JP2910370B2 - Optical wavelength conversion element and short wavelength laser light source using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art FIG. 12 shows a configuration diagram of a conventional optical wavelength conversion element. Hereinafter, generation of a harmonic (wavelength 0.53 μm) with respect to a fundamental wave having a wavelength of 1.06 μm will be described in detail with reference to the drawings.
(EJLim, MMFejer, RLByer and WJKozlovsky,
"Blue light generation by frequency doubling in
periodically-poled lithium niobate channel wavegui
de ", Electronics Letters, Vol.27, P731-732, 1989
Year, see). As shown in FIG. 12, an optical waveguide 2 is formed on a LiNbO ₃ substrate 1, and a layer 3 (a domain-inverted layer) having periodically inverted polarization is formed in the optical waveguide 2. This makes it possible to generate harmonics with high efficiency by compensating for the mismatch between the propagation constants of the fundamental wave P1 and the generated harmonics P2 with the periodic structure of the domain-inverted layer 3 and the non-domain-inverted layer 5.

First, the principle of harmonic amplification will be described with reference to FIG. In the non-polarization inversion element 31 in which the polarization has not been reversed, the polarization inversion layer is not formed, and the polarization inversion direction is one direction. The harmonic output 31a of this non-polarization inversion element
Is merely increasing and decreasing. On the other hand, the output 32a of the domain-inverted wavelength conversion element (primary period) 32 whose polarization is periodically inverted is proportional to the square of the length l of the optical waveguide formed in the element as shown in the figure. As a result, the harmonic output increases.

However, in the polarization reversal, the output of the harmonic wave P2 with respect to the fundamental wave P1 is obtained when quasi-phase matching is established. This quasi-phase matching is established when the period of the domain-inverted layer Λ1 (shown in FIG. 13) is λ / (2
(N2ω-Nω)). Here, Nω is the effective refractive index of the fundamental wave (wavelength λ), and N2ω is the effective refractive index of the harmonic wave (wavelength λ / 2). Such a conventional light wavelength conversion element has a domain-inverted structure as a basic component.

A method for manufacturing this device will be described with reference to FIG. In FIG. 3A, a non-linear optical crystal LiN
A pattern of Ti31 was formed on the bO ₃ substrate 1 by lift-off and vapor deposition with a period of several μm in width. Next, FIG.
Then, a heat treatment was performed at a temperature of about 1100 ° C. to form a domain-inverted layer 3 in which the polarization was inverted in the opposite direction to that of the LiNbO ₃ substrate 1. Next, as shown in FIG. 3 (c), a heat treatment is performed in benzoic acid (200 ° C.) for 20 minutes, followed by annealing at 350 ° C. for 3 hours to perform optical waveguide 2
To form The optical wavelength conversion element manufactured by the above benzoic acid treatment can obtain a power of 940 nW of the harmonic P2 when the length of the optical waveguide is 1 mm and the power of the fundamental wave P1 is 14.7 mW with respect to the fundamental wave P1 having a wavelength of 820 nm. Had been.

[0006]

In an optical wavelength conversion element based on a domain-inverted layer as described above, when the element length is 5 mm, the tolerance to the wavelength fluctuation of the laser of the fundamental wave is narrow and the half width is only 0.1 nm. . That is, when the wavelength of the laser is 0.1.
If it fluctuates by 1 nm, the output will be halved. Therefore, when the optical wavelength conversion element and the semiconductor laser are combined, there has been a problem that the semiconductor laser causes a wavelength change due to a temperature change, thereby eliminating harmonics, or greatly changing the output of the harmonics. This will be described in detail.

FIG. 15 shows the relationship between the harmonic output and the wavelength change of the semiconductor laser when the environmental temperature changes.
As shown in FIG. 15, the semiconductor laser has the largest output at the wavelength of 820 nm, but the harmonic output is halved only by shifting the wavelength of the laser by 0.05 nm, and the tolerance for the wavelength change of the semiconductor laser is very small. It is. Specifically, when the environmental temperature changes from 20 ° C. to 21 ° C. once, the oscillation wavelength of the semiconductor laser changes from 820 nm to 820.2 nm as much as 0.2 nm, and the output of the harmonic becomes zero. As described above, there is a disadvantage that the output of the harmonic is greatly affected by the change in the environmental temperature.

