first optical signal into a third polarization; and a combiner configured to form a combined optical signal by combining the first optical signal having the third polarization with a second optical signal having the first polarization.

[0031] In an example thereof, the combined optical signal is input into one or more optical transmission fibers.

[0032] In another example thereof, the first optical signal and the second optical signal are generated by a laser light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To facilitate a more comprehensive understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are denoted by like reference numerals. These drawings should not be construed as limiting the present disclosure, but are merely intended to be illustrative.

[0034] FIG. 1 shows an exemplary conventional PSR according to an example of the present disclosure.

[0035] FIG. 2 shows another exemplary conventional PSR according to an example of the present disclosure.

[0036] Figure 3 An integrated optical device according to some embodiments of the present disclosure is shown.

[0037] Figures 4A - 4E A diagram associated with a polarization splitter according to some embodiments of the present disclosure is shown.

[0038] Figures 5A - 5D A relationship between waveguide thickness variation and transmission according to some embodiments of the present disclosure is shown.

[0039] Figures 6A - 6D A diagram associated with a polarization converter according to some embodiments of the present disclosure is shown.

[0040] Figures 7A - 7D Shows a simulation diagram of polarization tolerance according to some embodiments of the present disclosure.

[0041] Figures 8A - 8C Shows a converter performance diagram according to some embodiments of the present disclosure.

[0042] Figures 9A - 9B Shows a simulation of the manufacturing tolerance of a converter according to some embodiments of the present disclosure.

[0043] Figures 10A - 10E Shows the PSR performance according to some embodiments of the present disclosure.

[0044] Figure 11 Shows how the proposed PSR design can be applied to a polarization-insensitive receiver.

[0045] Figure 12 Shows how the proposed PSR design can be applied to a polarization-division multiplexing transmitter. Detailed Description

[0046] In the following description and drawings, the present disclosure and related advantages are described and emphasized. The drawings are not necessarily to scale. Detailed descriptions of structures and processing techniques are omitted so as not to unnecessarily obscure the present disclosure. In addition, in the following description, many specific details regarding the systems and methods of the disclosed subject matter and the environments in which these systems and methods can operate are set forth in order to provide a thorough understanding of the disclosed subject matter. However, it will be apparent to those skilled in the art that the disclosed subject matter can be practiced without such specific details. In addition, in order to avoid complicating the disclosed subject matter, certain features well known in the art are not described in detail. Further, it should be understood that the examples provided below are exemplary and that other systems and methods are within the scope of the disclosed subject matter.

[0047] As described above, the conventional PSRs 100 and 200 of FIGS. 1 and 2 may have drawbacks. For example, both can exhibit a small (e.g., 1 decibel (dB)) bandwidth, where the wavelength range of the bandwidth has an optical loss variation of less than 1 dB, for example, and can be, for example, 30 to 40 nanometers (nm). In addition, both PSRs 100 and 200 may have a relatively high insertion loss (e.g., 1.5 to 2.5 dB) and sensitivity to manufacturing errors. Further, in order to operate properly, PSRs 100 and 200 may have to mix TE0 / TM0 mode beams rather than process them independently, which makes dual-polarization division multiplexing (DPDM) difficult.

[0048] Accordingly, a PSR such as the following may be desired, which overcomes the deficiencies of conventional devices and may include, for example, low insertion loss (e.g., less than 1 dB), flat and / or wide wavelength response, high manufacturing tolerance, and compact size. Such advancements may be applied to, for example, photonic transceivers and other related devices.

[0049] Compared with conventional systems, embodiments of the present disclosure achieve various improvements. First, embodiments of the present disclosure may use an MMI-based polarization splitter instead of a directional coupler-based splitter, which can achieve a flatter wavelength response and improved manufacturing tolerance. Second, the MMI splitter may be a particle swarm optimization MMI rather than a straight MMI or a quadratic curve MMI, which can simultaneously achieve low loss, compact size, a 1 dB large bandwidth, and acceptable manufacturing tolerance. Third, embodiments of the present disclosure may employ an asymmetric waveguide taper to replace an interferometer-based mode converter, which can improve manufacturing tolerance and reduce optical loss. Embodiments of the present disclosure may provide improved performance compared to conventional PSRs. Embodiments of the present disclosure may be related to optical receivers and transceivers (such as coherent transceivers) and other optical communication devices.

