Optical transport apparatus, optical demultiplexer, and method of controlling optical demultiplexing

An optical transport apparatus used in a wavelength division multiplexing system, comprising:

• an optical demultiplexer that separates a wavelength division multiplexed signal into light components of respective wavelengths,
• wherein the optical demultiplexer has at least one unit circuit formed by three asymmetric Mach-Zehnder interferometers having a same arm length difference,
• wherein the unit circuit has a tree structure in which two output ports of a first asymmetric Mach-Zehnder interferometer are connected to a second asymmetric Mach-Zehnder interferometer and a third asymmetric Mach-Zehnder interferometer, respectively, and
• wherein the unit circuit has
• a first monitor connected to a first output port of the second asymmetric Mach-Zehnder interferometer,
• a second monitor connected to a second output port of the second asymmetric Mach-Zehnder interferometer,
• a third monitor connected to a first output port of the third asymmetric Mach-Zehnder interferometer,
• a fourth monitor connected to a second output port of the third asymmetric Mach-Zehnder interferometer,
• a first control circuit that controls a first transmissivity of the first asymmetric Mach-Zehnder interferometer so as to increase a monitoring result acquired from the second monitor and the fourth monitor,
• a second control circuit that controls a second transmissivity of the second asymmetric Mach-Zehnder interferometer so as to decrease a monitoring result of the first monitor, and
• a third control circuit that controls a third transmissivity of the third asymmetric Mach-Zehnder interferometer so as to decrease a monitoring result of the third monitor, and
• wherein the second output port of the second asymmetric Mach-Zehnder interferometer outputs a first transmission spectrum and the second output port of the third asymmetric Mach-Zehnder interferometer outputs a second transmission spectrum.