JPH07244307A - Short wavelength light generator - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a short-wavelength light generation device that provides stable, highly efficient, short-wavelength light that is robust against light damage required for high-density recording and image processing of optical disks. . [Structure] Light emitted from the semiconductor laser 1 is LiTaO ₃
Wavelength conversion is performed by a wavelength conversion element having an optical waveguide 6 and a periodic domain inversion region 7 on a substrate 5. At this time, the refractive index of the wavelength conversion element changes due to optical damage, and the obtained harmonic output becomes unstable. By irradiating the wavelength conversion element with the ultraviolet lamp 11, the light damage resistance of the wavelength conversion element is improved, and a short wavelength light generation device capable of generating high output can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short wavelength light generating device used in the fields of optical information processing and optical application measurement control.

[0002]

2. Description of the Related Art As a wavelength conversion element made of a ferroelectric material, a waveguide type wavelength conversion element having a domain-inverted structure using LiTaO ₃ as a substrate is given as a conventional example. FIG. 5 shows a configuration diagram of a waveguide type wavelength conversion element having a periodically domain-inverted region using a LiTaO ₃ crystal as a substrate. The harmonic generation (wavelength 0.435 μm) with respect to the fundamental wave having a wavelength of 0.87 μm will be described below in detail with reference to FIG. (K.Mizuuchi, K.Yamamoto and
T. Taniuchi, Applied Physics Letters, Vol 58, 2732
Page, June 1991, see) Li as shown in FIG.
The optical waveguide 6 is formed on the TaO ₃ substrate 5, and the optical waveguide 6 is further formed.
A region (polarization inversion region 7) in which the polarization is periodically inverted is formed in. By compensating for the mismatch of the propagation constants of the fundamental wave P1 and the generated harmonic wave P2 with the periodic structure of the polarization inversion region 7 and the non-polarization inversion region, the harmonic wave P2 can be generated with high efficiency. When the fundamental wave P1 is incident on the incident end surface 19 of the optical waveguide 6, a harmonic wave P2 is efficiently generated from the emitting end surface 20 of the optical waveguide 6, and the harmonic wave P2 operates as a wavelength conversion element.

A method of manufacturing this element will be described. First, Ta is patterned on the LiTaO ₃ substrate 5 in a periodic shape (period 4.0 μm) by using a normal photoprocess and dry etching. Next, on the LiTaO ₃ substrate 5 on which the Ta pattern was formed,
Proton exchange is performed at 260 ° C. for 30 minutes to form a 0.8 μm-thick proton exchange layer directly below the slit not covered with Ta. Then, heat treatment is performed at a temperature of 590 ° C. for 10 minutes. The rising rate of heat treatment is 10 ° C / min, and the cooling rate is 50 ° C / min.
As a result, the domain inversion region 7 is formed. Just below the proton exchange layer, Li is reduced and the Curie temperature is lowered, so that polarization inversion can be partially performed. Then HF: H
Ta is removed by etching with a 1: 1 mixture of NF ₃ for 2 minutes. Further, the optical waveguide 6 is formed in the domain inversion layer region 7 by using proton exchange. T as an optical waveguide mask
By patterning a in a stripe pattern, a slit having a width of 4.0 μm and a length of 12 mm is formed on the Ta mask. The substrate 701 covered with this Ta mask is subjected to proton exchange at 260 ° C. for 16 minutes to form a 0.5 μm high refractive index layer. After removing the Ta mask, heat treatment is performed at 380 ° C. for 10 minutes. The region directly below the slit of the protective mask that has undergone the proton exchange becomes the optical waveguide 6 whose refractive index has increased by about 0.02.

