JP2004094200A - Laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a laser device small-sized and lightweight while stabilizing a laser light source and making its output high. <P>SOLUTION: After a polarization reversal layer 3 is formed on an LiTaO<SB>3</SB>substrate 1, an optical waveguide is formed. An optical wavelength conversion element which is thus formed is annealed at low temperature to form a stable proton exchange layer 8a whose refractive index increase caused in a high-temperature heat treatment is lowered, thereby obtaining the stable optical wavelength conversion element. <P>COPYRIGHT: (C)2004,JPO

Description

(Technical field)
The present invention relates to an optical element such as an optical wavelength conversion element suitable for use in the field of optical information processing using coherent light or the field of optical measurement and control, a laser light source and a laser device, and a method of manufacturing an optical element. is there.
[0001]
(Background technology)
A conventional laser light source using an optical wavelength conversion element will be described with reference to FIG.
This laser light source includes a semiconductor laser 20, a solid-state laser crystal 21, and a nonlinear optical crystal of KNbO. ₃ Is basically composed of a light wavelength conversion element 25 according to.
[0002]
As shown in FIG. 1, a pump light P1a emitted from a semiconductor laser 20 oscillating at 807 nm is condensed by a lens 30 to excite a solid laser crystal 21 YAG. On the incident surface of the solid-state laser crystal 21, a total reflection mirror 22 is formed. The total reflection mirror reflects 99% of light having a wavelength of 947 nm, but transmits light having a wavelength of 800 nm. Therefore, the pump light P1a is efficiently introduced into the solid-state laser crystal 21, but the light having a wavelength of 947 nm generated by the solid-state laser crystal 21 is not emitted to the semiconductor laser 20 side, and the light wavelength conversion is performed. The light is reflected toward the element 25. Further, a mirror 23 that reflects 99% of the light having the wavelength of 947 nm and transmits the light in the 400 nm band is disposed on the output side of the light wavelength conversion element 25. These mirrors 22 and 23 form a resonator (cavity) by taking light having a wavelength of 947 nm, and can generate oscillation of 947 nm serving as a fundamental wave P1 in this resonator.
[0003]
The optical wavelength conversion element 25 is inserted into the resonator defined by the mirrors 22 and 23, thereby generating a harmonic P2. The power of the fundamental wave P1 inside the resonator reaches 1 W or more. For this reason, the conversion from the fundamental wave P1 to the harmonic wave P2 increases, and a harmonic having a high power can be obtained. Using a semiconductor laser with a power of 500 mW, a harmonic of 1 mW can be obtained.
[0004]
Next, a conventional optical wavelength conversion device having an optical waveguide will be described with reference to FIG. The illustrated optical wavelength conversion element generates a second harmonic (wavelength 420 nm) with respect to a fundamental wave having a wavelength of 840 nm when the fundamental wave is incident. Such an optical wavelength conversion element is disclosed in Mizuuchi, K .; Yamamoto and T.M. Taniuchi, Applied Physics Letters,
Vol 58, page 2732, June 1991.
[0005]
In this optical wavelength conversion element, as shown in FIG. ₃ An optical waveguide 2 is formed on a substrate 1, and a layer 3 (a domain-inverted layer) whose polarization is inverted is periodically arranged along the optical waveguide 2. LiTaO ₃ The portion of the substrate 1 where the domain-inverted layer 3 is not formed becomes the non-domain-inverted layer 4.
[0006]
When the fundamental wave P1 is incident on one end (incident surface 10) of the optical waveguide 2, a harmonic P2 is generated inside the optical wavelength conversion element and output from the other end of the optical waveguide 2. At this time, since the light propagating through the optical waveguide 2 is affected by the periodic structure formed by the domain-inverted layer 3 and the non-domain-inverted layer 4, the propagation constant between the generated harmonic P2 and the fundamental wave P1 is reduced. The mismatch is compensated for by the periodic structure of the domain-inverted layer 3 and the non-domain-inverted layer 4. As a result, this optical wavelength conversion element can output the harmonic P2 with high efficiency.
[0007]
Such an optical wavelength conversion element has, as a basic component, an optical waveguide 2 manufactured by a proton exchange method.
[0008]
Hereinafter, a method for manufacturing such an optical wavelength conversion element will be described with reference to FIG.
[0009]
First, in step S10 of FIG. 3, a domain-inverted layer forming step is performed.
[0010]
More specifically, first, LiTaO ₃ After depositing a Ta film so as to cover the main surface of the substrate 1, the Ta film is patterned in a stripe shape using a normal photolithography technique and a dry etching technique to form a Ta mask.
[0011]
Next, LiTaO whose main surface is covered with a Ta mask ₃ The substrate 1 is subjected to a proton exchange treatment at 260 ° C. for 20 minutes. Thus, LiTaO ₃ A proton exchange layer having a thickness of 0.5 μm is formed on a portion of the substrate 1 that is not covered with the Ta mask. After this, HF: HNF ₃ The Ta mask is removed by etching for 2 minutes using a 1: 1 mixture of the above.
[0012]
Next, a heat treatment is performed at a temperature of 550 ° C. for 1 minute to form a domain-inverted layer in each proton exchange layer. The temperature rise rate of the heat treatment is 50 ° C./sec, and the cooling rate is 10 ° C./sec. LiTaO ₃ The amount of Li is reduced in the portion where the proton exchange is performed as compared with the portion where the proton exchange is not performed in the substrate 1. Therefore, the Curie temperature of the proton exchange layer decreases, and a domain-inverted layer can be partially formed in the proton exchange layer at a temperature of 550 ° C. By this heat treatment, a proton exchange layer having a pattern reflecting the pattern of the Ta mask can be formed.
[0013]
Next, in step 2 of FIG. 3, an optical waveguide forming step is performed.
[0014]
More specifically, Step 2 is largely divided into Step S21, Step S22, and Step S23. A mask pattern is formed in step S21, a proton exchange process is performed in step S22, and high-temperature annealing is performed in step S23.
[0015]
Hereinafter, these steps will be described.
[0016]
In step S21, a Ta mask for forming an optical waveguide is formed. In this Ta mask, a slit-shaped opening (width 4 μm, length 12 mm) is formed in a Ta film. In step S22, the LiTaO covered with this Ta mask ₃ By subjecting the substrate 1 to a proton exchange treatment at 260 ° C. for 16 minutes, a high refractive index layer (thickness 0.5 μm) linearly extending in one direction is made of LiTaO. ₃ It is formed in the substrate 1. This high refractive index layer will eventually function as a waveguide. However, in this state, the nonlinearity of the proton-exchanged portion (high-refractive-index layer) is deteriorated. In order to recover this nonlinearity, after removing the Ta mask, annealing is performed at 420 ° C. for 1 minute in step S22. This annealing expands the high refractive index layer in the vertical and horizontal directions, and diffuses Li into the high refractive index layer. Thus, the nonlinearity can be recovered by lowering the proton exchange concentration of the high refractive index layer. As a result, the refractive index of the region (high refractive index layer) located immediately below the slit of the Ta mask is increased by about 0.03 from the refractive index of the other regions, and the high refractive index layer functions as an optical waveguide.
[0017]
Next, by performing a protective film forming step (Step S30), an end face polishing step (Step S40), and an AR coating step (Step S50), the optical wavelength conversion element is completed.
[0018]
Here, if the arrangement period of the domain-inverted layers periodically arranged along the waveguide is 10.8 μm, a tertiary quasi-phase matching structure can be formed.
[0019]
According to the optical wavelength conversion element, when the length of the optical waveguide 2 is set to 9 mm, a harmonic P2 having a power of 0.13 mW can be obtained with respect to a fundamental wave P1 having a wavelength of 840 nm (power 27 mW) (conversion efficiency 0). .5%).
[0020]
When forming a first-order quasi-phase matching structure, the arrangement period of the domain-inverted layers may be set to 3.6 μm. In this case, a harmonic P2 of 0.3 mW is obtained with respect to the fundamental wave P1 of 27 mW (conversion efficiency 1%). The present inventors have prototyped a laser light source that outputs blue laser light by combining such an optical wavelength conversion element and a semiconductor laser.
[0021]
Such an optical wavelength conversion element has a problem that the phase matching wavelength changes over time, and as a result, harmonics cannot be obtained. Although the wavelength of the fundamental wave emitted from the semiconductor laser is kept constant, if the phase matching wavelength of the optical wavelength conversion element shifts, the output of the harmonic wave gradually decreases and eventually becomes zero. Become.
[0022]
An object of the present invention is to stabilize a laser light source and to increase the output thereof, and to reduce the size and weight of the laser light source by incorporating the high-output laser light source into a laser device or an optical disk device. .
[0023]
(Disclosure of the Invention)
The method for manufacturing an optical element according to the present invention uses LiNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) a step of forming a proton exchange layer on a substrate and an annealing step of heat-treating the substrate at a temperature of 120 ° C. or lower for 1 hour or more.
[0024]
The annealing step is preferably performed at a temperature of 50 ° C. or more and 90 ° C. or less.
[0025]
The annealing step may include a step of gradually lowering the temperature.
[0026]
In one embodiment, the step of forming the proton exchange layer includes a step of performing a proton exchange treatment on the substrate and a step of heat-treating the substrate at a temperature of 150 ° C. or higher.
[0027]
In one embodiment, the step of forming the proton exchange layer includes a step of forming a plurality of periodically poled layers in the substrate, and a step of forming an optical waveguide on a surface of the substrate. Include.
[0028]
Another method for manufacturing an optical element according to the present invention is directed to a method for manufacturing LiNb. _x Ta _1-x O ₃ (0 ≦ X ≦ 1) a step of performing a proton exchange treatment on the substrate; and an annealing step of performing a plurality of heat treatments including at least the first and second heat treatments on the substrate. The temperature of the second anneal is at least 200 ° C. lower than the temperature of the first anneal.
[0029]
The second annealing is preferably performed at a temperature of 50 ° C. or more and 90 ° C. or less.
[0030]
The optical element of the present invention is composed of LiNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) An optical device comprising a substrate and a proton exchange layer formed in the substrate, wherein stable proton exchange in which the refractive index of the proton exchange layer does not change with time during use. It is formed from layers.
[0031]
In one embodiment, at least a part of the proton exchange layer forms an optical waveguide.
[0032]
The laser light source of the present invention is a light source including a semiconductor laser, and a light wavelength conversion element that receives laser light emitted from the semiconductor laser and converts the laser light into a harmonic, and the light wavelength conversion element Has an optical waveguide for guiding the laser light, and a domain-inverted structure periodically arranged along the optical waveguide, and the refractive index of the optical waveguide and the domain-inverted structure with the passage of time when used. It is formed from a stable proton exchange layer that does not change in nature.
