JPH0367232A - Optical wavelength converting element - Google Patents

Abstract

PURPOSE:To relieve the conditions for phase matching by using an org. nonlinear optical material which is lower in the refractive index to the wavelength of a wavelength converting wave than the refractive index to the wavelength of a basic wave as a material to constitute a waveguide part so that the effective refractive indices sensed by the basic wave and wavelength converting wave respectively guided in zero order mode are equaled. CONSTITUTION:The optical wavelength converting element 10 is an optical fiber formed by packing a core 11 consisting of the nonlinear optical material into the hollow part at the center of a clad 12. The org. nonlinear optical material which is lower in the refractive index to the wavelength of the wavelength converting wave than the refractive index to the wavelength of the basic wave is used as this nonlinear optical material. This element is so formed that the effective refractive index to the basic wave guided in the zero order mode and the effective refractive index to the wavelength converting wave guided in the zero order mode are equaled. The phase matching of the basic wave and the wavelength converting wave is taken in this way after the conditions for the diameter and thickness of the waveguide part are releived down to the level which can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical wavelength conversion element, particularly a cladding part,
It consists of a waveguide section made of a nonlinear optical material with a higher refractive index and disposed within the cladding section, and is designed to achieve phase matching between the fundamental wave and the wavelength-converted wave traveling in each waveguide mode. The present invention relates to an optical wavelength conversion element.

(Prior Art) Various attempts have been made to convert the wavelength of laser light into a second harmonic or the like (shorten the wavelength) using nonlinear optical materials. Specifically, a bulk crystal type optical wavelength conversion element that performs wavelength conversion in this manner is well known. However, since this optical wavelength conversion element uses the birefringence of the crystal to satisfy the phase matching condition, there is a problem in that even if the nonlinearity is large, a material with no or small birefringence cannot be used.

As an optical wavelength conversion element that can solve the above problems,
A so-called fiber type has been proposed. This optical wavelength conversion element is an optical fiber whose cladding is filled with a core made of a nonlinear optical material, and is published in Journal of the Micro-Optics Research Group of the Japan Society of Applied Physics, Vol. 3. No
, 2. An example is shown on pages 28-32.

Since this fiber-type optical wavelength conversion element can easily achieve phase matching between the fundamental wave and the wavelength-converted wave, research on this fiber-type optical wavelength conversion element has been actively conducted recently. Also, for example, JP-A-63-15
As shown in No. 233 and No. 63-15234, two-dimensional optical waveguide type optical wavelength conversion elements are also known, in which a two-dimensional optical waveguide made of a nonlinear optical material is formed between two substrates serving as cladding parts. It is being Furthermore, a three-dimensional optical waveguide-type optical wavelength conversion element is also known in which a three-dimensional optical waveguide made of a nonlinear optical material is embedded in a glass substrate and emits a second harmonic wave into the glass substrate. These leading waveguide type optical wavelength conversion elements also have the above-mentioned features.

Further, in the specification of Japanese Patent Application No. 63-72752, it is described in detail that the sum frequency and the difference frequency are similarly generated by the fiber type wavelength conversion element. Regarding generation of sum-difference frequency in a waveguide type optical wavelength conversion element, a patent application filed in 1986
It is described in detail in the specification of No. 3-72753.

Furthermore, third harmonic generation using third-order nonlinearity is also fully possible.

The leading waveguide type (including fiber type) optical wavelength conversion elements listed above have the following characteristics from the point of view of the phase matching method: It is roughly divided into two types: the so-called Cerenkov radiation type, which achieves phase matching between the waves, and the so-called waveguide-waveguide type, which achieves phase matching between the fundamental wave and the wavelength-converted wave, each traveling in a waveguide mode. be done.

Compared to the Cherenkov radiation type optical wavelength conversion element described in (■), this waveguide-waveguide type wavelength conversion element (■) has a larger interaction between the fundamental wave and the wavelength-converted wave, so in principle it has a higher wavelength. Conversion efficiency can be expected. In other words, if the interaction length (length of the optical waveguide) is L, the wavelength conversion efficiency is
In the Cerenkov radiation type optical wavelength conversion element, it is proportional to L, whereas in the waveguide-waveguide type optical wavelength conversion element, it is proportional to the square of L.

