Phase modulation circuit, test apparatus, and communication system

A test apparatus for testing an electronic device, comprising:

• a pattern generating unit for generating a test signal to test said electronic device;
• a phase modulation circuit for supplying said electronic device with a modulation signal, which results from modulating a phase of said test signal to a desired phase;
• and
• a judgment unit for judging quality of said electronic device based on an output signal, which said electronic device outputs based on said modulation signal,
• wherein said phase modulation circuit comprises:
• a first light emitting element for emitting light according to said test signal and outputting a light emitting signal as said modulation signal;
• and
• a bias current control unit for supplying in advance said first light emitting element with a bias current, which is smaller than a light emitting threshold current whereby said first light emitting element starts to emit light.

A communication system for transmitting communication data, comprising:

• a transmission unit for outputting said communication data;
• a phase modulation circuit for receiving said communication data and modulating a phase of said communication data to a desired phase;
• a communication path for transmitting said communication data phase-modulated by said phase modulation circuit;
• and
• a receiving unit for receiving said communication data phase-modulated by said phase modulation circuit and demodulating said communication data received,
• wherein said phase modulation circuit comprises:
• a first light emitting element for emitting light according to said communication data received and outputting a light emitting signal as said communication data phase-modulated;
• and
• a first bias current source for supplying in advance said first light emitting element with a bias current, which is smaller than a light emitting threshold current whereby said first light emitting element starts to emit light.