[0033]
Another laser light source of the present invention is a semiconductor laser that emits a fundamental wave, a single mode fiber that transmits the fundamental wave, and an optical wavelength conversion element that receives the fundamental wave emitted from the fiber and generates a harmonic. , A light wavelength conversion element having a periodically poled structure.
[0034]
In one embodiment, the light wavelength conversion element has a modulation function.
[0035]
The light wavelength conversion element is LiNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) It is preferable that it is formed on a substrate.
[0036]
Still another laser light source according to the present invention is a semiconductor laser that emits pump light, a fiber that transmits the pump light, a solid-state laser crystal that receives pump light emitted from the fiber and generates a fundamental wave, And generating a harmonic wave, comprising an optical wavelength conversion element having a periodically poled structure.
[0037]
It is preferable that the light wavelength conversion element has a modulation function.
[0038]
The light wavelength conversion element is LiNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) It is preferable that it is formed on a substrate.
[0039]
In one embodiment, the solid-state laser crystal and the optical wavelength conversion element are integrated.
[0040]
Still another laser light source of the present invention is a semiconductor laser that emits pump light, a solid-state laser crystal that receives the pump light and generates a fundamental wave, a single mode fiber that transmits the fundamental wave, An optical wavelength conversion element that receives a wave and generates a harmonic, comprising an optical wavelength conversion element having a periodically poled structure.
[0041]
It is preferable that the light wavelength conversion element has a modulation function.
[0042]
Still another laser light source according to the present invention is a distributed feedback semiconductor laser that emits laser light, a semiconductor laser amplifier that amplifies the laser light, and a light wavelength converter that receives the amplified laser light and generates a harmonic. An optical wavelength conversion element having a periodically poled structure is provided.
[0043]
It is preferable that the light wavelength conversion element has a modulation function.
[0044]
The light wavelength conversion element is LiNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) It is preferable that it is formed on a substrate.
[0045]
In some embodiments, the semiconductor laser is wavelength locked.
[0046]
Still another laser light source according to the present invention is a laser light source including a semiconductor laser that emits laser light, and an optical wavelength conversion element in which a periodically poled structure and an optical waveguide are formed. The width and the thickness of the wave path are each 40 μm or more.
[0047]
The laser light source according to claim 26, wherein the light wavelength conversion element has a modulation function.
[0048]
The light wavelength conversion element is LiNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) Formed on a substrate.
[0049]
In one embodiment, the optical waveguide is of a graded type.
[0050]
A laser device of the present invention includes a semiconductor laser that emits laser light, a laser light source having an optical wavelength conversion element that generates a harmonic based on the laser light, a modulator that modulates the output intensity of the harmonic, A deflector for changing the direction of the harmonic emitted from the laser light source, wherein the optical wavelength conversion element has a periodically poled structure.
[0051]
In one embodiment, a high frequency is superimposed on the semiconductor laser during operation.
[0052]
In one embodiment, the laser light source includes a single mode fiber that transmits laser light from the semiconductor laser to the optical wavelength conversion device.
[0053]
In one embodiment, the laser light source includes a fiber that transmits laser light from the semiconductor laser, and a solid-state laser crystal that receives the laser light emitted from the fiber and generates a fundamental wave.
[0054]
In one embodiment, the semiconductor laser device is a distributed feedback semiconductor laser, and the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser.
[0055]
In one embodiment, an optical waveguide is formed in the optical wavelength conversion element, and each of the optical waveguide has a width and a thickness of 40 μm or more.
[0056]
Another laser device according to the present invention is a laser device including a laser light source that emits modulated ultraviolet laser light, and a deflector that changes the direction of the ultraviolet laser light, wherein the polarizer includes the ultraviolet laser light. To the screen, thereby generating red, green or blue light from the phosphor applied on the screen.
[0057]
In one embodiment, the laser light source includes a semiconductor laser, an optical wavelength conversion element that generates a harmonic, and a single mode fiber that transmits laser light from the semiconductor laser to the optical wavelength conversion element.
[0058]
In one embodiment, the laser light source includes a semiconductor laser, a fiber that transmits laser light from the semiconductor laser, a solid-state laser crystal that receives laser light emitted from the fiber and generates a fundamental wave, and An optical wavelength conversion element for generating a harmonic.
[0059]
In one embodiment, the laser light source further includes a semiconductor laser and a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser.
[0060]
In one embodiment, the laser light source includes a semiconductor laser that emits laser light, an optical waveguide that guides the laser light, and an optical wavelength conversion element in which a periodically poled structure is formed. The width and thickness are each 40 μm or more.
[0061]
Still another laser device according to the present invention includes three laser light sources that generate red, green, and blue laser lights, a modulator that changes the intensity of each laser light, and a deflector that changes the direction of each laser light. , Wherein the laser light source is constituted by a semiconductor laser.
[0062]
In one embodiment, a high frequency is superimposed on the semiconductor laser during operation.
[0063]
In one embodiment, the laser light source includes a semiconductor laser, an optical wavelength conversion element that generates a harmonic, and a single mode fiber that transmits laser light from the semiconductor laser to the optical wavelength conversion element.
[0064]
In one embodiment, the laser light source includes a semiconductor laser, a fiber that transmits laser light from the semiconductor laser, a solid-state laser crystal that receives laser light emitted from the fiber and generates a fundamental wave, and An optical wavelength conversion element for generating a harmonic.
[0065]
In one embodiment, the laser light source further includes a semiconductor laser and a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser.
[0066]
In one embodiment, the laser light source includes a semiconductor laser that emits laser light, an optical waveguide that guides the laser light, and an optical wavelength conversion element in which a periodically poled structure is formed. The width and thickness are each 40 μm or more.
[0067]
Still another laser device according to the present invention includes at least one or more laser light sources including a semiconductor laser, a sub-semiconductor laser, a modulator for changing the intensity of light from the laser light source, a screen, and the laser. A deflector that changes the direction of light from the light source and scans the screen with the light, and a light emitted from the sub semiconductor laser scans a peripheral portion of the screen, When the optical path of the light emitted from the sub semiconductor laser is interrupted, the irradiation of the laser light from the laser light source is stopped.
[0068]
In one embodiment, the laser light source includes an optical wavelength conversion element that generates a harmonic, and a single mode fiber that transmits laser light from the semiconductor laser to the optical wavelength conversion element.
[0069]
In one embodiment, the laser light source includes: the semiconductor laser; a fiber that transmits laser light from the semiconductor laser; a solid-state laser crystal that receives laser light emitted from the fiber and generates a fundamental wave; And a light wavelength conversion element for generating harmonics from the light.
[0070]
In one embodiment, the laser light source is a distributed feedback semiconductor laser, and the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser.
[0071]
In one embodiment, the laser light source includes an optical waveguide for guiding laser light from the semiconductor laser and an optical wavelength conversion element formed with a periodically poled structure, and the width and the thickness of the optical waveguide are Each is 40 μm or more.
[0072]
The laser device of the present invention includes at least one or more laser light sources including a semiconductor laser, and a deflector that changes a direction of laser light emitted from the laser light source and scans a screen with the laser light. A laser device, further comprising two or more detectors that generate a signal when a part of the laser is received, while the deflector scans the screen with the laser light. If no signal is generated within a certain period of time, generation of laser light from the laser light source is stopped.
[0073]
In one embodiment, the laser light source includes an optical wavelength conversion element that generates a harmonic, and a single mode fiber that transmits laser light from the semiconductor laser to the optical wavelength conversion element.
[0074]
In one embodiment, the laser light source includes: the semiconductor laser; a fiber that transmits laser light from the semiconductor laser; a solid-state laser crystal that receives laser light emitted from the fiber and generates a fundamental wave; And a light wavelength conversion element for generating a harmonic from the light.
[0075]
In one embodiment, the laser light source is a distributed feedback semiconductor laser, and the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser.
[0076]
In one embodiment, the laser light source includes an optical waveguide for guiding laser light from the semiconductor laser and an optical wavelength conversion element formed with a periodically poled structure, and the width and the thickness of the optical waveguide are Each is 40 μm or more.
[0077]
Still another laser device of the present invention includes at least one or more laser light sources including a semiconductor laser, a modulator that changes the intensity of each laser light, and a deflector that changes the direction of each laser light. And divides the laser light emitted from the laser light source into two or more optical paths and irradiates the screen from two directions.
[0078]
In one embodiment, the laser light source includes an optical wavelength conversion element that generates a harmonic, and a single mode fiber that transmits laser light from the semiconductor laser to the optical wavelength conversion element.
[0079]
In one embodiment, the laser light source includes: the semiconductor laser; a fiber that transmits laser light from the semiconductor laser; a solid-state laser crystal that receives laser light emitted from the fiber and generates a fundamental wave; And a light wavelength conversion element for generating a harmonic from the light.
[0080]
In one embodiment, the laser light source is a distributed feedback semiconductor laser, and the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser.
[0081]
In one embodiment, the laser light source includes an optical waveguide for guiding laser light from the semiconductor laser and an optical wavelength conversion element formed with a periodically poled structure, and the width and the thickness of the optical waveguide are Each is 40 μm or more.
[0082]
In some embodiments, two laser light sources form two light paths, and each laser light source is separately modulated.
[0083]
In some embodiments, the two optical paths switch in time.
[0084]
Still another laser device according to the present invention includes at least one or more laser light sources including a semiconductor laser, a first optical system for converting a laser beam emitted from the laser light source into a parallel beam, and spatially modulating the parallel beam. And a second optical system for irradiating the screen with light emitted from the liquid crystal cell.
[0085]
In one embodiment, the laser light source includes an optical wavelength conversion element that generates a harmonic, and a single mode fiber that transmits laser light from the semiconductor laser to the optical wavelength conversion element.
[0086]
In one embodiment, the laser light source includes: the semiconductor laser; a fiber that transmits laser light from the semiconductor laser; a solid-state laser crystal that receives laser light emitted from the fiber and generates a fundamental wave; And a light wavelength conversion element for generating a harmonic from the light.
[0087]
In one embodiment, the laser light source is a distributed feedback semiconductor laser, and the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser.
[0088]
In one embodiment, the laser light source includes an optical waveguide for guiding laser light from the semiconductor laser and an optical wavelength conversion element formed with a periodically poled structure, and the width and the thickness of the optical waveguide are Each is characterized by being at least 40 μm.
[0089]
In one embodiment, the sub semiconductor laser is an infrared semiconductor laser.
[0090]
In one embodiment, laser light irradiation is stopped by shifting the phase matching wavelength of the light wavelength conversion element.
[0091]
An optical disc device of the present invention includes a laser light source that generates a laser beam, an optical wavelength conversion element that converts a fundamental wave into a harmonic, an optical pickup that incorporates the optical wavelength conversion element, and an actuator that moves the optical pickup. Wherein the laser light emitted from the laser light source is incident on the optical pickup via an optical fiber.
