JP3884401B2 - Laser light source and optical disk apparatus - Google Patents

Description

(Technical field)
The present invention relates to an optical element such as an optical wavelength conversion element suitable for use in the optical information processing field or optical applied measurement control field using coherent light, a laser light source and a laser apparatus, and an optical element manufacturing method. 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 KNbO which is a nonlinear optical crystal. ₃ The optical wavelength conversion element 25 is basically configured.
[0002]
As shown in FIG. 1, the pump light P1a emitted from the semiconductor laser 20 oscillating at 807 nm is condensed by the lens 30 to excite the YAG which is the solid-state laser crystal 21. A total reflection mirror 22 is formed on the incident surface of the solid-state laser crystal 21. The total reflection mirror reflects 99% of light having a wavelength of 947 nm, but transmits light having a wavelength of 800 nm. For this reason, the pump light P1a is efficiently introduced into the solid-state laser crystal 21, but light with a wavelength of 947 nm generated by the solid-state laser crystal 21 is not emitted to the semiconductor laser 20 side, but is converted into an optical wavelength. Reflected to the element 25 side. Furthermore, a mirror 23 that reflects 99% of light having a wavelength of 947 nm and transmits light in the 400 nm band is also disposed on the output side of the optical wavelength conversion element 25. These mirrors 22 and 23 form a resonator (cavity) for light having a wavelength of 947 nm. In this resonator, oscillation of 947 nm, which is the fundamental wave P1, can be generated.
[0003]
The optical wavelength conversion element 25 is inserted into the resonator defined by the mirrors 22 and 23, thereby generating the 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 wave having high power is obtained. Using a semiconductor laser with 500 mW output, a harmonic of 1 mW can be obtained.
[0004]
Next, a conventional optical wavelength conversion element having an optical waveguide will be described with reference to FIG. When a fundamental wave having a wavelength of 840 nm is incident, the optical wavelength conversion element shown in the figure generates a second harmonic (wavelength: 420 nm) with respect to the fundamental wave. Such an optical wavelength conversion element is disclosed in K.K. Mizuchi, K. Yamamoto and T.K. Taniuchi, Applied Physics Letters, Vol 58, page 2732, June 1991.
[0005]
In this optical wavelength conversion element, as shown in FIG. 2, LiTaO ₃ An optical waveguide 2 is formed on the substrate 1, and layers (polarization inversion layers) 3 whose polarization is inverted are periodically arranged along the optical waveguide 2. LiTaO ₃ A 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 P <b> 1 enters one end (incident surface 10) of the optical waveguide 2, the harmonic P <b> 2 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 polarization inversion layer 3 and the non-polarization inversion layer 4, the propagation constant between the generated harmonic wave P2 and the fundamental wave P1 is reduced. Mismatch is compensated by the periodic structure of the domain inversion layer 3 and the non-domain inversion 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 an optical waveguide 2 manufactured by a proton exchange method as a basic component.
[0008]
Below, the manufacturing method of such an optical wavelength conversion element is demonstrated, referring FIG.
[0009]
First, in step S10 of FIG. 3, a polarization inversion layer forming step is performed.
[0010]
More specifically, first, LiTaO ₃ After a Ta film is deposited so as to cover the main surface of the substrate 1, the Ta film is patterned into 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 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 mixed solution.
[0012]
Next, a polarization inversion layer is formed in each proton exchange layer by performing a heat treatment at a temperature of 550 ° C. for 1 minute. The temperature increase rate of the heat treatment is 50 ° C./second, and the cooling rate is 10 ° C./second. LiTaO ₃ Compared to the portion of the substrate 1 where proton exchange is not performed, the amount of Li is reduced in the portion where proton exchange is performed. Therefore, the Curie temperature of the proton exchange layer is lowered, 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 process is performed.
[0014]
More specifically, Step 2 is roughly divided into Step S21, Step S22, and Step S23. A mask pattern is formed in step S21, proton exchange processing 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. This Ta mask is obtained by forming a slit-like opening (width 4 μm, length 12 mm) in a Ta film. In step S22, LiTaO covered with the Ta mask. ₃ The substrate 1 is subjected to a proton exchange treatment at 260 ° C. for 16 minutes, whereby a high refractive index layer (thickness 0.5 μm) linearly extending in one direction is formed on LiTaO. ₃ It is formed in the substrate 1. This high refractive index layer will ultimately 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. By this annealing, the high refractive index layer is expanded in the vertical direction and the horizontal direction, and Li is diffused into the high refractive index layer. Thus, 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 increases by about 0.03 from the refractive index of other regions, and the high refractive index layer functions as an optical waveguide.
[0017]
Next, the protective film forming step (step S30), the end surface polishing step (step S40), and the AR coating step (step S50) are performed, thereby completing the light wavelength conversion element.
[0018]
Here, if the arrangement period of the polarization inversion layers periodically arranged along the waveguide is 10.8 μm, a third-order quasi-phase matching structure can be formed.
[0019]
According to the optical wavelength conversion element, when the length of the optical waveguide 2 is 9 mm, the harmonic wave P2 having a power of 0.13 mW is obtained with respect to the fundamental wave P1 having a wavelength of 840 nm (power 27 mW) (conversion efficiency 0). .5%).
[0020]
In the case of forming a primary quasi-phase matching structure, the arrangement period of the polarization inversion layers may be 3.6 μm. In this case, a harmonic wave P2 of 0.3 mW is obtained with respect to the fundamental wave P1 of 27 mW (conversion efficiency 1%). The inventors of the present application have prototyped a laser light source that outputs blue laser light by combining such a light wavelength conversion element and a semiconductor laser.
[0021]
Such an optical wavelength conversion element has a problem that the phase matching wavelength changes with time, and as a result, harmonics cannot be obtained. Although the wavelength of the fundamental wave emitted from the semiconductor laser is kept constant, when the phase matching wavelength of the optical wavelength conversion element shifts, the output of the harmonic gradually decreases and eventually becomes zero. Become.
[0022]
An object of the present invention is to stabilize and increase the output of a laser light source, and to reduce the size and weight of these devices by incorporating the high output laser light source into a laser device or an optical disk device. .
[0023]
(Disclosure of the Invention)
The manufacturing method of the optical element of the present invention is LiNb. _x Ta _1-x O ₃ (0 ≦ X ≦ 1) including 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 longer.
[0024]
The annealing step is preferably performed at a temperature of 50 ° C. or higher and 90 ° C. or lower.
[0025]
The annealing step may include a step of gradually decreasing 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 polarization inversion layers arranged periodically in the substrate, and a step of forming an optical waveguide on the surface of the substrate. Include.
[0028]
Another method of manufacturing an optical element of the present invention is LiNb. _x Ta _1-x O ₃ (0 ≦ X ≦ 1) including 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 a first heat treatment and a second heat treatment on the substrate, The temperature of the second annealing is 200 ° C. or more lower than the temperature of the first annealing.
[0029]
The second annealing is preferably performed at a temperature of 50 ° C. or higher and 90 ° C. or lower.
[0030]
The optical element of the present invention is LiNb. _x Ta _1-x O ₃ An optical element comprising a (0 ≦ X ≦ 1) substrate and a proton exchange layer formed in the substrate, and stable proton exchange in which the refractive index of the proton exchange layer does not change with time during use Formed from layers.
[0031]
In one embodiment, at least a part of the proton exchange layer constitutes an optical waveguide.
[0032]
The laser light source of the present invention is a light source comprising a semiconductor laser and an optical wavelength conversion element that receives laser light emitted from the semiconductor laser and converts the laser light into a harmonic, and the optical wavelength conversion element Comprises an optical waveguide that guides the laser light, and a domain-inverted structure periodically arranged along the optical waveguide, and the optical waveguide and the domain-inverted structure have a refractive index that changes with time during use. It is formed from a stable proton exchange layer that does not change.
