A silicon-on-insulator polarization diversity scheme in the mid-infrared

Abstract

Abstract:We propose a silicon-on-insulator (SOI) polarization diversity scheme in the mid-infrared wavelength range. In consideration of absorption loss in silicon dioxide (SiO 2 ), the polarization splitter-rotator (PSR) is designed and optimized with silicon nitride (SiN) upper-cladding and SiO 2 lower-cladding. This asymmetry allows the PSR, which consists of mode-conversion tapers and subsequent mode-sorting asymmetric Yjunctions, to be fabricated with a simple one-step etching process. Simulation shows that our PSR has good performance with low mode conversion loss (< 0.25 dB) and low crosstalk (< -18 dB) in a very large wavelength range from 4.0 μm to 4.4 μm. The PSR also exhibits large fabrication tolerance with respect to the size deviations in waveguide width, height and refractive index of the upper-cladding. Additionally, PSR devices based on Y-junctions with SiO 2 upper-cladding, and SiN upper-and lower-claddings are designed for potential applications at shorter and longer wavelengths, respectively. These PSR devices could facilitate the development of silicon photonic devices in the mid-infrared.

Silicon Photonic Platform for Passive Waveguide Devices: Materials, Fabrication, and Applications

“…For a waveguide‐type PSR, an asymmetrical cross shape is required to break the waveguide symmetry. Several types of silicon‐based PSRs have been reported based on various structures, such as DCs, [ 179,180 ] MMI, [ 181 ] Y‐junction, [ 182 ] sub‐wavelength structures, [ 183,184 ] and slot waveguides. [ 185 ]…”

“…The conversion between the TM 0 mode and the TE 1 mode requires a mode hybridization region in a high index‐contrast optical waveguide with an asymmetrical cross section, such as a T‐shaped cross‐section waveguide, [ 187 ] an adiabatic taper waveguide with air cladding, [ 188 ] or a rib waveguide with SiO 2 cladding. [ 182,189 ] The mode converters used in the PSRs can be realized by many structures, including ADC, [ 179 ] asymmetrical Y‐junction, [ 182 ] and S‐bend waveguide. [ 187 ] A silicon PSR was demonstrated with a TM 0 ‐TE 1 polarization rotation and a TE 1 ‐TE 0 mode converter, [ 188 ] and the remaining TM 0 mode was filtered by a bent DC.…”

Graphene‐Based Silicon Photonic Devices for Optical Interconnects

“…Due to the presence of well‐established infrastructures and highly mature supply chains, silicon photonics has undergone rapid development in the past decade. [ 10–12 ] Multiple core functions of optical interconnect including modulation, [ 1,13–15 ] detection, [ 16–21 ] polarization manipulation, [ 22–26 ] and multiplexing/de‐multiplexing [ 27–32 ] could be simultaneously implemented on a millimeter‐scale silicon photonic chip. [ 12 ] Although the indirect band structure of silicon prevents an efficient light emission, heterogeneous integration approaches such as wafer bonding [ 33–40 ] and micro‐transfer printing [ 41–46 ] have been developed to offer on‐chip semiconductor optical amplifiers and light sources.…”

Ultracompact and high efficient silicon-based polarization splitter-rotator using a partially-etched subwavelength grating coupler

“…Thus, the total device length inevitably needs to be very long, e.g., ~100 μm10, 475 μm12, 96 μm14, ~200 μm15, 190 μm16 and ~120 μm13, to achieve reasonable performance, greatly limiting the integration density on-chip. Moreover, PSRs based on silicon nitride (Si 3 N 4 )-on-SOI platform20, operated at bi-wavelength (1310 nm and 1550 nm)21, 300 nm broadband around wavelength of 1550 nm22, or mid-infrared range23 have also been proposed, respectively, but the obtained device lengths are still quite long (576 μm20, 138 μm21, 300 μm22, and ~470 μm23). Therefore, it is greatly required to explore new approaches to effectively reduce the dimensions of PSRs to fulfill the requirements of dense integration on-chip with polarization-independence.…”

“…Meanwhile, an additional tapered waveguide extended from the partially-etched waveguide is added in the lateral end of the input SWG-tapered transition to better separate input polarizations. Compared with PSRs reported earlier, the present one has the shortest size since the input TE mode is directly coupled and converted to the output TM mode without some intermediate modes such as TE 1 mode as a bridge used in many previous schemes 10 12 13 14 15 16 17 20 21 22 23 , and the coupling and converting processes are reasonably combined together instead of using cascaded parts composed of separate splitters and rotators. From results, the obtained device length is only 8.2 μm, which is about one order of magnitude smaller than that of previous reports 10 13 14 15 16 17 18 21 and also quite smaller than that of SWG-based PSR assisted by an ADC structure 34 , more details are summarized in Fig.…”