JP3348297B2 - Wavelength conversion element and method of manufacturing wavelength conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion element utilizing harmonic generation, optical mixing, optical parametric oscillation and the like by a non-linear optical material. The present invention relates to a wavelength conversion element that generates highly efficient second harmonics that can directly convert light.

[0002]

2. Description of the Related Art In recent years, wavelength conversion elements utilizing optical harmonic generation, optical mixing, optical parametric oscillation, and the like using a nonlinear optical material have received considerable attention in recent years and have been studied. Particularly, in order to obtain blue or green coherent light, a highly efficient second harmonic generation wavelength conversion element capable of directly converting a near-infrared semiconductor laser is promising, and various materials and structures have been proposed, but they have been put to practical use. At present, elements with higher conversion efficiency are required for this purpose.

[0003] The conversion efficiency of the second harmonic generation increases in proportion to the power density of the fundamental wave and is proportional to the square of the interacting length (for example, proportional to the first power such as the phase matching method of Cherenkov radiation type). Optical waveguide structure that can confine light in a small area and propagate it over long distances.
It is applied to a highly efficient second harmonic generation wavelength conversion element.

In order to generate harmonics with higher efficiency, there is an important problem of phase matching. In general, since the optical material has a refractive index dispersion, the phase velocities of the fundamental wave and the second harmonic in the nonlinear optical medium are not equal. Therefore, the second harmonic generated in each part while the fundamental wave propagates through the nonlinear medium is out of phase with each other. Therefore, even if the light is propagated over a long distance equal to or longer than the coherent length, the generated second harmonics are canceled and not accumulated, and the total intensity is extremely small.

Therefore, various phase matching methods for matching the phase velocities of the fundamental wave and the second harmonic have been proposed. In the case of thin-film optical waveguides, phase matching between propagation waveguide modes has been studied. However, because high uniformity is required for the film thickness, there is no report with a very high conversion efficiency. On the other hand, a second harmonic wavelength conversion element having a high conversion efficiency even in a Cherenkov-type phase matching method having relatively moderate phase matching conditions has been recently announced, and this phase matching method has attracted attention.

The Cherenkov-type phase matching includes a case where the waveguide has optical nonlinearity, a case where the substrate has optical nonlinearity, and a mixed type thereof. Several examples of these types have been reported as second harmonic generation wavelength conversion elements based on the Cherenkov radiation type phase matching method.
Here, only the second harmonic generation wavelength conversion element in the case where the waveguide has optical nonlinearity will be described, but the same discussion can be made in other cases.

In the Cerenkov radiation type phase matching, when the fundamental wave is light propagating through an optical waveguide (guiding mode) and the harmonic wave is light radiating from the waveguide (radiation mode), the phase velocity of the fundamental wave becomes Although the discrete value is obtained by the effective refractive index of the waveguide, the phase velocity of the harmonic in the propagation direction of the fundamental wave is continuously changed by the radiation angle (Cherenkov angle). If the refractive index of the substrate and the optical waveguide satisfies a certain condition, the harmonic wave is a radiation angle at which phase matching is achieved, that is, the radiation angle at which the phase velocity in the propagation direction of the waveguide coincides with the phase velocity of the fundamental wave. Strongly radiated in the direction, and phase matching can be automatically achieved. The condition that must be satisfied for this is shown in Equation 1.

[0008]

(Equation 1)

At this time, the Cerenkov angle θ in the substrate is expressed as in equation 2 in the substrate.

[0010]

(Equation 2)

As described above, the phase matching condition is only an inequality relating to the relationship between the refractive index of the substrate and the refractive index of the waveguide, and is relatively loose. However, Equation 1 is simply a condition for achieving phase matching, and more severe conditions are added for high-efficiency conversion. One of those conditions is coupling efficiency.

Since the second harmonic is generated in the nonlinear optical medium in proportion to the square of the electric field intensity of the fundamental wave, its electric field intensity distribution is proportional to the square of the electric field intensity distribution of the fundamental wave. In order to radiate this as coherent light of the phase-matched Cerenkov radiation type, it is best if the electric field distribution of the generated second harmonic is the electric field intensity distribution of the Cherenkov radiation mode. That is, the electric field intensity distribution of the fundamental wave, which is proportional to the electric field distribution of the generated second harmonic, is 2
The larger the integral of the power and the electric field intensity distribution of the second harmonic of the Cherenkov radiation that can be phase-matched, the higher the coupling efficiency and the higher the conversion efficiency.

When trying to propagate a fundamental wave having a strong electric field intensity distribution in a waveguide, it is necessary to form a waveguide having a considerably thick film of about 0.6 μm, though it depends on the respective refractive indexes. At that time, in many cases, the electric field of the harmonic of the radiation mode is inverted once or more in the waveguide. There is a problem that the overlap integral at this time is canceled out because the electric field of the radiation mode is inverted and does not increase.

By applying the mode coupling theory to a Cherenkov radiation type phase matching wavelength conversion element, the electromagnetic field analysis results of the incident mode and the radiation mode in the active layer (optical waveguide) and the substrate in consideration of the refractive index of the cladding layer are shown. 21. In this example, analysis was performed using the numerical values of the above-mentioned hetero LB film of C12PPy and arachidic acid. The analysis based on the mode coupling theory is an analysis method in which the incident light and the harmonic light are developed in the fundamental propagation mode and the conversion efficiency is theoretically derived. In this analysis, the overlap integral between the incident light (fundamental mode) and the second harmonic light (SHG radiation mode) plays an important role. In FIG. 31, the broken line R is the square of the fundamental wave mode electric field, the solid line S is the SHG radiation mode electric field, and the solid line T is the nonlinear polarization wave obtained by inverting the sign of the square of the fundamental wave mode electric field indicated by the broken line R at the inversion position P. Is shown.

The SHG conversion efficiency is proportional to the square of the overlap integral of the nonlinear polarization wave induced by the fundamental wave and the SHG radiation mode field. As shown in FIG. 31, in many cases, the SHG radiation mode field is inverted in the active layer, and the nonlinear polarization wave and the SH
It can be seen that the overlap integral of the G radiation mode field cancels each other because their signs are different, and reduces the mode coupling efficiency, that is, the wavelength conversion efficiency. This is a major problem in improving the efficiency of the Cherenkov radiation phase matching wavelength conversion element.

In order to increase the coupling efficiency, as shown in FIG. 1, a non-linear optical material having a non-linear optical susceptibility code aligned in a predetermined direction and a non-linear optical material having a non-linear optical susceptibility code inverted on a substrate are provided. As for the method of arranging and introducing an inverted structure of the nonlinear optical susceptibility, there is a calculation example for a specific material system.

It is reported by Yanagawa, Hayata and Koshiba, "Improvement of efficiency of Cerenkov radiation type wavelength conversion device by domain inversion structure", IEICE Transactions Vol. J174─C
{I, NO. 4, 1991, PAGE 119.
(Reference 1)

Here, they describe L.sub.L as a nonlinear optical material.
Calculations are made for a proton exchange optical waveguide of iNbO ₃ . This waveguide was announced in 1987 by Matsushita Electric as a highly efficient Cerenkov radiation type second harmonic generation optical waveguide element. (Reference 2: Taniuchi et al., “Second Harmonic Generation of Semiconductor Laser”, Applied Physics, Vol. 56, 12, p. 163)
7 (1987)) This optical waveguide also has non-linearity on the substrate side, and it is already known that the second harmonic generation conversion efficiency is improved if the nonlinear optical constants of the waveguide and the substrate are inverted. Was. They independently move the index discontinuity surface (waveguide layer thickness) and nonlinear optical constant inversion surface (nonlinear optical inversion layer thickness) at the boundary between the waveguide and the substrate, and in each case, Calculate the conversion efficiency. At this time, as an example of the combination, the calculation is performed for the case where the nonlinear optical constant is inverted in the waveguide layer and the substrate also has the nonlinear optical constant of the same sign as the domain in contact with the substrate of the waveguide. No case is considered. Also, since the main part of the calculation is a numerical analysis, it is not so clear why the inverted structure is effective.

On the other hand, in order to realize a waveguide type wavelength conversion element having a large wavelength conversion efficiency, a material system having a large nonlinear susceptibility is required. Recently, organic nonlinear optical materials have attracted attention as key materials for high-efficiency wavelength conversion elements. Whereas nonlinear optical phenomena of inorganic materials are caused by lattice vibration,
In organic materials, high responsiveness and large optical constants can be obtained because of the conjugation of π electrons, and the variety of structures is expected to develop materials. Organic nonlinear optical materials exhibiting nonlinear optical characteristics actually exceeding those of inorganic materials have been obtained.

In order to realize a waveguide type nonlinear optical element (wavelength conversion element) using the above-mentioned nonlinear optical material, it is essential to use an organic material having a large nonlinearity as a thin film waveguide.
However, the technique for thinning the organic material described above is still under study and has not been established at present. One of the most prominent techniques for thinning organic materials is the Langmuir-Blodgett method (LB method). In order to obtain a good organic thin film by the LB method, an amphiphilic molecule (having both a hydrophilic group and a hydrophobic group in the molecule) is required. Many attempts have been made to convert an organic low-molecular material having a large nonlinearity into a thin film waveguide using the LB method, but there have been very few examples of organic thin films exhibiting good nonlinear characteristics.

As such an LB film material having excellent accumulation properties, for example, DCANP (2-docosylamino-) described in "Ferroelectrics" (1989, Vol. 91, pp. 193 to 207) by Dejar et al. 5-nitropyr
idine, 2-docosylamino-5-nitropyridine) LB
"Applied Physics (Vol. 60 of 1991, 586)
Pp. 590) described in "C12PPy (5- (P-dode
There is an example of a hetero LB film of cyloxy phenil) pyrazine-2-carboxylic acid, 5- (p-dodecyloxyphenyl) pyrazine-2-carboxylic acid) and arachiic acid. "Optics Communication" by Bosshard et al.
s (Optics Communications) (1991 85
Vol. 247-253) ", reports the results of evaluating the nonlinear optical characteristics of an optical waveguide fabricated using a DCANP LB film.

However, these reports are based on a special LB
Using a film material, a relatively thick organic thin film with good accumulative properties is produced, and only the optical waveguide characteristics are evaluated.
No studies have been made on a device structure of a wavelength conversion device that makes use of a feature unique to the LB method, in which a molecular layer can be controlled on the order of nanometers.

