At present most spectrometers, in particular for wavelengths longer than the VIS, are comparatively large, stationary and expensive. With the advent of micro-electro-mechanical systems (MEMS), it became possible to build pocket-sized spectrometers for various spectral ranges, including the near-IR or mid-IR. These systems are highly rugged and can measure spectral changes at ms time resolution or to co-add several hundreds of scans to one spectrum achieving adequate signal-to-noise ratios. Two spectrometer systems a Czerny-Turner type scanning monochromator and a FT-IR spectrometer both based on a micromechanical scanning mirror technology with in plane electrostatic actuation are presented.
In this paper we present a MOEMS based miniaturized Fourier-transform infrared (FTIR) spectrometer capable to perform time resolved measurements from NIR to MIR. The FTIR-spectrometer is based on a MOEMS translatory actuator which replaces the macroscopic mirror drive enabling a miniaturized, robust and low cost FTIR system. The MOEMS device is manufactured in a CMOS compatible process using SOI technology. Due to the electrostatic driving principle based on in-plane electrode combs, 200 μm stroke can be achieved with comparatively low voltages (<40 V) at an ambient pressure below 500 Pa. The actuator plate, acting as mirror with an area of 1.65 mm2, operates at a resonant frequency of 5 kHz. Consequently this yields a maximum spectral resolution of 25 cm-1 and an acquisition time of 200 μs per spectrum. Based on a Michelson setup the infrared optical bench of the presented FTIR system is designed to account for the mirror aperture and the desired spectral bandwidth of 2 μm to 5 μm. The integrated signal processing electronics has to cope with a bandwidth of 8 MHz as a result of the mirror motion. A digital signal processor manages system control and data processing. The high acquisition rate and integration level of the system makes it appropriate for applications like process control and surveillance of fast reactions. First results of transmission and absorbance measurements are shown. In addition we present a novel MOEMS device with increased mirror aperture and stroke which will be used for further optimization of the spectral FTIR-resolution.
We present several types of translatory MOEMS actuators developed for fast optical-path-length modulation [e.g., in confocal microscopes or Fourier-transform infrared (FTIR) spectrometers] and their application on miniaturized FTIR spectrometers capable of performing time-resolved measurements from the near infrared to the mid infrared. The MOEMS devices are manufactured in a complementary metal oxide semi conductor compatible silicon-on-insulator process. They are electrostatically resonant, driven using in-plane comb drives. A first translatory 5-kHz MOEMS device is used in a first prototype of a miniaturized MOEMS-based FTIR spectrometer where the MOEMS actuator replaces the macroscopic mirror drive, enabling a miniaturized, robust, and low-cost FTIR system. The mirror plate of 1.65 mm2 is suspended by bending springs. Due to the resonant operation, a 200-µm stroke can be achieved with low voltages (<40 V) at an ambient pressure below 500 Pa. Consequently, this yields a spectral resolution of 25 cm−1 and an acquisition time of 200 µs per spectrum. In addition, we present a novel MOEMS device with an increased mirror aperture of 7.1 mm2 and pantograph-like mirror suspension enabling up to a 500-µm stroke. This device is specifically optimized for miniaturized FTIR spectrometers to enable an improved spectral resolution of 10 cm−1 and a signal-to-noise ratio of >1000:1.
A translatory MOEMS actuator with extraordinary large stroke - especially developed for fast optical path length modulation in miniaturized FTIR-spectrometers - is presented. A precise translational out-of-plane oscillation at 500 Hz with large stroke of up to 1.2 mm is realized by means of a new suspension design of the comparative large mirror plate with 19.6 mm² aperture using four pantographs. The MOEMS device is driven electro - statically resonant and is manufactured in a CMOS compatible SOI process. Up to ± 600 μm amplitude (typically 1mm stroke) has been measured in vacuum of 30 Pa and 50 V driving voltage for an optimized pantograph design enabling reduced gas damping and higher driving efficiency.
Resonantly driven oscillating MOEMS mirrors are used in various fields in optics, telecommunications and spectroscopy. One of the important challenges in this context is to assure stable resonant oscillation with well controlled amplitude under varying environmental conditions. For this reason, we developed a compact device comprising a resonant MOEMS micro-mirror, optical position sensing, and driver electronics, with closed loop control, which ensures operation close to the mirror resonance. In this contribution we present this device and show experimental results with a 23 kHz MOEMS mirror, which demonstrate its capabilities and limitations.
