Laser diode control circuit and laser diode control method

A laser diode control circuit comprising:

• a load portion for generating a signal corresponding to a photocurrent which is generated by a photodetector in accordance with the optical power of the light received from a laser light generating portion;
• and
• a control portion for generating a first control signal using values which correspond to ΔX and X to modify one of the bias current Ib and the modulation current Im and for generating a second control signal using values which correspond to ΔY and Y to modify the other of the bias current Ib and the modulation current Im, wherein ΔX is defined in accordance with the result of a comparison between a value corresponding to said signal and a reference value, ΔY is generated by a function f(X,ΔX)=ΔY defined such that the light emission power displays a predetermined dependence and the extinction ratio displays a predetermined dependence, a set of variables (X,Y,ΔX,ΔY) is one of either (Db, Dm, ΔDb, ΔDm) or (Dm, Db, ΔDm, ΔDb), the symbol Db indicating a value corresponding to a bias current Ib, the symbol Dm indicating a value corresponding to a modulation current Im, the symbol ΔDb indicating a value corresponding to an amount of change ΔIb in the bias current Ib, and the symbol ΔDm indicating a value corresponding to an amount of change ΔIm in the modulation current Im;
• a bias current circuit portion for generating the bias current Ib to be provided to said laser light generating portion in accordance with said first control signal;
• and
• a modulation current circuit portion for generating the modulation current Im to be provided to said laser light generating portion in accordance with said second control signal.