Patent ID: 7945172

Claim:
A predistortion circuit for a laser sourced optical transmission system, for use with an input RF modulation signal carrying a plurality of subcarriers extending across a predetermined frequency band, comprising: an input port; a splitter having an input connected to the input port and having first, second and third outputs; a combiner having first, second and third inputs and an output; a first signal path connecting the first output of the splitter to the first input of the combiner; a second signal path connecting the second output of the splitter to the second input of the combiner, the second signal path providing precompensation for distortion in the laser source; and a third signal path connecting the third output of the splitter to the third input of the combiner, the third signal path including a second order distortion generator and a differentiator downstream of the second order distortion generator, wherein the differentiator has a magnitude response which differs by no more than 1 dB, throughout the predetermined frequency band, from a target magnitude response which increases at a rate of 6 dB/octave throughout the predetermined frequency band, wherein the differentiator has an insertion loss of no more than 4 dB throughout the predetermined frequency band, and wherein the differentiator has a phase response which differs by no more than 4°, throughout the predetermined frequency band, from a target fixed phase shift of 90°.