Browsing by Author "Wang, G. Z."
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- Effect Of External Index Of Refraction on Multimode Fiber CouplersWang, G. Z.; Murphy, Kent A.; Claus, Richard O. (Optical Society of America, 1995)The dependence of the performance of fused-taper multimode fiber couplers on the refractive index of the material surrounding the taper region has been investigated both theoretically and experimentally. It has been identified that for a 2 x 2 multimode fiber coupler there is a range of output-power-coupling ratios for which the effect of the external refractive index is negligible. When the coupler is tapered beyond this region, the performance becomes dependent on the external index of refraction and lossy. To analyze the multimode coupler-loss mechanism, we develop a two-dimensional ray-optics model that incorporates trapped cladding-mode loss and core-mode loss through frustrated total internal reflection. Computer-simulation results support the experimental observations. Related issues such as coupler fabrication and packaging are also discussed. (C) 1995 Optical Society of America
- Fiberoptic Temperature Sensors Based on Differential Spectral Transmittance Reflectivity And Multiplexed Sensing SystemsWang, A.; Wang, G. Z.; Murphy, Kent A.; Claus, Richard O. (Optical Society of America, 1995-07-01)A concept for optical temperature sensing based on the differential spectral reflectivity/transmittance from a multilayer dielectric edge filter is described and demonstrated. Two wavelengths, lambda(1) and lambda(2), from the spectrum of a broadband light source are selected so that they are located on the sloped and flat regions of the reflection or transmission spectrum of the filter, respectively. As temperature variations shift the reflection or transmission spectrum of the filter, they change the output power of the light at lambda(1), but the output power of the light at lambda(2) is insensitive to the shift and therefore to the temperature variation. The temperature information can be extracted from the ratio of the light powers at lambda(1) to the light at lambda(2). This ratio is immune to changes in the output power of the light source, fiber losses induced by microbending, and hence modal-power distribution fluctuations. The best resolution of 0.2 degrees C has been obtained over a range of 30-120 degrees C. Based on such a basic temperature-sensing concept, a wavelength-division-multiplexed, temperature-sensing system is constructed by cascading three sensing-edge filters that have different cutoff wavelengths along a multimode fiber. The signals from the three sensors are resolved by detecting the correspondent outputs at different wavelengths.