[0033]
Another laser light source of the present invention includes 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. And an optical wavelength conversion element having a periodic domain-inverted structure.
[0034]
In one embodiment, the optical wavelength conversion element has a modulation function.
[0035]
The optical wavelength conversion element is LiNb. _x Ta _1-x O ₃ (0 ≦ X ≦ 1) It is preferably formed on the substrate.
[0036]
Still another laser light source of the present invention includes a semiconductor laser that emits pump light, a fiber that transmits the pump light, a solid-state laser crystal that receives a pump light emitted from the fiber and generates a fundamental wave, and the fundamental wave Is an optical wavelength conversion element that generates harmonics, and includes an optical wavelength conversion element having a periodic polarization inversion structure.
[0037]
The optical wavelength conversion element preferably has a modulation function.
[0038]
The optical wavelength conversion element is LiNb. _x Ta _1-x O ₃ (0 ≦ X ≦ 1) It is preferably formed on the substrate.
[0039]
In one embodiment, the solid-state laser crystal and the light wavelength conversion element are integrated.
[0040]
Still another laser light source of the present invention includes 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, and the fundamental from the fiber. An optical wavelength conversion element that receives a wave and generates a harmonic wave, and includes an optical wavelength conversion element having a periodic polarization inversion structure.
[0041]
The optical wavelength conversion element preferably has a modulation function.
[0042]
Still another laser light source of the present invention includes a distributed feedback semiconductor laser that emits laser light, a semiconductor laser amplifier that amplifies the laser light, and optical wavelength conversion that receives the amplified laser light and generates harmonics. An optical wavelength conversion element having a periodic polarization inversion structure is provided.
[0043]
The optical wavelength conversion element preferably has a modulation function.
[0044]
The optical wavelength conversion element is LiNb. _x Ta _1-x O ₃ (0 ≦ X ≦ 1) It is preferably formed on the substrate.
[0045]
In some embodiments, the semiconductor laser is wavelength locked.
[0046]
Still another laser light source of 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 periodic domain-inverted structure and an optical waveguide are formed. The width and thickness of the waveguide are each 40 μm or more.
[0047]
27. The laser light source according to claim 26, wherein the optical wavelength conversion element has a modulation function.
[0048]
The optical wavelength conversion element is LiNb _x Ta _1-x O ₃ (0 ≦ X ≦ 1) formed on the 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 a light wavelength conversion element that generates harmonics based on the laser light, a modulator that modulates the output intensity of the harmonics, And a deflector for changing the direction of the harmonics emitted from the laser light source, wherein the optical wavelength conversion element has a periodic polarization inversion 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 element.
[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 element 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, the optical wavelength conversion element is formed with an optical waveguide, and the width and thickness of the optical waveguide are each 40 μm or more.
[0056]
Another laser device of 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, and the polarizer includes the ultraviolet laser light. Is irradiated onto 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 harmonics, 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 the laser light emitted from the fiber and generates a fundamental wave, and the fundamental wave. An optical wavelength conversion element that generates harmonics.
[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 periodic polarization inversion structure is formed. The width and thickness are each 40 μm or more.
[0061]
Still another laser apparatus of the present invention includes three laser light sources that generate red, green, and blue laser beams, a modulator that changes the intensity of each laser beam, and a deflector that changes the direction of each laser beam. 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 harmonics, 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 the laser light emitted from the fiber and generates a fundamental wave, and the fundamental wave. An optical wavelength conversion element that generates harmonics.
[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 apparatus according to the present invention includes at least one laser light source 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 the light emitted from the sub semiconductor laser scans the periphery 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 harmonics, 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 the laser light emitted from the fiber and generates a fundamental wave, and the fundamental wave And an optical wavelength conversion element that generates harmonics from the.
[0070]
In one embodiment, the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser, wherein the semiconductor laser is a distributed feedback semiconductor laser.
[0071]
In one embodiment, the laser light source includes an optical waveguide that guides laser light from the semiconductor laser and an optical wavelength conversion element in which a periodically poled structure is formed, and the width and thickness of the optical waveguide are Each is 40 μm or more.
[0072]
The laser apparatus of the present invention includes at least one laser light source including a semiconductor laser, and a deflector that changes the direction of the laser light emitted from the laser light source and scans the screen with the laser light. A laser device 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, the detector When no signal is generated within a certain 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 harmonics, 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 the laser light emitted from the fiber and generates a fundamental wave, and the fundamental wave And an optical wavelength conversion element that generates harmonics from.
[0075]
In one embodiment, the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser, wherein the semiconductor laser is a distributed feedback semiconductor laser.
[0076]
In one embodiment, the laser light source includes an optical waveguide that guides laser light from the semiconductor laser and an optical wavelength conversion element in which a periodically poled structure is formed, and the width and 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 laser light source including a semiconductor laser, a modulator that changes the intensity of each laser beam, and a deflector that changes the direction of each laser beam. The laser light emitted from the laser light source is divided into two or more optical paths, and the screen is irradiated from two directions.
[0078]
In one embodiment, the laser light source includes an optical wavelength conversion element that generates harmonics, 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 the laser light emitted from the fiber and generates a fundamental wave, and the fundamental wave And an optical wavelength conversion element that generates harmonics from.
[0080]
In one embodiment, the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser, wherein the semiconductor laser is a distributed feedback semiconductor laser.
[0081]
In one embodiment, the laser light source includes an optical waveguide that guides laser light from the semiconductor laser and an optical wavelength conversion element in which a periodically poled structure is formed, and the width and thickness of the optical waveguide are Each is 40 μm or more.
[0082]
In one embodiment, two laser light sources form two optical paths and each laser light source is separately modulated.
[0083]
In some embodiments, the two light paths switch in time.
[0084]
Still another laser apparatus of the present invention includes at least one laser light source including a semiconductor laser, a first optical system that converts the laser light 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 harmonics, 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 the laser light emitted from the fiber and generates a fundamental wave, and the fundamental wave And an optical wavelength conversion element that generates harmonics from.
[0087]
In one embodiment, the laser light source further includes a semiconductor laser amplifier that amplifies laser light from the distributed feedback semiconductor laser, wherein the semiconductor laser is a distributed feedback semiconductor laser.
[0088]
In one embodiment, the laser light source includes an optical waveguide that guides laser light from the semiconductor laser and an optical wavelength conversion element in which a periodically poled structure is formed, and the width and thickness of the optical waveguide are Each is 40 μm or more.
[0089]
In one embodiment, the sub semiconductor laser is an infrared semiconductor laser.
[0090]
In an embodiment, laser light irradiation is stopped by shifting the phase matching wavelength of the light wavelength conversion element.
[0091]
An optical disk apparatus according to the present invention includes a laser light source that generates laser light, an optical wavelength conversion element that converts a fundamental wave into a harmonic, an optical pickup that includes the optical wavelength conversion element, and an actuator that moves the optical pickup; 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 through the optical fiber.
[0096]
(Best Mode for Carrying Out the Invention)
The inventors of the present application have considered the cause of the above-described optical wavelength conversion element having an optical waveguide that the phase matching wavelength is shortened over time and no higher harmonics are generated.
[0097]
FIG. 4 shows the relationship between the elapsed time from immediately after fabrication of the conventional optical wavelength conversion element and the output of the harmonic. It can be seen that the harmonic output decreases rapidly with time.
[0098]
FIG. 5 shows the relationship between the elapsed time and the phase matching wavelength. The harmonic output is halved 3 days after the fabrication of the device. At this time, it can be seen that the phase matching wavelength is shifted to the short wavelength side. The phase matching wavelength λ is the effective refractive index n for the polarization inversion period Λ, harmonics, and fundamental wave _2W And n _W It depends on. More specifically, λ = 2 (n _2W -N _W ) · Λ.
