Patent ID: 7613403

Claim:
A differential multilevel optical signal receiver apparatus, comprising: a first optical splitter for splitting an input differential multilevel optical signal and for generating a first optical signal and a second optical signal; a second optical splitter for splitting the first optical signal and for generating a third optical signal and a fourth optical signal; a third optical splitter for splitting the second optical signal and for generating a fifth optical signal and a sixth optical signal; a 1-symbol delay element configured between the first optical splitter and the third optical splitter; a π/4 phase shifter element configured between the first optical splitter and the third optical splitter; first adjustment means, configured adjacent to the π/4 phase shifter element, for adjusting the amount of phase shift of the π/4 phase shifter element; a first optical coupler for coupling the third optical signal and the fifth optical signal; a second optical coupler for coupling the fourth optical signal and the sixth optical signal; a π/2 phase shifter element, configured between the second optical splitter and the first optical coupler, or between the second optical splitter and the second optical coupler; second adjustment means, configured adjacent to the π/2 phase shifter element, for adjusting the amount of phase shift of the π/2 phase shifter element; and a photodetector circuit for converting optical signals output from the first and second optical couplers into electrical signals.