JPH07114050A - Waveguide type wavelength conversion element - Google Patents

Abstract

PURPOSE:To provide the waveguide type wavelength conversion element which is greatly widened in the permissible width of the film thicknesses of waveguide layers at phase matching points, is enhanced in wavelength conversion efficiency and is easily producible. CONSTITUTION:At least either of the first layer 3 and second layer 2 of the four-layered waveguide type wavelength conversion element consist of linear media and at least one of the four layers consist of nonlinear media. The respective refractive index dispersions of the four layers are selected in such a manner that such ranges of the thicknesses of the first layer 3 and second layer 2 as to bring the respective dispersion curves of basic waves and second harmonic wave into contact with each other attain several tens Angstrom or above in the waveguide mode dispersion curves indicating a relation between the respective thicknesses of the first layer 3 and the second layer 2 and effective refractive indices.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type non-linear optical element, especially a wavelength converting element, which is useful for wavelength conversion of laser light and parametric amplification in the fields of optical communication and optical information processing.

[0002]

2. Description of the Related Art It is expected that a visible light coherent light source will be realized by using a semiconductor laser or the like as a fundamental light source and shortening its wavelength by a non-linear optical (NLO) element. The development of nonlinear optical materials for wavelength conversion (mainly second harmonic generation, hereinafter also referred to as SHG) has been extensively studied regardless of whether it is an inorganic or organic material. The technology is not established.

As a method of manufacturing a wavelength conversion element, a method of directly combining a bulk single crystal with a semiconductor laser, a method of inserting a crystal into an optical resonator and a method of using a thin film optical waveguide are used. Divided into streets.

In the method using a single crystal, (a) a single crystal of high quality and a size suitable for processing is required, (b) processing in the phase matching direction of the crystal is indispensable, and (c) polishing of the processed surface. It is necessary to process the non-reflective film and d) When using the resonator type, additional technology is indispensable, such as controlling the resonator. To satisfy these requirements, There are many problems that are difficult to solve.

On the other hand, in the method of using as a thin film optical waveguide, since the light wave power can be confined in a minute waveguiding layer of the order of several μm and the light can be propagated, a high light wave power density can be utilized and the optical waveguide In addition, it has the advantage that highly efficient wavelength conversion can be expected without using a resonator structure. Furthermore, there is an advantage that a nonlinear optical tensor which cannot be used in the method using a single crystal can be effectively used. However, conventionally, when the thin film optical waveguide is applied to a wavelength conversion element, it is necessary to control the film thickness of the waveguide layer with high accuracy, and it is technically difficult to manufacture a practical device.

Further, in order to efficiently obtain the second harmonic (hereinafter, also referred to as SH wave) in the optical waveguide type wavelength conversion element, 1) achieving phase matching with a long interaction length,
2) It is important to increase the overlap integral of the fundamental wave mode and the second harmonic mode. 1) is the propagation constant of the fundamental wave and the SH wave generated in the waveguide, that is,
It means that the phase velocities, that is, the effective refractive indexes are made equal.
2) means increasing the overlap between the amplitude distribution functions of the fundamental wave mode and the SH wave mode. If this overlap is small, conversion of light wave power will not occur sufficiently. The overlapping of the amplitude distribution functions can be realized by using conversion between lights of low-order modes. Therefore, the overlap of the amplitude distribution functions can be increased by appropriately selecting the refractive index of the waveguide layer and the substrate. For that purpose, the thickness of the waveguide layer is about 0.5 to 1 μm.
It is necessary to use about m waveguides.

As the phase matching method of 1), the mode dispersion peculiar to the waveguide can be used. In this case, the fundamental wave and S
The waveguide type wavelength conversion element may be manufactured by controlling the film thickness of the waveguide so that the effective refractive index of the H wave becomes equal. However, this is known to be technically very difficult. For example, see Shinsuke Umegaki, “Organic Nonlinear Optical Materials” (Bunshin Publishing, 1990). In the most common 3-layer waveguide (upper clad / waveguide layer / substrate),
SHG that is considered to have practical SHG conversion efficiency
The film thickness of the waveguide layer in the half-width of conversion efficiency (FWHM) is about several tens to 10 angstroms. In other words, the fluctuation of the wavelength of the fundamental wave must be controlled within about 0.1 nm to several nm. It is almost impossible to control the film thickness of the waveguide layer having a thickness of about 1 μm within the range of several angstroms by the current thin film manufacturing technology. Therefore, as an alternative method, the temperature of the waveguide is changed, an effective electric field is applied to change the effective refractive index or the film thickness, or a tapered waveguide layer (the film thickness of the waveguide layer is gradually changed). However, it has not been put to practical use yet.

[0008]

As described above, it is technically impossible to put into practical use a three-layer structure waveguide in which the thickness of the waveguide layer needs to be controlled within the range of several angstroms.
Therefore, the object of the present invention is to solve the above technical problems,
Significantly widening the allowable thickness of the waveguide layer at the phase matching point,
An object of the present invention is to provide a waveguide type wavelength conversion element which can increase the wavelength conversion efficiency and is easy to manufacture.

