Control circuit and optical circuit control method

A control circuit that controls at least one optical path difference among optical path differences of two optical paths of a single Mach-Zehnder interferometer or each of a plurality of the Mach-Zehnder interferometers included in an optical circuit, the control circuit comprising:

• a reference light generator configured to generate reference light having N types of wavelengths λ1 to λN each being different from a wavelength A of input light input to the optical circuit in parallel or in a time division manner where N is a natural number;
• a reference light input circuitry configured to input the reference light to the optical circuit;
• an optical power monitor configured to monitor a light intensity of propagated input light which is the input light that has been propagated through the single Mach-Zehnder interferometer or a plurality of the Mach-Zehnder interferometers, and at least one of a light intensity of propagated reference light which is the reference light that has been propagated through the single Mach-Zehnder interferometer or a plurality of the Mach-Zehnder interferometers through which the propagated input light has been propagated, and a light intensity of light obtained by multiplexing the propagated input light and the propagated reference light;
• and
• a controller configured to perform control to correct the optical path difference on a basis of light intensities P(λ1) to P(λN) of the propagated reference light having the N types of wavelengths λ1 to λN, which are obtained using a monitoring result by the optical power monitor.

An optical circuit control method for controlling at least one optical path difference among optical path differences of two optical paths of a single Mach-Zehnder interferometer or each of a plurality of the Mach-Zehnder interferometers included in an optical circuit, the method comprising:

• generating reference light having N types of wavelengths λ1 to λN each being different from a wavelength λ of input light input to the optical circuit in parallel or in a time division manner where N is a natural number;
• inputting the reference light to the optical circuit;
• monitoring a light intensity of propagated input light which is the input light that has been propagated through the single Mach-Zehnder interferometer or a plurality of the Mach-Zehnder interferometers included in the optical circuit, and at least one of a light intensity of propagated reference light which is the reference light that has been propagated through the single Mach-Zehnder interferometer or a plurality of the Mach-Zehnder interferometers through which the propagated input light has been propagated, and a light intensity of light obtained by multiplexing the propagated input light and the propagated reference light;
• and
• performing control to correct the optical path difference on a basis of a light intensity P(λ) of the propagated input light having the wavelength λ and light intensities P(λ1) to P(λN) of the propagated reference light having the N types of wavelengths λ1 to λN, which are obtained using a monitoring result in the monitor step or on a basis of the light intensities P(λ1) to P(λN) without using the light intensity P(λ).