Optical signal processing device and optical signal processing method

An optical signal processing device comprising:

• a first optical signal processing unit that generates a first digital signal by causing a received optical signal and a local optical signal to interfere with each other under a first condition;
• a second optical signal processing unit that generates a second digital signal by causing the received optical signal and the local optical signal to interfere with each other under a second condition;
• and
• a digital processing unit that processes the first digital signal and the second digital signal and extracts a signal included in the received optical signal,
• wherein the first optical signal processing unit includes:
• a first optical signal generation unit that generates a first optical signal by causing the received optical signal and the local optical signal to interfere with each other with a same phase;
• a second optical signal generation unit that generates a second optical signal by causing the received optical signal and the local optical signal to interfere with each other with a phase difference of π;
• a first photoelectric conversion element that converts the first optical signal into a first electrical signal;
• a second photoelectric conversion element that converts the second optical signal into a second electrical signal;
• a first direct-current component correction unit that reduces a difference between a direct-current component of the first electrical signal and a direct-current component of the second electrical signal;
• a differential first trans-impedance circuit into which the first electrical signal and the second electrical signal, which have been corrected by the first direct-current component correction unit, are input;
• and
• a first AD conversion unit that converts an output of the first trans-impedance circuit into the first digital signal, and
• the second optical signal processing unit includes:
• a third optical signal generation unit that generates a third optical signal by causing the received optical signal and the local optical signal to interfere with each other with a phase difference of π/2;
• a fourth optical signal generation unit that generates a fourth optical signal by causing the received optical signal and the local optical signal to interfere with each other with a phase difference of 3π/2;
• a third photoelectric conversion element that converts the third optical signal into a third electrical signal;
• a fourth photoelectric conversion element that converts the fourth optical signal into a fourth electrical signal;
• a second direct-current component correction unit that reduces a difference between a direct-current component of the third electrical signal and a direct-current component of the fourth electrical signal;
• a differential second trans-impedance circuit into which the third electrical signal and the fourth electrical signal, which have been corrected by the second direct-current component correction unit, are input;
• and
• a second AD conversion unit that converts an output of the second trans-impedance circuit into the second digital signal.

A trans-impedance amplifier comprising:

• a direct-current component correction unit that reduces a difference between a magnitude of a direct-current component of a first electrical signal and a magnitude of a direct-current component of a second electrical signal;
• and
• a differential trans-impedance circuit into which the first electrical signal and the second electrical signal, which have been corrected by the direct-current component correction unit, are input;
• wherein the direct-current component correction unit includes:
• a first transistor which is connected between the first photoelectric conversion element and the trans-impedance circuit;
• a second transistor which is connected between the second photoelectric conversion element and the trans-impedance circuit;
• and
• a constant current source or a third transistor which is connected between the first photoelectric conversion element and the trans-impedance circuit through the first transistor, and connected between the second photoelectric conversion element and the trans-impedance circuit through the second transistor.

An optical signal processing method comprising:

• generating a first optical signal by causing a received optical signal and a local optical signal which is output from a light source on a receiving side to interfere with each other with a first phase difference;
• generating a second optical signal by causing the received optical signal and the local optical signal to interfere with each other with a second phase difference shifted by π from the first phase difference;
• converting the first optical signal into a first electrical signal;
• converting the second optical signal into a second electrical signal;
• and
• reducing a difference between a direct-current component of the first electrical signal and a direct-current component of the second electrical signal, and then inputting the first electrical signal and the second electrical signal to a differential trans-impedance circuit.

An optical signal processing device comprising:

• a first optical signal generation unit that generates a first optical signal by causing a received optical signal and a local optical signal to interfere with each other with a first phase difference;
• a second optical signal generation unit that generates a second optical signal by causing the received optical signal and the local optical signal to interfere with each other with a second phase difference shifted by π from the first phase difference;
• a first photoelectric conversion element that converts the first optical signal into a first electrical signal;
• a second photoelectric conversion element that converts the second optical signal into a second electrical signal;
• a direct-current component correction unit that reduces a direct-current component of the first electrical signal and a direct-current component of the second electrical signal;
• and
• a differential trans-impedance circuit into which the first electrical signal and the second electrical signal, which have been corrected by the direct-current component correction unit, are input.

An optical signal processing device comprising:

• a first optical signal processing unit that generates a first digital signal by causing a received optical signal and a local optical signal to interfere with each other under a first condition;
• a second optical signal processing unit that generates a second digital signal by causing the received optical signal and the local optical signal to interfere with each other under a second condition;
• and
• a digital processing unit that processes the first digital signal and the second digital signal and extracts a signal included in the received optical signal,
• wherein the first optical signal processing unit includes:
• a first optical signal generation unit that generates a first optical signal by causing the received optical signal and the local optical signal to interfere with each other with a same phase;
• a second optical signal generation unit that generates a second optical signal by causing the received optical signal and the local optical signal to interfere with each other with a phase difference of t;
• a first photoelectric conversion element that converts the first optical signal into a first electrical signal;
• a second photoelectric conversion element that converts the second optical signal into a second electrical signal;
• a first direct-current component correction unit that reduces a direct-current component of the first electrical signal, and reduces a direct-current component of the second electrical signal;
• a differential first trans-impedance amplifier into which the first electrical signal and the second electrical signal, which have been after corrected by the direct-current component correction unit, are input, and
• a first AD conversion unit that converts an output of the first trans-impedance amplifier into the first digital signal, and
• the second optical signal processing unit includes:
• a third optical signal generation unit that generates a third optical signal by causing the received optical signal and the local optical signal to interfere with each other with a phase difference of π/2;
• a fourth optical signal generation unit that generates a fourth optical signal by causing the received optical signal and the local optical signal to interfere with each other with a phase difference of 3π/2;
• a third photoelectric conversion element that converts the third optical signal into a third electrical signal;
• a fourth photoelectric conversion element that converts the fourth optical signal into a fourth electrical signal;
• a second direct-current component correction unit that reduces a direct-current component of the third electrical signal, and reduces a direct-current component of the fourth electrical signal;
• a differential second trans-impedance amplifier into which the third electrical signal and the fourth electrical signal, which have been corrected by the direct-current component correction unit, are input;
• and
• a second AD conversion unit that converts an output of the second trans-impedance amplifier into the second digital signal.