A short-wavelength light generator using this wavelength conversion element will be described. In FIG. 6, 1 is 140 in the 0.87 μm band.
mW class AlGaAs semiconductor laser, 2 is a collimating lens with NA = 0.5, 3 is a λ / 2 plate, 4 is a focusing lens with NA = 0.5, 8 is a collimating lens with NA = 0.6, and 10 is the optical axis of the semiconductor laser. It is a grating installed at an angle. On the LiTaO ₃ substrate 5, an optical waveguide 6 and periodically poled regions 7 are formed. The laser light made parallel by the collimator lens 2 is rotated in the deflection direction by the λ / 2 plate 3 and is condensed by the focusing lens 4 on the end face of the optical waveguide 6 of the polarization inversion waveguide device, and the polarization of the period 4.0 μm is performed. The light propagates through the optical waveguide 6 having the inversion region 7 and is emitted from the emission end face of the optical waveguide 6. The light emitted from the optical waveguide 6 becomes parallel light by the collimator lens 8, and the wavelength selection mirror 9
And is guided to the grating 10. The wavelength selection mirror 9 is designed to be non-reflective for the fundamental wave and highly reflective for the harmonic wave. The grating 10 has a wavelength dispersion effect, and the light of wavelength 870 nm is recombined with the optical waveguide 6 and returned to the active layer of the semiconductor laser 1, and the wavelength of the semiconductor laser 1 is the phase matching wavelength of the polarization inversion waveguide device. The angle of the grating 10 is set so that it is fixed at 870 nm. The incident light intensity of the semiconductor laser 1 into the optical waveguide 6 is 3.2 mW for 40 mW (conversion efficiency: 200
% / W) blue light was obtained and separated from the fundamental wave by the wavelength selection mirror 9 to be extracted. In addition, Ti: Sap
Incident light intensity 1 into the optical waveguide 6 using the phire laser
20mW of blue light was obtained for 00mW.

[0005]

The nonlinear optical crystal that is the substrate of the wavelength conversion material is LiNb _x Ta _1-x O ₃ (0 ≦ x ≦
1) and other ferroelectric crystals such as K _x Rb _{1 -x} TiOMO ₄ (0 ≦ x ≦ 1, M = P or As), the photo-induced refractive index change ( Light damage).
The photo-induced refractive index change is that electrons in a trapped state are excited by light irradiation, a new space charge electric field is generated, and a refractive index change locally occurs due to an electro-optic effect. Light damage is likely to occur in the short wavelength region, and the higher the light intensity, the greater the decrease in the refractive index. When the refractive index in the optical waveguide changes, the period of the domain-inverted region also changes, resulting in a shift in the phase matching wavelength of about 1 nm. When the phase matching wavelength shifts, it is necessary to change the wavelength of the semiconductor laser to the phase matching wavelength again by the grating. Also,
When the incident power is increased and harmonic light of 20 mW or more is obtained, the polarization inversion regions at the incident part and the exit part of the optical waveguide have different periods, so the tolerance of the phase matching wavelength spreads over time and the conversion efficiency increases. The resulting output will be unstable.

LiNb _x Ta _1-x O ₃ (0 ≦ x ≦ 1) and K _x
Rb _1-x TiOMO ₄ (0 ≦ x ≦ 1, M = P or As)
The crystal has a large non-linear optical constant, and in the case of a wavelength conversion element having a polarization inversion structure, since the conversion efficiency is high, the output of short-wavelength light obtained is also large, so that the effect of the photo-induced refractive index change also appears significantly.

In order to stably obtain higher harmonic light, it is necessary to improve the light damage resistance of the nonlinear crystal which is the substrate. In order to improve the light damage resistance, the mobility of electrons inside the crystal is increased. It is important to cancel the generated space charge electric field.

[0008]

According to the present invention, in order to solve the above-mentioned problems, a new device is added to the optical wavelength conversion element to increase the mobility of electrons, improve the light damage resistance, and stabilize the output. It provides wavelength light. That is, the present invention provides (1) a wavelength conversion element made of a ferroelectric crystal with a wavelength of 550 n.
A device that increases the mobility of electrons inside the proton exchange waveguide by irradiating light of m or more and reduces the generation of an internal electric field, thereby improving the light damage resistance and generating stable short-wavelength light. Is provided.

The present invention also provides (2) a waveguide-type wavelength conversion element made of a ferroelectric crystal,
By propagating light of 550 nm or more at the same time as the semiconductor laser light, the mobility of electrons inside the proton exchange waveguide is increased, and the generation of internal electric field is reduced to improve the light damage resistance and stabilize the short wavelength. A device for generating light is provided.

