JP2002250949A - Optical waveguide element, optical wavelength converting element and method for manufacturing optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a stable oscillation by reducing a fluctuation of output even when increasing output of exit light from an optical waveguide in an optical waveguide type device. SOLUTION: An optical waveguide element 1A is provided with a three- dimensional optical waveguide 4 consisting of a bulk shaped non-linear optical crystal, a substrate 2 joined to the optical waveguide 4, and a joining layer 3 consisting of amorphous material which joins the optical waveguide 4 to the substrate 2. The joining layer 3 or the substrate 2 functions as an under clad of the optical waveguide 4. The optical waveguide is formed by machining (for example, grinding or dicing) or laser beam machining.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device suitable for, for example, a quasi-phase matching type second harmonic generation device and a method of manufacturing the same.

[0002]

2. Description of the Related Art In general optical information processing technology, in order to realize high-density optical recording, a blue light laser which oscillates blue light having a wavelength of about 400 to 430 nm stably at an output of 30 mW or more has been demanded. And there is a development competition. As a blue light source, an optical waveguide type wavelength conversion element combining a laser oscillating with infrared light as a fundamental wave and a quasi-phase matching type second harmonic generation element is expected.

In a second harmonic generator using a lithium niobate single crystal, when the output of light propagating through the crystal increases, the refractive index fluctuates in the crystal due to optical damage. Has limitations. Further, as the wavelength of the light is shorter, the optical damage becomes more remarkable. It is known that the use of a substrate obtained by adding MgO to lithium niobate increases the resistance to optical damage, and the addition ratio of MgO at this time is usually about 5 mol%.

[0004] For example, "Electronics Le"
ters, 24th April, 1997. Vo
l. 33, no. According to page 9, pages 806 to 807, a periodically poled structure is formed on a MgO-doped lithium niobate substrate, and a proton exchange optical waveguide is formed in a direction orthogonal to the structure. Thus, an optical waveguide type second harmonic generator is realized.

[0005]

However, in the second harmonic generator of this type, when the oscillation output of blue light is increased, a stable output cannot be obtained due to optical damage. For example, when a periodically poled structure is formed in lithium niobate doped with 5 mol% of MgO, a proton exchange optical waveguide is formed in a direction orthogonal to the structure, and blue light having a wavelength of 420 nm is oscillated. When the output was 10 mW or more, especially about 15 mW or more, the output beam and output fluctuated greatly due to optical damage. The cause of such a change in the output beam and its output was not clear.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical waveguide device in which, even when the output of the light emitted from the optical waveguide is increased, the fluctuation of the output is reduced and stable oscillation is possible.

Another object of the present invention is to provide a wavelength conversion element utilizing a quasi phase matching method, in which the wavelength of emitted light is shortened, preferably in the blue region, and the output of emitted light from the optical waveguide is increased. In some cases, it is an object to reduce fluctuations in output and to enable stable oscillation.

[0008]

According to the present invention, a three-dimensional optical waveguide made of a bulk nonlinear optical crystal, a substrate joined to the optical waveguide, and the optical waveguide and the substrate are joined. An optical waveguide device, comprising: a bonding layer made of an amorphous material.

Further, the present invention includes a three-dimensional optical waveguide made of a bulk nonlinear optical crystal and an under clad of the optical waveguide, and the three-dimensional optical waveguide is confined by mechanical processing of the nonlinear optical crystal. The optical waveguide device according to claim 1, wherein the under cladding is formed of an amorphous material.

Further, according to the present invention, a material for forming an optical waveguide formed of a bulk nonlinear optical crystal is bonded to a separate substrate via a bonding layer. The present invention relates to a method for manufacturing an optical waveguide element, characterized in that an optical waveguide is formed by lowering a refractive index of a layer and then processing the material.

The present invention also relates to a method for joining an optical waveguide molding material made of a bulk nonlinear optical crystal to a separate substrate, wherein the refractive index of the substrate is lower than that of the crystal. Then, an optical waveguide is formed by processing the above-mentioned material, and relates to a method of manufacturing an optical waveguide element.

Further, the present invention relates to an optical wavelength conversion element having a three-dimensional optical waveguide made of a slab-shaped nonlinear optical crystal and a cladding layer made of an amorphous material on the upper and lower surfaces of the optical waveguide.

The inventor of the present invention joins a three-dimensional optical waveguide made of a bulk nonlinear optical crystal to a substrate via a bonding layer or directly without a bonding layer, and forms a base of the optical waveguide. By using the bonding layer or the substrate as the under cladding, even if the output of the light propagating in the optical waveguide is increased and / or the wavelength is shortened, the optical damage is remarkably suppressed, and the fluctuation of the output is prevented. And found the present invention.

The present invention will be further described with reference to FIG.

In the optical waveguide device 1A shown in FIG.
An optical waveguide 4 is provided on the surface 2 a of the substrate 2 via the bonding layer 3.
Are joined. The optical waveguide 4 is of a ridge type, and plate-like extending portions 15 are respectively extended on both sides of the optical waveguide 4 in the cross-sectional direction. In this example, a thick portion 8 is further formed at each end (outside of the groove 7) of each extension portion 15. Above each extending portion 15, a space or groove 7 for forming a ridge-type optical waveguide is formed. 5
Is a periodically poled structure. In this example, the non-polarization inversion portion 6 remains above the optical waveguide, but this may be omitted. As a result, the ridge-type optical waveguide 4 has a so-called floating form on the separate support substrate 2 via the bonding layer 3. There is no example of such a three-dimensional optical waveguide. “Three-dimensional optical waveguide” refers to an optical waveguide that confine light in the height direction (vertical direction) and lateral direction (left-right direction) of the waveguide.

Such a three-dimensional optical waveguide can be obtained by physically processing and shaping a nonlinear optical crystal by, for example, machining or laser processing.

On the other hand, the conventional three-dimensional optical waveguide is
Usually, it is formed as follows. (1) By altering the surface region of the substrate made of the nonlinear optical crystal and partially changing the composition, an altered layer having a high refractive index, for example, a titanium diffusion layer or a proton exchange layer is provided in the surface region of the substrate. (2) A single crystal film having a refractive index higher than that of the substrate is formed on the surface of the substrate made of the nonlinear optical crystal, and the single crystal film is processed into an elongated planar shape.

However, it is difficult to form, for example, a periodically poled structure in the single crystal film after forming the single crystal film. On the other hand, as described above, it is known that a proton exchange layer having a periodically poled structure is formed in the surface region of a lithium niobate single crystal substrate and used as an optical waveguide. However, such a second harmonic generator suffers significant optical damage.

In such a second harmonic generation device, when light having a short wavelength of, for example, 400 to 430 nm is propagated at a high output, optical damage is caused by an output density of light confined in the optical waveguide. It is also considered that the reason is that the threshold value of the light resistance damage of the crystal is exceeded.

However, when the present inventor prototyped the device as shown in FIG. 1 and propagated a short wavelength light at a high power density, the output fluctuation of the second harmonic emitted from the optical waveguide was suppressed. It was found that optical damage in the optical waveguide was suppressed. In other words, even when light having a short wavelength of, for example, 400 to 430 nm is propagated at a high output, the output density of the light confined in the optical waveguide does not exceed the threshold of light resistance that the crystal originally has. I found that I could afford it. At the same time, it has been found that the optical damage when the optical waveguide is formed by the proton exchange method is caused by the deterioration of the crystallinity of the surface region in the proton exchange process and the deterioration of the light damage resistance property accompanying the deterioration.

As a result, according to the present invention, it is possible to provide an optical waveguide device with extremely small optical damage and with suppressed fluctuation of light output.

At the same time, it is important that the bulk three-dimensional optical waveguide formed by machining or the like is bonded to the substrate via a bonding layer made of an amorphous material. For example, when a three-dimensional optical waveguide is bonded to a substrate without a bonding layer, the thermal expansion between the substrate and the optical waveguide occurs during a temperature drop process after bonding or due to a temperature change after bonding. Due to the difference, a large stress is applied to the optical waveguide. This is because, in addition to the difference in thermal expansion due to the composition difference between the substrate and the optical waveguide, the crystal orientation of the substrate is different from that of the optical waveguide. Is much larger and bulky, so a large stress is applied from the substrate to the optical waveguide,
This causes distortion in the optical waveguide. For this reason, the waveguide mode of light propagating in the optical waveguide changes, and optical damage is likely to occur.

