Optical filter and amplifier, independent of polarisation

摘要

The incoming and outgoing optical fibres (10, 11) are linked to a respective polarisation separator (12) and combiner (18) which are dividers such as a double refractive crystal. The optical filter (15) is a transparent strip on which a multiple dielectric layer is deposited or a Fabry-Perot plate; alternatively it is double refractive crystal or a diffraction grating. The rotators of the polarisation (13-17) lie before the filter on one path and after the filter on the other. They consist of an element rotating the polarisation through 45 deg followed by a Faraday rotator, turning the polarisation through another 45 deg . The filter may be used at the output of a pumped optical amplifier.