[0092]
In one embodiment, the laser light source includes a semiconductor laser disposed outside the optical pickup.
[0093]
In one embodiment, the laser light source further includes a solid-state laser crystal that generates the fundamental wave using laser light emitted from the semiconductor laser as pump light.
[0094]
In one embodiment, the solid-state laser crystal is disposed outside the optical pickup, and a fundamental wave generated by the solid-state laser medium is incident on the optical wavelength conversion element via the optical fiber.
[0095]
In one embodiment, the solid-state laser crystal is disposed inside the optical pickup, and the laser light emitted from the semiconductor laser is incident on the solid-state laser via the optical fiber.
[0096]
(Best Mode for Carrying Out the Invention)
The inventors of the present application have considered the cause of the above-mentioned optical wavelength conversion element having an optical waveguide, in which the phase matching wavelength is shortened with the passage of time and harmonics are not generated.
[0097]
FIG. 4 shows the relationship between the time elapsed from immediately after the fabrication of the conventional optical wavelength conversion device and the output of harmonics. It can be seen that the harmonic output decreases rapidly with the passage of time.
[0098]
FIG. 5 shows the relationship between the elapsed time and the phase matching wavelength. The harmonic output is reduced by half three days after the device is manufactured. At this time, it can be seen that the phase matching wavelength has shifted to the shorter wavelength side. The phase matching wavelength λ is the polarization inversion period Λ and the effective refractive index n for the harmonics and the fundamental wave _2W And n _W Is determined by More specifically, λ = 2 (n _2W -N _W ) ・ Λ
[0099]
Since the period Λ of the domain-inverted layer is kept constant without changing over time, the decrease in the phase matching wavelength λ is caused by the effective refractive index n _2W And n _W Is thought to be due to the change in
[0100]
FIG. 6 shows the effective refractive index n _2W And the elapsed time. From FIG. 6, the effective refractive index n _2W It can be seen that the value decreases with the passage of time from the device fabrication date.
[0101]
The inventor of the present application considers this cause as follows.
[0102]
The high-temperature treatment of about 400 ° C. performed when forming the optical waveguide introduces strain or the like into the proton exchange layer, and as a result, a layer (change layer) having an increased refractive index is formed in the proton exchange layer. This distortion is gradually released with the passage of time, and the refractive index of the variable layer approaches the original refractive index.
[0103]
A deformed layer with an increased refractive index is formed due to strain and the like generated during high-temperature annealing, but the refractive index of the changed layer returns to its original size over time, and finally, the changed layer becomes a stable proton. Become an exchange layer. However, it takes many years for the variable layer to become such a stable proton exchange layer. In the specification of the present application, a proton exchange layer whose effective refractive index does not decrease with time depending on use at normal temperature (about 0 ° C. to about 50 ° C.) is referred to as “stable proton exchange layer”. I do.
[0104]
The above is the mechanism of the change with time considered by the present inventor. In order to confirm this, the sample whose refractive index decreased due to aging was subjected to annealing at 300 ° C. for 1 minute. At such an annealing temperature and time, diffusion of protons and the like hardly occurs, so that the waveguide does not spread. Therefore, according to the conventional concept, the refractive index of the proton exchange layer should not change at all. However, according to an experiment by the inventor, the refractive index increased again by annealing at 300 ° C. for 1 minute. Further, after the annealing, a phenomenon was observed that the refractive index decreased again with the passage of time.
[0105]
The present invention alleviates the strain generated in the proton exchange layer by the heat treatment at a relatively high temperature, thereby preventing the light wavelength conversion element from changing with time.
[0106]
Embodiments will be described below with reference to the drawings.
[0107]
(Example 1)
A first embodiment of the present invention will be described with reference to FIG.
[0108]
In the optical wavelength conversion device of the present embodiment, the optical waveguide composed of the stable proton exchange layer is made of LiTaO. ₃ The plurality of domain-inverted layers 3 are formed on the substrate 1 and arranged periodically along the optical waveguide. When the fundamental wave P1 enters the input end of the optical waveguide, the harmonic P2 is emitted from the output end. The length of the light wavelength conversion element (the length of the waveguide) of this embodiment is 9 mm. Further, the length of one period of the domain-inverted layer 3 is set to 3.7 μm so as to operate at a wavelength of 850 nm.
[0109]
Hereinafter, a method for manufacturing the optical wavelength conversion element will be described with reference to FIGS. 8A to 8E.
[0110]
As shown in FIG. 8A, first, LiTaO ₃ After depositing a Ta film so as to cover the main surface of the substrate 1, the Ta film (thickness: about 200 to 300 nm) is patterned in a stripe shape using a normal photolithography technique and a dry etching technique, and a Ta mask 6 is formed. To form The Ta mask 6 used in this embodiment has a pattern in which strips having a width of 1.2 μm and a length of 10 mm are arranged at equal intervals, and the arrangement cycle of the strips is 3.7 μm. A proton exchange treatment is performed on the LiTaO 3 substrate 1 whose main surface is covered with the Ta mask 6. This proton exchange treatment is performed by immersing the surface of the substrate 1 in pyrophosphoric acid heated to 230 ° C. for 14 minutes.
Thus, LiTaO ₃ A proton exchange layer 7 having a thickness of 0.5 μm is formed on a portion of the substrate 1 not covered with the Ta mask. After this, HF: HNF ₃ The Ta mask is removed by etching for 2 minutes using a 1: 1 mixture of the above.
[0111]
Next, as shown in FIG. 8B, a domain-inverted layer is formed in each proton exchange layer 7 by performing a heat treatment at a temperature of 550 ° C. for 15 seconds. The temperature rise rate of the heat treatment is 50 to 80 ° C./sec, and the cooling rate is 1 to 50 ° C./sec. LiTaO ₃ The amount (concentration) of Li is lower in the portion where the proton exchange is performed than in the portion where the proton exchange is not performed in the substrate 1. Therefore, the Curie temperature of the proton exchange layer 7 is lower than that of the other portions, and the domain-inverted layer 3 can be partially formed in the proton exchange layer 7 by the heat treatment at 550 ° C. By this heat treatment, the domain-inverted layer 3 having a periodic pattern reflecting the periodic pattern of the Ta mask 6 can be formed.
[0112]
Next, a Ta mask (not shown) for forming an optical waveguide is formed. This Ta mask is formed by forming a slit-shaped opening (width 4 μm, length 12 mm) in a Ta film (thickness: about 200 to 300 nm) deposited on the substrate 1. This opening defines the planar layout of the waveguide. It goes without saying that the shape of the waveguide is not limited to a linear one. The pattern of the Ta mask is determined according to the shape of the waveguide to be formed. LiTaO covered with Ta mask ₃ By performing a proton exchange treatment on the substrate 1 at 260 ° C. for 16 minutes, as shown in FIG. ₃ A proton exchange layer (thickness 0.5 μm, width 5 μm, length 10 mm) 5 extending linearly is formed in a region of the substrate 1 located below the opening of the Ta mask. The linearly extending proton exchange layer 5 eventually functions as a waveguide. After this, HF: HNF ₃ The Ta mask is removed by etching for 2 minutes using a 1: 1 mixture of the above.
[0113]
Next, annealing is performed at 420 ° C. for 1 minute using an infrared heating device. By this annealing, the nonlinearity of the proton exchange layer 5 is restored, and as shown in FIG. 8D, a variable layer 8b whose refractive index is increased by about 0.03 is formed. This annealing has a function of diffusing Li and protons in the substrate 1 and lowering the proton exchange concentration of the proton exchange layer 5 as described above. Thereafter, a 300 nm thick SiO 2 serving as a protective film is formed on the main surface of the substrate 1. ₂ Deposit a film (not shown).
[0114]
Next, the surface of the substrate 1 perpendicular to the variable layer 8b is optically polished to form an incident portion and an exit portion of the light wavelength conversion element, and then, as shown in FIG. An anti-reflection (AR) coat 15 is formed on the polished surface of.
[0115]
Next, low-temperature annealing is performed to prevent a temporal change. As used herein, "low temperature annealing" refers to a heat treatment performed at a temperature that does not substantially reduce the proton concentration of the proton exchange layer. For example, LiTaO ₃ In the case of a substrate, "low temperature annealing" refers to a heat treatment performed at a temperature of about 130C or lower. In this embodiment, heat treatment is performed in an air atmosphere at 60 ° C. for 40 hours using an oven. By such low-temperature annealing, a stable proton exchange layer 8a is formed. This stable proton exchange layer 8a forms an optical waveguide.
[0116]
With reference to FIG. 9, the flow of the above manufacturing process will be described.
[0117]
After the step of forming the domain-inverted layer on the substrate (step S10), the step of forming an optical waveguide (S20) is performed. The optical waveguide forming step (S20) is roughly divided into step S21, step S22, and step S23. A mask pattern is formed in step S21, a proton exchange process is performed in step S22, and high-temperature annealing is performed in step S23. Thereafter, a protective film forming step (Step S30), an end face polishing step (Step S40), and an AR coating step (Step S50) are performed. Since the wavelength conversion element changes with time in this state, low-temperature annealing is performed in step S60 to form a stable proton exchange layer.
[0118]
FIG. 10 shows the relationship between the annealing time when the low-temperature annealing temperature is 60 ° C. and 120 ° C. The phase matching wavelength shift amount becomes almost constant in several hours by annealing at 120 ° C., but takes several tens of hours to become almost constant by annealing at 60 ° C.
[0119]
From FIG. 10, it can be seen that the higher the temperature of the low-temperature annealing, the sooner the annealing time becomes a stable state. Further, the lower the annealing temperature, the closer the phase matching wavelength shift amount to zero when the state changes to the stable state. As described above, when the temperature of the low-temperature annealing is increased, the time required for returning the shift amount to zero is short, but on the other hand, a relatively large amount of distortion remains.
[0120]
FIG. 11 shows the relationship between the amount of phase matching wavelength shift when returning to a stable state and the temperature of low-temperature annealing. From FIG. 11, it can be seen that annealing at 120 ° C. stabilizes the phase matching wavelength shifted by about 0.5 nm. If annealing is performed at 150 ° C. or more, the amount of shift of the phase matching wavelength after stabilization becomes 0.8 nm or more. If such a large shift of the phase matching wavelength remains, it becomes difficult to use the optical wavelength conversion element for a long time. If the allowable range of the shift of the phase matching wavelength is 0.5 nm or less, the amount of shift cannot be reduced within the allowable range even if annealing is performed at a temperature exceeding 120 ° C. If the allowable range of the phase matching wavelength shift is widened, the conversion efficiency decreases. When the shift amount of the phase matching wavelength exceeds 0.5 nm, only about １ ／ of the output when the shift amount is zero can be obtained. If the low-temperature annealing temperature is set to 60 ° C., the annealing time becomes longer, but the shift amount can be reduced to 0.1 nm or less, so that the problem of lowering the conversion efficiency is eliminated. It is preferable that the shift amount of the phase matching wavelength be suppressed to about 0.2 nm or less.
