JPH0795176B2 - Optical wavelength conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical wavelength conversion element, and more particularly to converting two types of incident fundamental waves having different wavelengths into their sum frequency and difference frequency. Or, at the same time, the present invention relates to an optical wavelength conversion element that converts into any two or more wavelength conversion waves of the sum frequency, the difference frequency, and the second harmonic wave.

From (ART) Conventionally, by the incidence of light as a fundamental wave in a nonlinear optical material, a wavelength have been made various attempts to convert the second harmonic of 1/2, also, different wavelengths lambda ₁ to each other, Two types of fundamental waves of λ ₂ are incident on the nonlinear optical material, and the sum frequency (1 / λ ₃ = 1 / λ ₁ + 1 / λ ₂ ) of the wavelength λ ₃ and the difference frequency (1 / λ ₃ =
Attempts have also been made to extract 1 / λ ₁ −1 / λ ₂ ). As the optical wavelength conversion element that performs wavelength conversion using the above-mentioned nonlinear optical material, specifically, a bulk crystal type,
The three-dimensional optical waveguide type shown in "Applied Physics" magazine Vol.49 (1980) p1234 is known.

(Problems to be Solved by the Invention) In the above bulk crystal type optical wavelength conversion element, the power density of the incident fundamental wave cannot be sufficiently increased, and further, the interaction length is increased in terms of extraction of the converted wave. There is a problem that the wavelength conversion efficiency is extremely low because it cannot be taken for a long time.

Further, the bulk crystal type optical wavelength conversion element is adapted to achieve phase matching between the fundamental wave and the converted wave by utilizing the birefringence of the crystal, and the phase matching conditions are the first and second basic conditions. Wave number vector Wavenumber vector of sum frequency or difference frequency Then, Is. Note that the refractive index in the polarization direction of the first fundamental wave is n ₁ , And likewise (Λ ₁ <λ ₂ ). In order to satisfy the above-described phase matching condition, in order to satisfy the wavelengths λ ₁ , λ ₂ , and λ ₃ , the refractive indices n ₁ and n ₂ (the refractive index in the polarization direction of the second fundamental wave) and n ₃
The (refractive index in the polarization direction of the converted wave) needs to be a desired value, and therefore, in this case, only a very limited wavelength range can be used.

On the other hand, in the above-mentioned three-dimensional optical waveguide type optical wavelength conversion element, only an example in which a difference frequency is generated by using LiNbO ₃ for the substrate has been confirmed, but the phase matching condition in this case is
Let the effective refractive indices of the first and second fundamental waves of the optical waveguide be ▲ n ^ω1 _eff ▼ and ▲ n ^ω2 _eff ▼, and the effective refractive indices of the difference frequency be ▲ n ^ω3 _eff ▼, respectively. Is. In this type of optical wavelength conversion element, unlike the above-mentioned bulk crystal type, the power density of the fundamental wave to be incident can be increased, so a 1 cm long element is used, and several percent at 100 mW input is used. It has also been theoretically shown that the wavelength conversion efficiency can be realized. However, the above-mentioned phase matching condition is not satisfied unless the element temperature is controlled with an accuracy of 0.1 ° C. or less, so that this type of optical wavelength conversion element has not been put to practical use.

To obtain the converted wave (difference frequency) of the desired wavelength,
It is necessary to control the refractive index of the optical waveguide, but in this type of device using LiNbO ₃ as the substrate, the refractive index can only be controlled by diffusion method, proton exchange, etc., and therefore the flexibility of optical waveguide design is low. There is also a problem.

Further, the three-dimensional optical waveguide type optical wavelength conversion element described above is only an example in which only the difference frequency is extracted, and even in the bulk crystal type optical wavelength conversion element, each of the two types of the fundamental waves of the two types is used. No optical wavelength conversion element has yet been provided that can simultaneously extract harmonics or simultaneously extract one or both of these second harmonics and one or both of sum and difference frequencies.

