JPH04296731A - Short-wavelength laser beam source - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short wavelength laser light source used in the field of optical information processing using coherent light or in the field of optical measurement and control.

0002

2. Description of the Related Art FIG. 8 shows a configuration diagram of a conventional short wavelength laser light source. 20 is a semiconductor laser with a wavelength band of 800 nm, 2
5 is an optical wavelength conversion element, and 30 is a lens. In the optical wavelength conversion element 25, an optical waveguide 2 is formed on a LiNbO3 substrate 1, and a layer 3 whose polarization is periodically inverted (poling inversion layer) is further formed on the optical waveguide 2, so as to have a periodic polarization inversion structure. . By compensating for the mismatch between the propagation constants of the fundamental wave and the generated harmonics with the periodic structure of the polarization inversion layer 3, harmonics can be generated with high efficiency. When the fundamental wave P1 of the light P1 emitted from the semiconductor laser 20 is incident on the entrance surface 10 of the optical waveguide 2 through the lens 30, a harmonic wave P3 is efficiently generated from the optical waveguide 2, and the element operates as an optical wavelength conversion element. Such conventional optical wavelength conversion elements have a periodic polarization inversion structure as a basic component. (Nikkei New Material,
(Refer to August 20, 1990, page 65) This optical wavelength conversion element converts a fundamental wave P1 with a wavelength of 0.8 μm into a harmonic P3 when the length of the optical waveguide is 1 mm and the power of the fundamental wave P1 is 1 mW. A power of 0.5 nW was obtained. If the fundamental wave is incident at 40 mW, the element length is 10 mm and the
A harmonic output of μW is possible. In this case, the conversion efficiency per 1 W in a 10 mm element is 5%/W·cm. Furthermore, when KTP (KTiOPO4) was used in a similar configuration, an output of 2 mW was obtained with an input of 80 mW.

Next, a short wavelength laser light source, which is a second conventional example, will be explained. FIG. 9 shows its configuration diagram. This short wavelength laser light source includes a semiconductor laser 20 and a solid laser crystal 21.
and a light wavelength conversion element 25 made of KNbO3, which is a nonlinear optical crystal. (Refer to Nikkei New Materials, August 20, 1990, page 32) Light P1 emitted from the semiconductor laser 20 is focused by a lens 30 to excite YAG 21, which is a solid laser crystal. 22 is a total reflection mirror that totally reflects 99% of the light with a wavelength of 947 nm.
Light in the 00 nm band is transmitted. Further, 23 is also a total reflection mirror, which totally reflects 99% of light with a wavelength of 947 nm and transmits light with a wavelength of 400 nm. This causes 947 nm oscillation. By inserting the optical wavelength conversion element 25 into the resonator formed by the total reflection mirrors 22 and 23, the harmonic output is increased. This is because the power inside the resonator reaches 1 W or more, so conversion into harmonics increases. A harmonic of 1 mW was obtained from a 500 mW semiconductor laser.

0004

[Problem to be solved by the invention] In a short wavelength laser light source that combines an optical wavelength conversion element based on a polarization inversion layer and a semiconductor laser as described above, the tolerance of the optical wavelength conversion element to the wavelength of the fundamental wave from the semiconductor laser is For example, when the element length is 5 mm, the tolerance to the laser wavelength is narrow and the half width is only 0.4 nm. Therefore, when an optical wavelength conversion element and a semiconductor laser are combined, there is a problem that the semiconductor laser fluctuates in wavelength due to temperature changes, and harmonics are no longer produced, or the harmonic output fluctuates significantly. Specifically, when the temperature of a semiconductor laser changes by 1° C., the wavelength changes by 0.3 nm, so a problem arises in that a change of 2° C. causes the output to stop. In addition, the usable semiconductor laser is limited to a single stripe having an active layer with a width of 8 μm or less, since it is necessary to condense light on the submicron order when coupling with an optical waveguide is considered. Therefore, there was a problem in that only semiconductor lasers with a maximum output of about 100 mW could be used.

