We present the design and fabrication of micro-cavity semiconductor devices for enhanced Two-Photon-Absorption response, and demonstrate the use of these devices for implementing sensitive autocorrelation measurements on pico-second optical pulses

Barry, Liam P.

Bradley, Ann Louise

Donegan, John Francis

Folliot, H.

Hill, G.

Krug, T.

Lynch, Michael

Roberts, J.S.

English

DCU Online Research Access Service

Optoelectronics and semiconductor integrated Devices P2.19Design and fabrication of highly efficient nonlinear optical devices forimplementing high-speed optical processingL.P.Barry(l), T.Krug(2), H.Folliot(2), M.Lynch(2), A.L.Bradley(2), J.F.Donegan(2), J.S.Roberts(3), and G.lHill (3)(1) Department of Electronic Engineerng, Dublin City University, Dublin 9, Ireland (liam.barry@dcu.ie)(2) Physics Department, Trinity College, Dublin 2, Ireland(3) Department of Electronic and Electrical Engineering, University of Sheffield , Mappin Street, Sheffield, SI3JD, EnglandAbstract We present the design and fabrication of micro-cavity semiconductor devices for -enhanced Two-Photon-Absorption response, and demonstrate the use of these devices for itmplementing sensitiveautocorrelation measurements on pico-second optical ptlses.IntroductionTwo Photon Absorption (TPA) in semiconductorshas recently been shown to be a serious candidatefor optical autocorrelation of short pulses, and all-optical switching and sampling of high speed opticaldata signals in optical time division multiplexed(OTDM) systems. Experiments using TPA for theseapplications have been performed at many differentwavelengths, and using different types ofsemiconductor devices [1-4). However, as TPA isessentially a very inefficient non-linear process, itusually requires high intensity lasers or very longdetectors, which could make the TPA non-linearityunsuitable for use in practical autocorrelators, andoptical switches and sampling devices for realtelecommunication systems. One possible way toovercome the inefficiency of the TPA process is touse a Fabry-Prot micro-cavity to greatly enhancethe optical intensity, and thus exalt the non-linearproperties of the embedded nmaterial.In this paper we present the design and fabrcationof a TPA detector that has been specially designedfor TPA with an input wavelength around 880 nm.The semiconductor device that we have constructedis based on a microcavity structure, which greatlyenhances the interaction length in the device. Wealso demonstrate the use of this non-linear detectorfor carrying out autocorrelation measurements onpicosecond optical pulses.TPA Device FabricationThe device that we have specially fabricated forTPA is a GaAIAs PIN microcavity photodetectorgrown on a GaAs susbrate. It comprises a 0.27pmGa, ;A103As active region embedded between twoGa0 5Al0 5AsIAIAs Bragg mirrors. The front p doped(C-108cm3) mirror consists of 15.5 pairs while theback n (Si-10'8cm3) mirror contains 35.5 pairsdesigned for reflectivity at 880nm. The device wasdesigned to show significant TPA response (energybandgap of semiconductor material 1.3 timesgreater than photon enery at 880 nm). The devicestudied was a 400pm diameter vertical structure.SiN layer was deposited to passivate the sides ofthe mesa and thus limit the leakage current.Experimental resultsWe have used a tuneable Tsunami Ti:Sa laserdelivering 1.6ps pulses at 82MHz repetition rate toinitially characterise the device by employingstandard Lock-in techniques to measure thephotocurrent. Alignment was achieved by forwardbiasing the photodiode which then acts as an LEDemitting at 700nm. Firstly we performed aphotocurrent measuremient as a function of theincident power (Fig.1) close to the cavity resonance.The cavity resonance is around 888 nm, and themeasured cavity linewidth is 1.12nm, consistent withsimulations. As expected, a square dependence ofthe pthotocurrent otn the incident intenisity Is clealyobserved, evidencing the Two-Photon absorptionprocess. We also show the simulation results,where we took a TPA coefficient of [1=0.01 3cm/MWand a linear absorption of 0. 1 cm" which is observedat low Intensities.- 1 4c03 10OQU)> 10.lu ~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~~.1Oz iro--IO o4 10' 10'o 101 IC?Average Power (W)Fig. I Measured (triangles) and simulated (straightfine) average photocurrent versus average powerA Mcsurerents- simulationsK4_88G,Fnr.':nAAuthorized licensed use limited to: DUBLIN CITY UNIVERSITY. Downloaded on January 19, 2009 at 07:48 from IEEE Xplore.  