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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 4 — Feb. 24, 2014
  • pp: 3777–3786
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Polarization rotator-splitters in standard active silicon photonics platforms

Wesley D. Sacher, Tymon Barwicz, Benjamin J. F. Taylor, and Joyce K. S. Poon  »View Author Affiliations


Optics Express, Vol. 22, Issue 4, pp. 3777-3786 (2014)
http://dx.doi.org/10.1364/OE.22.003777


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Abstract

We demonstrate various silicon-on-insulator polarization management structures based on a polarization rotator-splitter that uses a bi-level taper TM0-TE1 mode converter. The designs are fully compatible with standard active silicon photonics platforms with no new levels required and were implemented in the IME baseline and IME-OpSIS silicon photonics processes. We demonstrate a polarization rotator-splitter with polarization crosstalk < −13 dB over a bandwidth of 50 nm. Then, we improve the crosstalk to < −22 dB over a bandwidth of 80 nm by integrating the polarization rotator-splitter with directional coupler polarization filters. Finally, we demonstrate a polarization controller by integrating the polarization rotator-splitters with directional couplers, thermal tuners, and PIN diode phase shifters.

© 2014 Optical Society of America

1. Introduction

Silicon-on-insulator (SOI) is becoming a common platform for integrated photonic circuits because the high refractive index contrast enables compact devices and the growing availability of foundry services allows complex silicon photonic chips to be fabricated at low costs [1

1. Editorial, “Simply silicon,” Nat. Photonics 4, 491 (2010). [CrossRef]

, 2

2. T. Baehr-Jones, L. Pinguet, S. Danziger, D. Prather, and M. Hochberg, “Myths and rumours of silicon photonics,” Nat. Photonics 6, 206–208 (2012). [CrossRef]

]. However, high index contrast waveguides also possesses a large birefringence. Because the polarization of the input light to a chip from an optical fiber is not usually fixed, polarization transparent photonic devices and circuits are needed at the receiver and along an optical communication link. To this end, polarization diversity can be implemented [3

3. T. Barwicz, M. R. Watts, M. A. Popovic, P. T. Rakich, L. Socci, F. X. Kartner, E. P. Ippen, and H. I. Smith, “Polarization-transparent microphotonic devices in the strong confinement limit,” Nat. Photonics 1, 57–60 (2007). [CrossRef]

5

5. M. R. Watts, H. A. Haus, and E. P. Ippen, “Integrated mode-evolution-based polarization splitter,” Opt. Lett. 30, 967–969 (2005). [CrossRef] [PubMed]

]. Essential elements in polarization diverse photonic circuits are polarization splitters and polarization rotators. A challenge for polarization splitters and rotators in SOI is that they often require high aspect ratio features, extra layers, or an air cladding [3

3. T. Barwicz, M. R. Watts, M. A. Popovic, P. T. Rakich, L. Socci, F. X. Kartner, E. P. Ippen, and H. I. Smith, “Polarization-transparent microphotonic devices in the strong confinement limit,” Nat. Photonics 1, 57–60 (2007). [CrossRef]

11

11. Y. Ding, H. Ou, and C. Peucheret, “Wideband polarization splitter and rotator with large fabrication tolerance and simple fabrication process,” Opt. Lett. 38, 1227–1229 (2013). [CrossRef] [PubMed]

], which are not compatible with common foundry processes.

In this work, we combine the splitter and rotator functionalities into a polarization rotator-splitter (PRS) that is fully compatible with standard foundry processes. The PRS requires only a single silicon (Si) material layer with top and bottom SiO2 cladding. This Si layer must be patterned with both a full and partially-etched level; no high aspect ratio features are required. The compatibility with standard foundry processes enables us to demonstrate the PRS and an active polarization controller using the IME baseline and IME-OpSIS silicon photonics processes [12

12. T.-Y. Liow, K.-W. Ang, Q. Fang, J.-F. Song, Y.-Z. Xiong, M.-B. Yu, G.-Q. Lo, and D.-L. Kwong, “Silicon modulators and germanium photodetectors on soi: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16, 307–315 (2010). [CrossRef]

