JPH05173213A - Guidewave type second harmonic generating element - Google Patents

Abstract

PURPOSE:To enable generation of the second harmonic where the efficiency is high, the wave aberration is small, and the converging is easy by periodically inverting the nonlinear optical coefficients of both one part of a substrate and a an optical wave guide layer. CONSTITUTION:In an optical element consisting of an optical substrate 14 and an optical wave guide layer 16 whose refraction factor is larger than that of the substrate 14, the nonlinear optical coefficients of both the optical substrate 14 and the optical waveguide layer 16 are periodically inverted. For example, in the optical element consisting of ZcutLibO3 monocrystal substrate 14 of 5 mol% MgO dope where the surface is +C, and LiNbO3 monocrystal substrate 16 of 1mol% MgO dope, the spontaneous polarization is normally faced upward while it is faced downward in the parts 15, 17 where the polarization is inverted. The sign of the nonlinear optical coefficient coincides with the direction of the spontaneous polarization in the case of the ferroelectric substance crystal of the space group R3c of LiNbO3, LiTaO3 or the like. Thus, the nonlinear optical coefficients of the substrate 14 and the light guide layer 16 are also periodically inverted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type second harmonic wave generating element, a method for manufacturing the same, a bulk type optical head and an integrated optical head using the second harmonic wave generating element, and the above-mentioned optical element. The present invention relates to an optical information processing device such as an optical disk device using a head and a laser beam printer.

[0002]

2. Description of the Related Art In recent years, as a compact and lightweight blue light source, attention has been paid to a semiconductor laser beam having a wavelength of about 800 nm which is converted to a half of about 400 nm by a waveguide type second harmonic generation element. For example, the one that was proposed early on,
As shown in, a fundamental wave 23 (power P ₁ ) is applied to one end of an optical waveguide 22 formed by thermally diffusing titanium (Ti) on the surface of a single crystal 21 of lithium niobate (hereinafter referred to as LiNbO ₃ ). There is a method to make it incident. Further, as described in, for example, Japanese Patent Laid-Open No. 61-18934, L
On the iNbO ₃ single crystal substrate, a proton exchange method (LiNb 3
A method of forming an optical waveguide by partially substituting Li ions and protons of O ₃ ) to form an optical waveguide, injecting a fundamental wave into one end face of the optical waveguide, and generating a second harmonic generated by Cherenkov radiation. The method of taking out is also proposed. This is shown in FIG. More recently, a method for performing phase matching using polarization reversal has been proposed, as discussed in, for example, Electronics Letters 25, 11 (1989), pages 731 to 732 (Electronics Letters, 25, 11). was suggested. That is, as shown in FIG.
A diffraction grating 41 is formed on the O ₃ crystal substrate 21 by diffusion of Ti, heated to about 1100 ° C. to invert the polarization of only the diffraction grating layer, and then an optical waveguide 42 is formed by a proton exchange method to generate a fundamental wave 23. It is incident and the second harmonic wave 24 is taken out. Lithium tantalate (hereinafter Li
In the case of using TaO ₃ ), a diffraction grating 41 is produced by a proton exchange method instead of Ti diffusion, and the diffusion rate is about 60.
A method has also been attempted in which the polarization of only the diffraction grating layer is inverted by heating to 0 ° C., and the optical waveguide 42 is manufactured by the proton exchange method.

[0003]

However, the above-mentioned prior art has the following problems. The method shown in FIG. 2 is to perform phase matching using an ordinary ray polarized in the z direction as the fundamental wave 23 and an extraordinary ray polarized in the y direction as the second harmonic wave 24. Since the temperature coefficient and the temperature coefficient of the refractive index of extraordinary light differ greatly,
It was necessary to control the temperature below 0.1 ° C.

On the other hand, in the method using the Cherenkov radiation shown in FIG. 3, the beam shape of the second harmonic wave is crescent like 32, and the wavefront aberration is extremely large, and it is almost impossible to narrow it down to the diffraction limit. Is.