In addition, in the case of Cerenkov radiation type optical wavelength conversion elements, the cross-sectional shape of the wavelength-converted wave emitted from the element is ring-shaped or crescent-shaped. Whereas a condensing optical system is required, in the case of a waveguide-waveguide type optical wavelength conversion element, if the wavelength-converted wave is guided in a single mode, the output beam will be approximately a Gaussian beam. Therefore, there is an advantage that this wavelength-converted wave can be easily narrowed down to the diffraction limit.

(Problem to be solved by the invention) However, since the waveguide-waveguide type optical wavelength conversion elements that have been proposed so far use an inorganic nonlinear optical material in the waveguide, it is difficult to achieve phase matching. Therefore, it is necessary to control the core diameter, the thickness of the leading waveguide, and the wavelength of the fundamental wave with extremely high precision. Moreover, in this optical wavelength conversion element,
In order to achieve phase matching while guiding the wavelength-converted wave in a single mode, the element temperature must be set to 100'C or higher and maintained at a specified temperature with a tolerance of ±o, t'c. There is a need. Since it is necessary to strictly control various conditions as described above, this waveguide-waveguide type optical wavelength conversion element has not been put into practical use at present.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a waveguide-waveguide type optical wavelength conversion element that has a relaxed phase matching condition and can be put to practical use.

(Means for Solving the Problems) A first optical wavelength conversion element according to the present invention constitutes a waveguide section in the optical waveguide type optical wavelength conversion element of the waveguide-waveguide type as described above. As a nonlinear optical material, an organic nonlinear optical material whose refractive index with respect to the wavelength of the wavelength-converted wave is lower than the refractive index with respect to the fundamental wave wavelength is used, and the effective refractive index with respect to the fundamental wave guided in the 0th-order mode and the 0th-order mode It is characterized by being formed so that the effective refractive indexes for the wavelength-converted waves guided by the refractive indexes are equal to each other.

Further, in the second optical wavelength conversion element according to the present invention, in the same waveguide-waveguide type optical wavelength conversion element, as a nonlinear optical material constituting the waveguide part, refraction with respect to the wavelength of the wavelength-converted wave is used. An organic nonlinear optical material whose refractive index is approximately equal to the refractive index for the wavelength of the fundamental wave is used, and a material is used as the material constituting the cladding portion, and the refractive index for the wavelength of the wavelength-converted wave is approximately equal to the refractive index for the fundamental wavelength. , the effective refractive index for the fundamental wave guided in the 0th mode, and 0
It is characterized by being formed so that the effective refractive indexes for wavelength-converted waves guided in the next mode are equal to each other.

(Function) FIG. 5 (2) shows an example of mode dispersion in a conventional waveguide-waveguide type fiber type optical wavelength conversion element. This mode dispersion is at room temperature, and is the effective refractive index n felt by the fundamental wave guided in the core in the zero-order mode.
;pp takes a value between the refractive index n of the cladding material with respect to the wavelength of the fundamental wave: LAD and the refractive index n''C0RE of the core material.On the other hand, the wavelength-converted wave guided in the core in the zero-order mode (this the effective refractive index n felt by the second harmonic)
gpp is the refractive index of the cladding material n CLAD and the refractive index of the core material n C0RE for the wavelength of this second harmonic.
Takes a value between . Since n″cLAD<nCLAD and nCOR+!<nC0R1, between the fundamental wave of the 0th mode and the second harmonic of the 0th mode, a waveguide-waveguide type optical wavelength conversion element is used. Phase matching condition n EPP = n
ttpp--A core diameter that satisfies (1) cannot exist.

At a temperature significantly different from room temperature, there may be a core diameter that satisfies the phase matching condition of equation (1) above, but in that case, as described above, it is necessary to control the temperature very strictly. On the other hand, as shown in Figure 5 < 2+, if the fundamental wave of the 0th mode and the second harmonic of the higher order (1st order as an example in the figure) mode, the phase matching condition of equation (1) above is satisfied. There can be core diameters of However, in this case, the portions of the two mode dispersion curves with greatly different slopes intersect with each other, so the above phase matching condition will not be satisfied unless the core diameter is strictly set to a predetermined value. Moreover, in this case, the second harmonic will be far from the Gaussian beam.