14]. The PRS uses a bi-level taper that converts a fundamental TM mode (TM0) input into a first-order TE mode (TE1) output, as proposed in [15

15. W. Yuan, K. Kojima, B. Wang, T. Koike-Akino, K. Parsons, S. Nishikawa, and E. Yagyu, “Mode-evolution-based polarization rotator-splitter design via simple fabrication process,” Opt. Express 20, 10163–10169 (2012). [CrossRef] [PubMed]

, 16

16. D. Dai, Y. Yang, and J. E. Bowers, “Mode conversion in tapered submicron silicon ridge optical waveguides,” Opt. Express 20, 13425–13439 (2012). [CrossRef] [PubMed]

]. Our work is the first demonstration of PRSs using this mode conversion in bi-level tapers, and we presented a preliminary report in [17

17. W. Sacher, T. Barwicz, and J. K. Poon, “Silicon-on-insulator polarization splitter-rotator based on TM0-TE1 mode conversion in a bi-level taper,” in “Conference on Lasers and Electro-Optics, OSA Technical Digest,” (2013), p. CTu3F.3.

]. Although TM0-TE1 mode conversion in bi-level tapers was demonstrated in [16

16. D. Dai, Y. Yang, and J. E. Bowers, “Mode conversion in tapered submicron silicon ridge optical waveguides,” Opt. Express 20, 13425–13439 (2012). [CrossRef] [PubMed]

], a full PRS was not demonstrated. Overall, our work paves the way for polarization diversity, polarization controllers, and polarization-multiplexed transmitters and receivers in standard active SOI photonic platforms.

The paper is organized as follows: we describe our adiabatic bi-level taper PRS design and demonstration in Section 2; then, we show the PRS integrated with directional coupler polarization filters for improved polarization crosstalk in Section 3; finally, we apply the PRS to an active polarization controller in Section 4.

2. Adiabatic bi-level taper polarization rotator-splitter

Our PRS design is shown in Fig. 1(a), where the red regions represent the full height of the Si and the purple regions represent the partially-etched level of Si. We designed the PRS for the IME baseline and OpSIS silicon photonics processes, which have a top silicon thickness of 220 nm and a partially-etched thickness of 90 nm. Our PRS uses a bi-level taper for TM0-TE1 mode conversion and symmetric SiO2 cladding. After the bi-level taper, the TE0 and TE1 modes are separated into two waveguides using an adiabatic coupler instead of the directional coupler proposed in [10

10. D. Dai and J. E. Bowers, “Novel concept for ultracompact polarization splitter-rotator based on silicon nanowires,” Opt. Express 19, 10940–10949 (2011). [CrossRef] [PubMed]

], the Y-branch proposed in [15

15. W. Yuan, K. Kojima, B. Wang, T. Koike-Akino, K. Parsons, S. Nishikawa, and E. Yagyu, “Mode-evolution-based polarization rotator-splitter design via simple fabrication process,” Opt. Express 20, 10163–10169 (2012). [CrossRef] [PubMed]

], or the Y-branch and multi-mode interferometer in [11

11. Y. Ding, H. Ou, and C. Peucheret, “Wideband polarization splitter and rotator with large fabrication tolerance and simple fabrication process,” Opt. Lett. 38, 1227–1229 (2013). [CrossRef] [PubMed]

]. Overall, our PRS design is entirely adiabatic. This is a key distinction from the earlier PRS designs in [10

10. D. Dai and J. E. Bowers, “Novel concept for ultracompact polarization splitter-rotator based on silicon nanowires,” Opt. Express 19, 10940–10949 (2011). [CrossRef] [PubMed]

, 11

11. Y. Ding, H. Ou, and C. Peucheret, “Wideband polarization splitter and rotator with large fabrication tolerance and simple fabrication process,” Opt. Lett. 38, 1227–1229 (2013). [CrossRef] [PubMed]

, 15

15. W. Yuan, K. Kojima, B. Wang, T. Koike-Akino, K. Parsons, S. Nishikawa, and E. Yagyu, “Mode-evolution-based polarization rotator-splitter design via simple fabrication process,” Opt. Express 20, 10163–10169 (2012). [CrossRef] [PubMed]

], which have non-adiabatic elements that limit the bandwidth, increase the senstivity to variations in waveguide dimensions, and increase the insertion loss. The total length of the PRS design is about 475 μm.

