Compact electro-optic polarization scramblers for optically amplified lightwave systems

Fast polarization scramblers have become important components in optically amplified transoceanic communication systems to eliminate anisotropic gain saturation (polarization hole burning) in the erbium-doped fiber amplifiers by depolarizing the launched optical carrier. This paper reviews the operation and implementation of compact electro-optic polarization scramblers on x-cut and z-cut lithium niobate. These integrated-optic devices employ low-loss single-mode waveguides and allow polarization modulation at variable frequencies ranging from a few 100 Hz to more than 10 GHz. We describe simple linear phase retarders that depolarize light in a fixed, well-maintained polarization state as well as cascaded multi-stage scramblers that are capable of depolarizing arbitrarily polarized light. These scramblers can be operated over a broad optical bandwidth of more than 40 nm with less than 5% residual degree of polarization and are further wavelength-tunable over more than 100 nm.