The newly proposed method for phase matching using polarization inversion shown in FIG. 4 for the above two examples is compared with Cherenkov radiated light because the second harmonic wave 24 is collimated light. It has the advantage that it is extremely easy to collect light. However, since the Ti diffused portion and the Ti non-diffused portion, or the proton-exchanged portion and the non-proton-exchanged portion have different refractive indexes for forming the polarization violation lattice, the Fresnel reflection loss at the boundary portion is different. It is inevitable that the fundamental wave suffers a loss due to such factors as a decrease in efficiency. Further, since the polarization inversion lattice is produced by diffusing Ti or exchanging protons, the cross-sectional shape of the polarization inversion lattice depends on the shape of the Ti diffusion layer or the proton exchange layer, and therefore, the polarization inversion lattice of rectangular cross section is produced. Is inherently difficult. Ti
The cross-sectional shape of the domain-inverted lattice produced by the diffusion method is substantially triangular, and the cross-sectional shape of the domain-inverted lattice produced by the proton exchange method is approximately semicircular. For this reason, the second harmonic cannot be generated with the original efficiency of the SHG element having an ideal polarization inversion grating with a rectangular cross section.

A first object of the present invention is to obtain a waveguide type second harmonic generating element which is highly efficient and has a small wavefront aberration and can easily generate a second harmonic.

A second object of the present invention is to obtain a method for manufacturing the above second harmonic wave generating element.

A third object of the present invention is to obtain a visible light generating light source using the above second harmonic generating element, an optical head using the same, and an optical information recording / reproducing apparatus using the optical head. Especially.

[0009]

The first object of the present invention is to:
In an optical element comprising an optical substrate and an optical waveguide layer having a higher refractive index than the substrate, a second harmonic generation element in which the nonlinear optical coefficients of both the part of the substrate and the optical waveguide layer are periodically inverted The optical substrate is MgO: L
iNbO ₃ and the optical waveguide layer is LiNbO ₃ or MgO: LiNbO in which the doping amount of magnesium is smaller than that of the substrate.
By a ₃ second harmonic generation device, also, the optical substrate is a LiTaO _3, the optical waveguide layer is achieved by the second harmonic generation element is tantalum lithium niobate.

A second object of the present invention is to prepare a MgO: LiNbO ₃ or LiTaO ₃ substrate in which the polarization is periodically inverted beforehand, and to prepare the raw material powder of the ferroelectric metal oxide constituting the optical waveguide layer in the presence of flux. 2. A step of preparing a melt by heating and melting with a step of: bringing the surface of the substrate whose polarization has been inverted into contact with the melt, lowering the temperature of the melt to a crystal precipitation temperature, and depositing on the substrate. 3. The method for producing a second harmonic generating element, comprising the step of liquid phase epitaxially growing a metal oxide film constituting the optical waveguide layer according to 3, and the flux used in the method for producing a second harmonic generating element is lithium vanadate. (LiVO ₃ ),
Alternatively, lithium borate (Li ₂ B ₂ O ₄ ), lithium fluoride (LiF), or potassium fluoride (K
This is achieved by the method of manufacturing the second harmonic generation element of F).

A third object of the present invention is to provide the second harmonic generation element, a near-infrared semiconductor laser light source having a wavelength of 780 nm to 1100 nm, and a lens system for converging laser light emitted from the laser light source on the end face of the waveguide. A visible light generating light source, and a visible light generating light source, a light collecting means for collecting light emitted from the light source on an optical recording medium, a recording surface of the optical recording medium, and recording of the optical recording medium, An optical head having a means for receiving and detecting the reflected light from the reproducing surface, and also a rotation drive control means for rotationally driving the optical recording medium, and optical information recording by being driven in the radial direction of the optical recording medium. In an optical information recording / reproducing apparatus including an optical head for reproducing, and an actuator for mounting and scanning the optical head, the optical head mounted on the actuator is an optical information recording device that is the optical head. It is achieved by the recording and reproducing apparatus.

[0012]

The present invention provides a second harmonic generating element capable of generating a second harmonic having a small wavefront aberration and a small size with high efficiency by the following operations.

Consider an optical waveguide having a three-layer structure as shown in FIG.