[0050] Figure 3 An integrated optical device 300 according to some embodiments of the present disclosure is shown. The optical device 300 is a PSR and includes a particle swarm optimization curved multimode interference (MMI) polarization splitter 310, a bilayer waveguide polarization rotator 320, and an asymmetric waveguide taper mode order converter 330. The incident optical signal at input 301 may be an unknown mixture of TE0 polarized light and TM0 polarized light. The MMI polarization splitter 310 separates the TE0 mode light from the TM0 mode light and outputs them at the through port 311 and the cross port 312, respectively. The bilayer waveguide-based polarization rotator 320 rotates the TM0 mode light into TE1 mode light, which is input into the asymmetric waveguide taper mode converter 330 at the input end 321. The asymmetric waveguide taper mode converter 330 further converts the TE1 mode light into TE0 mode light, which is output at port 331. Accordingly, two TE0 mode light beams may be output (one TE0 mode light beam is output at port 311, and the other TE0 mode light beam is output at port 331), and each of the light beams is independent of each other. The output light may be received by one or more receivers, such as a receiving photodetector (PD). In some embodiments, one or more receivers may include diverse receivers.

[0051] As described in further detail below, the MMI-based polarization splitter 310 is less sensitive to wavelength and more forgiving of fabrication compared to conventional splitters. The MMI-based polarization splitter 310 can exhibit a flat spectral bandwidth in its output signal. In one example, the MMI-based polarization splitter 310 is fabricated on a silicon layer and covered with a silica cladding. The silicon layer can be 220 nm thick. Below the silicon layer is a buried oxide (BOX) layer. The BOX layer can be approximately 2 micrometers (μm) thick. To achieve a 1 dB transmission bandwidth greater than 70 nm, the width of the MMI-based polarization splitter 310 can be made as small as possible. However, the dimensions of the left and right edges of the MMI-based polarization splitter 310 can be wide enough to accommodate two 420 nm-wide waveguides and a waveguide gap greater than 300 nm. The MMI-based polarization splitter 310 can include a curved rib layer of 220 nm-thick silicon. No other silicon layers of different thicknesses are used in addition to the rib layer.

[0052] Figure 4A is shown Figure 3 an example structure 400 of the MMI-based polarization splitter 310 shown. Structure 400 includes an input waveguide 410, an MMI polarization splitter 420, and output waveguides 430. In Figure 4A this, the incident optical signal at one of the input waveguides 410 can be an unknown mixture of TE0-polarized light and TM0-polarized light. The MMI polarization splitter 420 separates the TE0-mode light from the TM0-mode light and outputs them separately at the output waveguides 430, which correspond to Figure 3 ports 311 and 312 in Figure 4A this. As also shown in this, the MMI polarization splitter 420 can be separated into multiple segments, such as 34 segments, and is described in detail below.

[0053] Other MMI designs that include curves have been based on exponential or quadratic curves. These designs often violate the adiabatic standard and incur significant optical losses. While applying the adiabatic standard helps reduce losses, it can lead to an overly large volume. For an ideal polarization splitter, compact size, large extinction ratio, high manufacturing tolerance, and wide 1dB bandwidth are also highly desirable. Unfortunately, these figure of merit factors have generally not been considered in curved MMI designs. Thus, traditional exponential or quadratic curve MMIs are not suitable. There are trade-offs associated with polarization splitters, such as competing interests of low insertion loss and flat wavelength response. Another competing interest is high manufacturing tolerance and compact size. The polarization splitter of the present disclosure simultaneously exhibits compact size, relatively high manufacturing tolerance, large 1dB bandwidth, high extinction ratio, and low insertion loss. According to the embodiments described herein, numerical optimization can be relied upon to account for these trade-offs and achieve the final optimal design. For example, the particle swarm optimization (PSO) method can be relied upon, with all design parameters set as variables.

[0054] In one example, the MMI polarization splitter 420 can use a curved MMI coupler that can be divided into multiple segments. For example, the curved MMI coupler can be divided into 34 segments, as Figure 4A shown. The width of each segment and the position of the input and / or output waveguides can be adjusted and optimized using the PSO method. In one iteration, the PSO method can be relied upon to evaluate all design variables, examine different designs, calculate the above-described figure of merit factors of the designs, compare the results, and select the best design. Then, the next iteration can be made with reference to the results of the previous iteration to further refine the design. After hundreds of iterations, the optimal MMI polarization splitter design can be achieved.