[0099]
Since the period Λ of the domain-inverted layer does not change with time and remains constant, the decrease in the phase matching wavelength λ is reduced by the effective refractive index n. _2W And n _W It is thought to be caused by changes in
[0100]
FIG. 6 shows the effective refractive index n _2W And the relationship between 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]
High-temperature treatment at about 400 ° C. performed when forming an 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 over time, and the refractive index of the change layer approaches the original refractive index.
[0103]
A change layer with an increased refractive index is formed by strain generated during high-temperature annealing, but the refractive index of the change layer returns to its original size over time, and finally the change layer becomes a stable proton. Become an exchange layer. However, it takes many years for the change layer to become such a stable proton exchange layer. In the present specification, the proton exchange layer in which the effective refractive index does not decrease with time depending on use at room temperature (about 0 ° C. to about 50 ° C.) is referred to as “stable proton exchange layer”. To do.
[0104]
The above is the mechanism of change with time considered by the present inventors. In order to confirm this, annealing at 300 ° C. for 1 minute was performed on the sample whose refractive index was lowered due to the change over time. At such an annealing temperature and time, diffusion of protons or the like hardly occurs, so that the waveguide does not spread. For this reason, according to the conventional way of thinking, the refractive index of the proton exchange layer should not change anything. However, according to the inventors' experiment, the refractive index increased again by annealing at 300 ° C. for 1 minute. Furthermore, after this annealing, a phenomenon was observed in which the refractive index decreased again as time passed.
[0105]
The present invention can alleviate the distortion generated in the proton exchange layer by heat treatment at a relatively high temperature, thereby preventing the optical 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 element of this example, the optical waveguide composed of a stable proton exchange layer is LiTaO. ₃ A plurality of domain-inverted layers 3 are formed periodically on the substrate 1 along the optical waveguide. When the fundamental wave P1 is incident on the input end of the optical waveguide, the harmonic wave P2 is emitted from the output end. The length of the optical wavelength conversion element of this example (the length of the waveguide) is 9 mm. In addition, the length of one cycle of the polarization inversion layer 3 is set to 3.7 μm so as to operate for a wavelength of 850 nm.
[0109]
Below, the manufacturing method of an optical wavelength conversion element is demonstrated, referring FIG. 8A to FIG. 8E.
[0110]
As shown in FIG. 8A, first, LiTaO ₃ After a Ta film is deposited so as to cover the main surface of the substrate 1, the Ta film (thickness: about 200 to 300 nm) is patterned into a stripe shape using a normal photolithography technique and a dry etching technique, and a Ta mask 6 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 period of the strips is 3.7 μm. Proton exchange processing 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 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 mixed solution.
[0111]
Next, as shown in FIG. 8B, a polarization inversion layer is formed in each proton exchange layer 7 by performing heat treatment at a temperature of 550 ° C. for 15 seconds. The temperature increase rate of the heat treatment is 50 to 80 ° C./second, and the cooling rate is 1 to 50 ° C./second. LiTaO ₃ The amount (concentration) of Li is reduced in the portion where the proton exchange is performed 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 the other parts, and the domain-inverted layer 3 can be partially formed in the proton exchange layer 7 by 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 the optical waveguide is formed. This Ta mask is obtained by forming slit-like openings (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. Needless to say, the shape of the waveguide is not limited to a linear shape. 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 subjecting the substrate 1 to proton exchange treatment at 260 ° C. for 16 minutes, as shown in FIG. 8C, LiTaO ₃ A linearly extending proton exchange layer (thickness 0.5 μm, width 5 μm, length 10 mm) 5 is formed in a region of the substrate 1 located below the opening of the Ta mask. The proton exchange layer 5 extending in a straight line finally functions as a waveguide. After this, HF: HNF ₃ The Ta mask is removed by etching for 2 minutes using a 1: 1 mixed solution.
[0113]
Next, annealing is performed at 420 ° C. for 1 minute using an infrared heating apparatus. By this annealing, the non-linearity of the proton exchange layer 5 is restored, and as shown in FIG. 8D, a change layer 8b having a refractive index increased by about 0.03 is formed. As described above, this annealing functions to diffuse Li and protons in the substrate 1 and reduce the proton exchange concentration of the proton exchange layer 5. Thereafter, a 300 nm thick SiO 2 film functioning as a protective film on the main surface of the substrate 1. ₂ A film (not shown) is deposited.
[0114]
Next, after the surface of the substrate 1 perpendicular to the change layer 8b is optically polished to form the incident portion and the emission portion of the light wavelength conversion element, as shown in FIG. 8E, the incidence portion and the emission portion are formed. An antireflection (AR) coat 15 is formed on the polished surface.
[0115]
Next, low temperature annealing is performed to prevent a change with time. In the present specification, “low-temperature annealing” means 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” means a heat treatment performed at a temperature of about 130 ° C. or less. 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, the stable proton exchange layer 8a is formed. This stable proton exchange layer 8a constitutes an optical waveguide.
[0116]
The flow of the manufacturing process will be described with reference to FIG.
[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, proton exchange processing is performed in step S22, and high-temperature annealing is performed in step S23. Thereafter, a protective film forming step (step S30), an end surface polishing step (step S40), and an AR coating step (step S50) are performed. If the wavelength conversion element remains as it is, the 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 it takes 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 more stable the state becomes in a short annealing time. Further, as the annealing temperature is lower, the phase matching wavelength shift amount when changing to a stable state shows a value close to zero. As described above, if the temperature of the low-temperature annealing is increased, the time required for the shift amount to return to zero is short, but on the other hand, the distortion remains relatively large.
[0120]
FIG. 11 shows the relationship between the phase matching wavelength shift amount and the temperature of the low-temperature annealing when returning to the stable state. From FIG. 11, it can be seen that if annealing at 120 ° C. is performed, the phase matching wavelength is stabilized in a state shifted by about 0.5 nm. If annealing at 150 ° C. or higher is performed, the shift amount of the phase matching wavelength after stabilization becomes 0.8 nm or more. If the phase matching wavelength shift of such a magnitude remains, long-term use of the optical wavelength conversion element becomes difficult. If the allowable range of the phase matching wavelength shift is 0.5 nm or less, even if annealing is performed at a temperature exceeding 120 ° C., the shift amount cannot be reduced within the allowable range. 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 1/4 of the output when the shift amount is zero can be obtained. If the low-temperature annealing temperature is 60 ° C., the annealing time becomes longer, but the shift amount can be reduced to 0.1 nm or less, so the problem of reduction in conversion efficiency is eliminated. The shift amount of the phase matching wavelength is preferably suppressed to about 0.2 nm or less.
[0121]
According to this embodiment, the refractive index of the non-polarization inversion layer 4 and the polarization inversion layer 3 in the optical waveguide 2 does not change with time, and the propagation loss when light is guided is small. When laser light (wavelength 850 nm) 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 wave P2 having a wavelength of 425 nm is emitted from the emitting portion to the outside of the substrate. It was taken out to. The propagation loss of the optical waveguide 2 was as small as 1 dB / cm, and the harmonic P2 was obtained effectively. A harmonic of 1.2 mW (wavelength: 425 nm) was obtained with an input of a fundamental wave of 27 mW. In this case, the conversion efficiency 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 refractive index change.
