The major objective of this Mater thesis is to assess rotationally invariant codes known from the literature with respect to their applicability to the problem of cycle-slips in coherent fiber-optic communication systems. A $\pi/2$ rotationally invariant trellis coded modulation (TCM) scheme based on a four-dimensional signal set consisting of two 16QAM constellations is designed such that a cycle-slip-robust polarization-multiplexed coherent optical communication can be achieved. The designed scheme outperforms its conventional counterparts employing differential modulation schemes with traditional channel coding methods in terms of bit error rate and bandwidth efficiency though demanding higher decoding complexity.