[0010]

The light wavelength conversion element of the present invention cancels the space charge distribution of electrons generated by short wavelength light by increasing the mobility of electrons in the substrate by irradiation of short wavelength light, and improves the light damage resistance. The present invention is intended to realize a stable high-power short-wave dimming generator.

[0011]

[Example] The wavelength conversion element of the present invention has a peak wavelength of 550 nm.
A short-wavelength light generation device that is irradiated with the following light and has improved light damage resistance will be described with reference to FIG. In this example, as the wavelength conversion element, a polarization inversion type waveguide element having a periodic polarization inversion region formed on a ferroelectric material LiTaO ₃ substrate was used. The method of forming the domain-inverted region and the optical waveguide is the same as in the conventional example.

(Embodiment 1) In FIG. 1, 1 is a 0.87 μm band 140 mW class AlGaAs semiconductor laser, 2 is a collimating lens with NA = 0.5, 3 is a λ / 2 plate, 4 is a focusing lens with NA = 0.5, and 8 is Collimating lens with NA = 0.6, 10
Is a grating installed at an angle with respect to the optical axis of the semiconductor laser. On the LiTaO ₃ substrate 5, an optical waveguide 6 and periodically poled regions 7 are formed. The ultraviolet lamp 11 (wavelength 230 to 500 nm) is mounted on the wavelength conversion element in order to improve the light damage resistance of the wavelength conversion element.
The laser light collimated by the collimator lens 2 is λ
The / 2 plate 3 rotates the deflection direction, the focusing lens 4 collects the light on the end face of the optical waveguide 6 of the polarization inversion type waveguide element, propagates through the optical waveguide 6 having the polarization inversion region 7 with a period of 4.0 μm, and The light is emitted from the emission end face of the waveguide 6. The light emitted from the optical waveguide 6 becomes parallel light by the collimator lens 8, passes through the wavelength selection mirror 9, and is guided to the grating 10. The wavelength selection mirror 9 is designed so as to be non-reflective with respect to the fundamental wave and highly reflective with respect to the harmonic. The grating 10 has a wavelength dispersion effect,
Light having a wavelength of 870 nm is recombined with the optical waveguide 6 and is returned to the active layer of the semiconductor laser 1 so that the wavelength of the semiconductor laser 1 is fixed at 870 nm which is the phase matching wavelength of the polarization inversion waveguide device. An angle of 10 is set.
Blue light of 3.2 mW (conversion efficiency: 200% / W) was obtained for an incident light intensity of 40 mW into the optical waveguide 6 of the semiconductor laser 1. Using a Ti: Sapphire laser, a blue output of 20 mW was obtained for an incident light intensity of 100 mW. The LiTaO ₃ crystal has a large non-linear optical constant, and a wavelength conversion element having a periodic domain-inverted region has a large conversion efficiency and a large amount of blue light can be obtained.

In the conventional example, the intensity of incident light into the optical waveguide 6
The phase matching wavelength was shifted by 1 nm with respect to 40 mW. (When the incident light intensity was 1 mW, the phase matching wavelength was 869 nm,
It was 870 nm at 40 mW incidence. ) In addition, the incident light intensity
When it was set to 00 mW, 20 mW of blue light was obtained, but the blue output obtained decreased to 12 mW 3 minutes after the occurrence of blue.

In this embodiment, since the ultraviolet lamp 11 is mounted on the wavelength conversion element to improve the electron mobility in the optical waveguide 6 and the LiTaO ₃ substrate 5, the phase matching wavelength shift amount is 0.5. It was reduced to nm. In addition, a blue output of 15 mW was stably obtained for a long time with respect to a fundamental wave incident light intensity of 100 mW. The strength of the ultraviolet lamp 11 used in this example was 10 W / cm ² .

Even when a lamp in the visible light region (blue or green region) is used instead of the ultraviolet lamp 11, the improvement of the light damage resistance can be obtained. However, no improvement in light damage resistance was observed even when a lamp having a wavelength longer than 550 nm was irradiated.

Further, in this embodiment, the ultraviolet lamp 11 is mounted on the upper part of the wavelength conversion element, but the same effect can be obtained by mounting it on the lower part and the peripheral part of the wavelength conversion element.

