Polarization maintaining fiber lasers and amplifiers

Abstract

A number of variations are provided of a device that provides an amplified single polarization optical signal. Each of these relies on the use of a non-polarization maintaining gain medium through which the signal is directed, and a polarization shifter and reflector that direct the signal back through the same gain medium with a shifted polarization state. An input polarization beamsplitter directs the returning optical signal away to an output, based on its shifted polarization state. The embodiments of the invention include the use of double-clad fiber. Multiple stages may be used to provide specific amplification parameters. In one embodiment, both amplification stages reside in the same polarization shifting optical path. A polarization maintaining amplifier of this type may be used as part of a master oscillator-power amplifier, in which polarization maintaining fiber is used as part of the source laser. Wavelength selective components are also used in certain embodiments of the invention, to allow for wavelength selectivity, as well as a single polarization state, in amplifiers, lasers and amplified spontaneous emission (ASE). In one embodiment, an optical circulator is used to allow the amplified, shifted polarization state signals to be directed away from the input to a desired output port. A feedback loop may also be used to control the polarization state at the amplifier output. A polarization beamsplitter at the output directs light not having the desired polarization state to a photodetector, the output of which is used by a polarization controller at the input, such that the input polarization state is adjusted until the control signal from the photodetector is minimized.