Optical transmitter

摘要

A photodiode converts an optical signal output from a laser diode to a current signal, and a current-to-voltage conversion circuit converts the current signal to a voltage signal. A comparison amplifier compares the voltage signal with a reference voltage to control the current flowing from a variable current source and increases or decreases a bias current for driving the laser diode. The current-to-voltage conversion circuit comprises a resistor and a variable current source that are connected in parallel. Therefore, it is possible to change the bias current without changing the resistance value of the resistor and to avoid limiting the dynamic range of the optical signal that is output. In addition, since the resistance value of the resistor does not change, the loop gain does not change, thereby stabilizing the control operation.

主权项

1. An optical transmitter for outputting an optical signal, the optical transmitter comprising:
a light-emitting element that is driven and produces the optical signal; a light-receiving element that receives the optical signal and outputs a current signal indicating the strength of the optical signal received; a current-to-voltage conversion circuit that converts the current signal output by the light-receiving element to a voltage signal, the current-to-voltage conversion circuit including a resistor connected to the light-receiving element and a variable current source connected in parallel with the resistor, and the voltage signal being output from one end of the resistor; a comparator that compares a reference voltage and the voltage signal output by the current-to-voltage conversion circuit and outputs a comparison result from comparing the reference voltage and the voltage signal; a bias current driving circuit that passes a direct current corresponding to the comparison result from the comparator to the light-emitting element to drive the light-emitting element; a modulated current driving circuit that controls a modulated current to have an amplitude that changes in accordance with an input signal to the light-emitting element to modulate the strength of the optical signal; a temperature sensor that detects a temperature inside the optical transmitter; and a regulator that regulates an amplitude of the modulated current and a value of the current flowing to the variable current source based on the temperature detected by the temperature sensor.