[0023]

As described above, it is not clear how the introduction of the non-linear susceptibility inversion structure has an effect on the conversion efficiency of the second harmonic generation.
It was difficult to determine the optimal introduction position of the inverted structure.

Therefore, in the present invention, the inverted structure is surely introduced by orienting the nonlinear optical molecules at the optimum positions calculated by the calculation method developed from the mode coupling theory using the Langmuir-Blodgett method. Etc.
It is an object of the present invention to propose a more specific element structure and to provide a wavelength conversion element in which the second harmonic generation conversion efficiency is greatly improved.

[0025]

SUMMARY OF THE INVENTION The present invention has been proposed to achieve the above-mentioned object. The present invention provides a wavelength conversion element in which a light propagation portion has an optical waveguide shape, wherein the optical waveguide is made of a material having a second-order optical nonlinearity, and a second harmonic, a sum frequency, or a difference frequency generated. Is characterized in that at least one of the main tensor components of the nonlinear optical constant of the optical waveguide is inverted or changed at the node of the standing wave formed in the film thickness direction.

The present inventors analyzed the electric field distribution of the fundamental wave and the second harmonic in the nonlinear optical waveguide by a method different from the above-mentioned known report example. By further developing the mode coupling theory that has already been proven in the propagation mode analysis of optical waveguides, we established a calculation method for the electric field distribution of light for radiation type light with the optical waveguide part as the wave source. The electric field distribution in the film thickness direction was calculated for the radial second harmonic. By this calculation, the Cherenkov radiation type second
The position (in the thickness direction) where the electric field of the harmonic is inverted can be easily calculated.
It was found that harmonic conversion efficiency was obtained. (Reference 3:
H. Tamada, “Coupled-mode an
alysis of second harmonic
generation in the form o
f Cerenkov radiation from
a planar optical wavegui
de ", IEEE J. of QE vol.27,
no. 3,1991, pp. 502 The underlying theory is that Yariv, “Coupled-modeth
early for guided-wave opti
cs ", IEEEJ of QE, vol. QE-9,
no. 9, 1973, p. 919))

Inverting the sign of the nonlinear optical constant has the greatest effect in improving the conversion efficiency. However, since the sign is not completely inverted, even if the absolute value of the nonlinear optical constant is changed, the effect is not significant. appear. Then, according to the present invention, the waveguide section is manufactured with a design based on this calculation.

The wavelength conversion element of the present invention is characterized in that the optical waveguide is formed by orienting and stacking non-linear optical molecules using the Langmuir-Blodgett method (LB method).

That is, a structure in which a film direction is inverted is formed by accumulating films by the LB method. For example, 2 {docosylamino}
The LB film of 5-nitropyridine (DCANP) is shown. The structure of 2-docosylamino-5-nitropyridine is shown in Chemical formula 1.

[0030]

Embedded image

When the DCANP is formed on a Y-type LB film, the nonlinear optical thin film having a strong nonlinear optical susceptibility tensor in the pulling direction of the substrate on both sides has a considerably large thickness (1 μm).
~) Have already been reported by Decher et al., And their non-linear and linear optical properties have also been reported by Gu.
report. (Reference 4: G. Deche
r et. al. "Optical Second H
armonic Generation in Lan
gmuir-Blogett Films of No
vel Donor-acceptor Substi
tuted Pyridine and Benzen
Derivatives ", Ferroselectr
ics, 1989, vol. 91 pp. 193, Reference 5: C.I. Bosshard et. al. , "Opti
cal waveguiding and nonlin
ear optics in high qualit
y 2-docosylamino-5-nitoro
pyridine Langmuir-Blogett
film ", Appl. Phys. Lett. vo
l. 56 (13), 26 March 1990, p.
p. 1204)

The DCANP is dissolved in chloroform to prepare a developing solution. Pure water was filled as a subphase, and the developing solution was dropped on the water surface to form a monomolecular layer.
At this time, if the temperature of the experimental system is lowered below room temperature, the surface pressure at which the film starts to break when it is gradually compressed (collapse surface pressure)
And a clean monomolecular film is formed.

The substrate is subjected to a hydrophobic treatment using a silane coupling agent, and is dropped into a developing solution. The accumulation starts when the substrate is lowered. In this way, DCANP is applied to both sides of the substrate.
An LB film is formed.

FIG. 2 shows a state in which DCANP molecules accumulate on a substrate. When DCANP molecules accumulate on a substrate, they receive some strong alignment force, and when the substrate descends, the hydrophobic portion faces the substrate side and is drawn. The dipole moment α in the hydrophilic group is also arranged downward, and at the time of pulling up, the group having hydrophilic nonlinear optical properties faces the substrate side, and the dipole moment β is arranged downward. It is estimated to be. As described above, since the dipole moments α and β face downward, the orientation direction C of the nonlinear optical susceptibility also faces downward.

FIG. 3 shows that the substrate is turned upside down on
This shows a state in which ANP molecules are accumulated, and the dipole moment γ in the accumulated film before inversion becomes upward, and then the dipole moment δ in the accumulated film after inversion becomes downward, so that the nonlinear optical susceptibility C is reversed.

Therefore, the film may be accumulated by inverting the substrate up and down at the position where the electric field of the second harmonic of the Cerenkov radiation type calculated by the calculation is reversed. A DCANP LB film having a structure in which the nonlinear optical susceptibility is inverted is formed.

As a material that can be accumulated by such a structure,
As analogs of DCANP, C _{n + 1}─ANP (n ≧
20: Shown in Chemical Formula 2. ), C_{n + 1}−MNA (n ≧ 20: formula
3 is shown. ), C_{n + 1}-PNA (n ≧ 20: shown in Chemical formula 4)
You. ). Note that C_{n + 1}-MNA (n ≧ 20: Chemical formula 3)
Shown in ), C_{n + 1}-PNA (n ≧ 20: shown in Chemical formula 4)
You. ) For non-linear optical material, patent application
Applying.

[0038]

Embedded image

[0039]

Embedded image

[0040]

Embedded image

In this case, inverting the non-linear optical susceptibility is the largest in terms of the effect of improving the conversion efficiency, but it is not an accurate 180 ° rotation but, for example, 0, -1/2,
Alternatively, the effect is also obtained when the value is simply reduced to 1/2 without inverting the sign. For the DCANP LB film, 90
A case where the nonlinear optical constant became 0 was actually manufactured by performing the next accumulation by rotating the rotation, and it was confirmed that in this case also, the conversion efficiency was improved.

That is, since the symmetry of the DCANP LB film belongs to the point group 2 mm, the tensor of the nonlinear optical constant is expressed by the following equation (3)
FIG. 4 shows how to obtain the coordinates of the LB film. ).
As is well known, this tensor is described by a notation used in a determinant for calculating the nonlinear polarization vector shown in Expression 4 from the electric field vector of the fundamental wave.

[0043]

(Equation 3)

[0044]

(Equation 4)

Here, to continue the accumulation by inverting the substrate, mathematically, it is necessary to rotate the substrate around the y-axis (the axis in the film thickness direction).
The rotation operation is performed by 0 degrees, and the tensor of the nonlinear optical constant after inversion is represented by Expression 5. It is clear that z-direction of the diagonal tensor d ₃₃ is the main component is inverted.

[0046]

(Equation 5)

At this time, if the rotation of the substrate is exactly 180
Consider the case where the angle is φ (0 <φ ≦ 180 degrees) instead of the degree reversal (FIG. 5). Since it becomes complicated when all the tensor components are considered, only the change with respect to the angle φ of d ₃₃ (also called d _zzz ), which is the largest tensor component in the DCANP LB film, is shown in Equation 6. here,
d ₃₁ and d ₁₅ is left ignored because small compared to d _33.

[0048]

(Equation 6)

Now, assuming that the SHG radiation mode is inverted once in the waveguide layer, the overlap integral (I) is determined by comparing the upper layer component (-I ₁ ) and the lower layer (-I ₁ ) at the position where the radiation mode electric field is inverted. When the cumulative direction of the upper layer is inclined by φ with respect to the cumulative direction of the lower layer (this is used as a reference coordinate system), the overlap integral is expressed by the following equation (I ₂ ). It is represented as

[0050]

(Equation 7)

In this case, I ₁ > 0 and I ₂ > 0. I, −I ₁ cos of the condition in the case of Example 5 described later
³ phi, as shown in FIG. 26 changes to the phi of I ₂ and conversion efficiency. The rotation operation of φ = 180 degrees, that is, the inversion operation is most effective in increasing the conversion efficiency proportional to the square of the overlap integral and the overlap integral, but the rotation operation other than 0 degree is also effective for most rotation angles. It turns out that it is effective. Actually, at about φ = 170 degrees, the conversion efficiency is reduced by only about 10% compared to φ = 180 degrees.

Further, the wavelength conversion element of the present invention has an active layer in which an organic thin film having nonlinear optical characteristics is laminated on a substrate, and the active layer has a second-order nonlinear optical susceptibility.
The direction of ⁽²⁾ is reversed or changed at least at one position in the thickness direction of the active layer, and satisfies the refractive index condition under which the Cherenkov radiation type SHG occurs, and has an extreme activity in which the Cherenkov angle is 0 degree. In layer thickness, S
The phase matching condition between the HG guided mode and the fundamental wave guided mode is satisfied at a cutoff point of the SHG guided mode.

As shown in FIG. 6, an enlarged schematic cross-sectional view of one example of the wavelength conversion element 10
An active layer 2 is formed by stacking organic thin films having nonlinear optical characteristics, and the active layer 2 has a second-order nonlinear optical susceptibility.
The direction of ⁽²⁾ is at least one in the thickness direction of the active layer 2.
The cladding layer 3 made of an organic material having a refractive index smaller than that of the substrate 1 is laminated on the active layer 2.