[0055] The design of the MMI polarization splitter 420 can also be optimized in simulation, such as by using the 3D FDTD software tool of Lumerical Inc. in Vancouver, British Columbia, Canada for simulation. Figure 4B and Figure 4D show the optical power propagation of TE0 and TM0 light in the simulation region based on the FDTD simulation results. In Figure 4B and Figure 4D , the X-axis represents the coordinate in the propagation direction in the simulation region, while the Y-axis represents the coordinate perpendicular to the propagation direction in the simulation region. By observing Figure 4B and Figure 4D , it can be seen how the power of TE0 and TM0 mode light is separated. As Figure 4B and Figure 4DAs shown in the FDTD diagram, the TM0 mode light is successfully separated from the TE0 mode light and enters the upper and lower branches of the output waveguide 430 respectively. The polarization-mixed input signal is input from the upper input waveguide 410 into the MMI polarization splitter 420. The TE0 mode light is output in the lower right branch of the output waveguide 430, while the TM0 mode light is output in the upper right branch of the output waveguide 430.

[0056] Figure 4C and 4E respectively show Figure 4B and Figure 4D the calculated optical transmittances of the TM0 mode light and the TE0 mode light corresponding to the diagrams. By using the power monitor in the FDTD software tool, the optical transmittance from 1270 - 1340 nm is measured at a step of 0.1 nm. By inputting TE0 and TM0 light at the upper input waveguide 410 and reading the transmittance of TE0 and TM0 light at the lower and upper branches of the output waveguide 430, the optical losses and extinction ratios of the TE0 and TM0 mode lights can be quantitatively calculated. In Figure 4C the X-axis represents the wavelength in nm, while the Y-axis represents the absolute transmittance (e.g., 0.9 represents 90%). For example, the extinction ratios of TE0 and TM0 at 1310 nm are both greater than 20 dB, and the insertion loss is only 0.45 dB (i.e., 90.17%). The 1 dB bandwidth is far greater than 70 nm. In some embodiments, the size of the MMI polarization splitter 310 can be 17.12 μm long or approximately 17.12 μm long and can be 1.5 μm wide or approximately 1.5 μm wide. The diagram in Figure 4 can correspond to such a size design.

[0057] As Figure 5A and Figure 5B shown, the manufacturing tolerances of the MMI polarization splitter 310 have been checked on the waveguide thickness within the range of ±10 nm and the waveguide width within the range of ±30 nm. This range is selected according to the exemplary manufacturing error range. For example, Figure 5A and Figure 5B show that when the waveguide thickness varies from -10 nm to +10 nm, the TM0 transmittance change is less than 6%, while the TE0 transmittance change is less than 5%, indicating that the transmittance can tolerate tolerances. Figure 5C and Figure 5D show that when the waveguide width varies from -30 nm to +30 nm, compared with Figure 5A and Figure 5B , the TM0 and TE0 transmittances can change. For example, when the width change is within ±10 nm, the TM0 and TE0 transmittance changes are less than 10% and 15% respectively. In some embodiments, this tolerance is acceptable.

[0058] Figure 6AShows an example structure 600 of a double - layer waveguide polarization rotator 320 that can be used, for example, Figure 3 as shown. Structure 600 can have an asymmetry where the input port 610 is narrower than the output port 630. For example, region 620 can reflect the rib layer of structure 600.

[0059] Figure 6B Shows another schematic diagram of the exemplary structure 600 according to some embodiments of the present disclosure. For example, the width of port 610 can be 420 nm or about 420 nm. For example, the width of output port 630 can be 1000 nm or about 1000 nm. Structure 600 can be a double - etched structure that includes a ridge layer 660 that can be silicon and a rib layer 620 that can also be silicon. In one example case, the thickness of ridge layer 660 can be 220 nm. For example, the thickness of rib layer 620 can be 90 nm or about 90 nm. For example, the width of rib layer 620 in the first region can be 420 nm or about 420 nm, and can gradually taper outwards as the layer progresses towards output port 630. For example, the width of ridge layer 660 in the first region can be 420 nm or about 420 nm, and can gradually taper outwards to 530 nm and then to 1000 nm as the layer progresses towards output port 630. In some embodiments, both the silicon ridge layer 660 and the silicon rib layer 620 can be covered by a silica cladding. In some embodiments, under the silicon ridge layer 660 and the silicon rib layer 620, there can be a BOX layer that can be, for example, 2 μm thick.