The present invention has been made in view of the above circumstances, and an optical wavelength conversion element that has a high degree of freedom in design and is capable of extracting a high-intensity sum frequency or difference frequency, or both of them simultaneously. It is intended to be provided. The present invention also provides an optical wavelength conversion element capable of simultaneously extracting the sum frequency and / or the difference frequency as described above and one or both second harmonics of the fundamental wave, and further, two types of fundamental waves. It is also an object of the present invention to provide an optical wavelength conversion device that can simultaneously extract the second harmonic.

(Means and Actions for Solving the Problem) An optical wavelength conversion element according to the present invention is a fiber-type optical wavelength conversion device in which a core made of a nonlinear optical material is filled in a clad made of an amorphous material having a lower refractive index than that of the core. The element, more specifically, the phase matching between the radiation mode of the wavelength conversion wave in the cladding and the nonlinear polarization wave created by the guided mode of the fundamental wave in the core,
It is a so-called Cerenkov radiation type optical wavelength conversion element that wavelength-converts the first and second fundamental waves having different wavelengths incident on the core and radiates the fundamental waves.

In the above configuration, as the wavelength-converted wave, the sum frequency, the difference frequency, the sum frequency and the difference frequency, the second harmonics of the first and second fundamental waves, the sum frequency and the difference frequency, or both of them are added. In addition to the second harmonic of the fundamental wave, and also one or both of the sum frequency and the difference frequency, each second harmonic of the first and second fundamental waves is generated, and the wavelength-converted wave and the fundamental wave Phase matching can be achieved as described above.

The phase matching conditions when phase matching is performed as described above are as follows: for the sum frequency, the wavelengths of the first and second fundamental waves are λ ₁ and λ ₂ , respectively, and the wavelengths of the wavelength conversion waves are λ ₃ and λ. ₁ the angular frequency of the _first fundamental wave _omega, the angular frequency of the fundamental wave of wavelength lambda ₂ and omega _2, the refractive index with respect to the sum frequency of the cladding ▲ n
^{ω1 + ω2} _clad ▼, the radiation angle (phase matching angle) of the sum frequency to the cladding is θ ^{ω1 + ω2} , and the effective refractive indices of the cores for the first and second fundamental waves are ▲ n ^ω1 _eff ▼ and ▲ n ^ω2 _{eff, respectively.}
▼ Regarding the difference frequency, if the refractive index of the cladding with respect to the difference frequency is ▲ ^nω1-ω2 _clad ▼, and the radiation angle (phase matching angle) of the difference frequency to the cladding is ^θω1-ω2 , Is.

On the other hand, the phase matching condition for the second harmonic of the first fundamental wave is that the refractive index of the cladding for this second harmonic is ▲ n.
^2ω1 _clad ▼, and the radiation angle (phase matching angle) of the second harmonic to the clad is θ ^2ω1 , The phase matching condition for the second harmonic of the second fundamental wave is that the refractive index of the cladding with respect to this second harmonic is ▲ n ^2ω2 _clad ▼, and the radiation angle of the second harmonic to the cladding (phase If the matching angle is θ 2 ^ω2 , Is.

Since the radiation mode of the wavelength-converted wave radiated to the clad has a continuous spectrum, in other words, the radiation angle can take any value, the refractive index of the clad ▲ ^{nω1 + ω2}
_clad ▼, ▲ n ^ω1-ω2 _clad ▼, ▲ n 2 ^ω1 _clad ▼, ▲
n 2 ^{ω 2} _clad ▼ and effective refractive index ▲ n ^{ω 1} _eff ▼, ▲ n
^With respect to ^{ω 2} _eff ▼, the above (1)-
It is also possible to satisfy each condition of (4) at the same time. That is, if the phase matching angle is generally θ, cos θ <1. Therefore, with respect to the condition (1), Phase matching can be achieved as long as If the condition (3) is satisfied, the phase matching is ^achieved , and if the condition (3) is ▲ n ^2ω1 _clad ▼> ▲ n ^ω1 _eff ▼, the phase matching is ^achieved , and the condition (4) is ▲ n ^2ω2. _{If clad} ▼> ▲ n ^ω2 _eff ▼, phase matching can be achieved.