The wavelength conversion element 10 of the present invention is shown in FIG.
As described above, the active layer 2 made of an organic thin film has a second order nonlinear optical sensitivity.
Receipt rateχ⁽²⁾Is less in the thickness direction of the active layer 2
Are calculated once in advance because they are inverted once.
Calculate the reversal position of the SHG radiation mode field
At this reversal position P, for example, the arrow x₁And x _Two
As shown in the figure, the dipole moment of a nonlinear active molecule
Direction (nonlinear optical susceptibility χ⁽²⁾Direction), the film thickness direction
Is provided so as to rotate 180 ° toward
Of non-linear polarization wave and SHG radiation mode field in conductive layer 2
It is possible to avoid that the integration cancels each other. to this
The nonlinear polarization wave induced by the fundamental wave and the SHG emission
It is possible to increase the square of the overlap integral of the firing mode field.
Therefore, the SHG conversion efficiency can be improved.

On the other hand, the SHG conversion efficiency of Cherenkov SHG is shown by the following equation (1). P ^2W / P ^W = (1/2) πlω ² p ^W ε ₀ ² | ∫d _zzz E _z ² E ′ _z dy | ² cot θ (1) where P ^2W is the SHG power linear density and P ^W Is the fundamental power linear density, l is the waveguide length, ω is the fundamental frequency, _EZ is the electric field in the fundamental wave guided mode, E ' _Z is the electric field in the SHG radiation mode, d _ZZZ is the nonlinear optical constant, and θ is the Cherenkov angle. Is shown. Also, in this equation (1), ∫d _zzz E _z ² E ′ _z d
y indicates the overlap integral (I _QV ).

Further, since the cladding layer 3 made of an organic material having a refractive index smaller than that of the substrate 1 is laminated on the active layer 2, if the cladding layer does not exist, that is, the active layer 2 Compared to the case where the upper part is an air layer,
The value of cotθ could be increased without reducing the overlap integral between the nonlinear polarization wave and the SHG radiation mode field, and as a result, the SHG intensity could be increased. FIG. 8 shows the dependency of the SHG intensity on the thickness of the active layer. In FIG. 8, a shows the case where the clad layer 3 is provided on the active layer 2, and b shows the case where no clad layer is provided. As can be seen from this result, the cladding layer 3
By providing, it is possible to obtain a higher SHG intensity as compared with the case where the cladding layer is not provided, and it is possible to reduce the thickness of the active layer for obtaining the maximum intensity.

In FIG. 8A, the reason why the SHG intensity increases divergently is that cot θ divergently increases because the Cherenkov angle converges to the limit of 0. In terms of this physical meaning, it can be considered that the limit is such that the Cherenkov SHG radiation mode asymptotically approaches the first-order SHG waveguide mode.

Conversely, when the Cherenkov angle approaches zero, S
Under optical conditions in which the HG radiation mode does not asymptotically approach the SHG waveguide mode, the electric field amplitude in the active layer of the SHG radiation mode is
The conversion efficiency sharply decreases, and the conversion efficiency also rapidly decreases as the Cherenkov angle approaches zero.

In practice, when the Cherenkov angle approaches zero,
The optical conditions in which the SHG radiation mode asymptotically matches the SHG waveguide mode are not shown as a finite range in the optical conditions, so it is impossible to achieve it, but by bringing them as close as possible, Greater conversion efficiency can be achieved under conditions where the Cherenkov angle is smaller. FIG. 9 shows the electric field distribution at the limit where the Cherenkov angle is 0 in a waveguide satisfying the optical conditions when the SHG radiation mode gradually approaches the SHG waveguide mode when the Cherenkov angle approaches 0. The optical conditions are shown in Table 1. That is, Table 1 shows an example of the combination of the refractive index of the active layer, the substrate, and the cladding layer, which satisfies the optical condition that the SHG radiation mode asymptotically approaches the SHG waveguide mode when the Cherenkov angle approaches 0. This is the calculation condition of FIGS. 9 and 10.

[0060]

[Table 1]

It is apparent that the electric field distribution of the SHG radiation mode shown here is the electric field distribution of the first-order SHG waveguide mode at the so-called waveguide cut-off point thickness. FIG. 10 shows the result of calculating a so-called mode dispersion curve under these optical conditions. That is, FIG. 10 shows that when the Cherenkov angle approaches 0,
5 shows a mode dispersion curve in a waveguide satisfying an optical condition asymptotic to an HG waveguide mode. The solid curve is the fundamental wave guiding mode, and the broken curve is the SHG waveguide mode.

The zero-order guided mode of the fundamental wave coincides with the first-order guided mode of SHG at its cutoff point. This indicates that this is the phase matching condition of the waveguide mode SHG at the cutoff point.

As is clear from this figure, this condition can be approached by adjusting the refractive index of the substrate at the fundamental wave and the SHG wavelength, and the cladding can be formed of a transparent material other than air. Adjustment is also possible by changing the refractive index.

In the DCANP LB film, the relationship between the fundamental wave of the substrate and the refractive index at the SHG wavelength that satisfies this condition (optical conditions under which the SHG radiation mode gradually approaches the SHG waveguide mode when the Cherenkov angle approaches 0). Is shown in FIG. The solid line shows the relationship. Here, the refractive index of the clad is set to 1 (air), 1.3, 1.4.
(Organic polymer) is shown as an example, and other refractive indexes can be easily calculated. Here, the points indicated by open circles indicate the fundamental wave wavelength (1.064 nm) of various glasses and SHG.
The relation of the refractive index at the wavelength (532 nm) is shown. In this case, for example, C7 glass (manufactured by Hoya Co., Ltd.)
YTOP (Fluoropolymer manufactured by Asahi Glass Co., Ltd., refractive index 1.
34) Cladding system or PC2 (manufactured by Hoya Corporation)
A system in which poly (trifluoroethyl methacrylate, refractive index: 1.43) is clad on a glass substrate is suitable. This is, of course, easily calculated at other fundamental wavelengths (for example, 800 to 1000 nm, which is the wavelength of a semiconductor laser), so that material selection and waveguide design are possible.

The fact that the conversion efficiency of the Cherenkov radiation SHG becomes very strong by taking the phase matching condition of the waveguide mode SHG at the cut-off point means that the LB ^{(2 )} is inverted in the film thickness direction. This is true not only in the case of a film waveguide, but also in a Cherenkov radiation type SHG element of any general material system and element configuration.

In the present invention, the thickness of the cladding layer 3 of the wavelength conversion element 10 is not particularly limited,
If the thickness is set to 1 μm or more, the refractive index becomes substantially the same as that of a bulk state, and the clad and its outside (usually air)
The influence of the surface property of the interface with the substrate is reduced, which is advantageous in manufacturing.

Further, it is preferable that the cladding layer 3 of the wavelength conversion element 10 be constituted by a spin coat film. By using a spin coat film, the thickness of the LB film can be made uniform and the reliability can be increased.
Higher SHG conversion efficiency can be obtained.

The active layer 2 of the wavelength conversion element 10 described above
With 2-docosylamino-5-nitropyridine (DCA)
NP), N-docosyl-2-methyl-4-nitroaniline (DCMNA), or a Langmuir-Blodgett membrane (LB membrane) made of one of N-docosyl-paranitroaniline (DCPNA). It is preferable to configure.

The above-described DCANP, DCMNA or DC
By using an LB film made of one type of material among PNAs, a significantly higher S than that of a conventional SHG element can be achieved.
HG intensity could be obtained. That is, in the LB film,
Since the organic thin film can be controlled in units of molecular layers, the direction of the dipole moment can be controlled in units of molecular layers. Therefore, according to the present invention in which the active layer is constituted by the LB film made of these organic thin film materials, the dipole moment of the active layer is changed to the inversion position P of the sign of the SHG radiation mode field.
Can be inverted with high accuracy, and the SHG efficiency can be greatly improved.

Further, as a method of manufacturing the wavelength conversion element 10 according to the present invention, when a non-linear optical molecule is oriented and laminated using a Y-type Langmuir-Blodgett method, a monolayer of the non-linear optical molecule is developed. Substrate 1 against the water surface
The substrate 1 is rotated by a predetermined angle each time a predetermined number of times is repeated, and the substrate 1 has a second-order optical non-linearity in a direction parallel to the film surface and has a second harmonic, a sum frequency, or a difference frequency. Is at or near the node of the standing wave formed in the film thickness direction, the second-order optical nonlinear polarization susceptibility tensor χ
^The active layer 2 in which the sign of one or more components of ⁽²⁾ is inverted is accumulated, and a clad layer 3 made of an organic material having a refractive index smaller than that of the substrate 1 is accumulated on the accumulated active layer 2. Are laminated. Thereby, the dipole moment of the active layer is reduced to SH.
The inversion can be accurately performed at the inversion position P of the sign of the G radiation mode field, and the SHG efficiency can be greatly improved. Here, a single nonlinear optical molecule is used for the active layer to be formed cumulatively.

[0071]

[0072]

[0073]

[0074]

[0075]

In a wavelength conversion element in which a light propagation portion has an optical waveguide shape, the sign of the nonlinear optical susceptibility is inverted in the thickness direction of the optical waveguide portion, and the inverted position is the second harmonic of the Cherenkov radiation mode. In the vicinity of the node of the electric field distribution of the wave, what has been canceled by the overlap integration is integrated, so that the coupling constant is greatly increased and the second harmonic generation conversion efficiency is greatly improved.

At this time, the position at which the electric field of the second harmonic of the Cherenkov radiation type is reversed is calculated by a calculation method which is based on the mode coupling theory proposed in the present invention, and LB
By inverting the sign of the nonlinear optical susceptibility of the nonlinear optical molecule at that position using the method, a wavelength conversion element having a waveguide whose second harmonic generation conversion efficiency is significantly improved compared to the conventional wavelength conversion element can be obtained. Can be provided.

This structure is effective not only for the second harmonic generation wavelength conversion element but also for the phenomena involving even-order non-linear optical susceptibility such as sum frequency, difference frequency generation and parametric oscillation due to light mixing. It is also effective for improvement.

In the case of the channel type waveguide, if the nonlinear optical susceptibility is inverted not only in the film thickness direction but also in the width direction of the waveguide, Chalenkov radiation is emitted to the waveguide in the film plane. This is also effective when improving the efficiency of higher harmonics. Furthermore, not only waveguides formed from thin films such as slab type or channel type, but also fiber type waveguides, the core portion has a multilayer structure in which the nonlinear susceptibility is periodically inverted on a concentric circle. It is also effective.

