JP2002204038A - Ultraviolet laser light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultraviolet laser light source capable of obtaining a high output with a good efficiency at a low cost. SOLUTION: Laser beams B1 to B8 generated from a plurality of GaN semiconductor lasers LD1 to LD8 are combined by a multiplexing optical system 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet laser light source, and more particularly, to an ultraviolet laser light source for obtaining a high output by combining ultraviolet laser beams emitted from a plurality of GaN-based semiconductor lasers. It is about.

[0002]

2. Description of the Related Art Conventionally, an Ar laser has been known as one of ultraviolet laser light sources for generating an ultraviolet laser beam. The Ar laser having a maximum output of about 7 W is also commercially available.

There is also known a wavelength conversion laser that oscillates 1064 nm infrared light with a semiconductor laser-excited solid-state laser or fiber laser and converts it into a third harmonic to obtain a laser beam in the ultraviolet region.

Furthermore, recently, for example, Jpn.Ap issued in 1998
As shown in pl.phys.Lett., Vol.37.p.L1020, a GaN-based semiconductor laser that emits an ultraviolet laser beam is also provided.

[0005]

However, the above-mentioned Ar laser has a very low electro-optical efficiency of 0.005% and a lifetime of 1000 lasers.
There is a problem that time is very short.

[0006] Further, since a wavelength conversion laser for converting infrared light into a third harmonic in the ultraviolet region has a very low wavelength conversion efficiency, it is extremely difficult to obtain a high output. At present, a solid-state laser medium is excited by a 30-W semiconductor laser to oscillate a 10-W fundamental wave (wavelength: 1064 nm), which is converted into a 3W second harmonic (532-nm wavelength), and the sum frequency of both is 1W third harmonic (wavelength
355 nm) is the top data. In this case, the electro-optical efficiency of the semiconductor laser is about 50%, and the conversion efficiency to ultraviolet light is as low as about 1.7%. The cost of such a wavelength conversion laser is considerably high because an expensive optical wavelength conversion element is used.

On the other hand, in the case of a GaN-based semiconductor laser, 10%
Although it is expected that the above-mentioned electrical-optical efficiency can be obtained, the maximum output will be 100 m even if future high output is realized.
It is thought to stay at about W.

[0008] In view of the above circumstances, the present invention is efficient and efficient.
It is an object of the present invention to provide a low-cost ultraviolet laser light source capable of obtaining high output.

[0009]

The ultraviolet laser light source according to the present invention is intended to increase the output by combining an ultraviolet laser beam emitted from the GaN-based semiconductor laser described above. , A plurality of GaN-based semiconductor lasers emitting an ultraviolet laser beam, and
And a multiplexing optical system for multiplexing a laser beam emitted from a system semiconductor laser.

In the ultraviolet laser light source according to the present invention, it is desirable that the plurality of GaN-based semiconductor lasers emit laser beams having different wavelengths.

It is preferable that a means for returning the emitted light to the semiconductor laser and locking the oscillation wavelength is provided for each of the plurality of GaN-based semiconductor lasers.
As such a wavelength locking means, a waveguide-type wavelength selection element having a reflection diffraction grating at the optical waveguide can be suitably used.

On the other hand, as the multiplexing optical system, a plurality of G
aN-based semiconductor lasers are provided corresponding to each of the semiconductor lasers. The laser beams emitted from the corresponding semiconductor lasers are transmitted well, and the laser beams emitted from the other semiconductor lasers are reflected well to combine the laser beams. It is possible to suitably use a filter configured using a band pass filter.

In the case where such a multiplexing optical system is applied, means for partially reflecting the multiplexed laser beam, returning the laser beam to each semiconductor laser through the above bandpass filter, and locking the oscillation wavelength thereof is used. It is desirable to be provided.

[0014]

The ultraviolet laser light source of the present invention comprises a plurality of G lasers.
Since the ultraviolet laser beam emitted from the aN-based semiconductor laser is combined, even if the output of each GaN-based semiconductor laser is relatively low as described above,
A high-power ultraviolet laser beam can be obtained.

Further, in the ultraviolet laser light source according to the present invention, if a plurality of GaN-based semiconductor lasers emitting laser beams having different wavelengths from each other are used, a wavelength-multiplexed laser beam can be obtained. Such an ultraviolet laser light source can be suitably used as a light source for a stereolithography system using an optical fiber or a printing system such as a diazo PS plate.

