JPH04110805A - Proton exchange optical waveguide and production thereof - Google Patents

Abstract

PURPOSE:To obtain an optical deflector having high efficiency by having the optical waveguide with which DELTAn0 and (a) satisfy inequality DELTAn0<=(0.015a+0.005) when the difference in refractive index (n) between a substrate and an optical waveguide layer is designated as DELTAn0 and the depth to make the DELTAn to 1/3 the DELTAn0 as (a). CONSTITUTION:The reason that the optical deflector has extremely high optical deflecting efficiency lies in that an electrooptical coefft. rijk and an optical elasticity coefft. Pijkl are recovered to the same level as the level of bulk LiNbO3 and the large value of DELTAB13 is obtainable. The heat treating conditions have a deep relation with the thickness T(mum) of the proton exchange layer before the heat treatment. Namely, the heat treating temp. needs be set at 375 to 400 deg.C and the heat treating time (t) needs be set at least at t>=2T<2> in order to satisfy the conditions n0>=0.035, DELTAn0<=(0.015a+0.005) and to make the refractive index distribution into an error function type. If, however, the (t) is set too long, the DELTAn0 falls below 0.035 and, therefore, the heat treatment is executed at t 2T<2> (hour) as far as possible.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical waveguide for a waveguide type optical element, a method for manufacturing the same, an optical deflection device using the optical waveguide, an optical integrated head, and an optical information recording device. The present invention relates to applied devices such as playback devices.

[Conventional technology]

Electro-optic devices, acousto-optic devices, etc. using optical waveguides have conventionally been used in optical deflectors, integrated optical heads (also called optical integrated heads), optical modulators, optical switches, optical spectrum analyzers, etc. It is being

As a substrate for forming the above optical element, lithium niobate, lithium tantalate, or a mixed crystal system of both of these materials is used as a material with excellent piezoelectricity, photoelasticity, and electro-optic effect. LiNb□-yTayO3 However, single crystal substrates with ◯≦y≦1 are widely used.

Furthermore, recently, as a substrate resistant to optical damage, a substrate doped with Mg in one of the above three types, that is, a general formula (% formula %), has been developed.
As shown in FIG. 2 described in Publication No. 5, the mainstream was to propagate surface acoustic waves (SAW) 24 in a direction perpendicular to the optical axis and deflect guided light 25 from the optical axis to the left and right. However, recently, as shown in Figure 3, IEE's Integrated Guided Wave Optics Proceedings Paper TuAA4-1 (
1989) (IEEE, Integrated
GuidedWave 0ptics paper
TuAA4-1 (1989)), pages 138 to 141, surface acoustic waves are
The guided light is propagated in three directions and diffracted in the direction of the substrate 31, and the emission angle is adjusted by the surface acoustic wave excitation electrode 34.
A new method was proposed that changes the frequency of the AC voltage applied to the

[Problem to be solved by the invention]

In the above conventional technology, Y cut LiNbO3 is used as the substrate.
The optical waveguide is first made of titanium (T1).
After thermally diffusing the above substrate at high temperature, the substrate is treated with benzoic acid (C,
Low temperature heat treatment in a mixture of weak acids such as H5COOH) and pyrophosphoric acid (H, P2O7) and lithium salts of the weak acids,
It is fabricated using a method called the proton exchange method, in which a portion of the lithium ions (Li") near the substrate surface is replaced with protons (H+) in a weak acid. In the above method, (1) a transition metal called Ti is implanted. therefore, the threshold for optical damage is low.

(2) Since the proton exchange treatment is performed, the piezoelectric effect, electro-optic effect, and acousto-optic effect inherent to the LiNb*3 crystal are greatly reduced, and the light deflection efficiency is low.

There is a problem. For this reason, in the above-mentioned conventional technology, the optical waveguide is made into a channel as shown in Fig. 3, and an attempt is made to increase the efficiency through the interaction between the guided light and the surface acoustic wave. A few μm long
Because of its small size, large aberrations occur in the emitted light, which poses a problem that it cannot be applied to precision optical systems such as optical heads.

The present invention provides an optical waveguide with excellent electro-optic effects, piezoelectric effects, and photoelastic effects and greatly improved interaction between surface acoustic waves and guided light, and a method for manufacturing the same, and optical deflection using the optical waveguide. The purpose of the present invention is to develop a device and an optical integrated head, and further to obtain an optical information recording/reproducing device using the above-mentioned optical integrated head.

[Means to solve the problem]

Optical waveguides with greatly improved interaction between surface acoustic waves and guided light with excellent electro-optical effects, piezoelectric effects, and photoelastic effects are: (1) Lithium niobate and lithium tantalate that can be expressed by the following general formula: , or the general formula of a mixed crystal system of both: L x N b 1- y T a y O3
However, 0≦y≦1 or the general formula Ljxl'/igzNb+-, TayO in which magnesium is added
,, However, on the surface layer of a single crystal substrate consisting of 0≦X, y, and Z≦1, a modified layer having a refractive index higher than that of the substrate is formed by ion-exchanging some of the lithium ions Li+ with protons H1 in the substrate. In a proton exchange optical waveguide having as an optical waveguide layer, the difference between the refractive index nS of the substrate and the refractive index n(7) of the optical waveguide layer is Δn (=n ns), and the depth from the surface of the optical waveguide layer is When xl is the refractive index n of the optical waveguide layer, the refractive index n of the optical waveguide layer continuously and gradually decreases from the surface in the depth x1 direction, and has a refractive index distribution that substantially satisfies Δn=0 at the interface with the substrate. and Δn=Δno at the surface is 0
．． 035 and Δn is larger than Δn at the above wavelength
The depth a, which is 1/3 of s, satisfies the inequality Δno≦0.015
This is achieved by a proton exchange optical waveguide that satisfies a+0.005. (2) The ion exchange concentration profile of lithium ions Li+ by protons H+ in the depth direction y from the surface of the optical waveguide layer changes in accordance with an error function, and the ion exchange concentration increases in the depth direction from the surface in the y direction. This can be achieved by using the proton exchange optical waveguide described in (1) above, which has a concentration distribution that gradually decreases continuously.