By inverting the dipole moment of the active layer at the sign inversion position of the SHG radiation mode field obtained in advance by calculation, the square of the overlap integral of the nonlinear polarization wave induced by the fundamental wave and the SHG radiation mode field is obtained. And by providing a cladding layer on the active layer, the SHG radiation mode asymptotically approaches the SHG waveguide mode when the Cherenkov angle approaches 0, and is brought closer to the optical conditions that coincide with the SHG waveguide mode. Efficiency can be improved by about one digit or more compared to the SHG element of the conventional configuration.

By setting the thickness of the cladding layer to 1 μm or more, the effect of confining light is increased and higher SHG conversion efficiency can be obtained.

Further, by forming the above-mentioned clad layer by a spin coat film, the thickness of the LB film can be made uniform, and higher SHG conversion efficiency can be obtained.

Further, by forming the active layer 2 of the wavelength conversion element 10 from an LB film made of one of DCANP, DCMNA and DCPNA, the dipole of the active layer made of these organic thin film materials can be obtained. The moment can be inverted with high accuracy at the molecular layer unit at the position where the sign of the SHG radiation mode field is reversed, and the square of the overlap integral of the nonlinear polarization wave and the SHG radiation mode field is increased, thereby greatly improving the SHG efficiency. can do.

As a method of manufacturing the wavelength conversion element 10, when the non-linear optical molecules are oriented and laminated using the Y-type Langmuir-Blodgett method, the water surface on which the monomolecular layer of the non-linear optical molecules is developed On the other hand, the substrate is repeatedly lowered and raised in the vertical direction, and the substrate 1 is rotated by a predetermined angle each time the substrate is repeated a predetermined number of times, and has a second-order optical nonlinearity in a direction parallel to the film surface, a second harmonic, a sum frequency, Alternatively, at the node of the standing wave where the difference frequency is formed in the thickness direction or in the vicinity of the node, 2
The active layer 2 in which the sign of one or more components of the following optical nonlinear polarization susceptibility tensor χ ⁽²⁾ is inverted, and the refractive index is smaller than the refractive index of the substrate 1 on the accumulated active layer 2 The cladding layer 3 made of an organic material is laminated. Thereby, the dipole moment of the active layer 2 can be accurately inverted at the inversion position P of the sign of the SHG radiation mode field,
The SHG efficiency can be greatly improved. Here, a single nonlinear optical molecule is used for the active layer to be formed cumulatively.

[0084]

[0085]

[0086]

As described above, according to the wavelength conversion element of the present invention,
It is possible to obtain a high-performance wavelength conversion element, thereby realizing a short-wavelength coherent light source, and realizing a large-capacity optical disk system using the coherent light source.

[0088]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The characteristic of the analysis method of the present invention is that, as described in the above-mentioned reference 3, the mode coupling theory which has already been proven in the propagation mode analysis of an optical waveguide is further developed, and the optical waveguide portion is converted into a wave source. The present invention has established a calculation method for the electric field distribution of light with respect to the radiation type light, and calculated the electric field distribution in the film thickness direction for the second harmonic of the Cherenkov radiation type. By this calculation, the position (in the film thickness direction) where the electric field of the second harmonic of the Cherenkov radiation type is inverted is easily derived, and a large second harmonic conversion effect can be obtained by inverting the nonlinear constant at that position.

Further, the present invention is based on the finding that a technique for highly accumulating the LB film of 2-docosylamino-5-nitropyridine (DCANP) shown in the examples was established and a method for realizing the inverted structure was found. Hereinafter, preferred embodiments of the present invention will be described.

Example 1 (Computation Example) As an example, DCANP shown in Chemical Formula G, which is an organic molecule, was converted to L
The second harmonic generation wavelength conversion element of the slab type optical waveguide using the film accumulated by the method B as the optical waveguide, Nd: YA
An example of a film configuration designed for a G laser (wavelength: 1064 nm) and, at that time, showing that the conversion efficiency is greatly improved by introducing an inversion structure into the nonlinear optical waveguide, and LB
3 shows the results of cumulative experiments of the film.

The linear and second-order nonlinear optical constants of the DCANP LB film are as shown in Table 2.

[0092]

[Table 2]

FIG. 4 shows the direction of the nonlinear optical susceptibility of the DCANP LB film. When the DCANP LB film is accumulated on the substrate, the strongest second-order nonlinear optical susceptibility tensor d ₃₃ becomes the LB film accumulation. It is in the time pulling direction (pulling direction at dipping) D, and is the Z direction in the coordinate system of the refractive index expression. Therefore, in order to effectively use this tensor, a design was made to generate a radiation mode second harmonic of the TE mode by inserting a fundamental wave of the TE mode.
The condition of the refractive index of the substrate for satisfying the basic condition of the Charenkov radiation is as shown in the following equation (1). Although the effective refractive index of the optical waveguide is smaller than the refractive index of the bulk state, the refractive index of the substrate is 1.58 or less at a fundamental wave wavelength of 1.064 μm. It becomes 1.58 or more at a harmonic generation wavelength of 532 nm.

FIG. 12 shows the calculated slab type optical waveguide shape, and a glass PC2 of HOYA CORPORATION was used as a substrate.
And a DCANP LB film is formed thereon with a thickness t of 0.6.
This is a slab-type waveguide having a structure accumulated to 5 μm. At this time, the incident direction of the fundamental wave is indicated by X in the coordinate system of the refractive index expression. The square of the thickness direction of the distribution of the electric field of the TE ₀ mode of the fundamental wave to obtain the second value of the electric field distribution of the determined overlap their integral harmonics radiated satisfies therefrom Cherenkov radiation conditions. Table 3 shows the refractive index of PC2 glass.

[0095]

[Table 3]

FIG. 13 shows, as a specific design example, the square distribution of the electric field of the fundamental wave at each film thickness in the waveguide, that is, the second harmonic electric field distribution E generated from the fundamental wave and the Cherenkov radiation conditions for propagation. The second harmonic electric field distribution F to be satisfied is shown. The portion indicated by hatching is the nonlinear polarization wave intensity distribution at the film thickness b in the nonlinear waveguide.

The result of the overlap integration with the electric field distribution E of the generated second harmonic and the electric field distribution F of the second harmonic that satisfies the Cerenkov radiation condition was 43.6 (relative value). Next, FIG. 14 shows that the nonlinear optical susceptibility is inverted at 220 nm from the substrate side of the nonlinear waveguide at the position of the node e of the electric field distribution of the second harmonic, and the fundamental wave at each film thickness in the waveguide is inverted. A square distribution of an electric field, that is, an electric field distribution E of a second harmonic generated from a fundamental wave and a second harmonic electric field distribution F that satisfies the condition of propagating Cherenkov radiation are shown. This is a non-linear polarization wave intensity distribution when the non-linear optical susceptibility is inverted at the node e of the electric field distribution of the second harmonic at a film thickness b with a hatched portion.

The second wave generated from the fundamental wave at this certain film thickness
The overlap integral of the electric field distribution E of the harmonic and the electric field distribution F of the second harmonic which satisfies the Cherenkov radiation condition for propagation is 25
47, which is about 62 times that of the case without the inversion structure. The conversion efficiency is proportional to this square, which is about 3800 times. At this time, the phase matching conditions such as the Cerenkov angle are unchanged unless the refractive indices of the waveguide and the substrate are changed.

Example 2 (Preparation Example) Next, it will be shown that the DCANP LB film was actually formed with a thickness of several 100 nm and the nonlinear optical susceptibility was inverted. As described above, when DCANP is formed on a Y-type LB film, a nonlinear optical thin film having a strong nonlinear optical susceptibility tensor in the in-plane substrate pulling direction can be formed with a considerably large film thickness (from 1 μm). Have reported, and Gunter et al. Have reported on their nonlinear and linear optical properties. The present inventors have obtained almost the same results. Although a considerable part of the method is known, it will be described below.

DCANP was dissolved in chloroform to prepare a developing solution having a concentration of 0.6 mg / ml. An LB film forming apparatus manufactured by Joy Loble was used. Pure water was filled as a subphase, and a developing solution was dropped on 200 μl of the water surface to form a monomolecular layer. At this time, if the experimental system is cooled down from room temperature and kept at 15 ° C., the surface pressure (collapse surface pressure) at which the film starts to break when compressed gradually increases, and a clean monomolecular film may be formed. all right. FIG. 15 shows a π─A curve A at an experimental system temperature of 15 ° C. and a π─A curve B at an experimental system temperature of 22 ° C. It was found that a very clean monomolecular film was formed.

Through various studies, it has been found that an experimental system temperature of 15 ° C., a surface pressure of 20 mN / m, and a pulling speed of 3 to 5 mm / min are conditions for producing a high-quality LB film.
The substrate has been subjected to a hydrophobic treatment using a silane coupling agent, and the accumulation is started when the substrate is lowered. In this way, LB films of DCANP were formed on both surfaces of the substrate.

In order to examine the cumulative property, 20 and 130 monolayers were accumulated, and the optical nonlinearity of each was evaluated by measuring the second harmonic generation intensity by the Maker Fringe method.

FIG. 16 shows a maker fringe measuring device. This device has a light source section composed of a YAG laser 114 and a He-Ne laser 115 and an IR transmission filter 11.
6, ND filter 117, Fresnel rhomb prism 11
8, an optical system including a polarizer 119 and a lens 120, a sample stage 121 rotatable in a vertical direction, an IR absorption filter 122, a detection unit including a lens 123, a lens 124, and an analyzer 125, a detector for reference, and the like. It comprises an analysis unit comprising an optical system 126, an information processing device 127, and a calculator 128. This maker fringe measurement method is a typical method for measuring the nonlinear optical susceptibility. A sample 129 is placed on a sample stage 121 that rotates in the vertical direction, and an IR transmission filter 116, an ND filter 117,
Fresnel rhomb prism 118, polarizer 119, lens 1
Then, the second and third harmonics are measured by the IR absorption filter 122, the lens 123, the lens 124, and the analyzer 125. This is analyzed by the information processing device 127 and the arithmetic unit 128 to determine the maker fringe pattern by analyzing the laser beam transmitted through the optical system 126 including a detector for reference and the like.