Accordingly, an object of the present invention is to provide an optical wavelength conversion element which is not affected by the environmental temperature, that is, can obtain a stable harmonic output even when the environmental temperature changes, and a short wavelength laser light source using the same. And

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems by adding a new device to an optical wavelength conversion device based on a domain-inverted structure, thereby generating a higher harmonic wave with respect to a temperature change of a semiconductor laser. An object of the present invention is to provide an optical wavelength conversion element that outputs stably.

That is, the present invention provides a light wavelength conversion element having a domain-inverted layer and an optical waveguide in a nonlinear optical crystal, which has means for forming a thin film heater in an optical waveguide shape.

Further, the short wavelength laser light source of the present invention has an optical wavelength conversion element having a domain-inverted layer and an optical waveguide and a semiconductor laser in a nonlinear optical crystal in order to obtain a stable output. Is controlled by a heater.

[0012]

By controlling the temperature of the optical wavelength conversion element of the present invention using a thin film heater, the highest harmonic output can always be obtained by changing the temperature of the optical wavelength conversion element even if the wavelength of the semiconductor laser changes. Can be This will be described in detail.

When the environmental temperature changes, the wavelength of the semiconductor laser changes, and the quasi-phase matching condition of the optical wavelength conversion element does not match, so that the output of a harmonic cannot be obtained. As described above, the condition under which the fundamental wave and the harmonic wave are phase-matched is Λ1 =
λ / (2 (N2ω−Nω)). Here, the period Λ1 of the light wavelength conversion element is defined at the stage when the light wavelength conversion element is manufactured, and therefore does not change even when the environmental temperature changes.
However, when the environmental temperature changes, the wavelength λ of the semiconductor laser
Changes. Then, as shown in FIG. 15, the output of the harmonic wave fluctuates because the tolerance for the wavelength change of the semiconductor laser is small. Here, in order to satisfy the phase matching condition, even if the wavelength λ of the semiconductor laser changes, the value of (N2ω−Nω) is changed accordingly, and as a result, Λ1 = λ /
The conditional expression (2 (N2ω-Nω)) is satisfied.

The value of (N2ω-Nω) has a positive slope with respect to temperature as shown in FIG.
In order to increase the value of (Nω), the temperature of the optical wavelength conversion element may be increased. For this purpose, a thin-film heater is formed on the surface of the optical wavelength conversion element to forcibly control the temperature, and the temperature of the optical wavelength conversion element is controlled even if the environmental temperature changes and the wavelength λ of the semiconductor laser changes. And always Λ1 = λ /
The equation (2 (N2ω-Nω)) is satisfied.

Further, even if the wavelength λ of the semiconductor laser deviates from the phase matching wavelength from the beginning, the temperature of the thin-film heater is changed to change the refractive index difference (N 2 ω−Nω), so that the quasi-phase matching condition is obtained. Λ1 = λ / (2 (N2ω−
Nω)), so that harmonics can be extracted with high efficiency.

Further, according to the short-wavelength laser light source of the present invention, the output of harmonics can be greatly improved by the same action.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As one of the embodiments, the configuration of the optical wavelength conversion element of the present invention will be described with reference to the drawings. First, FIG. 1 shows a structural diagram of a first embodiment of an optical wavelength conversion device according to the present invention. The difference from the conventional optical wavelength conversion element is that a thin film heater is formed on an optical waveguide formed with a domain-inverted layer. In this embodiment, an optical waveguide 2 manufactured by using proton exchange in a LiNbO ₃ substrate 1 is used as a domain-inverted optical wavelength conversion element.
In FIG. 1, reference numeral 1 denotes a + Z plate (+ of a substrate cut out perpendicular to the Z axis).
Side) LiNbO ₃ substrate, 2 formed optical waveguide, 3 domain-inverted layer, 10 incident part of fundamental wave P1, 12 harmonic wave P2
Reference numeral 15 denotes a Ni-Cr thin film heater formed on the optical waveguide.

The fundamental wave P1 (wavelength 840) entering the optical waveguide 2
nm) is converted into a harmonic P2 (wavelength 420 nm) by the domain-inverted layer having the length L of the phase matching length, and the harmonic power is increased by the next non-domain-inverted layer having the same length L. Become. The harmonic P2 having increased power in the optical waveguide 2 in this manner is radiated from the emission unit 12.