[0123]
From these figures, it can be seen that the refractive index change and the phase matching wavelength are constant immediately after fabrication of the device. According to the method for manufacturing an optical wavelength conversion element of the present invention, an optical wavelength conversion element having a constant phase matching wavelength can be realized because the refractive index does not change with 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 a Ta film is deposited so as to cover the main surface of the substrate, a Ta mask is formed by patterning the Ta film (thickness: about 200 to 300 nm) into a stripe shape using ordinary photolithography technology and dry etching technology. To do. The Ta mask used in this example 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 period of the strips is 3.6 μm. LiTaO with main surface covered with Ta mask ₃ A proton exchange process is performed on the substrate 1. 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 mixed solution.
[0126]
Next, a polarization inversion layer is formed in each proton exchange layer 7 by performing heat treatment at a temperature of 550 ° C. for 15 seconds. The temperature increase rate of the heat treatment is 50 ° C./second, and the cooling rate is 10 ° C./second. 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, the flow of the process following the above process will be described.
[0128]
First, the surface on which the domain-inverted layers of the substrate are arranged is subjected to proton exchange treatment, thereby forming an optical waveguide (step S100). As a mask for forming an optical waveguide, a Ta film having slits with a width of 4 μm and a length of 12 mm is used.
[0129]
Next, proton exchange is performed in pyrophosphoric acid at 260 ° C. for 16 minutes (step S110), and then 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 in air for 200 hours in order to prevent the refractive index from increasing. 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 effectively perform wavelength conversion. In order to operate for a wavelength of 840 nm, the period of the polarization inversion 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-polarization inversion layer and the polarization inversion layer, and the light propagation loss is small. The surface perpendicular to the optical waveguide was optically polished to form an incident part and an emission part. In this way, an optical wavelength conversion element can be manufactured. The length of this element is 9 mm.
[0132]
When semiconductor laser light (wavelength 840 nm) was incident on the incident portion of the waveguide as the fundamental wave P1, a harmonic wave P2 having a wavelength of 420 nm was extracted from the emitting portion to the outside of the substrate. A harmonic (wavelength: 420 nm) having an output of 10 mW was obtained with respect to an input of a fundamental wave having an output of 80 mW. In this case, the conversion efficiency is 12%. There was no optical damage and there was no change over time, and the harmonic output was very stable. If the high temperature annealing step is not performed during 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 A case where a substrate (thickness: 0.4 to 0.5 mm) is used will be described.
[0134]
First, a Ta electrode (first Ta electrode) having a pattern similar to the pattern of the Ta mask used in each of the above examples is formed using LiNbO by using a normal photolithography technique and a dry etching technique. 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. 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 constitute an electrode structure for applying an electric field to the substrate.
[0136]
Next, a voltage (for example, 10 kilovolts) is applied between the first Ta electrode and the second Ta electrode, and LiNbO ₃ An electric field is formed in the substrate. By this voltage application, a polarization inversion layer extending from the portion of the surface of the substrate in contact with the first Ta electrode to the back surface of the substrate is formed.
[0137]
Next, HF: HNF ₃ Etch for 2 minutes with a 1: 1 mixture of 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, proton exchange treatment using pyrophosphoric acid (230 ° C., 10 minutes) is performed to form an optical waveguide. To do. After removing the Ta mask, annealing is performed at 420 ° C. for 2 minutes using an infrared heating apparatus. By this annealing, the nonlinearity in the optical waveguide is recovered, but a change layer having a refractive index increased by about 0.02 is formed.
[0138]
After this, a 300 nm thick SiO 2 film functioning as a protective film ₂ A film is deposited on the substrate. Next, in order to alleviate the distortion caused by the increase in the refractive index, after annealing at 100 ° C. for 20 hours (first-stage low-temperature annealing) in air, subsequently, 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 reason for performing the low temperature annealing in two stages is to reduce the total time required for the low temperature annealing. The annealing at 100 ° C. relaxes the strain faster than the annealing at 60 ° C., but the strain corresponding to the phase matching wavelength shift amount at 100 ° C. as shown in FIG. 11 remains. Therefore, additional low-temperature annealing at 60 ° C. is performed to completely eliminate the strain. By this two-stage annealing, it is possible to form a “stable proton exchange layer” that is less likely to change with time, quickly and completely.
[0139]
The thickness d of the optical waveguide formed by the above process is 1.8 μm. The arrangement period of the domain-inverted layers is 3 μm and operates for a wavelength of 840 nm. The surface perpendicular to the optical waveguide was optically polished to form an incident part and an output part. In this way, 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 wave P2 having a wavelength of 420 nm was extracted from the emitting part to the outside of the substrate. A harmonic of 13 mW (wavelength: 420 nm) was obtained at an input of a fundamental wave of 80 mW. There was no change over time, and the harmonic output was very stable.
[0140]
In this example, two types of low-temperature annealing (two-stage annealing) were performed at different temperatures. For example, low-temperature annealing was performed such that the temperature was gradually decreased from 100 ° C. to 60 ° C. over 30 hours. Also good.
[0141]
Example 4
Next, a fourth embodiment of the present invention will be described with reference to FIGS. 15A to 15C.
[0142]
First, as shown in FIG. 15A, LiNbO by liquid layer epitaxial growth method. ₃ And LiTaO ₃ A mixture film (LiNb _0.5 Ta _0.5 O ₃ Film) 16 ′ is grown on the LiTaO 3 substrate 1. At this time, the growth temperature exceeds 1000 ° C., and the strain is mixed with the mixture film 16 and LiTaO. ₃ It remains on 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, the portion of the mixture film 16 that is not covered with the resist mask 17 is removed by ion beam etching to leave, for example, the optical waveguide 16 having a width of 4 μm.
[0143]
300nm thick SiO2 by vapor deposition ₂ Is deposited on the substrate 1 and then low-temperature annealing is performed to alleviate the increase in refractive index. This annealing consists of 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 refractive index change is 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 surface perpendicular to the optical waveguide was optically polished to form an incident part and an emission part. When semiconductor laser light (wavelength 840 nm) was guided from the incident part, the waveguide loss was very small. The change in refractive index with time was also 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) and other optical materials may be used.
[0145]
(Example 5)
Next, a fifth embodiment of the present invention will be described.
[0146]
The outline of the process flow of the present embodiment will be described with reference to FIG.
[0147]
First, an optical waveguide forming process 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. Then, an electrode formation process (step S230), a low temperature annealing process (step S240), an end surface polishing process (step S250), and an AR coating process (step S260) are performed.
[0148]
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 with a Ta pattern formed ₃ The substrate 1 is subjected to proton exchange at 230 ° C. for 10 minutes to form a proton exchange layer having a thickness of 0.5 μm immediately below the slit. Next, HF: HNF ₃ Etch for 2 minutes with a 1: 1 mixture of Ta to remove Ta. Annealing (first annealing) is performed at 400 ° C. for 1 hour using a diffusion furnace to form a change 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 depositing Al in a stripe shape as an electrode mask. Next, low temperature annealing was performed to alleviate the increase in 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 reducing the temperature by 200 ° C. or more, the strain can be relieved greatly, which is effective. Finally, polishing and AR coating were performed.
[0150]
An optical waveguide with an electrode was manufactured by the process as described above. This functions as an optical modulator. The thickness of this optical waveguide is 8 μm. The surface perpendicular to the optical waveguide was optically polished to form an incident part and an emission part. In this way, an optical element can be manufactured. The length of this element is 9 mm. When a modulation signal was applied to the electrode and semiconductor laser light (wavelength 1.56 μm) was guided as a fundamental wave from the incident part, the modulated light was extracted from the emission part. There was no change over 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 a Fresnel lens or hologram that is a planar device. The present invention can also be applied. The change in refractive index with time due to the proton exchange treatment can be prevented, and deterioration of characteristics can be suppressed.
[0152]
(Example 6)
Next, a sixth embodiment of the present invention will be described with reference to FIG. The present embodiment is a short wavelength light source provided with 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 a lens 30 and excites a YAG 21 that is a solid-state laser crystal.