In contrast, the first waveguide-waveguide type optical wavelength conversion element according to the present invention (also - for example, fiber type)
The mode dispersion in is basically as shown in Figure 5 (1) at room temperature.
It becomes as shown in . In other words, for the cladding, based on the wavelength difference between the fundamental wave and the second harmonic, n CLAD < n CLAD, while for the core, n C0RII> n C0RE, so the basics of the 0th-order mode There exists a core diameter that satisfies the phase matching condition of equation (1) between the wave and the second harmonic of the zero-order mode. In addition, in this case, the two mode dispersion curves intersect with each other with similar slopes, so the range of intersection becomes wider. In other words, in this case, the phase matching condition is satisfied over a relatively wide range of core diameters.

On the other hand, the mode dispersion in the second waveguide-waveguide type optical wavelength conversion element (for example, a three-dimensional optical waveguide type) according to the present invention is basically shown in FIG. 5 (3) at room temperature. It becomes like this. In this case, n″CLAD” n CLAD
Katsn Co11! Since l= n C0RE, the two mode dispersion curves for the fundamental wave of the 0th mode and the second harmonic of the 0th mode intersect over almost the entire area, and the The phase matching condition is satisfied without being limited by the waveguide layer thickness.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an optical wavelength conversion element IO according to an embodiment of the present invention. This optical wavelength conversion element io is an optical fiber in which a core 11 made of a nonlinear optical material is filled in a hollow part at the center of a cladding 12. As described above, the nonlinear optical material used is an organic nonlinear optical material whose refractive index with respect to the wavelength of the wavelength-converted wave is lower than the refractive index with respect to the wavelength of the fundamental wave. In this example, as such an organic nonlinear optical material, JP-A-62-21
3,5-dimethyl-1-(4
-nitrophenyl) pyrazole (hereinafter referred to as PRA) is used to form the core 11. Further, in this embodiment, the cladding 12 is made of 5F15, which is an amorphous material.
formed from glass.

The bulk crystal structure of the above PRA is shown in FIG.

The crystal of this PRA has an orthorhombic crystal system, and the dots are mm2. Therefore, the tensor of nonlinear optical constants becomes . Here, d31 is the crystal axis a as shown in FIG.
Considering the optical axes x, y, and z determined for Sb%C, light linearly polarized in the X direction (hereinafter referred to as X-polarized light.7%
The same goes for 2. ) is incident as a fundamental wave and the second harmonic of two polarized lights is extracted.
Similarly, d3□ is the nonlinear optical constant when the fundamental wave of Y polarization is input and the second harmonic of Z polarization is extracted, and d33 is the Z
d24 is the nonlinear optical constant when the fundamental wave of polarized light is input and the second harmonic of Z polarization is extracted, and d24 is the nonlinear optical constant when the fundamental wave of Y and Z polarization is input and the second harmonic of Y polarization is extracted. , dis are nonlinear optical constants when the fundamental waves of X and Z polarization are input and the second harmonic of the X polarization is extracted. The magnitude of each nonlinear optical constant is shown in the table below.

In the above table, ■ is the value obtained by X-ray crystal structure analysis, ■
is an actual value measured by the Marker Frlnge method,
Both units are [X1O-9e sul.

As is clear from this table, d32, d33, and d24 have large values. In particular, d3□ and d24 are within the range that is currently clear, for example, JP-A-60-2503.
One nonlinear optical constant of MNA (2-methyl-4-nitroaniline) shown in Publication No. 34 etc. 600X10"
9es u, and J, Opt.

Soc, Am, B, Vol, 4 p977 (198
One nonlinear optical constant of NPP (N-(4-nitrophenyl)-L-prolinol) described in 7) 2
This is the second largest value after 00X to°9esu.

Therefore, when forming the fiber type optical wavelength conversion element 10 by filling the core (l) made of PRA into the cladding 12, as shown in FIG.
After oriented so that the axis (the optical axis is the X axis) extends in the direction of the core axis (this can be achieved by the method described below)
, the a-axis of the crystal (optical axis is 2
If a fundamental wave linearly polarized in the direction of the optical axis) or the b-axis (the Y-axis in the optical axis) is incident, the large nonlinear optical constants d12 and d33 described above can be used.