In the above system, if the wavelength of each multiplexed laser beam fluctuates, the multiplexing efficiency may change. Therefore, for each of the plurality of GaN-based semiconductor lasers, if means for returning the emitted light to the semiconductor laser and locking the oscillation wavelength is provided, wavelength fluctuation of each laser beam can be prevented, and high output power can be prevented. Stability can be ensured.

On the other hand, the multiplexing optical system is provided in correspondence with each of the plurality of GaN-based semiconductor lasers, the laser beam emitted from the corresponding semiconductor laser is transmitted well, and the laser emitted from the other semiconductor lasers is transmitted. If the beam is configured using a band-pass filter that reflects the beams well and multiplexes the laser beams, the number of multiplexed beams is not limited.
A higher output multiplexed beam can be obtained using a system semiconductor laser.

In the ultraviolet laser light source of the present invention to which the above-described one is applied as the multiplexing optical system, a part of the multiplexed laser beam is reflected and returned to each of the semiconductor lasers through the above-mentioned band-pass filter. In this case, it is possible to prevent fluctuations in the multiplexing efficiency of the laser beam. Therefore, if the ultraviolet laser light source having this configuration is used as a light source for stereolithography or a printing system, high output stability can be ensured as described above.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an ultraviolet laser light source according to a first embodiment of the present invention. As shown in the figure, this ultraviolet laser light source has eight single-mode GaN-based semiconductor lasers LD1, LD2, L as an example.
D3, LD4, LD5, LD6, LD7 and LD8
And a multiplexing optical system 20.

GaN-based semiconductor lasers LD1, LD2,
LD3, LD4, LD5, LD6, LD7, LD8 are
The oscillation wavelength is 395nm, 396nm, 397nm, 398n respectively.
m, 399 nm, 400 nm, 401 nm, and 402 nm, each of which differs by 1 nm, and the output is all 50 mW in common. These wavelengths are required for the GaN-based semiconductor laser to oscillate.
A wavelength capable of high-power oscillation is selected in the range of 0 to 410 nm. In addition to the wavelength interval of 1 nm,
It may be set to 2 nm or the like.

The GaN semiconductor lasers LD1, LD2, LD3, LD4, LD5, LD6, L
Laser beams B1, B2, B3, B4, B5 in a divergent light state respectively emitted from D7 and LD8.
Collimator lens C for collimating B6, B7, B8
1, C2, C3, C4, C5, C6, C7, and C8 are provided.

The multiplexing optical system 20 includes a parallel plate prism 21 and
Narrow band-pass filters F3, F5 and F7 attached to one surface 21a thereof and narrow-band band-pass filters F2 and F2 attached to other surface 21b of parallel plate prism 21.
F4, F6 and F8. These narrow bandpass filters F2, F3, F4, F5
F6, F7 and F8 have wavelengths of 396 nm, 397 nm,
Light of 398 nm, 399 nm, 400 nm, 401 nm, and 402 nm is transmitted at a transmittance of 90%, and light of other wavelengths has a reflectance of 98%.
It is formed so as to reflect light. FIG. 2 shows the transmission spectra of these narrow bandpass filters F2 to F8 together with the transmission spectra of the narrowband bandpass filter F1 described later.

For example, in the case of the band-pass filter F8 as an example, such a narrow-band band-pass filter has a single-sided transmittance of 95% for a wavelength of 402 nm and wavelengths of 395 to 401.
It can be formed, for example, by laminating a narrow band-pass filter having a reflectance of 90% with respect to nm. Since this type of bandpass filter has an in-plane distribution of transmission wavelengths and a variation in transmittance between lots, it is necessary to select the bandpass filters having the same transmission peak wavelength to perform the above-mentioned bonding. .

The GaN-based semiconductor laser LD1 is disposed such that a laser beam B1 having a wavelength of 395 nm emitted from the laser beam B1 is incident on the narrow band-pass filter F2 at an incident angle of 5 °.

In the GaN-based semiconductor laser LD2, a laser beam B2 having a wavelength of 396 nm emitted from the laser beam B2 enters the narrow-band bandpass filter F2 at an incident angle of 5 ° and is reflected by the narrow-band bandpass filter F2. It is arranged so as to follow the same optical path as the laser beam B1.

In the GaN-based semiconductor laser LD3, a laser beam B3 having a wavelength of 397 nm emitted from the GaN-based semiconductor laser LD3 enters the narrow-band bandpass filter F3 at an incident angle of 5 ° and is reflected by the narrow-band bandpass filter F3. The laser beams B1 and B2 are disposed so as to follow the same optical path.