[0060] TM0 - mode light can be input at input port 610. Due to the vertical asymmetry, TM0 - mode light can have a super - mode at certain waveguide segments with widths in the rib layer 620. TM0 - mode light can be converted into TE1 - mode light and then output at output port 630. Structure 600 can have one or more of high conversion efficiency, 1 dB bandwidth, high manufacturing tolerance, and / or compact size.

[0061] The 3D FDTD simulation performance of polarization rotator 320 is as Figure 6C and Figure 6D shown. As Figure 6C shown, TM0 light is input on the left side of the figure and is successfully transferred into two branches of TE1 - mode light on the right side of the figure. Figure 6D Shows that the conversion efficiency of polarization rotator 320 is 98.78%, or - 0.05 dB. As Figure 6D shown, the wavelength response of the rotator is flat, and the 1 dB bandwidth of the polarization rotator is much larger than 70 nm. In some embodiments, the size of polarization rotator 320 can be 24 μm×1 μm. The figure in FIG. 6 can correspond to a design of such a size.

[0062] Figures 7A - 7D Shows an exemplary tolerance simulation diagram of an exemplary polarization rotator 320. Figure 7A Shows that when the ridge waveguide thickness of the polarization rotator 320 varies from -10 nm to +10 nm, the conversion efficiency of the polarization rotator 320 can vary by less than 4.5%. Figure 7B Shows that when the ridge waveguide width of the polarization rotator 320 varies from -30 nm to +30 nm, the change in conversion efficiency can be less than 3.5%. Figure 7C Shows that when the ridge waveguide thickness of the polarization rotator 320 varies from -10 nm to +10 nm, the change in conversion efficiency can be less than 6%. Figure 7D Shows that when the ridge waveguide width of the polarization rotator 320 varies from -30 nm to +30 nm, the change in conversion efficiency is less than 1%. Therefore, Figures 7A - 7D The data shows that the exemplary polarization converter 320 can allow for high tolerances.

[0063] Figures 8A - 8C Displays a graph related to the mode order converter. Figure 8A Shows an example structure 800 of an asymmetric mode converter, which is Figure 3 An example of the asymmetric waveguide taper mode order converter 330 shown. The upper edge of the mode converter is asymmetric with the lower edge along the propagation direction. Taking the midpoint of the input port as the starting point and drawing a horizontal line through the example structure 800, the upper half of the mode converter is designed to be wider than the lower half. The left port of the example structure 800 can be connected to a polarization rotator to receive the TE1 mode. In the asymmetric mode converter, the two lobes of the TE1 mode light input to the structure 800 may experience different phase changes due to its shape and can be combined into the TE0 mode, which is output by the structure 800.

[0064] There is no analytical equation to describe what the specific shape of such an asymmetric mode converter should be. There are also trade-offs in the design of the structure 800, such as the relationship between low optical loss and flat spectrum and the relationship between compact size and high manufacturing tolerance. Therefore, the PSO algorithm can be used again to achieve the final optimal design. The design of the structure 800 can be divided into 20 segments along the propagation direction, and the width of each segment is optimized using particle swarm optimization (PSO) to achieve high conversion efficiency, large 1 dB bandwidth, high manufacturing tolerance, and compact size, as Figure 8A shown.

[0065] As Figure 8AAs shown, an exemplary structure 800 of the asymmetric waveguide tapered mode order converter 330 can be fabricated on a silicon layer and can be covered with a silica cladding. In one example, the thickness of the silicon layer can be 220 nm or approximately 220 nm. Below the silicon layer can be a BOX layer. In one example, the thickness of the BOX layer can be 2 μm thick or approximately 2 μm. The asymmetric layout layer is a 220-nm-thick silicon rib layer. No silicon layers with other different thicknesses are used except for the rib layer.

[0066] Figure 8B An exemplary 3D FDTD simulation performance of the exemplary structure 800 of the asymmetric waveguide tapered mode order converter 330 is shown. As shown, on the Figure 8B left side, TE1 mode light can be input and converted into TE0 mode light, and the TE0 mode light is on the Figure 8B right side. Figure 8C The relationship between the conversion efficiency of the exemplary polarization converter and the wavelength is shown. As shown, the conversion efficiency is 99.34%, or -0.03 dB. The 1 dB bandwidth of the polarization converter is much larger than 70 nm. In some embodiments, the size of the converter 330 can be 21 m × 3 m. The diagrams in FIGS. 8 and 9 can correspond to the design of such a size.