[0009]

As a result of intensive studies to solve the above problems, the present inventors have found that when the structure of the waveguide type wavelength conversion element has four layers, the film thickness of the waveguide layer is large. It has been found that the control can be relaxed and the object of the present invention can be achieved.

That is, according to the present invention, a waveguide type wavelength conversion element having a four-layer structure is provided. The waveguide type wavelength conversion element of the present invention is a substrate made of a linear or non-linear medium; a first layer provided on the substrate and made of a linear or non-linear medium having a refractive index higher than that of the substrate. First
A second layer overlying the first layer, the second layer comprising a linear medium having a refractive index greater than that of the substrate; and an upper cladding layer overlying the second layer, A four-layer waveguide type wavelength conversion element comprising a linear or nonlinear medium having a refractive index smaller than that of the first layer 3 and the second layer. At least one of the layers 2 comprises a linear medium and at least one of the four layers comprises a non-linear medium, and
In the guided mode dispersion curve showing the relationship between the respective thicknesses of the second layer and the second layer and the effective refractive index, the first layer and the second layer such that the respective dispersion curves of the fundamental wave and the second harmonic contact each other. The refractive index dispersion of each of the four layers is selected so that the thickness range (i.e., the allowable film thickness at the phase matching point) is several tens of liters or more.

As described above, in the conventional three-layer waveguide type wavelength conversion element, as shown in FIG. 6, the fundamental wave in the waveguide mode dispersion curve showing the relationship between the thickness of the waveguide layer and the effective refractive index is used. The respective dispersion curves of the second harmonic simply intersect. In other words, the allowable width of the thickness of the waveguide layer at the phase matching point of the fundamental wave and the second harmonic that can obtain a practical wavelength conversion efficiency is about 10 angstroms at most. On the other hand, in the present invention, the waveguide type wavelength conversion element has a four-layer structure, and by appropriately selecting the refractive index dispersion of each layer, the dispersion curves of the fundamental wave and the second harmonic wave are partially It will overlap. In other words, the allowable width of the thickness of the waveguide layer at the phase matching point between the fundamental wave and the second harmonic is several tens of liters.
That is all. The allowable width is preferably about 30Å or more, particularly preferably about 100Å or more, and further preferably about 300Å or more.

In the present invention, the linear medium means a substance whose interaction with light is linear. Linear media that may be used in the present invention include, for example, dielectrics of inorganic materials such as various glasses, especially SF15 glass, SFS01 glass,
LaK011 glass, BK6 glass, BK7 glass, B
Glass such as SK7 glass, SK4 glass and SF9 glass, quartz, sapphire, tantalum pentoxide (Ta ₂ O ₅ ),
Silicon dioxide (SiO ₂ ) and the like are available. In addition to these solid materials, gases such as air can also be used as the linear medium. Therefore, for example, when air is used as the linear medium for the upper cladding layer, the 4-layer waveguide type wavelength conversion element of the present invention apparently has a 3-layer structure.

In the present invention, the nonlinear medium is
A substance that undergoes a secondary or higher-order nonlinear interaction when light is incident. In the present invention, a substance having a second-order nonlinear optical effect is preferably used as the nonlinear medium. Non-linear media that can be used in the present invention include:
For example, ZnS, lithium niobate (LiNbO ₃ ),
Lithium tantalate (LiTaO ₃ ), potassium titanate phosphate (KTP), potassium dihydrogen phosphate (KD
P), ammonium dihydrogen phosphate (ADP), potassium dihydrogen arsenate (KDA), ammonium dihydrogen arsenate (AD)
Inorganic compounds such as A), urea, 2-methyl-4-nitroaniline (MNA), m-nitroaniline, p-nitroaniline, N, N-dimethyl-2-acetylamino-4-
Nitroaniline (DAN), 3-methyl-4-nitropyridine-N-oxide (POM), N- (4-nitrophenol)-(L) -purinol (NPP), 3,5-
Dimethyl-1- (4-nitrophenyl) pyrazole, 4
-Dimethylamino-4'-nitrostilbene (DEAN
S), N-isopropyl-N '-(4-acetylphenyl) urea, N- (4-nitrophenyl) -N-methylaminoacetonitrile (NPAN), 2-cyclooctylamino-5-nitropyridine (COANP), Cyanine-p-toluenesulfonic acid, organic compounds such as N- {5- (2-nitro) -pyridyl} -propynol, polymer materials such as poled polymers, sol-gel glass nonlinear optical materials, Langmuir -Blodgett film (hereinafter, also referred to as LB film), such as a non-linear optical material. Furthermore, the nonlinear optical materials described in Japanese Patent Application No. 4-268283 and Japanese Patent Application Laid-Open No. 6-18946 can also be used.