Further, in this embodiment, the period of the domain inversion region is
It is a wavelength conversion element of 4.0 μm, and when the wavelength of the fundamental wave was 870 nm, phase matching occurred and a blue output of 435 nm was obtained, but by setting the period of the domain inversion region to about 3.0 μm, the phase matching wavelength Becomes 800 nm, and the obtained harmonic is 400 nm, which is in the ultraviolet region. In this case, the amount of change in the refractive index due to light damage also increases, and it is even more important to improve the light damage resistance.
A harmonic output of 3 mW was obtained for a fundamental wave incident light intensity of 40 mW at a wavelength of 800 nm. When there was no irradiation 11 of the ultraviolet lamp, the shift amount of the phase matching wavelength was about 2 nm, but it was improved to about 0.6 nm by the irradiation of the ultraviolet lamp.

(Example 2) In this example, a GaN blue light emitting diode (peak wavelength 480 nm) was used instead of the ultraviolet lamp.
Was used. The output intensity of the light emitting diode (LED) 12 is about 1 mW. The output intensity is lower than that of an ultraviolet lamp, but the light condensing property is high. Therefore, the light is focused on the optical waveguide 6 by the cylindrical lens 13. Incident light intensity 40
When the blue output of 3.2 mW was obtained with respect to mW, the shift amount of the phase matching wavelength was about 0.3 nm, and the light damage resistance was significantly improved. Further, it was found that the light damage resistance was improved by increasing the light converging property and increasing the light density on the optical waveguide 6.

Even in the wavelength conversion element in which the period of the domain inversion region 7 is 3.0 μm, the shift amount of the phase matching wavelength is 0.4 n.
It was possible to reduce to m.

Further, even if the GaP green light emitting diode is used, the effect is smaller than that of the GaN light emitting diode, but the light damage resistance is improved. However, even if the InGaAlP-based red and yellow LEDs were irradiated, no improvement in the light damage resistance was observed.

The wavelength of the LED is particularly preferably 380 to 450 nm. Further, the LED is lower in cost than the ultraviolet lamp, and a practical device can be realized.

(Embodiment 3) In this embodiment, in order to improve the optical damage resistance of the optical waveguide of the polarization inversion waveguide device,
A short-wavelength light generator that simultaneously transmits a blue semiconductor laser will be described.

In FIG. 3, 1 is a 100 mW class AlGaA in the 0.8 μm band.
s Semiconductor laser, 2 is a collimating lens with NA = 0.5,
3 is a λ / 2 plate, 4 is a focusing lens with NA = 0.5,
Reference numeral 8 is a collimator lens with NA = 0.6, and 10 is a grating that is placed at an angle with respect to the optical axis of the semiconductor laser. On the LiTaO ₃ substrate 5, an optical waveguide 6 and periodically poled regions 7 are formed. In addition, 14 is ZnS with a wavelength of 480 nm
It is an e-based 1 mW class blue semiconductor laser, 15 is a collimating lens, and 16 is a λ / 2 plate. The collimated light having a wavelength of 800 nm from the semiconductor laser 1 and the light having a wavelength of 480 nm from the semiconductor laser 14 are combined by the wavelength selection mirror 17 and coupled to the optical waveguide 6 of the wavelength conversion element by the focusing lens 4. The light propagates through the optical waveguide 6 having the domain-inverted region 7 with a period of 3.0 μm and is emitted from the emission end face of the optical waveguide 6. The light emitted from the optical waveguide 6 is collimated by the collimator lens 8
Then, the light becomes parallel light, passes through the wavelength selection mirror 9, and is guided to the grating 10. The wavelength selection mirror 9 is designed so as to be non-reflective with respect to the fundamental wave and highly reflective with respect to the harmonic. The grating 10 has a wavelength dispersion effect, and the light of wavelength 800 nm is recombined with the optical waveguide 6 and returned to the active layer of the semiconductor laser 1, and the wavelength of the semiconductor laser 1 is the phase matching wavelength of the polarization inversion waveguide device. Is 800n
The angle of the grating 10 is set so that it is fixed at m. Blue light of 3.2 mW (conversion efficiency: 200% / W) was obtained for an incident light intensity of 40 mW into the optical waveguide 6 of the semiconductor laser 1. The light having a wavelength of 480 nm coupled into the optical waveguide 6 was about 100 μW, and the conventionally observed shift of the phase matching wavelength was only about 0.1 nm.

