Design of a Photonic Integrated Circuit (PIC)

for a BOTDR read-out unit.

R.F. Klein Breteler, M. Felicetti, J.J.G.M. van der Tol, G.D.J. Sasbrink, M.K. Smit

/ Department of electrical engineering – opto electronic devices

IntroductionIn the expanding field of fibre sensors Brillouin scattering is

a powerful effect for determining strain and temperature

distributions along fibres.

Circuit design

Brillouin scattering

COBRACOBRACOBRACOBRA

Chip layout

AcknowledgementsThis work is done within the European Europic project, and

has been supported by the Dutch Ministry of Economic

Affairs through the “Kenniswerkers” program BSGOC.

1550 nm

1550 nm

+ 11GHz

MMI

DET

DET

Delay

MMI MMIφ

MMI

DET

DET

<----------------switch1-------------- >

MMI MMIφ

MMI

MMICoherent receiver

-φ-φ

fibe

r

<----------------switch2-------------- >

BOTDRStrain and temperature affects the speed of sound and

thus the Brillouin spectrum.

Frequency tuningA switcheable digital delay line circuit is implemented into

the frequency locking circuit. This allows to tune the

frequency spacing between the two lasers and enables

homodyne detection of the full Brillouin spectrum.

∆f=1MHz/20με

∆f=1MHz/°C-Size: 6x3 mm

-Cost: €1000,- (existing instruments: >€50.000,-)

-Spatial resolution: 2m

-Strain resolution: 0.004%, temperature resolution: 2°C

-Sensor length: 50 km

We have designed a foudry-based Brillouin Optical Time

Domain Reflection (BOTDR) read-out unit with low-cost

potential.

Structures that can be monitored with fibre sensors.

Brillouin scattering is the reflection of light from a moving

grating, formed by acoustical phonons.

Spectrum of backscattered light from a fibre.

Backscattering in time provides spatial information.

- Dual laser circuit, allows homodyne detection

- Switch 1: laser selector

- Switch 2: injects pulse and enables coherent detection

- Laser locking circuit: stabilizes frequency spacing

Five elements of the digital delay line.