Laser diode driver circuit
A laser diode driver circuit is provided that has a loop including a laser diode, a drive capacitor for storing drive charge, and a switch element, a first inductor coupled in series with the laser diode, a parallel capacitor coupled in parallel with a series circuit composed of the laser diode and the first inductor, and a first diode coupled in parallel with the series circuit in opposite polarity to the laser diode.
1 . A laser diode driver circuit comprising:
a loop including a laser diode, a drive capacitor configured to store a drive charge, and a switch element;
a first inductor coupled in series with the laser diode;
a parallel capacitor coupled in parallel with a series circuit that includes the laser diode and the first inductor; and
a first diode coupled in parallel with the series circuit and in opposite polarity to the laser diode,
wherein a pair of power supply terminals of a direct current (DC) power source are coupled to respective sides of the switch element, and
R 2 LD1 <4 L 1/ C 2,
where C 2 is a capacitance of the parallel capacitor, L 1 is an inductance of the first inductor, and R LD1 is a resistance component of the laser diode.
2 . The laser diode driver circuit according to claim 1 , further comprising a series circuit that includes a second inductor and a second diode and that is disposed between one of the pair of power supply terminals of the DC power source and one of the respective sides of the switch element.
3 . The laser diode driver circuit according to claim 1 , further comprising a parallel circuit that is disposed between the switch element and the parallel capacitor and that includes a third diode configured to block reverse current and at least one of a resistance element and an additional inductor.
4 . The laser diode driver circuit according to claim 1 , wherein a current flowing in a circuit formed by the parallel capacitor, the first inductor, and the laser diode is a damped oscillating current, and a peak of the damped oscillating current coincides with a peak of a current flowing through a loop that includes the laser diode and the switch element.
5 . The laser diode driver circuit according to claim 1 , wherein, when Tz 1 is a time point at which a direction of a current flowing in the parallel capacitor changes from a forward direction to a reverse direction, Tz 2 is a time point at which the direction of the current flowing in the parallel capacitor changes from the reverse direction to the forward direction, and Tp is a time point at which a current flowing in the laser diode reaches a peak, a capacitance of the parallel capacitor is set to satisfy Tz 1 <Tp<Tz 2 .
6 . The laser diode driver circuit according to claim 1 , wherein the first inductor is provided by a parasitic inductance of an interconnection about the laser diode.
7 . The laser diode driver circuit according to claim 1 , wherein the parallel capacitor is provided by a parasitic capacitance of an interconnection about the laser diode.
8 . The laser diode driver circuit according to claim 1 , further comprising a resistance element disposed between one of the pair of power supply terminals of the DC power source and one of the respective sides of the switch element.