(3) Crystal lattice constant d' of the optical waveguide layer consisting of the above metamorphic layer
and the crystal lattice constant d of the above single crystal substrate Δd=d'−
The above (1
This is achieved by the proton exchange optical waveguide described in ).

In addition, as a method for manufacturing the optical waveguide, (4) in a mixed solution of a weak acid and a lithium salt of a weak acid, lithium niobate, lithium tantalate, or a mixed crystal system of both, which can be expressed by the following general formula; LiNb1-yTaxO3 However, ○≦y≦
1 or general formula L in which magnesium is added to these
jx M g z N b y T a x -y○3
, (O≦x, y, z≦1) is heat-treated, and a portion of the lithium ions Li+ in the surface layer is ion-exchanged with protons H1 to form a modified layer with a higher refractive index than the substrate. In the method for manufacturing a proton exchange optical waveguide formed as an optical waveguide layer, the surface layer portion of the single crystal substrate is heat-treated using a mixed solution of an organic acid having a degree of dissociation of 10-3 or less and a lithium salt of the acid as the weak acid. Lithium ion Li+
A part of the is ion-exchanged with proton H+, and then the single crystal substrate is heated at 375°C in air or oxygen atmosphere.
By performing heat treatment at 400° C. for at least t≧2T2 (hours), the protons H+ injected into the substrate by the ion exchange treatment are thermally diffused into the substrate, thereby increasing the refractive index nS of the substrate and the optical waveguide layer. The difference from the refraction In is Δn (
= n−〇,), and when the depth from the surface of the optical waveguide layer is x1, the refractive index n of the optical waveguide layer gradually decreases continuously from the surface in the depth x1 direction, and the substrate substantially satisfies Δn=o at the interface with
n=Δno is greater than 0.035 and ΔB is Δn
The depth y is 1/3 of o. This is achieved by a method for manufacturing a proton exchange optical waveguide in which the diameter is 3 μm or more. In addition, as the weak acid, an organic acid having a degree of dissociation of 10-5 or less is more preferable.

Furthermore, an optical deflection device using the above optical waveguide includes: (5) the optical waveguide described in any one of (1) to (3) above, in which the optical waveguide is formed on an optical substrate; A means for coupling light from the outside into the optical waveguide, and a surface acoustic wave having a function of emitting the guided light propagating within the optical waveguide to the outside of the substrate and changing the angle that the emitted light makes with the surface of the substrate. This is achieved by an optical deflector consisting of an exciting electrode. (6) a means for coupling light into the optical waveguide, and an elastic surface having a function of emitting the guided light propagating from the optical waveguide to the outside of the substrate and changing the angle that the emitted light makes with the substrate surface. This is achieved by the optical deflection device described in (5) above, which comprises an electrode that excites waves.

The optical integrated head using the above-mentioned optical waveguide includes (7) a laser light source, a guided light that guides the laser beam to an optical waveguide provided on an optical substrate, and recording of an optical recording medium in which the guided light is further arranged in a space outside the optical waveguide. , an optical head comprising means for condensing light onto a reproducing surface and receiving and detecting light reflected from the recording and reproducing surface, wherein an optical waveguide is formed on the optical substrate; The optical waveguide according to any one of item 3), a first diffraction grating that prevents a reduction in coupling efficiency of the laser beam to the optical waveguide due to wavelength fluctuation of the laser beam, and a crating that couples the laser beam to the optical waveguide. a coupler, and an electrode that is provided on the optical waveguide and excites a surface acoustic wave that has the function of emitting guided light propagating within the optical waveguide to the outside of the substrate and changing the angle that the emitted light makes with the substrate surface. , is achieved by having a second diffraction grating that prevents a change in the contrasting direction of the emitted light due to a laser wavelength fluctuation, and a lens means that focuses the emitted light to a point outside the waveguide, (8) the above recording. As a condensing beam splitter that constitutes an optical element that receives and detects reflected light from a medium, a diffraction grating with an irregularly spaced curved shape is installed between the grating coupler on the optical waveguide and the surface acoustic wave excitation electrode. arranged,
This is achieved by the optical integrated head described in (8) above, and (9) an optical recording medium comprising a laser light source, a guided light beam guided from the laser beam to an optical waveguide on an optical substrate, and further arranged in a space outside the optical waveguide. An optical head comprising a means for condensing light onto a recording/reproducing surface and receiving and detecting reflected light from the recording/reproducing surface, the optical head having an optical waveguide formed on the optical substrate (1). ) or 4), a first diffraction grating that prevents a reduction in coupling efficiency of the laser beam to the optical waveguide due to wavelength fluctuation of the laser beam, and a laser beam coupled to the optical waveguide. 1st
a grating coupler, and an electrode for surface acoustic wave excitation provided on the optical waveguide to emit the guided light to the outside of the optical waveguide layer and to change the angle between the substrate surface and the emitted light; A plane diffraction grating for tracking error detection, provided between the first grating coupler on the optical waveguide and the electrode for surface acoustic wave excitation, and a side opposite to the surface on which the optical waveguide layer is formed. a condensing beam splitter comprising a diffraction grating having an unevenly spaced curved shape, provided on the substrate between the first grating coupler and the surface acoustic wave excitation electrode facing each other; a reflective second diffraction grating that prevents changes due to fluctuations in the laser wavelength in the direction and reflects the emitted light, and records the reflected light from the second diffraction grating on the optical recording medium; A lens means for focusing onto a reproduction surface is provided, the reflected light focused by the lens means is irradiated onto the recording/reproduction surface of the optical recording medium, and the reflected signal light is transmitted through the lens means to a second diffraction grating. It is reflected and incident on the substrate, and is totally reflected on the substrate surface on the optical waveguide layer side.
This is achieved by making the light incident on the focused beam splitter and focusing the light into two parts, and detecting the focused reflected signal light with a light receiving element. Furthermore, (10) an optical system comprising the reflective second diffraction grating and a lens means for focusing the reflected light from the second diffraction grating onto the recording/reproducing surface of the optical recording medium; This is achieved by the optical integrated head described in (9) above, which is optically coupled to the main body on the substrate side on which the optical waveguide layer is formed, separated and independently mounted, and mounted on an actuator to serve as a movable part of the head.

