Ultralow Loss and High Extinction Ratio TM-Pass Polarizer in Silicon Photonics

Abstract

TM-pass polarizers are pivotal components of photonic integrated circuits (PICs), especially those intended for biosensing applications. In the literature, several silicon TM-pass polarizers have been proposed, designed and experimentally demonstrated, but their insertion loss is not compatible with the current trend of silicon photonics aimed at exponentially increasing the component density within PICs. Herein, we propose and design a TM-pass polarizer whose insertion loss is carefully minimized to 0.05 dB at wavelength 1.55 µm by utilizing a combination of an asymmetric directional coupler and a mode evolution section. The adoption of appropriate technical solutions makes this record insertion loss value compatible with a high extinction ratio equal to 38 dB. With a device footprint of only 2.5 × 20 µm 2 , the design exhibits an insertion loss less than 1.7 dB and extinction ratio better than 30 dB over a large bandwidth of 200 nm. The design assumes the constraints of a typical silicon photonics open-access technological process and a standard 220 nm silicon-on-insulator (SOI) wafer. A very low sensitivity of the achieved performance to reasonable fabrication inaccuracies is demonstrated, with a worst-case insertion loss of only 0.32 dB at wavelength 1.55 µm.

Adiabatic tapers based on photonic inverse design

“…Adiabatic tapers play a crucial role in photonic integrated circuits, particularly in applications that require high optical bandwidth and a high fabrication tolerance. Many photonic components including power splitters [1][2], mode converters [3][4][5] and spot size converters [6] can be designed based on the principle of adiabatic mode evolution. If the choice of taper length guarantees adiabatic mode evolution across the input wavelength spectrum, the resulting design secures broadband capability.…”

High performance TM-pass polarizer via subwavelength grating bandgap engineering

“…For TM-pass polarizers several solutions have been proposed, but most of them require a complex fabrication process [5] or reflect the fundamental TE mode back into the system [6], which can have detrimental sideeffects. Other approaches include using a polarization splitting mechanism with an air cladding, which can be problematic for integration [7], employing a Bragg grating with only 50 nm wide slots to radiate the TE polarization [8], or leveraging a directional coupler comprised of silicon and silicon nitride waveguides to couple only the TM mode [9].…”