A Compact Fourier Transform Spectrometer on a Silicon Optical Bench With an Electrothermal MEMS Mirror

Modeling and Control of a Large-Stroke Electrothermal MEMS Mirror for Fourier Transform Microspectrometers

“…The experimental results indicate that the measured OPD is 612.2 μm and 128.5 μm for 1 Hz and 10 Hz, corresponding to spectral resolutions of 32 cm −1 and 156 cm −1 , respectively. By comparing with prior work using open-loop tilting compensation scheme [18], both the piston scan range and drive frequency can be increased greatly due to high stiffness design of the closed-loop tilting control system. Additionally, the measurements are shown to be more stable over a long time.…”

“…The LSF micromirror is fabricated using a combined bulk and surface micromachining process [18]. Figure 1(b) shows an SEM of one released MEMS mirror, where the initial elevation of the raised mirror plate is about 680 μm when no voltage is applied.…”

“…For instance, the resistances of the two actuators are slightly different, within 5% for most of devices. Although the optimized drive signal ratio [17] or open-loop compensation method [18] can reduce the tilting during the piston scanning, the residual tilt angle is relatively large due to time-varying characteristics of thermal bimorph actuation. Figure 2 shows a conceptual model of the electrothermal micromirror device, representing the electrical to thermal, thermal to stress, and stress to motion conversions.…”

“…In the FTS setup [18], a red He-Ne laser (632.8 nm) is used as the reference light, and a green semiconductor laser (532.2 nm) is used as the unknown light to be measured. When the FTS system starts to run after the optical alignment is completed, the raw interferograms of the reference light and the unknown light are picked up concomitantly by two photodetectors and then digitized by a data acquisition module.…”

“…To further reduce the uncompensated tilt, Xie et al reported an MEMS mirror with a three-level ladder ISC actuator design and an unique configuration of 16 ISC actuators and demonstrated a very small uncompensated tilting of less than 0.03°over the full actuation range [13] but this tilt angle is still one order of magnitude larger than the optimal tilt. Recently, Wang et al reported a large-stroke electrothermal MEMS mirror and demonstrated a large OPD of 450 μm and reduced the tilt down to ±0.002°using an open-loop control method [18], but this method is susceptible to any environmental changes and device drifting; nevertheless, only 58% of the full scan range was used. Thus, relatively small scan range usage and large tilting effect are still two of the most significant problems for these electrothermal MEMS mirrors in practical FTS applications.…”