(Embodiment 4) This embodiment is not intended to improve the light damage resistance by irradiating light from the outside or propagating another semiconductor laser at the same time as in Embodiments 1 to 3. It is intended to improve the light damage resistance by propagating the harmonic light obtained by the wavelength conversion again to the optical waveguide.

In FIG. 4, 1 is a 0.87 μm band 140 mW class AlGa
As semiconductor laser, 2 is a collimating lens with NA = 0.5,
3 is a λ / 2 plate, 4 is a focusing lens with NA = 0.5,
Reference numeral 8 is a collimator lens with NA = 0.6, and 10 is a grating installed so as to be inclined with respect to the optical axis of the semiconductor laser. On the LiTaO ₃ substrate 5, an optical waveguide 6 and periodically poled regions 7 are formed. The laser light collimated by the collimator lens 2 is rotated in the deflection direction by the λ / 2 plate 3 and is condensed by the focusing lens 4 on the end face of the optical waveguide 6 of the polarization inversion type waveguide element, which has a period of 4.0 μm. The light propagates through the optical waveguide 6 having the domain-inverted region 7 and is emitted from the emission end face of the optical waveguide 6. The light emitted from the optical waveguide 6 becomes parallel light by the collimator lens 8, passes through the wavelength selection mirror 9, and is guided to the grating 10. Wavelength selection mirror 9
Is designed to be non-reflective for the fundamental wave and highly reflective for the harmonics. The grating 10 has a wavelength dispersion effect, and the light of wavelength 870 nm is recombined with the optical waveguide 6 and returned to the active layer of the semiconductor laser 1, and the wavelength of the semiconductor laser 1 is the phase matching wavelength of the polarization inversion waveguide device. Grating 1 to be fixed at 870 nm
An angle of 0 is set. In the optical waveguide 6 having the periodically domain-inverted regions 7, the light of the fundamental wave 870 nm is wavelength-converted into the light of wavelength 435 nm. A harmonic light reflection film 18 is formed on the emission end face of the optical waveguide 6, and the wavelength-converted harmonic wave 43 is formed.
20% of the 5 nm light propagates through the optical waveguide 6 again in the direction of the semiconductor laser 1. Optical waveguide 6 of semiconductor laser 1
A blue light of 2.5 mW was obtained for an incident light intensity of 40 mW. Also in this embodiment, the phase matching wavelength shift is 0.2 nm.
Only the degree was observed. However, if the reflectance of the harmonic light at the exit facet is set to 10% or less, the shift amount will be 0.6
The reflectance of the harmonic light reflection film 18 becomes 20 nm.
% Or more is desirable.

Further, the wavelength selection mirror 9 is installed between the collimating lens 3 and the focusing lens 4 and the reflectance of the higher harmonic light reflection film 18 for the higher harmonics is set to 100%, whereby the shift amount of the phase matching wavelength is 0.1. It was less than nm, and a significant improvement in light damage resistance was observed.

Further, in the present embodiment, the reflected light at the emission end face is used for improving the light damage resistance, but the same effect can be obtained by using the scattered light at the emission end face.

(Example 5) In Examples 1 to 4, LiTa was used.
The waveguide type wavelength conversion element having a periodically poled region using an O ₃ substrate has been described. Similar effects can be seen in wavelength conversion elements using other inorganic nonlinear optical crystals or organic nonlinear optical crystals as substrates. However, LiTaO ₃ , Li
Large nonlinear optical constants such as NbO ₃ and KTP (KTiOPO ₄ ),
Crystals with a high conversion efficiency as a wavelength conversion element produce a large harmonic light output and a large effect of changing the photo-induced refractive index.Therefore, the wavelength conversion element is irradiated with light with a wavelength of 550 nm or less to improve light damage resistance. When you do, the effect is very great.

