Optical transmitter

Patent metadata

Field	Value
Publication number	US-9319146-B2
Application number	US-201214365790-A
Country	US
Kind code	B2
Filing date	Mar 22, 2012
Priority date	Mar 22, 2012
Publication date	Apr 19, 2016
Grant date	Apr 19, 2016

Abstract

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.

First claim

The invention claimed is:

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.

2. The optical transmitter according to claim 1 , further comprising an optical system that conveys the optical signal produced by the light-emitting element;
wherein the light-receiving element receives a portion of the optical signal produced by the light-emitting element not via the optical system.

3. The optical transmitter according to claim 1 , wherein the regulator regulates the amplitude of the modulated current and the value of the current flowing to the variable current source so that the strength and extinction ratio of the optical signal produced by the light-emitting element become desired values.

4. The optical transmitter according to claim 2 , wherein the regulator regulates the amplitude of the modulated current and the value of the current flowing to the variable current source so that the strength and extinction ratio of the optical signal output via the optical system become desired values.

5. The optical transmitter according to claim 1 , wherein:
the regulator regulates the amplitude of the modulated current and the value of the current flowing to the variable current source by control values the regulator provides to the current-to-voltage conversion circuit and the modulated current driving circuit; and
the regulator determines the control values such that the strength and the extinction ratio of the optical signal produced by the light-emitting element become desired values for multiple temperatures, and the regulator determines the control values for temperatures other than the multiple temperatures through extrapolation and interpolation using the control values determined for the multiple temperatures.

6. The optical transmitter according to claim 5 , wherein the interpolation and extrapolation are accomplished through complementation combining exponential complementation and polynomial complementation.

Assignees

• Noda Masaki
• Mitsubishi Electric Corp

Inventors

• Noda Masaki

Classifications

• H04B10/564 Primary

  Power control · CPC title

• H04B10/504

  using direct modulation · CPC title

• H04B10/07955

  Monitoring or measuring power · CPC title