FIG. 2 shows the harmonics (Seco) with respect to the heater temperature.
nd Harmonic Generation) output. Now, since the oscillation wavelength of the semiconductor laser is 840 nm, the output of the harmonic is maximum when the temperature of the optical wavelength conversion element is 50 ° C. Therefore, the temperature of the light wavelength conversion element may be kept at 50 ° C.

The tolerance for the heater temperature is a small half-width T of 0.5 ° C. That is, the heater temperature is set to the optimum value of 50.
The output goes to zero when it deviates by 0.25 degrees from ° C. But,
Since the temperature of the light wavelength conversion element is controlled to be constant at 50 ° C. by the thin film heater 15, a constant harmonic output can be obtained even when the environmental temperature changes. Next, a method for manufacturing the optical wavelength conversion element will be described with reference to the drawings. In FIG. 3A, first, SiO ₂ 6 is patterned on the LiNbO ₃ substrate 1 by using a normal photo process and dry etching. Next, LiNbO ₃ on which SiO ₂ is formed in FIG.
The substrate 1 is subjected to a heat treatment at 1080 ° C. for 90 minutes to form SiO ₂ 6
A 1.4 μm-thick domain-inverted layer 3 is formed immediately below. The heat treatment rate is 10 ° C./min, and the cooling rate is 50 ° C./min. If the cooling rate is slow, non-uniform reversal occurs.
0 ° C./min or more is desirable.

[0021] Immediately below SiO ₂ , Li in the substrate 1 is reduced, and only the Curie temperature of that portion is lower than that of the substrate. Therefore the following substrate Curie temperature, and when the heat treatment at the Curie temperature or higher immediately under SiO ₂ 6, it is inverted polarization inversion layer of polarization with respect to the substrate only immediately below SiO ₂ 6. Here, the length L of the domain-inverted layer 3 is 1.5 μm.

Next, as shown in FIG. 2C, etching is performed for 20 minutes with a 1: 1 mixed solution of HF: HNF ₃ to remove SiO ₂ 6.
Next, a method of forming the optical waveguide 2 in the domain-inverted layer 3 using proton exchange will be described with reference to FIG.

In FIG. 4A, T is used as a mask for the optical waveguide 2.
a13 is sputter deposited. Next, after patterning in a stripe shape as shown in FIG.
FIG. 4 shows a slit having a slit of 25 μm and a length of 25 μm.
In (c), proton exchange was performed in pyrophosphoric acid at 230 ° C. for 2 minutes. Next, after removing the Ta mask 13 in FIG. 4D, annealing was performed at 350 ° C. for 1 hour. By the annealing treatment, the proton exchange layer is made uniform and the loss is reduced. The area immediately below the slit of the proton-exchanged protective mask becomes the high refractive index layer 2 whose refractive index has increased by about 0.03. Since light propagates through the high refractive index layer, this becomes the optical waveguide 2.

Finally, after adding 300 nm of SiO ₂ 14 by vapor deposition in FIG. 3D, a 200 nm thick Ni-Cr layer was formed. This Ni—Cr layer becomes the thin film heater 15. While if not SiO ₂ 14 temperature control is possible, of suppressing the propagation loss of light better to form a SiO ₂ 14 is guided through the optical waveguide from the thin film heater 15 and the optical waveguide 2 is not in direct contact is a metal effective.

The thin film heater 15 is formed by the above-described steps.
An optical waveguide was manufactured. The thickness d of the optical waveguide 2 is 1.2 μm, which is smaller than the thickness of the domain-inverted layer 3 of 1.4 μm. Since all light guided through the optical waveguide is guided through the domain-inverted layer, the wavelength is effectively converted. . The period of the domain-inverted layer 3 is 3 μm, and operates at a temperature of 50 ° C. for a wavelength of 840 nm. The surface perpendicular to the optical waveguide 2 is optically polished and
And the emission part 12 were formed. Thus, the optical wavelength conversion device shown in FIG. 1 can be manufactured.

Output result of harmonics In FIG. 1, semiconductor laser light (wavelength 840 nm) is used as fundamental wave P1.
When the light was guided from the incident part 10, it propagated in the single mode, and a harmonic P2 having a wavelength of 420 nm was extracted from the emission part 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 P2 was effectively extracted. One of the causes of high output is that a uniform optical waveguide is formed by pyrophosphoric acid.

