In-plane deeply-etched optical MEMS notch filter with high-speed tunability

Abstract

Notch filters are used in spectroscopy, multi-photon microscopy, fluorescence instrumentation, optical sensors and other life science applications. One type of notch filter is based on a fiber-coupled Fabry–Pérot cavity, which is formed by a reflector (external mirror) facing a dielectric-coated end of an optical fiber. Tailoring this kind of optical filter for different applications is possible because the external mirror has fewer mechanical and optical constraints. In this paper we present optical modeling and implementation of a fiber-coupled Fabry–Pérot filter based on dielectric-coated optical fiber inserted into a micromachined fiber groove facing a metallized micromirror, which is driven by a high-speed MEMS actuator. The optical MEMS chip is fabricated using deep reactive ion etching (DRIE) technology on a silicon on insulator wafer, where the optical axis is parallel to the substrate (in-plane) and the optical/mechanical components are self-aligned by the photolithographic process. The DRIE etching depth is 150 μm, chosen to increase the micromirror optical throughput and improving the out-of-plane stiffness of the MEMS actuator. The MEMS actuator type is closing-gap, while its quality factor is almost doubled by slotting the fixed plate. A low-finesse Fabry–Pérot interferometer is formed by the metallized surface of the micromirror and a cleaved end of a standard single-mode fiber, for characterization of the MEMS actuator stroke and resonance frequency. The actuator achieves a travel distance of 800 nm at a resonance frequency of 89.9 kHz. The notch filter characteristics were measured using an optical spectrum analyzer, and the filter exhibits a free spectral range up to 100 nm and a notch rejection ratio up to 20 dB around a wavelength of 1300 nm. The presented device provides batch processing and low-cost production of the filter.

Electrostatic Comb-Drive Actuator with High In-Plane Translational Velocity

“…There are many out-of-plane measurement techniques, such as laser Doppler velocimetry [ 33 ], stroboscopic imaging [ 34 ] and laser feedback interferometry [ 35 , 36 ] but an in-plane measuring technique was preferred for compatibility with the target micro-optical bench technology. An optical test method to characterize the mechanical displacement of the high speed MEMS actuators was developed [ 37 ]. The technique is based on optical interferometry.…”

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

“…Indeed, there are two kinds of loss due to the truncation [29]. The first one arises from the energy that escapes out of the micromirror physical dimension; i.e.…”

Translational MEMS Platform for Planar Optical Switching Fabrics

“…This makes them undesirable for the green optical data centers envisioned for the future. Thus, low voltage electrostatic actuators based upon widely used comb drives and parallel plate designs become the right choice for planar optical switching applications [24,25]. These can also be fabricated with ease through commercial SOI microfabrication processes to validate MEMS designs before integration with optical waveguides [26,27].…”