On the other hand, in a short wavelength laser light source using KNbO3 as an internal resonator, the temperature tolerance of KNbO3 is 0.
It was difficult to put it into practical use because it was small at 2°C and required ultra-precise temperature control. Further, since the length of the resonator is 1 cm or more and a longitudinal mode is established, the conversion efficiency of the optical wavelength conversion element changes and noise is generated, which is another problem.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a semiconductor laser, a solid-state laser crystal, an optical wavelength conversion element formed of a nonlinear optical crystal, and a semiconductor laser and a solid-state laser crystal. A first total reflection mirror installed between the solid-state laser crystal and a second total reflection mirror installed on the fundamental light emission side with respect to the solid-state laser crystal, and the optical wavelength conversion element has periodic polarization. The short wavelength laser light source is characterized in that an inverted structure is formed, the wavelength of fundamental light from the solid-state laser is converted, and harmonics are output. .

[0007]

[Operation] According to the short wavelength laser light source of the present invention, by interposing the solid-state laser crystal between the semiconductor laser and the optical wavelength conversion element, even if the wavelength of the semiconductor laser changes, the oscillation wavelength of the solid-state laser crystal changes. The maximum harmonic output is therefore obtained. Further, the semiconductor laser used can be a multi-stripe type or a wide stripe type with an active layer of 100 μm or more, and a maximum excitation power of 1 W can be used. Therefore, the fundamental wave from the solid-state laser crystal can be used up to about 250 mW, and the conversion efficiency to harmonics can be greatly increased.

Furthermore, since the short wavelength laser light source of the present invention is based on an optical wavelength conversion element having a polarization inversion structure, it has a wide tolerance with respect to temperature, and can be produced for practical use by simple temperature control.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As one of the embodiments, the structure of a short wavelength laser light source of the present invention will be explained with reference to the drawings. First, FIG. 1 shows a structural diagram of a first embodiment of a short wavelength laser light source according to the present invention. In Figure 1, 1 is a -Z board (a board cut out perpendicular to the Z axis).
side) LiTaO3 substrate, 2 is a formed optical waveguide, 3
10 is a polarization inversion layer, 10 is an entrance part for the fundamental wave P2, and 12 is an output part for the harmonic wave P3.

The operation will be described below. Semiconductor laser 2
The light P1 emitted from the laser beam P1 is focused by the lens 30 and excites the YAG 21, which is a solid laser crystal. 947 for YAG21
A total reflection mirror 22 that reflects 99% of nm light and a total reflection mirror 23 that also reflects 97% are formed, and a laser oscillates at a wavelength of 947 nm, and a fundamental wave P2 is emitted from the total reflection mirror 23 side. The fundamental wave P2 is the lens 31
The fundamental wave P2 is focused by the optical wavelength conversion element 25 and converted into a harmonic wave P3. In this example, an optical waveguide 2 fabricated using proton exchange in a LiTaO3 substrate 1 is used as an optical wavelength conversion element having a periodic polarization inversion structure in which a periodic structure is formed. The fundamental wave P2 that has entered the optical waveguide 2 is converted into a harmonic wave P3 in a polarization inversion layer having a phase matching length L, and then converted to harmonic power P3 in the next non-polation inversion layer 4, which also has a length L. will increase. The harmonic wave P3 whose power has been increased in the optical waveguide 2 in this manner is radiated from the output section 12.