[0121]
According to this embodiment, the refractive indices of the non-polarization inversion layer 4 and the polarization inversion layer 3 in the optical waveguide 2 do not change with time, and the propagation loss when light is guided is small. When a laser beam (850 nm in wavelength) from a semiconductor laser is incident on the incident portion as a fundamental wave P1 and propagates through the optical waveguide, the light propagates in a single mode, and a harmonic P2 having a wavelength of 425 nm is emitted from the emission portion to the outside of the substrate. Was taken out. The propagation loss of the optical waveguide 2 was as small as 1 dB / cm, and the harmonic P2 was effectively obtained. A harmonic of 1.2 mW (wavelength 425 nm) was obtained by inputting a fundamental wave of 27 mW. The conversion efficiency in this case is 4.5%.
[0122]
FIG. 12 shows the relationship between the elapsed days and the harmonic output. FIG. 13 shows the relationship between the elapsed days and the phase matching wavelength, and the relationship between the elapsed days and the change in the refractive index.
[0123]
From these figures, it can be seen that the change in the refractive index and the phase matching wavelength are constant immediately after the fabrication of the device. According to the method for manufacturing an optical wavelength conversion device of the present invention, an optical wavelength conversion device having a constant phase matching wavelength can be realized because a change in refractive index does not occur over time. When this element is combined with a semiconductor laser, a stable short-wavelength laser can be manufactured. At a temperature of about 60 ° C., low-temperature annealing for 40 hours or more is particularly effective.
[0124]
(Example 2)
Next, a second embodiment of the present invention will be described.
[0125]
First, LiTaO ₃ After depositing a Ta film so as to cover the main surface of the substrate, the Ta film (thickness: about 200 to 300 nm) is patterned in a stripe shape using a normal photolithography technique and a dry etching technique to form a Ta mask. I do. The Ta mask used in this embodiment has a pattern in which strips having a width of 1.2 μm and a length of 10 mm are arranged at equal intervals, and the arrangement cycle of the strips is 3.6 μm. LiTaO whose main surface is covered with Ta mask ₃ The substrate 1 is subjected to a proton exchange treatment. This proton exchange treatment is performed by immersing the surface of the substrate in pyrophosphoric acid heated to 260 ° C. for 20 minutes. Thus, LiTaO ₃ A proton exchange layer having a thickness of 0.5 μm is formed on a portion of the substrate that is not covered with the Ta mask. After this, HF: HNF ₃ The Ta mask is removed by etching for 2 minutes using a 1: 1 mixture of the above.
[0126]
Next, a heat treatment is performed at a temperature of 550 ° C. for 15 seconds to form a domain-inverted layer in each proton exchange layer 7. The temperature rise rate of the heat treatment is 50 ° C./sec, and the cooling rate is 10 ° C./sec. By this heat treatment, a domain-inverted layer having a periodic pattern reflecting the periodic pattern of the Ta mask can be formed.
[0127]
With reference to FIG. 14, a flow of a process following the above process will be described.
[0128]
First, a proton exchange treatment is performed on the surface of the substrate on which the domain-inverted layers are arranged, thereby forming an optical waveguide (step S100). As a mask for forming an optical waveguide, a mask in which a slit having a width of 4 μm and a length of 12 mm is formed on a Ta film is used.
[0129]
Next, after performing proton exchange in pyrophosphoric acid at 260 ° C. for 16 minutes (Step S110), the Ta mask is removed. 300nm thick SiO ₂ After covering the main surface of the substrate with the film, low-temperature annealing (step S120) is performed to complete the formation of the optical waveguide. In the low-temperature annealing, a heat treatment at 120 ° C. was performed for 200 hours in air in order to prevent an increase in the refractive index. By this low-temperature annealing, a stable proton exchange layer is formed.
[0130]
Through the above steps, the domain-inverted layer and the optical waveguide are formed on the substrate. When the thickness of the domain-inverted layer is 2.2 μm, the thickness d of the optical waveguide is set smaller than the thickness of the domain-inverted layer, for example, 1.8 μm in order to perform wavelength conversion effectively. To operate at a wavelength of 840 nm, the period of the domain-inverted layer is set to 3.6 μm.
[0131]
According to the above manufacturing method, the refractive index does not change with time in the non-polarized layer and the domain-inverted layer, and the light propagation loss is small. The plane perpendicular to the optical waveguide was optically polished to form an entrance and an exit. Thus, an optical wavelength conversion element can be manufactured. The length of this element is 9 mm.
[0132]
When a semiconductor laser beam (wavelength 840 nm) was made incident on the incident part of the waveguide as the fundamental wave P1, a harmonic P2 having a wavelength of 420 nm was extracted from the emission part to the outside of the substrate. A harmonic (wavelength: 420 nm) having an output of 10 mW was obtained with respect to the input of the fundamental wave having an output of 80 mW. The conversion efficiency in this case is 12%. The harmonic output was very stable with no light damage and no change over time. If the high-temperature annealing step is not inserted in the middle of the process as in this embodiment, the change with time can be prevented.
[0133]
(Example 3)
Next, as a third embodiment of the present invention, LiNbO ₃ The case where a substrate (thickness: 0.4 to 0.5 mm) is used will be described.
[0134]
First, using a normal photolithography technique and a dry etching technique, a Ta electrode (first Ta electrode) having a pattern similar to the pattern of the Ta mask used in each of the above-described embodiments is used for LiNbO. ₃ It is formed on the main surface of the substrate.
[0135]
Thereafter, a Ta film (second Ta electrode) is deposited on the entire back surface of the substrate. An electrode structure for applying an electric field to the substrate is constituted by the first Ta electrode formed on the main surface of the substrate and the second Ta electrode formed on the back surface of the substrate.
[0136]
Next, a voltage (for example, 10 kV) is applied between the first Ta electrode and the second Ta electrode, and LiNbO ₃ An electric field is formed in the substrate. This voltage application forms a domain-inverted layer extending from a portion of the front surface of the substrate that is in contact with the first Ta electrode to a back surface of the substrate.
[0137]
Next, HF: HNF ₃ Etching is performed for 2 minutes with a 1: 1 mixture of the above to remove the Ta electrode. Next, after forming a Ta mask having a slit-shaped opening (width 4 μm, length 12 mm) on the substrate, a proton exchange treatment using pyrophosphoric acid (230 ° C., 10 minutes) is performed to form an optical waveguide. I do. After removing the Ta mask, annealing is performed at 420 ° C. for 2 minutes using an infrared heating device. By this annealing, the nonlinearity in the optical waveguide is recovered, but a variable layer whose refractive index is increased by about 0.02 is formed.
[0138]
Thereafter, a 300 nm thick SiO 2 serving as a protective film is formed. ₂ A film is deposited on the substrate. Next, in order to alleviate the distortion caused by the increase in the refractive index, annealing at 100 ° C. for 20 hours (first-stage low-temperature annealing) is performed in air, followed by annealing at 60 ° C. for 10 hours (second-stage low-temperature annealing). )I do. Thus, in this embodiment, two-stage low-temperature annealing is performed. The low-temperature annealing is performed in two stages in order to reduce the total time required for the low-temperature annealing. According to the annealing at 100 ° C., the strain is relieved faster than the annealing at 60 ° C., but the strain corresponding to the amount of phase matching wavelength shift at 100 ° C. as shown in FIG. 11 remains. Therefore, low-temperature annealing at 60 ° C. is additionally performed to completely eliminate the strain. By this two-step annealing, it is possible to quickly and completely form a “stable proton exchange layer” that is unlikely to change with time.
[0139]
The thickness d of the optical waveguide formed by the above steps is 1.8 μm.
The arrangement period of the domain-inverted layers is 3 μm, and operates at a wavelength of 840 nm. The surface perpendicular to the optical waveguide was optically polished to form an incident part and an outgoing part. Thus, an optical wavelength conversion element can be manufactured. The length of this element is 10 mm. When a semiconductor laser beam (wavelength 840 nm) was guided from the incident part as the fundamental wave P1, a harmonic P2 having a wavelength of 420 nm was extracted outside the substrate from the emission part. A harmonic of 13 mW (wavelength 420 nm) was obtained by inputting a fundamental wave of 80 mW. The harmonic output was very stable with no change over time.
[0140]
In this embodiment, two types of low-temperature annealing (two-step annealing) are performed at different temperatures. For example, low-temperature annealing is performed by gradually lowering the temperature from 100 ° C. to 60 ° C. over 30 hours. Is also good.
[0141]
(Example 4)
Next, a fourth embodiment according to the present invention will be described with reference to FIGS. 15A to 15C.
[0142]
First, as shown in FIG. 15A, LiNbO ₃ And LiTaO ₃ Mixture film (LiNb _0.5 Ta _0.5 O ₃ A film 16 ′ is grown on the LiTaO 3 substrate 1. At this time, the growth temperature exceeds 1000 ° C., and the strain is increased with the mixture film 16 and LiTaO. ₃ It remains at the interface with the substrate 1. Next, as shown in FIG. 15B, a resist mask 17 is formed on the mixture film 16 'by using a normal photolithography technique. Next, as shown in FIG. 15C, a portion of the mixture film 16 that is not covered with the resist mask 17 is removed by ion beam etching, and the optical waveguide 16 having a width of, for example, 4 μm is left.
[0143]
300 nm thick SiO by evaporation method ₂ Is deposited on the substrate 1 and then low-temperature annealing is performed to alleviate a rise in the refractive index. This annealing includes a first-stage low-temperature annealing performed at 100 ° C. for 30 hours, and a subsequent first-stage low-temperature annealing performed at 70 ° C. for 60 hours. By this low-temperature annealing, a stable optical waveguide layer 16 having no change in refractive index can be obtained.
[0144]
The thickness d of the optical waveguide formed by the above process is 1.8 μm. The length of this element is 9 mm. The plane perpendicular to the optical waveguide was optically polished to form an entrance and an exit. When semiconductor laser light (wavelength 840 nm) was guided from the incident part, the waveguide loss was very small. The change over time in the refractive index was below the measurement limit and was very stable. The material of the mixture film is LiNb _0.5 Ta _0.5 O ₃ Not limited to LiNb _x Ta _1-x O ₃ (0 <x <1) or another optical material.
[0145]
(Example 5)
Next, a fifth embodiment of the present invention will be described.
[0146]
The outline of the process flow of this embodiment will be described with reference to FIG.
[0147]
First, an optical waveguide forming step is performed. The optical waveguide forming process is roughly divided into step S200, step S210 and step S220. A mask pattern is formed in step S200, proton exchange processing is performed in step S210, and high-temperature annealing is performed in step S220. Thereafter, an electrode forming step (Step S230), a low-temperature annealing step (Step S240), an end face polishing step (Step S250), and an AR coating step (Step S260) are performed.
