JPH0713211A - Pseudo phase matching waveguide type wavelength conversion element - Google Patents

Abstract

PURPOSE:To provide the pseudo phase matching waveguide type wavelength conversion element body which converts the wavelength of a laser beam to a half by utilizing a nonlinear optical characteristic and more particularly second harmonic generation. CONSTITUTION:This waveguide type wavelength conversion element consists of a poled polymer subjected to a periodic polarization treatment by an electric field and has comb-shaped electrode 3 on one side and a plane electrode 2 or a surface capable of applying an electric charge by a corona discharge, etc., on the other. The element described above is so constituted that the electrode width D1 of the comb-shaped electrodes is D1=LAMBDA-6t and the inter-electrode spacing D2 is D2=LAMBDA+6t to satisfy 6t<LAMBDA when the period of pseudo phase matching is defined as 2LAMBDA. and the waveguide thickness as t. The electrode width D1 of the comb-shaped electrodes and the inter-electrode spacing D2 is D1+D2=2lambdaand is D1<<D2 is satisfied to satisfy 6tiotaLAMBDA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quasi-phase-matching waveguide type wavelength conversion element for converting the wavelength of laser light into 1/2 by utilizing nonlinear optical characteristics, particularly the generation of second harmonics.
In particular, it is applied to light sources such as optical memories, laser printers, and post systems.

[0002]

2. Description of the Related Art Organic nonlinear optical materials have been found to have higher performance than conventional materials, and have been receiving attention as materials for wavelength conversion elements that generate second harmonics. However, it is difficult to fabricate a device having high performance as a device because of poor workability, and often having a crystal structure having a symmetric center and exhibiting no performance as a macro. In order to solve this problem, it has been proposed to disperse molecules having high non-linear performance in a polymer matrix and perform polarization treatment, or to polarize a polymer incorporating a molecular structure having high non-linear performance in the main chain or side chain. However, since the number of molecules that can be doped is limited, the performance does not increase so much, and the relaxation of the polarization causes the performance to decline over time.

Therefore, a material has been invented in which a monomer having a high nonlinear optical performance is subjected to a polarization treatment and then polymerized to improve the performance and reduce the relaxation time of the polarization [eg, D. Jungb
Auer, etc, Appl Phys, Lett 5
6 (26), p. 2610]. However, in order to manufacture a wavelength conversion element using a non-linear optical material and obtain high efficiency, the conditions for improving the incident power density and phase matching are indispensable. Since the polymer can be easily made into a thin film, the optical waveguide can be manufactured, and the incident power density can be improved by introducing the incident light into the optical waveguide. In order to perform phase matching with an optical waveguide element, Cherenkov phase matching,
There is phase matching between guided modes, but the former is low in efficiency,
Beam shaping is required, the latter is difficult to control due to strict waveguide film thickness conditions, and there is wavelength dispersion of the refractive index, making it impossible to perform highly efficient phase matching between zero-order modes. There are drawbacks.

As a means for solving this, the present applicant has made an attempt to periodically polarize a polymer to perform similar phase matching (Japanese Patent Application Nos. 4-93455 and 4-93456). . In each of the poled polymers of the above-mentioned methods, an electric field is applied to perform a polarization process, and the polarization process is periodically performed by changing the intensity of the electric field depending on the shape of the electrode or the like. When a strong and weak electric field is applied by the electrodes, the electric field strength generated by the electrodes as shown in FIG. 1 is as shown in FIG. Therefore, the configuration of the polarization state due to the electric field can be considered. At this time, it is considered that the change of the nonlinear optical constant d caused by the change is as shown in FIG.

The second value obtained when the d value periodically changes with respect to the light guiding direction and the period satisfies the quasi-phase condition.
It is self-evident that the intensity of the harmonic wave (SH wave) becomes large, and at this time, the intensity of the SH wave increases as compared with that before the phase matching regardless of the state of the periodic change of d. However, when a laser having a relatively low power such as a semiconductor laser is used, it is considered necessary to optimize the periodic structure of d value in order to obtain an SH wave having a practical power.

In the poled polymer described above, the SH wave output as originally predicted could not be obtained. This is because the SH wave output intensity was predicted assuming that the d value is as shown in FIG. 4, but it is considered that it is actually as shown in FIG. 3, and the periodic structure of the d value is not optimized. Conceivable. As one means to solve this,
For example, attempts have been made to change the d value as shown in FIG. 4, but good results have not always been obtained.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a highly efficient wavelength conversion element by optimizing the periodic structure of d value as compared with the above-mentioned prior art.

