Laser diode assembly
A laser diode assembly includes: a mode-locked laser diode device; a diffraction grating that configures an external resonator, returns primary or more order diffracted light to the mode-locked laser diode device, and outputs 0-order diffracted light outside; and an imaging section provided between the mode-locked laser diode device and the diffraction grating and imaging an image of a light output end face of the mode-locked laser diode device on the diffraction grating.
1. A laser diode assembly comprising:
a mode-locked laser diode device configured to emit a diffusion light beam;
a diffraction grating that configures an external resonator, and is configured to return primary or more order diffracted light to the mode-locked laser diode device, and output 0-order diffracted light outside;
an imaging section provided between the mode-locked laser diode device and the diffraction grating, and configured to convert the diffusion light beam into a focused light beam that is not a parallel light beam to form an image of a light output end face of the mode-locked laser diode device on the diffraction grating;
a reflecting mirror configured to reflect the 0-order diffracted light outputted from the diffraction grating; and
a collimation lens positioned and configured to convert light outputted from the reflecting mirror into a parallel light beam,
wherein a distance between the diffraction grating and the reflecting mirror is changed while the position relation between the diffraction grating and the reflecting mirror is kept in parallel with each other, and
wherein the distance between the diffraction grating and the reflecting mirror is expressed as follows:
d 0 ·sin(Ψ 0 )/sin(θ 0 +Ψ 0 )
where d 0 represents the distance between the diffraction grating and the reflecting mirror when a wavelength as reference is outputted, Ψ 0 represents an incident angle of laser light to the diffraction grating when the wavelength as reference is outputted, and θ 0 represents an angle change amount of the diffraction grating to the wavelength as reference.
2. The laser diode assembly according to claim 1 , further comprising a turning unit configured to turn the diffraction grating, wherein wavelength of laser light to be returned to the mode-locked laser diode device is controlled by turning of the diffraction grating caused by operation of the turning unit.
3. The laser diode assembly according to claim 2 , further comprising:
a correction mechanism configured to correct a shift of a light path of the 0-order diffracted light reflected by the reflecting mirror resulting from the turning of the diffraction grating caused by the operation of the turning unit.
4. The laser diode assembly according to claim 1 , wherein the imaging section comprises a lens having a positive power.
5. The laser diode assembly according to claim 4 , wherein the lens comprises an aspheric convex lens.
6. The laser diode assembly according to claim 1 , wherein the mode-locked laser diode device has oblique waveguide.
7. The laser diode assembly according to claim 6 , wherein the reflecting mirror is moved toward or away from the diffraction grating.
8. The laser diode assembly according to claim 1 , wherein the reflecting mirror is turned centering on an axis line that is parallel with an axis line of the turning of the diffraction grating with a position relation in parallel with the diffraction grating being retained.
9. The laser diode assembly according to claim 1 , wherein the following expression is satisfied:
1*10 <L 2 /L 1 <1*10 2
where a length in a lateral direction of laser light on the light output end face of the mode-locked laser diode device is L 1 , and a length in the lateral direction of the image on the diffraction grating is L 2 .