Publication No: 1176

Beat length measurement in directional couplers by thermo-optic modulation

H.Gnewuch
University of Cambridge, Institute of Biotechnology, Cambridge CB8 1QT, UK

J.E.Román, M.Hempstead, J.S.Wilkinson
Optoelectronics Research Centre, University of Southampton, UK

R.Ulrich
Technische Universitit Hamburg-Harburg, Optik und Meptechnik, 21 7071 Hamburg, Germany

Abstract

In integrated optical directional couplers formed by two parallel waveguides, we measure the difference Δβ = β_even - β_odd between the propagation constants of the 'supermodes'. They are coupled locally by heating a fine spot on one of the guides. When the spot is scanned along the coupler the output power from one of the guides is found to vary periodically. The period of variation is the modal beat length λ = 2π/Δβ. We demonstrate this technique with directional couplers fabricated by K⁺-exchange in glass. Beat lengths in the range of 0.6 ... 2.2 mm are measured with an accuracy of ±0.3%.

Optics Letters (1996) Vol.21(15) pp.1189-1191

doi: 10.1364/OL.21.001189

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