[0008]

In order to solve the above problems, in order to solve the above problems, a poled polymer which is periodically polarized by an electric field is used. A waveguide-type wavelength conversion element having a surface capable of giving a value of, where the period of quasi phase matching is 2Λ and the thickness of the waveguide is t, and when 6t <Λ is satisfied, The electrode width D ₁ is D ₁ = Λ−6t, and the electrode spacing D ₂ is D ₂ = Λ + 6t. A waveguide type wavelength conversion element having a structure which is made of poled polymer and has a surface on which one side can be provided with a comb-shaped electrode and the other side is a plane electrode or a corona discharge,
When 2 [lambda] the period of quasi phase matching, the waveguide thickness and t, 6t ≧ when satisfying lambda, comb electrode width D ₁ and the electrode spacing D ₂ of the electrodes _{D 1 + D 2 = 2Λ D} 1 «D 2 It was found that the quasi-phase matching waveguide type wavelength conversion element characterized by Furthermore, the poled polymer is a polymer of two or more amines having amino groups at least one of which is not substituted and epoxides having two or more epoxy rings, and in particular, first-order quasi phase matching This is effective when the electrode width of the submicron order created by the electron beam writing method is included in the period.

When performing periodic polarization processing for quasi-phase matching, it is desirable that the state of changes in d value is ideally as shown in FIG. In order to produce such a periodic structure, for example, an electrode configuration as shown in FIG. 6 can be considered. At this time, an electric field of equal intensity in the opposite direction may be applied to the waveguide layer by the electrodes 1, 2, or 1,3. For this purpose, a potential difference larger than the potential difference of 1, 2, or 1,3 is applied to the electrode 2. , 3 must be applied, so that the maximum electric field strength that can be applied to the waveguide layer is lower than the electric field strength generated between the electrodes 2 and 3. In order to increase the efficiency of the device, it is preferable that d is large, but the d value becomes larger as the applied electric field becomes stronger. Therefore, in the electrode configuration as shown in FIG. Since the electric field cannot be applied to the waveguide layer, the efficiency finally obtained becomes low.

Then, next, a case may be considered in which a periodic structure of d value as shown in FIG. 4 is considered, but this is simulated by forming an electrode structure as shown in FIG. A periodic structure can be achieved, and an electric field can be applied to the waveguiding layer up to the maximum electric field strength. This structure has the advantage that the fine processing of the electrode may be performed on only one of the electrodes, and the polarization treatment can be performed by a simple treatment such as corona poling. However,
It has been found that in such an electrode configuration, since there is "drooping" at the end portion of the electrode as described above, this may cause a significant decrease in efficiency.

Therefore, the author examined in detail the state of the electric field formed by the electrodes having the structure as shown in FIG. 1, and in the central portion of the waveguide layer, the distance d between the end portions of the electrodes was about 6 times the distance d between the electrodes. It was found by calculation by the finite element method that the electric field strength has a tail as shown in FIG. 7 up to the vicinity.

Further, the writer also examined what the expected device efficiency would be if the periodic structure of d value was changed. Periodic function d whose d value changes in a period of 2Λ
When it is (Z), when d is Fourier series expanded,

[0013]

[Equation 1]

Since a _q can be written in the form of Fourier coefficient, solving Maxwell's equation for SH wave generated in the waveguide using this, out of the nonlinear polarization generated by the fundamental wave,

[0015]

[Equation 2]

Since a term proportional to excites the SH wave, SH
Wave power

[0017]

[Equation 3]

Is approximately

[0019]

[Equation 4]

It can be seen that it is proportional to Therefore, if a ₁ is calculated according to t from a formula for obtaining a predetermined Fourier coefficient, the expected SH wave power can be found. When there is no one in the field strength over a length of about 6t Considering the above, in the case of lambda> 6t, electrodes, and the portion of d = d _0, as shown in FIG. 8 when the electrode spacing to lambda,
The length of the part of d = 0 becomes different, but this reduces efficiency, that is,

[0021]

[Equation 5]

It has been found that this may cause a decrease in

Therefore, at this time, it has been found that it is preferable to form the electrodes so that the d value changes as shown in FIG. 9, that is, D ₁ = Λ-6t D ₂ = Λ + 6t.

Further, when Λ≤6t, the result is as shown in FIG. 10, and d = 0 is not satisfied. Also in this case, the same calculation is performed.

[0025]

[Equation 6]

This may cause a decrease in At this time, a ₁ is shown in FIG.

[0027]

[Equation 7]

Since d is proportional to the size of d, it is necessary to make the electrode structure so that d ₂ is as small as possible when d = 0 cannot be achieved. Therefore, it suffices that D ₁ + D ₂ = 2Λ and D ₁ << D ₂ . (FIG. 11) As a material for forming the device of the present invention, a dispersion-type polymer material obtained by doping a polymer matrix with a low-molecular nonlinear optical material, or a polymer main chain or a side chain shows a nonlinear optical effect. Examples thereof include those having a group incorporated via a chemical bond.