The optical information recording/reproducing apparatus using the optical integrated head includes: (11) a rotational drive control means for rotationally driving an optical recording medium; In an optical information recording and reproducing apparatus, the optical head mounted on the actuator is equipped with an optical head that records and reproduces optical information by scanning and driving the optical head, and an actuator that carries the optical head and drives the optical head in a scanning manner. This is achieved by an optical information recording/reproducing device configured with the optical integrated head described in any one of 7) to 10).

[Effect]

The present invention has the following effects, making it possible to obtain an optical waveguide and an optical deflector that have excellent electro-optic effects, photoelastic effects, and piezoelectric effects, and have a large interaction between surface acoustic waves and guided light.

Hereinafter, LiNbO3 will be explained as a representative example of the crystal substrate.

L co-N b○3 is a trigonal uniaxial crystal, with its anisotropic axis as two axes, and the (211○) direction in hexagonal crystal display as the y-axis, and the y-axis and the right-handed system perpendicular to the y-axis. The y-axis is taken so as to compose the . In the future, I think that tensor display will be convenient, and I will change the y-axis to
The axes, y@, are written as the X2 axis and the y axis as the X3 axis. For this orthogonal coordinate system, the dielectric constant tensor is not only zero in its diagonal components, but can be written as . (However, ε□□=ε2□). The inverse tensor of the permittivity tensor is CB] = (E]-” (2)
When defined, it becomes for the above coordinate system.

When a strain [S] or an electrostatic field EC is applied to LiNbO3, a change occurs in the tensor CB). If we write this as [ΔB],
The photoelastic effect is ΔB ij” Σ P : Jkqskg
(4) 1 g, PijkQ is the photoelastic tensor, uQ is the displacement of the medium, and the electro-optic effect is ΔB i j ”Σr; JbE: (6
) However, rijk can be written as an electro-optic tensor. If both of these exist, △B ij”ΣP i jkQ S kQ+Σr; Jk
E: (7)k look
Become a secret.

Now, LiNb0. For example, a crossed electrode (I nt
er-Digital Transducer:
Surface acoustic waves (SA
Consider the case where W) is generated and propagated on its surface.

Since surface acoustic waves propagate on the substrate surface in the form of distortion, they are accompanied by distortion [S]. Also, the voltage field E due to the strain [S]. occurs. Therefore, by SAW (
7) ΔB ij expressed by the formula is induced.

In particular, the substrate 1 cut perpendicularly to the X1 axis as shown in FIG.
(Xcut board) is used.

IDT2 is placed in the direction perpendicular to the X2 axis, and the SAW is -
Propagates in the x2 direction. A TE wave (a light wave polarized in the X3 axis direction) is guided through the optical waveguide 4. The propagating SAW produces off-diagonal components of the tensor [ΔB]. If we write this down concretely, it becomes the following formula.

ΔB1. =2P work 313S13+2P□312S work 2+
2r0. , E-cho (8) Such [Δ
When the off-diagonal component of [B] occurs, mote coupling occurs between the TE wave and the TM wave polarized in the direction perpendicular to the TE wave (x1 axis direction).

In particular, when the refractive index is adjusted so that the TM wave is in the radiation mode, light can be extracted outside the substrate. The emission angle θ of the emitted light is determined by the wavelength of the SAW. That is, N: effective refractive index of guided TE mode, m: integer, no:
It is the ordinary refractive index of LiNb○.

Since the wavelength of the SAW can be changed by the frequency of the high-frequency voltage applied to the IDT', the emission angle θ, that is, the direction of the light, can be controlled depending on the frequency of the high-frequency voltage, and the SAW operates as an optical deflector. The efficiency η of the optical deflector is approximately expressed by the following equation.

η=1−e−”L(10) Here, L is the propagation length of the SAW, and α is a constant called a radiation loss coefficient, which is expressed by the following equation.

Here, ne: extraordinary refractive index of LiNbO2, ω: angular frequency of light, P2 waveguide optical power, El(xl): electric field distribution of TM radiation mode, E3(x): electric field distribution of TE radiation mode. . (10), (11), (12) above
) As is clear from the formula, in order to obtain a large η, α,
That is, it is necessary to increase C. In order to obtain a large C, it is necessary to make the value of the integral of equation (12) larger than that of equation (12) (hereinafter referred to as overlap integral). To achieve this, it is necessary to increase the overlap of (TE□(x+)+Ei(xx)) (^) and a large value of ΔB ij.

In order to achieve (2), it is necessary to optimize the waveguide structure. For example, the literature by Onomae et al. (Transactions of the Institute of Electronics and Communication Engineers, V
oQ,, J 64-C, N014゜pp288-29
4. (1981)), in order to obtain a large α, an anisotropic material (ordinary refractive index n[11 and extraordinary refractive index ne1
Also, an anisotropic material (having an ordinary refractive index n.2
In an optical waveguide formed with a thin film (having an extraordinary refractive index ne2), no yo, nel and n. It is known that it is sufficient that the magnitude relationship between 2 and ne2 is opposite to each other. For example, if it is nel, then n. 2kn. 2, and in order to form an optical waveguide structure, nO1<
n [12 or n el < n e2 must be satisfied. This is because in the optical waveguide structure as described above, the overlap between the electric field E3 (x□) and the electric field E (Xl) can be increased.

Recently, optical waveguides fabricated using proton exchange method,
n of LiNbO3 substrate and proton exchange layer. It was discovered that the dispersion relationships of and no are opposite.

Since proton-exchanged LiNb○ optical waveguides can be produced very easily and at low cost, optical deflectors such as the one shown in Figure 3 shown in the literature by Hjnkov described in the above-mentioned I.E. has become possible to produce.

However, when proton exchange is performed on LiNbO2, the photoelastic coefficients Pi, jkQ and the electro-optic coefficient rijk become extremely low.
”＼It is known that the temperature decreases. For example, the literature by Hu et al. (IEICE technical report ○QE86-119,
pp. 15-22), it is said that r333 becomes about 1/15 of the value before proton exchange after proton exchange. For this reason,
Even if the above condition (■) is satisfied, ΔB13 becomes small, so
There was a problem that condition (■) was not satisfied.

