A MEMS VOA with polymeric microactuators using microoptics is presented. Its insertion loss < 0.5 dB, dynamic range > 50 dB, power and time for 20 dB, < 40 mW and 40 ms resp

Dekker, R.

Diemeer, M.B.J.

English

A MEMS VOA with polymeric microactuators using microoptics is presented. Its insertion loss &lt; 0.5 dB, dynamic range &gt; 50 dB, power and time for 20 dB, &lt; 40 mW and 40 ms resp

Diemeer, Mart

University of Twente Research Information

Fibers and waveguide components P1.27MEMS VOA WITH POLYMERIC THERMAL MICROACTUATORSM.8.J Diemeer (1), R.Dekker (2)1: Lghtwave Devices Group, MESA* Research Institute, University of Twerte,P.O. Box 217, 7500AE Enschede, The Netherlands, E-mail: M.B.J.Diemeer@el.utwente.nil2: JDS Uniphase Corporation, Ottawa, E-mail: RonaId.Dekker@jdsu.comAbstract A MEMS VOA with polymenc microactuators using microoptics is presentedIts insertion loss c 0.5 dB, dynamic range > 50 dB, power and time for 20 dB, < 40mWand 40 ms resp.introductionIn fiber-optic networks varable optical attenuators(VOA's) are required to remotely control the power incross-oonnected nodes and the gain of opticalamplifiers in wavelength dMsion multiplexed "DM)systems. VOA's can be realized with bulk opto-mechanical components, side polished fibers, planarwaveguide componerns and microelectromechanicalsystems (MEMS)[1J. A MEMS approach with avaiable reflectivity mirror using microoptics isdescribed in [2J. We take the same approach in orderto take advantage of the relatively large diameter ofthe collimated beam that facilitates the MEMS chipfabrication. In our approach the attenuation is inducedby efficient polymedc thermal micmactuators that tilt amirror and that are fabricated by a low-coststencilprinting techrique.substrat gnssfiber dual fiber GIN S insulatbn6AM G_ ^N groovemirror gold_ - ~~~~glassout > X 101Off po"nr,125pmon polymerthwmally expandedFig. 1. VOA prnciple of operation with mirror titedbythermally expanding polymerbumpsVOA operationThe operation of the component is depicted in fig. 1,where its cross-section is shown with the ray paths inthe activated and inactivated case. It is based oncreating an offset from the minimum coupling losspoint of the mode fild of the irput fiber with respectto the output fiber. The offset is realized by firstcollimating the modefield of the input fiber using a %pitch GRIN rod lens. The beam is reflected and tiltedby the tilted mirror and refocused by the lens onto theoutput fiber. The lens thus transforms the beamtilt intoan offset of the modefield in proportion to its focallength. During assembly a fibertube is aligned in sucha way that minimum insertion loss is obtained with anuntilted mirror. The mirror tilting is realized bymounting it onto two silicone bumps en thertmallyexpanding one of these bumps by activating a thinfilm heater onto which the bump is deposited, Thecombination of high (linear) thermal expansion(a=270 ppm/°C) with high thermal stability (.45to+20O1C) and good adhesive properties of thesilicone bumps is ideal for this application.The attenuation, Aft (in dB's). in the Gaussian fibermodefield approximation, can be expressed as:Aft = 4.3431 2.f.c.cttTwhere t is the bumpthickness, w is the bumpspacing,) is the fiberspotsize radius, f Is the lens focallengthand c is an amplification factor (1 cc<3) due toconstrained in-plane expansion of the silicone bump.Because the temperature differenoe, AT between thebumps is proportional with the power dissipated in theheater, the attenuation will depend quadratic on thepower dissipation. It can be calculated that for 20 dBattenuation, a temperature difference of75 degrees isrequired in our VOA with t=125jum, w=2mm, f=3mmand w=5.25 Itm @ 1550 nm (Corring SMF 28 fiber).VOA fabricationThe substrate with photolithographic defined NiCrheaters for 350 chips (5x5mm) is a 10OxlOOmmborosilicate wafer. Square holes (2x2mm) to pass the6lghtbeam and thermal insulation grooves next andunder the heaters are made by dicing the front andbackside. Through that the heaters le on airblidges(width and thickness: 500 pn). This will reduce theFibers and waveguide components P1.27thermal crosstalk (power dissipation) and thermalmass (response time).The silicone bumps are stencilpirited onto theheaters and a thin [low thermal crssk). borosilicatesubstrate(100pm) with Au mirrors is adhered to thesebumps. After thermal curing, the individual chips arediced out of the wafer assembly and GRIN rod lenses(NSG SLW3) are adhered to their backsides of thechips. Dual fiber tubes are aligned and attached tothe back of the rod lenses. The chip (length with lensis 8 mm, width is 5 mm) fts in a TO-5.type package.ResultsThe insertion loss of the VOAs @ 1550 nm istypically< 0.5 dB. Fig. 2 shows the expected quadraticdependence of the VOA attenuation on dissipation.Less than 40 mW is required for 20 dB attenuation.The dynamic range is over 50 dB.can be reduced further to 4 ms (200 me withoutapphcabon of an overshoot) by optimising thedesign. Fig. 4 shows the wavelength dependence ofthe VOA attenuation.0-___In -840 --1 6 - _ _ .~40.45- -40 -14D 0 110 160 10 1670Ww "4011[rn60*0II:U.0 20 40 60dissipation [mWJ80 100Fig2. VOA attenuation vs. heatsipationFig. 3 Shows the VOA time response after applicationof a voltage to a heater. The voltage has an Iritialovershoot to reduce the response time to 40 ms forabout 20 dB atternation. Calculations show that this°1 1 T0 _ _ _ 14040~~~~~~~-- _ _ _ _ - - - l00'0~~~~~~~.- ~ 2Fi. V 102vO 0.46 0e1 an 2IA J .8 efig3. VOA vohtsgeo/urrent and aftenueatin vs. hmeFig4. VOA attenuation vs. wavelengthThe tiHt at higher attenuations can be fully attributed tothe fiber spotsizeradius dependence on wavelength. Itis < 0.001 dBlnm per dB attenuation. The PDL asmeasured is <0.01 dB per dB attenuation. Theinsertion loss in the off-state is stable within 0.25 dBfor ambient temperature between -20 and 120 "3C.ConclusionsWe dewribe a MEMS VOA based polyneric thermalmicroactuators using microoptics. This approachyields excellent devices: < 0.5 dB insertion loss, > 50dB dynamic range, < 40 mW power consumption and40 me response time for 20 dB attenuation with lowPDL and with low sensitiity for wavelength andambient temperature. The fabriation process issimple with high yield and based on low-costtechniques.AcknowledgementThis work has been done for JDS UniphaseCorportifon. We thank Gary Duck of JDS Uniphasefor fruitful discussions and permission to publish thispaperReferencesI B.Barber et al, IEEE Photon Technol. Left., Vol.10,(1998), pp. 1262-12642 J.E. Ford et al, J. Ughtwave Technol., Vol.16(1998), p.p.1663-1670

MEMS VOA with polymeric thermal microactuators

Ughtwave Technol.,

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MEMS VOA with polymeric thermal microactuators

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