We discuss recent improvements of our MEMS- based FT-IR spectrometer. A novel MEMS actuator design of the translational mirrors features an increased mirror surface of 7 mm 2 and enables larger translation amplitudes (up to ±250 µm), leading to improved performance of the spectrometer. Furthermore we present a new method for accurate position detection of the MEMS device, thus enabling the implementation of closed-loop control. A dedicated circuit demodulates the reference signal and generates a highly accurate control signal returning the zero-crossing position of the mirror. The implementation of a closed-loop control ensures optimally stable MEMS mirror movement and maximal mechanical amplitude, even under varying environmental conditions allowing building robust MEMS- based Fourier-transform infrared (FT-IR) spectrometers with large mechanical amplitudes and thus good spectral resolutions.
Spectroscopy in the infrared region is today an important application to measure, control and investigate liquids or gases in industrial, medical or environmental applications. We have developed a small, transportable NIRspectrometer with a size of only 120 x 80 x 80 mm3, and a MOEMS-scanning-grating chip as main element. The scanning-grating chip is resonantly driven by a pulsed voltage of only 36V, has a mirror aperture of 3 x 3 mm2 and reaches maximum deflection angles of +/- 11o. The NIR-micro-spectrometer works currently in a spectral range of 1200 - 1900 nm with a resolution of less than 10 nm using only one single InGaAs-diode as detector. Additionally, scanning grating chips have been already developed for spectral ranges of 900 - 1800 nm and 1250 - 2500 nm. One entire spectral measurement is done within 6 milliseconds, calculated by a digital signal processor, which is included in the spectrometer. Results can be either displayed by special computer software or directly by a graphical user interface. In this paper, we will focus on the control of the grating fabrication process, which can be done by microscopy, using new control structures. A time-consuming control with SEM (Scanning electron microscope) is no longer needed. Furthermore the characterization of the fabrication process and its consequence on the spectrometer properties will be discussed, as well as the characterization of the scanning grating chip itself (frequency, movement, static deformation, spectral efficiency...). Characteristic measurement results of an argon calibration lamp, which shows the performance of the NIR-micro-spectrometer, will be presented as well.
In this paper we present a novel translatory MOEMS device with extraordinary large stroke especially designed for fast optical path modulation in an improved miniaturized Fourier-transform infrared (FTIR) spectrometer capable to perform time resolved measurements from NIR to MIR. Recently, we presented a first MOEMS based FTIR system using a different translatory MOEMS actuator with bending suspensions of the mirror plate and ±100μm oscillation amplitude resulting in a limited spectral resolution of 30 cm-1. For the novel MOEMS actuator an advanced pantograph suspension of the mirror plate was used to guarantee an extraordinary large stroke of up to 500 μm required for an improved spectral resolution. To optimize the optical throughput of the spectrometer the mirror aperture was increased to 7 mm2. The MOEMS actuators are driven electro statically resonant using out-of-plane comb drives and operate at a resonant frequency of 500 (1000) Hz, respectively. Hence, this enables to realize an improved MOEMS based FTIR-spectrometer with a spectral resolution of up to 10 cm-1, a SNR of > 1000:1 and an acquisition time of 1 ms per spectrum of the miniaturized FTIR-system. In this article we discuss in detail the design and the experimental characteristics of the novel large stroke translatory MOEMS device. The application and system integration, especially the optical vacuum packaging, of this MOEMS device in an improved miniaturized MOEMS based FTIR spectrometer enabling ultra rapid measurements in the NIRMIR spectral region with 12cm-1 spectral resolution is discussed in a separate paper submitted to this conference.
In recent years, Micro Opto Electro Mechanical Systems (MOEMS) have been reached more and more importance in technical applications. This is caused by the increased reliability of micro systems combined with the reduction of costs by high volume production. In this paper, we will present a resonant scanning grating chip with high diffraction efficiency, developed for the NIR region (900 - 2500 nm), which is based on our resonant micro scanning mirror. The grating was additionally applied to the silicon mirror plate by a chemical wet etch process. Therefore, three different fabrication technologies have been developed, showing high efficiencies in the first diffraction order. Compared to investigations with direct structured gratings in the reflective aluminium surface, gratings with up to 714 lines/mm could be fabricated combined with an improved process parameter control. These new resonant driven scanning gratings are still compatible to the scanning mirror fabrication process. They have a large surface of 3x3 mm2 and resonant frequencies of down to 150 Hz, which results in a lower demand on the bandwidth of the electronic read out, when applied to a spectrometer set-up. The maximum mechanically scan angle of the grating mirror plate could be increased to +/- 12° at a driving voltage of 36 V. First measurement results and an improved design of a micro spectrometer, working with only one single InGaAs-Detector in a spectral range of 900 to 2500 nm will be presented and discussed.