In the present invention, by changing the refractive index distribution, which was conventionally shown in FIG. 5(a), to the one shown in FIG. 5(b), a decrease in the electro-optic coefficient rijk and the photoelastic coefficient P; Jki can be suppressed. , conditions (stalks are satisfied and the wavelength λ=633
〇 change in the extraordinary refractive index of the surface for nm light
is larger than 0.035, and Δn is 1/3 of Δno
By making the depth a satisfy a predetermined inequality, it is also possible to satisfy the condition (2).

In FIG. 6, the value of Δno is defined as a and the value of Δno is a parameter. The relationship between the values of veyQap is shown. From Figure 6,
The larger Δns or the smaller a, ■. verQ
It can be seen that the value of ap is large. However, if a is made too small, the value of ΔB13 will drop rapidly, and therefore the value of C in equation (12) will become small. In order to obtain ΔB, 3 close to the bulk value, it is necessary to fabricate the optical waveguide so that the values of a and Δno fall in the lower right portion of the broken line in FIG. Therefore,
big craft. In order to obtain the values of verQap and large ΔB, if the optical waveguide is manufactured so that Δno and a satisfy Δno≧0.035 and Δno≦0.015 a+0.005, a large optical deflection efficiency η can be obtained. It is possible to construct an optical deflector with

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the optical deflector according to the present invention, FIG. 2 is a perspective view of a conventional Bragg type optical deflector, and FIG. 3 is a perspective view of a conventional collinear type optical deflector. Figure 4 is a diagram explaining the principle of the optical deflector, (a) is a plan view, (b)
is a cross-sectional view, and Figure 5 is a diagram showing the refractive index distribution of the optical waveguide.
a) is a diagram showing the conventional one, (b) is a diagram showing the one according to the present invention, and FIG. 6 is a diagram showing the diffusion depth a and the surface refractive index change Δn.
Overlapping integral with o. Diagram showing the relationship between verQu, 7th
The figures show the refractive index distribution of the optical waveguide. (a) is the diagram before heat treatment, (b) is the diagram after heat treatment, and FIG.
A diagram showing the configuration of an optical integrated head equipped with the optical deflector shown in the figure, FIG. 9 is a manufacturing process diagram of the optical integrated head,
FIG. 10 is a manufacturing process diagram of the aberration correction diffraction grating mounted on the optical integration head, and FIG. 11 is a configuration diagram of an optical information/storage/reproduction device equipped with the optical integration head shown in FIG. 8. .

First Embodiment FIG. 1 shows an example of the configuration of an optical deflector using surface acoustic waves (SAW) manufactured on an optical waveguide according to the present invention. In Figure 1, 1 is X cut L
iNbO3 single crystal substrate, 2 is a proton exchange optical waveguide layer, 3
is guided light, 4 is SAW, 5 is IDT for SAW excitation, 6 is emission light, 7 is high frequency power supply for SAW excitation, 8 is condenser lens, 9 is polarization scanning direction of light, 10 is surface acoustic wave absorption Represents material.

Next, the structure of the optical waveguide layer 2 and its manufacturing method will be described, and the manufacturing method will be explained separately into a first manufacturing step using a proton exchange method and a second manufacturing step including a subsequent heat treatment.

(1) First production step by proton exchange method: First, L
A so-called x-cut LiNb○ wafer, which is cut perpendicular to the X-axis of the iNb○3 single crystal, is prepared, and its −
The surface is polished to about 1/10 of the wavelength λ of the laser beam used, and used as a substrate. Note that it is desirable that the transition metal impurity concentration of the crystal substrate be as low as possible. Currently commercially available high-purity LiNb01 substrates have an Fe concentration of 0. O5p
pm, and it has been confirmed that the use of this high-purity LiNbO3 substrate increases the optical damage threshold by about one order of magnitude. After optically polishing the substrate 1, trichlorethylene,
Ultrasonic cleaning was performed in isopropyl alcohol, ethanol, and pure water, followed by nitrogen blowing and drying.

Next, the substrate 1 was subjected to proton exchange treatment as described below. The proton exchange treatment was carried out in a quartz container. Weak acids as proton exchange sources include carboxylic acids such as benzoic acid and phosphoric acids such as pyrophosphoric acid. In this example, the dissociation constant is 6×10−
A mixture of benzoic acid and lithium benzoate in No. 5 was used.

The mixing ratio M is defined by the following formula, and in this example, M
= 1.

That is, 1.92 g of lithium benzoate and 181.35 g of benzoic acid were placed together with the substrate into a quartz container, thoroughly mixed, and heat treated at 235° C. for 15 minutes. After the heat treatment, the substrate taken out from the quartz container was ultrasonically cleaned with ethanol and pure water. In this way, an optical waveguide 2 with a thickness of 0.9 μm was formed on the surface layer of the LiNb◯ substrate 1 by the proton exchange method. In order to adjust the optical characteristics of the optical waveguide obtained in this way, we used a rutile prism to
When a 33 nm He-Ne laser beam was propagated in the y-axis direction within the optical waveguide 2, TEo, TE
Two modes of l were excited, and the effective refractive index of the guided light was 2.2886 and 2.2251, respectively. In addition, as a result of investigating the optical propagation loss using the usual two-prism method, we found that TE
The o-mode was 3 dB/cm, and the threshold for optical damage caused by laser light of the same wavelength was about 750 W/cm2.

In addition, in order to investigate the concentration profile of protons injected into the optical waveguide, we used SIMS (Secondar
As a result of analysis using yIon Mass Spectroscopy, it was found that the proton concentration changed in a step-like manner around a depth of 0.9 μm. Therefore, if the refractive index distribution of the optical waveguide at this stage is estimated by the well-known inverse WKB method, it will be as shown in Figure 7(a), and the concentration profile of the injected protons and the refractive index profile are in good agreement. show.

Next, an IDT 5 for surface acoustic wave excitation was formed on the optical waveguide 2 formed on the surface layer of the substrate by performing the above proton exchange treatment, and an optical deflector was manufactured and evaluated. Note that the surface acoustic wave velocity in the x2 axis direction (progressing direction of the guided light) of x cutLiNb○3 in this example is 3696.
m/sec, and the pitch A of IDT5 = 16.8μ
It is m. In addition, the width of IDT is 4.3111m,
The propagation length of the SAW is 20 mm. At this time, the center frequency is f. = 220 MHz, the diffraction order m uses the +1st order, the output angle θ is 6 degrees, and the deflection angle is 4.5 m in air.
It is rad.

