Microelectromechanical systems (MEMS) and optics are a natural match. There are several reasons: MEMS devices have dimensions and achievable actuation distances comparable to the wavelength of light; smooth-surfaced dielectrics, semiconductors, and metals can be used in various combinations; and, since redirection of photons does not require large forces, the relatively feeble MEMS actuators can easily manipulate them. Micro-optical-electromechanical systems (MOEMS) are those where optics merge with MEMS. Many MOEMS devices are based on mirror arrays that can be tilted using electrostatic actuation. This work, however, focuses on programmable diffraction gratings and their uses for projection displays, spectroscopy, and wavelength management in modern optical telecommunication systems.
We describe the development of a MEMS-based correlation radiometer for remote detection of chemical species. The radiometer utilizes a new type of MEMS programmable diffraction grating called the Polychromator. The Polychromator contains an array of 1024 electrostatically actuated reflective beams that are 10 microns wide by 1 cm long, and have a vertical travel of approximately 2 - 4 microns. The Polychromator grating is used to replace the reference cell of conventional correlation radiometry. Appropriate programming of the deflection profile of the grating array enables the production of any spectral transfer function desired for the correlation measurement. Advantages of this approach to correlation radiometry include the ability to detect multiple chemical species with a compact
instrument, the ability to optimize the reference spectra to eliminate chemical interferences, and the ability to produce
reference spectra for hazardous and transient species.
Microelectromechanical Systems ("MEMS") and optics are a natural match. There are several reasons: MEMS devices have dimensions and achievable actuation distances comparable to the wavelength of light; smooth-surfaced dielectrics, semiconductors, and metals can be used in various combinations; and, photons don't weigh anything, so relatively feeble MEMS actuators can easily manipulate them. Many optical MEMS devices are based on mirror arrays that can be tilted using electrostatic actuation. This paper, however, focuses on programmable diffraction gratings and their uses for projection displays, spectroscopy, and wavelength management in modern optical telecommunication systems.
Fabrication- and measurement-induced stresses in surface micromachined structures are investigated by wafer-level probing of electrostatically actuated polysilicon test structures fabricated by the MUMPs process of MCNC. The test structures are based on M-Test, an electrostatic pull-in approach for monitoring process uniformity and reproducibility, and, when used in conjunction with suitable geometric data, for measuring material properties. The sensitivity of the pull-in technique reveals that the simple step of placing the die on a vacuum probe station can significantly affect the measured results. The presence of strain gradients in the polysilicon and compliant structural supports for the beams makes the modeling more complex than for ideal geometries, but with appropriate adjustments to the models, and with knowledge of the strain gradient obtained from cantilever tip deflection as a function of beam length, the technique enables a measurement of the elastic modulus and the fabrication-induced residual stress.
We present the design and analysis of a microfabricated silicon pressure transducer. The operating principle for this device is based on the evanescent modulation of power in an integrated optical waveguide. A silicon diaphragm attenuator is initially separated from the waveguide by a precise microfabricated gap spacing. When external pressure is applied to the sensor, the silicon attenuator is moved into closer proximity with the waveguide, and light is coupled out of the waveguide into the attenuator. Thus, by monitoring the light intensity at the output of the waveguide, one can deduce the pressure applied to the silicon diaphragm. Packaging considerations have played an important role in the development of the device and have led to the use of anti-resonant reflecting optical waveguides (ARROWs), which are etched down to form a rib in order to provide confinement in the lateral direction. These waveguides provide good spatial and index matches to single-mode optical fibers. Numerical simulations of device performance have provided information critical to the design of the sensor.