Wavelength converter and image display device
View Patent ↗Since the absorption of a fundamental wave by a fiber increases if it is tried to obtain a wavelength conversion light of watt-class high output, the fiber length needs to be shortened. However, since oscillation efficiency conversely decreases if the fiber length is shortened, it is difficult to obtain a high-output fundamental wave. Thus, by reflecting an excitation light incident on the fiber in the fiber, the excitation light is efficiently absorbed to amplify the fundamental wave with a high gain. Further, by shortening the fiber length, the absorption of the fundamental wave is also reduced to improve a fundamental wave output. Consequently, a wavelength converter capable of ensuring a stable high output up to watt-class is achieved.
1. A wavelength converter, comprising:
a laser resonator including a fiber containing a laser active material and formed with a fiber grating;
a laser light source for emitting an excitation light to the fiber; and
a wavelength conversion element for converting a fundamental wave of a laser light emerging from the laser resonator into a harmonic,
wherein:
the laser resonator includes a first reflection surface arranged near the fiber grating and a second reflection surface arranged near the laser light source;
the fundamental wave of the laser light emerging from the laser resonator reciprocates between the fiber grating and the second reflection surface,
the excitation light emitted from the laser light source makes a round trip between the second and first reflection surfaces by being reflected by the first reflection surface after being incident through the second reflection surface, and
the reflectances of the fiber grating and the first reflection surface satisfy a relationship that the reflectance of the fiber grating is larger than that of the first reflection surface for the wavelength of the fundamental wave and satisfy a relationship that the reflectance of the fiber grating is smaller than that of the first reflection surface for the wavelength of the excitation light.
2. A wavelength converter according to claim 1 , further comprising a light propagating portion for propagating the excitation light emitted from the laser light source to the second reflection surface and propagating the fundamental wave of the laser light emerging from the laser resonator to the wavelength conversion element.
3. A wavelength converter according to claim 2 , wherein the light propagating portion includes a reflecting member for transmitting the excitation light emitted from the laser light source and reflecting the fundamental wave of the laser light emerging from the laser resonator.
4. A wavelength converter according to claim 3 , wherein a wavelength selecting layer for transmitting the excitation light emitted from the laser light source and reflecting the fundamental wave of the laser light emerging from the laser resonator is formed on a surface of the reflecting member.
5. A wavelength converter according to claim 4 , wherein the wavelength selecting layer of the reflecting member is formed by a multilayer film.
6. A wavelength converter according to claim 3 , wherein the reflecting member includes a narrow band transmission filter.
7. A wavelength converter according to claim 6 , wherein the wavelength bandwidth of the narrow band transmission filter is 0.1 nm or shorter.
8. A wavelength converter according to claim 3 , further comprising a diffraction member for diffracting only light components having wavelengths in a specified narrow band out of the excitation light reflected by the reflecting member after being emitted from the laser light source, wherein the diffracted light by the diffraction member returns to the laser light source to fix an oscillation wavelength of the laser light source to the wavelength of the diffracted light by the diffraction member.
9. A wavelength converter according to claim 8 , wherein the diffraction member includes a reflective diffraction grating for reflecting an incident light.
10. A wavelength converter according to claim 8 , wherein the diffraction member includes a transmissive diffraction grating for transmitting an incident light and a reflection mirror for reflecting the light transmitting the diffraction grating.
11. A wavelength converter according to claim 2 , further comprising a fundamental wave detector for detecting a part of the output of the fundamental wave and an output controller for controlling the output of the harmonic output emerging from the wavelength conversion element based on a detection value by the fundamental wave detector.
12. A wavelength converter according to claim 11 , wherein the output controller stores a table inputted beforehand and controls the temperature of at least one of the fiber grating and the wavelength conversion element based on the table.
13. A wavelength converter according to claim 12 , wherein the table includes data on a phase-matching wavelength change amount in the wavelength conversion element in relation to the fundamental wave output.
14. A wavelength converter according to claim 12 , wherein the table includes data on a reflection wavelength change amount of the fundamental wave in the fiber grating in relation to the fundamental wave output.
15. A wavelength converter according to claim 11 , wherein the fundamental wave detector includes a light receiving element for receiving a light branched from the fundamental wave in the fiber.
16. A wavelength converter according to claim 11 , wherein the fundamental wave detector includes a light receiving element for receiving a leakage light of the fundamental wave in the fiber grating.
17. A wavelength converter according to claim 11 , wherein the fundamental wave detector includes a light receiving element for receiving the fundamental wave output having passed through the first reflection surface.
18. A wavelength converter according to claim 11 , wherein the output controller controls the fundamental wave output by causing the light propagating portion to reflect the excitation light and detecting a part of the excitation light by means of a light receiving element.
19. A wavelength converter according to claim 1 , wherein the fiber is such that a first fiber and a second fiber formed with the fiber grating are optically connected.
20. A wavelength converter according to claim 1 , wherein the first reflection surface is formed by a multilayer film.
21. A wavelength converter according to claim 1 , wherein the second reflection surface is formed by a polarizing mirror.
22. A wavelength converter according to claim 1 , wherein the laser light source includes a laser element for emitting the excitation light, a lens for beam-shaping the excitation light emitted from the laser element and a container for storing the laser element and the lens.
23. A wavelength converter according to claim 22 , wherein the lens is a cylindrical lens.
24. A wavelength converter according to claim 1 , wherein the reflectance of the second reflection surface is 10 to 20%.
25. A wavelength converter according to claim 1 , wherein the wavelength of the harmonic output is 510 to 540 nm and the output of the harmonic output is 1 W or higher.
26. A wavelength converter according to claim 1 , wherein the wavelength of the fundamental wave is 1020 to 1060 nm and the wavelength bandwidth of the fiber grating is 0.05 nm or shorter.
27. An image display device, comprising:
a plurality of laser light sources;
a scanning unit for scanning laser lights emitted from the respective laser light sources; and
a screen for displaying an image using the laser lights emitted from the respective laser light sources,
the laser light sources including light sources for emitting at least red, green and blue lights,
wherein, out of the laser light sources, at least the green light source includes a wavelength converter according to claim 1 .