Polarization-insensitive Silicon Research Articles

Ultra-compact and polarization-insensitive silicon waveguide 3×3 star-crossing based on composite subwavelength grating metamaterials

Ultra-compact and polarization-insensitive silicon waveguide 3×3 star-crossing based on composite subwavelength grating metamaterials

Polarization-Insensitive Silicon Photonic Filter With Multimode Waveguide Gratings

Polarization-Insensitive Silicon Photonic Filter With Multimode Waveguide Gratings

A 4×112 Gb/s Ultra-Compact Polarization-Insensitive Silicon Photonics WDM Receiver with CMOS TIA for Co-Packaged Optics and Optical I/O

A 4×112 Gb/s Ultra-Compact Polarization-Insensitive Silicon Photonics WDM Receiver with CMOS TIA for Co-Packaged Optics and Optical I/O

Polarization-insensitive silicon nitride photonic receiver at 1 μm for optical interconnects

Polarization-insensitive silicon nitride photonic receiver at 1 μm for optical interconnects

Ultra-low loss SOI waveguide crossings designed by a hybrid global optimization based on deep learning

We demonstrate an ultra-low loss single-mode silicon waveguide crossing and an ultra-compact and ultra-low loss polarization-insensitive silicon waveguide crossing using a hybrid global optimizer based on a physics-informed generative adversarial network with a direct binary search refinement. By adopting this method, a parallel waveguide crossing structure with a footprint of 3 × 4 μm2 for transverse electric(TE) mode which has an insertion loss better than 0.03 dB and has crosstalk lower than −27 dB in 1500∼1600 nm bands is designed. A polarization-insensitive waveguide crossing with the same footprint is also designed in 1530∼1570 nm bands, which can provide insertion loss lower than 0.2 dB and crosstalk lower than −26.3 dB for TE mode and insertion loss lower than 0.1 dB and crosstalk lower than −27.8 dB transverse magnetic(TM) mode. The results show that this global optimizer produced high-efficiency devices while avoiding being trapped in the local optimal solutions compared to the traditional stochastic inverse design algorithm.

Polarization-insensitive silicon optic switch based on mode manipulated power splitters and phase shifters

A polarization-insensitive thermo-optic switch is proposed and demonstrated on the silicon-on-insulator platform with a 220 nm silicon core layer. The present device is based on the Mach–Zehnder interferometer structure, consisting of polarization-insensitive power splitters and polarization-insensitive phase shifters (PIPSs). The polarization-insensitive power splitter has been realized by employing an adiabatic directional coupler, which utilizes the fast adiabatic mode evolution by introducing cubic Bézier curves on outer contours, providing broadband 3-dB power splitting for TE and TM polarization modes with only 70 µm coupling length. For the novel PIPSs, the ridge waveguide with large aspect ratio, based on the mode hybridness property, could obtain the same power consumption (Pπ) for an optical switch working at TE and TM polarizations. Experimental results indicate that the measured insertion losses are less than 2 dB and the extinction ratios are larger than 15 dB over a 40 nm wavelength band (covering the C-band).

Ultra-compact silicon multimode waveguide bends based on special curves for dual polarizations

Multimode waveguide bends (MWBs) with very compact sizes are the key building blocks in the applications of different mode-division multiplexing (MDM) systems. To further increase the transmission capacity, the silicon MWBs for dual polarizations are of particular interest considering the very distinct mode behaviors under different polarizations in the silicon waveguides. Few silicon MWBs suitable for both polarizations have been studied. In this paper, we analyze several dual-polarization-MWBs based on different bending curve functions. These special curve-based silicon MWBs have the advantages of easy fabrication and low loss compared with other structures based on subwavelength structures, such as gratings. A comparison is made between the free-form curve (FFC), Bezier curve, and Euler curve, which are used in the bending region instead of a conventional arc. The transmission spectra of the first three TE and TM modes in the silicon multimode waveguide with a core thickness of 340 nm are investigated. The simulation results indicate that, with the premise of having the same effective radius, which is only 10 μm in this paper, the six-mode MWB based on the FFC has the optimal performances, including an extremely low loss <0.052 dB and low crosstalk below −25.97 dB for all six modes in the wide band of 1500 to 1600 nm. The MWBs based on the Bezier and Euler curve have degraded performances in terms of the loss and crosstalk. The results of this paper provide an efficient design method of the polarization insensitive silicon MWBs, which may leverage research for establishing complicated optical transmission systems that incorporate both the MDM and polarization-DM technology.