The low molecular weight non-linear optical material is not particularly limited, and various materials can be used.
For example, 3-nitro-5- (N, N-dimethylamino)-
Acetanilide, 3- (N, N-dimethylamino) -aniline, N- (4'-methoxybenzoyl) -4-cyanoaniline, N-methyl-N- (4-cyanophenyl)
Aminoacetonitrile, N- (4-cyanophenyl) aminoacetonitrile, 4-nitrobenzylidene-2,3
-Dimethylaniline, 4-nitrobenzylidene-2,4
-Dimethylaniline, 4-nitrobenzylidene-2,5
-Dimethylaniline, 4-nitrobenzylidene-3,4
-Dimethylaniline, 4-nitrobenzylidene-3,5
-Dimethylaniline, 4-nitrobenzylidene-2,4
-Dimethoxyaniline, 4-nitrobenzylidene-3,
4,5-Trimethoxyaniline, 3-nitrobenzylidene-3,4,5-trimethoxyaniline, 2-nitrobenzylidene-3,4,5-trimethoxyaniline, 3-
Nitrobenzylidene-2,3-dimethylaniline, 3-
Nitrobenzylidene-2,5-dimethylaniline, 3-
Nitrobenzylidene-3,5-dimethylaniline, 2-
Methyl-4-nitroaniline (MNA), 4- (N, N
-Dimethylamino) -3-acetamidonitrobenzene (DAN), 4,5-dimethyl-1,3-dithiol-
2-ylidene cyanoacetate, 1,3-dithiol-
2-ylidene cyanoacetate, N- (4-nitrophenyl)-(S) -prolinol (NPP), N- (5-
Examples thereof include nitro-2-pyridyl)-(S) -phenylaralinol (NPPA) and 9-methylcarbazole-3-carboxaldehyde.

As the polymer forming the polymer matrix, polyvinylidene fluoride, methacrylic resin (MM
Although various polymer substances such as A), polyethylene, and polysiloxane can be used, an energy curable resin that can be easily three-dimensionally crosslinked (cured) by using radiation such as heat, ultraviolet rays, and electron beams as an energy source. Can also be used. Specifically, for example, epoxy resin, urethane resin, unsaturated polyester resin, polyimide resin, silicon resin, diallyl phthalate resin, phenol resin, fluororesin and the like can be mentioned, but as a resin particularly suitable for ultraviolet ray and electron beam curing, Examples thereof include polyester (meth) acrylate resin, epoxy (meth) acrylate resin, polyurethane (meth) acrylate resin and the like.

A polyfunctional monomer having two or more reactive functional groups may be used in combination as a curing aid for effectively three-dimensionally crosslinking (curing) such an energy curable resin. . Among these, a crosslinkable polymer having a stable nonlinear optical effect after poling and a crosslinkable polymer of an amine and an epoxide capable of incorporating a large amount of units exhibiting the nonlinear optical effect is particularly desirable.

Further, for example, when a single-layer slab type waveguide is manufactured by using this copolymer of amine and epoxide, the period of the first-order quasi phase matching is

[0033]

[Equation 8]

This is a very small value. At this time, since the waveguide thickness is about t = 1 to μm, Λ << 6t. Therefore, at this time, D ₁ << D ₂ , but in order to satisfy this condition, it is necessary to make D ₁ much smaller than 1.7 μm (= Λ). At present, it is possible to perform fine processing of electrodes by a technique such as photolithography, but an EB drawing technique is indispensable for performing fine processing on the order of submicrons or less. Therefore, for EB writing, it is more desirable to manufacture an electrode as fine as possible, that is, an electrode having a sub-half-micron order width in a predetermined cycle for high efficiency.

[0035]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 34 μm width (D ₁ ) spacing 40 on Pyrex glass
An ITO comb-shaped electrode of μm (D ₂ ) is provided over a length of 1 cm, and a high-refractive-index glass SF1 has a thickness of 0.25 μm.
m by a sputtering method, and then apply
l. Phys, Lett 56 (26), P.P. 2610
The cross-linked polarized polymer described above was formed into a film with a thickness of about 0.25 μm by the spin coating method, and then poled by the corona poling method described in the same document to prepare a periodically polarized structure.