Hereinafter, GaN-based semiconductor lasers LD4-8
Are arranged in the same manner, whereby the respective GaN-based semiconductor lasers LD1, LD2, LD3, LD4, LD5,
Wavelengths of 395 nm and 396 emitted from LD6, LD7 and LD8
nm, 397 nm, 398 nm, 399 nm, 400 nm, 401 n
m, 402 nm laser beam B1, B2, B3, B
4, B5, B6, B7, and B8 are multiplexed into one beam and output from the parallel plate prism 21.

Hereinafter, the light use efficiency in this embodiment will be described in detail. Narrow bandpass filter F
Since the characteristics of 2 to 8 are as described above, the wavelength is 402 nm.
With respect to the laser beam B8, the transmittance of the narrow bandpass filter F8 at a wavelength of 402 nm of 90% is
The output after multiplexing is 50 mW × 0.9. For the laser beam B7 having a wavelength of 401 nm, the transmittance of the narrow-band bandpass filter F7 for the wavelength of 401 nm is 90%, and
Based on the reflectance of 98% for the wavelength of 401 nm of the narrow band-pass filter F8, the output after multiplexing is 50 mW × 0.9 × 0.98.
Becomes Further, with respect to the laser beam B6 having a wavelength of 400 nm, the wavelength 400 nm of the narrow band-pass filter F6 is used.
The output after multiplexing is 50 mW × 0.9 × (0.98) ² , based on a transmittance of 90% for the wavelength band and a reflectance of 98% for the wavelength of 400 nm of the narrow band pass filters F7 and F8.

Since the same applies hereinafter, the output of the combined laser beam B is 50 mW × 0.9 + 50 mW × 0.9 × 0.98 + 50 mW × 0.9 × (0.98) ² +50 mW × 0.9 × (0.98) ³ +50 mW × 0.9 × (0.98) ) ⁴ +50 mW × 0.9 × (0.98) ⁵ +50 mW × 0.9 × (0.98) ⁶ +50 mW × (0.98) ⁷ ≒ 340 mW Since 50 mW × 8 = 400 mW, the light use efficiency in this case is about 85%. As described above, in this embodiment, a high-output wavelength-multiplexed laser beam B can be obtained with extremely high light use efficiency.

Further, since this ultraviolet laser light source does not perform wavelength conversion using an expensive optical wavelength conversion element, the cost is lower than that of a conventional apparatus that obtains a laser beam in the ultraviolet region with such a configuration. Can be manufactured.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 3, elements that are the same as the elements in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted unless otherwise necessary (the same applies hereinafter).

The ultraviolet laser light source of the second embodiment is
Compared with the one shown in FIG. 1, a condensing lens 10 for condensing the combined laser beam B on a wavelength-locking band-pass filter 11 described later, and a condensing laser beam B
Wavelength band-pass filter 11 in the optical path
And a narrow band pass filter F1 is provided. Narrow band pass filter F1
Is formed so that light having a wavelength of 395 nm is transmitted at a transmittance of 90%, and light having other wavelengths is reflected at a reflectance of 98%.

A wavelength-locking band-pass filter 11 is also provided.
Has a spectral transmittance characteristic shown in FIG.
The transmittance for light of 5 to 402 nm is 90%, and the reflectance is 10%. By providing such a filter 11, the laser beams B1, B2, B
10% of each of B3, B4, B5, B6, B7 and B8 is reflected on the parallel plate prism 21 side, and each of the narrowband bandpass filters F1, F2, F3, F4, F5, F6 and F7.
GaN-based semiconductor laser LD
1, LD2, LD3, LD4, LD5, LD6, LD
7. Returned to LD8.

By performing such a so-called optical feedback, the GaN-based semiconductor lasers LD 1 and L
D2, LD3, LD4, LD5, LD6, LD7, LD
8 are narrow band pass filters F1, F2, F3, F4, F5, F6, F7 and F8, respectively.
Peak wavelength of 395 nm, 396 nm, 397 n
Locked to m, 398 nm, 399 nm, 400 nm, 401 nm, 402 nm. Here, the condenser lens 10 is inserted to efficiently and stably return the feedback light from the wavelength-locking bandpass filter 11.

Thus, the GaN semiconductor lasers LD1 to LD1
By locking the oscillation wavelength of 8, when this ultraviolet laser light source is used, for example, as a light source for stereolithography or a printing system described above, it is possible to prevent a change in coupling efficiency due to a wavelength change of the laser beams B1 to B8. , Very preferred.

