In this work, we report a novel notch optical filter based on the imaging properties of a MEMS-based Multimode Interference (MMI) waveguide. The concept is based on the dependence of the imaging lengths on the different wavelengths, where each wavelength exits the waveguide at a different lateral position. Thus, by properly choosing the output waveguide position, it is possible to have a good selective optical filter as well as a good notch optical filter (the complementary response). To validate this concept an MMI structure is fabricated using Deep Reactive Ion Etching (DRIE) technology on a silicon-on-insulator (SOI) wafer. The walls of the waveguide are metalized with Aluminum to decrease the insertion loss. The design makes use of the compactness of the parabolic butterfly shape to reduce the MMI length. The structure is fed by a 9/125 single-mode fiber and the Amplified Spontaneous Emission ASE out of a Semiconductor Optical Amplifier is used as a wideband source for the optical response characterization. The output is measured on an optical spectrum analyzer demonstrating a notch filter response around 1550 nm with about 20-dB rejection ratio. The reported results open the door for integrated, low-cost and fabrication insensitive optical MEMS notch filter.
MEMS-based FTIR spectrometers are good candidates for handheld and IoT applications due to their high speed of operation, ultra-compact size and low cost. Light sources used for FTIR spectroscopy are usually limited to thermal light sources that continuously emit black body radiation. However, the use of pulsed sources has many advantages, such as reducing detector noise and enabling new kinds of spectroscopy measurements that depend on pulsed sources such as supercontinuum sources and non-linear infrared spectroscopy. The use of these pulsed sources with the high-speed MEMS is, thus, of great interest. In this work, we study the effect of using a pulsed IR source with a MEMS FTIR spectrometer on the obtained spectrum. The system is analyzed for different operation regimes from quasi-static to high-speed pulses for different duty cycles and repetition rates. Two measurement setups are used. The first involves using pulsed white light output from a thermal source with an optical chopper. The chopper frequency is changed from 20 Hz to 1 kHz at duty cycle values from 1% to 50%. The second setup uses an acousto-optic modulator to square-wave modulate the amplified spontaneous emission of a semiconductor optical amplifier with a repetition rate ranging from 20 Hz to 2 MHz and duty cycle values from 5% to 50%. Degradation in signal-to-noise ratio as well as spectral distortion are analyzed for different regimes of operation.