When a single crystal is used as the material of the bonding layer, distortion is apt to occur in the optical waveguide due to the difference between the crystal orientation in the bonding layer and the crystal orientation in the optical waveguide. Further, when polycrystal is used as a material for the bonding layer, light that has leaked out of the optical waveguide to the bonding layer side is scattered in the bonding layer at a crystal grain boundary or the like, and the propagation loss increases.

On the other hand, in the present invention, by joining a bulk three-dimensional optical waveguide on a substrate, the bulk optical waveguide is brought into direct contact in addition to utilizing the inherent good crystallinity of the bulk. Is the bonding layer, not the substrate,
Since the bonding layer is much smaller in volume than the substrate, the stress is easily released to the bonding layer, and therefore, a large stress is hardly applied from the bonding layer to the optical waveguide. In addition, since the bonding layer is made of an amorphous material, the stress applied to the bonding layer is easily dispersed, and the distortion of the optical waveguide is further reduced.

In addition, IEICE Technical Report "TECHNICAL R"
EPORT OF IEICE US95-24: EM
According to D95-20: CPM95-32 (1995-07), pp. 31-38, a lithium niobate substrate is directly bonded to a lithium tantalate substrate, the lithium niobate substrate is thinned, and a prototype optical waveguide structure is manufactured. are doing. In this method, the substrates are directly joined to each other by utilizing the intermolecular force of the hydroxyl group adsorbed on the substrate surface, which is different from the present invention.

According to Japanese Patent Application Laid-Open No. 7-225403, an optical waveguide device comprising a core made of a nonlinear optical material and a clad substrate surrounding the core is disclosed. This is different from a structure in which a three-dimensional optical waveguide is joined to a substrate via an amorphous material.

In the present invention, a periodically poled structure is formed at least in the optical waveguide, so that the optical waveguide element can function as an element for generating harmonics. In this case, light having a shorter wavelength (higher energy) than the fundamental wave propagates in the optical waveguide, so that the effect of the present invention is particularly large.

When the device of the present invention is used as a harmonic generator, particularly a second harmonic generator, the wavelength of the harmonic is preferably from 330 to 550 nm, more preferably from 400 to 430 nm.
Is particularly preferred.

In a preferred embodiment, the optical waveguide comprises:
A ridge-type optical waveguide protruding from the bonding layer or the substrate.

In a preferred embodiment, a pair of extending portions extending toward both sides of the optical waveguide in the cross-sectional direction are provided. Such an extension stabilizes the bonding state of the optical waveguide on the substrate. Further, by providing the extending portions on both sides of the optical waveguide, the light propagation state is also symmetric.

The nonlinear optical crystal constituting the optical waveguide is not particularly limited, but is preferably a ferroelectric single crystal which can easily form a periodically poled structure, and is preferably a lithium niobate (LiNbO.sub.3).
₃ ), lithium tantalate (LiTaO ₃ ), lithium niobate-lithium tantalate solid solution, K ₃ Li ₂ Nb
Each single crystal of ₅ O ₁₅ is particularly preferred.

In such a crystal, magnesium (M) is used in order to further improve the light damage resistance of the three-dimensional optical waveguide.
g), one or more metal elements selected from the group consisting of zinc (Zn), scandium (Sc) and indium (In), and magnesium is particularly preferred.

When a periodically poled structure is formed in an optical waveguide, lithium niobate single crystal, lithium niobate-lithium tantalate solid solution single crystal, Or those obtained by adding magnesium to them are particularly preferable.

When a bonding layer is provided, the material of the substrate
The present invention is not limited to this, and may have a predetermined structural strength. Was
However, it is preferable that physical properties such as the coefficient of thermal expansion are close to those of the optical waveguide.
Lithium niobate (LiNbO)_Three ), Tantalic acid
Lithium (LiTaO)_Three ), Lithium niobate-tanta
Lithium luate solid solution, K_Three Li_Two Nb_Five O ₁₅Each single crystal
Is particularly preferred.

Further, another film can be formed on the surface of the substrate. As the film forming method, a liquid phase epitaxial method, a sputtering method, a vapor deposition method, a spin coating method,
There is a chemical vapor deposition method and the like. The material of the film is not limited, for example, silicon oxide, niobium pentoxide, tantalum pentoxide,
Examples thereof include lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate solid solution.

When at least the surface region of the substrate functions as an under cladding, the refractive index of at least the surface region of the substrate needs to be lower than the refractive index of the material of the optical waveguide.

It is necessary that the refractive index of the material of the bonding layer be lower than the refractive index of the material of the optical waveguide. This difference in refractive index is preferably 5% or more, and more preferably 10% or more. Further, the material of the bonding layer is preferably an organic resin or glass (particularly preferably low-melting glass). Examples of the organic resin include an acrylic resin, an epoxy resin, and a silicone resin. As glass,
Low-melting glass containing silicon oxide as a main component is preferable.

In order for the bonding layer to function as an under clad, the thickness of the bonding layer is preferably 0.1 μm or more, and more preferably 0.2 μm or more. Further, from the viewpoint of the positional stability of the three-dimensional optical waveguide, the thickness of the bonding layer is preferably set to 3 μm or less.

In order to manufacture the optical waveguide device shown in FIGS. 1A and 1B, for example, the following method is used. That is, FIG.
As shown in (1), the periodically poled structure 5 is formed on the surface of the optical waveguide molding material 9. A surface (bonding surface) 9a of the optical waveguide molding material 9 on the structure 5 side is bonded to the surface 2a of the substrate 2. Next, as shown in FIG. 2B, the back surface (non-joining surface) 9b of the optical waveguide molding material 9 is ground to thin the material 9A. At this stage, it is difficult to reduce the thickness of the material 9A to such a size that light can be confined in the thickness direction. Therefore, as shown in FIG. 1, the groove 7 is formed, and the optical waveguide 4 having a ridge structure is formed. At this time, the thickness of the optical waveguide is also adjusted. Such processing can be performed by, for example, a dicing processing apparatus or a laser processing apparatus, but mechanical processing such as dicing processing is preferable.

The method for forming the periodically poled structure is not limited. As a method of forming a periodically poled structure on an electro-optic crystal substrate, for example, a lithium niobate substrate, a diffusion method in Ti, a diffusion method in Li ₂ O, a heat treatment method for loading SiO ₂ , a thermal oxidation method in Ti, a proton exchange heat treatment method, An electron beam scanning irradiation method, a voltage application method, a corona charging method and the like are preferable. Among these methods, the voltage application method is particularly preferable when an X-cut or Y-cut or its off-cut substrate is used from the viewpoint of forming a deep periodically poled structure with high accuracy. When a Z-cut substrate is used, it is particularly preferable to carry out the method by a corona charging method or a voltage application method.

As a method of grinding the height of the optical waveguide to a predetermined dimension, a distance between the cutting outer peripheral blade rotating perpendicular to the optical waveguide bottom and the optical waveguide bottom is set to a predetermined height. It is preferable that the thickness of the optical waveguide be set to a required value by cutting. The reason is as follows.

Conventionally, when the thickness of a substantially flat workpiece is prepared by grinding, it is common practice to grind the surface of the workpiece with an outer peripheral blade rotating in parallel with the surface. . However, in this method, the thickness is likely to be non-uniform due to a slight inclination of the rotating surface of the outer peripheral blade. Was difficult to control.

On the other hand, if the gap between the cutting outer peripheral blade rotating perpendicular to the bottom surface and the bottom surface of the optical waveguide is set to a predetermined height, and the cutting is performed, the height of the outer peripheral blade is adjusted to thereby increase the height. The adjustment in the vertical direction can be easily performed, and the accuracy at this time is similar to the processing accuracy (submicron order) of a general processing apparatus.

As in the optical waveguide device 1B shown in FIG. 4, the thick portion 8 of the extension can be omitted. The thick part 8
For example, it can be removed by the dicing apparatus described above.

In forming the ridge structure, a groove can be formed in the substrate. For example, the optical waveguide device 1C of FIG.
A is similar to A, but a groove 2c is also formed in the substrate 2, and grooves 17 on both sides of the ridge structure 8 extend into the substrate 2. As a result, the ridge structure 18 includes the protrusion 2b of the substrate, the bonding layer 3 on the protrusion 2b, and the optical waveguide 4 on the bonding layer 3.

In the optical waveguide device 1D of FIG. 6, as in the case of the optical waveguide device 1C, the groove 2c is formed in the substrate, and the projection 1b of the substrate 2 is thereby formed.
Incidentally, 20 is the same material as the bonding layer 3, but the thick portion 8 is removed.

In FIGS. 1, 4, 5 and 6, the lower portion of the optical waveguide is the domain-inverted portion 5 and the upper portion is the non-inverted portion 6. However, in some cases, the entire optical waveguide becomes a domain-inverted portion. Also, the upper part of the optical waveguide may be the domain-inverted part 5 and the lower part may be the non-inverted part 6.