The poled polymer is a polymer containing atomic groups having a nonlinear optical effect, and the atomic groups are oriented in a certain direction. Such polymers include, for example, polyvinyl alcohol having p-nitroaniline as a pendant group (PVA-PNA) and poly [6- (4-nitrobiphenyloxy) as described in International Application WO92 / 07288. Hexyl methacrylate], poly [L-N-p-nitrophenyl-
2-piperidine methyl acrylate], 4- [N-
(2-methacryloyloxyethyl) -N-methylamino] -4′-nitrostilbene and a copolymer of C ₁ -C ₆ alkyl acrylate or methacrylate. One of the means for orienting atomic groups having a nonlinear optical effect in these polymers is poling (polin
There is g). In order to carry out poling, first, the above polymer is formed into a film by a method such as spin coating, and the film is heated to room temperature or higher, typically to the glass transition temperature of the polymer or higher. When an electric field is applied to the polymer under heating (for example, DC50 to 150
V / μm), the atomic group having a dipole moment is oriented in the direction of the applied electric field. The electric field is preferably applied so that the largest NLO tensor exists in the waveguide cross section. When the polymer is cooled to room temperature while maintaining this state, a film in which the above atomic groups are oriented in a certain direction can be obtained.

[0015] The LB film nonlinear optical material is a nonlinear optical effect.
It refers to an LB film composed of a single molecule having fruits. The unit
A child typically has an aliphatic main chain at both ends.
It has a hydrophilic group and a hydrophobic group, respectively, and has an electron as a side chain.
It has an atomic group of π-electron conjugated system including a donor and an electron acceptor.
To do. The nonlinear optical activity of LB film is
There are many reports, among them, hemicyanine, merocyanine
Type, azo type, nitroaniline type, aminobenzoic acid type and
The stilbene system is being studied. For example, J.
D. Swalen's Annu. Rev. Mater. First
See Volume 373, page 21 (1991).

The sol-gel glass non-linear optical material is a non-linear optical material which is subjected to poling in the process of hydrolyzing / gelling a metal alkoxide mixed with an organic molecule having a non-linear optical effect so that the organic molecule having a non-linear optical effect is oriented in a certain direction. It means an amorphous body. Pauling is performed by applying an electrostatic field while heating to room temperature or higher after forming an amorphous thin film on a glass substrate using a method such as spin coating, as in the case of producing a poled polymer film. It can be carried out.

Examples of the metal alkoxide include Si
A silicon alkoxide represented by (OR) ₄ can be used. Here, R is a methyl group, an ethyl group, a propyl group, or the like. For example, a silicon alkoxide is used as a metal alkoxide, water and an alcohol such as methanol are added thereto, and a mixed solution in which organic molecules having a nonlinear optical effect are mixed is coated on a substrate and subjected to hydrolysis / dehydration condensation at room temperature. Make progress. Silicon alkoxide is hydrolyzed to SiO ₂ , which is dehydrated and condensed to become a solid called gel. In this case, it is considered that the organic molecule having the nonlinear optical effect is incorporated into the SiO ₂ network structure without being affected by the structure.

Organic molecules having a nonlinear optical effect used in the sol-gel glass nonlinear optical material include, for example, nitro-2-aminotoluene, chloro-4-nitroaniline, 2-methyl-4-nitro-N-methylaniline. Two
-Amino 3-nitropyridine. 2-chloro-3,5-dinitropyridine, 1,3-dimethylurea, 5-indole and the like.

In the waveguide type wavelength conversion element of the present invention, at least one of the first layer 3 and the second layer 2 is made of a linear medium. That is, one of the first layer 3 and the second layer 2 is made of a linear medium, or both layers are made of a linear medium. In the former case, the refractive index of the layer made of the linear medium is preferably higher than the refractive index of the other layer from the viewpoint of device fabrication. In the latter case, it is preferable that the refractive index of the second layer 2 is larger than that of the first layer 3.

In the waveguide type wavelength conversion element of the present invention, a nonlinear medium is used in at least one of the four layers. The nonlinear media used for these layers may be the same or different. However, of the first layer 3 and the second layer 2, it is preferable not to use a non-linear medium for the layer acting as a waveguide layer. The reason for this is that it is theoretically possible to use a nonlinear medium for the waveguide layer, but precise control of the film thickness of a thin film made of a nonlinear medium is
This is because it is technically much more difficult than controlling the film thickness of a thin film made of a linear medium, and is not advantageous.

In a preferred embodiment of the invention, the substrate 4, the first layer 3 and the second layer 2 are made of a linear medium,
It is technically advantageous to manufacture the upper clad layer 1 from a nonlinear medium. The reason is that, as described above, the waveguide layer in the waveguide type wavelength conversion element of the present invention is both the first layer 3 and the second layer 2 or either one of them. This is because it is technically very difficult to control the film thickness when a non-linear medium is used for these layers that act as. Therefore, it is preferable to use a linear medium for the first layer 3 and the second layer 2. When a nonlinear medium is used for the upper clad layer 1, the nonlinear polarization wave is generated by the leaching of the guided mode, that is, the evanescent wave, so that the power transfer, that is, the overlap integral is performed in the upper clad layer 4. .