When the nonlinear material can be processed into a parallel plate, the sample is rotated to change the incident angle of the laser. In the case of a wedge-shaped sample, the sample is moved in parallel to change the irradiation position of the laser. While continuously changing the optical path of the laser passing through the medium, a pattern (fringe pattern) in which the harmonic generation efficiency changes periodically due to the phase shift caused by the refractive index dispersion of the fundamental wave and the harmonic wave is observed. Absolute measurement of nonlinear optical susceptibility (easier method by comparison with reference material, but absolute measurement in strict sense is also possible), coherent length (basic wave and long wave are shifted by half wavelength due to refractive index difference) Required propagation distance,
In particular, it is an important parameter for studying phase matching. ) Important data such as measurement can be obtained. Further, there is a feature that a tensor component that cannot be phase-matched can be evaluated.

Since the LB film accumulation substrate measured this time has optical nonlinearity only in extremely thin portions (less than the coherent length) on both surfaces of the sample, the second harmonic generated in these two portions interferes. A fringe pattern is obtained. In this case, the cause of the phase shift is the coherent length of the substrate, and the coherent length of the LB film cannot be obtained. However, relative comparison of the nonlinear optical susceptibility is possible, and if the film thickness is known, its absolute value can be obtained.

The sample stage 121 rotates about a vertical axis. The sample 129 was rotated by ± 40 degrees with the substrate normal to the laser beam of the fundamental wave at 0 degree with the substrate pulling direction oriented horizontally, and the angle dependence of the intensity of the second harmonic generation was measured.

FIG. 17 shows DCANP consisting of 20 monolayers.
Maker fringe pattern of LB film (× 40) G, 1
The maker fringe pattern H of the DCANP LB film composed of 30 monolayers was shown, and both the fundamental wave and the second harmonic wave showed the maker fringe pattern with the polarization in the horizontal direction, and a clear fringe pattern was obtained.

FIG. 18 plots the second harmonic generation intensity I generated in each film thickness sample.

FIG. 18 is a log-log plot, and the result of measuring the slope of a straight line connecting the respective points was 2.0. This indicates that the second harmonic generation intensity increases in proportion to the square of the film thickness. Generally, the intensity of second harmonic generation induced by a laser propagating in a nonlinear optical medium is shown in Equation 8.

[0110]

(Equation 8)

In this measurement, since the film thickness is a region sufficiently smaller than the coherent length, the last vibration component can be ignored, and as a result, it is proportional to the square of the propagation length. The measurement result is L
It shows that the performance of the B film meets this equation,
This shows that there is no change in the nonlinear optical constant between the portion accumulated first and the portion accumulated later in the preparation of the B film.
In other words, it is shown that a high-quality LB film can be manufactured without deteriorating nonlinear optical performance even with a multilayer film having 100 or more layers.

Next, it will be shown that a film structure in which the nonlinear optical susceptibility was inverted was formed. According to the method already described in detail, two DCANP LB films each composed of 10 monolayers are produced. Among them, one monolayer accumulated 20 monolayers without changing the top and bottom of the substrate, and the other one accumulated 10 monolayers, then inverted the top and bottom of the substrate and accumulated 10 monolayers,
20 monolayers. The former was Comparative Example 1 and the latter was Sample 1. These nonlinearities were compared by the maker fringe method. As a result, in Comparative Example 1, the second harmonic generation intensity was almost the same as that of the above-described LB film in which 20 monolayers were accumulated, but in Sample 1, the second harmonic generation intensity was extremely small.
It was 2% or less of Comparative Example 1.

Next, the linear dichroism absorption of Sample 1 and Comparative Example 1 was measured. In FIG. 19, a line J represents an absorption spectrum of Sample 1 when light was irradiated in parallel with the substrate lifting direction,
Line K is the absorption spectrum of Sample 1 when light is irradiated perpendicular to the substrate lifting direction, line L is the absorption spectrum of Comparative Example 1 when light is irradiated parallel to the substrate lifting direction,
Line M shows the absorption spectrum of Comparative Example 1 when light was irradiated perpendicularly to the substrate lifting direction.
No difference was seen between them.

These results indicate that the nonlinearity of the sample 1 was much smaller than that of the comparative example 1 because the orientation of the LB film was not randomly disturbed (if the orientation was random, if the absorption spectrum was Does not change),
This indicates that an LB film applied in an anti-parallel orientation to the orientation direction of the LB film applied first was formed.

Example 3 (Preparation of DCANP LB film) Based on the design example, an LB film of 2-docosylamino-5-nitropyridine (DCANP) having an inverted structure was prepared. DCA
It is known that the thickness of one layer of the NP LB film is 2.21 nm. (Reference 6: G. Descher et.
al. “Spectroscopicinvestig
ations of LB mono- and mu
ltilaiers of 2-docosylami
no-5-nitropyridine; promi
sing candidates for non-l
inear and integrated opti
cs ", Ann. Int. Conf. of the I
EEE Engineering in Medici
ne and Biology Society, vo
l. 12, no. 4,1990, pp. 1708) The substrate used was crown glass (B270-superw).
item; DESAG). Although the accuracy of the refractive index data of the glass is not good, it slightly deviates from the condition for obtaining a high conversion efficiency, but the film thickness is slightly reduced so as to obtain the Cerenkov radiation type second harmonic generation more reliably. So accumulated.

That is, according to the method of Example 2, 10
After accumulating 0 monolayers, inverting the substrate, 160
Monolayers were accumulated. This was designated as Sample 2. Also,
As a comparative sample, a film in which 260 monolayers were accumulated without inverting the substrate was also prepared. This was designated as Comparative Example 2.

When the nonlinearity of the LB sample 2 of the DCANP having the inverted structure was measured by the maker fringe method in the same manner as in Example 2, only the second harmonic generation intensity of the same level as that of the LB film in which 60 monolayers were accumulated was obtained. It could not be obtained, and it could be estimated that the structure had the nonlinear optical susceptibility inverted. FIG. 20 shows the linear dichroic absorption spectra of Sample 2 and Comparative Example 2. In the figure, the dotted line shows the absorption spectrum of Sample 2, and the solid line shows the absorption spectrum of Comparative Example 2. The results of the dichroic absorption spectrum also indicated that the DCANP molecules were arranged in one direction. In addition, it was found from the interference pattern appearing at the time of the absorption spectrum measurement that the film thickness of these two samples did not differ by 1%.

The second harmonic generation intensities were compared.
The experimental apparatus is shown in FIG. This device is a YAG laser 3
A light source unit composed of 0 and He-Ne laser 31, a Fresnel rhomb prism 32, an ND filter 33, an ND filter 34, an IR transmission filter 35, an iris 3φ 36,
An optical system including an XYZ fine-tunable objective lens (NA / 0.25) 37, and XY fine-tuning θ {fine-tunable sample stage
The sample part consisting of two parts, IR cut filter 39, Si-
It comprises a detection section comprising a photodetector 40. YA
The G laser 30 is incident on the sample 38 from the end face of the Langmuir-Blodgett film. YAG laser 30
Before entering into the objective lens (NA / 0.25) 37, the beam pattern was adjusted to about 3 mm through an iris 3φ36. In the vicinity of the surface of the sample 38, the diameter is reduced to about 20 μ. The pulse width of the YAG laser 30 is 10 ns,
The beam power intensity at the position where the light repeatedly enters the sample at 10 Hz is about 10 ⁴ W /.

FIG. 22 shows a method of forming the sample 38.
The glass substrate 41 is divided at the center along the substrate pulling direction N of the sample 2 and a laser is applied from the end face a of the glass substrate 41 in the polarization direction O along the Langmuir-Blodgett film 42 on the substrate surface in a direction perpendicular to the substrate pulling direction N. When incident
The second harmonic was generated as in the second harmonic generation direction P.

When the second harmonic generation intensity was measured using the apparatus shown in FIG. 21, the second harmonic of 532 nm was about 8 degrees from the end face opposite to the end face on which the YAG laser was incident, as at an angle d. It was confirmed that the light was emitted as Charenkov radiation toward the substrate surface without the Langmuir-Blodgett film at an angle. Therefore, when the second harmonic generation intensity of Sample 2 was compared with that of Comparative Example 2, as shown in FIG. 23, the second harmonic generation intensity Q of Sample 2 in which the nonlinear optical constant of the film was inverted halfway was obtained. It was confirmed that the second harmonic was emitted about three times or more stronger than the second harmonic generation intensity R of Comparative Example 2.

As an example of a sequence that does not completely invert the molecule, φ
Examples 4 and 5 for the case of = 90 degrees will be described.

Example 4 The glass substrate was made of the same material as in Examples 2 and 3, but 5 cm × 5
cm and a thickness of 1 mm were prepared. Two sheets of glass are laminated in the same manner as in Example 2, and DCANP is applied to the outer surface.
LB film is accumulated. After accumulating the first five molecular layers in the same manner as in Example 2, one of the substrates was rotated 90 degrees in air, and then another five molecular layers were accumulated. The so-called cumulative trace at this time is shown in FIG. 26, but it is almost the same before and after the rotation by 90 degrees, and it is determined that a beautiful accumulation has been achieved. The absorption dichroic ratio of these samples was measured. The dichroic ratio of the sample accumulated by rotating it by 90 degrees was approximately 1, and the dichroic ratio of the sample not rotated was 1.5, which was substantially the same as in Example 2. From this, DCANP LB rotated 90 degrees and accumulated
In the film, it was determined that the molecules were rotated by 90 degrees in the first accumulation and the second accumulation as expected.

Example 5 Next, a waveguide was manufactured in the same manner as in Example 3. The glass substrate is the same material as in Examples 2 and 3, but 5cm x 5c
m and a thickness of 1 mm were prepared. After accumulating 50 molecular layers for the first time in the same manner as in Example 3, the substrate was rotated by 90 degrees, and an additional 80 molecular layers were accumulated. On the other hand, a layer obtained by accumulating 130 molecular layers as they were was prepared for reference.

The accumulated central portion of these samples was cut out into a ribbon shape having a width of about 10 mm so that the substrate pulling direction (first cumulative substrate pulling direction in the case of a sample rotated by 90 degrees) was oriented in the longitudinal direction. . For these two, the same experimental method and experimental apparatus as in Example 3 were used to generate Cerenkov radiation SHG, and their intensities were compared. The laser beam is incident in the width direction of 10 mm from the cut end face.