In one embodiment of the present invention, a so-called dielectric-loaded three-dimensional optical waveguide can be used. For example, in the optical waveguide device 1E of FIG. 7, the three-dimensional optical waveguide 10 and the pair of extension portions 1 are provided on the surface 2a of the substrate 2 with the bonding layer 3 interposed therebetween.
5 and a pair of thick portions 8 are joined. The three-dimensional optical waveguide 10 and the extending portion 15 constitute a thin portion,
The thickness of the thin portion is set to a thickness that allows light to be confined in the thickness direction. The three-dimensional optical waveguide 10 is formed on the dielectric layer 12 by forming a predetermined dielectric layer 12 on the surface of the thin portion. In this example, the dielectric layer 12 protrudes into the bonding layer 3.

In order to manufacture the optical waveguide device shown in FIG. 7, for example, the following method is used. That is, as shown in FIG.
The periodically poled structure 5 is formed on the surface of the optical waveguide forming material 9, and the dielectric layer 12 is further formed. Dielectric layer 1
The material of No. 2 is not particularly limited as long as it has a higher refractive index than the material 9, but for example, niobium pentoxide is preferable. The bonding surface 9 a of the optical waveguide molding material 9 is bonded to the surface 2 a of the substrate 2. Next, as shown in FIG. 8B, the back surface (non-joining surface) 9b of the material 9 is ground to thin the material 9A.
Next, as shown in FIG. 7, a concave portion 11 is formed, and a thick portion 8 and thin portions 10 and 15 are formed. For such processing, the above-described processing method can be diverted.

As in the case of the optical waveguide device 1F shown in FIG. 9, the thick portion 8 of the extending portion can be omitted.

The dielectric can be loaded above the optical waveguide (on the side opposite to the substrate). In the optical waveguide device 1G of FIG. 10, a dielectric 12 is loaded on the optical waveguide 10. Further, in the optical waveguide device 1H of FIG. 11, the dielectric 12 is loaded on the optical waveguide 10,
In addition, in the element of FIG. 10, the thick portion 8 of the extension portion is omitted.

In the present invention, the extended portion 15 can be removed by further increasing the depth of the groove 7 in FIG. 1 and forming the groove to the inside of the bonding layer 3. In this case, as in an element 1J shown in FIG. 12, for example, the groove 7 reaches the bonding layer 3, and the ridge-type optical waveguide 4 projects directly from the bonding layer 3.

Further, an overcoat layer covering at least the optical waveguide can be provided. FIG. 13 shows an element 1K according to this embodiment. The surface of this element on the optical waveguide 4 side is covered with an overcoat layer 21.

As a result, the surface of the optical waveguide does not come into direct contact with the atmosphere, but comes into contact with the overcoat layer. For this reason, for example, when the surface of the optical waveguide is rough or finely chipped, light scattering is reduced as compared with the case where the optical waveguide is exposed to the atmosphere.

Although the material of the overcoat layer is not limited, for example, silicon oxide (SiO ₂ ), niobium pentoxide, tantalum pentoxide, or various resin materials are preferable.

In a preferred embodiment, the optical waveguide device of the present invention includes a pair of extended portions, and a ridge-shaped optical waveguide projecting from the extended portions toward the bonding layer.
FIG. 14 shows an element 1L according to this embodiment.

The substrate 2 is provided with a pair of thick portions 8, a pair of extending portions 26, and an optical waveguide 24 projecting from the extending portions toward the bonding layer 3. A pair of grooves 23 is formed between the thick portion 8 and the optical waveguide 24,
The groove 23 is filled with an amorphous material 22. The filling 22 of the amorphous material is preferably continuous with the bonding layer 3.

In this embodiment, the optical waveguide 24 is composed of the periodically poled portion 5 and the protrusion 25 that has not been poled, and the poled portion 5 is provided on the tip side near the substrate 2. .

According to such a structure, the surface of the optical waveguide comes into contact with the amorphous material. For this reason, for example, when the surface of the optical waveguide is rough or finely chipped, light scattering is reduced as compared with the case where the optical waveguide is exposed to the atmosphere. Therefore, the variation of the optical insertion loss is reduced.

The method for producing such an element is not particularly limited, but it is preferable to divert the above-mentioned method. That is, FIG.
As shown in FIG. 5A, the periodically poled structure 5 is formed on the surface of the optical waveguide molding material 9. Next, as shown in FIG. 15B, a groove 23 having a predetermined shape is formed by the aforementioned machining or laser processing, and a pair of grooves 23 is formed.
An optical waveguide 24 having a ridge structure is formed therebetween.

Next, as shown in FIG. 15C, the surface (bonding surface) 9 a of the optical waveguide molding material 9 on the structure 5 side is bonded to the surface 2 a of the substrate 2. At this time, the amorphous material 22 is filled in the groove 23. Next, the back surface (non-joining surface) 9b of the optical waveguide molding material 9 is ground.
The material 9 is thinned, and the thick portion 8 and the extension portion 26 shown in FIG.
To form

In a preferred embodiment, when a pair of extending portions extending toward both sides in the cross-sectional direction of the optical waveguide is provided, the wavelength of the fundamental wave of the harmonic generation element and the wavelength of the wavelength-converted wave are reduced. Single mode propagation for both. Particularly preferably, the width of the optical waveguide is 1-10 μm, the height from the extending portion of the optical waveguide is 0.2-5 μm, and the thickness of the extending portion is 0.5-5 μm.

This embodiment will be described.

In order to find a waveguide structure that satisfies the single mode condition for both the pump light and the wavelength-converted light, a detailed study was performed using an optical waveguide structure analysis method by the finite element method, and the characteristics were confirmed by experiments. As a result, it has been found that, for example, the waveguide of FIG. 1 satisfies this condition and has a very large waveguide dimensional tolerance for realizing high performance, and is therefore easy to manufacture.

The device shown in FIG. 1 has a portion of the three-dimensional optical waveguide 4 and a pair of extending portions 15 extending on both sides thereof.
Such a structure is also seen in the devices of FIGS. 3, 4, 13 and 14.

A specific study was performed with the wavelength of the excitation light λ1 = 810 nm and the wavelength of the converted light λ2 = 405 nm. In this study, examination was made based on the model shown in FIG. Here, 2 is a substrate, 3 is a bonding layer, 4 is a ridge portion, and 30 is a lower portion of a conductive path divided for the purpose of calculating the structure of FIG.

The pump light laser and the waveguide fundamental mode (wavelength λ
FIGS. 17 and 18 show examples of the calculation results of the coupling loss when direct optical coupling is performed with 1). FIG. 17, FIG.
In the calculation example in the above, the material of the ridge portion 4 and the extension portion 15 is the same nonlinear optical material, and the nonlinear optical material is
2.14 refraction index for wavelength λ1, refraction index for wavelength λ2
It was 2.29. The refractive index of the bonding layer 3 was 1.51 for both wavelengths λ1 and λ2. In addition, a Gaussian beam having a radius of 1.5 μm in the x direction and a radius of 1.0 μm in the y direction was assumed as a spot of the excitation light laser to be coupled with the present waveguide.

The width w of the ridge portion 4 is plotted on the horizontal axis. The vertical axis shows the coupling loss η between the waveguide mode field and a Gaussian beam having a diameter of 3 μm in the x direction and a diameter of 2 μm in the y direction assuming an excitation light laser. In FIG. 17, the ridge portion 4
Is fixed at 1.0 μm, and in FIG.
It was fixed to μm. In each graph, the thickness t2 of the extension portion
Was changed between 1.0-4.0 mm. FIG. 17, FIG.
A portion indicated by a solid line in FIG.

In each graph, the width W of the ridge portion 4 is:
There is a certain threshold ws. For example, t1 = 1.0 μm, t
It can be seen that when 2 is 2.0 μm or more, single mode propagation occurs under w below each threshold. ws is shown in FIG.
In No. 7, the value fluctuated within a range of 4 to 10 μm.
However, if w becomes unnecessarily small, the state becomes close to the slab mode, and a cutoff state occurs (η increases). When t2 is about 1.0 μm or less, the state of confinement becomes extremely strong.
1.01.0 μm or less, and the coupling loss also increases.

In the calculation example of FIG. 17, the width w of the ridge portion 4 is
= 2.5 μm, height t1 of the ridge portion 4 = 1.0 μm, and thickness of the extension t2 = 1.5 μm. In the vicinity of a single mode mode of the waveguide, an optimum structure that minimizes the coupling loss. Becomes

Similarly, in the calculation example of FIG. 18, w =
A waveguide structure near 2.5 μm, t1 = 2.0 μm, and t2 = 1.5 μm is the optimum structure.

