Perturbations on Effective Index of Refraction from Prism Coupling

摘要

We investigate the accuracy and precision of effective index of refractionmeasurements using prism coupling. The coupling gap's geometry is critical to predicting the accuracy and resolution of measurements. We provide experimental evidence that there are advantages to using high coupling pressures that yield long coupling lengths. Furthermore, effective index perturbations vary with mode number in some cases. We present and evaluate an experimental technique aimed at reducing the effects of perturbation and find that it may not be applicable to all situations. We extend a previous model of prism coupling to include a finite coupling length. This allows us to explain some of our experimental observations of m-line characteristics. We find disagreements between previous models when predicting effective index perturbations. Also, we introduce an alternative model of prism coupling based upon a local normal-mode expansion and present its preliminary numerical results. Finally, our results indicate that using prism coupling to measure effective index beyond the fourth decimal place will require additional experimental techniques and theoretical models.