This paper reports for the first time that a novel MEMS-based micromirror switch has successfully demonstrated for optical switching in a multi-channel fiber optics spectrophotometer system. The conventional optomechanical fiber optic switches for multi-channel spectrophotometers available in market are bulky, slow, low numbers of channels and expensive. Our foundry MEMS-based micromirror switch designed for integrating with commercially available spectrophotometers offers more compact devices, increased number of probing channels, higher performance and cheaper. Our MEMS-based micromirror switch is a surface micromachined mirror fabricated through MUMPs foundry. The 280 μm x 280 μm gold coated mirror is suspended by the double-gimbal structure for X and Y axis scanning. Self-assembly by solders is used to elevate the torsion mirror 30 μm over the substrate to achieve large scan angle. The solder self-assembly approach dramatically reduces the time to assembly the switch. The scan mirror is electrostatically controlled by applying voltages. The individual probing signal from each probing head is guided by fibers with collimated lenses and incidents on the center of the mirror. The operating scan angle is in the range of 3.5 degrees with driving voltage of 0-100 V. The fastest switching time of 4 millisecond (1 ms rise time and 3 ms fall time) is measured corresponding to the maximum speed of the mirror of 0.25 kHz when the mirror is scanning at ± 1.5 degrees. The micromirror switch is packaged with a multi-mode fiber bundle using active alignment technique. A centered fiber is the output fiber that is connected to spectrophotometer. Maximum insertion loss of 5 dB has been obtained. The accuracy of measured spectral data is equivalent to the single channel spectrophotometer with a small degradation on probing signal due to fiber coupling.
The emerging technology of micro-optical-electro-mechanical systems (MOEMS) offer promise for automating the alignment of free-space optical systems, especially intra-computer optical interconnects. MOEMS-based microlenses and micromirrors have been fabricated for the purpose of providing initial system alignment and dynamic alignment.
The performance of different MEMS mirrors from Boston University, MEMS Optical LLC, University of Colorado and OKO Technologies was studied in respect to an application in a model-free adaptive optics system. The frequency response characteristic was determined in a simple laser beam focusing set-up. Closed-loop adaptation experiments were performed using a VLSI controller system implementing a stochastic parallel gradient descent optimization algorithm. The system behavior using different MEMS mirror types, esp. adaptation speed, was compared.
Lenslet integrated Micro-Electro-Mechanical Deformable Micromirrors (LMEM-DMs) are electrostatic micromirror arrays fabricated through a commercial surface micromachining process and integrated with polymer or glass microlenses. The electronics resins (Photo-BCB) which are photo-sensitive polymers were used to fabricate polymer microlens arrays. A 4 X 4 element photo-BCB Cyclotene microlens array was fabricated on a thin quartz substrate. Self-aligned soldering flip-chip assembly is applied to integrate microlens arrays directly over the micromirrors. The lens/mirror gap is controlled using the final height of solder balls, and the lateral alignment is achieved by the solder self-aligning mechanism. The LMEM-DM is attractive due to its low cost and the low drive voltages. The use of a lenslet to focus the incoming laser beam onto the reflective surface of a micromirror substantially increases overall optical fill factor of the micromirror array. The LMEM-DM provides superior aberration correction with low residual diffraction effects. For mirror deflections much smaller than the lenslet focal length, the LMEM-DM behaves as a phase-only modulating optical element. The LMEM-DM thus serves as a rugged, compact optical element for beam steering, beam shaping, and aberration correction applications.
A packaging technology has been developed to integrate a lenslet array with surface micromachined segmented deformable micromirrors. 12 X 12 electrostatic micromirror arrays were fabricated through a commercial surface micromachining process and integrated with glass microlenses positioned directly over the micromirror. Control of the spacing and the lateral alignment between the lenslet array and the micromirrors was important for effective fill factor. The spacing control was accomplished using glass spacer, and the lateral alignments were achieved by the use of an interferometric microscope. Measured results of the micromirrors' optical performance demonstrated the success of the packaging technology.
Flip chip assembly technology offers a reliable and advanced packaging approach for hybrid integration of micromachined optical components. In this paper we present flip chip integration of microlens arrays with surface micromachined segmented deformable micromirrors. 12 by 12 electrostatic micromirror arrays were fabricated through a commercial surface micromachining process and integrated with glass microlenses. A commercial glass microlens array is positioned directly over the micromirror. The use of a lenslet to focus the incoming laser beam onto the reflective surface of a micromirror substantially increases optical efficiency of the hybrid microsystem. For mirror deflections much smaller than the lenslet focal length, the lenslet/micromirror combination behaves as a phase-only modulating optical element. The hybrid lenslet/MEMS arrays thus serve as rugged, compact optical elements for beam steering, beam shaping, and aberration correction applications.
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