[0148]
The details of the process will be described below.
[0149]
First, Ta is patterned into slits using a normal photo process and dry etching. Next, LiTaO on which a pattern of Ta is formed ₃ Proton exchange is performed on the substrate 1 at 230 ° C. for 10 minutes to form a 0.5 μm-thick proton exchange layer immediately below the slit. Next, HF: HNF ₃ Etching is performed for 2 minutes with a 1: 1 mixture of the above to remove Ta. Annealing (first annealing) is performed at 400 ° C. for 1 hour using a diffusion furnace to form a variable layer having a refractive index increased by about 0.01. Next, as an electrode forming step, 300 nm of SiO2 was added by vapor deposition. Then, patterning was performed after Al was deposited in a stripe shape as an electrode mask. Next, low-temperature annealing was performed to alleviate the increase in the refractive index. Annealing was performed in air at 70 ° C. for 10 hours. Thereby, a stable proton exchange layer is formed. Here, the second annealing was performed at a temperature lower by 330 ° C. than the first annealing. By lowering the temperature by 200 ° C. or more, distortion can be greatly reduced, which is effective. Finally, polishing and AR coating were performed.
[0150]
An optical waveguide with electrodes was manufactured by the above-described steps. This functions as an optical modulator. The thickness of this optical waveguide is 8 μm. The plane perpendicular to the optical waveguide was optically polished to form an entrance and an exit. Thus, an optical element can be manufactured.
The length of this element is 9 mm. A modulation signal was applied to the electrode, and a semiconductor laser beam (wavelength: 1.56 μm) was guided as a fundamental wave from the incident portion. The modulated light was extracted from the emitting portion. There was no change with time and the bias voltage was stable for 2000 hours or more.
[0151]
In each of the above embodiments, the present invention has been described with respect to an optical wavelength conversion element and an optical modulator as an example of an optical element. However, the present invention is not limited to this, and the present invention is not limited to this. And so on. The change in refractive index with time due to the proton exchange treatment can be prevented, and the deterioration of characteristics can be suppressed.
[0152]
(Example 6)
Next, a sixth embodiment of the present invention will be described with reference to FIG. This embodiment is a short wavelength light source including a semiconductor laser and an optical wavelength conversion element.
[0153]
As shown in FIG. 17, the pump light P1a emitted from the semiconductor laser 20 is condensed by the lens 30 and excites the YAG 21 which is a solid-state laser crystal.
[0154]
The YAG 21 has a total reflection mirror 22 for 947 nm, oscillates at a wavelength of 947 nm, and emits a fundamental wave P1. On the other hand, the total reflection mirror 23 for the fundamental wave P1 is formed on the emission side of the optical wavelength conversion element 25, and the laser oscillation occurs during this period. The fundamental wave P1 is condensed by the lens 31, and the fundamental wave P1 is converted by the optical wavelength conversion element 25 into a harmonic P2. In this embodiment, LiTaO is used as an optical wavelength conversion element having a periodically poled structure in which a periodic structure is formed. ₃ An optical waveguide 2 manufactured using proton exchange in a substrate 1 is used.
[0155]
In FIG. 17, 1 is LiTaO of Z plate. ₃ The substrate 2 is the formed optical waveguide, 3 is the domain-inverted layer, 10 is the incidence part of the fundamental wave P1, and 12 is the emission part of the harmonic P2. The fundamental wave P1 entering the optical waveguide 2 is converted into a harmonic P2 by the domain-inverted layer 3 having the length of the phase matching length L, and then converted into a harmonic by the non-domain-inverted layer 4 having the same length L. Power will increase.
[0156]
The harmonic P2 having increased power in the optical waveguide 2 is radiated from the emission unit 12. The divergent harmonic P2 is made parallel by the lens 32.
[0157]
Further, the electrode 14 is formed on the light wavelength conversion element 25 via the protective film 13. Next, a method for manufacturing the optical wavelength conversion element 25 will be briefly described with reference to the drawings.
[0158]
First, as shown in FIG. 18A, using a normal photolithography technique and a dry etching technique, a Ta electrode (first Ta electrode) 6 having a pattern similar to the pattern of the Ta mask used in each of the above embodiments. With a 0.3 mm thick LiNbO ₃ It is formed on the main surface of the substrate 1.
[0159]
Thereafter, a Ta film (second Ta electrode) 6b is deposited on the entire back surface of the substrate 1. The first Ta electrode 6 formed on the main surface of the substrate 1 and the second Ta electrode 6b formed on the back surface of the substrate 1 form an electrode structure for applying an electric field to the substrate 1.
[0160]
Next, a voltage (for example, 10 kV) is applied between the first Ta electrode 6 and the second Ta electrode 6b, and LiNbO ₃ An electric field is formed in the substrate 1. By this voltage application, as shown in FIG. 18B, the domain-inverted layer 3 extending from the portion of the front surface of the substrate 1 that is in contact with the first Ta electrode 6 to the back surface of the substrate 1 is formed. The length L of the domain-inverted layer 3 along the direction in which light propagates is 2.5 μm. Thereafter, etching is performed for 20 minutes with a 1: 1 mixed solution of HF: HNF3 to remove the Ta electrodes 6 and 6b.
[0161]
Next, after forming a Ta mask (not shown) having a slit-shaped opening (width 4 μm, length 12 mm) on the substrate 1, a proton exchange treatment (260 ° C., 40 minutes) using pyrophosphoric acid is performed. Thus, the optical waveguide 2 is formed as shown in FIG. 18C. The Ta mask has a slit (width 6 μm, length 10 mm), and this slit defines a planar layout of the optical waveguide 2. After removing the Ta mask, annealing is performed at 460 ° C. for 5 hours using an infrared heating device. By this annealing, the nonlinearity of the proton-exchanged optical waveguide is restored, and the refractive index of that portion is increased by about 0.002. Light propagates along the optical waveguide 2 having a high refractive index. The thickness d of the optical waveguide 2 is 50 μm and the width is 70 μm. The arrangement period of the domain-inverted layers 3 along the direction in which the waveguide 2 extends is 5 μm, and this optical wavelength conversion element operates with respect to a fundamental wave having a wavelength of 947 nm.
[0162]
Next, as shown in FIG. ₂ After forming a protective film (thickness 300 to 400 nm) 13 formed on the substrate 1, an Al film (thickness 200 nm) is formed on the protective film 13 by vapor deposition. The Al film is patterned by photolithography to form an Al electrode 14. The Al electrode 14 is used for intensity modulation of output light.
[0163]
A plane perpendicular to the direction in which the optical waveguide 2 extends is optically polished to form the entrance 10 and the exit 12 shown in FIG. Further, the incident portion 10 is provided with a non-reflection coating for the fundamental wave P1. The emission section 12 is provided with a reflection coat (99%) for the fundamental wave P1 and a non-reflection coat for the harmonic wave P2.
[0164]
Thus, the light wavelength conversion element 25 (element length 10 mm) shown in FIG. 17 can be manufactured.
[0165]
In FIG. 17, when a wavelength of 947 nm was guided from the incident part 10 as the fundamental wave P1, the single-mode propagation was performed, and a harmonic P2 having a wavelength of 473 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 0.1 dB / cm, the performance of the resonator was improved, the power density of the fundamental wave P1 was increased, and the harmonic wave P2 was generated with high efficiency.
[0166]
Possible causes of the low loss are that a uniform optical waveguide was formed by phosphoric acid and that the confinement of the waveguide was reduced. In addition, due to the weakly confined optical waveguide, the harmonic density was reduced, and the optical damage was greatly improved. This is because by making the area 100 times the conventional area, it is possible to withstand 100 times the optical damage.
[0167]
FIG. 19 shows the relationship between the optical waveguide thickness and the light damage resistance power. The light-tolerant damage power is a power of how much the blue harmonics can withstand, that is, does not cause light fluctuation. It can be seen that when the thickness of the optical waveguide is increased, the width is also increased by diffusion, so that the light damage resistance power is improved with respect to almost the square of the optical waveguide thickness. Since the power required for laser projection is at least 2 W, the thickness of the optical waveguide is desirably 40 μm or more.
[0168]
Further, in a case where the distribution of the refractive index in the waveguide and its peripheral portion changes stepwise, if the cross section of the waveguide is enlarged, a multi-mode propagation phenomenon occurs. In order to avoid this, in the present embodiment, a waveguide having a graded refractive index distribution is formed.
[0169]
When the output of the output light P1a of the semiconductor laser 20 was 10W, a harmonic P3 having an output of 3W was obtained. The conversion efficiency in this case is 30%. The tolerance of the optical wavelength conversion element to wavelength fluctuation is 0.4 nm. Even when the wavelength was shifted by 0.4 nm, the oscillation wavelength of the solid-state laser was constant, and the harmonic output was stable. By applying a voltage to the modulation Al electrode 14, the refractive index of the waveguide and the vicinity thereof changes, and the phase matching wavelength of the optical wavelength conversion element shifts. By utilizing the phenomenon that the phase matching wavelength is largely shifted by the application of a voltage, it is possible to modulate the harmonic output by applying a relatively low voltage of about 100 V.
[0170]
As described above, according to the optical wavelength conversion device using the periodically poled structure used in the present embodiment, it is possible to easily modulate the harmonic output by applying a voltage, and the required applied voltage is low. High utility value.
[0171]
Thus, the modulator can be integrated, and the size, weight, and cost can be reduced. Further, the non-linear optical crystal used in the present invention, LiTaO ₃ Is characterized in that a large crystal can be obtained, and mass production of an optical wavelength conversion element using an optical IC process is easy. In multi-mode propagation with respect to the fundamental wave, the output of the harmonic is unstable and impractical, and the single mode is effective. When an optical wavelength conversion element having a periodically poled structure is used as in this embodiment, high efficiency can be achieved, and an optical modulator can be integrated. Red and green laser light can be extracted, and its value is great. Note that the optical modulator may be separated.
[0172]
Next, an embodiment of the laser projection apparatus of the present invention will be described with reference to FIG.
As shown in FIG. 20, a blue laser light source shown in FIG. 17 was used as a light source of the laser projection device. Reference numeral 45 denotes a blue 473 nm laser light source. The blue light is modulated by inputting a modulation signal to the modulation electrode. The modulated blue laser light enters the deflector. 56 is a vertical deflector, 57 is a horizontal deflector, and both use a rotating polygon mirror. Using a screen 70 with a gain of 3 and a luminance of 300 cd / m2 at a screen size of 4 m × 3 m ² A contrast ratio of 100: 1 and a horizontal resolution of 1000 TV were obtained. In this way, the resolution is greatly improved as compared with the conventional case. Further, as compared with the configuration using a gas laser, the weight was reduced to 1/1000, the capacity was reduced to 1/1000, and the power consumption was significantly improved to 1/100. This largely contributes to the fact that the laser light source used is small in size and low in power consumption, and that the optical modulator is integrated. That is, the configuration using the semiconductor laser and the optical wavelength conversion element can be made ultra-small, and the conversion efficiency from electricity is about two orders of magnitude higher than that of the gas laser. In particular, when an optical wavelength conversion element having a periodic polarization inversion structure is used, high efficiency can be achieved, and an optical modulator can be integrated, so that the effect is enormous. In this embodiment, the laser beam is irradiated from the back of the screen, but the laser beam may be irradiated from the front.