The thin film heater 15 was heated by applying a voltage of 10 V to the thin film heater 15 to control the temperature of the light wavelength conversion element to 50 ° C. Then 1m with input of fundamental wave 40mW
A harmonic of W (wavelength 0.42 μm) was obtained. Features of the present invention Although the tolerance for the wavelength of the optical wavelength conversion element is small, the wavelength fluctuation of this semiconductor laser is corrected by changing the temperature of the optical wavelength conversion element so that harmonics can be output stably. This is a major feature of the invention.

Next, the relationship between the wavelength change of the semiconductor laser and the optimum temperature of the optical wavelength conversion element of the present invention is shown in FIG.
Shown in From this figure, when the wavelength of the semiconductor laser is 840 nm, the temperature of the optical wavelength conversion element is set so that the optimum temperature is 50 ° C. Further, from this figure, even if the wavelength of the semiconductor laser is shifted by 1 nm, if the temperature is changed by 5 ° C. by the heater, the optimum temperature is reached, and the harmonic output becomes maximum. As described above, the stability of the harmonic output was greatly improved as compared with the conventional optical wavelength conversion element, and the practicality was increased.

Now, the ambient temperature is 20 ° C. and the heater is 50 ° C.
It is assumed that the phases are matched and harmonics are output efficiently.
From this state, the ambient temperature changes from 20 ° C. to 40 ° C. by about 20 degrees, and the oscillation wavelength of the semiconductor laser changes from 840 nm to 844 nm.
Let's say However, the temperature of the optical waveguide is changed from 50 ° C. to the optimum temperature of 70 ° C. by the thin film heater, and the harmonic output can be stably obtained by satisfying the phase matching condition. Further, the thin film heater consumes less power and can respond at a speed of about μs, so that it is effective to follow the wavelength fluctuation.

In the multi-mode propagation with respect to the fundamental wave, the output of the harmonic is unstable and impractical, and the single mode is effective.

In this embodiment, the optimum temperature of the optical wavelength conversion device with respect to the wavelength of the semiconductor laser (FIG. 5) is set in consideration of the use conditions of the optical wavelength conversion device of the present invention. That is, as one of the environmental conditions for using the light wavelength conversion element, the use temperature is usually around room temperature and does not exceed 50 ° C. Therefore, here, the optimum temperature is set to 50 ° C., which is higher than the use temperature. If the ambient temperature is 10
If used in a place where the temperature will be 0 ° C, the optimal temperature is 10
It is desirable to set the temperature to 0 ° C. or higher. If the environmental temperature exceeds the optimum temperature, the light wavelength conversion element is not a heater but may be affected by the environmental temperature.

Next, a description will be given of a second embodiment of the short wavelength laser light source according to the present invention. FIG. 7 shows a configuration diagram of the short wavelength laser light source of FIG. 6. The short wavelength laser light source basically includes a semiconductor laser 21 and an optical wavelength conversion element 22. The fundamental wave P1 emitted from the semiconductor laser 21 fixed to the Al frame 20 is converted into parallel light by the collimator lens 24, and then introduced into the optical waveguide 2 of the optical wavelength conversion element 22 by the focus lens 25 to become a harmonic P2. Is converted. Reference numeral 23 denotes a quartz plate for heat insulation. Here, the configuration of the optical wavelength conversion element is the same as that of the first embodiment. The LiNbO ₃ strong MgO doped optical damage than the LiNbO ₃ substrate used in this example 110
Heat treatment was performed at 0 ° C. to form a domain-inverted layer. The processing temperature is higher than that of LiNbO ₃ because the Curie temperature is higher by about 80 ° C. due to MgO doping. In addition, a proton exchange optical waveguide that can be processed at a lower temperature than the heat treatment temperature at the time of forming the domain-inverted layer was used as the optical waveguide.