Fig. 1 (a) Schematic of the polarization rotator-splitter (PRS). Widths are labeled in red and purple; lengths use green labels. (b) Schematic showing the profiles of the modes with the first and second highest effective indices (i.e., “mode 1” and “mode 2”) at different points along the PRS. In the adiabatic coupler, “mode 1” and “mode 2” refer to supermodes of the composite waveguide. (c) Effective indices (neff) along the first half of the bi-level taper for modes 1 to 3 at a wavelength of 1550 nm.

The remainder of this section is organized as follows: in Section 2.1, we provide a detailed description of the PRS design and operating principles, and in Section 2.2, we describe our experimental demonstration of a bi-level taper PRS.

2.1. Detailed polarization rotator-splitter design and operation

The PRS operation relies on the principle of mode evolution [4

4. M. R. Watts and H. A. Haus, “Integrated mode-evolution-based polarization rotators,” Opt. Lett. 30, 139–140 (2005).

,5

5. M. R. Watts, H. A. Haus, and E. P. Ippen, “Integrated mode-evolution-based polarization splitter,” Opt. Lett. 30, 967–969 (2005). [CrossRef] [PubMed]

]. The evolution of the modes with the first and second highest effective indices (i.e., “mode 1” and “mode 2”) in the PRS is illustrated in Fig. 1(b). In the first half of the bi-level taper, the Si ridge and partially-etched slab continuously widen, and this is where the TM0-TE1 mode conversion occurs. The partially-etched slab breaks the vertical symmetry of the waveguide [10

10. D. Dai and J. E. Bowers, “Novel concept for ultracompact polarization splitter-rotator based on silicon nanowires,” Opt. Express 19, 10940–10949 (2011). [CrossRef] [PubMed]

, 16

16. D. Dai, Y. Yang, and J. E. Bowers, “Mode conversion in tapered submicron silicon ridge optical waveguides,” Opt. Express 20, 13425–13439 (2012). [CrossRef] [PubMed]

], which produces a large difference in the effective indices of modes 2 and 3 throughout the structure, as shown in Fig. 1(c). This allows a TM0 input to remain in mode 2 all along the bi-level taper and evolve into, first, a “hybridized” mode with TM0 and TE1 features, and finally, the TE1 mode. A TE0 input simply remains in mode 1 and exits the bi-level taper in the TE0 mode. The second half of the bi-level taper, where the Si ridge continues to widen and the partially-etched slab narrows, is used to provide a fully-etched, wide waveguide as the input to the adiabatic coupler.

2.2. Polarization rotator-splitter measurements

PRSs were fabricated in the IME baseline process, and optical micrographs of the PRS are shown in Fig. 2. The PRS inputs and outputs lead to edge couplers with 220 nm wide square tips. We measured the PRS by coupling light from a tunable laser from free-space using objective lenses. Manually-adjustable, free-space, linear polarizers were placed at the input and output of the chip to control the input polarization and analyze the output polarization.

Fig. 2 (a) An optical micrograph of the polarization rotator-splitter fabricated in the IME baseline process. Magnified optical micrographs are shown for (b), the bi-level taper, and (c), the end of the adiabatic coupler.