[0067] Figure 9A and Figure 9B An example simulation manufacturing tolerance of the exemplary structure 800 of the asymmetric waveguide tapered mode order converter 330 is shown. As Figure 9A shown, when the waveguide thickness varies within the range of ±10 nm, the conversion efficiency changes by less than 1%. As Figure 9B shown, similar results may occur when the waveguide width varies within the range of ±30 nm. Therefore, these simulations demonstrate the suitable manufacturing tolerance of the structure 800.

[0068] Figures 10A - 10E A diagram related to the simulation of the integrated optical device 300 according to some embodiments of the present disclosure is shown. In the wavelength range of 1270 nm to 1340 nm, the simulation performance. Figure 10A shows Figure 3 the entire structure 1000 of the integrated optical device 300 shown. In some embodiments, the size of the structure 1000 can be 89 μm or approximately 89 μm × 8 μm or approximately 8 μm, such that it has an area of 712 μm 2 of area. Figure 10A An incident optical signal at the input waveguide 410 is shown, which may be an unknown mixture of TE0 and TM0 polarized light. The MMI polarization separator 420 reflects the Figure 3 structure of the separator 310 shown. The structure 600 reflects the Figure 3The structure of the polarization rotator 320 shown. The structure 800 reflects Figure 3 The structure of the converter 330 shown.

[0069] As Figure 10B shown, when TM0 mode light is input on the left side of the figure as shown, it can be converted into TE0 mode light and output through the output port, as shown in the upper right corner of the figure. For example, as Figure 10C shown, in the range of 1270 nm to 1340 nm, the conversion efficiency can be about 80% to 90% (i.e., 0.5 to 0.9 dB). The 1 dB bandwidth is greater than 70 nm. For example, the extinction ratio exceeds 25 dB at 1310 nm and may decrease to between 9 and 10 dB at the spectral edge. Figure 10D shown when TE0 mode light is input on the left side of the figure as shown, it can remain as TE0 mode light and be output at the output port, as shown in the lower right corner of the figure. For example, as Figure 10E shown, in the range of 1270 nm to 1340 nm, the transmittance can be about 71 - 90% (i.e., 0.5 to 1.4 dB). The 1 dB bandwidth is greater than 70 nm. The extinction ratio at 1310 nm exceeds 25 dB and can drop to 10 dB at the spectral edge.

[0070] It should be noted that the discussion so far has focused on Figure 3 the applicability of the PSR in receiving data and processing optical signals in

[0071] Figure 11 is a schematic diagram of an exemplary polarization-insensitive WDM receiver (RX) 1100. The WDM RX 1100 includes a polarization splitter 1110, which can be implemented as Figure 3The optical device 300 shown. As shown, the polarization splitter 1110 is used to separate the incident signal 1101 having two mixed orthogonal polarization states (TE0 and TM0), send TE0 to the TE demultiplexer 1120, rotate TM0 to another TE0 mode 1113, and send it to another TE demultiplexer 1130. Then, each signal is demultiplexed by a 1×4 WDM demultiplexer into individual component wavelength signals, the wavelengths of which are given by λ1, λ2, λ3, and λ4, where λ1 < λ2 < λ3 < λ4. The signals of different wavelengths reach their respective bidirectional PDs. The routing waveguides 1121, 1122, 1123, and 1124 for TE0 and the routing waveguides 1131, 1132, 1133, and 1134 for TE'0 (converted from TM0) are carefully arranged such that the signals from both sides reach the PD at the same timing. The powers from both sides are not necessarily equal. The ratio between them can be any value. The bidirectional PD collects the two polarization signals of each wavelength, making the entire RX system polarization-insensitive. In other embodiments, a number of discrete wavelengths other than 4 can be used. In different embodiments, N wavelengths are used, where N is greater than 1, and for wavelengths λ for 1 ≤ i ≤ N i are all different from each other.

[0072] The optical device 300 can also be used in a polarization multiplexed transmitter. This concept operates the PSR in reverse, performing the function of taking two incident TE polarization signals (TE and TE', which are independent channels from each other) and outputting the two signal streams into a single path having two orthogonal polarization states (TE and TM). In this way, a laser diode (usually TE polarized), a TE waveguide, a TE modulator, and a TE multiplexer (each of which is constructed to operate only under TE polarization) can be used with the PSR to multiplex the modulated multi-channel signal streams onto a single output path. The same design for the output path specified for TE can be used upstream of the PSR on the path specified for TE' (and then converted to TM). When used in this way, the PSR can be referred to as a polarization rotator + combiner (PRC). To support multiple wavelengths simultaneously, the PRC can be broadband, providing good polarization extinction ratio performance and low loss over a wide wavelength range, as Figure 11 shown.

