Patent ID: 7787507
Filing Date: 2010-08-31
Classification: H01S

Abstract:
1. An apparatus for controlling modulation of a laser, the apparatus comprising: a laser capable of being driven to produce light; a laser driver that generates an electrical bias current signal and an electrical modulation current signal that are used to drive the laser to cause the laser to produce light; a laser output power monitoring device that receives a fraction of the light produced by the laser as optical feedback and generates an electrical feedback signal based on the fraction of the light received from the laser; a laser controller comprising an integrated circuit configured to receive the electrical feedback signal and to perform a control algorithm that obtains a measurement of an average output power level of the laser based on the electrical feedback signal and produces a bias current control signal and a modulation current control signal based on the measured average output power level of the laser, the bias current and modulation current control signals being received by the laser driver, and wherein the laser driver uses the bias current control signal and the modulation current control signal to set an amplitude for the electrical current bias signal and an amplitude for the electrical modulation current signal, respectively, wherein when the laser controller performs said at least one control algorithm, the laser controller detects whether the laser is being over-modulated or under-modulated based on the measured average laser output power level, wherein if the laser controller detects that the laser is being over-modulated or under-modulated, the modulation current control signal produced by the laser controller and received by the laser driver causes the laser driver to adjust the amplitude of the electrical modulation current signal to reduce or eliminate the over-modulation or under-modulation of the laser; wherein when the laser controller detects the laser is being over-modulated by determining if the average laser output power level has increased, the laser controller initially causes the modulation current control signal to decrease the amplitude of the modulation current while maintaining the amplitude of the bias current; and when the laser controller detects that the laser is being under-modulated by determining if the average laser output power level has decreased, the laser controller initially causes the bias current control signal to decrease the amplitude of the bias current while maintaining the amplitude of the modulation current.