When a linear medium is used for the substrate 4 and the upper cladding layer 1 and a nonlinear medium is used for either the first layer 3 or the second layer, the nonlinear medium may be an organic or inorganic material. It is preferred to use crystals of nonlinear optical materials, poled polymers, sol-gel glass NLO materials or LB film NLO materials.

In a further preferred embodiment of the invention, the substrate 4 is made of glass, the first layer 3 and the second layer 2 are made of an inorganic dielectric, and the upper cladding layer 1 is a crystal of an organic or inorganic nonlinear optical material. , Poled polymer or N-isopropyl-N '-(4-acetylphenyl) urea or N
It consists of-(4-aminobenzenesulfonyl) acetamide. In this case, it goes without saying that the refractive indices of the inorganic dielectric materials forming the first layer 3 and the second layer 2 are different.

When designing the waveguide type wavelength conversion element of the present invention, it is generally advantageous to follow the following procedure.
First, of the four layers constituting the waveguide type wavelength conversion element of the present invention, what kind of material is used for the layer using the nonlinear medium, for example, the upper clad layer or the first layer is selected. At the time of selection, the degree of nonlinear optical effect of the substance, easiness of processing, refractive index, etc. are considered. The material used for the layer with the linear medium is then selected. When selecting the linear medium, a waveguide mode dispersion curve showing the relationship between the thickness of each of the first layer and the second layer and the effective refractive index is drawn by theoretical calculation described later, and the fundamental wave and the second harmonic wave are drawn. A substance having a refractive index dispersion is selected so that the thickness ranges of the first layer and the second layer with which the respective dispersion curves are in contact are several tens of liters. When there is no single linear medium that has a refractive index that meets the optimum conditions and is transparent in the visible light region, a composition in which two or more substances are combined in a specific composition can be used as the linear medium. . For example, it has been reported that a composite thin film having a refractive index dispersion corresponding to a composition ratio can be obtained by a sputtering method using a target in which a substance having a large refractive index and a substance having a small refractive index are compounded in arbitrary compositions. In this regard, A of M. Kobayashi and H. Terui
See ppl.Opt., vol.22, No.19, p.3121. Thus, by using the transparent two-component composite target and adjusting the composition ratio thereof, a transparent thin film having an ideal refractive index dispersion can be produced. As an example, when the required refractive index is around 2.2 to 2.3, 2
Sputtering was performed using a target in which zinc sulfide (ZnS, n = 2.3 to 2.4) and silicon dioxide (SiO ₂ , n = 1.45) were mixed as a component at a molar ratio of about 9: 1, A thin film having a desired refractive index dispersion can be produced.

One mode of the waveguide type nonlinear optical element of the present invention is shown in FIG. 1 is an upper clad (refractive index n ₁ ), 2 is a waveguide layer with a thickness d (refractive index n ₂ ), 3 is a waveguide layer with a thickness w (refractive index n ₃ ), and 4 is a substrate (refractive index n _4). ).
The waveguide mode dispersion equation of this waveguide type nonlinear optical element is represented by the following equation (1) or equation (2).

N ₁ , n ₄ <n ₃ , n _2, and n ₁ and n
_When n _clad <N _eff <n _core1 , the larger one of ₄ is n _clad , the smaller one of n ₂ and n ₃ is n _core1 , and the larger one is n _core2.

[Equation 1] ii) When n _core1 <N _eff <n _core2

[Equation 2] Here, C _{1 to} C ₄ are TE mode C ₁ = C ₂ = C ₃ = 1 TM mode

[Equation 3] In addition, k _{1 to} k ₄ are

[Equation 4] Further, m is a mode order, m = 0, 1, 2, ..., β is a propagation constant, β = k ₀ N _eff , and k ₀ is 2π / λ, where λ is the wavelength of the laser light, and N _eff is the effective refractive index.

As described above, it is understood that the layer acting as the waveguide layer is different depending on the magnitude of the values of N _eff , n ₂ and n ₃ . That is, n ₂ > n ₃ and N _eff <n
_{If 3} <n ₂ , both the first layer 3 and the second layer 2 act as a waveguiding layer. In this case, it is preferable that both the first layer 3 and the second layer 2 are made of a linear medium. On the other hand, when n ₃ <N _eff <n ₂ , only the second layer 2 acts as a waveguide layer. In this case, the second layer 2 preferably comprises a linear medium. If a non-linear medium is used for the second layer 2, this non-linear medium is preferably a poled polymer or LB film NLO material.

On the other hand, n ₂ <n ₃ and N
_{If eff} <n ₂ <n ₃ , both the first layer 3 and the second layer 2 act as a waveguiding layer. In this case, it is preferable that both the first layer 3 and the second layer 2 are made of a linear medium. On the other _hand, in the case of _{n 2 <N e ff <n} 3 is
Only the first layer 3 acts as a waveguiding layer. In this case, the first layer 3 preferably consists of a linear medium. If a non-linear medium is used for the first layer 3, this non-linear medium is preferably a poled polymer or LB film NLO material.