In this calculation example, t1 is 1.0 and 2.0 μm
However, it is obvious that a similar single mode propagation region can be obtained for the other t1. It has been confirmed by calculation and experiment that the threshold value ws is reduced by increasing the value of t1, thereby increasing the confinement of the waveguide.

For t2, t2 = 1.0, 1.5, 2.0, 2.
Although described only for the cases of 5, 3.0, 3.5, and 4.0 μm, a similar single mode propagation region exists at other t2. Increasing t2 results in a situation where the confinement of the waveguide is weak, and thus the threshold value ws increases. On the other hand, by reducing t2, the confinement of the waveguide becomes stronger, and ws tends to decrease.

Further, the relative refractive index difference (n1-n2) / n2 between the refractive index (n1) of the ridge portion 4 and the extension portion 15 and the refractive index (n2) of the base layer 30; The relative refractive index difference (n1-n2) / n2 between the refractive index (n1) of the portion 15 and the refractive index of air (the refractive index of the overcoat layer instead of air when overcoating the optical waveguide) (n2).
If one or both of these becomes large, the refractive index n1,
Regardless atmosphere of n2, confinement of the waveguide becomes high state, ws is reduced. On the other hand, when one or both of the relative refractive index differences are reduced, it is obvious that the confinement of the waveguide is weakened and ws is increased regardless of the magnitude of n1 and n2.

In this calculation example, only the case where the spot radius of the excitation light laser is 1.5 μm in the x direction and 1.0 μm in the y direction is shown. , Structure and dimensions are selected, and their size is determined by their combination. In some cases, the light spot can be coupled to an optical waveguide via a lens. In view of these facts, the effective spot diameter is different from about 0.5 μm to about 5 μm.

For example, when a laser having a small effective spot diameter is used, w and t2 at which the coupling loss η between the excitation light laser and the present optical waveguide is minimized are reduced, or the spot diameter of the excitation light laser is increased. In that case, w and t2 will increase.

Although an example has been shown in this study, the refractive index of a general nonlinear optical crystal or nonlinear polymer material is in the range of 1.3 to 2.5 in consideration of the fact that the refractive index greatly changes depending on the operating environment temperature. The refractive index of the adhesive layer ranges from 1.3 to 2.0. Therefore, for the effective spot diameter of the laser used, while satisfying the single mode condition according to the present invention, and as a structure to reduce the coupling loss with the laser, the shape of the ridge type optical waveguide,
The width of the ridge portion 4 is 1 to 10 μm, and the height of the ridge portion 4 is 0.
2 to 5 μm, thickness of extension 15 and underlayer 30 0.5 to
In the range of 5 μm, a single mode can be obtained.

It is also obvious that the results of the study are the same for both models with a substrate layer functioning as a cladding and without a substrate layer.

(Regarding the Refractive Index of the Bonding Layer) In the case of forming an optical waveguide type optical wavelength conversion element, the overlapping of the fundamental and harmonic modes in the optical waveguide greatly affects the conversion efficiency. The shape of the guided mode is affected by the refractive index of the bonding layer. FIG. 19 shows the relationship between the refractive index difference between the waveguide and the bonding layer and the electric field distribution. Wavelength 850 nm, waveguide LiNbO3 (refractive index 2.166)
The substrate was calculated using LiTaO3 (refractive index: 2.158).
As the refractive index difference increased, the symmetry of the mode profile increased and the confinement improved. As can be seen from FIG. 19, when the refractive index difference Δn between the waveguide and the bonding layer is 5% or more, the symmetry of the mode is increased and the efficiency is improved, which is preferable. Further, when Δn becomes 10% or more, confinement is strengthened, and conversion efficiency can be improved.

(Satisfaction of Single Mode Condition) In a waveguide type optical wavelength conversion element, the condition of single mode propagation in an optical waveguide is indispensable for performing high-efficiency wavelength conversion. In particular, it is desirable that the optical waveguide satisfies the single mode condition with respect to the fundamental wave (when the wavelength of the converted light <the fundamental wave). The reason is that when a fundamental wave is input to the waveguide, the propagating fundamental wave may be dispersed into a plurality of waveguide modes in the multi-mode waveguide. In the optical wavelength conversion element, since the conversion efficiency depends on the power density of the fundamental wave, if the propagation mode of the fundamental wave is dispersed in the multi-mode waveguide, the conversion efficiency becomes extremely low. In addition, there is a problem that the output becomes unstable due to dispersion of the propagation mode to be guided.

The single mode condition in the optical waveguide will be described. For light with a wavelength of 800 nm, MgO-doped LiNbO
FIG. 20 shows the relationship between the refractive index difference dn from the bonding layer and the maximum thickness satisfying the single mode condition when 3 is a waveguide layer.
It was shown to. When the refractive index difference Δn = 5%, the single mode depth is about 1 μm. As the refractive index difference increases, the single mode condition becomes more severe. This result indicates that the thickness of the waveguide layer must be 1 μm in order to realize a refractive index (5% or more) with the bonding layer for realizing the optical waveguide with strong confinement.
The following shows what must be controlled. However, when the thickness of the waveguide is reduced, the aspect ratio of the guided mode increases, and the aspect ratio of the mode profile of the emitted light is proportional to this. Is required. Further, when light is coupled into the waveguide, the beam profile is significantly different from the beam profile of a normal semiconductor laser or solid-state laser, which causes a reduction in coupling efficiency. Further, since the change in the effective refractive index with respect to the fluctuation in the thickness of the waveguide increases, the non-uniformity of the waveguide increases. To improve this, it is necessary to increase the single mode depth of the waveguide. Considering high-efficiency coupling with a semiconductor laser, a single-mode depth of 1 μm or more is required. Therefore, a material having a refractive index difference of 5% or less from the optical waveguide is required as the refractive index of the bonding layer. Thus, it is difficult to realize an optical waveguide structure having excellent symmetry and strong confinement.

Accordingly, a new waveguide structure is proposed as a method for increasing the single mode depth. As a refractive index distribution in the depth direction of the waveguide, as shown in FIG. 21, when a three-layer structure of a waveguide, a bonding layer (refractive index of the bonding layer <refractive index of the substrate), and a substrate is adopted, In the state where the electric field distribution of the propagating light exists on the substrate side, it is found that the single mode condition of the optical waveguide largely depends on the refractive index difference between the waveguide and the substrate, not the refractive index difference between the waveguide and the bonding layer. Was. That is, by using a substrate having a refractive index close to that of the optical waveguide, the single mode condition of the waveguide can be greatly reduced.

More specifically, the relationship between the refractive index difference and the single mode depth shown in FIG. 20 is substantially the same as the relationship between the refractive index difference and the refractive index difference between the waveguide and the substrate. That is, the depth of the single-mode waveguide can be set to 1 μm or more by setting the refractive index difference between the substrate and the waveguide to 5% or less. On the other hand, the electric field distribution of the guided light existing in the optical waveguide can be controlled by the refractive index of the bonding layer. As mentioned above,
By making the refractive index of the bonding layer smaller than the refractive index of the waveguide by 5% or more, it is possible to improve the symmetry of the electric field distribution of the waveguide mode and enhance the confinement. By providing the bonding layer, the single mode condition of the waveguide and the electric field distribution of the waveguide mode can be independently designed. (However, this condition is limited only when the electric field distribution of the guided mode exists on the substrate side. The reason is that if the bonding layer becomes too thick, the guided mode will not exist on the substrate side, and the waveguide and the bonding layer will not be present. This is because the single mode condition is satisfied by the refractive index difference.

The following two conditions are required as conditions for the waveguide via the bonding layer. The refractive index of the bonding layer is lower than the refractive index of the substrate. An electric field distribution of a waveguide mode propagating through the waveguide exists in the substrate. Specifically, it is necessary that the electric field strength in the substrate is at least 1/1000 of the maximum value of the electric field strength in the waveguide. When the value is smaller than this, the influence of the substrate on the waveguide mode does not appear.

FIGS. 22 and 23 show electric field distributions with and without a bonding layer. The presence of the bonding layer greatly increases the confinement of the waveguide and increases the symmetry. I understand. As a result, it was found that the overlap between the fundamental wave and the higher harmonic wave in the waveguide could be increased, and that the conversion efficiency in the waveguide having the bonding layer was increased by a factor of two or more.