Next, a method for manufacturing the optical wavelength conversion element 25 will be briefly explained using the drawings. In Figure 2(a), first L
Ta6a is patterned on the iTaO3 substrate 1 using a normal photo process and dry etching. Next, in the same figure (b), 2
Perform proton exchange at 60°C for 50 minutes. Then the same figure (c)
A heat treatment is performed at 580° C. for 5 minutes to form a polarization inversion layer 3 with a thickness of 2.7 μm on the proton exchange layer 5. The proton exchange layer 5 has a reduced Li content compared to the substrate 1, and its Curie temperature is lowered. Therefore, by heat treatment at 580°C, which is higher than the Curie temperature of the proton exchange layer 5 and lower than the Curie temperature of the substrate, polarization can be partially inverted. can. The length L of the polarization inversion layer 3 is 2.7 μm. Then HF:HNF3 1:1
Etching was performed for 20 minutes using the mixed solution to remove Ta6a. Next, as shown in FIG. 3(d), an optical waveguide 2 is formed in the polarization inversion layer 3 using proton exchange. After patterning Ta into stripes as a mask for the optical waveguide 2,
Proton exchange was performed at 260° C. for 16 minutes using a mask in which a slit of 6 μm in width and 10 mm in length was formed. Next, after removing the mask, annealing was performed at 380° C. for 10 minutes. The region directly under the slit of the protective mask where protons have been exchanged becomes a high refractive index layer 2 whose refractive index has increased by about 0.01. The light propagates through the high refractive index layer 2, which becomes the optical waveguide 2. The thickness d of this optical waveguide 2 is 2 μm, which is smaller than the thickness 2.7 μm of the polarization inversion layer 3, and the wavelength of the guided light is effectively converted. The period Λ of the polarization inversion layer 3 is 5.5 μm, and it operates at a wavelength of 947 nm. A surface perpendicular to the optical waveguide 2 was optically polished to form an input section 10 and an output section 12. In this way, the optical wavelength conversion element 25 shown in FIG.
can be manufactured.

[0012] Furthermore, the length of this element is 10 mm. In Fig. 1, when a fundamental wave P2 with a wavelength of 947 nm is guided from the input section 10, single mode propagation occurs, and the wavelength is 473 nm.
The harmonic P3 of nm was taken out from the output section 12 to the outside of the substrate. The propagation loss of the optical waveguide 2 was as small as 1 dB/cm, and the harmonic P3 was effectively extracted. The output light P1 of the semiconductor laser 20 was 400 mW, and the YAG 21 generated 80 mW of light with a wavelength of 947 nm. When the fundamental wave P2 was inputted at 40 mW, a harmonic wave P3 of 2 mW was obtained. The conversion efficiency in this case is 5%. Further, the output light P1 of the semiconductor laser 20 is 1
When the power is W, a fundamental wave P2 of 250 mW is obtained. 120 mW was incident on the optical waveguide 2 of the optical wavelength conversion element 25. The generated harmonic P2 was 20 mW. The wavelength tolerance of the optical wavelength conversion element is 0.4 nm. Wavelength is 0.4n
Even with a shift of m, the oscillation wavelength of the solid-state laser remained constant, and the harmonic output was stable.

FIG. 3 shows a comparison of the temperature characteristics of the optical wavelength conversion element of the conventional short wavelength laser light source using KNbO3 and the short wavelength laser light source of the present invention. The optical wavelength conversion element used in the conventional short wavelength laser light source has a permissible half width of only 0.2°C with respect to temperature, whereas the optical wavelength conversion element used in the short wavelength laser light source of the present invention has a permissible half width of only 0.2°C. The temperature is significantly wider at 4.5°C, and harmonic output can be stabilized over a wide temperature range by simple temperature control. Furthermore, LiTaO3, which is the nonlinear optical crystal used in the present invention, has the characteristics that large crystals are available and it is easy to mass-produce optical wavelength conversion elements using an optical IC process. The stability of harmonic output has been greatly improved compared to conventional optical wavelength conversion elements, making it more practical. The semiconductor laser was able to stably obtain harmonic output even when the environmental temperature changed by about 20°C. In contrast to the fundamental wave, in multimode propagation, the output of harmonics is unstable and is not practical, so single mode is effective.

