ICSE2004 Proc. 2004, Kuala Lumpur, Malaysia

Glass Based 16 Channels Arrayed Waveguide Grating By IonExchange Technique

Heng Cherng Woei and Sahbudin Shaari, Member, IEEE, Member, SPIEPhotonics Technology Laboratory,

Institute of MicroEngineering and Nanoelectronics,Universiti Kebangsaan Malaysia,

43600 UKM Bangi, Selangor, MALAYSIA.Email: hengcw@vlsi.eng.ukm.my

Abstract - Arrayed waveguide grating (AWG)with 16 channels, 100 GHz channel spacingwas fabricated on silica glass substrate byusing ion exchange technique. The minimuminsertion loss is 26.18 dB with channelcrosstalk below -4.13 dB and the channeluniformity is <2.55 dB. The AWG canfunction as demultiplexing butperformance is low due to the existenceerror of ion exchange technique.

I. INTRODUCTION

Arrayed waveguide grating (AWG) multiplexeris a key element for wavelength divisionmultiplexing (WDM) systems in opticaltelecommunication. WDM is an importanttechnology which offers another opticaltechnique to increase the bandwidth.

Many materials are being used to fabricateAWG device such as silica on silicon [1],polymer [2], glass [3], silicon on insulator [4]and InP [5]. Types of waveguide like ribwaveguide, buried-strip, rib waveguide and striploaded waveguide have been used. All thesetypes of waveguide usually involve depositionprocess like flame hydrolysis deposition (FHD)and involve etching process such as reactive ionetching (RIE). The first AWG with ionexchanged waveguides in glass was developedby Buchold and Voges [3].

In this paper, we present work on AWGdevice fabricated by using glass material withone step ion exchange process to achieve lowcost optical device. This process will produce agraded-index channel waveguide. The AWGdevice consists of 16 channels input/output with100 GHz channel spacing.

II. DESIGN

Basically, the AWG consists of N input/outputwaveguides connected by slab waveguide to thearrayed grating, which is composed of Mwaveguides with constant path difference AL.The standard equations ofAWG have been usedto determine the design parameters [6].

Firstly, the profile of graded-indexwaveguide was determined in the design [7]. Therefractive index of this glass at 1.55 Ftm is 1.505and the refractive index change at the surface ofwaveguide is An=0.04 where the effective depthof this waveguide is 4 ptm. We use this indexprofile to design AWG with 3 gm width ofwaveguide. The AWG consists of 16x16channels input/output with 100 GHz channelspacing in 25.4x13.5 mm wafer size. There are64 channels waveguide at arrayed grating withpath difference of AL=76.63 pnm. Fig. 1 showsthe layout of 16x16 channels AWG with 100GHz channel spacing.

- 64 channelswaveguide at

i arrayed grating

Input port Output port

Figure I Layout of 16x 16 channels AWG withOOGHz channel spacing at center wavelength 1.55ptm.

III. FABRICATION

The waveguides of AWG are fabricated byion-exchange technique on Glass Coming 0215

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ICSE2004 Proc. 2004, Kuala Lumpur, Malaysia

substrate. A flow chart of AWG waveguidesfabrication process is shown in Fig 2.

First, a clean glass is deposited withaluminium layer at 300 nm thickness by usingevaporation technique. Next, the AWGwaveguides pattern is transferred byphotolithography. Then, the aluminium layer isetched by using wet etching to obtain the AWGwaveguides pattern from photolithographyprocess. The glass with aluminium layer that hasAWG waveguides pattern is immersed in anitrate mixtures melt at 300 'C. In the ionexchange process, the waveguides is created bypercentage mol of AgNO3 which contains in 50mole % KNO3 + 50 mole % NaNO3 [8]. After theion exchange process, the aluminium layer withAWG waveguides pattern is etched by using wetetching method. Finally the GRIN waveguides ofAWG are created in the silica glass substrate.