Silicon non-blocking 4 × 4 optical switch with automated polarization adjustment

We demonstrate a polarization-insensitive silicon 4×4 optical switch based on Mach–Zehnder interferometer (MZI) switch elements. On-chip polarization controllers are integrated before the switch fabric to automatically adjust an arbitrary input polarization to the transverse electric mode. The 4×4 switch fabric is based on a dilated double-layer network architecture to completely cancel the first-order crosstalk. Thermo-optic phase shifters are integrated in the MZI switch elements and the polarization controllers for adjustment of the switching state and polarization, respectively. We develop a polarization control algorithm based on a gradient descent method for automated polarization control. The polarization recovery time is less than 4 ms, and the measured polarization-dependent loss is ∼2 dB. The scheme provides a new solution for realizing polarization-insensitive silicon optical switches.

Polarization insensitive silicon waveguide wavelength filter using polarization rotator and mode conversion Bragg grating with resonator cavity

We demonstrate a polarization insensitive silicon waveguide wavelength filter using a polarization rotator and Bragg grating which exchanges TE0 and TE1 modes. A resonator cavity structure is used to obtain a narrow filter peak width. Two cascaded resonator cavities are used to attain a flat top transmission wavelength peak.

A compact and polarization-insensitive silicon waveguide crossing based on subwavelength grating MMI couplers.

In this work, we proposed and experimentally demonstrated a compact and low polarization-dependent silicon waveguide crossing based on subwavelength grating multimode interference couplers. The subwavelength grating structure decreases the effective refractive index difference and shrinks the device footprint. Our designed device is fabricated on the 220-nm SOI platform and performs well. The measured crossing is characterized with low insertion loss (< 1 dB), low polarization-dependence loss (< 0.6 dB), and low crosstalk (< -35 dB) for both TE and TM polarizations with a compact footprint of 12.5 μm × 12.5 μm.

Polarization-insensitive silicon nitride arrayed waveguide grating.

Next-generation passive optical networks require integrated, polarization-insensitive wavelength-division multiplexing solutions, for which the recently emerging low-loss silicon nitride nanophotonic platforms hold great potential. A novel polarization-insensitive arrayed waveguide grating (AWG) built with silicon nitride waveguides is presented in this Letter. Polarization insensitivity is obtained when both the channel spacing and the center wavelength of the two orthogonal polarization states (i.e., the TE and TM waveguide modes) are simultaneously aligned. In our design, the channel spacing alignment between the polarization states is obtained by optimizing the geometry of the arrayed waveguides, whereas the central wavelength polarization insensitivity is obtained by splitting the two polarization states and adjusting their angle of incidence at the input star coupler to compensate for the polarization mode dispersion of the AWG. A 100GHz 1×8 wavelength-division multiplexer with crosstalk levels below -16 dB is demonstrated experimentally.