(Thickness of Bonding Layer) The thickness of the bonding layer will be described. When the thickness of the bonding layer is increased, the influence of the substrate on the waveguide is eliminated as described above, so that it is difficult to satisfy the single mode condition. On the other hand, when the thickness of the bonding layer decreases, the effect of the thickness of the bonding layer on the effective refractive index of the waveguide increases. This indicates that the uniformity of the optical waveguide device largely depends on the thickness of the bonding layer. The waveguide type optical wavelength conversion element has a very tight phase matching wavelength tolerance of about 0.1 nm. Become.

FIG. 24 shows the relationship between the thickness of the bonding layer and the phase matching wavelength. When the thickness of the bonding layer is 0.1 μm or less, the phase matching wavelength greatly depends on the thickness of the bonding layer. When the thickness is 0.15 μm or more, the dependency gradually decreases, and when the thickness is 0.2 μm or less, the dependency is further reduced. Therefore, the thickness of the bonding layer is preferably such that the phase matching wavelength is less dependent on the thickness of the bonding layer. At the same time, it is necessary to reduce the thickness so that the electric field distribution of the waveguide mode exists on the substrate side.

In the above description, the electric field distribution in the depth direction of the waveguide is described. However, the present invention can be applied to any waveguide such as a loaded waveguide, a ridge waveguide, and a machined waveguide.
In order to realize the lateral confinement of the waveguide, it is necessary to adopt these structures.

(Formation of Periodically Poled Structure Using Off-Cut Substrate) In order to construct a highly efficient optical wavelength conversion element, the overlap between the periodically poled structure and light propagating through the optical waveguide must be increased. is important. Assuming a case where a second harmonic having a wavelength of about 410 nm is generated from a fundamental wave having a wavelength of about 820 nm as an optical waveguide shape, the depth of the optical waveguide is about 2 μm, and the depth of the periodic polarization inversion is 2 μm or more. Required.

As a method of forming a deep domain inversion structure,
There is a method using an off-cut substrate in which the crystal axis is inclined with respect to the substrate surface. For example, in an X off-cut substrate,
X of X plate (substrate with X axis of crystal perpendicular to substrate surface)
The axis and the Z axis are inclined by θ about the Y axis. In a Y-offcut substrate, the Y-axis and the Z-axis of a Y-plate (a substrate in which the Y-axis of the crystal is perpendicular to the substrate surface) are inclined by θ about the X-axis. By forming a domain-inverted structure using such an X-off cut substrate and a Y-off-cut substrate, it is possible to form a deep domain-inverted structure, thereby realizing high efficiency of the optical wavelength conversion element. The polarization inversion depth increases as the off-cut angle increases. For example, if the period of the periodically poled structure is 3 μm
When the off-cut angle θ is 1.5 °, a periodically poled structure having a domain inversion depth of 1 μm, 1.7 μm at θ = 3 °, and 2.5 μm at θ = 5 ° can be realized. Therefore, in order to realize a sufficient overlap between the optical waveguide and the periodically poled structure, a substrate having an off-cut angle θ of 3 ° or more is desirable.

However, there are the following problems when forming a domain-inverted structure on an off-cut substrate. (1) When the proton exchange optical waveguide is applied to an off-cut substrate, the propagation loss increases in proportion to the off-cut angle. (2) When a proton exchange optical waveguide is formed on a Y off-cut substrate, there is a propagation loss more than twice that in the case of an X off-cut substrate.

That is, in the case of a proton exchange optical waveguide conventionally used in an optical waveguide type wavelength conversion element, if deep polarization reversal by an off-cut substrate is to be used, the characteristics are deteriorated due to the propagation loss of the optical waveguide. At most, only X off-cut substrates having θ of less than 3 ° are used. In the case of using the Y off-cut substrate, the propagation loss of the optical waveguide becomes 4-5dB / cm or more, in order to significantly degrade the characteristics of the second harmonic generation device, a proton exchanged optical <br/> waveguide There was a problem that it was difficult to use.
The cause of the propagation loss in these optical waveguides is due to chemical damage generated during proton exchange.

As a method for solving these problems, the optical wavelength conversion device of the present invention is very effective. Since the optical wavelength conversion device of the present invention can form an optical waveguide without using a proton exchange step, no chemical damage occurs. Therefore, X which has an off-cut angle of 3 ° or more, which has been difficult to use conventionally,
Off-cut substrates and Y-off-cut substrates can be used. When an X, Y off-cut substrate with θ = 5 ° is used,
The X-cut substrate has a waveguide loss of 2 dB / cm or more, and the Y-off cut substrate has a waveguide loss of 4-5 dB / cm or more. However, with the configuration of the present invention, it is possible to form an optical waveguide having a low propagation loss of 1 dB / cm or less even when an off-cut substrate with θ = 5 ° is used. As a result, the conversion efficiency of the second harmonic generation element can be increased by a factor of two or more by using a waveguide structure with deep polarization reversal and low loss.

Further, it has been clarified that the use of a Y off-cut substrate (a substrate whose X axis is parallel to the substrate surface) can provide a more efficient light wavelength conversion element structure. It has been found that a thicker domain-inverted structure is formed on a Y off-cut substrate than on a conventionally used X-off cut substrate. In the case of the Y-offcut substrate, a domain-inverted portion 1.2 times deeper than that of the X-offcut substrate was obtained. As a result, it has become possible to increase the conversion efficiency of the optical wavelength conversion element by 1.2 times. Regarding the polarization inversion period, the inversion structure formed on the Y off-cut substrate can shorten the period, which is advantageous for realizing a short wavelength light wavelength conversion element. In a conventional optical wavelength conversion device using a proton-exchanged optical waveguide, the Y-off-cut substrate has not been studied because the waveguide loss is large, but by using the optical wavelength conversion device of the present invention, a low-loss waveguide is realized. A waveguide structure can be formed, and a highly efficient optical wavelength conversion element has been realized.

(Modification of Element) In one embodiment of the present invention, the three-dimensional optical waveguide projects from the extending portion in a direction away from the substrate and in a direction approaching the substrate. And a projection. Element 1 shown in FIG.
M relates to this embodiment.

In the element 1M, the surface of the substrate 2, the three-dimensional optical waveguide 34 and the pair of extending portions 15 are joined by the joining layer 3A. The three-dimensional optical waveguide includes a projection 34b extending toward the substrate 2, a projection 34a extending away from the substrate, and projections 34a and 3b.
4b. The protruding portions 34a and 34b have a substantially symmetrical shape when viewed from the central portion 34c.

When a three-dimensional optical waveguide having such a configuration is employed, the cross-sectional shape of a light beam propagating in the optical waveguide becomes close to a perfect circle. Therefore, the coupling loss when the element is coupled to an external optical fiber is further reduced. Alternatively, energy loss at the time of focusing and focusing light propagating through the optical waveguide is reduced.

Further, it is possible to form a concave portion or a protrusion on the surface 2a of the substrate 2. In a particularly preferred embodiment, the thickness of the bonding layer is increased between the three-dimensional optical waveguide and the surface of the substrate, and the thickness of the bonding layer is reduced between the extending portion and the surface of the substrate. Alternatively, a three-dimensional optical waveguide is provided on the concave portion on the substrate surface. Thus, the stress applied to the three-dimensional optical waveguide from the bonding layer and the substrate side is further reduced.

FIG. 28 shows an element 1N according to this embodiment. A concave portion 31 is formed on the surface 2 a of the substrate 2. The three-dimensional optical waveguide 4 and the pair of extending portions 15 are joined to the substrate surface 2a via the joining layer 3. The three-dimensional optical waveguide 4 is located on the concave portion 31,
The material 32 of the bonding layer is also filled therein. As a result,
The thickness of the bonding layer is relatively large between the three-dimensional optical waveguide and the substrate, and relatively small between the extension and the substrate.

In such an embodiment, the ratio between the thickness of the bonding layer between the three-dimensional optical waveguide and the substrate and the thickness of the bonding layer between the extended portion and the substrate may be 10-1: 1. preferable.

In a preferred embodiment, a concave portion is provided on the substrate surface, and at least a part of the three-dimensional optical waveguide is located in the concave portion. FIG. 29 shows an element 1P according to this embodiment.

In the element 1 P, a concave portion 31 is formed on the surface 2 a of the substrate 2. Also, the three-dimensional optical waveguide 24
A protrudes toward the substrate 2, and the tip of the optical waveguide 24 </ b> A is located in the recess 31. Recess 3
1 is filled with the material 32 of the bonding layer. Since the surface of this element is substantially flat, the above-mentioned effects can be obtained.