Next, a second embodiment of the short wavelength laser light source of the present invention will be described. FIG. 4 shows a configuration diagram of a short wavelength laser light source according to the second embodiment. The short wavelength laser light source of this embodiment basically consists of a semiconductor laser 20 and an optical wavelength conversion element 25. The light P1 emitted from the semiconductor laser 20 is Y
Excite AG21. The fundamental wave P2 thus obtained is introduced into the optical wavelength conversion element 25 and converted into a harmonic wave P3. In this embodiment, a polarization inversion structure having polarization inversion layers 3 periodically formed over the entire surface of the LiTaO3 substrate. 947
The operating point is 55° C. at a wavelength of nm. Since a heater is used, the operating point must be set on the high temperature side relative to room temperature.
Considering the case where the room temperature rises to 40°C, a temperature of 50°C or higher is particularly desirable. The optical wavelength conversion element is placed between the total reflection mirrors 22 and 23 and has high internal power, so it can convert with high efficiency. Even when the wavelength of the semiconductor laser changes, the oscillation wavelength of the solid-state laser remains constant, and the harmonic output of the optical wavelength conversion element 22 is stabilized. The conversion efficiency to harmonics is 4 for light P1
It was 2% of 0 mW, and the output was also very stable over a range of about 30°C.

A third embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows a configuration diagram of a short wavelength laser light source according to an embodiment. Light P1 emitted from the semiconductor laser 20 with a wavelength of 806 nm is focused by the lens 30 and enters the optical wavelength conversion element 25. The material of the optical wavelength conversion element 25 is LiTaO3 doped with Nd, which is a rare earth element, and a polarization inversion structure with a period Λ5.6 μm is formed. The amount of Nd doped is 1m
It is ol/%. 22 is a total reflection mirror with a wavelength of 947 nm.
It completely reflects 99% of the light and transmits light in the 800 nm band. In addition, 23 is a total reflection mirror that absorbs 99% of the light with a wavelength of 947 nm.
It undergoes total reflection and transmits light in the 400 nm band. Nd is excited by the semiconductor laser 20 and oscillates at a wavelength of 947 nm, and is further converted into a harmonic P3 by the periodic polarization inversion structure and emitted to the outside. When the light P1 was 200 mW, harmonics of 10 mW were obtained. The length of the short wavelength laser light source in this embodiment is 20 mm, and it can be made very compact by doping the optical wavelength conversion element with a rare earth element.

In the example, Li was used as the nonlinear optical crystal.
NbO3, LiTaO3 were used, but KNbO3, KTP
It is also applicable to ferroelectric materials such as ferroelectric materials, organic materials such as MNA, and materials doped with rare earth elements. Also,
As rare earth elements, not only Nd used in the embodiment but also Er and Tl are promising.

Next, a fourth embodiment of the short wavelength laser light source of the present invention will be described. The configuration of the optical wavelength conversion element is the same as in the second embodiment. In this example, instead of the LiTaO3 substrate, L
iNbO3 was used as a substrate. A LiNbO3 substrate is characterized by high nonlinearity. The period of polarization reversal is 3
μm, and the element length is 7 mm. The conversion efficiency in this example is 10% at 200 mW input. There was no optical damage and the harmonic output was very stable.

Finally, a fifth embodiment of the present invention will be explained. In this embodiment, a modulation function is added to the short wavelength laser light source. FIG. 6 shows a configuration diagram of the short wavelength laser light source of this embodiment. The configuration is similar to that of Example 1, and in addition, a modulation electrode made of an Al film is formed above the optical waveguide 2 of the optical wavelength conversion element 25. In the conventional optical wavelength conversion element using KNbO3, when a modulated electrical signal enters the semiconductor laser 20 as shown in FIG. 7(a), the light P1 from the semiconductor laser 20 is similarly modulated and output. However, when it enters YAG21, which is a solid-state laser crystal, the response time of YAG21 is on the order of μS, so the fundamental wave P2
It becomes difficult to modulate the MHZ order. Therefore KNb
The harmonic P3 converted from O3 also becomes unmodulated light in a constant state. In contrast, in this embodiment, by applying a modulated electrical signal to the modulating electrode 28, it is possible to extract a harmonic P3 modulated with respect to a constant fundamental wave P2. This utilizes the electro-optic effect of LiTaO3 by applying an electric field to an optical wavelength conversion element made of LiTaO3 to change the refractive index of the optical waveguide 2 and deviate from the phase matching condition. As shown in FIG. 7(b), the same modulated harmonic output as the electrical signal could be generated. This method is particularly effective since the modulation frequency of the semiconductor laser 20 is up to 1 GHz, but can be up to about 20 GHz.