In order to investigate the electro-acoustic conversion characteristics of the obtained optical deflector,
The radiation conductance was measured using a network analyzer, and the effective electromechanical coupling coefficient K was measured, and compared with that produced on a bulk substrate without proton exchange treatment. As a result of the measurement, the effective K value in the case of the surface acoustic wave excitation electrode fabricated on the proton exchange optical waveguide of this example was approximately 20% of that of the electrode fabricated on the bulk substrate of the comparative example.
Met.

Furthermore, λ”633r+rr+ of HeNe is added to the optical waveguide.
Laser light was coupled by a prism coupler and the TE1 wave was excited to adjust the characteristics of the optical deflector. The optical deflection efficiency η at the center frequency was only 0.1%. This is the electro-optic coefficient r'jk and photoelastic coefficient Pi in the optical waveguide layer.
This is because jkQ is very small, and the value of C in equation (12) becomes very small.

(2) Second manufacturing step including heat treatment step after proton exchange: Next, the substrate subjected to the proton exchange treatment in the first manufacturing step was placed in a thermal diffusion furnace, heat treated in the atmosphere at 400°C for 65 minutes, and then rapidly cooled. .

In order to investigate the characteristics of the optical waveguide manufactured in this way,
Again, similar to (1) above, the wavelength λ = 6 with a rutile prism.
A 33 nm He-Ne laser beam was guided into the waveguide and propagated in the y-axis direction. Three TE modes are excited in the waveguide, and the effective refractive index of the TEo mode is 2.2291. When the refractive index distribution in the depth direction of the optical waveguide layer is estimated by the inverse WKB method, it is shown in Fig. 5 (b). This is the profile of the error function shape. As is clear from Figure 5(b), the refractive index is high at the surface and gradually decreases as you go deeper into the optical waveguide layer, following a smooth attenuation curve distribution, and at the interface with the substrate. It is substantially approaching the refractive index of the substrate.

In addition, by the two-prism method, the optical propagation loss α of the TEo mode
As a result of measurement, a value of α=0.3 dB/cm, which is equivalent to that of the Ti-diffused optical waveguide, was obtained, which was a dramatic improvement compared to 3 dB/cm at the first manufacturing stage before heat treatment.

In addition, as carried out in the first manufacturing step in (1) above, in order to adjust the characteristics of the optical deflector, comb-shaped electrodes for surface acoustic wave excitation were created on the optical waveguide, and a network analyzer was used to adjust the characteristics of the optical deflector. When we measured the effective electromechanical coupling coefficient K of surface acoustic waves in two directions, we found that it was about 95% of the value of a comparative example fabricated on a bulk substrate without proton exchange treatment, and about 95% of the value before heat treatment. This is a dramatic improvement compared to 20%.

Furthermore, the threshold value of optical damage of the TEo mote caused by laser light of the same wavelength was approximately 600 W/cm2, which was slightly lower than the value before heat treatment of 750 W/cm2, but good characteristic values were obtained.

Furthermore, in order to investigate how the concentration distribution of injected protons in the depth y direction of the optical waveguide layer changes due to heat treatment,
When analyzed by SIMS, the concentration distribution had an error function type, and showed good agreement with the refractive index distribution curve shown in FIG. 5(b).

In addition, in order to investigate the optical deflection efficiency of the above optical deflector, we also investigated the wavelength λ
-0,633 μm He-Ne laser light is guided into the proton exchange optical waveguide layer 2 obtained by the above heat treatment using a prism coupler, propagated in the y-axis direction, and propagated in the Z-axis direction.Surface acoustic wave electrode The optical deflection efficiency was measured by inputting a power of O to IW to No. 5. This measurement shows that the power is 0.5
A diffraction efficiency of 60% was obtained with W. This value is 80 in the above document.
%, but the IDT width in the above document is 40 μm.
In contrast, in this example, the diameter is 4.3 mm, which is approximately 100 mm.
Since the surface acoustic wave density is 1/2, +-00, the actual efficiency is about 75 times that of the optical deflector in the above-mentioned document.

As described above, the reason why the optical deflector of this example has extremely high optical deflection efficiency compared to the optical deflector manufactured by the method (1) above is that the electro-optic coefficient rijk is
, photoelastic coefficient P; Jku recovered to the same level as bulk L i N b○3, and a large ΔB1. This is because the value of .

In addition, in the second manufacturing stage including the above heat treatment step, the heat treatment conditions are the thickness T (μ
It was found that there is a deep relationship with m).

That is, the above condition Δn. ≧0.035. 8ns≦0.015 a +O0
In order to satisfy O○5 and make the refractive index distribution into an error function type, the heat treatment temperature must be 375°C to 400°C, and the heat treatment time t (hours) must be at least 2T2. . However, if t is made too long, Δ
Since no is smaller than 0.035, t≧ as much as possible
It is desirable to perform heat treatment for 2T2 (hours).

Second Embodiment FIG. 8 is a diagram showing an embodiment of a thin film integrated optical head equipped with the optical deflector shown in FIG. 1. In Figure 8,
1 is a LiNb○3 single crystal substrate, 2 is a proton exchange optical waveguide layer, 81 is a semiconductor laser, 82 is a collimating lens, 8
4 is a beam shaping prism, 85 is a transmission type diffraction grating that prevents a decrease in laser beam coupling efficiency to the optical waveguide layer 2 due to wavelength fluctuation of the laser beam, and 86 is a linear shaped prism that couples the laser beam to the optical waveguide layer 2. Grating coupler, 3 is waveguide light,
87 is a plane diffraction grating for creating a three-spot beam for creating a tracking error signal, and 4 is a surface acoustic wave (SAW).
), which has the effect of emitting the guided light 3 into the substrate 1 and changing the emission angle of the emitted light 6. 5 is SAW
IDT for excitation, 89 is a beam shaping prism, 810
811 is a reflection type diffraction grating for suppressing the direction change of the emitted light 6 due to wavelength fluctuation of the semiconductor laser beam; 811 is an objective lens for forming an image of the emitted light 6 on an optical disk 813; and 88 is for dividing the reflected signal light into two parts. , and is a condensing beam splitter that condenses light onto the photodiode 83.