When the mode dispersion of the effective refractive index of this polymer waveguide is a YAG laser and the wavelength is 1.064 μm as a fundamental wave, the change of the effective refractive index of the waveguide with respect to the polymer genus is as shown in FIG. 12, and the SHG active polymer is shown. The overlap integral in the genus becomes large. TMω (0) mode and TM2ω
(1) The quasi phase matching structure with the mode is

[0037]

[Equation 9]

[0038]

Therefore, when the pitch was adjusted by changing the propagation direction of the incident laser, SH light with quasi-phase matching was confirmed at a place inclined by about 9.6 ° (FIG. 13). The obtained SH light was stronger than that when the electrode width and the electrode interval were made equal.

Example 2 0.1 μm in design by EB drawing technique on a silicon substrate
When a comb-shaped electrode was formed with a width electrode interval of 3.2 μm, the electrodes could be actually formed with a width of 0.2 μm (D ₁ ) and an interval of 3.1 μm (D ₂ ). A vinylidene fluoride-tetrafluoroethylene copolymer dissolved in acetone was applied onto the electrode by spin coating, and dried by heating to form a clad layer. Further, the nonlinear polymer used in Example 1 was formed into a film by the same method and poled to prepare a waveguide having a thickness of about 2.1 μm. The mode dispersion of the effective refractive index of this polymer waveguide is as shown in FIG. 14 when the YAG laser and the wavelength of 1.064 μm are the fundamental waves, and the first-order quasi phase matching structure is

[0041]

[Equation 10]

It is

Therefore, when the pitch was adjusted by changing the propagation direction of the incident laser, SH light with quasi-phase matching was confirmed at a position inclined by about 7.0 ° (FIG. 15). At this time, the same effect as in Example 1 was confirmed.

[0044]

As described above, according to the present invention,
Compared with the conventional technique, the periodic structure of d value is optimized, and highly efficient quasi-phase matching wavelength conversion can be performed. Further, the present invention provides a wavelength conversion element capable of optimizing the periodic structure of d value by using a poled polymer having a stable nonlinear effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an electrode of the present invention.

FIG. 2 is an explanatory diagram showing electric field strength.

FIG. 3 is an explanatory diagram showing a change in nonlinear optical constant d.

FIG. 4 is an explanatory diagram showing changes in the nonlinear optical constant d.

FIG. 5 is an explanatory diagram showing changes in the nonlinear optical constant d.

FIG. 6 is a cross-sectional view showing an electrode configuration for creating a periodic polarization structure.

FIG. 7 is an explanatory diagram showing electric field strength.

FIG. 8 is an explanatory diagram showing changes in the nonlinear optical constant d.

FIG. 9 is an explanatory diagram showing changes in the nonlinear optical constant d.

FIG. 10 is an explanatory diagram showing changes in the nonlinear optical constant d.

FIG. 11 is an explanatory diagram showing changes in the nonlinear optical constant d.

FIG. 12 is a mode dispersion of effective efficiency according to the first embodiment.

FIG. 13 is a perspective view of the first embodiment.

FIG. 14 is a mode dispersion of effective efficiency according to the second embodiment.

FIG. 15 is a perspective view of the second embodiment.

[Explanation of symbols]

 1 Waveguide 2 Electrode or Corona Discharge Surface 3 Electrode 4 Substrate, Clad 5 Substrate 6 Clad 7 Incident Laser Light 8 Coupling Prism 9 SH Light 10 Polymer 11 SFI

Claims (3)

[Claims] 1. A conductor having a structure which is made of a poled polymer which is periodically polarized by an electric field and has a comb-shaped electrode on one side and a flat electrode on the other side or a surface capable of giving a charge by corona discharge or the like. In the waveguide type wavelength conversion element, when the quasi-phase matching period is 2Λ and the waveguide thickness is t, when 6t <Λ is satisfied, the electrode width D ₁ of the comb electrode is D ₁ = Λ-6t. The quasi-phase matching waveguide type wavelength conversion element, wherein the electrode spacing D ₂ is D ₂ = Λ + 6t. 2. A conductor having a structure which is made of a poled polymer which is periodically polarized by an electric field, and has a comb-shaped electrode on one side and a flat electrode on the other side or a surface to which a charge can be given by corona discharge or the like. In the waveguide type wavelength conversion element, when the quasi phase matching period is 2Λ and the waveguide thickness is t, when 6t ≧ Λ is satisfied, the electrode width D ₁ and the electrode spacing D ₂ of the comb electrode are D ₁ quasi-phase matching waveguide type wavelength converting element which is a _{+ D 2 = 2Λ D 1 «D} 2. 3. The quasi-phase according to claim 1, wherein the poled polymer is a polymer of two or more amines having amino groups at least one of which is not substituted and epoxides having two or more epoxy rings. Matched waveguide wavelength converter.