Optical transmitter and method for controlling optical carrier frequency

An optical transmitter, comprising:

• an optical signal generating section configured to add a first optical component to a first optical carrier and add a second optical component to a second optical carrier;
• a multiplexer configured to multiplex the first optical carrier and the second optical carrier to generate a multiplexed optical signal;
• a monitoring section configured to monitor the multiplexed optical signal to detect a monitor signal having a difference frequency between the first optical component and the second optical component;
• and
• a controller configured to control a carrier frequency of at least one of the first optical carrier and the second optical carrier according to the monitor signal.

An optical node device, comprising:

• a switch configured to switch optical signals wavelength-selectively;
• an optical signal generating section configured to add a first optical component to a first optical carrier and add a second optical component to a second optical carrier, and multiplex the first optical carrier and the second optical carrier to generate a multiplexed optical signal;
• and
• a monitoring and controlling section configured to monitor the multiplexed optical signal to detect a monitor signal having a difference frequency between the first optical component and the second optical component, and control a carrier frequency of at least one of the first optical carrier and the second optical carrier according to the monitor signal.