Reference numeral 51 is a substrate, 56 is a portion in which the polarization is inverted in the substrate, and 52 is an optical waveguide layer in which the polarization direction is inverted with a period Λ. That is, 54 is a portion whose polarization is upward and 55 is a portion whose polarization is downward. 53 is a clad layer, usually an air layer. The substrate 51 and the optical waveguide layer 52 are made of, for example, LiN.
In the case of a ferroelectric of the space group R3C such as bO ₃ , M. Di
domenco Jr. Et al., Journal of Applied Physics Vo
According to L.40, No.2, pp720-734, the refractive index n does not depend on the direction of spontaneous polarization. Therefore, from the viewpoint of the refractive index, the structure as shown in FIG. 5A is as shown in FIG. 5B for the incident light wavelength λ. on the other hand,
According to the above-mentioned document, the coefficient d representing the generation performance of the second harmonic wave
Is proportional to the spontaneous polarization. Therefore, looking at the structure as shown in FIG. 5A, the structure has the same period Λ as that of FIG. 5A (FIG. 5C). Considering the guided light confined in the optical waveguide layer in particular, since the nonlinear effect of the substrate layer can be almost ignored, the structure of FIG. 5C can be approximated with the structure of FIG. 5D with sufficient accuracy. Figure 5 as incident light
When the TM wave polarized in the direction (z direction) perpendicular to the substrate in the coordinate system of (d) is considered and its propagation direction is the x direction, the z component of the electric field is represented by Formula 1.

[0015]

[Equation 1]

Similarly, assuming that the second harmonic is also a TM wave polarized in the direction perpendicular to the substrate, the z component of the electric field is expressed by equation 2.

[0017]

[Equation 2]

The non-linear polarization for generating the second harmonic is expressed by Equation 3
It is represented by.

[0019]

[Equation 3]

On the other hand, Maxwell considering nonlinear polarization
The equation of l is expressed by the equation 4.

[0021]

[Equation 4]

Substituting equation 3 into equation 4, the wave equation expressed by equation 5,

[0023]

[Equation 5]

And the approximation expressed by the equation (6)

[0025]

[Equation 6]

By using, Equation 7 is obtained.

[0027]

[Equation 7]

By multiplying Eq. 7 by Eq. 8 and integrating from Z =-. Infin. To Z = .infin., Eq. 9 that governs the power transfer from the fundamental wave to the second harmonic is obtained.

[0029]

[Equation 8]

[0030]

[Equation 9]

In the case of FIG. 5, since the non-linear optical coefficient d ₃₃₃ changes its direction periodically, it can be expanded into a Fourier series as shown in Eq.

[0032]

[Equation 10]

The above-mentioned period Λ is determined as shown in equation 11 so as to satisfy the phase matching condition.

[0034]

[Equation 11]

As a result, the phase matching of the fundamental wave and the second harmonic wave is easily performed, and the equation 9 is expressed as the equation 12.

[0036]

[Equation 12]

[Mathematical formula-see original document] Integrating Expression 12 from x = 0 to x = 1 (however, it is assumed that the power of the fundamental wave is almost unchanged and constant),
If the boundary condition that x = 0 and the amplitude of the second harmonic is zero is used, the conversion efficiency η from the fundamental wave to the second harmonic is expressed by Equation 13.

[0038]

[Equation 13]

As described above, according to the present invention, (1) by simply selecting the period of the polarization inversion grating so as to satisfy Eq. 11, it is possible to easily obtain the fundamental wave in the structure in which the polarization is inverted as shown in FIG. Phase matching of the second harmonic can be realized,
A highly efficient second harmonic generation element can be constructed.

(2) Since the generated second harmonic is collimated guided light, the wavefront aberration of the emitted second harmonic is small, and the light can be narrowed down to the diffraction limit.

(3) Since the refractive index is uniform in the traveling direction of the guided light, light scattering is small. A high-performance second harmonic generation element having the above-mentioned characteristics can be configured.

[0042]

Embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of a second harmonic generation element according to the present invention, (a) is a plan view, (b) is a sectional view, FIG. 5 is an operation explanatory view of the element of the present invention, and FIG. 6 is a book. FIG. 7 is a diagram showing a second embodiment of the invention, FIG. 7 is an operation explanatory diagram of the second embodiment of the invention, and FIG.
(A) ~ (f) is a diagram showing the manufacturing process of the second harmonic generation device, respectively, FIG. 9 is a diagram showing the manufacturing process of the second harmonic generation device of the second embodiment of the present invention, respectively 10 is a schematic view of a write-once type optical head equipped with the second harmonic generation element of the present invention, FIG. 11 is a schematic view of a magneto-optical type optical head equipped with the second harmonic generation element of the present invention, and FIG. FIG. 3 is a schematic view of an optical information recording / reproducing apparatus equipped with the second harmonic generation element of the present invention.