[0073] Figure 12FIG. 1200 shows a polarization multiplexed transmitter system. For example, light may be generated by a laser 1210. The output light from the light source 1210 may be split by a 3 dB power splitter. One half is modulated by a modulator 1220 and the other half is modulated by a modulator 1230. Since the modulators 1220 and 1230 are driven by different RF signals, the signals generated from 1220 and 1230 are independent channels of each other. In an embodiment, each of the modulators A-D of the modulator 1220 is driven by the same RF signal. In an embodiment, each of the modulators A-D of the modulator 1220 is driven by a separate RF signal. In an embodiment, each of the modulators A'-D' of the modulator 1230 is driven by the same RF signal. In an embodiment, each of the modulators A'-D' of the modulator 1230 is driven by a separate RF signal. The optical signal modulated by the modulator 1220 will then be multiplexed by a MUX 1240. The other optical signal generated by the modulator 1230 will be multiplexed by a MUX 1250 and then converted to TM polarization by a polarization rotator in 1260. Then, the multiplexed TE signals of wavelengths λ A , λ B , λ C , λ D from 1240 are combined with the TM signals of wavelengths λ A , λ B , λ C , λ D by a polarization combiner in 1260. Finally, the signals of eight independent channels (TE_A / TE_B / TE_C / TE_D / TM_A / TM_B / TM_C / TM_D) will be output to a fiber optic system 500. As described above, the PSR introduced here is designed for broadband. Therefore, more wavelength channels can be easily added, not limited to only 4 wavelengths.

[0074] The scope of the present disclosure is not limited to the specific embodiments described herein. In fact, various other embodiments and modifications of the present disclosure will be apparent to those of ordinary skill in the art in light of the foregoing description and drawings. Accordingly, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Additionally, although the present disclosure has been described herein in the context of at least one specific implementation in at least one specific environment for at least one specific purpose, those of ordinary skill in the art will recognize that the usefulness of the present disclosure is not limited thereto, and the present disclosure may be beneficially implemented in any number of environments for any number of purposes.

Claims

1. A method for transmitting multiple optical modulation signals for output to an optical fiber system, the method comprising the steps of: Providing a first laser source configured to emit light of a first wavelength having a first polarization and a second laser source configured to emit light of a second wavelength having the first polarization, the second wavelength being different from the first wavelength; Receiving a first portion of the light emitted by the first laser source with a first modulator and receiving a second portion of the light emitted by the first laser source with a second modulator; Receiving a first portion of the light emitted by the second laser source with a third modulator and receiving a second portion of the light emitted by the second laser source with a fourth modulator; Outputting a first modulated optical signal from the first modulator, the first modulated optical signal having the first polarization; Outputting a second modulated optical signal from the second modulator, the second modulated optical signal having the first polarization; Outputting a third modulated optical signal from the third modulator, the third modulated optical signal having the first polarization; Outputting a fourth modulated optical signal from the fourth modulator, the fourth modulated optical signal having the first polarization; Multiplexing the first modulated optical signal and the third modulated optical signal to provide a first multiplexed optical signal having the first polarization; Multiplexing the second modulated optical signal and the fourth modulated optical signal to provide a second multiplexed optical signal having the first polarization; Changing the second multiplexed optical signal to have a second polarization, the second polarization being different from the first polarization; And Combining the first multiplexed optical signal having the first polarization and the second multiplexed optical signal having the second polarization into a third optical signal.

2. The method according to claim 1, the method further comprising the step of providing the third optical signal to an optical fiber system.

3. The method according to claim 1, wherein each of the first laser source and the second laser source is a laser diode.

4. The method according to claim 1, wherein the step of changing the second multiplexed optical signal to have the second polarization comprises the step of passing the second multiplexed optical signal having the first polarization through a waveguide polarization rotator.

5. The method according to any one of claims 1-4, wherein the first polarization is TE mode polarization.

6. The method according to any one of claims 1-4, wherein the first polarization is TE mode polarization and the second polarization is TM mode polarization.

Images