UV trimming of arrayed waveguide gratings

Technische Universität Hamburg-Harburg

Frank KnappeTechnical University Hamburg-Harburg

Jörg GehlerAlcatel Corporate Research Center

now with Alcatel USA

December 2000

Technische Universität Hamburg-HarburgOutline

- Objective

- Influence of phase errors

- Mesurement of phase distributions

- Compensation of phase errors with UV trimming

- Results

- Conclusion/Prospect

Technische Universität Hamburg-HarburgObjective I

N = 25 … 250

Technische Universität Hamburg-HarburgObjective II

- Used for:multiplexer/demultiplexerchannel equalizerchannel switching

- important characteristics:crosstalkchromatic dispersionbirefringencePDLPMD

Technische Universität Hamburg-HarburgObjective III

-70

-60

-50

-40

-30

-20

-10

0

1542 1547 1552 1557 1562

Wavelength [nm]

Tra

nsm

issio

n[d

B] Crosstalk: 27dB

Technische Universität Hamburg-HarburgInfluence of phase errors I

- Full characterization of a device by the complex transfer function

- amplitude spectrum is given by the focussing slab regions

- more critical: phase spectrum

- fast fluctuations responsible for crosstalk

- slow fluctuations responsible for chromatic dispersion

H. Yamada et al "Measurement of Phase and Amplitude Error Distributionsin Arrayed-Waveguide Grating Multi/Demultiplexers Based on Dispersive Waveguide”,Journal of Lightwave Technol. , p.1309 (2000)18

Technische Universität Hamburg-HarburgInfluence of phase errors II

H. Yamada et al "Measurement of Phase and Amplitude Error Distributionsin Arrayed-Waveguide Grating Multi/Demultiplexers Based on Dispersive Waveguide”,Journal of Lightwave Technol. , p.1309 (2000)18

Technische Universität Hamburg-HarburgInfluence of phase errors III

H. Yamada et al "Measurement of Phase and Amplitude Error Distributionsin Arrayed-Waveguide Grating Multi/Demultiplexers Based on Dispersive Waveguide”,Journal of Lightwave Technol. , p.1309 (2000)18

Technische Universität Hamburg-HarburgCompensation techniques I

- thin flim heatersH. Yamada et al "10 GHz spaced arrayed-waveguide grating multiplexer with

phase-error-compensating thin-film heaters,” Electron. Lett. , p.360 (1995)

-

H. Yamada et al "Statically-phase-compensated 10 GHz-spaced arrayed-waveguidegrating multiplexer", Electron. Lett. , p.1580 (1996)

-

H. Yamada et al "Low-crosstalk arrayed-waveguide grating multi/demultiplexer withphase compensatingplate”, Electron. Lett. , p.1698 (1997)

31

32

33

�-Si strip loaded waveguides

phase compensating plates

permanent power consumptionadditional clean room processesincreased insertion losses

problems:

Technische Universität Hamburg-HarburgCompensation techniques II

- most AWG’s are based on silica on silicon

- refractive index can be increased (or decreased) by UV illumination

nL

- required phase changes: ~ 0.5 rad

- realistic values for n: 5e-4 … 1e-3

- required trimming length: ~ 250 µm

- = 2 /� � � � �

�

Technische Universität Hamburg-HarburgCompensation techniques III

- Why no H loading?

- AWG’s + attached fibers to big for loading chamber

- no H -induced shift of central wavelength

- no H outdiffusion to take into account

- Problem: such values for n also possible without H loading ?

2

2

2

2�

Technische Universität Hamburg-HarburgCompensation techniques IV

1,45

1,455

1,46

1,465

1,47

57 58 59 60 61 62 63 64 65

µm

refr

acti

ve

ind

ex

UV illuminated

non-UV illuminated

UV-illuminated

�n ~ 10-3

Technische Universität Hamburg-Harburg

Laser1,3 µm

AWG

WDM1.3/1.5

samplingtrigger

Voltmeter

waveformrecorder

cube-cornermirror

LED1,55 µm

polarisationcontroller

Measurement of phase distribution I

K. Takada et al "Measurement of phase error distribution in silica-based arrayed waveguidegrating multiplexers by using Fourier transform spectroscopy”, Electron. Lett. , p.1671 (1994)

J. Gehler and K. Lösch, "Dispersion measurement of AWG´s by Fourier-transform spectroscopy”,ECOC´99, Nice, P2.30, 1999

30

-3

-2

-1

0

1

2

3

0 2 4 6 8 10

Optical path change [mm]

Inte

ns

ity

[a.u

.]

Technische Universität Hamburg-HarburgMeasurement of phase distribution II

H. Yamada et al "Measurement of Phase and Amplitude Error Distributionsin Arrayed-Waveguide Grating Multi/Demultiplexers Based on Dispersive Waveguide”,Journal of Lightwave Technol. , p.1309 (2000)18

Technische Universität Hamburg-Harburg

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 10 20 30 40 50 60 70

Arrayed waveguide number

Ph

ase

[rad

]

phase as fabricated

desired phase distribution

Aim

Technische Universität Hamburg-HarburgExperimental Setup

Technische Universität Hamburg-HarburgExperimental procedure I

-2

-1,5

-1

-0,5

0

0,5

1

1,5

2

2,5

3

0 10 20 30 40 50 60

Arrayed waveguide number

Ph

as

e[r

ad

]

trimming step 1

trimming step 2

trimming step 3

Technische Universität Hamburg-HarburgExperimental procedure II

-0,5

-0,45

-0,4

-0,35

-0,3

-0,25

-0,2

-0,15

-0,1

-0,05

0

0 10 20 30 40 50 60

Arrayed waveguide number

Ph

as

e[r

ad

]

trimming step 1

trimming step 2

trimming step 3

Technische Universität Hamburg-Harburg

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 10 20 30 40 50 60

Arrayed waveguide number

Ph

ase

[rad

]

before UV-trimming

after UV-trimming

Results I

Technische Universität Hamburg-Harburg

-70

-60

-50

-40

-30

-20

-10

0

1542 1547 1552 1557 1562

Wavelength [nm]

Tra

nsm

issio

n[d

B]

before UV-trimming

after UV-trimming

Results II

Technische Universität Hamburg-HarburgConclusion

- UV trimming using frequency doubled Ar-laser

Power: 35 mW @ =244 nm, trimming speed: 0.5 µm/s

- UV-induced index change: n =10

- Reduction of crosstalk level by 8 dB to below -35 dB

- residual crosstalk mainly caused by amplitude errors in the waveguidegrating

- phase correction up to 5 rad without perceptible additional losses

- chromatic dispersion reduced from -0.7ps/nm to 0.1ps/nm

�

�-3

Technische Universität Hamburg-HarburgProspect

- faster trimming

- main requirement: On-line phase measurement

- computer controlled trimming

- UV-written AWG’s ?