[0173]
Next, another embodiment of the laser light source of the present invention will be described with reference to FIG.
[0174]
As shown in FIG. 21, the fundamental wave P1 emitted from the semiconductor laser 20 is guided to the optical wavelength conversion element 25 via the lens 30, the half-wave plate 37, and the condenser lens 31, and is converted into a harmonic wave P2. That is, in this example, blue light is obtained without using a solid-state laser. The configuration of the light wavelength conversion element 25 is almost the same as that of the first embodiment. Also in this embodiment, LiTaO ₃ A substrate and an optical waveguide type optical wavelength conversion element are used. Further, an electrode 14 and a protective film 13 are formed for performing light modulation. However, the present embodiment does not have a resonator structure.
[0175]
FIG. 22 shows an internal configuration of the semiconductor laser 20. The semiconductor laser 20 comprises a distributed feedback (hereinafter abbreviated as DBR) semiconductor laser 20a and a semiconductor laser amplifier 20b. The DBR semiconductor laser 20a has a DBR portion 27 formed by a grating and oscillates stably at a constant wavelength. The stabilized fundamental wave P0 emitted from the DBR semiconductor laser 20a is guided to the semiconductor laser amplifier 20b by the lens 30a. The power is amplified by the active layer 26b of the semiconductor laser amplifier 20b, and a stable fundamental wave P1 is obtained. By introducing this into the optical wavelength conversion element 25, the conversion efficiency and the harmonic output are greatly improved. The period of the polarization inversion is 3 μm, and the optical waveguide length is 7 mm. The oscillation wavelength of the semiconductor laser in this example was 960 nm, the wavelength of the generated harmonic P2 was 480 nm, and the color was blue. The conversion efficiency is 10% at 10 W input. There was no light damage and the harmonic output was very stable. The DBR semiconductor laser has a stable oscillation wavelength, which is advantageous for stabilizing the output of harmonics.
[0176]
Next, RF superposition (high frequency superposition) was performed on this DBR semiconductor laser. An 800 MHz sinusoidal electric waveform was applied to the DBR semiconductor, and the semiconductor laser was converted to a pulse train light output using relaxation oscillation. When the DBR semiconductor laser is RF-superimposed in this way, the peak output of the fundamental wave is greatly improved while the oscillation wavelength is kept constant. A harmonic with a conversion efficiency of 50% and 5 W were obtained from an average output of 10 W of the fundamental wave. The 5-fold conversion efficiency when no RF superposition was performed was improved.
[0177]
In the present embodiment, the DBR semiconductor laser and the semiconductor laser amplifier are separated from each other.
[0178]
Next, still another embodiment of the laser light source of the present invention will be described with reference to the sectional view of FIG. The fundamental wave P1 from the semiconductor laser 20 is gradually focused on the optical wavelength conversion element 25 by the lens 30. In this embodiment, LiNbO 3 is used instead of the LiTaO 3 substrate. ₃ Was used as a substrate. Further, a bulk type optical wavelength conversion element 25 is used. LiNbO ₃ The substrate 1a is characterized by a large nonlinearity. By driving the semiconductor laser 20 by RF, the peak power is improved, and the conversion efficiency of the optical wavelength conversion device is greatly improved. The period of the domain-inverted layer 3 is 3.5 μm, and the length of the light wavelength conversion element 25 is 7 mm. In this embodiment, the output of the harmonic P2 is stabilized using the optical feedback method. This is because the wavelength tolerance of the light wavelength conversion element 25 is as narrow as about 0.1 nm. The fundamental wave P1 not converted by the light wavelength conversion element 25 is collimated by the lens 32, reflected by the grating 36, and returns to the semiconductor laser 20. As a result, the oscillation wavelength of the semiconductor laser 20 is locked to the reflection wavelength of the grating 36. To adjust the oscillation wavelength to the phase matching wavelength of the optical wavelength conversion element 25, the angle of the grating 36 may be changed.
[0179]
On the other hand, the harmonic P2 is reflected by the dichroic mirror 35 and taken out in another direction. In this example, the oscillation wavelength of the semiconductor laser was 980 nm, and the harmonic P2 extracted was 490 nm blue. At this time, an electric waveform having an RF frequency of 810 MHz and an output of 5 W was applied. In addition, a harmonic of 3 W was obtained with an average output of 15 W of the fundamental wave. There was no light damage and the harmonic output was very stable. There is no optical damage because the fundamental wave is focused only to about 100 μm, and the harmonics are not so large in terms of density.
[0180]
In the present embodiment, the wavelength is locked by optical feedback using a grating. However, the present invention is not limited to this, such as selecting a wavelength with a filter and performing optical feedback. In addition, when the laser projection device is configured using the laser light source of the present embodiment, the size, weight, and cost can be reduced. Further, in this embodiment, the harmonic can be modulated by directly modulating the semiconductor laser, so that the configuration is simple and the cost can be reduced.
[0181]
Next, another embodiment of the laser light source of the present invention will be described with reference to FIG.
FIG. 24 shows a cross section of a light wavelength conversion element (bulk type) 25.
[0182]
Pump light P1a emitted from the semiconductor laser 20 having a wavelength of 806 nm enters the fiber 40 and propagates through the fiber 40. The pump light P1a emitted from the fiber 40 enters the optical wavelength conversion element 25. The material of the light wavelength conversion element 25 is LiTaO doped with Nd which is a rare earth element. ₃ The substrate 1b has a domain-inverted structure with a period of 5.1 μm. The doping amount of Nd is 1 mol%. Reference numeral 22 denotes a total reflection mirror that totally reflects 99% of light having a wavelength of 947 nm and transmits light in the 800 nm band. Also, 23 is a total reflection mirror that totally reflects 99% of light having a wavelength of 947 nm and transmits light in the 470 nm band. The portion of the total reflection mirror 23 is processed into a spherical shape. That is, it plays the role of a spherical mirror. The optical wavelength conversion element 25 oscillates at a wavelength of 947 nm excited by the semiconductor laser 20, is further converted into a harmonic P2 by a periodic domain inversion structure by the domain inversion layer 3, and is emitted to the outside. When the pump light P1 was 20 W, a harmonic of 2 W was obtained. Further, the temperature is stabilized by a Peltier element so that the temperature of the light wavelength conversion element does not greatly change. The length of the conversion part of the laser light source of this embodiment is 10 mm, and it can be made very compact by doping the optical wavelength conversion element with a rare earth element and propagating the pump light through a fiber. Further, by keeping the optical wavelength conversion element away from heat generated by the semiconductor laser, a temperature change can be prevented.
[0183]
Also, by changing the coating of the total reflection mirrors 22 and 23 to reflect in the 1060 nm band and changing the period of the domain-inverted layer 3 to 1060 nm, 1060 nm oscillates and green laser light (wavelength 530 nm) is obtained as the harmonic P2. Was. Further, by changing the coating of the total reflection mirrors 22 and 23 to reflect in the 1300 nm band and changing the period of the domain-inverted layer 3 to 1300 nm, 1300 nm oscillates and red laser light (wavelength 650 nm) is obtained as the harmonic P2. Was. With this configuration, three primary color laser beams of blue, green, and red can be easily obtained. Next, FIG. 25 shows a configuration in which the solid-state laser crystal and the light wavelength conversion element are separated. Nd: YVO as solid-state laser crystal 21 ₄ Was attached to the output side of the fiber. LiTaO ₃ The optical wavelength conversion element 25 of the substrate 1 has a periodically domain-inverted structure. Even with the laser light source having this configuration, a 2 W blue laser beam could be stably obtained.
[0184]
Another embodiment of the present invention will be described with reference to the drawings. FIG. 26 shows a configuration diagram of the laser light source of this embodiment. The pump light P1a emitted from the semiconductor laser 20 having a wavelength of 806 nm is converted into a fundamental wave P1 by the solid-state laser crystal 21, enters the fiber 40, and propagates through the fiber 40. This fiber 40 is a single mode fiber. The fundamental wave P1 emitted from the fiber 40 enters the optical wavelength conversion element 25. In this embodiment, LiTaO is used as the optical wavelength conversion element 25 having a periodically poled structure. ₃ An optical waveguide 2 manufactured using proton exchange in a substrate 1 is used. In the figure, reference numeral 1 denotes a Z plate LiTaO. ₃ The substrate 2 is the formed optical waveguide, 3 is the domain-inverted layer, 10 is the incidence part of the fundamental wave P1, and 12 is the emission part of the harmonic P2. The fundamental wave P1 entering the optical waveguide 2 is converted into a harmonic P2 by the domain-inverted layer 3. In this way, the harmonic P2 having increased power in the optical waveguide 2 is radiated from the emission unit 12. The divergent harmonic P2 is made parallel by the lens 32.
[0185]
Further, an electrode 14 is formed on the element via a protective film 13. When the pump light P1a was 30W, a harmonic P2 of 10W was obtained. By applying a modulation signal to the electrode 14 formed on the light wavelength conversion element 25, the blue laser light was modulated at 30 MHz. The length of the conversion part of the laser light source of this embodiment is 10 mm, and it can be made very compact by propagating the fundamental wave P1 through a fiber. Further, the temperature rise can be prevented by moving the optical wavelength conversion element away from the semiconductor laser.
[0186]
FIG. 26 shows an embodiment in which no solid-state laser crystal is used.
[0187]
A semiconductor laser having a wavelength of 980 nm and an output of 10 W is used. This is coupled to the optical wavelength conversion element 25 through the fiber 40 to perform direct conversion. At a wavelength of 490 nm, an output of 2 W was obtained.
[0188]
Next, the laser projection device of the present invention will be described with reference to FIG. As the light source, three colors of the blue laser light source, the green laser light source, and the red laser light source of Example 5 were used. Reference numeral 45 denotes a blue 473 nm laser light source. 46 is a green laser light source with a wavelength of 530 nm, and 47 is a red laser light source with a wavelength of 650 nm. Each light wavelength conversion element is provided with a modulation electrode. By inputting a modulation signal to the modulation electrode, each light source output is modulated. The green laser light is combined with the blue laser light by the dichroic mirror 61. The dichroic mirror 62 combines the red laser beam and the other two colors. 56 is a vertical deflector, 57 is a horizontal deflector, and both use a rotating polygon mirror. Using a screen 70 with a gain of 3 and a luminance of 2000 cd / m2 at a screen size of 2 m × 1 m ² , A contrast ratio of 100: 1, a horizontal resolution of 1000 TV lines, and a vertical resolution of 1000 TV lines. As described above, the laser projection device of the present invention is bright, has high resolution, consumes very little power, and has a great effect.