Figure 3 shows the measured transmission spectra of the two PRS outputs for TE and TM inputs. The transmission spectra have been normalized to the transmission spectra of the edge couplers to extract the spectral characteristics of the PRS only. From Figs. 3(a) and 3(b), the polarization crosstalk at both output ports was less than −13 dB over a wavelength range between 1530 nm and 1580 nm; the crosstalk increased to about −10 dB for wavelengths between 1500 nm and 1530 nm. Due to inaccuracies in aligning the coupling lenses between measurements, the error in the transmission values was about ± 0.5 dB. Other than normalizing out the edge coupler transmission, no post-processing was applied to the data in Figs. 3(a) and 3(b).

Fig. 3 Measurement data for the PRS in Fig. 2. (a) Transmission spectra of the PRS TE branch (top) output. (b) Transmission spectra of the PRS TM branch (bottom) output. (c) Magnified TE component of the TE branch transmission for a TE input. (d) Magnified TE component of the TM branch transmission for a TM input. The legends in (a) and (b) indicate the settings of the input and output polarizers (i.e., TE→TM means we had a TE input and measured the TM component of the output). (c) and (d) represent the PRS insertion loss, and the red curves have been post-processed to remove Fabry-Perot oscillations from the edge coupler facets and the measurement apparatus.

The extracted insertion loss of the PRS is shown in Figs. 3(c) and 3(d). The raw transmission spectra in the black curves overestimate the PRS insertion loss since Fabry-Perot oscillations from the chip facets and measurement apparatus were not fully removed by normalizing the data to the transmission of the edge couplers. The edge coupler loss calibration structures and PRS had different Fabry-Perot oscillations, and the Fabry-Perot oscillations of the measurement setup changed between measurements due to realignments. We post-processed the raw transmission spectra of the PRS and edge couplers to reduce the contribution of the Fabry-Perot oscillations and obtained the more accurate insertion loss data in the red curves. Chip facet Fabry-Perot oscillations were easily identified from the waveguide lengths and group indices, and oscillations that differed little between devices and polarization settings were attributed to the measurement apparatus. From the post-processed data, the insertion loss and polarization-dependent loss (PDL) were less than 1.5 dB and 1.6 dB, respectively, over a wavelength range from 1530 nm to 1580 nm. Our ± 0.5 dB realignment error estimate is evident from the red curves, which have some points with transmission > 0 dB. The large-period oscillations in Fig. 3(d) may be Fabry-Perot oscillations from reflections at the chip facets and the waveguide discontinuity at the beginning of the adiabatic coupler or within the bi-level taper.

Through this first demonstration of a bi-level taper PRS, we can identify four simple design improvements to reduce the crosstalk and increase the bandwidth. First, the blunt-tip at the start of the adiabatic coupler in Fig. 1(a) could be replaced by an arc with a large radius to eliminate any mode coupling caused by the waveguide discontinuity. Second, reducing the waveguide gap in the adiabatic coupler will reduce the crosstalk or the coupler length required to achieve the crosstalk we demonstrated; this is due to an increase in the effective index difference between the TE0 and TE1 modes [4

4. M. R. Watts and H. A. Haus, “Integrated mode-evolution-based polarization rotators,” Opt. Lett. 30, 139–140 (2005).

, 5

5. M. R. Watts, H. A. Haus, and E. P. Ippen, “Integrated mode-evolution-based polarization splitter,” Opt. Lett. 30, 967–969 (2005). [CrossRef] [PubMed]

]. Third, the widths and length of the bi-level taper can be optimized; from Fig. 3(a), the incomplete TM0-TE1 mode conversion in the bi-level taper is a large component of the crosstalk. Finally, the PRS can be cascaded with additional PRSs or other types of polarization clean-up filters [6

6. L. Chen, C. R. Doerr, and Y.-K. Chen, “Compact polarization rotator on silicon for polarization-diversified circuits,” Opt. Lett. 36, 469–471 (2011). [CrossRef] [PubMed]

]. This latter approach is demonstrated in Section 3 where the PRS is integrated with directional coupler clean-up filters for reduced crosstalk.