First Example In FIG. 1, 14 is 5 mol% Mg whose surface is + c plane.
O-doped ZcutLiNbO ₃ single crystal substrate, 16 is 1 m
In the ol% MgO-doped LiNbO ₃ single crystal thin film, the spontaneous polarization is usually upward. 15 and 17 are the parts where the polarization is inverted, and the polarization is downward in this part. M. Didom
enico Jr. Et al., Journal of Applied Physics (Journal of Appl)
ied Physics) Vol. 40, No. Two
According to pages 720 to 734, the sign of the nonlinear optical coefficient coincides with the direction of spontaneous polarization in the case of a ferroelectric crystal of the space group R3c such as LiNbO ₃ or LiTaO ₃ . Therefore, it can be said that the nonlinear optical coefficients of the substrate and the optical waveguide layer of this example are also periodically inverted. Reference numeral 18 denotes a ridge-type optical waveguide section, in which both the fundamental wave and the second harmonic wave are confined and propagated. Reference numeral 13 is the incident fundamental wave, which is polarized in the direction perpendicular to the crystal surface. Reference numeral 19 denotes the second harmonic generated by the polarization inversion diffraction grating portion 17, which is also polarized in the direction perpendicular to the crystal surface.

Next, a method of manufacturing the above second harmonic generating element using the liquid phase epitaxial growth method will be described with reference to FIG.

First, the surface was periodically poled at 5 m.
An ol% MgO-doped LiNbO ₃ substrate is prepared. The domain-inverted lattice was formed on the surface of the substrate as follows. + C
The substrate whose surface has been polished to about 1/10 of the laser light wavelength λ is ultrasonically cleaned in acetone, isopropyl alcohol, and pure water, and then dried.
Å The film was formed by sputtering. Photoresist 82 was applied on the Ti 81 film by a spinner, and the photoresist 82 was patterned by a normal photolithography technique using a photomask in which a portion where polarization inversion 17 was performed was opened. Using the patterned photoresist 82 as a mask, CF ₃
The Ti 81 was patterned by RIE using Cl gas, and then the photoresist 82 was removed. Eleven kinds of photomasks each having a pattern period different from 2.5 to 3.5 μm by 0.1 μm were manufactured. Next, the above substrate was placed in an electric furnace and passed through a bubbler of warm water at about 80 ° C. in an atmosphere of Ar containing water vapor at about 1100 ° C.
And heat treated for about 10 minutes. During cooling, the atmosphere was changed to O ₂ containing water vapor. As a result, the domain inversion area 1
5 formed.

Next, + c of the substrate prepared as described above
On the surface, a MgO-doped LiNbO ₃ single crystal thin film in which a domain of the substrate is transferred is grown by a liquid phase epitaxial crystal growth method. This was done as follows. First, the melt was adjusted during epitaxial growth. Optical waveguide material 1m
20 mol% of MgO-doped LiNbO _{3 and} 80 mol% of lithium borate Li ₂ B ₂ O _{4 as} a flux material
As a raw material, powders of lithium carbonate Li ₂ CO ₃ , boric acid H ₃ BO ₃ , niobium pentoxide Nb ₂ O ₅ and magnesium oxide MgO were weighed and mixed well in a mortar and then platinum crucible. And heated in an electric furnace at a temperature of 1200 ° C. for 5 hours in an electric furnace to prepare a uniform melt. This melt up to 800 ℃ 60 ℃ /
The 5 mol% MgO-doped ZcutLiNbO ₃ in which the + c plane was periodically poled at a cooling rate of h
The single crystal substrate is contacted with the melt for a predetermined time,
As shown in (f), 1 mol% MgO-doped Li on the substrate
The NbO ₃ thin film 2 was grown to 2.5 μm. Then, the melt and the substrate are separated, and the substrate is heated to room temperature in an electric furnace at 30 ° C /
It was gradually cooled at a cooling rate of h. When the content of Mg was examined by EPMA, it was about 1 mol%. In addition, the domain in the grown single crystal thin film is defined as nitric acid: hydrofluoric acid =
Observed from the difference in etching state after etching with a 1: 2 etching solution, the direction of polarization was the same as the polarization of the underlying substrate, and the domain boundaries in the thin film were relative to the interface between the substrate and the thin film. It was almost vertical. That is, a polarization inversion grating having a substantially rectangular cross section could be formed. The amount of the flux material added is 70 to 90 mol.
The range of% is desirable. The contact time varies depending on the film thickness of the thin film, but is 10 to 30 minutes when the film thickness is 0.5 to 3 μm. In addition to the above lithium borate, lithium fluoride LiF, potassium fluoride KF, lithium vanadate LiVO ₃ or the like may be used as the flux material.