[0154]
The YAG 21 is provided with a total reflection mirror 22 for 947 nm, which oscillates at a wavelength of 947 nm and emits a fundamental wave P1. On the other hand, a total reflection mirror 23 of the fundamental wave P1 is formed on the emission side of the optical wavelength conversion element 25, and laser oscillation occurs during this time. The fundamental wave P1 is condensed by the lens 31, and the fundamental wave P1 is converted into the harmonic wave P2 by the optical wavelength conversion element 25. In this embodiment, LiTaO is used as an optical wavelength conversion element having a periodic domain-inverted structure in which a periodic structure is formed. ₃ An optical waveguide 2 produced using proton exchange in a substrate 1 is used.
[0155]
In FIG. 17, reference numeral 1 denotes a Z-plate LiTaO. ₃ Substrate, 2 is an optical waveguide formed, 3 is a polarization inversion layer, 10 is an incident part of the fundamental wave P1, and 12 is an emission part of the harmonic wave P2. The fundamental wave P1 entering the optical waveguide 2 is converted into the harmonic P2 by the polarization inversion layer 3 having the length of the phase matching length L, and the next harmonic by the non-polarization inversion layer 4 having the same length L. Power will increase.
[0156]
The harmonic wave P2 whose power is increased in the optical waveguide 2 in this way is radiated from the emitting portion 12. The diverged harmonic P2 is converted into parallel light by the lens 32.
[0157]
In addition, an electrode 14 is formed on the optical wavelength conversion element 25 via a 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, a Ta electrode (first Ta electrode) 6 having a pattern similar to the pattern of the Ta mask used in each of the above-described embodiments using a normal photolithography technique and a dry etching technique. LiNbO with a thickness of 0.3 mm ₃ It is formed on the main surface of the substrate 1.
[0159]
Thereafter, a Ta film (second Ta electrode) 6 b 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 constitute an electrode structure for applying an electric field to the substrate 1.
[0160]
Next, a voltage (for example, 10 kilovolts) 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 polarization inversion layer 3 extending from the portion of the 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 with a 1: 1 mixture of HF: HNF3 for 20 minutes to remove the Ta electrodes 6 and 6b.
[0161]
Next, after forming a Ta mask (not shown) having a slit-like opening (width 4 μm, length 12 mm) on the substrate 1, proton exchange treatment (260 ° C., 40 minutes) using pyrophosphoric acid is performed. Then, as shown in FIG. 18C, the optical waveguide 2 is formed. The Ta mask has a slit (width 6 μm, length 10 mm), and this slit defines the 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 apparatus. By this annealing, the proton-exchanged optical waveguide recovers its nonlinearity, and the refractive index of the portion increases 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 polarization inversion 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 the 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 a photolithographic technique to form an Al electrode 14. The Al electrode 14 is used for intensity modulation of output light.
[0163]
A surface perpendicular to the extending direction of the optical waveguide 2 is optically polished to form the incident portion 10 and the emitting portion 12 shown in FIG. Further, the incident portion 10 is provided with a non-reflective coating for the fundamental wave P1. The emitting portion 12 is provided with a reflective coat (99%) for the fundamental wave P1 and a non-reflective coat for the harmonic wave P2.
[0164]
In this way, the optical 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 is guided from the incident portion 10 as the fundamental wave P1, it propagates in a single mode, and a harmonic wave P2 having a wavelength of 473 nm is extracted from the emitting portion 12 to the outside of the substrate. The propagation loss of the optical waveguide 2 is as small as 0.1 dB / cm, the performance of the resonator is improved, the power density of the fundamental wave P1 is increased, and the harmonic wave P2 is generated with high efficiency.
[0166]
Possible causes of the low loss are that a uniform optical waveguide can be formed with phosphoric acid, and that the confinement of the waveguide is reduced. In addition, the weakly confined optical waveguide reduces the harmonic density and significantly improves optical damage. This is because by making the area 100 times that of 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 damage-resistant power is the power that can withstand up to blue harmonics, that is, light fluctuation does not occur. It can be seen that when the thickness of the optical waveguide is increased, the width of the optical waveguide is increased by diffusion at the same time. Since the power required for laser projection is at least 2 W, the optical waveguide thickness is desirably 40 μm or more.
[0168]
Further, when the cross section of the waveguide is enlarged in a field where the refractive index distribution in the waveguide and its peripheral portion changes in a step shape, a multimode propagation phenomenon occurs. In order to avoid this, in this embodiment, a waveguide having a graded refractive index profile is formed.
[0169]
When the output light P1a of the semiconductor laser 20 was 10 W, a harmonic wave P3 with an output of 3 W was obtained. The conversion efficiency in this case is 30%. The tolerance for wavelength variation of the optical wavelength conversion element 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 its vicinity changes, and the phase matching wavelength of the optical wavelength conversion element shifts. By utilizing the phenomenon that the phase matching wavelength is greatly shifted by applying a voltage, the harmonic output can be modulated by applying a relatively low voltage of about 100V.
[0170]
As described above, according to the optical wavelength conversion element using the periodic domain-inverted structure used in this example, the harmonic output can be easily modulated by applying a voltage, and the required applied voltage is low. The above utility value is high.
[0171]
Thus, the modulator can be integrated, and the size, weight, and cost can be reduced. In addition, LiTaO which is a nonlinear optical crystal used in the present invention ₃ Has a feature that a large crystal is available and mass production of an optical wavelength conversion element using an optical IC process is easy. Note that in multimode propagation with respect to the fundamental wave, the output of the harmonics is unstable and impractical, and single mode is effective. As in this example, when a device having a periodic polarization inversion structure is used as the light wavelength conversion element, high efficiency can be achieved, and the optical modulator can be integrated, and not only blue when the period is changed, Red and green laser light can also be extracted, and its value is great. 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, the blue laser light source shown in FIG. 17 was used as the light source of this laser projection apparatus. Reference numeral 45 denotes a laser light source having a wavelength of 473 nm which is blue. Further, blue light is modulated by inputting a modulation signal to the modulation electrode. The modulated blue laser light is incident on the deflector. 56 is a vertical deflector and 57 is a horizontal deflector, both of which use a rotating polygon mirror. Using a screen 70 with a gain of 3, a luminance of 300 cd / m 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 has been greatly improved compared to the conventional case. Further, compared with the configuration using a gas laser, the weight was reduced to 1/1000, the capacity was 1/1000, and the power consumption was 1/100. This greatly contributes to the fact that the laser light source used is small in size and has low power consumption, and that the optical modulator is integrated. In other words, the configuration using the semiconductor laser and the optical wavelength conversion element can be miniaturized, 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, the efficiency can be improved and the optical modulator can be integrated, and the effect is great. In this embodiment, the laser beam is irradiated from the rear of the screen, but it can also 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 through the lens 30, the half-wave plate 37, and the condenser lens 31, and is converted into the harmonic wave P2. That is, in this example, blue light is obtained without using a solid-state laser. The configuration of the optical wavelength conversion element 25 is substantially the same as that of the first embodiment. In this example, LiTaO ₃ A substrate or an optical waveguide type optical wavelength conversion element is used. In addition, an electrode 14 and a protective film 13 are formed to perform light modulation. However, this embodiment does not have a resonator structure.
[0175]
FIG. 22 shows the internal configuration of the semiconductor laser 20. The semiconductor laser 20 includes 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 to become a stable fundamental wave P1. By putting this in the optical wavelength conversion element 25, the conversion efficiency and the harmonic output are greatly improved. The period of polarization inversion is 3 μm, and the optical waveguide length is 7 mm. In this example, the oscillation wavelength of the semiconductor laser was 960 nm, the wavelength of the generated harmonic P2 was 480 nm, and the color was blue. Conversion efficiency is 10% at 10W input. There was no optical damage and the harmonic output was very stable. The DBR semiconductor laser has a stable oscillation wavelength and is convenient for stabilizing the harmonic output.
