JPH0479279A - Laser light generator - Google Patents

Abstract

PURPOSE:To have a small change in wave length by building an optical resonator of semiconductor laser as if only light of a first wave length were resonated within the scope of the optical gain distribution of the semiconductor laser. CONSTITUTION:On an n-type GaAs substrate 1, an Al-5Ga-5As clad layer 2, a quantum well-structured active layer 3 and a p-type Al-5Ga--5As clad layer 4 are deposited in this order. Next the periodic unevenness 10 is formed on the p-type Al-3Ga-7As clad layer 4. After that, a p-type Al-5Ga-5As layer 5 and an n-type GaAs layer 6 are deposited. Then, an SiO2 film is formed and three pieces of stripe patterns are so formed that they may cross the unevenness 10 at right angles. After Zn is diffused in the n-type GaAs layer 6 using the SiO2 film as a mask, a Cr/Au electrode 8 is formed on the front surface while an AuGaNi/Cr/Au electrode 9 is formed on the rear surface of the lamination. Then, end faces that cross a plurality of the stripe patterns at right angles are removed to turn the lamination into an optical resonator. After that, SiO2 coating films 11, 12 are formed alternately on the end face of each stripe pattern to convert light of 180-degree phase to light of zero-degree phase. By this method, a reduced-size and high-output device is manufactured without any necessity of temperature control, etc.

Description

[Detailed description of the invention]

rIndustrial Application Fields The present invention relates to a laser light generation device, more specifically, a device that excites a solid-state laser using a semiconductor laser as an excitation light source to generate laser light with a stable output light wavelength and a narrow spectral width. , particularly regarding the configuration of a semiconductor laser section.

[Conventional technology] Conventionally, as a device that generates a single mode laser beam,
A semiconductor laser as shown in FIG. 6, which uses a high-output broad-area semiconductor laser 23 as an excitation light source in a solid-state laser composed of an optical resonator consisting of a YAG crystal 15, a selective reflection film 16, and a mirror 17. Pumped solid-state lasers are known (for example, "Yamaro et al.: Proceedings of the 50th Japan Society of Applied Physics Conference, p. 854"). Specifically, light with a wavelength of 807 nm from the semiconductor laser 23 is supplied to the YAG crystal 15 through the lens 25 to pump the YAG laser. A selective reflection film 16 is provided on the end face of the YAG crystal 15 so as to transmit only light with a wavelength of 807 nm and reflect light with a wavelength of 11060 nm, which is the oscillation wavelength of the YAG laser.
The light from the semiconductor laser is introduced into the YAG crystal 15, and the YAG
The crystal 15 is excited with light. As a result, the laser oscillation requirements of the negative temperature state of the YAG crystal and the optical resonator are satisfied, and laser light with a wavelength of 11060n is obtained. Semiconductor laser-pumped solid-state lasers have the advantage of producing high-output, single-mode laser light with a narrow spectral linewidth using a small device. [Problems to be Solved by the Invention] The semiconductor laser-excited solid-state laser of the above-mentioned prior art uses YAG
The linewidth of the absorption spectrum of the crystal 15 is narrower than the wavelength variation width due to temperature fluctuations of the semiconductor laser, and it was necessary to control the wavelength within a certain range by controlling the temperature of the semiconductor laser using a Peltier device 24 or the like. . However, when a higher output laser is required, such as when obtaining second harmonics by irradiating optical nonlinear materials with laser light from this semiconductor laser-excited solid-state laser, the increased power consumption of the Peltier element reduces the cooling efficiency. This leads to a decrease in the output power, and we are reaching the limit of high output. Furthermore, the installation of the Peltier element 24 makes the device complicated and expensive, which is a major problem. Therefore, an object of the present invention is to realize a laser light generation device that uses a semiconductor laser as an excitation light source, which has little wavelength fluctuation and has high output, without performing temperature control of the semiconductor laser. Means for Solving the Problems In order to achieve the above object, the present invention configures an optical resonator of a semiconductor laser to resonate only at a specific wavelength within the optical gain spectrum of the semiconductor laser. As a means for realizing the above optical resonator, (1) the above semiconductor laser is a distributed feedback semiconductor laser,
In other words, it is a phase-locked array structure in which a plurality of stripes are provided at a distance sufficient for optical coupling on the upper part of the active layer of a semiconductor laser, which has a diffraction grating that causes Bragg reflection due to periodic fluctuations in the refractive index near the active layer. By using Bragg reflection caused by the above-mentioned periodic fluctuation of the refractive index, only light of a specific wavelength is selectively resonated. (2) A reflective surface that reflects light is provided on the semiconductor laser at a certain distance from the light emitting end facet of the semiconductor laser, and the distance between the reflective surface and the semiconductor laser is such that only the light of the first wavelength resonates. In the case of (1) semiconductor laser described above, the phase difference of each emitted light is set to 0 phase in each light emitting part corresponding to the plurality of stripe patterns described above. Phase correction is performed by providing a transparent thin film with a thickness of

