Method of controlling semiconductor optical device that includes semiconductor optical amplifier

A method of controlling a transmitter optical sub-assembly (TOSA) that outputs the optical signal and includes a semiconductor laser diode (LD), a semiconductor modulator, a semiconductor optical amplifier (SOA), and a temperature controller, the semiconductor LD generating continuous wave (CW) light responding to a first bias current, the semiconductor modulator generating modulated light by modulating the CW light responding to a driving signal, the SOA generating the optical signal by amplifying the modulated signal depending on a second bias current, the thermo-electric cooler (TEC) that mounts the semiconductor LD, the semiconductor modulator, and the SOA thereon, and controls a temperature of the semiconductor LD, the semiconductor modulator, and the SOA provided with a driving current, the method comprising steps of:

• providing initial conditions to the semiconductor LD, the semiconductor modulator, the SOA, and the TEC, respectively;
• adjusting the second bias current supplied to the SOA depending on a waveform of the optical signal after a transmission of a predetermined distance;
• and
• after adjusting the second bias current, adjusting the driving current for the TEC such that the optical signal has a target wavelength, adjusting the first bias current such that the optical signal shows target power, and adjusting the driving signal such that the optical signal shows a target extinction ration, a target cross point, and a target pulse mask margin (PMM),
• wherein the second bias current is set in a region where the optical signal shows a negative relation against the second bias current.