Modelling a Fiber Half-block with Multimode Overlay Waveguide

Abstract

We report a simple numerical analysis to model the performance of in-line fiber optic components which rely on selective coupling between a polished single-mode fiber half-block and a highly multimode overlay waveguide. Important device performance characteristics of these devices are describable in terms of throughput power as a function of various waveguide parameters. Our model is based on treating the fiber as an equivalent planar waveguide (EPG) and obtaining the normal modes of the resultant multilayer structure through a matrix formalism. Throughput power exiting the fiber is obtained by calculating the overlap between the EPG mode and the normal modes. The agreement between our model and the reported experimental results on inline fiber modulators is shown to be excellent. This model should, therefore, be very useful in estimating the performance of a host of such in-line fiber components.

High Sensitive Fiber Optic Temperature Sensor Based on a Side-polished Single-mode Fiber Coupled to a Tapered Multimode Overlay Waveguide

“…1 (a), in which a SPF having limited cladding on one side of the fiber core up to a desired extent is loaded on its top with an appropriate thermo-optic MMOW. In order to model this device, we have used a semi-numerical normal mode analysis [5,7], which involves approximating the SPF by an equivalent planar guide (EPG) [15] and the composite structure can then be treated as a planar multi-layered structure as shown in Fig. 1 (b).…”

“…Side-polished fibers (SPF) are the building blocks of many single-mode fiber components such as directional couplers, polarizers, modulators, switches and wavelength filters [1][2][3][4][5] due to the accessibility of a significant fraction of the evanescent field of the propagating mode close to the polished surface. The evanescent field coupling between a SPF and an appropriate multimode overlay waveguide (MMOW) has yielded an important platform to realize various fiber optic sensors such as refractive index, pH and temperature sensors [6][7][8][9][10][11][12].…”

“…Such a composite structure essentially functions as an asymmetric directional coupler with a band-stop characteristic attributable to the wavelengthdependent resonant coupling between the guided mode of the SPF and one or more modes of the MMOW. The throughput power of the SPF exhibits dip(s) at the phasematching (or resonant) wavelength(s) [5,6]. Since the refractive index (n0) of the film of the MMOW depends on temperature, any change in n0 would modify the mode spectrum of the MMOW and hence the throughput power spectrum of the device, which shifts the resonance wavelength.…”

Estimating Performance of Fiber Optic Modulators/Switches with Multimode Electrooptic Overlay/Interlay Waveguide

“…L, the interaction length appearing in Eq. (14), is taken to be equal to the coupling length L c ‫ס(‬ /( 1 − 2 )) between the two normal modes at a given wavelength.…”

“…The CMT approach, on the other hand, involved solutions of complex differential equations; however, to date this analysis has been applied to passive device structures only. In a recent paper [14], we have reported a normal mode analysis which is relatively simple, quite general, and rigorous to model all such SPFto-MMOW evanescent coupler devices. Our theory is based on replacing the SPF with an equivalent planar waveguide (EPG) [15], thus reducing the resulting composite device structure of study to a 1-D multilayer structure (MLS).…”