Next, a method for manufacturing the optical integrated head will be described in detail with reference to FIGS. 9 and 10. First, explanation will be given according to the manufacturing process diagram shown in FIG. As shown in FIG. 9(a),
cut LiNbO3 substrate 1 (3 inch φ x 3 mm thickness)
Both sides of the 0.78 μm laser beam wavelength λ were polished to 1/10 of the wavelength λ of the laser beam, and as shown in (b) near the surface, the first
The proton exchange optical waveguide layer 2 is manufactured according to the second manufacturing step including the manufacturing step and the subsequent heat treatment step shown in (2).

Next, as shown in (C), an optical glass layer 91 (manufactured by Corning Inc., trade name 7
059) was formed into a 10nrn film by sputtering. The sputtering conditions were: high frequency power 100W, argon gas pressure 0.35Pa, and sputtering speed 0.2.
nm/sec.Furthermore, as shown in (d), T is applied as a loading layer (for forming a diffraction grating) on the buffer layer 91.
The i02 layer 92 is formed by reactive sputtering to 1100nm.
Formed. The sputtering conditions were T as the target.
Argon (Ar) was used as sputtering gas using iO2.
) and oxygen (02), the flow rate ratio of Ar and 02 is 0.7.
, sputtering gas pressure 0.42 Pa.

High frequency power 500W, sputtering speed 0.1nm
/sec.

Next, as shown in (e), in order to process the loading layer 92 and buffer layer 91 into the shape of a predetermined waveguide type optical element, chloromethylated polystyrene (trade name: CMS-EX: Toyo Soda Co., Ltd.) is used as a resist for electron beam exposure. )93 to 0.
It was spin coded to a thickness of 5 μm. Furthermore, as shown in (f), after the above-described cyst 93 is baked at 130° C. for 20 minutes, each pattern of the uniformly spaced linear diffraction grating 86 and the unevenly spaced curved diffraction grating 87 is formed using an electron beam 94. exposed. As described above, as shown in Fig. 9 (g
), after exposure to electron beams, development was performed to form a resist mask 93.

Next, as shown in (h), the loading layer 92 and the buffer layer 91 were selectively microfabricated by ion etching. Using CF as etching gas, pressure 3.8
Pa, high frequency power 200W, etching time 15m1
It was set as n. After etching, the resist was removed.

Next, in order to fabricate the surface acoustic wave electrode 5, as shown in (i), a positive photoresist 95 was applied and heated at 80°C for 30 minutes.
Prebaked for a minute. Next, a photomask (not shown) having an opening only in the area where the electrode 5 of FIG. 8 is to be formed is placed on top of the photomask and exposed and developed to perform selective etching of the resist 95. Next, as shown in (j), after forming an AQ film 96 to a thickness of 150 nm using an electron beam evaporation device, the resist 95 was removed by immersion in acetone, and the AQ film was left only in the above-mentioned window portion by lift-off. Ta.

After that, as shown in (k) again, a positive photoresist 9 is applied.
After applying 5 and pre-baking at 80℃ for 30 minutes,
A photomask (not shown) having a predetermined electrode shape and shielding parts other than the window openings was layered, exposed and developed, and post-I-baked for 20 minutes at 140'c. Next, as shown in (-Q), wet etching was performed using a phosphoric acid-based etching solution to transfer the electrode pattern 96, and then the resist 95 was removed. In this way, the electrode 5 consisting of the AQ pattern 96 was formed.

Next, a method for manufacturing the diffraction gratings shown at 85 and 810 in FIG. 8 will be described in detail using FIG. 10.

First, as shown in FIG. 10(a), optical glass (manufactured by Corning, trade name BK-7 glass) 100 is used as a substrate.
1, and on top of that, as shown in (b), 5102 film 1
002 with a thickness of 10 μm was produced by CVD, vapor deposition, or sputtering using 5iCf14 and 02 as raw materials.

Next, as shown in (c), in order to process the S io2 film into a predetermined lattice shape by photolithography, 1 μm of positive photoresist 95 was applied, prebaked at 80° C. for 30 minutes, and then a predetermined lattice shape was drawn. After exposure using a photomask (not shown) and immersion treatment in chlorobenzene at 40° C. for 5 minutes, development was performed to form a grating pattern 95 made of resist. Next, as shown in (d), Cr1O03 was deposited on the resist grid pattern 95, and the resist was removed by ultrasonic cleaning in acetone.
A Cr mask 1003 was produced as shown in (e).

Thereafter, as shown in (f), Si○2 was etched using a Cr mask 1003 by ion etching using CF4 gas.
After selectively finely processing the film 1002, a Cr mask 1 is formed.
003 was removed by etching, and the target diffraction gratings 85 and 810 of FIG. 8, each consisting of a grating pattern of a 5in2 film 1002, were fabricated.

The photolithography technique described above can also be applied to the production technique of the loading layer 92 or the buffer layer 91 or the surface acoustic wave excitation electrode 5.

Finally, the optical element substrate 1, the diffraction gratings 85, 810, and the optical glass block (manufactured by Corning, trade name BK-7) 84°89, which were produced as described above, were cut into predetermined shapes and polished, respectively. A semiconductor laser 81 and a photodiode 83 are mounted on the eighth
The optical integration head shown in the figure was fabricated.

Next, the operation of the optical integrated head shown in FIG. 8 will be explained.

Emitted light from the semiconductor laser 81 (wavelength λ = 0.78 μm
) has its propagation direction corrected by the diffraction grating 85, and then
It is coupled to the optical waveguide layer 2 by a grating coupler 86 . Next, the planar diffraction grating 87 generates ±1st order extremely weak diffracted light for tracking error signal detection.

This makes it possible to detect tracking error signals using the three-spot method of the optical disk device. Next, these guided lights are surface acoustic waves 4 generated by electrodes 5.
is injected into the substrate. At this time, by changing the center frequency of the AC electric field applied to the electrode 5, the emitted light 6
The output angle can be changed by deflecting the beam in a direction perpendicular to the substrate surface. After the propagation direction of the deflected emitted light 6 is corrected by a reflective diffraction grating 810, it is focused by an objective lens 812 onto the recording/reproducing surface of the optical disc. The reflected light (optical recording information signal) 6 from this focused surface passes through a lens 811, a reflective diffraction grating 810,
The light is totally reflected on the surface of the substrate 1, divided into two by a condensing beam splinter 88 provided on the opposite surface, and focused on a five-divided photodiode 83 for signal detection.