[0176]
Next, RF superposition (high frequency superposition) was performed on the DBR semiconductor laser. An 800 MHz sine-shaped electric waveform was applied to the DBR semiconductor, and the semiconductor laser was converted into a pulse train optical output using relaxation oscillation. When the DBR semiconductor laser is RF-superposed in this way, the peak output of the fundamental wave is greatly improved while the oscillation wavelength remains 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 conversion efficiency is improved by 5 times when RF is not superimposed.
[0177]
In this embodiment, the DBR semiconductor laser and the semiconductor laser amplifier are separated. However, when integrated, the size can be further reduced.
[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 P <b> 1 from the semiconductor laser 20 is gently focused on the light wavelength conversion element 25 by the lens 30. In this embodiment, LiNbO is used instead of the LiTaO3 substrate. ₃ Was used as a substrate. A bulk type light wavelength conversion element 25 is used. LiNbO ₃ The board | substrate 1a has the characteristics that nonlinearity is large. By driving the semiconductor laser 20 by RF, the peak power is improved and the conversion efficiency of the optical wavelength conversion element is greatly improved. The period of the polarization inversion layer 3 is 3.5 μm, and the length of the optical wavelength conversion element 25 is 7 mm. In this embodiment, the output of the harmonic P2 is stabilized using an optical feedback method. This is because the wavelength tolerance of the optical wavelength conversion element 25 is as narrow as about 0.1 nm. The fundamental wave P1 that has not been converted by the optical wavelength conversion element 25 is collimated by the lens 32, reflected by the grating 36, and returned 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. In order to match 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 extracted in another direction. In this example, the oscillation wavelength of the semiconductor laser was 980 nm, and the extracted harmonic P2 was blue of 490 nm. At this time, an electric waveform with an RF frequency of 810 MHz and an output of 5 W was input. In addition, a harmonic of 3 W was obtained with an average output of 15 W of the fundamental wave. There was no optical damage and the harmonic output was very stable. There is no optical damage because the fundamental wave is condensed only to about 100 μm, and the harmonics are not as large as the same density.
[0180]
In this embodiment, wavelength locking is performed by optical feedback using a grating. However, the present invention is not limited to this, such as selecting a wavelength using a filter and performing optical feedback. In addition, when a laser projection apparatus is configured using the laser light source of this embodiment, it is possible to reduce the size, weight, and cost. Further, in this embodiment, the harmonics can also be modulated by directly modulating the semiconductor laser, 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. In FIG. 24, a cross section of an optical wavelength conversion element (bulk type) 25 is shown.
[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 optical wavelength conversion element 25 is LiTaO doped with rare earth Nd. ₃ The substrate 1b is formed with a domain-inverted structure having 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. Reference numeral 23 denotes 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 total reflection mirror 23 is processed into a spherical shape. In other words, 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, and is further converted into the harmonic P2 by the periodic polarization inversion structure by the polarization inversion layer 3 and emitted to the outside. A harmonic of 2 W was obtained when the pump light P1 was 20 W. Further, the temperature is stabilized by a Peltier element so that the temperature of the optical wavelength conversion element does not change greatly. 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 rare earth element into the light wavelength conversion element and propagating the pump light with the fiber. Further, the temperature change can be prevented by keeping the optical wavelength conversion element away from the heat generated from the semiconductor laser.
[0183]
Further, by changing the coating of the total reflection mirrors 22 and 23 to the 1060 nm band reflection and changing the period of the polarization inversion layer 3 to 1060 nm, 1060 nm oscillates and green laser light (wavelength 530 nm) is obtained as the harmonic P2. It was. Furthermore, by changing the coating of the total reflection mirrors 22 and 23 to 1300 nm band reflection and changing the period of the polarization inversion layer 3 to 1300 nm, 1300 nm oscillates and red laser light (wavelength 650 nm) is obtained as the harmonic P2. It was. With this configuration, it is possible to easily obtain three primary color laser beams of blue, green, and red. Next, FIG. 25 shows a configuration in which the solid-state laser crystal and the light wavelength conversion element are separated. Nd: YVO as the 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 is periodically formed with a domain-inverted structure. Even with the laser light source having this configuration, a 2 W blue laser beam could be stably obtained.
[0184]
Still 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 the present embodiment. Pump light P <b> 1 a emitted from the semiconductor laser 20 with a wavelength of 806 nm is converted into a fundamental wave P <b> 1 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 P <b> 1 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 periodic domain-inverted structure. ₃ An optical waveguide 2 produced using proton exchange in a substrate 1 is used. In the figure, 1 is a Z-plate LiTaO. ₃ Substrate, 2 is an optical waveguide formed, 3 is a polarization inversion layer, 10 is an incident part of the fundamental wave P1, and 12 is an emission part of the harmonic wave P2. The fundamental wave P1 entering the optical waveguide 2 is converted into the harmonic wave P2 by the polarization inversion layer 3. In this way, the harmonic wave P2 whose power is increased in the optical waveguide 2 is radiated from the emitting portion 12. The diverged harmonic P2 is converted into parallel light by the lens 32.
[0185]
In addition, an electrode 14 is formed on the element through a protective film 13. When the pump light P1a was 30W, a harmonic wave P2 of 10W was obtained. The blue laser light was modulated at 30 MHz by inputting a modulation signal to the electrode 14 formed in the optical wavelength conversion element 25. 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 with a fiber. Further, the temperature rise can be prevented by moving the optical wavelength conversion element away from the semiconductor laser.
[0186]
next Examples that do not use solid-state laser crystals explain .
[0187]
A semiconductor laser having a power 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. An output of 2 W was obtained at a wavelength of 490 nm.
[0188]
Next, the laser projection apparatus of the present invention will be described with reference to FIG. Three colors of the blue laser light source, the green laser light source, and the red laser light source of Example 5 were used as the light source. Reference numeral 45 denotes a laser light source having a wavelength of 473 nm which is blue. 46 is a green laser light source having a wavelength of 530 nm, and 47 is a red laser light source having a wavelength of 650 nm. Each optical wavelength conversion element is provided with a modulation electrode. Each light source output is modulated by inputting a modulation signal to the modulation electrode. The green laser light is combined with the blue laser light by the dichroic mirror 61. Further, the red laser beam and the other two colors are combined by the dichroic mirror 62. 56 is a vertical deflector and 57 is a horizontal deflector, both of which use a rotating polygon mirror. Using a screen 70 with a gain of 3, a luminance of 2000 cd / m 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 were obtained. As described above, the laser projection apparatus of the present invention is bright, has high resolution, consumes very little power, and has a great effect.
[0189]
In this embodiment, the polarization inversion type optical wavelength conversion element is used, but the present invention is not limited to this. Further, if a laser light source that emits red light directly from a semiconductor laser is used, the cost can be further reduced. In addition, semiconductor lasers that directly oscillate can be used as blue and green lasers. The combination is free.
[0190]
In the present embodiment, the following measures are taken for safety. When the scanning of the laser beam is stopped, the laser power is automatically turned off. In addition, an infrared laser beam, which is a sub-semiconductor laser with weak output, scans the surroundings around the projected laser beam, and the laser beam is automatically turned off when an object touches this light. . Infrared semiconductor lasers are characterized by low cost and long life.
[0191]
Next, these will be described with reference to FIG. Three laser beams that are the three primary colors are scanned in the drawing range 71 on the screen 70 by a deflector. This laser light passes over the sensors A and B located around the drawing range 71. The output signals of 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 from every point in the peripheral part enters the sensor C.