It was confirmed that the sample accumulated by rotating by 90 degrees generated Cherenkov radiation SHG twice or more brighter than the sample accumulated without rotating.

Example 6 (Fabrication of Channel-Type Waveguide) A nonlinear optical material 44 in which the signs of the nonlinear optical susceptibility are arranged in a predetermined direction on a substrate 43 as shown in FIG. It is apparent from the structure that the inverted structure of the present invention does not cause any obstacle in producing a channel type waveguide in which the nonlinear optical material 45 is disposed and the cap layer 46 is covered thereon. Since the fundamental wave having high light intensity can be propagated over a long distance, the structure is extremely effective for improving the wavelength conversion efficiency.

Embodiment 7 As shown in FIG. 25, on a substrate 47, a nonlinear optical material 48 in which the signs of the nonlinear optical susceptibility are arranged in a predetermined direction and a nonlinear optical material 49 in which the sign of the nonlinear optical susceptibility is inverted are arranged. In constructing the domain inversion structure within the coherent length l in the waveguide direction S, the inversion structure in the film thickness direction according to the present invention does not cause any obstacle and can be used together. Is obvious, and in this case, a very large conversion efficiency can be expected.

The present invention is described below with reference to a YAG laser beam (wavelength
Regarding a wavelength conversion element that converts (64 nm) into coherent light having a wavelength of 532 nm, another example of element structure design, a method of manufacturing the element, and evaluation of element characteristics will be described.

Example 8 (1) Device Structure Design A device was designed using an electromagnetic analysis result in an optical waveguide based on mode coupling theory. Since the dipole moment of the DCANP LB film is oriented parallel to the substrate, the second-order nonlinear optical constant χ ⁽²⁾ is also oriented parallel to the substrate. Therefore, the wavelength conversion is performed in the TE mode-TE
Mode conversion was assumed. For the phase matching of the SHG, a Cerenkov phase matching method was used.

In the Cerenkov phase matching system, the selection of the substrate is important. In this case, a glass substrate PC2 having a refractive index of 1.51 was used. The thickness of the organic nonlinear waveguide was designed by the mode coupling theory, and the total thickness T ₁ of the active layer 2 composed of the organic thin film was set to 570 nm.

FIG. 6 shows an element structure of a two-dimensional slab waveguide type SHG. The first organic thin film 2a and the second organic thin film 2b made of the aforementioned DCANP were accumulated on the substrate 1 made of the above-mentioned PC2 glass by the LB method. Each of the first and second organic thin films 1 and 2 has the direction of the second-order nonlinear optical susceptibility χ ⁽²⁾ inverted, and the first thin film 1 has a thickness t ₁ of 330 nm and a second The thickness t _{2 of the} thin film ₂ was set to 250 nm. Then, a cladding layer 3 having a thickness of about 1 μm is formed thereon.

FIG. 27 is a sectional view of a three-dimensional ridge optical waveguide type organic nonlinear optical element. In this case, it is possible to configure the same material and film thickness as those of the element shown in FIG.

(2) Element Manufacturing Method In this example, an apparatus manufactured by Joysle Bull Co., Ltd. was used as an LB film manufacturing apparatus. DCANP is dissolved in a chloroform solution to prepare a developing solution having a concentration of 0.5 mg / ml. The subphase was pure, and the developing solution was dropped on 300 μl water surface. Considering the cumulative nature of the LB film,
It is necessary that the collapse surface pressure is large and that the monomolecular film area has little change with time when kept under a certain cumulative condition (constant surface pressure). A surface pressure of 20 mN / m was employed as one of the cumulative conditions that satisfy such conditions.

Next, a cumulative experiment of the LB film was performed. Substrate 1
Was used, a hydrophobic treatment was performed using a silane coupling agent before accumulation, and accumulation was performed. Since the surface of the substrate 2 is hydrophobic, the accumulation starts from the lowering of the substrate, and the moving speed of the substrate during the accumulation is 10 to 15 m.
m / min. After the first organic thin film 2a was formed by accumulating 150 molecular layers of the organic thin film material composed of DCANP, the substrate 1 was inverted, and further 114 molecular layers were accumulated to form the second organic thin film 2b. From the trace at the time of accumulation (the relationship between the position of the substrate and the accumulated and reduced surface area), it was confirmed in this accumulation experiment that a good Y-type LB film having an accumulation ratio of 1 was formed. In this cumulative experiment, all operations were performed by computer control, including the vertical movement of the substrate.

After the accumulation of the LB film, Poly (trifluoroethyl methacryol) having a refractive index of 1.43 was obtained by a well-known spin coating method.
late) An organic material such as (poly (trifluoroethyl methacrylate)) was formed to a thickness of 1 μm.

In order to fabricate a three-dimensional ridge waveguide type organic nonlinear optical element shown in FIG. 27 later, the two-dimensional waveguide type organic nonlinear optical element shown in FIG. 6 was fabricated by the above-described fabrication method. Thereafter, it can be formed by patterning into a predetermined pattern by applying photolithography or the like.

(3) Element Evaluation First, as an example of nonlinear optical characteristics, accumulated DCAN
The second-order nonlinear optical susceptibility χ ⁽²⁾ of the PLB film was evaluated. The evaluation sample was produced by accumulating 10 LB film samples on one side of the glass substrate by the LB method. The well-known maker fringe method was used as the evaluation method. First, a glass substrate was measured, and it was confirmed that the glass substrate did not exhibit nonlinearity. Next, an LB film sample was measured. As a result, SH
The dependence of the G intensity on the incident angle was observed, and it was confirmed that the produced LB film sample had second-order nonlinear optical characteristics. From the anomalous direction of the d constant obtained from the evaluation results, it was found that the dipole moment was in a direction parallel to the substrate in this case.

Before spin coating of the cladding layer 3, the polarized UV-visible spectrum of the active layer 2 (optical waveguide) made of the LB film was measured. The normalized linear dichroic ratio was about 0.23. This value is DCANP L
The value coincided with the value of the normal accumulation sample of the B film, and it was confirmed that the produced active layer 2 had a favorable molecular arrangement structure.

Next, optical waveguide characteristics as a wavelength conversion element will be described. Here, as an example of the nonlinear optical element using the organic nonlinear optical material, the characteristic evaluation of the Cerenkov radiation type SHG element shown in FIG. 6 was performed by an evaluation experiment system shown in FIG. In FIG. 28, a laser beam L from a YAG laser 11 passes through a cylindrical lens 12, is collected by an objective lens 13, and passes through a sample 14 to emit a second harmonic light SHG. 15 is infrared light (I
R) It is a cut filter. The arrow d indicates that this sample 14
Shows the accumulation direction of the LB film in FIG. In such a configuration, YAG laser light is introduced into the optical waveguide, that is, the active layer 2 by using the lens coupling method, and the SAG emitted from the active layer 2 is emitted.
HG light was detected by a photomultiplier (not shown) to evaluate the device. As a result, coherent SHG light having a wavelength of 532 nm could be observed from the end of the active layer 2.

In this case, it was found that the SHG intensity was improved by one digit or more as compared with the sample in which the cladding layer 3 was not provided. Accordingly, it was confirmed that the structure in which the cladding layer was provided on the active layer in the organic nonlinear optical element of the present invention was effective for improving the SHG conversion efficiency.

In this embodiment, the organic thin film material is DC
Although the case where the LB film made of ANP is used is shown,
Other materials, for example, DCMNA (N-
L comprising docosyl-2-methyl-4nitroaniline)
Similar effects could be obtained even if each of the organic thin films 2a and 2b of the active layer 2 was composed of the B film or the LB film composed of DCPNA (N-docosyl-paranitroaniline) shown in Chemical Formula 6 below. .

[0142]

Embedded image

[0143]

Embedded image

Embodiment 9 Next, the active layer 2 is constituted by an organic nonlinear optical element according to another embodiment of the present invention, that is, an organic superlattice in which two or more kinds of organic materials are periodically laminated one by one. Show the case.

(1) Element Structural Design In this case as well, the element was designed using the results of electromagnetic analysis in the optical waveguide based on the mode coupling theory. In this example, as a material constituting the organic superlattice,
Shown in C12PPy (5- (p-dodecyloxyphenyl) pyrazine-2-carboxyl acid) and arachidic acid (C ₁₉ H ₃₉ COOH) were used.

[0146]

Embedded image

Since the dipole moment of the organic superlattice formed by the hetero LB film with C12PPy and arachinic acid is oriented in a direction perpendicular to the substrate, the second-order nonlinear optical constant χ ⁽²⁾ also increases with respect to the substrate. Orientated vertically. Therefore, TM mode-TM mode conversion was assumed for wavelength conversion. FIG. 29 shows the electric field distribution in the hetero LB film optical waveguide in this case, that is, in the active layer. R is the square of the fundamental mode,
S indicates the SHG radiation mode, and P indicates the sign inversion position.

Also in this case, the SHG phase matching was performed by using a Cherenkov phase matching method, and a PC2 glass substrate having a refractive index of 1.51 was used as the substrate. Organic nonlinear waveguide by the mode coupling theory, i.e. the total thickness T ₁ of the active layer 2 made of an organic superlattice was 570 nm.

The first organic superlattice
The organic thin film 2a to the thickness t ₁ 320 nm, and the thickness t ₂ of the second organic thin film 2b configured as 250 nm. FIG. 30A is a schematic enlarged sectional view of each of these organic thin films 2a and 2b.
And B. Each of the thin films 2a and 2b is formed by alternately laminating a first material layer 5 or 7 and a second material layer 6 or 8 alternately on a monomolecular layer basis. From these thin films 2a and 2b orientation of the nonlinear optical susceptibility of the secondary chi ⁽²⁾ is opposite to as shown by the arrow y ₁ and y _2. Then, a cladding layer 3 having a thickness of about 1 μm is formed thereon.

In this case, as shown in FIG. 27, a three-dimensional ridge type optical waveguide element structure can be adopted.

(2) Element Fabrication Method In this case, as in Example 8, the active layer 2 made of an organic superlattice made of C12PPy-arachinic acid was fabricated by using the LB method. In this case, a hetero LB film manufacturing apparatus was used.

First, C12PPy and arachidic acid are dissolved in a chloroform solution to prepare a developing solution having a concentration of 0.5 mg / ml. The subphase was barium chloride, and the developing solution was dropped on 200 μl of water. Also in this case, the surface pressure is set to 25 in consideration of the cumulative property of the LB film.
mN / m.