Then, the thin film produced as shown in FIG. 8 (f) was annealed in an ozone atmosphere to compensate for oxygen deficiency.

Finally, a channel part was prepared. First, the photoresist was patterned using a photoresist having only the channel portion as a light shielding portion, and then the thin film was etched by 2 μm by ion milling using this photoresist as a mask. The channel width is 3 μm.
Then, the photoresist was removed to produce a channel part. The ion milling device used in this step has a structure in which a plasma chamber has a plurality of permanent magnets arranged on the outer periphery of a conical hollow vacuum container, and ions generated in the plasma generation chamber are an acceleration electrode, a deceleration electrode, It is a structure that is drawn out by three electrodes of a ground electrode. Therefore, the spatial density distribution of ions is uniform, the directivity is extremely high, and etching with extremely high precision is possible.

This prepared 1 mol% MgO-doped L
When the Ti-S laser light tuned to a wavelength of 830 nm was polarized in the iNbO ₃ channel thin film in the direction perpendicular to the substrate surface and was made incident using a prism coupler, the main component of the electric field was in the direction perpendicular to the substrate surface. Is excited, and its effective refractive index N (ω) =
It was 2.1686. On the other hand, when the same measurement is performed with a dye laser whose wavelength is tuned to 415 nm, two modes are excited and the effective refractive index of the lower mode is N (2
ω) = 2.3016. Further, when the light propagation loss for light of 830 nm was measured by the cutback method, a good value of 1 dB / cm was obtained. The reason for this is
First of all, liquid phase epitaxial growth allowed the growth of high-quality thin films that were close to the stoichiometric composition, and second, because etching could be performed using a highly directional ion milling device, the sidewall of the channel section Was able to be processed with extremely high precision.

When the polarization inversion period is calculated by the equation 11, (M
= 1) is about 3.1 μm, so that a sample having a period of 3.1 μm has a length of 10 in the direction parallel to the channel portion.
mm, cut to a vertical length of 5 mm,
A 5 mm side was polished and a second harmonic generation experiment was conducted. A Ti-S laser was used as a laser light source, and light was condensed on the end surface of the channel portion by an objective lens. The sample was placed on a copper block connected to a Peltier device, and the temperature was monitored with a thermocouple. First, the temperature was set to 25 ° C. and the generation efficiency of the second harmonic was measured. The wavelength of the laser light source was changed to find the wavelength that maximized the efficiency. As a result, the second harmonic output obtained when a fundamental wave of 40 mW was input was 4 mW, and the efficiency considering Fresnel reflection loss was 11.8%. This is about 1/3 of the theoretical value of 40% calculated from the equation 18, but a sufficiently high efficiency was obtained as compared with the conventional example.
Coupling efficiency of a high power semiconductor laser with an output of 200 mW in the future 5
If it is coupled to the optical waveguide at 0%, the efficiency will be about 30%.
A second harmonic wave output of 0 mW is obtained and can be used as a light source for writing and reproducing on a magneto-optical disc or a phase change optical disc.

Second Example Next, lithium tantalate (hereinafter referred to as LiTaO) was used as a substrate.
_A second embodiment using a single crystal substrate and lithium tantalum niobate as an optical waveguide layer will be shown.

In FIG. 6, reference numeral 64 is Z whose surface is the + c plane.
A cut lithium tantalate single crystal substrate, 66 is a lithium tantalum niobate thin film, the chemical formula of which is represented by Chemical Formula 1.
However, the composition ratio x of Ta and Nb is between 0 and 0.1, and the direction of spontaneous polarization is usually upward. Reference numeral 65 is a portion where the polarization is inverted, and the direction of spontaneous polarization in this portion is downward. Reference numeral 68 denotes a ridge-type optical waveguide section, in which both the fundamental wave and the second harmonic wave are confined and propagated. Reference numeral 13 is the incident fundamental wave, which is polarized in the direction perpendicular to the crystal surface. 69 is the second harmonic generated in the optical waveguide, which is also polarized in the direction perpendicular to the crystal surface.