Note that the optical wavelength conversion element 10, which is an optical fiber, is manufactured using both of the above materials and with the crystal orientation of PRA as described above.
For example, the method disclosed in Japanese Unexamined Patent Publication No. 64-73327 may be used.

This optical wavelength conversion element 10 is used as shown in FIG. In this embodiment, a YAG laser 21 is used as a light source that generates a fundamental wave, and a laser beam (fundamental wave) 15, which is a parallel beam with a wavelength of 11064n, is emitted from the YAG laser 21 and is converted into a beam by a beam expander 22. The beam is enlarged in diameter and passed through the λ/2 plate 25, focused into a small beam spot by the condenser lens 2B, and then irradiated onto the incident end face 10a of the optical wavelength conversion element IO. Thereby, this fundamental wave 15 enters into the optical wavelength conversion element 10. As mentioned above, the PRA constituting the core 11 is
The crystal is oriented in such a way that the axis extends in the direction of the core axis. Further, in this example, by rotating the λ/2 plate 25 of the light source device 20, the fundamental wave 15 in the Y polarization state is input to the optical wavelength conversion element 10.

In this example, the diameter of the core it is 1.422 μm, and the fundamental wave 15 that has entered the optical wavelength conversion element 10 is guided through the core 11 only in the zero-order mode, and the PR that constitutes this core 11 is
A converts it to the second harmonic (5") with a wavelength of 1/2 (-532 nm). This second harmonic 15' becomes Z-polarized light, and only the 0th-order mode is excited, resulting in a single mode. The wave is guided through the core 11 in this state.Hereinafter, this second harmonic wave 15
The phase matching of ° will be explained.

FIG. 4 shows the dispersion characteristics of the refractive index nv in the Y-axis direction and the refractive index n2 in the Z-axis direction of PRA constituting the core 11, and the refractive index nCLAD of the 5F15 glass constituting the cladding 12. Note that this characteristic is at 25°C. Fundamental wave 1 with wavelength 1084 nm which is Y polarized light
5 is the effective refractive index n; pp is the refractive index n CLA
Value n of D for wavelength 11064n: LAD, and value n of refractive index ny for wavelength 11084n: OR+! takes a value between . On the other hand, the effective refractive index n gpp felt by the second harmonic 15' with a wavelength of 512 nm, which is bipolarized light, is the value n CLA of the refractive index n CLAD at a wavelength of 532 nm.
D and the value n of the refractive index nz for a wavelength of 532 nm North R
Takes a value between a. As shown in the figure, for the refractive index of the cladding 12, n CLAD < n CLAD, but on the contrary, for the refractive index of the core 11, n C
0RB> n C0RB. In other words, the mode dispersion of the fundamental wave 15 and the second harmonic 15° at 25° C. is as shown in FIG. 5(1). Core diameter in this example -1,422
The value of μm is approximately at the center of the region where the dispersion curve of the fundamental wave 15 in the 0th-order mode and the dispersion curve of the second harmonic 15° in the 0th-order mode overlap.

Therefore, the phase matching condition n of equation (1) explained earlier
gpp n app is satisfied, and phase matching is achieved between the second harmonic 15° of the zero-order mode and the fundamental wave 15 of the zero-order mode.

From the output end surface tab of the optical wavelength conversion element 10, the second
A beam 15" which is a mixture of harmonics 15° and fundamental waves 15 is emitted. This emitted beam 15" is passed through a condensing lens 27 and condensed, and then the second harmonics of 532 nm are emitted.
5' is passed through a band pass filter 28 which absorbs the fundamental wave 15 of 10B4 nm while allowing only the second harmonic 15' to be extracted. Using a polarizing plate or the like, it was confirmed that the second harmonic 15' was Z-polarized light. That is, in this example, the nonlinear optical constant d32 of the PRA described above is used.

The optical power meter 29 measures the optical intensity of this second harmonic 15'.
When the wavelength conversion efficiency was determined by measurement, it was about 10% in terms of IW when the element length was 5 mm.

Since the second harmonic wave 15' is guided by the core (1) in a single mode, the second harmonic wave 15' emitted from the optical wavelength conversion element 10 becomes a nearly Gaussian beam, and therefore consists of a spherical lens. Using a general condensing optical system, it is possible to narrow down this second harmonic of 15° to the diffraction limit.

