In-Line Optical MEMS Phase Modulator and Application in Ring Laser Frequency Modulation

Optical phase modulators are essential building components in a wide range of applications, for instance, optical communication systems, tunable lasers, optical phase locked loops, and optical sensors. The production of in-plane MEMS-based optical phase modulator with self-aligned mirrors, actuator, and fiber grooves enables the low cost and easy integration with fiber-based lasers and sensors or photonic microsystems. In this paper, we report an in-plane transmission type MEMS-based optical phase modulator fabricated by deep reactive ion etching technology on a silicon-on-insulator (SOI) substrate. Detailed optical analysis of the MEMS phase modulator considering the diffraction of the single-mode fiber output beam, the asymmetric truncation of the beam by the limited aperture of the micromirrors and the tilt angle of the deeply etched mirrors is presented. The device layer height of the fabricated SOI wafer is 100 μm, and the sidewalls are etched with verticality that is better than 89.98°. The micromechanical system is characterized experimentally using electrical technique, and the resonance frequency and quality factor are 11.3 kHz and 163, respectively. The MEMS device is integrated into fiber ring laser (FRL) enabling the achievement of low- and high-frequency modulation indices. The frequency modulation of the FRL using the presented phase modulator is supported with numerical analysis and experimental results.