Study of Wavelength-Dependent Bend Loss in Step-Index Multimode Fiber-Optic Microbend Displacement Sensor

Study of Wavelength-Dependent Bend Loss in Step-Index Multimode Fiber-Optic Microbend Displacement Sensor

Sami D. Alaruri (Independent Scholar, Mill Creek, USA)
DOI: 10.4018/IJMTIE.2017010102

Abstract

In this article, the wavelength dependence of bend loss in a step-index multimode optical fiber (100 µm core diameter; fused silica) was investigated for fiber bend radii ranging between 2.0 and 4.5 mm using six excitation wavelengths, namely, 337.1, 470, 590, 632.8, 750 and 810 nm. The results obtained from fitting the bend loss measurements to Kao's model and utilizing MATLAB indicate that bend loss is wavelength dependent and transmission loss in multimode optical fibers increases with the decrease in the fiber bend radius. Furthermore, the response of a microbend fiber optic displacement sensor was characterized at 337.1, 470, 632.8, 750 and 810 nm. Measurements obtained from the microbend sensor indicate that the sensor output power is linear with the applied displacement and the sensor output is wavelength dependent.
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1. Introduction

Loss introduced by bends in optical fibers has been recognized as a factor which contributes to the attenuation of the optical signal transmitted along an optical fiber (Marcuse, 1976; Berthold, 1995; Lagakos, Cole, & Bucaro 1987; Arya, Murphy, Wang, Claus 1995; Al-Aruri, 1991; Boechat, Hall & Jones, 1991; Donlagic, 2009; Schermer & Cole, 2007). Decreasing the optical fiber bend radius increases the transmitted signal loss due to the transfer of power from the guided modes to the radiation modes supported by the core of the fiber. Considerable theoretical and experimental research has been conducted on the subject of wavelength dependence of bend loss in single-mode optical fibers (Marcuse, 1976; Berthold, 1995; Lagakos et al., 1987; Arya et al., 1995). However, due to the complex nature of bend loss in multimode fibers there are few publications in this area (Schermer et al., 2007; Kao, 1982; Snyder, White & Mitchell, 1975). The two mathematical models proposed by Kao (1982) and Snyder (1975) are two examples of theoretical models dealing with the subject matter of bend loss in multimode fibers.

The primary goal of this paper is to examine the wavelength dependence of bend loss in multimode fibers at low power levels (< 10 mW) and to compare experimental measurements to the values predicted by Kao’s model. Here, it is worth noting that Kao’s model was selected for modeling the bend loss in multimode optical fibers as a function of wavelength because of its simplicity.

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