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Power Monitor for Optical Fibers

IP.com Disclosure Number: IPCOM000038734D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Fan, B: AUTHOR

Abstract

This article describes a method to monitor the power transmitted through an optical fiber. The power in an optical fiber can be monitored by measuring scattered light from the fiber. The advantage is that no sampling with a beam splitter is required. In addition, power can be monitored along a fiber without breaking it. Light scatterings due to material inhomogeneities and diameter variations are extremely small for low-loss optical fibers. But minute light scatterings can be obtained by slightly bending a fiber. Scatterings increase with increasing curvature. Microbendings, which also result in light scatterings, can be introduced by gently pressuring against fiber. Dielectric discontinuity at the fiber end, even with AR-coated, also causes light scatterings.

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Power Monitor for Optical Fibers

This article describes a method to monitor the power transmitted through an optical fiber. The power in an optical fiber can be monitored by measuring scattered light from the fiber. The advantage is that no sampling with a beam splitter is required. In addition, power can be monitored along a fiber without breaking it. Light scatterings due to material inhomogeneities and diameter variations are extremely small for low-loss optical fibers. But minute light scatterings can be obtained by slightly bending a fiber. Scatterings increase with increasing curvature. Microbendings, which also result in light scatterings, can be introduced by gently pressuring against fiber. Dielectric discontinuity at the fiber end, even with AR-coated, also causes light scatterings. These scatterings are proportional to the power transmitted in the fiber. A prototype monitor has been demonstrated in an arrangement shown in Fig. 1. The He-Ne laser beam with nominal 2 mW is coupled into an optical fiber with a microscope objective. The laser power in the fiber is adjusted by a variable attenuator which is placed between the laser and the coupling lens. The fiber has an NA of 0.3 and a core diameter of 100 microns. The fiber is about 5 meters long and is coiled in several loops in order to reduce light transmission through fiber cladding. The mode pattern through the multimode fiber is observed independent of the coupling optics. The laser beam emerging fr...