Optical transmitter and method of controlling optical transmitter

A method of controlling an optical transmitter comprising:

• detecting an assertion of a transmitter disable signal from an external host device,
• changing an operation of a bias control circuit, the bias control circuit controlling bias voltages applied to a multi-level modulator, the multi-level modulator comprising a first optical waveguide and a second optical waveguide, the bias voltages being adjusted such that a phase difference between light passing through the first optical waveguide and light passing through the second optical waveguide becomes π,
• turning on an attenuation operation of an optical switch, the optical switch blocking an output light output from the multi-level modulator,
• decreasing an amplitude of a driving voltage signal, the driving voltage signal being applied to the multi-level modulator to modulate a continuous wave light generated by a light source,
• increasing a resistance of a variable resistor element, the variable resistor element generating a potential by a monitor current flowing through the variable resistor element, the monitor current being generated by an optical detector configured to detect an optical power of the output light, and
• resuming the operation of the bias control circuit.