In this embodiment, a short wavelength laser light source is manufactured by combining the optical wavelength conversion element 22 and the semiconductor laser 21. The output of the output harmonic P2 is split by the beam splitter 26, detected by the Si detector 27 and fed back by electric processing, and the temperature of the thin film heater formed on the light wavelength conversion element 22 at the maximum point of the output of the harmonic is reduced. Be kept constant. The operating point is 55 ° C. at a wavelength of 830 nm. Since the heater is used, it is necessary to set an operating point on the high temperature side with respect to the room temperature.
Considering the case where the temperature rises to 50 ° C., it is particularly desirable that the operating point be 50 ° C. or higher. This point has been described in the first embodiment.
This operating point can be freely set only by changing the period of the domain-inverted layer. The temperature of the optical waveguide 2 of the light wavelength conversion element 22 changes by the thin film heater formed on the light wavelength conversion element 22 following the wavelength fluctuation of the semiconductor laser 21, and the harmonic output is stabilized. FIG. 7 shows the environmental temperature dependency of the manufactured short wavelength laser light source.

In the conventional short wavelength laser light source, when the ambient temperature changes, the harmonic output becomes zero. However, the laser light source of the present invention can obtain the harmonic output even when the environmental temperature changes. In fact, the output was very stable over the range of about 30 ° C.

As shown in FIG. 8, the ambient temperature of the conventional short-wavelength laser light source and that of the short-wavelength laser light source of the present invention are 25.degree.
3 shows a comparison of harmonic output at ° C. At an ambient temperature of 25 ° C., the optical wavelength conversion element of the conventional short-wavelength laser light source also satisfies the quasi-phase matching condition, so that the highest harmonic has a maximum output of 3 mW. Harmonic output is 0 because of deviation from quasi-phase matching condition under the influence of environmental temperature. On the other hand, in the optical wavelength conversion device of the present invention, even if the environmental temperature changes, the temperature of the optical waveguide of the optical wavelength conversion device is controlled by the heater, and the maximum harmonic output (3 mW) is always maintained. Become.

In this embodiment, a thin film heater is used, but it is also possible to control with a normal heater.

Next, a description will be given of a third embodiment of the optical wavelength conversion element according to the present invention. The configuration of the light wavelength conversion element is the same as that of the first embodiment. In this example, LiTaO ₃ was used as the substrate instead of the LiNbO ₃ substrate. LiTaO ₃ has a low Curie temperature of 620 ° C. and can be subjected to polarization reversal at a low temperature. The optical waveguide 2 is manufactured by proton exchange in pyrophosphoric acid and has a thickness of 2 μm.
m, width 4 μm, and length 2 cm. Further, Ti is formed as a thin film heater on the optical waveguide by 200 nm vapor deposition. The period of the domain inversion is 4 μm, and the thickness of the domain inversion layer is 1.5 μm. FIG. 9 shows the relationship between the wavelength of the semiconductor laser and the optimum temperature of the optical wavelength conversion element. 862n wavelength
The operating point for m is 55 ° C. The conversion efficiency in this embodiment is 2% at 40 mW input. There was no light damage and the harmonic output was very stable.

Next, a fourth embodiment of the optical wavelength conversion device of the present invention will be described. FIG. 10 shows the configuration of the optical wavelength conversion element.
In this embodiment, LiTaO ₃ was used as the substrate. LiTaO ₃ substrate 1
The domain-inverted layer 3 and the optical waveguide 2 are formed on the -Z plane of a, and a thin film heater 15 is formed thereon with three different thicknesses in the traveling direction of the optical waveguide 2. Here, the reason why the thickness of the thin film heater is changed is to increase the tolerance of the output of the harmonic with respect to the fundamental wave P1 (the wavelength of the semiconductor laser). The reason will be described in detail.

As described in the problem to be solved and as shown in FIG. 15, the tolerance of the harmonic to the wavelength of the fundamental wave P1 is small. Therefore, in the first to third embodiments, a thin film heater is formed on the light wavelength conversion element to control the temperature and output a stable harmonic. In this embodiment, a temperature gradient is given to the light wavelength conversion element by changing the thickness of the thin film heater on the light wavelength conversion element, thereby increasing the tolerance. That is, the phase matching condition for outputting a harmonic with respect to the wavelength λ of the fundamental wave was Λ1 = λ / (2 (N2ω−Nω)). By changing the temperature of the optical wavelength conversion element from this equation, FIG.
Since the value of (N2ω-Nω) changes as shown in FIG.
It can be seen that the wavelength λ for phase matching changes. This phenomenon may be used to increase the wavelength tolerance of the fundamental wave. This will be described with reference to FIG.