Next, a method of manufacturing the second harmonic wave generating element using the liquid phase epitaxial growth method will be described.

First, LiT whose surface is periodically poled
An aO ₃ single crystal substrate was prepared as follows. Figure 9
As shown in (b), a Cr film 91 of 100 n is formed on the thin film.
Patterning of the photoresist 92 is performed by ordinary photolithography using a photomask formed by m-sputtering and having a window in which a portion for polarization reversal is opened, as shown in FIG. 9C.
Then, etching was performed to pattern the Cr film, and then the photoresist was removed. Eleven kinds of photomasks each having a pattern period different from 2.5 to 3.5 μm by 0.1 μm were manufactured. Next, benzoic acid powder was placed in a quartz container, heated and melted, and the substrate was immersed in the powder to perform proton exchange. At this time, the processing temperature was 200 ° C. and the processing time was 15 minutes. afterwards,
After thorough ultrasonic cleaning in ethanol, Cr was removed, and the above sample was put in a platinum container together with LiTaO ₃ powder and heat treated. The heat treatment temperature at this time is 58
The temperature is 0 ° C., and the heat treatment time is 15 minutes. This allows
As shown in FIG. 9E, the domain inversion area 65 was formed on the substrate surface.

Next, a lithium tantalum niobate single crystal thin film, in which the domain of the substrate was transferred, was grown on the + c surface of the prepared substrate by the liquid phase epitaxial crystal growth method as follows. That is, first, the melt was adjusted during epitaxial growth. Lithium carbonate Li ₂ CO ₃ , boric acid H ₃ BO ₃ , pentoxide so that the lithium tantalum niobate which is the optical waveguide layer material is 20 mol% and the lithium borate Li ₂ B ₂ O _{4 which} is the flux material is 80 mol%. Powders of niobium Nb ₂ O ₅ and tantalum pentoxide Ta ₂ O ₅ were weighed and mixed well in a mortar, and then put in a platinum crucible and put in an electric furnace.
A uniform melt was prepared by heating at a temperature of 0 ° C. for 3 hours.
This melt was cooled to 1000 ° C. at a cooling rate of 60 ° C./h, and ZcutL in which the above surface was periodically poled
An iTaO ₃ single crystal substrate was brought into contact with the melt for a predetermined time, and a domain of the substrate was transferred onto the substrate to grow a lithium tantalum niobate thin film 86 to a thickness of 5 μm. The melt and the substrate are then separated and the substrate is brought to room temperature in an electric furnace for 30 minutes.
It was gradually cooled at a cooling rate of ° C / h. When the composition ratio of Nb and Ta was examined by EPMA, it was about 1: 9. Further, when the domains in the grown single crystal thin film were etched with an etching solution of nitric acid: hydrofluoric acid = 1: 2 and observed from the difference in etching state, the direction of polarization was the same as that of the underlying substrate. The domain interface of the thin film was almost perpendicular to the interface between the substrate and the thin film. That is, a polarization inversion grating having a substantially rectangular cross section could be formed.
The addition amount of the above flux material is 70 to 90 mo
A range of 1% is desirable. The contact time varies depending on the film thickness of the thin film, but if the film thickness is 0.5 to 5 μm, the contact time is 10
From 50 minutes. In addition to the above lithium borate, lithium fluoride LiF, potassium fluoride KF, lithium vanadate LiVO ₃ or the like may be used as the flux material.

After that, the produced thin film was annealed in an ozone atmosphere to compensate for oxygen deficiency.

Finally, a channel part was prepared. First,
The photoresist was patterned using a photoresist having only the channel portion as a light shielding portion, and then the thin film was etched by 4 μm by ion milling using this photoresist as a mask. The channel width is 3 μm. Then, the photoresist was removed to produce a channel part.