3. Polarization splitter-rotator with improved crosstalk

One approach to improving the performance of the PRS is to cascade it with polarization cleanup filters. This is demonstrated here using directional coupler clean-up filters [6

6. L. Chen, C. R. Doerr, and Y.-K. Chen, “Compact polarization rotator on silicon for polarization-diversified circuits,” Opt. Lett. 36, 469–471 (2011). [CrossRef] [PubMed]

, 7

7. H. Fukuda, K. Yamada, T. Tsuchizawa, T. Watanabe, H. Shinojima, and S. Itabashi, “Silicon photonic circuit with polarization diversity,” Opt. Express 16, 4872–4880 (2008). [CrossRef] [PubMed]

] placed in front of the PRS as shown in Fig. 4. In this configuration, it is more appropriate to refer to this structure as a polarization splitter-rotator (PSR) than a polarization rotator-splitter (PRS). In contrast to the PRS by itself, which converts the TM polarization to the TE1 mode before splitting, here, the polarizations are first split with a directional coupler before TM is rotated into TE. This device was fabricated with the IME baseline process as well.

Fig. 4 Annotated optical micrograph of the polarization splitter-rotator (PSR) with improved crosstalk.

The detailed operation of the PSR can be understood from the annotated micrograph in Fig. 4. The input is first separated into TE (top branch) and TM (bottom branch) polarizations using a directional coupler. Directional coupler clean-up filters are integrated into both branches to reduce the polarization crosstalk. All directional couplers in the PSR are nominally identical and use 440 nm wide strip waveguides, 10 μm long coupling regions, 400 nm wide coupling gaps, and 10 μm radius bends leading to and from the coupling region. The TE (top) branch uses four clean-up filters. The TM (bottom) branch uses two clean-up filters followed by a PRS for polarization rotation and then two additional clean-up filters. The unused ports of the PRS and directional couplers are terminated with waveguide tapers leading to 200 nm wide blunt tips. The PRS is nominally identical to the PRS demonstrated in Section 2. The inputs and outputs of the whole PSR lead to edge couplers with 220 nm wide tips.

The PSR was measured using the same method as Section 2.2 (i.e., free-space coupling with linear polarizers at the input and output of the chip). Figures 5(a) and 5(b) show the measured transmission spectra of the two PSR outputs normalized to the transmission spectra of the edge couplers for TE and TM inputs. The polarization crosstalk at both outputs was less than −22 dB over a wavelength range from 1500 nm to 1580 nm, which was an improvement of 9 dB over the PRS in Section 2.2. In principle, the clean-up filters should have provided a significantly lower crosstalk, but the measurements may have been limited by the accuracy of the input and output polarizers.

Fig. 5 Measurement data for the PSR in Fig. 4. (a) Transmission spectra of the PSR TE branch (top) output. (b) Transmission spectra of the PSR TM branch (bottom) output. (c) Magnified TE component of the TE branch transmission for a TE input. (d) Magnified TE component of the TM branch transmission for a TM input. The legends in (a) and (b) indicate the settings of the input and output polarizers (i.e., TE→TM means we had a TE input and measured the TM component of the output). The red curves in (c) and (d) have been post-processed to remove Fabry-Perot oscillations from the chip facets and the measurement setup.

The insertion loss of the PSR is shown in Figs. 5(c) and 5(d). The black curves are raw data and the red curves have been post-processed to remove Fabry-Perot oscillations from the chip facets and the measurement apparatus, as explained in Section 2.2. From the post-processed data, the insertion loss and PDL of the PSR were less than 2.3 dB and 1.9 dB over a wavelength range from 1530 nm to 1580 nm; the error in the insertion loss was roughly ± 0.5 dB due to realignment error of the coupling lenses. Compared to the PRS in Section 2.2, the insertion loss of the PSR in this section was larger and varied more with wavelength due to the loss and limited bandwidth of the directional coupler polarization splitter and clean-up filters.

A more optimal design that has low polarization crosstalk, low insertion loss, and a broad bandwidth will likely involve optimizing our PRS design using the methods we described at the end of Section 2.2 and then cascading the PRSs (i.e., the two outputs of a PRS are routed to additional PRSs, which act as polarization clean-up filters). This will result in an entirely adiabatic design that is not subject to the bandwidth and insertion loss limitations of directional couplers.