FIG. 17A is a sectional view of an optical wavelength conversion element in which the thickness of the thin film heater is changed in three stages. The thickness of the thin-film heater changes depending on the region A, the region B, and the region C. The larger the thickness of the heater, the lower the current resistance and the lower the temperature. As shown in FIG. 3B, the temperature gradient by the heater is T _{A in} the area _A , T _{B in} the area _B , and T _{C in} the area C (T _A <T _B <T _C ).

FIG. 3C shows the harmonic (SHG) output with respect to the wavelength of the fundamental wave. From this figure, it can be seen that the optimum wavelength at which the fundamental wave is converted into a harmonic changes depending on the temperature of the heater. It is the phase matching condition, Λ1 = λ / (2
Since the value of (N2ω-Nω) in the equation (N2ω-Nω) changes with temperature, in order to satisfy this phase matching condition,
λ changes. The optimum wavelength in the region A is λ _A , the optimum wavelength in the region B is λ _B , and the optimum wavelength in the region C is λ _C.

Here, when the fundamental light having the wavelength λ _B is incident on the wavelength conversion element, the region A is shifted from the wavelength range in which the wavelength can be converted in the region A, so that the wavelength conversion is not performed and the fundamental wave passes. The passed fundamental wave is wavelength-converted in the region B so as to satisfy the wavelength range in which the wavelength can be converted. In the regions B and C, the harmonics and B
The fundamental wave which has not been converted by the above passes as it is and is taken out of the element.

Similarly, the fundamental waves of wavelengths λ _A and λ _C are wavelength-converted only in the corresponding regions (regions A and C), and pass through the other regions as they are.

The operation of the optical wavelength conversion element of this embodiment has been described above. All the fundamental waves of wavelengths λ _A , λ _B and λ _C can be converted, and the fundamental wave λ in the range of wavelengths λ _A to λ _C can be converted. If you enter
It can be converted to harmonic P2, and the wavelength tolerance is 3
It is to be doubled.

As described above, in the present embodiment, a temperature gradient is provided by using a thin film heater on the optical wavelength conversion element to increase the tolerance of the output of the harmonic with respect to the fundamental wave.

Hereinafter, a method for manufacturing the optical wavelength conversion element will be described with reference to FIG. Patterning the periodic the Ta6a using ordinary photo process and dry etching the LiTaO ₃ substrate 1a in FIG. 11 (a). Next, proton exchange is performed in pyrophosphoric acid at 260 ° C. for 30 minutes on the LiTaO ₃ substrate 1 a on which the pattern of Ta6a is formed in FIG. At a temperature of 1 minute. Thereby, the domain-inverted layer 3 is formed periodically. Next, after patterning Ta into a 30 nm stripe as a protective mask for proton exchange in FIG. 3C, proton exchange was performed at 260 ° C. for 16 minutes. Thereafter, annealing is performed at 380 ° C. for 10 minutes to form the optical waveguide 2. Further, after forming SiO ₂ 14 as a protective film in FIG. 3D, a Ti film to be the thin film heater 15 is formed. Next, as shown in FIG. 4E, a Ti pattern was further deposited by changing the thickness in two steps using a mask process. Ti
Are 100 nm, 200 nm, and 300 nm. Finally, an incoming / outgoing surface is formed by polishing. The optical waveguide 2 has a thickness of 1.9 μm,
The width is 4 μm and the length is 1 cm. The period of domain inversion Λ1 is 3.8 μm, and the thickness of the domain-inverted layer is 1.8 μm. By changing the thickness of Ti which becomes the thin film heater 15 stepwise, the temperature of the optical waveguide changes in the traveling direction of the optical waveguide. Thereby, the accuracy of the temperature control can be eased. If there is no stepwise change with respect to the wavelength tolerance of 0.1 nm, temperature control with an accuracy of 2 ° C. is necessary. The operating point for a wavelength of 840 nm is 55 ° C.

In the embodiment, the thickness of the thin film heater is changed stepwise, but it can be realized by changing the width, the composition and the like in the traveling direction of the optical waveguide. The same effect can be obtained by smoothly changing the value instead of changing the value stepwise.

In the embodiment, the non-linear optical crystal is Li
Although NbO ₃ and LiTaO ₃ are used, the present invention is also applicable to ferroelectrics such as KNbO ₃ and KTP, and organic materials such as MNA.