Further, in the element 1Q shown in FIG.
A concave portion 31 is formed on the surface 2 a of the substrate 2. Also,
The three-dimensional optical waveguide 34 has a pair of protrusions 34a and 34b.
And the tip of the protruding portion 34 b is located in the recess 31.

It is not necessary that a bonding layer is continuously provided over the entire surface of the substrate between the three-dimensional optical waveguide and the substrate or between the extension and the substrate. For example, a part between the three-dimensional optical waveguide and the substrate may be a gap, or the gap may be filled with a filler material other than the bonding material. Further, a portion between the extension portion and the substrate may be a gap, or a filling material other than the bonding material may be filled in the gap.

The bonding layer may be made of a plurality of types of materials. For example, in the element 1R of FIG. 31, the surface 2a of the substrate 2 and the extending portion 15 and the three-dimensional optical waveguide 4 are joined by two kinds of joining layers 3B and 3C.

Hereinafter, more specific examples will be described. Example 1 An optical waveguide device 1A shown in FIG. 1 was manufactured.
Specifically, on a lithium niobate material 9 (thickness: 0.5 mm) doped with 5 mol% of MgO on the X-plane (87 ° Z-cut) of a three-degree off-cut substrate, a period of 3.2 μm was applied by a voltage application method. A periodically poled structure 5 having a poled depth of 2 μm was formed. Specifically, as shown in FIGS. 25 and 26, the domain-inverted structure 25 is generated on the off-cut (three-degree) X plate 21 (made of MgO-doped lithium niobate) at a pitch of 3.2 μm by a voltage application method. Was. On the surface 21a of the substrate 21, a comb-shaped electrode 23 and a stripe electrode 22 were formed so as to extend in the Z direction and face each other. A uniform planar electrode 2 is formed on the back surface 21b of the substrate 21.
4 was formed. Between the comb electrode 23 and the plane electrode 24 (V
1) and V1 = 5 kV / mm and V2 = 5 k between the comb electrode 23 and the stripe electrode 22 (V2), respectively.
By applying a voltage of V / mm, a periodically poled structure 25 was formed.

Here, since the substrate 21 is off-cut, the formed inverted pattern has a polarization direction (P
s), and thus extends from the substrate surface 21a to the inside of the substrate in a direction inclined at 3 degrees with respect to the surface 21a.

Next, the bonding surface 9a of the material 9 and the substrate 2
(The x-cut lithium niobate substrate, thickness 1 mm) was bonded to the surface 2a. As the adhesive, a low-melting glass mainly containing silicon oxide was used. Adhesion temperature is about 500
° C. The thickness of the adhesive layer 3 was about 0.5 μm.

Next, the material 9 was ground by a mechanical grinding device to reduce the thickness of the material 9A to 50 μm. Then
The ridge structure shown in FIGS. 1 and 3 was formed using a dicing machine. At this time, in FIG. 3, the thickness A of the extension portion 15 is set to 1 μm, and the height (ridge height) of the optical waveguide 4 is set.
B was 1.5 μm, and the width C of the ridge structure was 4 μm. As the dicing blade, a resin-bonded diamond grindstone “SD6000” (outer diameter φ about 52 mm, thickness 0.1 mm) was used. The blade rotation speed is 30,
000 rpm and the blade feed speed is 1.0 mm /
Seconds. After forming the ridge structure, the substrate was cut in the cross-sectional direction to form a device having a length of 10 mm. Both end surfaces of the optical waveguide 4 were chemically and mechanically polished.

Using this device, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength is 850 nm, and the wavelength of the second harmonic is 425 nm.
Met. The SHG conversion efficiency was about 500% / W.
When the incident power of the fundamental wave was 100 mW, a second harmonic output of 50 mW was obtained, and no characteristic deterioration due to optical damage or the like was observed in the second harmonic. Table 1 shows the relationship between the fundamental wave output and the second harmonic output.

[0111]

[Table 1]

(Comparative Example 1) In the same manner as in Example 1, 3 times of MgO on the X-plane (87 ° Z-cut) of the off-cut substrate was 5 mo.
1% doped lithium niobate material 9 (0.5 m thick)
m), a periodically poled structure 5 having a period of 3.2 μm and a polarization reversal depth of 2 μm was formed by a voltage application method.

Next, a three-dimensional optical waveguide extending in a direction perpendicular to the domain-inverted pattern of the substrate was formed by a proton exchange method using pyrophosphoric acid. In particular,
The surface of the substrate was masked with a mask made of tantalum. At this time, an elongated linear opening having a width of 4 μm was formed in the mask. This substrate was immersed in pyrophosphoric acid heated to 200 ° C. for 10 minutes. The mask was removed from the substrate, and the substrate was annealed in air at 350 ° for 4 hours to form a three-dimensional optical waveguide. The substrate was cut to form a device having a length of 10 mm. Both ends of the optical waveguide were chemically and mechanically polished.

Using this device, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength is 850 nm, and the wavelength of the second harmonic is 425 nm.
Met. The SHG conversion efficiency was about 500% / W.
Until the output of the second harmonic reached about 15 mW, deterioration of characteristics such as optical damage did not occur, and stable oscillation of the second harmonic was possible. However, the output of the second harmonic is about 1
Above 5 mW, the output beam fluctuated due to optical damage. When this output reached 20 mW, stable oscillation of the second harmonic was impossible.

(Embodiment 2) Optical waveguide device 1D shown in FIG.
Was manufactured. Specifically, MgO on the X-plane (87 ° Z-cut) of the three-time off-cut substrate was reduced to 5 in the same manner as in Example 1.
mol% doped lithium niobate material 9 (thickness of 0.
5 mm), a periodic domain inversion structure 5 having a period of 3.2 μm and a domain inversion depth of 2 μm was formed by a voltage application method.

Next, a width of 4 μm and a thickness of 300 μm were formed on the bonding surface of the material 9 in a direction perpendicular to the direction of the domain inversion pattern.
An Nb ₂ O ₅ film (dielectric layer) having a stripe shape (stripe shape) of nm was formed.

Next, the bonding surface 9a of the material 9 and the surface 2a of the substrate 2 (x-cut lithium niobate substrate, 1 m thick)
m). As the adhesive, an epoxy-based room temperature-curable resin was used. The thickness of the adhesive layer 3 is about 0.5 μm
And

Next, the material 9 was ground by a mechanical grinding device to make the thickness of the material 9A 20 μm. Then
The concave portion 11 shown in FIG. 6 was formed using a dicing device. At this time, the thickness of the extension portion 15 was set to 3 μm. As a dicing blade, a resin-bonded diamond grindstone “SD5000” (outer diameter φ about 52 m
m, thickness 0.1 mm). The rotation speed of the blade is 10,000 rpm, and the feed speed of the blade is 0.5.
mm / sec. The substrate was cut in the cross-sectional direction to form a device having a length of 10 mm. Both ends of the optical waveguide were chemically and mechanically polished.

Using this device, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength is 850 nm, and the wavelength of the second harmonic is 425 nm.
Met. The SHG conversion efficiency was about 500% / W.
When the incident power of the fundamental wave was 100 mW, a second harmonic output of 50 mW was obtained, and no characteristic deterioration due to optical damage or the like was observed in the second harmonic.

Example 3 An element 1L shown in FIG. 14 was manufactured according to the procedures shown in FIGS.

More specifically, in the same manner as in the first embodiment, MgO on the X-plane (87 ° Z-cut) of
The mol.-doped lithium niobate material 9 was subjected to a voltage application method by a period of 2.8 μm and a polarization inversion depth of 2.5 μm
m of periodically poled structures 5 were formed.

Next, two rows of grooves 23 having a depth of 1.5 μm and a width of 5 μm were formed on the surface of the material 9 by laser processing using an excimer laser. The interval between the pair of grooves 23 was 5 μm.

Next, the grooved surface 9a of the material 9 is
Substrate 2 (X-cut lithium niobate substrate, 1 m thick
m) was adhered to the surface 2a. As the adhesive, an acrylic room temperature-curable resin was used. The thickness of the bonding layer 3 was about 0.3 μm. The groove 23 is filled with an adhesive.

Next, the material 9 was ground by a mechanical grinding device to obtain the structure shown in FIG. The thickness of the thick part 8 is 3
μm. This substrate was cut in the cross-sectional direction to form a device having a length of 10 mm. Both ends of the optical waveguide were chemically and mechanically polished.

Using this device, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength is 820 nm, and the wavelength of the second harmonic is 410 nm.
Met. When input of fundamental wave is 100mW, 60m
A second harmonic of W was obtained, and no characteristic deterioration due to optical damage or the like was observed.

