Efficient, Compact and Low Loss Thermo-Optic Phase Shifter in Silicon

TL;DR

This paper presents a silicon thermo-optic phase shifter with high efficiency, low optical loss, and compact design, suitable for dense photonic integration, achieved through optimized resistive heating and waveguide engineering.

Contribution

The authors design and fabricate a low-loss, efficient thermo-optic phase shifter with a novel doping profile and waveguide geometry, demonstrating improved performance over existing devices.

Findings

Phase shifter efficiency of 24.77 mW/pi

Insertion loss of 0.23 dB across multiple devices

Modulation bandwidth of 130 kHz

Abstract

We design a resistive heater optimized for efficient and low-loss optical phase modulation in a silicon-on-insulator (SOI) waveguide and characterize the fabricated devices. Modulation is achieved by flowing current perpendicular to a new ridge waveguide geometry. The resistance profile is engineered using different dopant concentrations to obtain localized heat generation and maximize the overlap between the optical mode and the high temperature regions, while simultaneously minimizing optical loss due to free-carrier absorption. A 61.6 micrometer-long phase shifter was fabricated in a CMOS process with oxide cladding and two metal layers. The device features a phase-shifting efficiency of 24.77 +/- 0.43 mW/pi and a -3 dB modulation bandwidth of 130.0 +/- 5.59 kHz. The insertion loss measured for 21 devices across an 8-inch wafer was only 0.23 +/- 0.13 dB. Considering the prospect of densely integrated photonic circuits, we also quantify the separation necessary to isolate thermo-optic devices in the standard 220 nm SOI platform.