As described above, in the present invention, it is preferable that, of the first layer 3 and the second layer 2, the layer acting as a waveguide layer is made of a linear medium. This is the fundamental wave and the second
In order to achieve phase matching with higher harmonics, it is necessary to precisely control the thickness of the waveguide layer as described above, and it is easier to control the thickness of a linear medium than a nonlinear medium. When a nonlinear medium is used for the waveguide layer, it is of course possible to control the thickness by using a crystalline material such as a crystal of an organic or inorganic nonlinear optical material, but preferably a poled polymer or More preferably LB film NLO
It is easier to control the thickness when using a material.

Further, TE in the waveguide type wavelength conversion element
The conversion efficiency of the SHG of the (ω) → TE (2ω) conversion is represented by the following formula (3).

[0031]

[Equation 5] Here, P (ω) is the power of the fundamental wave, and P (2ω)
Is the power of the second harmonic, d is the nonlinear optical constant, I _nm is the overlap integral, W _eff is the effective film thickness, L is the interaction distance (propagation length), and D is the fundamental. The spread width of the light wave mode in the y direction, and Δβ is the amount of phase mismatch, which is represented by β ^(2ω) −2β ^(ω) .

Similarly, the SHG conversion efficiency of TM (ω) → TM (2ω) conversion is expressed by the following equation (4).

[0033]

[Equation 6] As is clear from the above equation, in order to improve the efficiency in the waveguide type wavelength conversion element, it is important to make the phase matching between the fundamental wave and the SH wave a long interaction length and increase the overlap integral. .

Next, the model calculation of the optimum four-layer structure slab waveguide type wavelength conversion element will be shown, and the effect of relaxing the control of the thickness of the waveguide layer will be explained together with the theoretical efficiency of wavelength conversion.

Calculation Example 1 SF15 glass is used for the upper clad 1 and the substrate 4 in FIG. 1, SFS01 glass is used for the second layer 2, and N-isopropyl-N which is an organic nonlinear optical material is used for the first layer 3. '-(4-acetylphenyl) urea (hereinafter,
The refractive index dispersion of the fundamental wave and SH wave of a four-layer slab waveguide type wavelength conversion element using IAPU) was calculated. Here, the wavelength of the fundamental wave is 0.86 μm, and the wavelength of the SH wave is 0.
The thickness of the first layer 3 was 43 μm, and the thickness of the first layer 3 was 0.4 μm. The result is shown in FIG. In FIG. 2, the horizontal axis represents the thickness of the second layer 2, and the vertical axis represents the effective refractive index of the waveguide layer.
The lower limit of the vertical axis is the refractive index of the fundamental wave of SF15 glass, and the upper limit is the refractive index of the SHG wave of SFS01 glass. Further, the solid line represents the refractive index dispersion of the fundamental wave, and the broken line represents S
It represents the refractive index dispersion of H waves.

As is clear from FIG. 2, TE0 of the fundamental wave
The second mode and the TE second mode of the SH wave are phase-matched, and in this case, the allowable width of the film thickness of the second layer 2 and the first layer 3 is about 100Å, and the allowable width can be extremely wide. I understand.

Also, d ₂₂ = 40 pm / V, L = 5 m
When m, P (ω) = 100 mW and D = 0.1 mm, the wavelength conversion efficiency is about 3 to 5%.

Calculation Example 2 IAPU is used for the upper clad 1 in FIG. 1, and a dielectric thin film with n ₂ (ω) = 2.0 and n ₂ (2ω) = 2.06 is used for the second layer 2. In the first layer 3, n ₃ (ω) = 1.
83, n ₃ (2ω) = 1.887 was used, and the refractive index dispersion of the fundamental wave and SH wave of the four-layer slab waveguide type wavelength conversion element using SF15 glass for the substrate 4 was calculated. . The conditions are the same as in Calculation Example 1. The result is shown in FIG. In FIG. 3, the lower limit of the vertical axis is IAPU.
2 is the same as that of FIG. 2 except that the upper limit is the refractive index of the SHG wave of the dielectric of the second layer 2.

From FIG. 3, the TE0 order mode of the fundamental wave and SH
The TE first-order mode of the wave is phase-matched, and the thickness allowable widths of the second layer 2 and the first layer 3 in that case are about 80, respectively.
It is Å and about 300Å, and it can be seen that the allowable width can be made very wide.

Also, d ₂₂ = 40 pm / V, L = 5 m
When m, P (ω) = 100 mW and D = 0.1 mm, the wavelength conversion efficiency is about 1 to 3%.