Example 4 Z-cut lithium niobate material 9 doped with 5 mol% of MgO (thickness: 0.3 m)
m), a periodically poled structure having a period of 2.8 μm was formed by a corona charging method. Specifically, a periodically poled structure having a pitch of 2.7 μm is formed on the + Z plane of the substrate,
By scanning the surface with a corona wire, a domain-inverted structure was generated. The domain-inverted structure was formed uniformly over the entire thickness of the substrate.

Next, a width of 0.5 mm from the material 9 in the Y direction
Was cut out, and the cut surface (X) of the plate was chemically and mechanically polished.

Next, the X-plane of the strip-shaped plate,
The substrate (single crystal silicon, thickness 0.35 mm) was bonded. Acrylic room temperature curing resin was used as the adhesive. The thickness of the adhesive layer 3 was about 0.3 μm. Then
The material 9 was ground by a mechanical grinding device to make the thickness of the material 9A 3.5 μm. Next, the surface of the material 9A was subjected to laser processing using an excimer laser to a depth of 2 μm.
Two rows of grooves 23 having a width of 5 μm and a width of 5 μm were formed. The interval between the pair of grooves 23 was 4 μm.

Next, the substrate is cut in the direction of its cross section,
An element having a length of 10 mm was formed. Both ends of the optical waveguide were chemically and mechanically polished.

Using this device, a second harmonic was generated using a titanium-sapphire laser. The phase matching wavelength is 820 nm, and the wavelength of the second harmonic is 410 nm.
Met. 100m when the fundamental wave input is 150mW
A second harmonic of W was obtained, and no characteristic deterioration due to optical damage or the like was observed.

[0131]

As is apparent from the above, according to the present invention, in the optical waveguide device, even when the output of the light emitted from the optical waveguide is increased, the fluctuation of the output is reduced and the stable oscillation is achieved. Can be realized.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view schematically showing an optical waveguide device 1A according to an embodiment of the present invention, in which a ridge-type three-dimensional optical waveguide 4 and a periodically poled structure 5 are formed. . FIG. 2B is a perspective view schematically showing the element of FIG.

FIGS. 2 (a) and 2 (b) are cross-sectional views schematically showing a process for producing the optical waveguide device of FIG.

FIG. 3 is an enlarged view of a ridge structure portion of the device of FIG. 1;

FIG. 4 is an optical waveguide device 1B according to another embodiment of the present invention.
FIG. 2 is a cross-sectional view schematically showing the device of FIG. 1 from which a thick portion 8 is removed.

FIG. 5 is an optical waveguide device 1C according to another embodiment of the present invention.
Is a cross-sectional view schematically showing a substrate 2 in which a groove 2c is formed.

FIG. 6 is an optical waveguide device 1D according to another embodiment of the present invention.
FIG. 6 is a cross-sectional view schematically showing a substrate 2 in which a groove 2c is formed, and a thick portion 8 is removed from the device of FIG.

FIG. 7 is an optical waveguide device 1E according to another embodiment of the present invention.
1 is a cross-sectional view schematically showing a dielectric-loaded optical waveguide 10.

FIGS. 8A and 8B are cross-sectional views schematically showing a process for producing the optical waveguide device of FIG. 7;

FIG. 9 is an optical waveguide device 1F according to another embodiment of the present invention.
FIG. 8 is a cross-sectional view schematically showing the optical waveguide device of FIG. 7, in which a thick portion is removed.

FIG. 10 is an optical waveguide device 1 according to another embodiment of the present invention.
FIG. 2 is a cross-sectional view schematically showing G, in which a dielectric 12 is loaded on the optical waveguide 10.

FIG. 11 is an optical waveguide device 1 according to another embodiment of the present invention.
FIG. 11 is a cross-sectional view schematically showing H, with the thick portion 8 removed from the device of FIG. 10.

FIG. 12 is a cross-sectional view schematically showing an element 1J according to an embodiment of the present invention, in which a groove 7 is formed in the bonding layer 3 and an extension 15 is removed.

FIG. 13 is a cross-sectional view schematically showing a device 1K according to another embodiment of the present invention, in which an overcoat layer 21 is formed on the entire surface of the device and covers the optical waveguide.

FIG. 14 is a cross-sectional view schematically showing an element 1L according to another embodiment of the present invention.
And a ridge-type optical waveguide 24 protruding from the extension 26 toward the bonding layer 3.

FIGS. 15A, 15B, and 15C are cross-sectional views showing the steps of manufacturing the device of FIG.

FIG. 16 shows a model for calculating a single mode propagation condition of a fundamental wave (excitation light) and a harmonic when a pair of extending portions are formed on both sides of a ridge-type optical waveguide in the device of the present invention.

FIG. 17 shows the height t1 of the ridge portion 4 set to 1.0 μm,
6 is a graph showing a single mode condition of the waveguide when the width w of the ridge portion 4 and the thickness t2 of the extension portion 15 are changed.

FIG. 18 shows that the height t1 of the ridge portion 4 is 2.0 μm,
6 is a graph showing a single mode condition of the waveguide when the width w of the ridge portion 4 and the thickness t2 of the extension portion 15 are changed.

FIG. 19 is a graph showing a relationship between a refractive index difference between an optical waveguide and a bonding layer and an electric field distribution.

FIG. 20 is a graph showing the relationship between the refractive index difference dn between the optical waveguide and the bonding layer when MgO-doped LiNbO3 is used as the optical waveguide, and the maximum thickness satisfying the single mode condition.

FIG. 21 is a schematic diagram showing the relationship between the refractive index of each layer when a three-layer structure of a waveguide, a bonding layer (refractive index of the bonding layer <refractive index of the substrate), and a substrate is adopted.

FIG. 22 is a graph showing the relationship between the intensity of guided light and the depth when a bonding layer is provided.

FIG. 23 is a graph showing the relationship between the guided light intensity and the depth when no bonding layer is provided.

FIG. 24 is a graph showing the relationship between the thickness of the bonding layer, the phase matching wavelength, and the effective refractive index.

FIG. 25 is a perspective view showing a state in which a voltage application method is applied to an off-cut substrate.

FIG. 26 is a schematic diagram showing the direction of a domain-inverted pattern on an off-cut substrate.

FIG. 27 is a cross-sectional view showing an element 1M according to an embodiment of the present invention, in which the three-dimensional optical waveguide 34 includes a pair of protrusions 34a.
And 34b.

FIG. 28 is a sectional view showing an element 1N according to one embodiment of the present invention, in which a concave portion 31 is formed on the surface 2a side of the substrate 2.

FIG. 29 is a cross-sectional view showing an element 1P according to an embodiment of the present invention, in which a concave portion 31 is formed on the surface 2a side of the substrate 2, and a part of the optical waveguide 24A is inserted into the concave portion 31. I have.

FIG. 30 is a cross-sectional view showing an element 1Q according to an embodiment of the present invention, in which a concave portion 31 is formed on the surface 2a side of the substrate 2, and the three-dimensional optical waveguide 34 has a pair of protrusions 34a and 34b. The projection 34 b is inserted into the recess 31.

FIG. 31 is a cross-sectional view showing an element 1R according to an embodiment of the present invention, using two types of bonding layers 3B and 3C.

[Explanation of symbols]

1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1
J, 1K, 1L, 1M, 1N, 1P, 1Q, 1R Optical waveguide element 2 Substrate 2a Substrate surface 2
b Projection of substrate 2c Groove of substrate 3, 3A, 3B, 3C Bonding layer 4, 24 Ridge type three-dimensional optical waveguide 5 Periodically poled structure 7 Groove 8 Thick portion 9 Optical waveguide forming material 9a Material 9 bonding surface REFERENCE SIGNS LIST 10 dielectric-loaded three-dimensional optical waveguide 11 recess 12 dielectric layer
15, 26 A pair of extending portions 17 Grooves on both sides of the ridge structure 18 Ridge structure 21 Overcoat layer 22 Amorphous material filled in the groove 23 23 A groove between the optical waveguide 24 and the thick portion 8 3
0 Underlayer of optical waveguide 4 34 Three-dimensional optical waveguide having a pair of protrusions

Continued on the front page (72) Inventor Kazuhisa Yamamoto 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Tatsuo Kawaguchi 2-56 Sudacho, Mizuho-ku, Nagoya-shi, Aichi Japan (72) Inventor Takashi Yoshino 2-56, Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside Nihon Insulator Co., Ltd. (72) Inventor Kenji Aoki 2-56, Suda-cho, Mizuho-ku, Nagoya, Aichi Prefecture Inside Nihon Insulators Co., Ltd. F term in the company (reference) 2K002 AA01 AB12 CA03 CA22 CA25 DA06 FA27 GA04 HA20

