Wavelength Division Multiplexed Optical Fibre System

Abstract

<p>The design, construction techniques and results of evaluation of two types of optical fibre multiplexing and demultiplexing devices are given.</p> <p>The first type of device is a three channel optical multiplexer/demultiplexer operating in the 750 to 900 nm band. This device allows the simultaneous transmission of 3 different wavelengths through the same optical fibre. It employs a diffraction grating, in the Littrow configuration, as the wavelength selective element. The device is compact and rugged due to the use of a gradient index lens to which the other assemblies are cemented. The wavelength channels have centre wavelengths of 790, 830 and 870 nm and are nominally 30 nm wide at the -1 dB points. The loss is 2.2 to 2.5 dB when used as a demultiplexer and 7 to 8 dB when used as a multiplexer. Crosstalk is less than -30 dB at the channel centres.</p> <p>The other device is a two channel multiplexer-demultiplexer which allows a bidirectional system to be constructed. This device has a short wavelength channel from 770 to 890 nm and a long wavelength channel from 1100 to 1400 nm. It employs an interference filter as the wavelength selective element. The filter is cemented between two gradient index lenses to form a compact rugged device. The loss is 1.5 dB for the 770 to 890 nm wavelength channel and 3.5 dB for the 1100 to 1400 nm wavelength channel.</p> <p>Combining the two and three channel devices results in a four channel bidirectional system for use in integrated distribution services.</p> <p>Suggestions for improvements in the design and construction of the devices are also given.</p>