Restrictions apply.Optoelectronics and semiconductor integrated Devices P2.19Then, for a given incident average intensity of 10rnW, we performed a wavelength dependenicephotocurrent measurement around the resonance,a-s shown on Fig. 2. An experimental enhancementclose of 12000 is reached, which is close to thesimulation results that take the spectral dispersionof the pulses into account.10U rmasurmeltnso -¢siniAaUoo21 0'0W)M)8w 8W 890 89 9w(nf(nm)Fig, 2 Photocurrent vs. wavelength across thecavity resonance.We then examined the use of the microcavity TPAdetector for carryinlg out autocorrelationme,asurements on the picosecond optical pulsesfrom) the Ti St laser. We repla3ced the BBO crystal ina standard autocorrelator witti ttie TPA detector,and used lock-in techniques to measure theautocorrelation trace of the optical pulses. Fig. 3dis.plays the measured pulse inr addifion to the resultwhen the non-linear crystal was used at the outputof 4he, autocorelator's interferometer.1.1 .|,..._X3 BB0 1 2C6In105D m(nm)Fi. 2 Potocurrentio? si. avsng acrosthefrea*}/e) a cavietyAmiresnacavt e. ie#Whe thencexmiethe useatofthemyaricrocavity TPAmeasurements onThe pcosty}fieond eoptialtulesthautocorrlationetace ofthe optias use.Fgdheisplaysothemeasurdtplsinadiontthedyai repnesultwhnthe non-inrcrystaltwaics usednato thesoupuofmeasureetocorrelao cainterlferometer. gte hexpected for sech2 pulse shape), compared with2.89ps for the TPA device. This broadening of theautocorrelation measurement due to the cavitylifetime has been confirmed through simulations,and is clearly a function of the reflectivity of themicro-cavity reflectivity, In order to determine thesensitivity of autocorrelation measurements carredout using our TPA detector we attenuated the powerin the optical pulses incident otn the TPA detector.The minimum average power in the pulse train thatwe were able to autocorrelate was 10 pW, whichcorresponds to a peak power of 77 mW, andi asensitivity of 0.77 mW2. It should be noted that theautocorrelation arrangement using the TPA detectorproved to be more sensitive that the usual set-upbased on Second Harmonic Generation in anonlinear crystal.ConclusionsIn conclusion we have shown that by using asemiconductor micro-cavity structure, we are able tofabricate a device in which significant TPAenhancement can be achieved. This enhancementin the TPA efficiency may be extremely important forusing this specific non-linearity for constructing highspeed optical processing devices for use in futurebroadband photonic communication systems. Ourinitial results have shown the use of our TPA micro-cavity structure for autocorrelation measurementson pico-second optical pulses at 880 nm, and wehave also discussed the impact of the photonlifetime of the cavity structure on the results from theTPA autocorrelation. In addition, it should be notedthat the cavity structure can be optimised forwhatever application and wavelength the device isbeing designed for, thus allowing us to design high-speed and highly efficient non-linear optical devicesfor application specific functions. We wish to thankEnterprise Ireland for supporting this project undergrant No. S30/00245,References1, L.P. Barry et al., 'Autocorrelation and ultrafastoptical thresholding at 1.5mm using a commercialInGaAsP 1.3mm laser diode', Electron. Lett,, 34(1998), pp. 358-360.2. Z. Zheng et al., 'Ultrafast optical thresholdingbased on two-photon absorption GaAs waveguidephotodetectors', IEEE Photonics Technol. Lett., 9(1997), pp. 493-495.3. B.C. Thomsen et al., 'Ultra-sensitive all-opticalsampling at 1.5Sim using waveguide two-photonabsorption', Electron. Lett., I 35 (1999), pp. 1483-1484.4, C. Xu et al., 'Ultra-sensitive autocorrelaton of 1.5lmlight with single photon counting avalanchephotodiode', Electron. Lett., 38 (2002), pp. 86-88measured autocorrelation pulse width. Using a1.6ps pulse, an autocorrelation pulse width of2.39ps was recorded for the BBO crystal (asAuthorized licensed use limited to: DUBLIN CITY UNIVERSITY. Downloaded on January 19, 2009 at 07:48 from IEEE Xplore.  Restrictions apply.

39ps was recorded for the BBO crystal (as Authorized licensed use limited to:

6ps pulse, an autocorrelation pulse width of

Autocorrelation and ultrafast optical thresholding at 1.5mm using a commercial InGaAsP 1.3mm laser diode',

Ultra-sensitive all-optical sampling at 1.5Sim using waveguide two-photon absorption',

Ultra-sensitive autocorrelaton of 1.5 lmlight with single photon counting avalanche photodiode',

Ultrafast optical thresholding based on two-photon absorption GaAs waveguide photodetectors',

Design and fabrication of highly efficient non-linear optical devices for implementing high-speed optical processing

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Design and fabrication of highly efficient non-linear optical devices for implementing high-speed optical processing

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