Calculation Example 3 LiTaO ₃ was used for the upper clad 1 in FIG. 1, a ZnS thin film was used for the second layer 2, and ZnS--S was used for the first layer 3.
Using an iO ₂ thin film (molar ratio of ZnS: 10 mol%, n ₃
(Ω) = 1.83, n ₃ (2ω) = 1.8787), and the basics of a four-layer slab waveguide type wavelength conversion element using ZnS—SiO ₂ (ZnS mole ratio: 25 mole%) for the substrate 4. The refractive index dispersion of the wave and SH wave was calculated. Here, the same conditions as in Calculation Example 1 were used except that the wavelength of the fundamental wave was 0.9 μm and the wavelength of the SH wave was 0.45 μm. The result is shown in Figure 4.
Shown in. In FIG. 4, the lower limit of the vertical axis is the refractive index of the fundamental wave of LiTaO ₃ , and the upper limit is the SHG of the ZnS dielectric.
2 except that it is the refractive index of the wave.

From FIG. 4, the TE0 order mode of the fundamental wave and SH
The TE second-order modes of the waves are phase-matched, and in that case, the film thickness allowable widths of the second layer 2 and the first layer 3 are each about 10
It is 0Å, and it can be seen that the allowable range can be made very wide.

Also, d = 20 pm / V, L = 5 mm, P
When (ω) = 100 mW and D = 0.1 mm, the wavelength conversion efficiency is about 0.2%.

Calculation Example 4 PVA-PNA (paranitroaniline) poled polymer was used for the upper clad 1 in FIG. 1, LaK011 glass thin film was used for the second layer 2, and SF9 glass thin film was used for the first layer 3. Then, the refractive index dispersion of the fundamental wave and the SH wave of the four-layer slab waveguide type wavelength conversion element using BK6 glass for the substrate 4 was calculated. Here, the wavelength of the fundamental wave is 1.06
4 μm, the wavelength of SH wave is 0.532 μm, and the first
The layer 3 had a thickness of 0.8 μm. The result is shown in FIG. In FIG. 5, the lower limit of the vertical axis is the refractive index of the fundamental wave of BK6 glass, and the upper limit is the same as that of FIG. 2 except that it is the refractive index of the SH wave of LaK011 glass.

From FIG. 5, the TM0 order mode of the fundamental wave and the SH
It can be seen that the TM first-order mode of the wave is phase-matched and the film thickness allowable width of the second layer 2 and the first layer 3 in that case is about 200 Å, and the allowable width can be made very wide.

Also, d = 20 pm / V, L = 5 mm, P
When (ω) = 100 mW and D = 0.1 mm, the wavelength conversion efficiency is about 0.3%.

When manufacturing the waveguide type wavelength conversion element of the present invention, a known thin film forming method or the like can be used. For example, when the first layer 3, the second layer 2 and the upper cladding layer 1 are provided on the substrate 4, when these layers are made of a linear medium, vapor deposition, sputtering, ion plating, chemical A method such as vapor phase growth method (CVD) can be used. For this, refer to "The Handbook of Thin Film Fabrication", Kyoritsu Shuppan, 1991, edited by Japan Society of Applied Physics / Subcommittee for Thin Film and Surface Physics. On the other hand, when these layers are made of a non-linear medium, a crystal growth method such as a spin coating method, a Bridgman method (melt method), or a solvent evaporation method can be used. When using the solvent evaporation method, it is important to crystallize so that the largest NLO tensor is oriented parallel or perpendicular to the substrate. For this purpose, a method of crystallizing while applying an electric field can be used.

As described above, it is preferable to use a linear medium for the layer that acts as the waveguiding layer, but it is of course possible to use a nonlinear medium. When manufacturing such a wavelength conversion element, first, a channel-type four-layer structure waveguide having a hollow core in a layer functioning as a waveguide layer is formed by lithography and sputtering using an appropriate material, Finally, a method of sucking a nonlinear medium into the hollow core portion to grow a single crystal from a melt or a solution can be used. When a poled polymer is used for the waveguiding layer, a polymer prepared by dissolving a polymer containing an atomic group having a non-linear optical effect in an appropriate solvent such as trichloropropane is applied by spin coating and then poling is performed. Corrugated layers can be formed. Further, when the LB film NLO material is used for the waveguide layer, the waveguide layer can be formed using a commercially available LB film manufacturing apparatus.

In order to perform the wavelength conversion of light with high efficiency, it is also important to enhance the input / output coupling of light. In the waveguide type wavelength conversion element of the present invention, both the first layer 3 and the second layer 2 act as a waveguide layer, or either one acts as a waveguide layer. In this case, since these layers are made of a linear medium, it is easy to optically polish the end faces of the layers or apply a non-reflection coating, and the input / output coupling can be further enhanced. Further, since it is possible to provide a grating between the layer acting as the waveguiding layer and the substrate 4 by the interference exposure method, it is possible to achieve highly efficient coupling.

In order to further improve the efficiency of wavelength conversion of light, the waveguide may be channelized. Ideally, it is possible to improve the efficiency by 10 times or more by forming a channel, so that SH light can be obtained with a conversion efficiency of 10% or more. The channel is formed by forming the four-layer waveguide of the present invention and then performing fine processing such as etching by a lithography technique, or forming the waveguide up to the third layer and then forming the channel, and then forming the upper clad layer on the channel. It is achieved by applying.

The present invention will be described in more detail by the following examples, which are not intended to limit the scope of the present invention.

