Abstract: A method and apparatus is provided for controlling the bias point of a Mach-Zehnder modulator. The method begins by applying a dither signal to a DC bias that is applied to a Mach-Zehnder modulator. A component of an optical output signal provided by the Mach-Zehnder modulator that is synchronous with the dither signal is detected. The dither signal is adjusted to maintain the detected component of the optical output signal at a substantially constant value.

Abstract: A method an apparatus for symmetric line coding is provided where a binary input signal d is received; a value for each of a pair of binary bits p and q are dynamically defined in response to the input stream; and a pair of output bitstreams v1 and v2 are dynamically generated in accordance with the following: if d=1, then v1=p and v2=p, and if d=0, then v1=(1?q) and v2=q. In illustrative embodiments of the invention, the generation may be performed by symmetric-line coding machines, including: a bitstream symmetric line coding machine, a regular bitstream symmetric line coding machine, a complementary regular bitstream symmetric line coding machine, a binary complementary regular symmetric line coding machine, a bitstream parallel symmetric line coding machine, a regular bitstream parallel symmetric line coding machine, a complementary regular bitstream parallel symmetric line coding machine, and a binary complementary regular parallel symmetric line coding machine.