| 摘要 |
PROBLEM TO BE SOLVED: To accurately determine bias current with a simple structure even when characteristics of a laser diode changes.SOLUTION: A laser driver 11 acquires a calculated threshold current Ith on the basis of driving current (I1, I4) applied when an amount of light emission of LD (Laser Diode) 12 is controlled to two target amounts of light emission having different values. It is determined as a characteristic change of the LD 12 whether the temperature of the LD 12 has risen or declined between the past and the present on the basis of the relation of the magnitudes of driving currents (Iop1, Iop2) when the LD 12 is illuminated at a prescribed amount of light emission between the past and the present. Either a first threshold current Ith1'(Ith(n-1)) which was calculated and stored in the past or a second threshold current Ith2'(Ith(n)) calculated this time is selected as the threshold current Ith on the basis of the determination result. A bias current Ib is then determined based on the threshold current Ith. |