[Effect]

According to the present invention, laser wavelength control of a semiconductor laser is performed by
This is done automatically, solely due to the structure of the resonator itself. As a specific means of wavelength control, firstly, by providing a stripe mechanism with periodic refractive index fluctuations corresponding to a specific wavelength inside the semiconductor laser resonator, the laser resonator resonates only with light of a specific wavelength. did. In this case, the stripe structure of the semiconductor laser is required to oscillate in a single longitudinal mode, so a phase-locked array structure is used. Due to Bragg reflection caused by periodic refractive index fluctuations, strong optical feedback occurs only for light of a specific wavelength, and only light of this wavelength oscillates as a laser regardless of the temperature of the element. Furthermore, when a transparent thin film for phase correction is provided on the light emitting surface of the semiconductor laser, it is possible to obtain light with a good O-shifted phase from a phase-locked array laser, which normally has difficulty in O-shifted phase oscillation. In this example, a resonator is formed by Bragg reflection due to periodic refractive index fluctuations, so a high-quality laser end face like a conventional cleaved semiconductor laser is not required. A transparent thin film for correction can be easily processed using SiO2, and by changing the thickness of this SiO2 for each laser stripe by the thickness corresponding to the wavelength λ, a light component with a 180 degree phase difference can be reduced to around 0 degree. It can be converted into a phase difference and made into a high-output optical signal. Further, a reflective surface that reflects light to the semiconductor laser is provided at a certain distance from the end face of the semiconductor laser in (2) above, and depending on the distance between the reflective surface and the semiconductor laser, only the light of the first wavelength is reflected. In a semiconductor laser that forms a resonator that resonates, when the reflected light from the reflective surface returns to the laser end face, the phase of the return light from the reflective surface is determined by the distance between the reflective surface and the laser end face and the wavelength of the laser. be done. In other words, a resonator is formed only for light with wavelengths in which the phase of the light returning from the reflecting surface to the laser facet is the same as that of the light reflected on the laser facet and strengthens each other, and a resonator is formed only for light with wavelengths where these lights have opposite phases and weaken each other. No resonator is formed for this. The effective refractive index of the reflective surface changes depending on the wavelength as shown in Figure 5.
If the distance between the reflecting surface and the light emitting end facet of the semiconductor laser is set appropriately, only one wavelength within the gain spectrum of the semiconductor laser will satisfy this condition.
It is possible to oscillate only light of a specific wavelength without temperature control. [Examples] Examples of the present invention will be described in detail below. The first is a perspective view showing the structure of a semiconductor laser used in an embodiment of the laser light generating device according to the present invention. The structure of this semiconductor laser will be explained along with the manufacturing method. Al is deposited on the n-type GaAs substrate 1 by the MOCVD method.
, , 5G a-HA s cladding layer 2, quantum well structure active layer 3, p A 1-, Ga-5A s cladding layer 4 are sequentially grown. Next, p-A l-, G a-7
On the As cladding layer 4, (110>
Periodic unevenness (diffraction grating) 10 is formed in the direction. Next, the p-Al-, Ga-, As layer 5 is formed again by the MOCVD method.
and an n-GaAs layer 6. Next, Si
n. A film (not shown) is formed by a normal thermal CVD method, and a three-stripe pattern (phase-locked array structure) is formed on the SiO2 film using photolithography so that it is perpendicular to the periodic unevenness 10. to form. This Sin
