Mach-Zehnder type optical modulator, optical transceiver, and dispersion compensation method

An optical transceiver comprising:

• a transmitter configured to transmit an optical signal having a light source and a Mach-Zehnder type optical modulator configured to modulate light from the light source;
• a receiver configured to receive an optical signal to be input;
• and
• a control unit configured to control the transmitter and the receiver, wherein
• the Mach-Zehnder type optical modulator includes:
• a first directional coupler configured to branch light being input from the light source into a cross-port path having a cross-port branching ratio η and a bar-port path having a bar-port branching ratio 1-η;
• a first arm configured to propagate light from the cross-port path of the first directional coupler;
• a second arm configured to propagate light from the bar-port path of the first directional coupler;
• a second directional coupler configured to have two inputs and two outputs, input light from the first arm to one input and light from the second arm to another input, and have a cross-port branching ratio of γ and a bar-port branching ratio of 1-γ;
• and
• a phase modulation unit configured to provide a phase difference between the light propagating through the first arm and the light propagating through the second arm, wherein
• the cross-port branching ratio η and the bar-port branching ratio 1-η, and the cross-port branching ratio γ and the bar-port branching ratio 1-γ are determined in such a way that an α parameter being a chirp parameter is a negative value.

A dispersion compensation method comprising:

• branching input light into a cross-port path having a cross-port branching ratio η and a bar-port path having a bar-port branching ratio 1-η by a first directional coupler;
• inputting light from the cross-port path of the first directional coupler to a first arm;
• inputting light from the bar-port path of the first directional coupler to a second arm;
• inputting light from the first arm to one input of a second directional coupler with two inputs and two outputs and inputting light from the second arm to another input, the second directional coupler having a cross-port branching ratio of γ and a bar-port branching ratio of 1-γ;
• providing a phase difference between the light propagating through the first arm and the light propagating through the second arm;
• and
• determining the cross-port branching ratio η and the bar-port branching ratio 1-η, and the cross-port branching ratio γ and the bar-port branching ratio 1-γ in such a way that an α parameter being a chirp parameter is a negative value.