In the optical wavelength conversion element of the present invention, for the reasons described above, even if the core diameter accuracy is relatively low, the above-mentioned phase matching can be realized and high wavelength conversion efficiency can be obtained. FIG. 6 shows how the wavelength conversion efficiency changes when the core diameter changes in the optical wavelength conversion element IO of the above embodiment. Note that the wavelength conversion efficiency is determined when the core diameter is the ideal value (-1,422 μm
) is assumed to be 1, and the values are shown relative to that value.

As shown in the figure, the allowable error in the core diameter that can ensure wavelength conversion efficiency of 1/2 or more of the maximum value is approximately ±2 nm.

It is fully possible with current technology to form an optical fiber with a core diameter error within this range.

Further, FIG. 7 shows how the wavelength conversion efficiency changes when the fundamental wave wavelength changes. As shown in the figure, the allowable error of the fundamental wavelength that can ensure 1/2 or more of the wavelength conversion efficiency when the fundamental wavelength is an ideal value (-1064,0 nm) is approximately ±0.6 nm.

Further, FIG. 8 shows how the wavelength conversion efficiency changes when the temperature of the optical wavelength conversion element changes. As shown in the figure, the temperature tolerance that can ensure 1/2 or more of the wavelength conversion efficiency when the temperature is at the ideal value (-25'C) is approximately ±5"C.
becomes.

In the embodiment described above, P is used as the material for the core (2).
Although RA is used, in the present invention,
The organic nonlinear optical materials whose refractive index for the wavelength of the wavelength-converted wave is lower than the refractive index for the fundamental wave wavelength include the above-mentioned PR.
In addition to A, it is also possible to use, for example, TRI shown in Japanese Patent Application No. 63-224195. On the other hand, in the present invention, the cladding portion is not limited to the 5F15 glass in the above embodiments, but may be formed from other amorphous materials or crystalline materials. However, it is very preferable to use an amorphous material because the degree of freedom in selecting the refractive index and the dispersion of the refractive index becomes extremely high.

Furthermore, although the optical wavelength conversion element 10 in the above embodiment is of the fiber type, the optical wavelength conversion element of the present invention can also be formed as the aforementioned two-dimensional or three-dimensional optical waveguide type.

Next, another embodiment of the present invention will be described with reference to FIG. 9 and FIG. 1O. Note that in FIGS. 9 and 10, elements equivalent to those already explained are given the same numbers, and explanations thereof will be omitted unless particularly necessary.

The optical wavelength conversion element 50 of this embodiment is of a three-dimensional optical waveguide type, and the three-dimensional optical waveguide 5 made of the above-mentioned PRA.
1 is embedded in a cladding (substrate) 52 made of aromatic polyamide having birefringence.

In the PRA constituting the optical waveguide 51, by appropriately setting the aspect ratio of the optical waveguide 51, etc., the C-axis (X-axis in the optical axis) of the crystal extends in the wave-guiding direction, that is, the longitudinal direction of the leading waveguide, and the a-axis (optical (Z-axis for optical axis), b-axis (Y-axis for optical axis)
are oriented so as to extend vertically in a direction perpendicular to the paper plane of FIG. 10, respectively.

On the other hand, aromatic polyamide, which is a cladding material, is used so that its two optical axes extend in directions parallel to the Y-axis and Z-axis of the PRA, respectively.

The refractive index of this aromatic polyamide for light polarized in the same direction as the Y axis is n CLAD (Y), and the refractive index for light polarized in the same direction as the Z axis is n CL
Denoted as AD(Z).

The optical wavelength conversion element 50 having the above configuration is used as shown in FIG. In this embodiment, a semiconductor laser 61 is used as a light source that generates a fundamental wave.
The laser beam (fundamental wave) 65, which is a diverging beam with a wavelength of 980 nm, is emitted from the collimator lens 62.
The beam is made into parallel light, passed through the λ/2 plate 25, focused into a small beam spot by the condenser lens 26, and then irradiated onto the incident end surface 51a of the optical waveguide 51. Thereby, this fundamental wave 65 enters into the optical wavelength conversion element 50.

Note that in this example as well, by rotating the λ/2 plate 25,
The fundamental wave B5 in the Y polarization state is manually applied to the optical wavelength conversion element 50.