The feature of this optical integration head is that the movable part of the head mounted on the actuator is a reflective diffraction grating 810 as shown in the figure.
There is only an optical system consisting of the and objective lens 811,
Most of the remaining portions of the head body constitute a fixed portion. The entire head is constructed by simply separating the optical system of the movable part of the head mounted on this actuator and the fixed part constituting the head body and optically coupling them together. Therefore, the movable parts of the head are lightweight and compact, and the optical deflection on the input side can be achieved by changing the center frequency of the alternating current electric field applied to the electrode 5 for generating surface acoustic waves, which greatly reduces access time. can be done.

Note that, as shown in FIG. 8, the optical integration head may be configured as an integrated head without being divided into a movable part and a fixed part, and this integrated head may be mounted on an actuator. .

Third Embodiment FIG. 11 schematically shows a case where the optical integrated head of the second embodiment shown in FIG. 8 is applied to a conventional optical information recording/reproducing apparatus. The optical information recording and reproducing apparatus shown in FIG. 11 is characterized in that only the optical system consisting of a reflective diffraction grating 810 and an objective lens 811, which constitute the movable part 1103 of the head, is mounted on the actuator 1102. The fixed part 1101 constituting the main body of the optical integrated head is optically coupled to the movable part 1103, but physically, it is separated and fixed. Therefore, the overall structure of the head consists of a movable part 1103 and a fixed part 11 depending on the function.
However, since only a light and small optical system is mounted on the actuator 1102, it is extremely advantageous for access, and the access time can be reduced to 20 m5ec or less.

As described above, in this example, the substrate is lithium niobate (T-iN).
b O3) Although the case of a single crystal substrate has been described as a representative example, in the present invention, a crystal system LiNb1-yT in which part or all of niobium is replaced with tantalum Ta is also used.
axO3 system (however, O<y≦1), or a crystalline system to which Mg is added LixMg2NbnyTax
Similar proton replacement treatment was performed for O3, but
As a result, LiNb0. We were able to obtain similar results as in the case of

〔Effect of the invention〕

As described above, the optical deflector and the method for manufacturing the same according to the present invention are manufactured by using lithium niobate, lithium tantalate, or a mixed crystal system of both of them, represented by the general formula L
iNb□-, TayO3 (however, 0≦y≦1) or the general formula LixMgzNb with magnesium added thereto
x-yTayO, (where ○≦X+Z+ y≦1) is formed on the surface layer of a single-crystal substrate by ion-exchanging some of the lithium ions Li+ with protons H+, and has a refractive index lower than that of the substrate. In an optical deflector equipped with a proton exchange optical waveguide having a highly modified layer as an optical waveguide layer, the difference between the refractive index ns of the substrate and the refractive index n of the optical waveguide layer is Δn
(=n ns) and the depth from the surface of the optical waveguide layer is X□, the refractive index n of the optical waveguide layer gradually decreases continuously from the surface in the depth x1 direction, and The interface has a refractive index distribution that substantially satisfies Δn=○, and when a is the depth at which Δn becomes 1/3 of Δno in the optical waveguide, Δn.

By having an optical waveguide where and a satisfy the inequality Δns≦0.015a+0.005, it is resistant to optical damage,
Moreover, by making it possible to realize an optical waveguide in which a highly efficient optical functional element can be easily produced, and by incorporating an optical deflection element into this optical waveguide, a highly efficient optical deflection device can be obtained. Therefore, it is possible to realize a compact, lightweight, and high-speed accessible optical integrated head using the above-mentioned optical deflection device, and also an optical information recording/reproducing device in which the above-mentioned optical integrated head is mounted on an actuator.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of an optical deflector having a proton exchange optical waveguide according to the present invention, Fig. 2 is a perspective view showing a conventional Bragg type optical deflector, and Fig. 3 is a perspective view showing a conventional collinear type optical deflector. FIG. 4 is a perspective view showing the deflector, and FIG. 4 is a diagram explaining the principle of the optical deflector.
a) is a diagram showing the refractive index distribution of a conventional optical waveguide, (b) is a diagram showing the refractive index distribution of an optical waveguide according to the present invention, and FIG. 6 is a diagram showing the diffusion depth a, the surface refractive index change amount Δno, and the overlap integral. I
FIG. 7 is a diagram showing the refractive index distribution of the optical waveguide, (a) shows before heat treatment, (b)
8 shows the state after heat treatment, FIG. 8 is a block diagram of the optical integration head equipped with the optical deflector shown in FIG. 1, and FIGS. 9 (, ) to (
Ω) are diagrams showing the manufacturing process of the optical integrated head, respectively;
10(a) to 10(f) are diagrams showing the manufacturing process of the aberration correction diffraction grating mounted on the optical integration head, respectively.
FIG. 1 is a diagram showing the configuration of an optical information recording/reproducing apparatus equipped with the above optical integrated head. 1.21.31...Substrate 2.22.32-Optical waveguide layer 4, 24, 34...Surface acoustic wave (SAW)5.
23... Surface acoustic wave generating electrode 81... Laser light source 83... Light receiving element 85... First diffraction grating 86... Grating coupler 87... Second diffraction grating 88... Focused beam Splitter 813... Optical recording medium 1102... Actuator representative patent attorney Junnosuke Nakamura Bullet surface caries tSAW15.23-
---3 Grass-like surface waves! 1!1 Electric liner 81-----Left at source 83-----First receiver fL Katsuko 85-----First diffraction grating J 86----2' and Tire force, Ara s7---
1! J2 rotation link 88--1 Hikari, Shima-Musbu j8, 2813-119 Book 02-11 actuator (a) Fig. 5 (pm) Fig. 6 ( a) times] Σ ding = 1] To 1 (b) “〒〒〒〒 に 1 (C) ■De ■ 匡Mi 1 Fig. 9 (a) 17] 1100 Fig. 10

Claims (1)

