Design, Simulation, Fabrication, and Characterization of a Digital Variable Optical Attenuator

Abstract

In this paper, we present the design, simulation, fabrication, and some measurement and characterization of a novel 16-bit digital variable optical attenuator (VOA) that attenuates by switching individual mirror of an array as an attempt to achieve input voltage variation independence and output linearization. The design was aided by a simulation package that features coupled electrostatic and mechanical solver. The mirror array spans an area of 1500 1500 m 2 and contains 16 equal-length rectangular micromirrors. Each mirror is suspended by two torsion beams. Experiments on beam design and width variations are conducted. Assuming Gaussian distribution, the mirror widths computed by an iteration algorithm vary from about 40 to 250 m. Based on silicon-on-insulator (SOI) technology, two fabrication schemes to open the backside optical entrance were investigated . A hydrofluoric (HF) acid vapor-phase-etching (VPE)setup built to release the microstructure anhydrously is the key to achieve high yield especially for fragile components. Surface flatness, resonance frequencies, and tilt angles of selected mirrors were characterized. Quartz chips patterned with aluminum electrodes and 10 m-high SU8 spacer columns were fabricated and assembled to corresponding device chips. Optical performance adversely affected by mirror bending is believed to originate from the intrinsic stress of the SOI wafer.[1271]Index Terms-Deep reactive ion etch (DRIE), hydrofluoric (HF) vapor-phase-etching (VPE), micro mirrors, silicon-on-insulator (SOI), variable optical attenuator (VOA).

Study of hybrid driven micromirrors for 3-D variable optical attenuator applications

“…VOA is commonly considered to be a key component to groom power levels across the wavelength division multiplexing spectrum, minimizing crosstalk and maintaining the desired signal-to-noise ratio. Most of the designs of MEMS VOAs reported in the literature adopted attenuation schemes that can be generally classified into three groups: shutter-type [12][13][14][15][16], planar reflective-type [17][18][19][20][21][22] and three-dimensional (3-D) reflective-type [23][24][25][26][27]. Pioneering works of MEMS-based VOAs based on shutter-type designs were first conducted in 1998 by Giles et al [12] and Marxer et al [13].…”

“…Another key approach of making MEMS VOA devices involves the integration of large reflective mirrors with optics typically realized in 3-D free space configuration [23][24][25][26][27]. When such tilt reflective mirrors are deployed for 3-D optical attenuation in conjunction with large micro-optics such as dual fiber collimator, the resulting VOA device can gain excellent data in terms of return loss and WDL under reasonable driving voltage.…”

“…When such tilt reflective mirrors are deployed for 3-D optical attenuation in conjunction with large micro-optics such as dual fiber collimator, the resulting VOA device can gain excellent data in terms of return loss and WDL under reasonable driving voltage. A 3-D VOA based on DMD mirror array from Texas Instruments has been demonstrated in 1999 [23], while Sun et al deployed a digital VOA using an array of 16 equal-length rectangular micromirrors [24]. Besides using an array of micromirrors to form a multi-bit digital VOA, a large single reflective mirror may also be used for attenuation purpose.…”