4. Polarization controller

Finally, as an example of integration of the PRS with tuning and modulation elements, we demonstrate the simple polarization controller shown in Fig. 6. The polarization controller consists of a PRS followed by a variable 2×2 Mach-Zehnder interferometer (MZI), phase-shifters, and a second PRS to combine the two branches. The MZI and phase-shifters modify the relative amplitudes and phases of the output TE and TM-components to control the output polarization. Although this design uses both PIN diode and thermal phase-shifters to demonstrate the compatibility of the PRS with a standard active Si photonic platform, in practice, only one type of phase-shifter (thermal tuner or PIN diode) would be needed depending on the desired tuning speed.

Fig. 6 (a) Schematic of the polarization controller. “3-dB DC” is a 3 dB directional coupler. (b) Optical micrograph of the polarizaton controller fabricated in the IME-OpSIS process.

The polarization controllers were fabricated at IME using the OpSIS service [14]. The thermal tuners and PIN diodes are each 500 μm long and use the same etch depths as the PRS. The 3-dB directional couplers use 500 nm wide fully-etched waveguides, a 13.5 μm long coupling region with a 200 nm gap, and 20 μm radius S-bends leading to and from the coupling region. Tuning voltages were only applied to the top thermal tuners and PIN diodes in Fig. 6(a), while the bottom PIN diodes and thermal tuners balanced the loss in the two arms of the polarization controller. Figure 7(a) shows the measured current-voltage characteristics of the top-left PIN diode and thermal tuner in the polarization controller.

Fig. 7 Polarization controller measurement data. (a) Current-voltage characteristics of the top-left thermal tuner and PIN diode. (b) Normalized output power as the output polarizer was rotated. With a TE-polarized input, bias conditions were chosen to obtain a TM-polarized output (black curve), a −45° linearly-polarized output (blue curve), and a circularly-polarized output (red curve). (c) Normalized output power as the top-left thermal tuner power was swept. (d) Normalized output power as the top-left PIN diode current was swept. In (c) and (d), the output polarizer was set to pass either TE or TM or removed from the optical path (“Total out”). The optical output power curves were normalized to the maximum value in each plot. The magenta labels and dashed lines indicate points where a TM or TE output was generated from the TE input (marked “TE→TM” and “TE→TE”, respectively).

We measured the polarization controllers using the method in Section 2.2 (i.e., free-space coupling with linear polarizers at the input and output of the chip); the input wavelength was fixed at 1570 nm and the input was chosen to be TE-polarized for simplicity. This simple measurement setup did not allow for the extraction of the phase between the output TE and TM polarization components. The polarization controller insertion loss was < 2.5 dB. By driving the top-left and top-right thermal tuners, we generated TM-polarized, −45° linearly-polarized, and circularly-polarized outputs, which is evident from the output power as a function of the output polarizer angle in Fig. 7(b). 0° corresponds to a horizontal (TE) polarization axis; the uncertainty in the angle was about ±2°. Crosstalk in the PRSs and non-ideal 3-dB directional couplers limited the extinction for the TM and −45° measurements. The red curve corresponds to a circularly-polarized output since the power only fluctuates by about 0.2 dB over all output polarizer angles. It was achieved with powers of 15 mW and 12 mW dissipated in the top-left and top-right thermal tuners, respectively.

Next, as a simple demonstration of switching between TM and TE-polarized outputs, we input TE light into the polarization controller and applied voltages only to the top-left thermal tuner [Fig. 7(c)] or the top-left PIN diode [Fig. 7(d)]; the other tuning elements were not driven. The applied voltage was swept with the output polarizer fixed to pass either TE or TM (marked “TE out” and “TM out” in the plots) or with the output polarizer removed from the optical path (marked “Total out” in the plots). Increasing the voltage on the thermal tuner or the PIN diode shifted the output polarization between TM and TE. At PIN diode currents beyond 10 mA, the optical loss increased substantially, which imbalanced the MZI and increased the total insertion loss of the polarization controller.

