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Spotlight on Optics

Spotlight on Optics


  • November 2010

Optics InfoBase > Spotlight on Optics > Resolving optical illumination distributions along an axially symmetric photodetecting fiber

Resolving optical illumination distributions along an axially symmetric photodetecting fiber

Published in Optics Express, Vol. 18 Issue 23, pp.24264-24275 (2010)
by Fabien Sorin, Guillaume Lestoquoy, Sylvain Danto, John D. Joannopoulos, and Yoel Fink

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Spotlight summary: The awareness of the limited resources of our planet has turned the efficiency of electronic and photonic devices into a major concern. Integration has become truly important to minimize material usage and to reduce the distance that signals need to propagate, with consequent attenuation and energy wastage. The use of the one-dimensional world of optical fibers to allow for the integration of photonic devices is in its infancy. The motivation to make photonic components in fibers is to exploit the best waveguide available, the low cost, and the obvious compatibility with fiber technology. Besides, the cross section of a fiber is typically in the micrometer scale, resulting in large surface-to-volume ratio and avoiding waste with thick substrates. Efficient integration will be possible when devices can be processed along the fiber length.

The authors of the current paper belong to the leading group in the integration of electronic and photonic devices into an optical fiber. The MIT group has shown that it is possible to draw optical fibers potentially in kilometer lengths, incorporating metals, semiconductors, and isolating materials. They have shown in previous work transistors, photodiodes, and other functional devices in fiber. In this research, the authors introduce a new degree of freedom to be exploited in fiber devices with electrodes, starting from an ~1-m-long fiber that behaves as a distributed (1-m long) photodetector. They create a position-dependent voltage bias along the fiber, exploiting the different resistivities of a semiconductor core, a thin film of semiconductor, and a conducting polycarbonate. Each fiber segment is thus subjected to a different potential in the open-circuit bias condition (one power supply) and when both fiber extremes are biased with different power supplies. The electrical response of the fiber to external perturbation—in this case illumination of the fiber from the side—allows determining where the perturbation occurs. The interesting aspect of this development is that one does not need to have an electrical contact for every fiber segment. In this paper, the authors demonstrate the detection of up to three illuminated points simultaneously. Through the original use of a nonuniform bias along the fiber, the authors are able to avoid time-resolving the reading signal to extract the spatial information desired. In contrast to (electrical) time-domain reflectometry, the current technique does not use high-speed electronics and is not affected by dispersion.

The principle of the position-dependent voltage bias to determine the location of the perturbation can be possibly extended to other applications. In piezoelectric fibers, as the ones demonstrated by the authors, one could determine the position of a mechanical perturbation in a distributed way. They introduce a new way to treat a fiber as composed of a sequence of short-length elements, without the need to address each one with its own contacts. This paper adds a powerful tool to help in integrating many short-length devices in a single optical fiber.

--Walter Margulis

Technical Division: Optoelectronics
ToC Category: Detectors
OCIS Codes: (040.5160) Detectors : Photodetectors
(160.2290) Materials : Fiber materials

Posted on November 15, 2010

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