Next, a cumulative experiment of the LB film was performed. A glass substrate was used as a substrate, and a hydrophobic treatment was performed using a silane coupling agent before accumulation. Since the surface of the substrate is hydrophobic, the accumulation starts from the lowering of the substrate, and the moving speed of the substrate during the accumulation is 10 to 15 mm / min. And FIG.
As shown in 0A, performs the first material layer 5 arachidic acid of the first organic thin film 2a, the second material layer 6 as C12PPy, hereinafter arachidic acid, C12PPy, the cumulative _.... order of, An organic superlattice hetero LB film was produced. From the trace at the time of accumulation, in this accumulation experiment, a good Y with an accumulation ratio of 1 was obtained.
It was confirmed that a mold LB film was formed. In this cumulative experiment, all the operations, including the vertical movement of the substrate, were performed by computer control.

After the first organic thin film 2a is formed to a thickness of 320 nm by the above-described accumulation method, the accumulation order of the LB film materials is reversed, and as shown in FIG.
Is C12PPy, the second material layer 8 is arachidic acid,
Subsequently, 250 nm of the second organic thin film 2b was accumulated in the order of C12PPy, arachidic acid, _.... In the hetero LB film manufacturing apparatus, the accumulation order of the LB film materials can be easily inverted by reversing the moving direction of the substrate.

Next, a cladding layer 3 made of poly (trifluoroethyl methacrylate) or the like was formed thereon to a thickness of 1 μm by a well-known spin coating method. In this case, the refractive index of the cladding layer 3 is 1.43.

Thereafter, the cladding layer 3 and the active layer 2 were patterned into a predetermined pattern by applying photolithography or the like, thereby producing a three-dimensional ridge waveguide type SHG element shown in FIG.

(3) Element Evaluation In this case as well, as an example of the nonlinear optical characteristics, the accumulated C12PPy-arachinic acid organic superlattice (hetero L
(B film) was evaluated for the second-order nonlinear optical susceptibility χ ⁽²⁾ . The evaluation sample was placed on one side of the glass substrate by LB method.
Film samples were made by accumulating 10 layers. The maker fringe method was used as an evaluation method. After confirming that no nonlinearity was exhibited by measuring the glass substrate, an LB film sample was measured. As a result, the dependency of the SHG intensity on the incident angle was observed, and it was confirmed that the produced LB film sample had second-order nonlinear optical characteristics. From the anomalous direction of the d constant obtained from the evaluation results, it was found that the dipole moment was in a direction perpendicular to the substrate.

Next, the optical waveguide characteristics of the organic nonlinear optical element will be described. Also in this case, the evaluation experiment system described with reference to FIG.
The laser light was introduced into the optical waveguide, that is, the active layer 2, and the SHG light emitted from the active layer 2 was detected by a photomultiplier (not shown) to evaluate the device. As a result, coherent SHG light having a wavelength of 532 nm could be observed from the end of the active layer 2.

In this case, it was found that the SHG intensity was improved by one digit or more compared to the sample in which the clad layer 3 was not provided. Thus, it was confirmed that the configuration in which the active layer 10 clad layer in the organic nonlinear optical element of the present invention was provided was effective for improving the SHG conversion efficiency.

In this embodiment, the organic thin film is made of C12PPy
Of the organic superlattice hetero-LB film composed of
Hetero LB film in place of Py laminating a C ₁₆ H ₃₃ -P3CNQ and arachidic acid shown in the formula 8 below, or more composed hetero LB film as C ₁₆ H ₃₃ -Q3CNQ and arachidic acid shown in chemical formula 9 below Thus, the same effect could be obtained even if the organic thin films 2a and 2b of the active layer 2 were formed.

[0161]

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[0162]

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Embodiment 10 Next, an example of an organic nonlinear optical element according to another embodiment of the present invention shown in FIG. 7 will be described in detail.

(1) Element structure design In this case, electromagnetic analysis in an optical waveguide by mode coupling theory
An element was designed using the results. Also in this example
As in Example 9, the material constituting the organic superlattice was
To obtain hetero LB using C12PPy and arachidic acid.
An organic superlattice structure with a film was adopted. As mentioned above
Second-order nonlinear optical constant χ ⁽²⁾Is on the board
Orientated vertically. Therefore, the wavelength conversion is TM
Mode-TM mode conversion was assumed. Fig. 31
, The electric field in the hetero LB film waveguide, that is, the active layer 2
Equivalent to distribution.

Also in this case, the above-mentioned embodiment 8
And 9, using the Cherenkov phase matching scheme
HG phase matching is performed, and a substrate having a refractive index of 1.51 P
With C2 glass substrate, a C12PPy- arachidic organic total thickness T ₂ of the superlattice hetero LB film was 650 nm.
Then, a three-dimensional ridge waveguide type SHG element shown in FIG. 7 was manufactured.

(2) Element Fabrication Method In this case as well, as in the above Examples 8 and 9,
Using the LB method, an active layer 2 made of an organic superlattice made of C12PPy-arachinic acid was produced. In this case hetero L
A B film production apparatus was used.

First, C12PPy and arachidic acid are dissolved in a chloroform solution to prepare a developing solution having a concentration of 0.5 mg / ml. The subphase was barium chloride, and the developing solution was dropped on 200 μl of water. Also in this case, the surface pressure is set to 25 in consideration of the cumulative property of the LB film.
mN / m.

Next, a cumulative experiment of the LB film was performed. A glass substrate was used as a substrate, and a hydrophobic treatment was performed using a silane coupling agent before accumulation. Since the surface of the substrate is hydrophobic, the accumulation starts from the lowering of the substrate, and the moving speed of the substrate during the accumulation is 10 to 15 mm / min. And FIG.
As shown in 0A, performs the first material layer 5 arachidic acid of the first organic thin film 2a, the second material layer 6 as C12PPy, hereinafter arachidic acid, C12PPy, the cumulative _.... order of, An organic superlattice hetero LB film was produced. From the trace at the time of accumulation, in this accumulation experiment, a good Y with an accumulation ratio of 1 was obtained.
It was confirmed that a mold LB film was formed. In this cumulative experiment, all the operations, including the vertical movement of the substrate, were performed by computer control.

After the first organic thin film 2a is formed to a thickness of 400 nm by the above-described accumulation method, the accumulation order of the LB film materials is reversed, and as shown in FIG.
Is C12PPy, the second material layer 8 is arachidic acid,
Subsequently, 250 nm of the second organic thin film 2b was accumulated in the order of C12PPy, arachidic acid, _.... Then, after that, the cladding layer 3 and the active layer 2 are patterned into a predetermined pattern by applying photolithography or the like.
The three-dimensional ridge waveguide type SHG element shown in FIG.

(3) Element Evaluation In this case as well, as an example of the nonlinear optical characteristics, the accumulated C12PPy-arachinic acid organic superlattice (hetero L
The second-order nonlinear optical susceptibility χ ⁽²⁾ of the ⁽ B film) was evaluated by the Maker Fringe method in the same manner as in Example 9 above, and it was confirmed that the dipole moment was in a direction perpendicular to the substrate.

Next, the optical waveguide characteristics of the wavelength conversion element will be described. Also in this case, the YAG laser light is introduced into the optical waveguide, that is, the active layer 2 using the lens coupling method by the evaluation experiment system described in FIG. 28, and the SHG light emitted from the active layer 2 is converted into a photomultiplier ( (Not shown), and the device was evaluated. As a result, a coherent SHG having a wavelength of 532 nm from the end of the active layer 2
Light could be observed.

In this case, in spite of the configuration in which the cladding layer 3 is not provided, the SHG element of the conventional configuration, ie, in which the direction of the nonlinear optical susceptibility χ ⁽²⁾ is not inverted at the sign inversion position of the SHG radiation mode is compared. Thus, the SHG intensity could be improved by one digit or more.

Also in this case, as the organic superlattice, C12PPy is replaced by C
₁₆ H ₃₃ -P3CNQ or C ₁₆ H ₃₃ various materials such -Q3CNQ can be used.

Further, in Examples 8 and 9, only one of the two or more organic materials constituting the organic superlattice, that is, in this case, only C12PPy has a second-order nonlinear optical susceptibility χ ⁽²⁾ Although the case of having is described, in order to further increase the SHG conversion efficiency, each organic material has a non-linear optical susceptibility, and the direction of the non-linear optical susceptibility of adjacent molecular layers is in the same direction. It is desirable.

Further, the wavelength conversion element of the present invention is not limited to the case of obtaining SHG light with respect to laser light of 1064 nm wavelength by the above-described YAG laser, but may be any other wavelength conversion element that obtains coherent SHG light of various wavelengths. It is needless to say that the present invention can be applied to the case where it is used and various modifications can be made without departing from the configuration of the present invention.

[0176]

According to the present invention, there is provided a wavelength conversion element having a light propagation portion having an optical waveguide shape, wherein a sign of a main nonlinear optical susceptibility tensor component is inverted in a thickness direction of the optical waveguide portion.
If the reversal position is near the node of the electric field distribution of the second harmonic generation light in the Charenkov radiation mode, those that have been canceled by the overlap integration will be integrated and the coupling constant will increase significantly, The conversion efficiency of the second harmonic generation is greatly improved.

This structure is effective not only in the second harmonic generation wavelength conversion element but also in the phenomena involving even-order nonlinear optical susceptibility, such as sum frequency and difference frequency generation due to light mixing, and parametric oscillation. It is also effective for improvement.

In the case of the channel type waveguide, if the nonlinear optical susceptibility is inverted not only in the film thickness direction but also in the width direction of the waveguide, the Chalenkov radiation is emitted to the waveguide in the film plane. This is also effective when improving the efficiency of higher harmonics. Furthermore, not only waveguides formed from thin films such as slab type or channel type, but also fiber type waveguides, the core portion has a multilayer structure in which the nonlinear susceptibility is periodically inverted on a concentric circle. It is also effective.

By inverting the dipole moment of the active layer at the sign inversion position of the SHG radiation mode field obtained in advance by calculation, the square of the overlap integral of the nonlinear polarization wave induced by the fundamental wave and the SHG radiation mode field is obtained. By providing a cladding layer on the active layer, the SHG conversion efficiency can be increased by about one digit or more as compared with a conventional SHG element.