[0192]
Next, control will be described with reference to FIG. In FIG. 29, when one of the signals of sensors A and B does not enter the control circuit for a certain time, the main power source of the laser light source is turned off, and the blue, red, and green laser light sources are stopped. That is, by stopping the scan, it is possible to prevent the laser beam from being intensively applied to a specific portion. Further, when the signal of the sensor C is interrupted even for a moment, the power source of the laser light source is turned off by the control circuit. That is, it is safe because humans do not touch the high-output short wavelength laser beam. Thus, the safety of the laser projection apparatus is maintained.
[0193]
In the embodiment, the laser light source is turned off, but the optical path of the laser may be cut off. Further, the generation of the short wavelength laser light may be stopped by shifting the phase matching wavelength of the optical wavelength conversion element with a voltage or the like, or changing the oscillation wavelength of the semiconductor laser as the fundamental light source. This method can significantly reduce the time until re-return.
[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, the device looks three-dimensional when viewed from the viewing side. FIG. 30 shows a configuration diagram of the laser projection apparatus of the present embodiment. As shown in FIG. 30, the laser beam is divided in two directions by inserting a prism type optical path changer 66 into the three-color laser beam. The divided laser beams are reflected by the respective mirrors 64 and 65, modulated by the modulators 5a and 5b, and enter the screen 70. The images viewed from the right direction and the image information viewed from the left direction are put on by the modulators 5a and 5b, respectively, and light enters the screen 70 from different directions to make it appear three-dimensional. In addition, the optical path 1 and the optical path 2 are interchanged in a certain time, so that a human feels that an image in another direction has come from two directions, and the stereoscopic image becomes clearer. As in this embodiment, a stereoscopic image can be easily seen without stereoscopic glasses.
[0196]
The light may be divided into two parts by a half mirror or the like. Further, although one light source is divided, two laser light sources having the same color may be used to irradiate the screen from different directions. In this case, one light source output is 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 apparatus of the present embodiment. As the light source, an ultraviolet laser light source based on an optical wavelength conversion element is used. By irradiating the screen 70 coated with the phosphor, red, green and blue RGB light is emitted. The laser light source is composed of a red laser beam 650 nm, which is a direct oscillation of a semiconductor laser, and LiTaO. ₃ The wavelength was halved to 325 nm with the optical wavelength conversion element. This optical wavelength conversion element is a bulk type and has a domain-inverted structure. Reference numeral 48 denotes this laser light source. Here, an ultraviolet modulation signal is obtained by directly modulating a red semiconductor laser. The modulated ultraviolet laser light enters the deflector. 56 is a vertical deflector and 57 is a horizontal deflector, both of which use a rotating polygon mirror. The screen 70 is coated with phosphors that generate red, green, and blue to generate fluorescence. Brightness 300 cd / m at screen size 1m x 0.5m ² A contrast ratio of 100: 1 and a horizontal resolution of 600 TV were obtained. As in this embodiment, the three primary color lights of red, green and blue can be generated with one laser light source, and the size and cost can be reduced. It is also effective to omit the dichroic mirror for multiplexing at this time.
[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 an optical wavelength conversion element is used as the 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 beam. By applying a signal to the liquid crystal light valve 68, it is spatially modulated, and this light can be magnified by the lens 31 and projected onto a screen to view an image. Colorization can be achieved by using three primary color laser light sources.
[0200]
Compared with the conventional system, the efficiency is greatly improved and the power consumption is reduced. Also, the heat generation is small and effective.
[0201]
Next, the laser projection apparatus 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. The blue laser light source shown in FIG. 23 is used as the light source, and the semiconductor laser here is RF-superposed. Further, blue light is modulated by inputting a modulation signal in addition to RF superposition. The modulated blue laser light is incident on the deflector. Using a screen with a gain of 2 and a luminance of 200 cd / m at a screen size of 2 m x 1 m ² Got. Speckle noise caused by laser light interference was not observed on the screen. This is because the coherency of the laser beam is reduced by RF superimposition, and the RF superimposition of the semiconductor laser makes an important contribution to speckle noise countermeasures. In this embodiment, the configuration of the laser light source shown in FIG. 23 is used, but RF superposition is effective for a laser projection apparatus using a laser light source by direct wavelength conversion of a semiconductor laser. Further, speckle noise can be prevented also when red, green, or blue laser light is directly generated by semiconductor laser light. Needless to say, it is effective for a color laser projection apparatus.
[0202]
In the above embodiment, LiNbO is used as the nonlinear optical crystal. ₃ And LiTaO ₃ Was used, but KNbO ₃ The present invention is also applicable to ferroelectric materials such as KTP, organic materials such as MNA, and those materials doped with rare earths. Further, for rare earths, not only Nd used in the examples but also Er and Tl are promising. Although YAG was used as the solid-state laser crystal, other YLF, YVO ₄ Etc. are also effective. LiSAF and LiCAF are also effective as a solid-state laser.
[0203]
Next, an example in which the laser light source of the present invention is applied to an optical disc apparatus will be described with reference to FIG.
[0204]
This optical disk apparatus is provided in an optical pickup 104 having an optical wavelength conversion element 25 having a periodic inversion structure, and the laser light emitted from the semiconductor laser 20 is converted into the optical wavelength in the optical pickup 104 via the fiber 40. This is applied to the element 25.
[0205]
In addition to the optical wavelength conversion element 25, the optical pickup 104 includes 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 condensing lens 106 that collects the light on the optical disk, and a detector 103 that detects reflected light from the optical disk. The polarization beam splitter 105 selectively reflects the reflected light from the optical disc and gives it to the detector 103.
[0206]
The optical pickup 104 is driven by an actuator, but the semiconductor laser 20 is fixed in the optical disc apparatus. The optical pickup 104 can reliably receive the laser light from the semiconductor laser 20 fixed in the optical disk device by a flexible optical fiber.
[0207]
Next, tax the operation.
[0208]
The light (pump light) emitted from the semiconductor laser 20 is converted into the fundamental wave P1 by the solid-state laser 21 and irradiated to the light wavelength conversion element 25 through the optical fiber 40. The optical wavelength conversion element 25 has the same configuration as that of the above-described embodiment, and converts the fundamental wave P1 into the harmonic wave P2. The harmonic wave P2 is collimated by the collimator lens 32, passes through the polarization beam splitter 105, and is condensed on the optical disk medium 102 via the condenser lens 106. The reflected light from the optical disk medium 102 returns again through the same optical path, 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 harmonic forward and backward paths.
[0210]
When the 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 the harmonic is 473 nm.
[0211]
By using a high-power laser beam with an output of 200 mW, it is possible to perform recording at a speed 10 times the recording speed when using an optical disc apparatus using a conventional output light of 20 mW. The transfer rate was 60 Mbps.
[0212]
In addition, the semiconductor laser 20 that generates heat during operation is fixed to the housing of the optical disk apparatus and is away from the optical pickup. For this reason, as a result of removing the semiconductor laser from the optical pickup, it is not necessary to provide a special ripening structure for the semiconductor laser. For this reason, an ultra-small and lightweight optical pickup can be configured. As a result, since the actuator can be driven at high speed in the optical pickup, high-speed recording with a high transfer rate is achieved.
[0213]
In this embodiment, the solid state laser is disposed on the semiconductor laser side, but may be disposed on the optical wavelength conversion element side. Further, light from a semiconductor laser may be directly converted into a harmonic as a fundamental wave without using a solid-state laser.
[0214]
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, it is possible to omit the lens and the polarization beam splitter. Then, the optical pickup can be further downsized.