Inverse-designed low-loss and wideband polarization-insensitive silicon waveguide crossing

Waveguide crossings are an essential component for constructing complex and functional on-chip photonic networks. Polarization-insensitive waveguide crossings are desired because photonic networks usually involve light with different polarizations. Here, we propose a polarization-insensitive waveguide crossing on a 250-nm silicon-on-insulator platform by using an inverse design method. In simulation, the designed waveguide crossing can maintain insertion loss below 0.18 (0.25)dB in the wavelength range of 1440-1640nm for the TE0 (TM0) mode and achieve minimal insertion loss as small as 0.08 (0.07)dB at the wavelength of 1550nm. The cross talk maintains below -32 dB and -35 dB for the TE0 and TM0 modes, respectively. Experimentally, the fabricated waveguide crossing achieves measured insertion loss less than 0.20 (0.25)dB for the TE0 (TM0) mode with minimal insertion loss as small as 0.1dB. The measured cross talk is below -28 dB and -31 dB for the TE0 and TM0 modes, respectively. Therefore, our proposed waveguide crossing can be widely applied in photonic integrated circuits to construct photonic systems with the capabilities of polarization control and mode (de)multiplexing.

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 1610nm bands.

Polarization-insensitive silicon nitride Mach-Zehnder lattice wavelength demultiplexers for CWDM in the O-band.

Polarization-insensitive silicon nitride (SiN) 4-channel wavelength (de)multiplexers based on Mach-Zehnder interferometer lattice filters for coarse wavelength division multiplexing (CWDM) in the O-band are demonstrated in a SiN-on-silicon photonic platform. For the best-performing device, the insertion loss was < 2.8 dB, the inter-channel crosstalk was < -11.5 dB for a polarization scrambled input, and the passband shift between the orthogonal polarizations was < 1.5 nm. Across the 200mm wafer, the die-averaged insertion loss and maximum crosstalk were 3.1 dB and -10.6 dB, respectively. The higher-than-expected crosstalk was due to dimensional variations. This work shows the potential of SiN photonic circuits for CWDM without polarization diversity.

Simultaneous four-channel thermal adaptation of polarization insensitive silicon photonics WDM receiver.

We propose a novel approach to demonstrate simultaneous multi-wavelength locking during temperature changes in a silicon photonic polarization insensitive microring-based wavelength division multiplexing (WDM) receiver. The DC component of a single monitoring photodetector at the through port of the microring filter array is exploited as a feedback signal with no additional power consumption. This feedback signal is used in control circuitry to properly tune the microring filters using ohmic heating, thus creating a feedback loop for thermal adaptation. We describe the necessary information, specifically each microring filter's room temperature resonant wavelength and tunability, which can be used to calibrate and achieve proper wavelength configurability and locking. In addition, we describe a simple control algorithm based on an adaptive gradient method often used in machine learning, allowing the receiver to endlessly demultiplex at different temperatures. We successfully achieve thermal adaptation over a temperature range >37°C and demultiplex a 4 × 25 Gb/s on-off-keying signal of 150 GHz channel spacing, all while the polarization is scrambling.

Polarization insensitive silicon photonic ROADM with selectable communication direction for radio access networks.

We report on an experimental prototype of a low-cost silicon photonic reconfigurable optical add/drop multiplexer (ROADM). The device is able to operate with up to 12 wavelength division multiplexing channels. In order to control the polarization of the multi-wavelength signal at the input of the device, an integrated polarization controller is investigated as an alternative to the polarization diversity device architecture. The integrated ROADM is equipped with optical switches for the selection of the path direction and variable optical attenuators for optical power control. We demonstrate the polarization insensitive routing of 10 Gb/s channels between two ROADM nodes with error-free transmission.

Polarization insensitive silicon immersion grating based on total internal reflection

We describe an immersion grating (IG) with both low polarization-dependent loss (PDL) and high diffraction efficiency. Our immersion grating consists of a silicon (Si) prism and a Si grating coated with dielectric film. We analyze the effect of the refractive index of dielectric film and clarify the refractive index ratio between a Si grating and dielectric film. Selecting an adequate material for the dielectric film, we design the diffraction efficiency of TM polarization without changing that of TE polarization. The simulation results for the optimized IG show a PDL of 0.2 dB and diffraction efficiency of -0.4 dB. A prototype with high dispersion power provides a low PDL of 0.6 dB, while maintaining a high diffraction efficiency of -0.4 dB.