Optical signal demodulator

A demodulator for demodulating an optical signal on which a DQPSK (Differential Quadrature Phase Shift Keying) is applied, the demodulator comprising:

• a Michelson interferometer that includes:
• a splitting section for splitting the optical signal into a first split light and a second split light, and emitting the first split light and the second split light;
• a half-mirror which is disposed on an emission optical axis of the splitting section, the half-mirror for splitting the first split light into a third split light and a fourth split light, emitting the third split light to a first optical path, emitting the fourth split light to a second optical path, splitting the second split light into a fifth split light and a sixth split light, emitting the fifth split light to a third optical path, and emitting the sixth split light to a fourth optical path;
• a first reflector for reflecting the third split light and the fifth split light to the half-mirror, the first reflector being disposed on the first optical path and the third optical path;
• and
• a second reflector for reflecting the fourth split light and the sixth split light to the half-mirror, the second reflector being disposed on the second optical path and the fourth optical path,
• wherein the half-mirror recombines the third split light incident from the first reflector and the fourth split light incident from the second reflector, and emits a first recombined optical signal while splitting the first recombined optical signal in two branches, and
• the half-mirror recombines the fifth split light incident from the first reflector and the sixth split light incident from the second reflector, and emits a second recombined optical signal while splitting the second recombined optical signal in two branches;
• a first balanced optical detector that includes:
• two light receiving elements for receiving the first recombined optical signals being emitted in two branches from the Michelson interferometer,
• wherein the first balanced optical detector generates a first demodulated signal based on the first recombined optical signals;
• and
• a second balanced optical detector that includes:
• two light receiving elements for receiving the second recombined optical signals being emitted in two branches from the Michelson interferometer,
• wherein the second balanced optical detector generates a second demodulated signal based on the second recombined optical signals,
• wherein an optical path length difference between the first optical path and the second optical path is set so that the fourth split light has a delay time which is equal to a symbol period of the optical signal, with respect to the third split light,
• an optical path length difference between the third optical path and the fourth optical path is set so that the sixth split light has a delay time which is equal to a symbol period of the optical signal, with respect to the fifth split light, and
• the Michelson interferometer further includes a phase adjusting section for setting a phase difference between the first recombined optical signal and the second recombined optical signal to π/2, the phase adjusting section being disposed between the half-mirror and at least one of the first reflector or the second reflector.

A demodulator for demodulating an optical signal on which a DQPSK (Differential Quadrature Phase Shift Keying) is applied, the demodulator comprising:

• a Michelson interferometer that includes:
• a half-mirror for splitting the optical signal into a first split light and a second split light;
• a first reflector for reflecting the first split light to the half-mirror while splitting the first split light into a third split light and a fourth split light;
• and
• a second reflector for reflecting the second split light into the half-mirror while splitting the second split light into a fifth split light and a sixth split light,
• wherein the half-mirror recombines the third split light incident from the first reflector and the fifth split light incident from the second reflector, and emits a first recombined optical signal while splitting the first recombined optical signal in two branches, and
• the half-mirror recombines the fourth split light incident from the first reflector and the sixth split light incident from the second reflector, and emits a second recombined optical signal while splitting the second recombined optical signal in two branches;
• a first balanced optical detector that includes:
• two light receiving elements for receiving the first recombined optical signals being emitted in two branches from the Michelson interferometer,
• wherein the first balanced optical detector generates a first demodulated signal based on the first recombined optical signals;
• and
• a second balanced optical detector that includes:
• two light receiving elements for receiving the second recombined optical signals being emitted in two branches from the Michelson interferometer,
• wherein the second balanced optical detector generates a second demodulated signal based on the second recombined optical signals,
• wherein an optical path length difference between a first optical path through which the first split light and the third split light pass and a second optical path through which the second split light and the fifth split light pass is set so that the fifth split light has a delay time which is equal to a symbol period of the optical signal, with respect to the third split light,
• an optical path length difference between a third optical path through which the first split light and the fourth split light pass and a fourth optical path through which the second split light and the sixth split light pass is set so that the sixth split light has a delay time which is equal to a symbol period of the optical signal, with respect to the fourth split light, and
• the Michelson interferometer further includes a phase adjusting section for setting a phase difference between the first recombined optical signal and the second recombined optical signal to π/2, the phase adjusting section being disposed between the half-mirror and at least one of the first reflector or the second reflector.