Claims (45)

[Claims] 1. A three-dimensional optical waveguide made of a bulk nonlinear optical crystal, a substrate joined to the optical waveguide, and an amorphous material joining the optical waveguide and the substrate. An optical waveguide device comprising: a bonding layer. 2. The optical waveguide device according to claim 1, wherein said bonding layer functions as an under clad of said optical waveguide. 3. The optical waveguide device according to claim 1, wherein said substrate functions as an under clad of said optical waveguide. 4. The optical waveguide device according to claim 1, wherein a periodically poled structure is formed at least in said optical waveguide, and said optical waveguide element functions as an element for generating harmonics.
The optical waveguide device according to claim 1. 5. The optical waveguide device according to claim 1, wherein a cross-sectional shape of said optical waveguide is substantially rectangular. 6. The optical waveguide device according to claim 1, wherein the optical waveguide is formed by machining the nonlinear optical crystal. 7. The optical waveguide according to claim 1, wherein said optical waveguide is a ridge-type optical waveguide protruding from said bonding layer.
The optical waveguide device according to claim 6. 8. An optical waveguide comprising a pair of extending portions extending toward both sides in a cross-sectional direction of the optical waveguide.
An optical waveguide device according to any one of claims 1 to 7. 9. The optical waveguide device according to claim 8, wherein said optical waveguide protrudes from said extending portion toward said bonding layer. 10. A thick portion made of a bulk nonlinear optical crystal is provided outside each of the extending portions, and a concave portion is formed between the thick portion and the optical waveguide. 10. The optical waveguide device according to claim 9, wherein the concave portion is filled with the amorphous material. 11. The optical waveguide according to claim 1, wherein said optical waveguide is a dielectric-loaded optical waveguide, and further comprises a dielectric layer for forming said optical waveguide. The optical waveguide device according to claim. 12. The optical waveguide device according to claim 11, wherein said dielectric layer faces said substrate with said bonding layer interposed therebetween. 13. The method according to claim 8, wherein single-mode propagation is performed for both the wavelength of the fundamental wave and the wavelength of the converted wavelength wave of said harmonic generation element. An optical waveguide device as described in the above. 14. The optical waveguide according to claim 1, wherein the width of the optical waveguide is 1 to 10 μm, and the height of the optical waveguide from the extending portion is 0.2 to 5 μm.
14. The optical waveguide device according to claim 13, wherein the thickness of the extension is 0.5-5 [mu] m. 15. The optical waveguide device according to claim 1, wherein a refractive index of said bonding layer is lower than a refractive index of said substrate. 16. The optical fiber according to claim 1, wherein the refractive index of said bonding layer is lower than that of said optical waveguide by 5% or more.
The optical waveguide device according to claim 4. 17. The substrate according to claim 1, wherein a refractive index of said substrate is slightly lower than a refractive index of said optical waveguide, and an electric field distribution of an optical waveguide mode propagating through said optical waveguide exists in said substrate. The optical waveguide device according to any one of -14. 18. The method according to claim 17, wherein a difference between a refractive index of said substrate and a refractive index of said waveguide is 5% or less.
An optical waveguide device as described in the above. 19. The optical waveguide device according to claim 1, wherein said bonding layer is made of glass containing silicon oxide as a main component. 20. The optical waveguide according to claim 11, wherein the optical waveguide is LiNb _x Ta _(1-x).
20. The optical waveguide device according to claim 1, wherein the optical waveguide device is made of a nonlinear optical material containing O ₃ (0 ≦ x ≦ 1) as a main component. 21. The optical waveguide device according to claim 20, wherein said bonding layer is made of glass containing silicon oxide as a main component, and said bonding layer has a thickness of 0.1 μm or more. 22. An apparatus according to claim 1, further comprising an overcoat layer covering at least said optical waveguide.
The optical waveguide device according to claim 21. 23. A three-dimensional optical waveguide comprising a bulk nonlinear optical crystal, and an under cladding of the optical waveguide, wherein the three-dimensional optical waveguide can confine light by machining the nonlinear optical crystal. An optical waveguide device, wherein the optical waveguide device is formed to have an appropriate thickness, and the undercladding is made of an amorphous material. 24. The semiconductor device according to claim 23, further comprising a substrate joined to the optical waveguide, wherein the under cladding is a joining layer joining the optical waveguide and the substrate. An optical waveguide device as described in the above. 25. A semiconductor device comprising: a substrate joined to the optical waveguide; and a joining layer joining the optical waveguide and the substrate, wherein the substrate also functions as the under cladding. The optical waveguide device according to claim 23, wherein: 26. A semiconductor device according to claim 23, wherein a periodically poled structure is formed at least in said optical waveguide, and said optical waveguide element functions as an element for generating harmonics.
The optical waveguide device according to claim 25. 27. The optical waveguide device according to claim 23, wherein a cross-sectional shape of said optical waveguide is substantially rectangular. 28. The optical waveguide device according to claim 23, wherein said optical waveguide is a ridge type optical waveguide. 29. The optical waveguide according to claim 23, wherein the optical waveguide is a dielectric-loaded optical waveguide, and further comprises a dielectric layer for forming the optical waveguide. The optical waveguide device according to claim. 30. The optical waveguide device according to claim 24, wherein a refractive index of said bonding layer is lower than a refractive index of said substrate. 31. The method according to claim 24, wherein the refractive index of the bonding layer is lower than that of the waveguide by 5% or more.
The optical waveguide device according to claim 9. 32. The substrate according to claim 24, wherein the refractive index of the substrate is slightly lower than the refractive index of the optical waveguide, and an electric field distribution of an optical waveguide mode propagating through the optical waveguide exists in the substrate. The optical waveguide device according to any one of -29. 33. The method according to claim 3, wherein a difference between a refractive index of the substrate and a refractive index of the optical waveguide is 5% or less.
3. The optical waveguide device according to 2. 34. The optical waveguide device according to claim 23, wherein said amorphous material is glass containing silicon oxide as a main component. 35. The optical waveguide according to claim 30, wherein the optical waveguide is LiNb _x Ta _(1-x).
The optical waveguide device according to any one of claims 23 to 34, wherein the optical waveguide device is made of a nonlinear optical material containing O ₃ (0 ≦ x ≦ 1) as a main component. 36. The optical waveguide according to claim 35, wherein the amorphous material is glass containing silicon oxide as a main component, and the thickness of the amorphous material is 0.1 μm or more. element. 37. The three-dimensional optical waveguide is formed by processing an optical waveguide molding material made of a bulk nonlinear optical crystal, wherein the optical waveguide molding material is made of an off-cut substrate, and the nonlinear optical crystal is made of an off-cut substrate. 37. The optical waveguide device according to claim 1, wherein a C-axis of the optical waveguide device is inclined with respect to a normal to a surface of the off-cut substrate. 38. The optical waveguide device according to claim 37, wherein a C-axis of said nonlinear optical crystal is inclined by 3 ° or more and 87 ° or less with respect to a normal to a surface of said off-cut substrate. . 39. An X-axis of the nonlinear optical crystal is parallel to a surface of the off-cut substrate.
An optical waveguide device according to claim 37 or 38. 40. A material for forming an optical waveguide made of a bulk nonlinear optical crystal is bonded to a separate substrate via a bonding layer made of an amorphous material. A method of manufacturing the optical waveguide element, wherein the three-dimensional optical waveguide is formed by lowering the refractive index of the bonding layer than the refractive index, and then processing the optical waveguide forming material. 41. A material for molding an optical waveguide made of a bulk nonlinear optical crystal is bonded to a separate substrate via a bonding layer made of an amorphous material. A method of manufacturing the optical waveguide element, wherein the three-dimensional optical waveguide is formed by lowering the refractive index of the substrate than the refractive index, and then processing the optical waveguide forming material. 42. A method of forming a periodically poled structure on the bonding surface side of the optical waveguide molding material to the substrate, and thereafter bonding the optical waveguide molding material to the substrate. The method for manufacturing an optical waveguide device according to claim 40 or 41. 43. The optical waveguide molding material according to claim 40, wherein after bonding the optical waveguide molding material to the substrate, the optical waveguide molding material is machined. A method for manufacturing an optical waveguide device. 44. An optical wavelength conversion element having a three-dimensional optical waveguide made of a slab-shaped nonlinear optical crystal and a cladding layer made of an amorphous material on upper and lower surfaces of the optical waveguide. 45. The optical wavelength conversion device according to claim 44, wherein said optical waveguide satisfies a single mode condition for guided light.