Optical transmitter with forward controlled peltier device

An optical transmitter having a semiconductor light-emitting device and an forward controlled Peltier device without any sensing resistor for monitoring an current flowing in said Peltier device, said Peltier device controlling a temperature of said light-emitting device, said optical transmitter comprising:

• a temperature sensor for monitoring said temperature of said light-emitting device, and for outputting a temperature-monitored signal;
• and
• a controller for controlling a current flowing in said Peltier device, said controller including,
• a first comparator for comparing said temperature-monitored signal with a target temperature signal denoting a target temperature for said light-emitting device, and for generating a temperature difference signal,
• a limiter for cramping said temperature difference signal between a preset maximum value and a preset minimum value,
• a second comparator for slicing a periodic signal by said temperature difference signal, said periodic signal having a triangular waveform with a positive peak value greater than said preset maximum value and a negative peak value smaller than said preset minimum value, and for outputting a control signal with a pulsed wave form, and
• a switching ladder including a pair of two switches each having two switching devices operating in complementary, said Peltier device being connected between said two switches through a low pass filter including an inductor and a capacitor, said switches being driven by said control signal and another control signal complementary to said control signal.