Patent ID: 7869478

Claim:
An apparatus for maintaining a constant extinction ratio of a laser diode (LD) as a function of temperature, the apparatus comprising: an automatic power control (APC) circuit maintaining a constant optical power of the LD as a function of temperature by using empirical non-linear static reference values stored in the apparatus in which the empirical non-linear static reference values are previously obtained from a prototype of a given product model of the LD of the apparatus and not obtained from the apparatus, wherein the empirical non-linear static reference values are associated with modulation current control voltage data and LD bias current data from the prototype as a function of temperature; a correlation deriver deriving linear correlations from within the empirical non-linear static reference values of the prototype by using a monitored bias current of the LD such that the correlation deriver is used to maintain the constant extinction ratio of the LD when a monitored optical power level of the LD is found not to be equal to the constant optical power level of the LD; and a modulation current control circuit controlling the modulation current to maintain the constant extinction ratio of the LD based on the correlations, wherein the apparatus does not use a temperature sensor, wherein when the monitored optical power is below the constant optical power then the monitored bias current corresponds to a temperature below a normal working temperature of the LD and the inclination has the formula: slope A =(Δ modulation current control voltage)/(Δ bias current) wherein (Δ modulation current control voltage) is the change in modulation current control voltage, and the (Δ bias current) is the change in bias current and is centered at or near the monitored bias current, wherein the modulation current control circuit controlling the modulation current control voltage uses the following function: Y =+(slope A)×(monitored bias current)+(current C ) wherein the (current C) is defined as the bias current at the normal working temperature of the LD.