[0049]

As described above, according to the optical wavelength conversion device of the present invention, quasi-phase matching is achieved by forming a thin film heater on an optical wavelength conversion device having a domain-inverted layer and controlling the temperature of the optical wavelength conversion device. Harmonic generation can be performed easily and stably by adjusting to the wavelength. Further, according to the short-wavelength laser light source of the present invention, a stable operation of emitting harmonics can be realized by correcting the wavelength fluctuation of the semiconductor laser by controlling the temperature with a heater.

Further, the harmonics can be extracted from the optical waveguide by the optical wavelength conversion element of the present invention, and a spot free of astigmatism can be easily and stably obtained, and its practical effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a first embodiment of an optical wavelength conversion element of the present invention.

FIG. 2 is a diagram showing a relationship between a harmonic output and a temperature of the optical wavelength conversion element of the present invention.

FIG. 3 is a sectional view showing a manufacturing process of the optical wavelength conversion element of the present invention.

FIG. 4 is a cross-sectional view illustrating a manufacturing process of the optical waveguide of the optical wavelength conversion element of the present invention.

FIG. 5 is a diagram showing an optimum temperature of an optical wavelength conversion element with respect to a wavelength change of a semiconductor laser.

FIG. 6 is a sectional view showing the configuration of a short wavelength laser light source according to the present invention.

FIG. 7 is a comparison diagram of a conventional example and the short wavelength laser light source according to the present invention in which the harmonic output depends on the environmental temperature.

FIG. 8 is a comparison diagram of the harmonic output of the conventional example and the short wavelength laser light source of the present invention with respect to the environmental temperature.

FIG. 9 is a diagram showing an optimum temperature value of the optical wavelength conversion element with respect to a change in the wavelength of the semiconductor laser.

FIG. 10 is a configuration diagram of an optical wavelength conversion element according to a fourth embodiment of the present invention.

FIG. 11 is a manufacturing process diagram of an optical wavelength conversion element according to a fourth embodiment of the present invention.

FIG. 12 is a configuration diagram of a conventional optical wavelength conversion element.

FIG. 13 is a diagram illustrating the principle of wavelength conversion by an optical wavelength conversion element.

FIG. 14 is a sectional view showing a manufacturing process of a conventional optical wavelength conversion element.

FIG. 15 is a diagram showing the harmonic output of the optical wavelength conversion element with respect to the wavelength when the temperature is changed.

FIG. 16 is a diagram showing the relationship between temperature and refractive index difference (N2ω-Nω).

FIG. 17 (a) is a sectional view of an optical wavelength conversion element of the present invention. (B) It is a figure which shows the temperature distribution of each area | region. (C) is a diagram showing the output of the harmonic with respect to the optimum wavelength.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 LiNbO ₃ substrate 2 optical waveguide 3 domain inversion layer 15 thin film heater 21 semiconductor laser 22 optical wavelength conversion element P1 fundamental wave P2 harmonic

Continuation of front page (56) References JP-A-64-70703 (JP, A) SPIE vol. 651 Integrated Optical Circuit Engineering II I pp. 221-228 (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/37

Claims (3)

(57) [Claims] 1. A nonlinear optical crystal optical wavelength conversion element having a polarization inversion layer and the optical waveguide in the thin film heater is formed on the optical waveguide, in the thin film heater
The temperature of the optical waveguide, which is further heated, increases the progress of the optical waveguide.
An optical wavelength conversion element characterized by changing smoothly or stepwise in a direction . 2. An optical wavelength conversion device having a domain-inverted layer and an optical waveguide in a nonlinear optical crystal, and a semiconductor laser.
The light wavelength conversion element is temperature-controlled by a heater .
The temperature of the light wavelength conversion element heated by the heater.
The degree is smoothly and smoothly with respect to the traveling direction of the optical waveguide.
Short-wavelength laser light source other, characterized in that you are changed stepwise. 3. A polarization-inverted layer and a light guide in a nonlinear optical crystal.
An optical wavelength conversion element having a waveguide, wherein the optical waveguide
A thin film heater is formed in the thin film heater.
At least one of a thickness, a width, and a composition is the optical waveguide.
Characterized by changing along the light traveling direction at
Light wavelength conversion element.