Third Embodiment A third embodiment shown in FIG. 10 is a head for an optical disk using a small visible light source equipped with the waveguide type second harmonic generation element of the first embodiment or the second embodiment. Is. 11 is a high-power (about 100 mW, wavelength λ = 840 nm) semiconductor laser, 13 is a lens that focuses the semiconductor laser light on the end face of the optical waveguide, 101 is the waveguide type second harmonic generation of the first or second embodiment. Reference numeral 102 is an element, and 102 is a polarization beam splitter. The laser light passes through the polarization beam splitter 102 and enters the collimator lens system 103. Reference numeral 104 is a λ / 4 wavelength plate that converts linearly polarized light into circularly polarized light, and 105 is an objective lens that focuses laser light on the optical disk 106. The reflected light from the optical disk 106 is reflected by the polarization beam splitter 102, condensed by the focusing lens 108, and then the half mirror 109.
Is divided into two and guided to the two-division photo sensor 110 and the four-division photo sensor 111, and the tracking signal, the focusing signal and the reproduction signal are detected.

Fourth Embodiment A fourth embodiment shown in FIG. 11 is a magneto-optical disk using a small visible light source equipped with the waveguide type second harmonic generation element of the first embodiment or the second embodiment. Is the head. In the figure, 11, 13 and 101 are high power semiconductor lasers, focusing lenses and waveguide type second harmonic generating elements similar to those of FIG. 10 of the third embodiment, and 203 is a lens system for beam shaping. The laser light passes through this and is shaped into parallel light. 202
Is a polarizing beam splitter that also functions as a beam shaping prism.
It is launched by and is focused on the optical disc surface 206 by the objective lens 105. Reference numeral 207 is a magnetic coil for applying a magnetic field used for writing and erasing. The reflected light from the optical disc surface 206 is reflected by the polarization beam splitter 202, passes through the half-wave plate 204, is condensed by the focusing lens 207, and is split into two light beams by the polarization beam splitter 102.
The tracking signal, the focusing signal, and the reproduction signal are detected by being guided to the 00 and four-division photosensors 111.

If the optical system is changed, the waveguide wavelength conversion element 101 can be applied to a read-only type optical disc or a phase change type rewritable optical disc.

Fifth Embodiment FIG. 12 shows an optical information recording / reproducing apparatus in which the optical head shown in the third embodiment is applied to a conventional optical information recording / reproducing apparatus.
It is a figure which shows the outline of 304. The feature of this embodiment is that the optical head 301 is mounted on the actuator 302 and the configuration of the optical system is simplified. The operating principle of this device is the same as the conventional device. That is, the optical recording medium 305 is rotated by the motor 303 controlled by the rotation control means.
Actuator in the radial direction of the rotating optical recording medium 305.
The optical head 301 mounted on the optical disk 302 is driven to scan by the scanning control means, and in synchronization therewith, the optical information 30 from the optical recording medium is transmitted.
6 is converted into an electric signal in the optical head 301 and processed by a necessary signal processing means.

In this optical information recording / reproducing apparatus, since the laser light can be focused by the optical head to a spot diameter of 0.5 μm, which is half that of the conventional one, the recording density can be made four times that of the conventional head. Since the weight of the waveguide type wavelength conversion element mounted is extremely small, the access time is the same as that of the conventional one.

[0063]

As described above, the waveguide type second harmonic wave generating element according to the present invention comprises a substrate having spontaneous polarization and an optical waveguide layer having a refractive index higher than that of the substrate. In the above, since the spontaneous polarization of the substrate and the optical waveguide layer is periodically inverted, phase matching is easy, the refractive index of the optical waveguide layer is uniform, and the cross-sectional shape of the polarization inversion grating is By making it rectangular, a highly efficient waveguide type wavelength conversion element can be manufactured. Further, by combining the above element with a semiconductor laser and a focusing lens, a small and lightweight visible light source can be constructed.
Further, by incorporating the above light source into the conventional optical information recording / reproducing apparatus, an optical information recording / reproducing apparatus having a recording density of 4 times and an access time equivalent to that of the conventional apparatus can be constructed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a light source for generating visible light according to the present invention, in which (a) is a plan view and (b) is a sectional view.

FIG. 2 is a diagram showing a conventional second harmonic generation element using a temperature phase matching method.

FIG. 3 is a diagram showing a conventional second harmonic generation element using Cherenkov radiation.

FIG. 4 is a diagram showing a conventional second harmonic generation element using polarization inversion.

5 (a) to 5 (d) are explanatory views of the principle of second harmonic generation by the device of the present invention.

6A and 6B are configuration diagrams showing a second embodiment of the light source for generating visible light according to the present invention, FIG. 6A is a plan view and FIG. 6B is a sectional view.