[0215]
(Possibility of industrial use)
As described above, according to the optical wavelength conversion element of the present invention, LiNb _x Ta _1-x O ₃ (0.ltoreq.X.ltoreq.1) After the optical element is fabricated on the substrate, low-temperature annealing is performed to restore the refractive index increase caused by heat treatment such as high-temperature annealing, thereby forming a stable proton exchange layer, thereby forming a stable optical element. be able to. In particular, the present invention is indispensable for practical application of an optical wavelength conversion element in which the phase matching wavelength changes with a change in refractive index.
[0216]
In addition, the two-step annealing in which the temperature is set to two steps as the low-temperature annealing is effective because it is possible to return to the stable proton exchange layer in a state where there is no change with time. Further, by performing the second annealing at a temperature lower by 200 ° C. than the first annealing, the strain can be greatly relieved and a stable proton exchange layer can be formed, which is effective. Further, the low temperature annealing temperature is 120 ° C. or less, and if it is carried out for at least 1 hour, the change with time is 0.5 nm or less, which is particularly effective. If the temperature is 50 ° C. or lower, the annealing time becomes extremely long, which causes a problem.
[0217]
Further, according to the laser light source of the present invention, the oscillation wavelength of the semiconductor laser is stabilized and the fundamental wave output is increased by passing the semiconductor laser amplifier between the distributed feedback semiconductor laser and the optical wavelength conversion element, and By using an optical wavelength conversion element having a polarization inversion structure that is highly efficient, the highest harmonic output can be stably obtained.
[0218]
Further, in the laser light source of the present invention, the optical wavelength conversion element portion can be made very compact by propagating the pump light or the fundamental wave through the fiber. Further, the optical wavelength conversion element can be kept away from the heat generated from the semiconductor laser, temperature change can be prevented, and a high-power semiconductor laser can be used.
[0219]
In addition, when a periodic polarization inversion structure is used as an optical wavelength conversion element, not only the 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 adopting an optical waveguide with weak confinement as an optical wavelength conversion element, the density of harmonics is reduced, and optical damage is greatly improved. For example, it is possible to withstand 100 times optical damage by making the area 100 times that of the conventional area. In addition, according to the laser light source of the present invention, a multi-stripe or wide-stripe high-power semiconductor laser can be used and high-power harmonics can be obtained by converting the pump light from the solid laser crystal into the fundamental wave. .
[0220]
From these, for example, it is possible to obtain a total conversion efficiency of 20% by multiplying the conversion efficiency of the optical wavelength conversion element of 30% of the conversion efficiency between electricity and light of the semiconductor laser by 70%. In addition, for example, when the semiconductor laser is RF-superposed in the laser light source of the present invention, the conversion efficiency is improved, for example, when the RF is not superposed.
[0221]
Furthermore, according to the laser projection apparatus of the present invention, since it is based on a semiconductor laser, it is possible to achieve a significant reduction in size, weight, and cost. In addition, by using a high-power laser light source based on a semiconductor laser and an optical wavelength conversion element, the apparatus can be reduced in size, weight, and cost. In addition, power consumption can be extremely reduced. One of the factors is that this apparatus does not have a laser light modulator and is integrated with an optical wavelength conversion element. Also, the resolution is greatly improved as compared with the conventional case. For example, compared with the configuration using a gas laser, the weight was reduced to 1/1000, the capacity was 1/1000, and the power consumption was 1/100. This greatly contributes to the fact that the laser light source used is small in size and has low power consumption, and that the optical modulator is integrated. In other words, the configuration using the semiconductor laser and the optical wavelength conversion element can be miniaturized, 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 at a low voltage can be integrated, and the effect is great.
[0222]
Further, since the three primary colors can be produced by striking a phosphor with an ultraviolet laser light source, further miniaturization and cost reduction can be achieved, and its industrial value is great. Thus, the three primary color lights of red, green and blue can be generated with one laser light source. It is also effective to omit the dichroic mirror for multiplexing at this time.
[0223]
In addition, according to the laser projection apparatus of the present invention, when the scan is stopped, there is a laser light stop or cut function in order to prevent the laser light from being intensively applied to a specific portion. Further, when the sensor signal is interrupted even for a moment, the laser light source is turned off by the control circuit. That is, it is safe because humans do not touch the high-output short wavelength laser beam. Thus, the safety of the laser projection apparatus 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 beautiful images can be reproduced. Further, speckle noise can be prevented also 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 time change of harmonic output of a conventional optical wavelength conversion element.
FIG. 5 is a view showing a change with time of a phase matching wavelength of a conventional optical wavelength conversion element;
FIG. 6 is a graph showing a change in refractive index with time 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 process diagram of a method of manufacturing an optical wavelength conversion element according to the first example of the present invention.
FIG. 8B is a process diagram of the method for manufacturing the optical wavelength conversion element according to the first embodiment of the present invention.
FIG. 8C is a process drawing of the method for manufacturing the optical wavelength conversion element according to the first embodiment of the present invention.
FIG. 8D is a process diagram of a method of manufacturing an optical wavelength conversion element according to the first example of the present invention.
FIG. 8E is a process diagram of a method of manufacturing an optical wavelength conversion element according to the first example 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 the change of the phase matching wavelength with the annealing time as a parameter with respect to the annealing time.
FIG. 11 is a characteristic diagram showing the relationship between annealing temperature and phase matching wavelength variation.
FIG. 12 is a graph 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 time characteristics of a phase matching wavelength and an 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 element according to the second embodiment of the present invention.
FIG. 15A is a process diagram of an optical element manufacturing method according to a fourth embodiment of the present invention.
FIG. 15B is a process drawing of the method of manufacturing the optical element in the fourth example of the present invention.
FIG. 15C is a process diagram of the manufacturing method of the optical element according to the fourth embodiment of the present invention.
FIG. 16 is a process flowchart of an optical element manufacturing method according to a fifth embodiment of the present invention.
FIG. 17 is a structural diagram of an embodiment of a laser light source of the present invention.
FIG. 18A is a manufacturing process diagram of an optical wavelength conversion element in a laser light source of the present invention.
FIG. 18B is a manufacturing process diagram of an optical wavelength conversion element in the laser light source of the present invention.
FIG. 81C is a manufacturing process diagram of an optical wavelength conversion element in a laser light source of the present invention.
FIG. 18D is a manufacturing process diagram of an optical wavelength conversion element in the laser light source of the present invention.
FIG. 19 is a characteristic diagram showing the relationship between the optical waveguide thickness and the optical damage resistance of the optical wavelength conversion element used in the laser light source of the present invention.
FIG. 20 is a configuration diagram of a laser apparatus 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 block 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 apparatus according to an embodiment of the present invention.
FIG. 28 is a configuration diagram of an automatic stop device for a laser apparatus according to an embodiment of the present invention.
FIG. 29 is a diagram of a control system of the automatic stop device of the laser apparatus according to the embodiment of the present invention.
FIG. 30 is a configuration diagram of a laser apparatus according to an embodiment of the present invention.
FIG. 31 is a configuration diagram of a laser apparatus according to an embodiment of the present invention.
FIG. 32 is a configuration diagram of a laser apparatus according to an embodiment of the present invention.
FIG. 33 is a block diagram of an optical disc apparatus according to an embodiment of the present invention.

Claims (2)

Comprising an optical pickup having a built-in optical wavelength conversion device for converting a fundamental wave into a harmonic, a laser light source for generating a laser beam is provided to be separated from said optical pickup, and an actuator for moving the optical pickup An optical disk device,
The laser light source includes a semiconductor laser,
The optical wavelength conversion element is a bulk type, and a periodic polarization inversion structure is formed,
The laser beam emitted from the laser light source via the optical fiber, is incident on the light wavelength converting element,
By the optical fiber, due to heat generation from the laser light source, an optical disk device you characterized by having a configuration for preventing a change in temperature of the optical wavelength conversion element. The optical disk apparatus according to claim 1 , wherein 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.

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