The light use efficiency of the present embodiment is lower than that of about 85% in the first embodiment by the insertion of the band-pass filter 11 having a transmittance of 90%, and is about 76.5%.
Becomes Therefore, in this case, the output of each of the GaN-based semiconductor lasers LD1 to LD8 is 50 m, as in the first embodiment.
If W, the output of the combined laser beam B is 306 m
W. If the output of each of the GaN-based semiconductor lasers LD1 to LD8 is 100 mW, the output of the combined laser beam B is 612 mW.

Next, a third embodiment of the present invention will be described with reference to FIG. The ultraviolet laser light source according to the third embodiment is different from that shown in FIG. 1 in that a condensing lens 30 for condensing the combined laser beam B and a condensed laser beam B are combined. And a multi-mode optical fiber 31 arranged in the first embodiment.

The laser beam B can be focused by the condenser lens 30 to a spot of about 2 μm. In contrast, the diameter of the core 31a of the multimode optical fiber 31 covered by the cladding 31b is, for example, 50 μm in diameter.
It is. As described above, if the diameter of the core 31a is sufficiently large with respect to the convergent spot diameter of the laser beam B,
Even if the positioning accuracy of the GaN-based semiconductor lasers LD1 to LD8 is relatively low and the environmental temperature and the like change, the laser beam B can be easily incident on the core 31a. Therefore, a stable output can be obtained by suppressing an output change when an environmental change occurs.

When an ultraviolet laser beam having a single mode characteristic is desired to be obtained, a single mode optical fiber may be used instead of the multimode optical fiber 31. By doing so, a low-cost, long-life coherent ultraviolet laser light source can be obtained.

The GaN semiconductor lasers LD1 to LD8
It is also possible to apply a high output broad area laser. For example, when a broad area laser having a 1 W output is used, assuming that the light use efficiency is about 85% as in the first embodiment, 6.8 W (= 1 W × 8 × 0.85)
Ultra-high-power ultraviolet laser light can be emitted from the optical fiber 31.

The ultraviolet laser light source of the third embodiment described above also employs the wavelength lock configuration including the filter 11 shown in FIG. 3 to lock the oscillation wavelength of the GaN semiconductor lasers LD1 to LD8. It is possible.

Further, for such a wavelength lock, a configuration shown in FIG. 6 can be adopted. This figure 6
Is disclosed, for example, in Japanese Patent Application No. 2000-196 filed by the present applicant.
No. 166, a waveguide type wavelength selecting element 41 is directly coupled to a GaN type semiconductor laser 40, and the GaN type semiconductor laser
It locks 40 oscillation wavelengths.

The GaN-based semiconductor laser 40 has an oscillation wavelength of, for example, 400 nm, and the rear end face has a wavelength of 400 nm.
A HR (high reflection) coat 42 having a reflectivity of 95% is applied to the front end face, that is, the end face of the side directly coupled to the waveguide type wavelength selecting element 41, with a reflectivity of 5% for a wavelength of 400 nm. % LR (low reflection) coat 43 is applied.

On the other hand, in the waveguide type wavelength selecting element 41, a channel type optical waveguide 45 is formed on a substrate 44 made of, for example, quartz, and a grating (diffraction grating) 46 which repeats in the optical waveguide 45 along the waveguide direction. Are formed. Then, AR (non-reflection) coatings 47 and 48 having a reflectance of 0.5% or less, preferably about 0.1% with respect to a wavelength of 400 nm are applied to both end faces of the wavelength selecting element 41, respectively.

The period Λg of the grating 46 is set such that 波長 g = qλ / 2n _eff , where λ is the wavelength of the guided light and n _eff is the effective refractive index of the optical waveguide.
Here, q is the grating order, and q = 1, λ = 400
If nm, n _eff = 1.5, 1.5g = 0.133 μm.

In this configuration, a part of the laser beam 49 emitted forward from the GaN-based semiconductor laser 40, that is, toward the waveguide-type wavelength selection element 41, is reflected and diffracted by the grating 46 and fed back to the GaN-based semiconductor laser 40. . At this time, the wavelength of the light to be reflected and diffracted is selected to be 400 nm in accordance with the grating period Λg.
The oscillation wavelength of the system semiconductor laser 40 is locked at 400 nm.

The grating 46 is designed to reflect and diffract the incident laser beam 49 by about 5%. The element length of the waveguide-type wavelength selection element 41 is set as short as possible to about 1 to 3 mm in order to suppress the waveguide loss. As described above, it is possible to lock the wavelength while avoiding a large loss of the laser beam 49 by the waveguide type wavelength selection element 41, and to extract the high-power laser beam 49.