[0189]
In this embodiment, a polarization inversion type optical wavelength conversion element is used, but the invention is not limited to this.
Further, by using a laser light source that emits red light from a semiconductor laser directly, the cost can be further reduced. In addition, a semiconductor laser directly oscillating can be used as the blue and green lasers. The combination is free.
[0190]
In this embodiment, the following measures are taken for safety. When the scanning of the laser beam is stopped, the power of the laser is automatically turned off. In addition, an infrared laser beam, which is a sub-semiconductor laser having a weak output, scans around the projected laser beam, and the laser beam is automatically cut off when an object touches this beam. . Infrared semiconductor lasers are characterized by low cost and long life.
[0191]
Next, these will be described with reference to FIG. The three laser beams of the three primary colors are scanned by the deflector in the drawing area 71 on the screen 70.
This laser light passes over sensors A and B located around the drawing area 71. The output signals of the sensors A and B are constantly monitored. On the other hand, the laser light from the infrared laser light source by the infrared semiconductor laser is constantly scanned around the screen 70 by the deflector 58. This reflected light enters the sensor C. That is, the reflected light at all points in the peripheral portion enters the sensor C.
[0192]
Next, control will be described with reference to FIG. In FIG. 29, when any of the signals from the sensors A and B does not enter the control circuit for a predetermined time, the main power supply of the laser light source is turned off, and the blue, red, and green laser light sources are stopped. In other words, by stopping the scanning, it is possible to prevent a specific portion from being intensively irradiated with laser light. If the signal of the sensor C is interrupted even for a moment, the power of the laser light source is turned off by the control circuit. In other words, humans and the like do not touch the high-output short-wavelength laser light, which is safe. As described above, the safety of the laser projection device is maintained.
[0193]
In the embodiment, the power of the laser light source is turned off, but the optical path of the laser may be cut off. Further, the generation of short-wavelength laser light may be stopped by shifting the phase matching wavelength of the optical wavelength conversion element by a voltage or the like, or by changing the oscillation wavelength of the semiconductor laser that is the fundamental wave light source. According to this method, the time until re-return can be greatly reduced.
[0194]
Next, an embodiment of the three-dimensional laser projection apparatus of the present invention will be described with reference to FIG.
[0195]
In other words, it is a device that looks three-dimensional from the viewer's side. FIG. 30 shows a configuration diagram of the laser projection apparatus of the present embodiment. As shown in FIG. 30, the laser light is split in two directions by putting the prism type optical path converter 66 into the three-color laser light. The split laser light is reflected by respective mirrors 64 and 65, modulated by modulators 5a and 5b, and enters screen 70. The images viewed from the right direction and the image information viewed from the left direction are loaded by the modulators 5a and 5b, respectively, and light enters the screen 70 from different directions and looks three-dimensionally. In addition, the optical path 1 and the optical path 2 are switched at a certain time, and a human feels as if images in different directions come from two directions, and the stereoscopic image is further cleared. A stereoscopic image can be easily viewed without stereoscopic glasses as in this embodiment.
[0196]
Note that the light may be divided into two by a half mirror or the like to be three-dimensional. Although one light source is divided, two laser light sources of the same color may be used to irradiate the screen from different directions. In this case, the output of one light source can be reduced to half.
[0197]
Next, still another embodiment of the laser projection apparatus of the present invention will be described.
[0198]
FIG. 31 shows a configuration diagram of the laser projection device of the present embodiment. An ultraviolet laser light source based on a light wavelength conversion element is used as a light source. By irradiating this on the screen 70 coated with the phosphor, red, green and blue RGB light is emitted. The configuration of the laser light source is such that red laser light 650 nm, which is a direct oscillation of a semiconductor laser, is used for LiTaO ₃ The wavelength was halved to 325 nm by the optical wavelength conversion element of No. This optical wavelength conversion element is a bulk type in which a domain-inverted structure is formed. Reference numeral 48 denotes this laser light source. Here, an ultraviolet modulation signal is obtained by directly modulating the red semiconductor laser. The modulated ultraviolet laser light enters the deflector. 56 is a vertical deflector, 57 is a horizontal deflector, and both use a rotating polygon mirror. The screen 70 is coated with a phosphor that generates red, green, and blue, and generates fluorescent light. Brightness 300 cd / m at screen size 1m × 0.5m ² And a horizontal resolution of 600 TV with a contrast ratio of 100: 1. As in this embodiment, three primary color lights of red, green, and blue can be generated by one laser light source, and the size and cost can be reduced. At this time, it is also effective to omit the dichroic mirror for multiplexing.
[0199]
Next, an embodiment of the laser projection apparatus of the present invention will be described with reference to FIG.
As shown in FIG. 32, a blue laser light source 45 based on a light wavelength conversion element is used as a light source. Laser light emitted from the laser light source 45 is collimated by the lens 30. A liquid crystal light bubble 68 is inserted into the collimated laser light. The signal is spatially modulated by applying a signal to the liquid crystal light valve 68, and the light can be enlarged by the lens 31 and projected on a screen so that an image can be viewed. The use of laser light sources of three primary colors enables colorization.
[0200]
The efficiency has been greatly improved and the power consumption has been reduced as compared with the conventional case. In addition, heat generation is small and effective.
[0201]
Next, the laser projection device of the present invention will be described with reference to FIG. The external configuration is the same as that of the embodiment of the laser projection apparatus shown in FIG. As the light source, a blue laser light source shown in FIG. 23 is used, and the semiconductor laser here is RF-superimposed. The blue light is modulated by inputting a modulation signal in addition to the RF superposition. The modulated blue laser light enters the deflector. Using a screen with a gain of 2 and a luminance of 200 cd / m2 at a screen size of 2 m × 1 m ² Got. No speckle noise caused by laser light interference was observed on the screen. This is because the coherence of the laser light is reduced by the RF superposition, and the RF superposition of the semiconductor laser plays an important contribution to the countermeasures against speckle noise. In this embodiment, the configuration of the laser light source shown in FIG. 23 is used. However, RF superposition is effective for a laser projection apparatus using a laser light source by direct wavelength conversion of a semiconductor laser. Speckle noise can also be prevented when red, green, or blue laser light is directly generated by semiconductor laser light. Needless to say, the present invention is effective for a color laser projector.
[0202]
In the above embodiment, LiNbO was used as the nonlinear optical crystal. ₃ And LiTaO ₃ Was used, but KNbO ₃ , KTP, etc., organic materials such as MNA, and those materials doped with rare earth elements. Also, rare earths are promising not only for Nd used in the examples but also for Er and Tl. Although YAG was used as the solid-state laser crystal, other than YLF, YVO ₄ Are effective. LiSAF and LiCAF are also effective as solid-state lasers.
[0203]
Next, an example in which the laser light source of the present invention is applied to an optical disk device will be described with reference to FIG.
[0204]
This optical disk device is provided in an optical pickup 104 having an optical wavelength conversion element 25 having a periodic inversion structure. The laser light emitted from the semiconductor laser 20 is converted into an optical wavelength in the optical pickup 104 via a fiber 40. It is provided to element 25.
[0205]
The optical pickup 104 includes, in addition to the optical wavelength conversion element 25, a collimator lens 32 that converts harmonics emitted from the optical wavelength conversion element 25 into parallel light, and a polarization beam splitter that transmits the collimated light toward the optical disc. 105, a condenser lens 106 for collecting the light on the optical disk, and a detector 103 for detecting the reflected light from the optical disk. The polarization beam splitter 105 selectively reflects the reflected light from the optical disk and supplies the reflected light to the detector 103.
[0206]
The optical pickup 104 is driven by an actuator, and the semiconductor laser 20 is fixed in the optical disk device. The optical pickup 104 can reliably receive laser light from the semiconductor laser 20 fixed in the optical disk device by a flexible optical fiber.
[0207]
Next, the operation will be described.
[0208]
The light (pump light) emitted from the semiconductor laser 20 is converted into a fundamental wave P <b> 1 by the solid-state laser 21, and is applied to the light wavelength conversion element 25 through the optical fiber 40. The optical wavelength conversion element 25 has a configuration similar to that of the above-described embodiment, and converts the fundamental wave P1 into a harmonic P2. The harmonic P2 is collimated by the collimator lens 32, passes through the polarizing beam splitter 105, and is condensed on the optical disc medium 102 via the condensing lens 106. The reflected light from the optical disk medium 102 returns to the same optical path again, is reflected by the polarization beam splitter 105, and is detected by the detector 103.
Thus, a signal is recorded on the optical disk medium, or the recorded signal can be reproduced.
[0209]
A quarter-wave plate 108 is inserted between the polarization beam splitter 105 and the condenser lens 106, and rotates the polarization direction by 90 degrees in the forward and backward paths of the harmonic.
[0210]
When a semiconductor laser 20 having an output of 1 W was used, a harmonic P2 of 200 mW was obtained. The wavelength of light emitted from the solid-state laser 21 is 947 nm, and the wavelength of a harmonic is 473 nm.
[0211]
By using a high-power laser beam with an output of 200 mW, recording can be performed at a speed that is 10 times faster than the recording speed of an optical disk device using a conventional 20 mW output light. The transfer rate was 60 Mbps.
[0212]
The semiconductor laser 20, which generates heat during operation, is fixed to the housing of the optical disk device and is separated from the optical pickup. Therefore, as a result of removing the semiconductor laser from the inside of the optical pickup, it is not necessary to provide a special ripening structure for the semiconductor laser. Therefore, an ultra-small and lightweight optical pickup can be configured. As a result, the actuator of the optical pickup can be driven at a high speed, and high-speed recording at a high transfer rate is achieved.
[0213]
Although the solid-state laser is arranged on the semiconductor laser side in this embodiment, it may be arranged on the optical wavelength conversion element side. Instead of using a solid-state laser, light from a semiconductor laser may be directly converted into a harmonic as a fundamental wave.
[0214]
Note that the internal configuration of the optical pickup 104 is not limited to that of the present embodiment.
For example, by using a polarization separation hologram, a lens and a polarization beam splitter can be omitted. Then, the size of the optical pickup can be further reduced.
[0215]
(Possibility of industrial use)
As described above, according to the optical wavelength conversion device of the present invention, LiNb _x Ta _1-x O ₃ (0.ltoreq.X.ltoreq.1) After fabricating an optical device on a substrate, low-temperature annealing restores the increase in refractive index caused during heat treatment such as high-temperature annealing, and forms a stable proton exchange layer, thereby forming a stable optical device. be able to. In particular, the present invention is indispensable for practical use of an optical wavelength conversion element whose phase matching wavelength changes with a change in the refractive index.