[0052]

Example 1 On a SF15 glass plate, Ta ₂ O ₅ —Si was formed.
An O ₂ (Ta ₂ O ₅ molar ratio: 58 mol%) mixed thin film was sputtered so that the film thickness was about 0.42 μm. On this thin film, Ta ₂ O ₅ —SiO ₂ (Ta ₂ O ₅ molar ratio: 7
The mixed thin film (6 mol%) was sputtered to a film thickness of about 0.25 μm. On this mixed thin film, IAPU was crystallized from a methanol solution by a solvent evaporation method to prepare a four-layer slab waveguide type wavelength conversion element. At this time, IAP
The U crystal was crystallized such that its largest NLO tensor, d _22, was aligned parallel to the substrate. A Ti: sapphire laser was applied as a fundamental wave to the end face of the thus obtained waveguide element. As a result, the wavelength of the fundamental wave is 855-
In the range of 865 nm, blue light, which is the second harmonic, was generated with high efficiency.

[0053]

Example 2 On a BSL7 glass plate, Ta ₂ O ₅ —Si was formed.
An O ₂ (Ta ₂ O ₅ molar ratio: 40 mol%) mixed thin film was sputtered so that the film thickness was 0.25 μm. The refractive index dispersion of this thin film is n (ω) = at a wavelength of 884 nm.
1.863 and n (2ω) = 1.929.

On this thin film, Ta ₂ O ₅ --SiO
_A mixed thin film of ₂ (Ta ₂ O ₅ molar ratio: 85 mol%) was sputtered to a film thickness of 0.2 μm. The refractive index dispersion of this thin film is n (ω) = 2.0 at a wavelength of 884 nm.
37 and n (2ω) = 2.138.

On this mixed thin film, IAPU was crystallized from a methanol solution by a solvent evaporation method to prepare a four-layer slab waveguide type wavelength conversion element. In this case, the allowable range of film thickness was about 100Å or more. At this time, the IAPU crystal was crystallized so that its maximum NLO tensor, d ₂₂ was aligned parallel to the substrate.

A Ti: sapphire laser was made to enter the end face of the thus obtained waveguide device as a fundamental wave.
As a result, blue light, which is the second harmonic, was generated with high efficiency in the range where the wavelength of the fundamental wave was 875 to 895 nm.

[0057]

On Example 3 BK7 glass _plate, Ta ₂ O 5 -SiO
_{A 2} (Ta ₂ O ₅ mol ratio: 75 mol%) mixed thin film was sputtered to a film thickness of 0.31 μm. The refractive index dispersion of this thin film is n (ω) = at a wavelength of 1064 nm.
The values were 2.025 and n (2ω) = 2.080.

PVA-PNA was spin-coated on this thin film at 80 ° C. to a film thickness of 0.325 μm,
The solvent was dried at 100 ° C. for 2 hours and then subjected to corona poling at a voltage of 5 kV. The poling temperature is 150 ° C,
The polling time was 15 minutes. In this case, the upper cladding layer is air.

A YAG laser (wavelength 1064 nm) was made to enter the end face of the thus obtained four-layer waveguide type wavelength conversion element as a fundamental wave. At this time, the permissible width of film thickness is about 300Å
That was all. As a result, the second harmonic, green light, was generated with high efficiency.

[0060]

Example 4 On a SF15 glass plate, Ta ₂ O ₅ —Si was formed.
An O ₂ (Ta ₂ O ₅ molar ratio: 45 mol%) mixed thin film was sputtered so that the film thickness was 0.545 μm. The refractive index dispersion of this thin film is n (ω) = at a wavelength of 860 nm.
It was 1.881 and n (2ω) = 1.952.

On this thin film, Ta ₂ O ₅ -SiO
_A mixed thin film of ₂ (Ta ₂ O ₅ molar ratio: 76 mol%) was sputtered to a thickness of 0.31 μm. The refractive index dispersion of this thin film is n (ω) = 2.
004 and n (2ω) = 2.098.

On this mixed thin film, IAPU was crystallized from a methanol solution by a solvent evaporation method to prepare a four-layer slab waveguide type wavelength conversion element. In this case, the allowable range of film thickness was about 100Å or more. At this time, the IAPU crystal was crystallized so that its maximum NLO tensor, d ₂₂ was aligned parallel to the substrate.

A Ti: sapphire laser was applied as a fundamental wave to the end face of the thus obtained waveguide element.
As a result, blue light, which is the second harmonic, was generated with high efficiency in the wavelength range of the fundamental wave of 855 to 865 nm.

[0064]

Example 5 SF15 glass was sputtered on a BK7 glass plate to a film thickness of 0.24 μm. The refractive index dispersion of this thin film is n (ω) = 1.66 and n (2ω) =
It was 1.70.

On this thin film, DCANP, which is an LB film nonlinear optical material, was accumulated by the vertical dipping method so that the film thickness became 0.48 μm. The refractive index dispersion of this cumulative thin film is n
(Ω) = 1.574 and n (2ω) = 1.625.

