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Optical Engineering

Amplitude And Phase Characterisation Of Polished Directional Half-Couplers With Variable Refractive Index Overlays
Author(s): M. C. Brierley; C. A. Millar
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Paper Abstract

We report a characterisation technique for both amplitude and phase variations of polished fibre half-couplers in the proximity of variable index bulk overlays. Experimental results are compared with simple theoretical models. In addition, simple derivative fibre-based devices are reported. Amplitude measurements were performed using a single fibre embedded in a block with a 25 cm radius groove, polished to within 1um of the core. A linear (in decibels) change in attenuation resulted for overlay indices greater than the effective mode index. An attenuation change of 40 dB was observed for a 0.0026 change in index. To observe phase changes, an interferometric approach was taken. Two fibres were embedded, one above the other, in a block identical to that above. The core of the top fibre only was exposed by polishing. Low loss 50:50 fused taper couplers were spliced to both sides of the block, forming a fibre Mach-Zehnder interferometer. For overlay indices less than the effective mode index, a phase change of rad was observed for an index change of 0.0045, with an interaction length of 700um.

Paper Details

Date Published: 1 January 1988
PDF: 5 pages
Opt. Eng. 27(1) 270145 doi: 10.1117/12.7976640
Published in: Optical Engineering Volume 27, Issue 1
Show Author Affiliations
M. C. Brierley, British Telecom Research Laboratories (England)
C. A. Millar, British Telecom Research Laboratories (England)


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