Compact 2 × 2 polarization-diversity Si-wire switch

Automated control algorithms for silicon photonic polarization receiver

We demonstrate greedy linear descent-based, basic gradient descent-based, two-point step size gradient descent-based, and two-stage optimization method-based automated control algorithms and examine their performance for use with a silicon photonic polarization receiver. With an active feedback loop control process, time-varying arbitrary polarization states from an optical fiber can be automatically adapted and stabilized to the transverse-electric (TE) mode of a single-mode silicon waveguide. Using the proposed control algorithms, we successfully realize automated adaptations for a 10 Gb/s on-off keying signal in the polarization receiver. Based on the large-signal measurement results, the control algorithms are examined and compared with regard to the iteration number and the output response. In addition, we implemented a long-duration experiment to track, adapt, and stabilize arbitrary input polarization states using the two-point step size gradient descent-based and two-stage optimization method-based control algorithms. The experimental results show that these control algorithms enable the polarization receiver to achieve real-time and continuous polarization management.

Polarization-insensitive silicon waveguide crossing based on multimode interference couplers

A polarization-insensitive waveguide crossing based on multimode interference (MMI) couplers is proposed and demonstrated on a silicon-on-insulator (SOI) platform. By utilizing two orthogonal MMIs, the footprint of the device is about 23  μm×23  μm. The proposed device, easily fabricated with only one fully etched step, is characterized with low insertion losses and low crosstalks for both transverse-electric and transverse-magnetic polarizations from 1520 to 1610 nm bands.

Crossing-free on-chip 2 × 2 polarization-transparent switch with signals regrouping function

We propose and demonstrate an on-chip 2×2 polarization-transparent switch for simultaneously handling two-group polarization-division multiplexing (PDM) signals. By introducing the polarization-transparent power splitter/combiner (PPS/PPC), waveguide crossings such as those in conventional PDM switches can be avoided and, thus, the insertion losses and complexity of the device can be reduced. Furthermore, each input polarization tributary can be independently switched and routed thanks to the output selectivity of the PPS/PPC. Thus, not only a basic switch between the dual-group PDM signals, but also a precise four-channel-signal regrouping can be achieved, enabling a complete and non-redundant switching functionality. A polarization extinction ratio larger than 15 dB with reasonable insertion losses is experimentally observed. Clear and open eye diagrams can be obtained with less than 1 dB power penalties for all the measured paths.

Polarization-insensitive 2 × 2 thermo-optic Mach-Zehnder switch on silicon

A polarization-insensitive 2×2 thermo-optic Mach-Zehnder switch (MZS) on silicon is proposed and demonstrated experimentally by utilizing silicon-on-insulator (SOI) nanophotonic waveguides with a 340-nm-thick silicon core layer. The present MZS consists of two 2×2 3 dB multimode interference (MMI) couplers, which are designed to be polarization-insensitive by choosing the core width optimally. Meanwhile, the MZS arms are designed with square SOI nanophotonic waveguides with a cross section of 340  nm×340  nm in order to achieve polarization-insensitive phase shift. The fabricated silicon MZS has an excess loss of 1∼4  dB and an extinction ratio of >20  dB in the C-band (1530∼1565  nm) for both TM and TE polarizations.

Reconfigurable SDM Switching Using Novel Silicon Photonic Integrated Circuit

Space division multiplexing using multicore fibers is becoming a more and more promising technology. In space-division multiplexing fiber network, the reconfigurable switch is one of the most critical components in network nodes. In this paper we for the first time demonstrate reconfigurable space-division multiplexing switching using silicon photonic integrated circuit, which is fabricated on a novel silicon-on-insulator platform with buried Al mirror. The silicon photonic integrated circuit is composed of a 7 × 7 switch and low loss grating coupler array based multicore fiber couplers. Thanks to the Al mirror, grating couplers with ultra-low coupling loss with optical multicore fibers is achieved. The lowest total insertion loss of the silicon integrated circuit is as low as 4.5 dB, with low crosstalk lower than −30 dB. Excellent performances in terms of low insertion loss and low crosstalk are obtained for the whole C-band. 1 Tb/s/core transmission over a 2-km 7-core fiber and space-division multiplexing switching is demonstrated successfully. Bit error rate performance below 10⁻⁹ is obtained for all spatial channels with low power penalty. The proposed design can be easily upgraded to reconfigurable optical add/drop multiplexer capable of switching several multicore fibers.

Ultra-high-extinction-ratio 2 × 2 silicon optical switch with variable splitter

We demonstrate a record-high extinction-ratio of 50.4 dB in a 2 × 2 silicon Mach-Zehnder switch equipped with a variable splitter as the front 3-dB splitter. The variable splitter is adjusted to compensate for the splitting-ratio mismatch between the front and rear 3-dB splitters. The high extinction ratio does not rely on waveguide crossings and meets a strong demand in applications to multiport circuit switches. Large fabrication tolerance will make the high extinction ratio compatible with a volume production with standard complementary metal-oxide semiconductor fabrication facilities.