[0216]
In addition, a two-step annealing in which the temperature is set to two steps as a low-temperature annealing can quickly and completely return to a stable proton exchange layer in which there is no change with time, which is effective.
Further, by performing the second annealing at a temperature lower by 200 ° C. than the first annealing, the strain can be greatly reduced and a stable proton exchange layer can be formed, which is effective. The low-temperature annealing temperature is 120 ° C. or less, and if it is performed for at least 1 hour, the change with the passage of time is 0.5 nm or less, which is effective. If the temperature is lower than 50 ° C., the annealing time becomes extremely long and causes a problem.
[0217]
Further, according to the laser light source of the present invention, by interposing a semiconductor laser amplifier between the distributed feedback semiconductor laser and the optical wavelength conversion element, to stabilize the oscillation wavelength of the semiconductor laser and increase the fundamental wave output, and By using an optical wavelength conversion element having a highly efficient domain-inverted structure, the highest harmonic output can be stably obtained.
[0218]
Further, in the laser light source of the present invention, by propagating the pump light or the fundamental wave through the fiber, the optical wavelength conversion element can be made very compact. Further, the optical wavelength conversion element can be kept away from heat generated by the semiconductor laser, a temperature change can be prevented, and a high-power semiconductor laser can be used.
[0219]
When a periodically poled structure is used as an optical wavelength conversion element, not only conversion efficiency is greatly improved, but also modulation can be easily performed by applying a voltage, and the voltage is low and industrial. . Thus, the modulator can be integrated, and the size, weight, and cost can be reduced. In addition, by using an optical waveguide with weak confinement as an optical wavelength conversion element, the density of harmonics was reduced, and optical damage was greatly improved. For example, by making the area 100 times the conventional area, it is possible to withstand 100 times the optical damage. Further, according to the laser light source of the present invention, by converting the pump light into the fundamental wave by the solid-state laser crystal, a multi-stripe or wide-stripe high-power semiconductor laser can be used, and a high-power harmonic can be obtained. .
[0220]
Thus, for example, the conversion efficiency of the optical wavelength conversion element having the conversion efficiency of 30% between the light and the light of the semiconductor laser is multiplied by 70%, and a total conversion efficiency of 20% can be obtained. In addition, by performing the RF superposition of the semiconductor laser in the laser light source of the present invention, for example, the 5-fold conversion efficiency when the RF superposition is not performed is improved.
[0221]
Further, according to the laser projector of the present invention, since it is based on a semiconductor laser, it is possible to significantly reduce its size, weight, and cost. Further, by using a high-power laser light source based on a semiconductor laser and an optical wavelength conversion element, the size, weight and cost of the device can be reduced at once. Further, power consumption can be extremely reduced. One of the factors is that this device does not have a laser light modulator and is integrated with a light wavelength conversion element. Further, the resolution is greatly improved as compared with the conventional case. For example, as compared with the configuration using a gas laser, the weight was reduced to 1/1000, the capacity was reduced to 1/1000, and the power consumption was significantly improved to 1/100. This largely contributes to the fact that the laser light source used is small in size and low in power consumption, and that the optical modulator is integrated. That is, the configuration using the semiconductor laser and the optical wavelength conversion element can be made ultra-small, and the conversion efficiency from electricity is about two orders of magnitude higher than that of the gas laser. In particular, when an optical wavelength conversion element having a periodic polarization inversion structure is used, high efficiency can be achieved, and an optical modulator driven by low voltage can be integrated, so that the effect is remarkable.
[0222]
Further, since the three primary colors can be emitted by hitting the phosphor with an ultraviolet laser light source, the size and cost can be further reduced and the industrial value is great. In this way, three primary color lights of red, green and blue can be generated by one laser light source. At this time, it is also effective to omit the dichroic mirror for multiplexing.
[0223]
Further, according to the laser projection apparatus of the present invention, when scanning is stopped, a laser beam stop or cut function is provided in order to prevent a specific portion from being intensively irradiated with laser light. If the signal of the sensor is interrupted even for a moment, the power of the laser light source is turned off by the control circuit. In other words, humans and the like do not touch the high-output short-wavelength laser light, which is safe. As described above, the safety of the laser projection device is maintained.
[0224]
RF superposition is effective for a laser projection apparatus using a laser light source by direct wavelength conversion of a semiconductor laser. This is because speckle noise can be prevented and a clear image can be reproduced. Speckle noise can also be prevented when red, green, or blue laser light is directly generated by semiconductor laser light.
[Brief description of the drawings]
FIG. 1 is a diagram showing a conventional short wavelength light source.
FIG. 2 is a configuration diagram of a conventional optical wavelength conversion element.
FIG. 3 is a process flowchart of a method for manufacturing an optical wavelength conversion element according to a conventional method.
FIG. 4 is a diagram showing a temporal change of a harmonic output of a conventional optical wavelength conversion element.
FIG. 5 is a diagram showing a change over time of a phase matching wavelength of a conventional optical wavelength conversion element.
FIG. 6 is a diagram showing a change with time of the refractive index of a conventional optical element.
FIG. 7 is a configuration diagram of an optical wavelength conversion element according to the first embodiment of the present invention.
FIG. 8A is a view showing a step of the method for manufacturing an optical wavelength conversion element according to the first embodiment of the present invention;
FIG. 8B is a view showing a step of the method for manufacturing an optical wavelength conversion element according to the first embodiment of the present invention.
FIG. 8C is a view showing a step of the method for manufacturing an optical wavelength conversion element according to the first embodiment of the present invention;
FIG. 8D is a view showing the step of the method for manufacturing the optical wavelength conversion element according to the first embodiment of the present invention.
FIG. 8E is a view showing a step of the method for manufacturing an optical wavelength conversion element according to the first embodiment of the present invention.
FIG. 9 is a process flowchart of a method for manufacturing an optical wavelength conversion element according to the first embodiment of the present invention.
FIG. 10 is a characteristic diagram showing a change in a phase matching wavelength with respect to an annealing time when an annealing temperature is used as a parameter.
FIG. 11 is a characteristic diagram showing a relationship between an annealing temperature and a phase matching wavelength change amount.
FIG. 12 is a diagram showing output time characteristics of the optical wavelength conversion device according to the first embodiment of the present invention.
FIG. 13 is a diagram showing the time characteristics of the phase matching wavelength and the effective refractive index of the optical wavelength conversion device according to the first embodiment of the present invention.
FIG. 14 is a process flowchart of a method of manufacturing an optical wavelength conversion device according to a second embodiment of the present invention.
FIG. 15A is a view showing a step of the method for producing an optical element according to the fourth embodiment of the present invention;
FIG. 15B is a view showing a step of the method for manufacturing an optical element according to the fourth embodiment of the present invention;
FIG. 15C is a view showing a step of the method for producing an optical element according to the fourth embodiment of the present invention;
FIG. 16 is a process flowchart of a method of manufacturing an optical device according to a fifth embodiment of the present invention.
FIG. 17 is a structural view of an embodiment of a laser light source according to the present invention.
FIG. 18A is a manufacturing process diagram of the optical wavelength conversion element in the laser light source of the present invention.
FIG. 18B is a manufacturing step diagram of the optical wavelength conversion element in the laser light source of the present invention.
FIG. 81C is a view showing the manufacturing process of the optical wavelength conversion element in the laser light source of the present invention.
FIG. 18D is a view showing the manufacturing process of the optical wavelength conversion element in the laser light source of the present invention.
FIG. 19 is a characteristic diagram showing a relationship between an optical waveguide thickness and light damage resistance of an optical wavelength conversion element used in the laser light source of the present invention.
FIG. 20 is a configuration diagram of a laser device according to an embodiment of the present invention.
FIG. 21 is a configuration diagram of a laser light source according to an embodiment of the present invention.
FIG. 22 is a configuration diagram of a semiconductor laser used for a laser light source according to an embodiment of the present invention.
FIG. 23 is a configuration diagram of a laser light source according to an embodiment of the present invention.
FIG. 24 is a configuration diagram of a laser light source according to an embodiment of the present invention.
FIG. 25 is a configuration diagram of a separation type laser light source according to an embodiment of the present invention.
FIG. 26 is a configuration diagram of a laser light source according to an embodiment of the present invention.
FIG. 27 is a configuration diagram of a laser device according to an embodiment of the present invention.
FIG. 28 is a configuration diagram of an automatic stop device of the laser device according to the embodiment of the present invention.
FIG. 29 is a diagram of a control system of an automatic stop device of the laser device according to the embodiment of the present invention.
FIG. 30 is a configuration diagram of a laser device according to an embodiment of the present invention.
FIG. 31 is a configuration diagram of a laser device according to an embodiment of the present invention.
FIG. 32 is a configuration diagram of a laser device according to an embodiment of the present invention.
FIG. 33 is a configuration diagram of an optical disc device according to an embodiment of the present invention.

Claims (7)

At least one or more laser light sources including a semiconductor laser,
A first optical system that irradiates a laser beam emitted from the laser light source to a spatial modulation element;
A second optical system for irradiating the screen with light emitted from the spatial modulation element,
The laser light source is
An optical wavelength conversion element for generating a harmonic,
A single mode fiber for transmitting laser light from the semiconductor laser to the optical wavelength conversion element,
A laser device, further comprising: At least one or more laser light sources including a semiconductor laser,
A first optical system that irradiates a laser beam emitted from the laser light source to a spatial modulation element;
A second optical system for irradiating the screen with light emitted from the spatial modulation element,
The laser light source is
A fiber for transmitting laser light from the semiconductor laser,
A solid-state laser crystal that receives a laser beam emitted from the fiber and generates a fundamental wave;
An optical wavelength conversion element that generates a harmonic from the fundamental wave,
A laser device, further comprising: At least one or more laser light sources including a semiconductor laser,
A first optical system that irradiates a laser beam emitted from the laser light source to a spatial modulation element;
A second optical system for irradiating the screen with light emitted from the spatial modulation element,
The laser device, wherein the semiconductor laser is a distributed feedback semiconductor laser, and the laser light source further includes a semiconductor laser amplifier that amplifies a laser beam from the distributed feedback semiconductor laser. At least one or more laser light sources including a semiconductor laser,
A first optical system that irradiates a laser beam emitted from the laser light source to a spatial modulation element;
A second optical system for irradiating the screen with light emitted from the spatial modulation element,
The laser light source is
A laser device further comprising an optical wavelength conversion element having a periodically poled structure. The laser device according to claim 1, wherein the spatial modulation element is a liquid crystal cell. The laser device according to claim 4, wherein the laser light source further includes an optical waveguide that guides laser light from the semiconductor laser. The laser device according to claim 1, wherein the semiconductor laser is wavelength-locked.

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