Differential multilevel modulated optical signal receiver apparatus

A differential multilevel optical signal receiver apparatus, comprising:

• a first optical device for splitting an input differential multilevel optical signal and for generating a first optical signal and a second optical signal;
• a second optical device for splitting the first optical signal and for generating a third optical signal and a fourth optical signal;
• a third optical device for splitting the second optical signal and for generating a fifth optical signal and a sixth optical signal;
• a fourth optical device for coupling the third optical signal and the fifth optical signal;
• a fifth optical device for coupling the fourth optical signal and the sixth optical signal;
• a π/4 phase shifter element for shifting the phase of the second optical signal by π/4;
• 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 1-symbol delay element comprising a part of an optical path configured between the first optical device and the third optical device, a part of an optical path configured between the third optical device and the fourth optical device, and a part of an optical path configured between the third optical device and the fifth optical device;
• a π/2 phase shifter element for shifting the phase of the fourth optical signal by π/2;
• 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 fourth optical device and the fifth optical device into electrical signals, wherein
• the 1-symbol delay element makes the propagation time of an optical path from the first optical device to the fourth optical device via the third optical device 1-symbol time period longer than the propagation time of an optical path from the first optical device to the fourth optical device via the second optical device,
• the 1-symbol delay element makes the propagation time of an optical path from the first optical device to the fifth optical device via the third optical devive 1-symbol time period longer than the propagation time of an optical path from the first optical device to the fifth optical device via the second optical device.

A differential multilevel optical signal receiver apparatus, comprising:

• a first optical device for splitting an input differential multilevel optical signal and for generating a first optical signal and a second optical signal;
• a second optical device for splitting the first optical signal and for generating a third optical signal and a fourth optical signal;
• a third optical device for splitting the second optical signal and for generating a fifth optical signal and a sixth optical signal;
• a fourth optical device for coupling the third optical signal and the fifth optical signal;
• a fifth optical device for coupling the fourth optical signal and the sixth optical signal;
• a π/4 phase shifter element for shifting the phase of the second optical signal by π/4;
• 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 1-symbol delay element for delaying each of the fifth and the sixth optical signals by 1-symbol time period;
• a π/2 phase shifter element for shifting the phase of the fourth optical signal by π/2;
• 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 fourth optical device and the fifth optical device into an electrical signals.