Note that the YAG crystal also has an oscillation wavelength of 1064 nm, and the generation of green light (532 nm) according to the present invention is also effective. Furthermore, although YAG was used as the solid-state laser crystal, other crystals such as YLF and YVO4 are also effective.

[0020]

[Effects of the Invention] As explained above, according to the short wavelength laser light source of the present invention, by stabilizing the wavelength fluctuation of the semiconductor laser using a solid-state laser, the output can be significantly increased compared to the conventional short wavelength laser light source. Stabilization can be achieved. Further, a multi-stripe or wide-stripe high-output semiconductor laser can be used, and high-output harmonics can be obtained.

Furthermore, according to the short wavelength laser light source of the present invention, the temperature characteristics can be significantly improved compared to the conventional short wavelength laser light source using KNbO3. Furthermore, an electrode can be provided on the optical wavelength conversion element to provide a modulation function.

As described above, the short wavelength laser light source of the present invention can provide practical output and temperature characteristics, and its effects are extremely large.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a first embodiment of a short wavelength laser light source of the present invention.

FIG. 2 is a manufacturing process diagram of the optical wavelength conversion element in the short wavelength laser light source of the present invention.

FIG. 3 is a characteristic diagram showing the temperature characteristics of a conventional short wavelength laser light source and an optical wavelength conversion element used in the short wavelength laser light source of the present invention.

FIG. 4 is a configuration diagram of a short wavelength laser light source according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a short wavelength laser light source according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a short wavelength laser light source according to a fifth embodiment of the present invention.

FIG. 7 is a modulation curve diagram of a short wavelength laser light source according to the present invention and a conventional example.

FIG. 8 is a configuration diagram of a conventional short wavelength laser light source.

FIG. 9 is a configuration diagram of a second conventional short wavelength laser light source.

[Explanation of symbols]

1 LiTaO3 substrate 2 Optical waveguide 3 Polarization inversion layer 20 Semiconductor laser 21 Solid state laser crystal 25 Optical wavelength conversion element P1 Light P2 Fundamental wave P3 harmonic

Claims (6)

[Claims] [Claim 1] A semiconductor laser, a solid-state laser crystal,
an optical wavelength conversion element formed of a nonlinear optical crystal; and a first optical wavelength conversion element installed between the semiconductor laser and the solid-state laser crystal.
and a second total reflection mirror installed on the fundamental wave emission side with respect to the solid-state laser crystal, a periodic polarization inversion structure is formed in the optical wavelength conversion element, and the solid-state laser A short wavelength laser light source that converts the wavelength of the fundamental wave from the source and outputs harmonics. 2. A claim characterized in that the first reflecting mirror is formed on the laser beam incident side surface of the solid laser crystal, and the second reflecting mirror is formed on the laser beam output side surface of the solid laser crystal. Item 1. Short wavelength laser light source. 3. The short wavelength laser light source according to claim 1, wherein an optical wavelength conversion element formed of a nonlinear optical crystal doped with rare earth elements is used. 4. The short wavelength laser light source according to claim 1, wherein an optical waveguide is formed in the nonlinear optical element crystal. 5. The nonlinear optical crystal is LiNbxTa1-
The short wavelength laser light source according to claim 1 or 2, which is an xO3 (0≦X≦1) substrate. 6. The short wavelength laser light source according to claim 1, wherein the solid laser crystal is YAG.