7 (a) to 7 (d) are explanatory views of the second harmonic generation principle by the element of the second embodiment of the present invention.

8A to 8F are views showing respective manufacturing steps of the light source for generating visible light by the second harmonic.

9 (a) to 9 (f) are views showing a manufacturing process of a light source for generating visible light by the second harmonic of the second embodiment.

FIG. 10 is a schematic view of a write-once type optical head equipped with the second harmonic generation element of the present invention.

FIG. 11 is a schematic view of a magneto-optical head equipped with the second harmonic generation element of the present invention.

FIG. 12 is a configuration diagram of an optical information recording / reproducing apparatus equipped with a second harmonic generation element of the present invention.

[Explanation of symbols]

14 ... Substrate (LiNbO ₃ ) 64 ... Substrate (LiTaO ₃ ) 17 ... Inverted polarization portion of thin film 31, 42 ... Proton exchange channel type optical waveguide 51, 71 ... Substrate with spontaneous polarization 52, 72 ... Optical Wave layer 105 ... Converging lens system 301 ... Optical head 106, 206, 305 ... Optical recording medium

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Kaede Inventor Hiroshi Kaede 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd., Institute of Industrial Science, Hitachi, Ltd. (72) Kohei Ito 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Within Hitachi Metals Co., Ltd. (72) Inventor Satoshi Makio 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Within Hitachi Metals Co., Ltd. (72) Masazumi Sato 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Hitachi Metals Co., Ltd. Within

Claims (9)

[Claims] 1. A second harmonic generation element comprising an optical substrate and an optical waveguide layer having a refractive index higher than that of the substrate, wherein nonlinear optical coefficients of both the optical waveguide layer and a part of the substrate are periodically inverted. Second harmonic generation element characterized by 2. The optical device according to claim 1, wherein the boundary line between the periodic inversion of the nonlinear optical coefficient in the optical waveguide layer and the boundary line between the substrate and the optical waveguide layer is 75 ° to 105 °. The second harmonic generation element according to claim 1, characterized in that 3. The substrate according to claim 1, wherein the optical waveguide layer is lithium niobate doped with magnesium, or the optical waveguide layer is lithium niobate having a smaller amount of magnesium doped than the substrate. The second harmonic generation element according to claim 1 or 2, which is characterized. 4. The substrate according to claim 1 or 2 is lithium tantalate, and the optical waveguide layer is lithium tantalum niobate (compositional formula is shown in Chemical formula 1). The second harmonic generation element described. [Chemical 1] 5. The substrate according to claim 1 or 2 is a substrate in which the polarization is periodically inverted beforehand, and a method of forming an optical waveguide layer on the substrate is a ferroelectric metal oxide forming the optical waveguide layer. A step of preparing a melt by heating and melting a raw material powder of a product in the presence of a flux, bringing the surface of the substrate whose polarization has been inverted into contact with the melt, and lowering the temperature of the melt to a crystal precipitation temperature. 3. A method of manufacturing a second harmonic generation element according to claim 1 or 2, further comprising a step of liquid phase epitaxially growing a metal oxide film forming the optical waveguide layer according to claim 1 or 4 on the substrate. .. 6. The method for manufacturing a second harmonic generation element according to claim 5, wherein the flux used is lithium vanadate (LiVO ₃ ) or lithium borate (Li ₂ B _2).
O ₄ ), lithium fluoride (LiF), or potassium fluoride (KF), The manufacturing method of the second harmonic generation element according to claim 1 or 2 characterized by things. 7. A second harmonic generation element according to claim 1 or 2, a near infrared semiconductor laser light source having a wavelength of 780 nm to 1100 nm, and a laser beam emitted from the laser light source is condensed on an end face of a waveguide. Visible light source consisting of a lens system. 8. A light source for generating visible light according to claim 7,
An optical head provided with a condensing means for condensing the light emitted from the light source on the recording / reproducing surface of the optical recording medium, and means for receiving and detecting the reflected light from the recording / reproducing surface of the optical recording medium. 9. A rotation drive control means for rotationally driving an optical recording medium, an optical head for recording and reproducing optical information which is driven at predetermined intervals in a radial direction of the optical recording medium, and the optical head is mounted. 9. An optical information recording / reproducing apparatus provided with an actuator for scanning and driving the optical information recording / reproducing apparatus, wherein the optical head mounted on the actuator is the optical head according to claim 8.