Patent ID: 7277647

Claim:
An apparatus for encoding a sequence of optical pulses in accordance with a sequence of input data, comprising: means for generating a series of optical pulses, and means for modulating the phase of said optical pulses such that a digital “1” in the input data is represented by a π/2 phase shift of a current optical pulse with respect to the previous pulse, and a digital “0” in the input data is represented by a-π/2 phase shift of a current optical pulse with respect to the previous pulse; said modulating means including: a continuous wave (CW) laser source for generating optical pulses at a desired clock rate; an optical pulse generator for generating, responsive to said optical pulses at said desired clock rate, a 90-degree-alternate-phase (90°-AP) output in which successive pulses have a 90 degree phase difference, means for generating a differential MSK encoded signal in accordance with the input data such that the differential MSK encoded signal represents the result of exclusive OR'ing (a) a first data signal representing said input data and (b) a clock signal having a rate that is one half of the rate of said desired clock rate, and a chirp-free DPSK data modulator for encoding the phase of said 90-degree-alternate-phase (90°-AP) output in accordance with said differential MSK encoded signal.