After Zn is diffused into the n-GaAs layer 6 using , as a mask, Cr/Au is deposited on the surface of the wafer by vacuum evaporation.
The electrode 8 is made of AuGaNi/Cr/on the back side.
An Au electrode 9 was formed. Next, as shown in the perspective view of FIG. 2, this wafer was subjected to reactive ion beam etching to remove the edge portion perpendicular to the plurality of Zn-diffused stripe patterns.
An optical resonator having a length of about 400 μm in the X direction was formed. Next, in order to convert the 180-degree shifted phase emitted from the laser of the phase-locked array structure into an O-shifted phase, a 450 nm thick
11 and 150 nm 12 SiO,:I-ting films were alternately formed on the end faces of each stripe. That is, since the phases of the lights of the light emitting parts of each of the plurality of stripe patterns have a phase difference of 180 degrees from each other, in order to eliminate this phase difference, the central stripe pattern part has a phase difference of 180 degrees.
The thickness is 1/4 wavelength, and the stripe pattern portions on both sides have a thickness of 3/4 wavelength, giving a thickness difference of 1 wavelength. Both of the SiO2 coating films with a thickness of 150 nm and 750 nm act as anti-reflection films for laser light, so this semiconductor laser forms a resonator only by distributed optical feedback due to Bragg reflection from the periodic asperities 10, and It oscillates only at a specific wavelength determined by the period 10. FIG. 3 shows the configuration of an embodiment of a laser light generating device according to the present invention using the semiconductor laser shown in FIGS. 1 and 2 as an excitation light source. Laser light emitted from the semiconductor laser 13 is focused onto a YAG crystal 15 by a lens 14. On the lens side of the YGA crystal 15, 11060n of light emitted from the YGA crystal 15 is emitted.
A selective reflection film 16 is provided to reflect the light. The selective reflection film 16 and the mirror 17 form an optical resonator for 11060n light, and laser oscillation by the YAG crystal 15 is obtained. A KTP crystal 26, which is an optical nonlinear medium, is installed inside the YAG laser resonator, and from this KTP crystal 26, Y
Laser light with a wavelength of 530 nm, which is the first harmonic of the light with a wavelength of 11060 nm of the AG laser, is obtained. FIG. 4 is a diagram showing the structure of another embodiment of the laser light generating device according to the present invention. This embodiment utilizes reflected light from a quartz fiber 19 to a broad area semiconductor laser 18 to
The structure is designed to stabilize the oscillation wavelength. Semiconductor laser 18
The laser light emitted from the semiconductor laser 18 is introduced into a quartz fiber having a core diameter of 100 μm and having an end face located approximately 30 μm from the end face of the semiconductor laser 18 . At this time, coating films of 5 in 220 and 5 i 3 N 421 were provided on opposing end faces of the semiconductor laser 18 and the quartz fiber 19, respectively, so that the reflectance was 7%. As a result, the effective amount of optical feedback of the optical resonator of the semiconductor laser 18 varies as shown in FIG. When the distance between the quartz fiber 19 and the semiconductor laser 18 is about 30 μm, there is only one peak of the optical feedback rate in the gain spectrum range of the semiconductor laser. The distance between quartz fiber 19 and laser 18 is 1 quartz fiber and piezoelectric element 2
By applying a voltage to the piezoelectric element 22, the position of this peak can be precisely controlled. The light incident on the quartz fiber 19 propagates through the fiber for about 30 cm and then enters the YAG crystal 15. The configuration and operation of the YAG crystal 15, selective reflection film 16, and mirror 17 are the same as in the embodiment shown in FIG. In addition, in the above embodiment, YAG by semiconductor laser excitation
Although we have talked about lasers, this also applies to laser light generators that excite other solid-state lasers that require control of the excitation wavelength.
It goes without saying that the same technical idea can be applied, just by using different materials and wavelengths of semiconductor lasers.