The grating order q is not limited to the above-described first order, and a higher-order period such as the third order may be applied.
In this case, the loss due to the radiation mode from the grating 46 slightly increases, but since only the wavelength lock is performed, the coupling coefficient of the grating 46 may be relatively small, and by doing so, the loss due to this radiation mode is also reduced. It can be kept low.

It is desirable that the mode field diameters of the laser beam 49 in the GaN-based semiconductor laser 40 and the waveguide-type wavelength selection element 41 be substantially equal to each other. In such a case, the mode matching between the two is satisfactorily performed, and a sufficient amount of feedback light can be secured.

In the multiplexing method of the first to third embodiments described above, since the laser beam can be multiplexed on the same optical axis, the multiplexed beam is coupled not only to the multimode optical fiber but also to the single mode optical fiber. Can be done. On the other hand, in the multiplexing method in which a plurality of laser beams are converged on the end face of one optical fiber and multiplexed in the optical fiber, the multiplexed beam can be combined only with the multi-mode optical fiber.

When the multiplexing method of the first to third embodiments is compared with the multiplexing method in which a plurality of laser beams are converged on the end face of one optical fiber, the former is convergent spot of the multiplexed beam. The diameter can be made smaller. Therefore, when combining a multiplexed beam with an optical fiber, the former multiplexing method is more tolerant of positional deviation between the two, and a stable output with respect to environmental changes can be obtained.

In the multiplexing method according to the first to third embodiments, when a multiplexed beam is combined with an optical fiber, the number of multiplexed beams is the same as in the multiplexing method in which a plurality of laser beams are converged on the end face of one optical fiber. Is not limited by the NA of the optical fiber. Therefore, the multiplexing system of the first to third embodiments can increase the number of multiplexing, and can obtain a multiplexed beam with higher output.

[Brief description of the drawings]

FIG. 1 is a plan view showing an ultraviolet laser light source according to a first embodiment of the present invention.

FIG. 2 is a graph showing transmittance characteristics of a narrow band pass filter constituting the ultraviolet laser light source.

FIG. 3 is a plan view showing an ultraviolet laser light source according to a second embodiment of the present invention.

FIG. 4 is a graph showing transmittance characteristics of a wavelength-locking bandpass filter constituting the ultraviolet laser light source of FIG. 3;

FIG. 5 is a plan view showing an ultraviolet laser light source according to a third embodiment of the present invention.

FIG. 6 is a schematic plan view showing a GaN-based semiconductor laser with a wavelength locking function used in the ultraviolet laser light source of the present invention.

[Explanation of symbols]

 10 Condensing Lens 11 Wavelength Locking Bandpass Filter 20 Combining Optical System 21 Parallel Plate Prism 30 Condensing Lens 31 Multimode Optical Fiber 40 GaN-Based Semiconductor Laser 41 Waveguide-Type Wavelength Selector 49 Laser Beam B1-8 Laser Beam B Waved laser beam C1-8 Collimator lens F1-8 Narrow bandpass filter LD1-8 GaN semiconductor laser

Claims (6)

[Claims] 1. An ultraviolet laser light source comprising: a plurality of GaN-based semiconductor lasers that emit an ultraviolet laser beam; and a multiplexing optical system that multiplexes laser beams emitted from these GaN-based semiconductor lasers. 2. The ultraviolet laser light source according to claim 1, wherein the plurality of GaN-based semiconductor lasers emit laser beams having different wavelengths. 3. An ultraviolet light according to claim 2, wherein each of the plurality of GaN-based semiconductor lasers is provided with a means for returning the emitted light to the semiconductor laser and locking the oscillation wavelength. Laser light source. 4. The ultraviolet laser light source according to claim 3, wherein said means for locking the oscillation wavelength comprises a waveguide type wavelength selecting element having a reflection diffraction grating at a portion of the optical waveguide. 5. The multiplexing optical system is provided in correspondence with each of the plurality of GaN-based semiconductor lasers, and a laser beam emitted from a corresponding semiconductor laser is transmitted well and emitted from another semiconductor laser. The ultraviolet laser light source according to any one of claims 1 to 4, wherein the ultraviolet light source comprises a band-pass filter that reflects the laser beam well and combines the laser beams. 6. A means for partially reflecting a laser beam multiplexed by the multiplexing optical system, returning the laser beam to each semiconductor laser through the band-pass filter, and locking an oscillation wavelength thereof. Claim 5
The ultraviolet laser light source as described.