The polarization controller presented here is intended to show the full compatability of the PRS with a standard Si photonics platform. Its simple design limits its optical bandwidth and the polarization states that it can create. A complete polarization controller can be achieved with two simple design modifications. First, the optical bandwidth can be extended by compensating for the group delay differences between the TE0 and TM0/TE1 modes in the PRS. This compensation should be applied to both PRSs and can be implemented as an extra length of straight waveguide at one of the PRS outputs. Second, an additional set of phase-shifters should be included before the 2×2 MZI to create the full range of relative weights between the TE and TM components required to convert any arbitrary input polarization to an arbitrary output polarization. An endless polarization controller, which can be used in polarization-division multiplexed receivers for polarization-tracking, would further require two extra sets of phase-shifters and two extra directional couplers [18

18. N. Walker and G. Walker, “Polarization control for coherent communications,” J. Lightwave Technol. 8, 438–458 (1990). [CrossRef]

21

21. C. Doerr, N. Fontaine, and L. Buhl, “PDM-DQPSK silicon receiver with integrated monitor and minimum number of controls,” IEEE Photon. Technol. Lett. 24, 697–699 (2012). [CrossRef]

].

5. Conclusion

In summary, we have demonstrated the first polarization rotator-splitter using a TM0-TE1 mode converter based on an adiabatic bi-level taper and extended the concept to a polarization controller and a polarization splitter-rotator with improved crosstalk using directional coupler clean-up filters. The main advantage of the designs in this work is that they are fully compatible with standard silicon photonic foundry processes and do not require specialty high aspect ratio features, extra layers, or an air cladding. Although the adiabatic transitions make the polarization rotator-splitter long, the design is inherently broadband and tolerant to dimensional variations.

Acknowledgments

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W. Yuan, K. Kojima, B. Wang, T. Koike-Akino, K. Parsons, S. Nishikawa, and E. Yagyu, “Mode-evolution-based polarization rotator-splitter design via simple fabrication process,” Opt. Express 20, 10163–10169 (2012). [CrossRef] [PubMed]

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D. Dai, Y. Yang, and J. E. Bowers, “Mode conversion in tapered submicron silicon ridge optical waveguides,” Opt. Express 20, 13425–13439 (2012). [CrossRef] [PubMed]

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N. Walker and G. Walker, “Polarization control for coherent communications,” J. Lightwave Technol. 8, 438–458 (1990). [CrossRef]

19.

T. Saida, K. Takiguchi, S. Kuwahara, Y. Kisaka, Y. Miyamoto, Y. Hashizume, T. Shibata, and K. Okamoto, “Planar lightwave circuit polarization-mode dispersion compensator,” IEEE Photon. Technol. Lett. 14, 507–509 (2002). [CrossRef]

20.

C. Doerr and L. Chen, “Monolithic PDM-DQPSK receiver in silicon,” in “Optical Communication (ECOC), 2010 36th European Conference and Exhibition on,” (2010), pp. 1–3.

21.

C. Doerr, N. Fontaine, and L. Buhl, “PDM-DQPSK silicon receiver with integrated monitor and minimum number of controls,” IEEE Photon. Technol. Lett. 24, 697–699 (2012). [CrossRef]

OCIS Codes
(130.3120) Integrated optics : Integrated optics devices
(230.5440) Optical devices : Polarization-selective devices

ToC Category:
Integrated Optics

History
Original Manuscript: December 3, 2013
Revised Manuscript: January 19, 2014
Manuscript Accepted: January 20, 2014
Published: February 10, 2014

Citation
Wesley D. Sacher, Tymon Barwicz, Benjamin J. F. Taylor, and Joyce K. S. Poon, "Polarization rotator-splitters in standard active silicon photonics platforms," Opt. Express 22, 3777-3786 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-4-3777


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References

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