【Effect of the invention】

According to the first embodiment of the present invention, which uses a distributed feedback semiconductor laser, it is possible to obtain light with a stable single wavelength and an O-shifted phase. A semiconductor laser pumped YAG laser is obtained. According to the second embodiment of the present invention using a broad-area semiconductor laser, a YAG laser with characteristics comparable to those of the first embodiment can be obtained with a simpler device configuration.

[Brief explanation of the drawing]

1 and 2 are both perspective views showing the structure of a semiconductor laser used in an embodiment of the laser beam generator tube 1 according to the present invention, and FIGS. 3 and 4 are both perspective views showing the structure of a laser beam generator according to the present invention. FIG. 5 is an explanatory diagram of the wavelength selection mechanism of the semiconductor laser of the embodiment shown in FIG. 4; 6th
The figure shows a configuration diagram of a conventional semiconductor laser pumped YAG laser device. Explanation of symbols 1: n GaAs substrate, 2: n-A 1. , Ga, As cladding layer, 3
: Quantum well structure active layer, 4 : p A l 63 Ga 1) 7 A s
Cladding layer, 5: p-A 1. ,G a,,A s
Layer, 13: 15: 17: 19: 21: 23: 25: p-GaAs layer, 7: Zn diffusion layer. A u G e Ni/Cr/A u electrode. CrAu electrode, lO2 periodic unevenness 5in2 coating film, 12:SiO2 coating film. Phase-locked array, 14: Lens, YAG crystal,
16: Selective reflection film. Mirror, 18 nib broad area laser, quartz fiber, 20: SiO2 coating, Si, N4 coating, 22: Piezoelectric element, semiconductor laser, 24: Peltier element. Lens 26: KTP crystal. Representative Patent Attorney Susuki 1) Yuki Tori Figure 3 3-1--v-Buihonshi-Sai +4--Lens +5--YAG spin crystal 6-----Reflection 11X 7 ----Mirror 8-1-Fold area-Syber 19--Quartz fiber' Fig. 4 Quantum well structure occupied layer 2 Fig. Vice length (nrn) Fig. 5 15--YAG Crystal+6----Selective reflection film 17---・Mirror No. 6 FIG.

Claims (8)

[Claims] 1. In the laser light generation device, the laser light generating device includes a solid-state laser that lases light of a second wavelength by absorbing light of the first wavelength, and a semiconductor laser that supplies the light of the first wavelength to the solid-state laser. 1. A laser light generating device, wherein an optical resonator of a semiconductor laser is configured so that only light of the first wavelength is resonated within a range of an optical gain distribution of the semiconductor laser. 2. 2. The laser light generating device according to claim 1, wherein the semiconductor laser is a distributed feedback semiconductor laser having a diffraction grating structure near the active layer. 3. In a second aspect of the present invention, the semiconductor laser has a phase-locked array structure formed of a plurality of stripe patterns provided above the active layer and perpendicular to the diffraction grating and separated from each other by a sufficient distance for optical coupling. A laser beam generator characterized in that it is configured as follows. 4. A third aspect of the present invention is characterized in that a transparent medium having a thickness such that a phase difference of the emitted light generated by the phase-locked array structure is 0 degree phase is disposed near the light emitting surface of the semiconductor laser. Laser light generator. 5. In claim 1, the resonator of the semiconductor laser is provided with a reflective surface that reflects light on the semiconductor laser at a certain distance from the light emitting end face of the semiconductor laser, and the distance between the reflective surface and the semiconductor laser is such that the resonator of the semiconductor laser A laser beam generating device characterized in that it is configured so that only light of a first wavelength resonates. 6. 6. The laser light generating device according to claim 5, wherein the reflective surface is formed by an end face of an optical fiber that guides the emitted light of the semiconductor laser to the solid-state laser. 7. A phase-locked array structure consisting of a plurality of stripe patterns extending parallel to the direction of the emitted light and provided at a distance sufficient for optical coupling on the top of the active layer, and each corresponding to the plurality of stripe patterns. 1. A semiconductor laser comprising a transparent thin film having a thickness such that the phase difference between the respective emitted lights is 0 phase in the light emitting part. 8. 8. The distributed feedback semiconductor laser according to claim 7, further comprising a diffraction grating near the active layer that is orthogonal to the stripe pattern.