1 January 1988 Amplitude And Phase Characterisation Of Polished Directional Half-Couplers With Variable Refractive Index Overlays
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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.
M. C. Brierley, M. C. Brierley, C. A. Millar, C. A. Millar, } "Amplitude And Phase Characterisation Of Polished Directional Half-Couplers With Variable Refractive Index Overlays," Optical Engineering 27(1), 270145 (1 January 1988). https://doi.org/10.1117/12.7976640 . Submission:
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