In the first to fourth embodiments, the wavelength conversion element has been described by taking the waveguide type as an example. However, the wavelength conversion element may be provided inside the external resonator type of the semiconductor laser or the internal resonator type of the semiconductor laser pumped solid state laser. Even in the inserted bulk type wavelength conversion element, the light damage resistance can be improved by irradiating the light with a wavelength of 550 nm or less. However,
Since the waveguide type wavelength conversion element has a high light density in the light propagating portion, the effect obtained when the light having a wavelength of 550 nm or less is irradiated to improve the light damage resistance is larger than that of the bulk type wavelength conversion element. .

Not only the polarization inversion type phase matching method, but also the angle phase matching method or the temperature phase matching method using the dispersion relation of the refractive index is used to stably stabilize the light by improving the light damage resistance. It is possible to obtain high power short wavelength light,
The effect is great.

[0031]

EFFECTS OF THE INVENTION By irradiating a wavelength conversion element made of a ferroelectric crystal with light having a peak wavelength of 550 nm or less, the light damage resistance of the wavelength light wavelength conversion element is improved, and a highly efficient and stable wavelength resistant to light damage. The conversion is realized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a short wavelength light generating device having an ultraviolet lamp of the present invention.

FIG. 2 is a schematic configuration diagram of a short wavelength light generating device having a light emitting diode of the present invention.

FIG. 3 is a schematic configuration diagram of a short wavelength light generating device having a visible light semiconductor laser of the present invention.

FIG. 4 is a schematic configuration diagram of a short wavelength light generating device having a harmonic light reflecting film of the present invention.

FIG. 5 is a schematic configuration diagram of a waveguide type wavelength conversion element having a periodic domain inversion region of the present invention.

FIG. 6 is a schematic configuration diagram of a conventional short wavelength light generator.

[Explanation of symbols]

1 Semiconductor Laser 2 Collimating Lens 3 λ / 2 Plate 4 Focusing Lens 5 LiTaO ₃ Substrate 6 Optical Waveguide 7 Polarization Inversion Area 8 Collimating Lens 9 Wavelength Selecting Mirror 10 Grating 11 UV Lamp 12 Light Emitting Diode 13 Cylindrical Lens 14 Visible Light Semiconductor Laser 15 Collimating Lens 16 λ / 2 plate 17 Wavelength selection mirror 18 Harmonic light reflection film 19 Incident end face 20 Emitting end face P1 fundamental wave P2 harmonic

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshikazu Hori 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (9)

[Claims] 1. A short-wavelength light generation device comprising at least a semiconductor laser and a wavelength conversion element, wherein the wavelength conversion element is irradiated with light having a peak wavelength of 550 nm or less. 2. A semiconductor laser, a wavelength conversion element, and a light source that emits light having a peak wavelength of 550 nm or less, which is located in the peripheral portion of the wavelength conversion element, and the light from the light source is transmitted to the wavelength conversion element. A short-wavelength light generation device characterized in that a fundamental wave emitted and emitted from the semiconductor laser is converted into a harmonic in the wavelength conversion element. 3. A semiconductor laser and a waveguide type wavelength conversion element are provided at least, and a peak wavelength of 550 nm is provided in the waveguide of the waveguide type wavelength conversion element simultaneously with the semiconductor laser light.
A short wavelength light generating device characterized in that the following light is propagated. 4. At least a semiconductor laser and a waveguide type wavelength conversion element, wherein the harmonic light wavelength-converted by the waveguide type wavelength conversion element is reflected by an emission end face of the waveguide type wavelength conversion element, and reflected light is obtained. Is propagated again through the waveguide type wavelength conversion element. 5. The short wavelength light generating device according to claim 1, wherein the light having a peak wavelength of 550 nm or less is light emitted from a light emitting diode, a semiconductor laser or a lamp. 6. The substrate of the wavelength conversion element is LiNb _x Ta _1-x O ₃
(0≤x≤1), wherein:
3. The short wavelength light generator according to 3 or 4. 7. The substrate of the wavelength conversion element is K _x Rb _1-x TiOM.
5. The short wavelength light generating device according to claim 1, wherein O ₄ (0 ≦ x ≦ 1, M = P or As). 8. The short wavelength light generating device according to claim 3, wherein the waveguide type wavelength conversion element has a periodic domain inversion region. 9. The short-wavelength light generation device according to claim 3, wherein the output end face of the optical waveguide in the waveguide type wavelength conversion element has a reflectance of 20% or more for harmonic light.