The fundamental wave 65 that has entered the optical wavelength conversion element 50 is guided through the leading waveguide 51 only in the 0th order mode, and due to the PRA that constitutes this optical waveguide 51, the wavelength is reduced to 1/2 (-49 Qnm).
is converted to the second harmonic of 65°. This second harmonic 65
° becomes Z-polarized light, and only the zero-order mode is excited and guided through the optical waveguide 5i in a single mode state.

The phase matching of this second harmonic 65' will be explained below. FIG. 11 shows the Y of PRA constituting the optical waveguide 51.
The dispersion characteristics of the refractive index ny in the axial direction, the refractive index nz in the Z-axis direction, and the refractive indexes ncLAD(Y) and ncLAD(z) of the aromatic polyamide constituting the cladding 62 are shown. Note that this characteristic is at 25°C. The effective refractive index n sensed by the fundamental wave 65 with a wavelength of 940 nm, which is Y-polarized light, is the refractive index n.
It takes a value between the value n'C0RII+ for a wavelength of 980 nm. On the other hand, the effective refractive index n, ;=, felt by the second harmonic 65' with a wavelength of 490 nm, which is bipolarized light, is the refractive index n
Value n CL for wavelength 490 nm of CLAD (Z)
AD and the value n C of the refractive index nz for a wavelength of 490 nm
It takes a value between 0RE and 0RE. As shown in the figure, in this example, n″cLAD=nCLAD (both about 1.H)
and n'coRa=n C0RE (both about 1
．． 78). In other words, the mode dispersion curves of the fundamental wave 65 and the second harmonic 65' at 25°C are as shown in Figure 5 (
As shown in 3), they intersect over almost the entire area. Therefore, the phase matching condition n app = n EPP is satisfied without being limited by the waveguide layer thickness, and the second harmonic 65' of the 0th mode and the fundamental wave 65 of the 0th mode Phase matching is achieved between the two.

In the optical wavelength conversion element 10 of the embodiment described above,
As shown in Figure 6, the allowable error in the core diameter that can ensure wavelength conversion efficiency of 172 or more, which is the maximum value, is approximately 2 nm.
In this example, the tolerance for the thickness of the leading waveguide layer under similar conditions is significantly relaxed to about 50 nm.

Note that the optical wavelength conversion element of the present invention is not limited to the one that generates the second harmonic as described above, but can be formed to convert the wavelength of the fundamental wave into other third harmonics, sum frequency, difference frequency, etc. You can also do it.

(Effects of the Invention) As explained above in detail, the first optical wavelength conversion element of the present invention uses a material constituting the waveguide section, and the refractive index for the wavelength of the wavelength-converted wave is higher than the refractive index for the wavelength of the fundamental wave. By using a low organic nonlinear optical material, the fundamental wave guided in the 0th-order mode and the wavelength-converted wave are constructed so that the effective refractive index felt is equal to each other, so the conditions for the diameter and thickness of the waveguide section are It becomes possible to achieve phase matching between the fundamental wave and the wavelength-converted wave by slowing down to a feasible level.

On the other hand, in the second optical wavelength conversion element of the present invention, the material constituting the waveguide section has a refractive index with respect to the wavelength of the wavelength-converted wave.
An organic nonlinear optical material is used that has a refractive index that is approximately equal to the wavelength of the fundamental wave, and a material that has a refractive index that is approximately equal to the wavelength of the wavelength-converted wave is used as the material for the cladding. In the above, the fundamental wave guided in the 0th-order mode and the wavelength-converted wave are configured so that the effective refractive index felt is equal over a wide range, so the conditions for the diameter and thickness of the waveguide section can be made considerably looser. After that,
It becomes possible to achieve phase matching between the fundamental wave and the wavelength-converted wave.

Furthermore, since the optical wavelength conversion element of the present invention achieves phase matching as described above, phase matching is possible at room temperature. Since the optical wavelength conversion element of the present invention has a waveguide section formed using an organic nonlinear optical material, it is compared with a conventional waveguide-waveguide type optical wavelength conversion element in which the waveguide section is formed from an inorganic material. For example, the change in the effective refractive index of the fundamental wave and wavelength-converted wave due to changes in temperature or fundamental wavelength is small, so even if the precision of temperature and fundamental wavelength is made looser than that of the conventional optical wavelength conversion element, phase matching cannot be achieved. Realized.