Glass

Photolithography &Aluminium etching

Ora an Al

Glass

Ion Exchange

Al

Glass

Aluminium Etching

Core

Cladding

Glass

Figure 2 Waveguide fabrication flow chart

IV. EXPERIMENTAL RESULTS

The refractive index profile of the planarwaveguide is determined with a prism couplingat 633 nm wavelength. The maximum refractiveindex difference at the surface is An=0.057 andthe effective depth of the waveguide is 3.27 gm.The measured coupling loss of fiber to straightwaveguide (25.4 mm length and 5 gm width) is9.07 dB at 1.55 gm wavelength. Thedemultiplexer performance is investigated usinga tunable laser source and an optical spectrumanalyzer. Fig 3 shows the testing photograph ofAWG using laser source with 633 ramwavelength. Fig. 4 illustrates the transmissionmaximum of 16 channels, 100 GHz AW6. Theminimum insertion loss is 26.18 dB, the crosstalkis below -4.13 dB and the channel uniformity is<2.55 dB.

Figure 3 Photograph ot guildir633 nm wavelength to AWG

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1-20 00

-25.00

--35.00

-40.00Gfn

1540 00 1545.00 155000 1555 00

Wavelength, ptmFigure 4 Demultiplexing properties of 16 channels,100 GHz AWG at around 1.55 pm.

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ICSE2004 Proc. 2004, Kuala Lumpur, Malaysia

The prism coupling test shows us that theprofile of waveguide is different from designparameter and affects the output wavelength.From the measurement, insertion loss ofAWG ishigh due to coupling loss of fiber to waveguide,bending loss, scattering loss and transition lossbetween slab and channel waveguide. We expectthe transition loss between slab and channelwaveguide is very high. The difference betweenthe depths of channel and slab waveguides isabout 3 ,um which leads to heavy light losses, asthe input light must pass these transitions 4times. This phenomenon occurred due to thediffusion rate in bigger opening windows such asslab waveguide is higher than smaller openingwindows like channel waveguide.

Usually, the cross talk becomes low whenthe insertion loss is high for optical device. Wealso found that some of the light is not couplingperfectly into the input waveguide. Some of thelight transmits straightly though the silica glassto output waveguide thus this light will becomenoise at output waveguide and affect the opticaldetector. Thus, the optical detector will give us alow cross talk.

[2] H.H. Yao, C. Zawadzki & N. Keil, "Athermal all-polymer arrayed waveguide grating multiplexer",OFC'2002, Paper TuC 1: 12-14, 2002.

[3] B. Buchold, and E. Voges, "Polarisation insensitivearrayed-waveguide grating multiplexers with ion-exchanged waveguides in glass", Electron. Lett.32(24): 2248-2250, 1996.

[4] P.D. Trinh, S. Yegnanarayanan, F. Coppinger & B.Jalali, "Silicon-on-insulator (SOI) phased-arraywavelenght multi/demultiplexers with extremely low-polarization sensitivity", IEEE Photon. Technol. Lett.,9(7): 940-942, 1997.

[5] H. Bissessur, P. Pagned-Rossiaux, R. Mestric, & B.Martin, "Extremely small polarization independentphased-array demultiplexers on InP", IEEE Photon.Technol. Leti., 8(4): 554-556, 1996.

[6] M.K. Smit, "PHASAR-based WDM- Devices:Principles, Design and Applications," IEEE J. Sel.Topics in Quantum Electron., vol. 2, pp. 216-250,1996.

[7] C.W. Heng and Sahbudin S., "Design of 16 channelgraded index silica glass arrayed waveguide grating forWDM", Malaysia IEEE National Symposium onMicroelctronics 2003., 195-197, 2003.

[8] C.W. Heng, C.S. Ooi, Kembangi M. M., A. AnnuarE. and Sahbudin S., "Effective diffusion coefficient ofsilver ion in glass waveguide fabricated by nitratemixtures ion-exchange technique", ISMOA 2003.

V. CONCLUSION

16 channels, 100 GHz AWG is fabricated onglass using simple one step ion exchangetechnique. The AWG can function asdemultiplexing but performance is low due to theexistence error of ion exchange technique. Wealso speculate that one sided graded index profileof the waveguides is major contributing factor,because in the design step index profile is used.However, we are still interested with the ionexchange technique because it can provide us alow cost method.

ACKNOWLEDGEMENT

The authors would like to thank theMalaysian Ministry of Science, Technology andthe Environment for sponsoring this work underNational Photonics Top Down Research Project020202T00 1.

REFERENCE

[I] A. Himeno, K. Kato, and T. Miya "Silica-based planarlightwave circuits", IEEE J. Sel. Topics in QuiantuntElectr-on., vol. 4, pp. 913-924, 1998.

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