[Claims] 1. Lithium niobate, lithium tantalate, or a mixed crystal system of both represented by the general formula LiNb_1_-_yTa_yO_3 (0≦y≦1), or a general formula in which magnesium is added thereto. Li_xMg_2N
b_1_−_yTa_yO_3 (however, 0≦x, y,
A modified layer having a refractive index higher than that of the above substrate, which is formed by ion-exchanging some of the lithium ions Li^+ with protons H^+, is light-guided on the surface layer of a single crystal substrate consisting of z≦1). In a proton exchange optical waveguide having a wave layer,
When the difference between the refractive index n_s of the substrate and the refractive index n of the optical waveguide layer is Δn (=n-n_s), and the depth from the surface of the optical waveguide layer is x_1, the refraction of the optical waveguide layer is rate n
gradually decreases from the surface in the depth x_1 direction, and has a refractive index distribution that substantially satisfies Δn=0 at the interface with the substrate, and the magnitude of Δn in the optical waveguide layer is defined as Δn_
0, and when Δn_0 is greater than 0.035 and the depth at which Δn is 1/3 of Δn_0 is a, then Δ
n_0 and a are inequality Δn_0≦0.015a+0.0
A proton exchange optical waveguide characterized by satisfying 05. 2. Lithium ion Li^+ by the above proton H^+
The ion exchange is characterized in that the exchange concentration profile in the depth direction y from the surface of the optical waveguide layer changes like an error function, and has a concentration distribution that gradually decreases from the surface in the depth direction y. A proton exchange optical waveguide according to claim 1. 3. The optical waveguide layer consisting of the above metamorphic layer has a crystal lattice constant d'
and the crystal lattice constant d of the above single crystal substrate Δd=d′−
d has a crystal lattice constant distribution that changes in the depth direction y from the surface of the optical waveguide layer like an error function and gradually decreases continuously from the surface in the depth direction y. The proton exchange optical waveguide described in Section 1. 4. In a mixed solution of a weak acid and a lithium salt of the weak acid, the general formula LiNb_1_-_xTa_xO_3 (however, 0≦y
≦1) Lithium niobate, lithium tantalate, or a mixed crystal system of both, or a general formula Li_xMg_2Nb_yTa_1 with magnesium added thereto
A single crystal substrate consisting of ____xO_3 (0≦x, y, z≦1) is heat-treated, and a part of the lithium ions Li^+ in the surface layer is ion-exchanged with protons H^+,
In the method for manufacturing a proton exchange optical waveguide in which a modified layer having a refractive index higher than that of the substrate is formed as an optical waveguide layer, a mixed solution of an organic acid having a degree of dissociation of 10^-^3 or less as the weak acid and a lithium salt of the weak acid. A part of the lithium ions Li^+ in the surface layer of the single crystal substrate is ion-exchanged with protons H^+ by heat treatment to form an exchange layer having a thickness T (μm), and then the single crystal substrate in air or oxygen atmosphere for at least 2T^2 (hours) at 375℃~
By heat treatment in a temperature range of 400°C, the protons H^+ injected into the substrate by the ion exchange treatment are thermally diffused into the substrate, and the refractive index n_s of the substrate and the refractive index n of the optical waveguide layer are changed. When the difference is Δn (=n-n_s) and the depth from the surface of the optical waveguide layer is y, the refractive index n of the optical waveguide layer gradually decreases in the depth y direction, and the refractive index n of the optical waveguide layer gradually decreases in the depth y direction. A method for manufacturing a proton exchange optical waveguide including an optical waveguide layer having a refractive index distribution such that Δn=0 at the interface thereof. 5. The optical waveguide according to any one of claims 1 to 3, the guided light propagating within the optical waveguide is emitted from the optical waveguide to the outside of the substrate, and the emitted light is directed to the surface of the substrate. 1. An optical deflector comprising: an electrode that generates a surface acoustic wave that has the function of changing the angle formed by the surface acoustic wave; 6. The optical deflector according to claim 5, wherein the optical waveguide has means for coupling light into the optical waveguide from the outside. 7. Recording of an optical recording medium in which guided light, which is a laser beam from a laser light source, is guided to the optical waveguide according to any one of claims 1 to 3 and arranged in a space outside the optical waveguide. - An optical head equipped with a means for condensing light onto a reproduction surface and receiving and detecting reflected light from the recording and reproduction surfaces, the coupling efficiency of which is determined by the wavelength fluctuation of the optical waveguide and the laser beam. a first diffraction grating that prevents degradation; a grating coupler that couples the laser beam to the optical waveguide; and a grating coupler that emits the guided light from the optical waveguide to the outside of the substrate and changes the angle that the emitted light makes with the substrate surface. an optical integrated circuit comprising: an electrode that generates a functional surface acoustic wave; a second diffraction grating that prevents variations in the laser wavelength in the emission direction; and lens means that focuses the emitted light to a point outside the waveguide. head. 8. The grating coupler serves as a condensing beam splitter constituting an optical element that receives and detects reflected light from the optical recording medium on the optical waveguide between the surface acoustic wave generating electrode and the surface acoustic wave generating electrode. 8. The optical integration head according to claim 7, further comprising a curved diffraction grating. 9. The lens means irradiates the recording/reproducing surface of the optical recording medium with focused reflected light, transmits the reflected signal light, reflects it on a second diffraction grating, and makes it enter the substrate;
The light is totally reflected on the substrate surface on the optical waveguide layer side, and is incident on the focusing beam splitter to be divided into two and focused, and the focused reflected signal light is detected by a light receiving element. A light focusing head according to claim 8. 10. An optical system comprising the reflective second diffraction grating and a lens means for focusing the reflected light from the second diffraction grating onto the recording/reproducing surface of the optical recording medium is formed by the optical waveguide layer. 10. The optical condensing head according to claim 9, wherein the optical condensing head is mounted on an actuator while being optically coupled to and separated from the substrate-side main body, thereby forming a movable part of the optical head. 11. Rotation drive control means for rotationally driving the optical recording medium;
an optical head that records and reproduces optical information by scanning and driving in the radial direction of the optical recording medium while keeping a predetermined distance from the surface of the rotating optical recording medium; and an actuator mounted with the optical head that scans and drives the optical head. An optical information recording/reproducing apparatus comprising: an optical information recording/reproducing apparatus, wherein the actuator is equipped with any one of the optical integrated heads set forth in claims 7 to 10 above. Device.