Micro-mirror Micromechatronics System FH AACHEN University of Applied Science Supervisor: Prof. Kämper Team member: Chun Wa George Young Issis Contreras Ramanathan Swaminathan Spandan Shroff 10-10-2011

Advantage of MEMS Spectrometer over conventional small size low cost, fast response – filter unwanted wavelengths high signal to noise ratio reduced complexity and low power consumption

Key features of micromirror array a 100% fill-factor minimum surface roughness and high reflectivity (ideally 100%) in the wavelength range of interest zero insertion loss zero noise simple control identical deflection versus input energy response

A unique application of micromachined mirrors can be performance enhancement of a spectrometer by selectively focusing a particular spectral component on a detector thereby reducing the number of detectors required. improves the signal to noise ratio of the spectrometer device

IR Range Spectrometer Littrow configuration Source: FhG-IZM

Portable Universial Spectrometer Small mirror – reducing bandpass - higher resolution But low light intensity Variable band pass filter

Diffraction grating Monochromatic light d sina + d sinb = wavelength So leading to constructive interference Sensors andActuators

Diffraction grating When a diffraction grating is used, care must be taken in the design of broadband monochromators because the diffraction pattern has overlapping orders. In-plane diffraction refers to a diffraction technique in which both the incident and diffracted beams are nearly parallel to the sample surface. The grating diffracts the light, which converges toward the exit slit; the spectrum is scanned by rotating the grating to bring different wavelengths into focus at or near the exit slit. The spectrum is scanned by rotating the grating; this moves the grating normal relative to the incident and diffracted beams, which (by Eq. (2-1)) changes the wavelength diffracted toward the second mirror. Sensors andActuators

Grat scanning The spectrum is scanned by rotating the grating; this moves the grating normal relative to the incident and diffracted beams, which (by Eq. (2-1)) changes the wavelength diffracted toward the second mirror.  the grating is rotated to bring different wavelengths into focus at the (stationary) exit slit. The grating diffracts the light, which converges toward the exit slit; the spectrum is scanned by rotating the grating to bring different wavelengths into focus at or near the exit slit. The efficiency is maximal when the grating is used in the Littrow configuration Sensors andActuators

Plan grating and mounts The Czerny-Turner monochromator the light incident on and diffracted by the grating is collimated, the spectrum remains at focus at the exit slit for each wavelength, The Ebert-Fastie monochromator This design is a special case of a Czerny-Turner mount Disadvantage This can be seen by recognizing that the Ebert-Fastie monochromator is a special case of the Czerny-Turner monochromator in which both concave mirror radii are the same, and for which their centers of curvature coincide. Advantage However, an advantage that the Ebert-Fastie mount provides is the avoidance of relative misalignment of the two mirrors Sensors andActuators

Plan grating and mounts The Monk-Gillieson monochromator Advantage Often the angles of reflection (from the primary mirror), incidence and diffraction are small (measured from the appropriate surface normals), which keeps aberrations (especially off-axis astigmatism) to a minimum. Disadvantage Consequently the spectrum cannot remain in focus at a fixed exit slit when the grating is rotated (unless this rotation is about an axis displaced from the central groove of the grating42). Sensors andActuators

Plan grating and mounts The Littrow monochromator The same auxiliary optics can be used as both collimator and camera, since the diffracted rays retrace the incident rays. Sensors andActuators

Definition In-plane diffraction refers to a diffraction technique in which both the incident and diffracted beams are nearly parallel to the sample surface. The blaze wavelength is defined as that wavelength, in a given diffraction order m, for which the efficiency curve reaches its maximum. ml = d (sina + sinb) Sensors andActuators

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Fabrication polysilicon (poly-Si) and gold micromirror is fabricated by a surface -micromachining process Drawback: residual stress Result: curvature of the mirror surface which results in high insertion loss and crosstalk So monocrystalline silicon best results and closely resembles an ideal reflector surface. Sensors andActuators

1 dimension array micro mirror Sensors andActuators

Type of micro mirror Sensors andActuators

Question The proposal is workable? Mirror size? Sensors andActuators

Optics definition Aberrations are departures of the performance of an optical system from the predictions of paraxial optics Sensors andActuators

Slit The entrance slit is placed at the effective focus of the collimator so that the light from the slit reflected from the mirror is collimated (focused at infinity) Sensors andActuators

Portable Monochromator 300nm – 5um Sensors andActuators

Portable Monochromator Sensors andActuators