Furthermore, since the optical wavelength conversion element of the present invention achieves phase matching between the wavelength converted wave guided in a single mode and the fundamental wave, the wavelength converted wave emitted from the element becomes an approximately Gaussian beam. Therefore, it is possible to narrow down this wavelength-converted wave to the diffraction limit using a condensing optical system consisting of an in-shell spherical lens.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a diagram of the bulk crystal structure of PRA used as the core material in the above embodiment, and Fig. 3 shows the crystal orientation of the core in the above embodiment. Explanatory diagram: Figure 4 is a graph showing the refractive index dispersion characteristics of the core material and cladding material in the above example, and Figure 5 (1) is a graph showing the fundamental wave and wavelength converted wave in the first optical wavelength conversion element of the present invention. Graph showing the mode dispersion. FIG. 5 (2) is a graph showing the mode dispersion of the fundamental wave and wavelength converted wave in the conventional waveguide-waveguide type wavelength conversion element. FIG. FIG. 6 is a graph showing the mode dispersion of the fundamental wave and the wavelength-converted wave in the optical wavelength conversion element of Example 2; FIG. 6 is a graph showing the relationship between the core diameter and wavelength conversion efficiency (relative value) in the optical wavelength conversion element of the above embodiment; FIG. 7 is a graph showing the relationship between the fundamental wavelength and wavelength conversion efficiency in the optical wavelength conversion element of the above example, and FIG. 8 is a graph showing the relationship between temperature and wavelength conversion efficiency in the optical wavelength conversion element of the above example. 9 is a perspective view showing another embodiment of the present invention, FIG. 10 is a schematic diagram showing how the optical wavelength conversion element shown in FIG. 9 is used, and FIG. 11 is a perspective view showing another embodiment of the present invention. , is a graph showing the refractive index dispersion characteristics of the waveguide material and the cladding material. 10.50... Optical wavelength conversion element 11... Core 12
．． 52...Clad 15.65...Fundamental wave 15', 65°...2nd harmonic 51...Optical waveguide Figure 1 Figure 5 (1) Figure 2 (2) Figure 3 Core Hinoki 5 Fig. (3) % Shiblade E R/i) Half 1 Fig. Core 伶 (1m) 060 Fig. 065 +070 Fig.

Claims (2)

[Claims] (1) Consisting of a cladding part and a waveguide part formed from a nonlinear optical material with a higher refractive index than the cladding part and disposed within the cladding part, the fundamental wave guided through this waveguide part is transmitted to the nonlinear optical material. In an optical wavelength conversion element that performs wavelength conversion by converting the wavelength and achieving phase matching between the wavelength-converted wave traveling through the waveguide in a waveguide mode and the fundamental wave, the nonlinear optical material constituting the waveguide includes the An organic nonlinear optical material is used in which the refractive index with respect to the wavelength of the wavelength-converted wave is lower than the refractive index with respect to the wavelength of the fundamental wave, and the effective refractive index with respect to the fundamental wave guided in the zero-order mode is 0.
An optical wavelength conversion element characterized in that it is formed so that effective refractive indexes for wavelength-converted waves guided in the next mode are equal to each other. (2) It consists of a cladding part and a waveguide part formed from a nonlinear optical material with a higher refractive index than the cladding part and disposed within the cladding part, and the fundamental wave guided through this waveguide part is transmitted to the nonlinear optical material. In an optical wavelength conversion element that performs wavelength conversion by converting the wavelength and achieving phase matching between the wavelength-converted wave traveling through the waveguide in a waveguide mode and the fundamental wave, the nonlinear optical material constituting the waveguide includes the An organic nonlinear optical material is used in which the refractive index with respect to the wavelength of the wavelength-converted wave is approximately equal to the refractive index with respect to the wavelength of the fundamental wave, and the material constituting the cladding portion has a refractive index with respect to the wavelength of the wavelength-converted wave. A material is used whose refractive index is approximately equal to the wavelength of the fundamental wave, and the effective refractive index for the fundamental wave guided in the 0th-order mode is equal to the effective refractive index for the wavelength-converted wave guided in the 0th-order mode. An optical wavelength conversion element characterized in that it is formed as follows.