At this time, the maximum NLO tensor of DCANP was oriented in the film plane in the direction of accumulation. In this case, the upper cladding is air. The allowable film thickness at the phase matching point of the sputtered film in this four-layer structure was 300Å or more.

When a YAG laser (wavelength 1064 nm) was made to enter the end face of the thus obtained waveguide element as a fundamental wave, the second harmonic green light was generated with high efficiency.

[0068]

Example 6 On a Pyrex glass plate, Ta ₂ O ₅ −
A SiO ₂ (Ta ₂ O ₅ mol ratio: 27 mol%) mixed thin film was sputtered to a film thickness of 0.31 μm. The refractive index dispersion of this thin film is n (ω) at a wavelength of 860 nm.
= 1.77 and n (2ω) = 1.83.

On this thin film, an amorphous silica thin film doped with 10% by weight of ABSA was prepared by spin coating so as to have a film thickness of 0.43 μm, dried and gelled.
Polled at 150 ° C. for 30 minutes. The refractive index dispersion of this thin film is n (ω) = 1.58 at a wavelength of 860 nm.
And n (2ω) = 1.65. In this case, the upper cladding is air. The allowable film thickness at the phase matching point of the sputtered film in this four-layer structure was 150Å or more.

A Ti: sapphire laser was made to enter the end face of the thus obtained waveguide element as a fundamental wave.
As a result, blue light, which is the second harmonic, was generated with high efficiency in the wavelength range of the fundamental wave of 855 to 865 nm.

[0071]

In the waveguide type wavelength conversion element of the present invention, the overlap integral can be increased and the phase matching can be achieved with a long propagation length, so that the wavelength conversion can be performed with high efficiency. Furthermore, since the control of the thickness of the waveguide can be relaxed, its manufacture is very easy.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a structure of a waveguide type wavelength conversion element of the present invention.

FIG. 2 is a diagram showing a waveguide mode dispersion curve showing the relationship between effective refractive index and film thickness.

FIG. 3 is a diagram showing a waveguide mode dispersion curve showing the relationship between effective refractive index and film thickness.

FIG. 4 is a diagram showing a waveguide mode dispersion curve showing the relationship between effective refractive index and film thickness.

FIG. 5 is a diagram showing a waveguide mode dispersion curve showing the relationship between effective refractive index and film thickness.

FIG. 6 is a diagram showing a waveguide mode dispersion curve showing the relationship between the effective refractive index and the film thickness of a three-layer structure waveguide type wavelength conversion element.

[Explanation of symbols]

 1 Upper Clad Layer 2 Second Layer 3 First Layer 4 Substrate

Claims (7)

[Claims] 1. A substrate (4) comprising a linear or non-linear medium; a first layer (3) provided on the substrate (4) having a refractive index greater than that of the substrate (4). Or a non-linear medium; a second layer (2) provided on the first layer (3), comprising a linear or non-linear medium having a refractive index higher than that of the substrate;
And an upper clad layer (1) provided on the second layer (2) having a refractive index smaller than that of the first layer (3) and the second layer (2). A four-layer waveguide type wavelength conversion element comprising a nonlinear medium, wherein at least one of the first layer (3) and the second layer (2) is a linear medium and has four layers. At least one of the first and second layers (3) and (2) is made of a nonlinear medium, and the fundamental wave is included in the waveguide mode dispersion curve showing the relationship between the effective refractive index and the thickness of each of the first layer (3) and the second layer (2). The first layer (3) and the second layer (2) such that the respective dispersion curves of the second and second harmonics are in contact with each other.
The wavelength conversion element is characterized in that the refractive index dispersion of each of the four layers is selected so that the thickness range of each of the layers is several tens of liters or more. 2. The wavelength conversion element according to claim 1, wherein the nonlinear medium has a second-order nonlinear optical effect. 3. The substrate (4), the first layer (3) and the second layer (2) consist of a linear medium and the upper cladding layer (1) consists of a non-linear medium. Wavelength converter. 4. The substrate (4) comprises a glass substrate, the first
The layer (3) and the second layer (2) are made of an inorganic dielectric,
The wavelength conversion element according to claim 3, wherein the upper cladding layer (1) is made of a crystal of an organic or inorganic nonlinear optical material. 5. The wavelength conversion element according to claim 4, wherein the upper cladding layer (1) is made of a polymer nonlinear optical material. 6. The upper clad layer (1) is a poled polymer or N-isopropyl-N ′-(4-acetylphenyl) urea or N- (4-aminobenzenesulfonyl).
The wavelength conversion element according to claim 4, which is composed of acetamide. 7. The substrate (4) comprises a glass substrate; first
Either layer (3) or second layer (2) of organic or inorganic nonlinear optical material crystals, poled polymers, sol-gel glass nonlinear optical materials or Langmuir-Blodgett film nonlinear optical materials; First layer (3)
Or the other of the second layers (2) consists of an inorganic dielectric;
The wavelength conversion element according to claim 1 or 2, wherein the upper cladding layer (1) is made of a linear medium.