New optical hybrid device for Raman amplifiers

This article describes a new hybrid fiber-optic component invented by the authors, iPBC TM /iPBS$_TM), which has the functionality of a Polarization Beam Combiner/splitter (PBC/PBS) with isolation in the backward optical path. 0.3dB combining loss and 30dB isolation are demonstrated in the forward and backward optical paths respectively. PBCs are widely used in Raman amplifiers. They provide a simple way to combine two optical pumping sources into a single beam to increase the optical pumping power and provide equal polarizations in two orthogonal directions. Inside pump lasers, it is difficult to use a free space isolator to get rid of back reflections since most of the Raman pump lasers use Fiber Bragg Gratings (FBGs) to stabilize pumping wavelengths. One way to solve this problem is to use an iPBC TM to provide high combining efficiency in the forward direction and high optical isolation in the backward direction. This new hybrid device has been designed and fabricated in our laboratory and has demonstrated 0.3dB combining loss and 30dB peak isolation. It enables a new generation of Raman amplifiers with higher performance, smaller footprint and lower cost.