Further, by setting the thickness of the cladding layer to 1 μm or more, the effect of confining light is increased and higher SHG conversion efficiency can be obtained.

Further, by forming the above-mentioned clad layer by a spin coat film, the thickness of the LB film can be made uniform, and higher SHG conversion efficiency can be obtained.

Furthermore, by forming the active layer 2 of the wavelength conversion element 10 from an LB film made of one of DCANP, DCMNA and DCPNA, the dipole of the active layer made of these organic thin film materials is obtained. The moment can be inverted with high accuracy at the molecular layer unit at the position where the sign of the SHG radiation mode field is reversed, and the square of the overlap integral of the nonlinear polarization wave and the SHG radiation mode field is increased, thereby greatly improving the SHG efficiency. can do.

The active layer 2 of the wavelength conversion element 10
Is composed of an organic superlattice in which two or more types of organic materials are periodically stacked one by one for each molecule. Therefore, the direction of the dipole moment can be easily and accurately adjusted in units of molecular layers by changing the stacking order. The SHG conversion efficiency can be changed by at least one order of magnitude compared to the conventional configuration, that is, the SHG device having the configuration in which the nonlinear optical constant χ ⁽²⁾ is not inverted in the film thickness direction. Can be obtained.

As a method for manufacturing the wavelength conversion element 10, when the non-linear optical molecules are oriented and laminated using the Y-type Langmuir-Blodgett method, the monomolecular layer of the non-linear optical molecules is spread on the water surface. On the other hand, the substrate is repeatedly lowered and raised in the vertical direction, and the substrate 1 is rotated by a predetermined angle each time the substrate is repeated a predetermined number of times, and has a second-order optical nonlinearity in a direction parallel to the film surface, a second harmonic, a sum frequency, Alternatively, at the node of the standing wave where the difference frequency is formed in the thickness direction or in the vicinity of the node,
The active layer 2 in which the sign of one or more components of the following optical nonlinear polarization susceptibility tensor χ ⁽²⁾ is inverted, and the refractive index is smaller than the refractive index of the substrate 1 on the accumulated active layer 2 The cladding layer 3 made of an organic material is laminated. Thereby, the dipole moment of the active layer 2 can be accurately inverted at the inversion position P of the sign of the SHG radiation mode field,
The SHG efficiency can be greatly improved. Here, a single nonlinear optical molecule is used for the active layer to be formed cumulatively.

[0185]

[0186]

[0187]

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a nonlinear optical susceptibility inversion structure.

FIG. 2 is a schematic diagram showing the sequence of 2-dokosylamino-5-nitropyridine during accumulation.

FIG. 3 is a schematic diagram showing an arrangement of 2-docosylamino-5-nitropyridine after the substrate is turned upside down.

FIG. 4 is a schematic diagram showing a direction of a nonlinear optical susceptibility.

FIG. 5 is a schematic diagram showing a direction of a rotation angle of a substrate.

FIG. 6 is a schematic enlarged sectional view of an example of the organic nonlinear optical element of the present invention.

FIG. 7 is a schematic enlarged cross-sectional view of an example of the organic nonlinear optical element of the present invention.

FIG. 8 is a diagram showing the relationship between SHG intensity and the thickness of an active layer.

FIG. 9 is a characteristic diagram showing a relationship between a length in a depth direction and an electric field intensity.

FIG. 10 is a characteristic diagram showing a relationship between an active layer thickness and an effective refractive index.

FIG. 11 is a characteristic diagram showing a relationship between a substrate refractive index of a fundamental wave and a refractive index of an SHG wavelength.

FIG. 12 is a schematic perspective view showing a calculated slab type optical waveguide shape.

FIG. 13 is a characteristic diagram showing respective electric field distributions of a generated second harmonic and a radiated second harmonic.

FIG. 14 is a characteristic diagram showing electric field distributions when nonlinear optical susceptibility inversion is included.

FIG. 15 is a characteristic diagram showing a π─A curve of a 2- {docosylamino} 5-nitropyridine monomolecular film.

FIG. 16 is a schematic diagram showing a maker fringe measuring device.

FIG. 17 is a characteristic diagram showing a maker fringe pattern of a 2-docosylamino-5-nitropyridine Langmuir-Blodgett film composed of 20,130 monomolecular layers.

FIG. 18 is a characteristic diagram showing a relationship between the second harmonic generation intensity and the total number of Langmuir-Blodgett films.

19 is a linear dichroic absorption spectrum diagram of Sample 1 and Comparative Example 1. FIG.

FIG. 20 is a linear dichroic absorption spectrum diagram of Sample 2 and Comparative Example 2.

FIG. 21 is a schematic diagram showing a Charenkov radiation type second harmonic generation experimental device.

FIG. 22 is a schematic diagram showing a molding method of a sample 2 and a laser incident direction.

FIG. 23 is a characteristic diagram illustrating second harmonic generation intensities of Sample 2 and Comparative Example 2.

FIG. 24 is a schematic perspective view showing the shape of a channel waveguide.

FIG. 25 is a schematic view showing a combination with a waveguide direction inversion distribution.

FIG. 26 is a characteristic diagram showing a change in conversion efficiency with respect to φ.

FIG. 27 is a schematic enlarged sectional view of another example of the organic nonlinear optical element of the present invention.

FIG. 28 is a block diagram of an SHG light evaluation experiment system.

FIG. 29 is a diagram showing electric field distributions of a fundamental wave and a second harmonic in the active layer and the substrate of the organic nonlinear optical element.

FIG. 30 is a schematic enlarged sectional view of a main part of another example of the organic nonlinear optical element of the present invention.

FIG. 31 is a diagram showing electric field distributions of a fundamental wave and a second harmonic in an active layer and a substrate of an organic nonlinear optical element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Active layer 2a ... 1st organic thin film 2b ... 2nd organic thin film 3 ... Cladding layer 5 ... 1st material layer 6 ... 2nd 7 ... First material layer 8 ... Second material layer 43 ... Substrate 44 ... Non-linear optical material 45 ... Non-linear optical material 46 ... Cap layer 47 ... Substrate 48: Non-linear optical material 49: Non-linear optical material C: Non-linear optical susceptibility Orientation direction S: Guide direction l: Coherent length

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Born Haworth 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Yoshiyoshi Ishibashi 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (56) References JP-A-5-210133 (JP, A) Opt. Spectrosc. (US SR), Vol. 58, No. 4,558-559 Polymers in Nonlinear near Optics, Electronic and Photonic Applications of Polymers, American Chemical Society, 297-330 IEEE J.C. Quan. Select ron. , Vol. 27, No. 3, 502-508 IEICE Transactions, Vol. J 74-CI, No. 4,119-125 Jpn. J. Appl. Phys. , Vol. 30, No. 5,957-982 Optics Communications, Vol. 85, No. 2, 3, 247-253 Proc. SPIE Int. SoC. Opt. Eng. , Vol. 1361, Pt. 1, 589-598 Electron. Lett. , Vol. 22, No. 9,460-462 Applied Physics, Vol. 60, No. 6, 586-590 Applied Physics, September 10, 1992, Vol. 61, No. 9, 910-917 (58) investigated the field (Int.Cl. ⁷ , DB name) G02F 1/37 JICST file (JOIS)

Claims (8)

(57) [Claims] 1. A wavelength conversion element in which a nonlinear optical waveguide is formed on a substrate by orienting and stacking nonlinear optical molecules using the Langmuir-Blodgett method, comprising one kind of nonlinear optical molecules, The second harmonic, the sum frequency, or the difference frequency has a second-order optical nonlinearity in a direction parallel to the substrate surface, and a generated second harmonic, a sum frequency, or a difference frequency is formed at or near a node of a standing wave formed in the film thickness direction. An active layer in which the sign of one or more components of the second-order optical nonlinear polarization susceptibility tensor χ ⁽²⁾ is inverted; and an organic layer laminated on the active layer and having a refractive index smaller than that of the substrate. A wavelength conversion element having a cladding layer made of a material. 2. The method according to claim 1, wherein the active layer is 2-docosylamino-5.
2. A Langmuir-Blodgett membrane formed from one material selected from the group consisting of -nitropyridine, N-docosyl-2-methyl-4nitroaniline, and N-docosyl-paranitroaniline. Wavelength conversion element. 3. The method according to claim 1, wherein the cladding layer is made of a fluorine-based polymer soluble in a fluorine-based solvent.
The wavelength conversion element as described in the above. 4. The second harmonic of a Cerenkov radiation type having a Cerenkov angle of approximately 0 degrees by adjusting the refractive index of the substrate, the refractive index and thickness of the nonlinear optical molecule, and the refractive index and thickness of the cladding layer. 2. The wavelength conversion element according to claim 1, wherein a wave is obtained. 5. A method for manufacturing a wavelength conversion element having a nonlinear optical waveguide formed on a substrate by orienting and stacking nonlinear optical molecules using a Y-type Langmuir-Blodgett method, The substrate is repeatedly lowered and raised in the vertical direction with respect to the water surface on which the monomolecular layer is developed, and the substrate is rotated by a predetermined angle each time the substrate is repeated a predetermined number of times, so that the second-order optical nonlinearity is parallel to the film surface. One or more of the second-order optical non-linear polarization susceptibility tensor χ ⁽²⁾ at or near a node of the standing wave where the second harmonic, sum frequency, or difference frequency forms in the film thickness direction. Accumulating an active layer in which the signs of the components are inverted; and laminating a clad layer made of an organic material having a refractive index smaller than the refractive index of the substrate on the accumulated active layer. Features Method for manufacturing a wavelength conversion element that. 6. The method according to claim 5, wherein in the step of accumulating the active layers, a single nonlinear optical molecule is stacked.
A method for manufacturing the wavelength conversion element according to the above. 7. The method according to claim 7, wherein the single nonlinear optical molecule is 2-
Docosylamino-5-nitropyridine, N-docosyl-
The method according to claim 6, wherein one kind of material selected from 2-methyl-4nitroaniline and N-docosyl-paranitroaniline is used. 8. The method according to claim 5, wherein in the step of laminating the cladding layer, a cladding layer is formed by spin-coating a fluorine-based polymer soluble in a fluorine-based solvent. .