Further, a refractive index ▲ n ^{ω1 + ω2} _clad ▼, ▲ ^nω1-ω2 _clad ▼, which simultaneously satisfies a plurality of formulas (1) to (4),
▲ n ^2ω1 _clad ▼, ▲ n ^2ω2 _clad ▼, and effective refractive index ▲
If n ^ω1 _eff ▼ and ▲ n ^ω2 _eff ▼ can be set, a plurality of wavelength conversion waves can be taken out at the same time. However, in the optical wavelength conversion element of the present invention, since an amorphous material is used for the cladding, It is also possible. That is, when this clad is made of, for example, glass, its refractive index is in a wide range of 1.4 to 1.9 (value for sodium d line having a wavelength of 587.6 nm), and the wavelength dispersion of the refractive index is ν _d.
= 20 to 85 over a wide range, it is possible to form a clad that can satisfy a plurality of the phase matching conditions (1) to (4). Also, the effective refractive index ▲ n ^ω1 _eff ▼,
^▲ n ω2 _eff ▼ is the refractive index of the cladding and the fundamental wavelength and the like will be univocally determined depending on the core diameter if Kimare, freedom of refractive index and choice of wavelength dispersion of the refractive index of the cladding, as described above Is large, the desired effective refractive index can be obtained without controlling the core diameter precisely and arbitrarily changing it.

Further, in order to realize high wavelength conversion efficiency, it is necessary to guide both the first fundamental wave and the second fundamental wave in a single mode, which is also caused by the amorphous material in the cladding as described above. Can be realized by using. That is, since the wavelength dispersion of the refractive index of this amorphous material has a wide range of values as described above, it is also possible to select a clad material having the same wavelength dispersion as the core material, as shown in FIG. Become. In this way, substantially equal to the refractive index difference [Delta] n ₁ of the core and the cladding with respect to the wavelength lambda ₁ of the first fundamental wave, and a refractive index difference [Delta] n ₁ of the core and the cladding with respect to the wavelength lambda ₂ of the second fundamental wave can do. Therefore, as can be seen from the mode dispersion curve shown in FIG. 6, it is possible to easily set the core diameter capable of guiding both the light having the wavelength λ _{1 and} the light having the wavelength λ _{2 in} the single mode. In FIG. 6, n _core is the refractive index of the core.

Further, since the degree of freedom in selecting the refractive index of the cladding is high as described above, the degree of freedom in setting the mode field diameter for each wavelength λ ₁ and λ ₂ is also high. Therefore, it is possible to facilitate the light input to the device by preventing the mold field diameter from becoming extremely small.

(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 device according to an embodiment of the present invention. The optical wavelength conversion element 10 is an optical fiber in which a core 11 is filled in a clad 12 having a lower refractive index than that, and a first fundamental wave having a wavelength of 1300 nm and a wavelength of 800 nm are included.
The second fundamental wave is input to obtain wavelength-converted waves of three colors of red, green, and blue. Core 11 has the following molecular formula The nonlinear optical material (3.5-dimethyl-1- (4
-Nitrophenyl) pyrazole: hereinafter referred to as PRA), and the crystal orientation direction of PRA constituting this core is set such that its c-axis extends substantially in the long axis direction of the core. The bulk crystal structure of this PRA is shown in FIG. The crystals of PRA are orthorhombic and the point cloud is mm2. So the tensor of the nonlinear optical constant is Becomes Here, d ₃₁ is the crystal axis a, as shown in FIG.
Considering the optical axes X, Y, and Z defined for b and c,
Light linearly polarized in the X direction (hereinafter referred to as X polarized light. Y, Z
Is also the same. ) Is a non-linear optical constant when a Z-polarized wavelength conversion sheet is taken out by inputting as a fundamental wave, and similarly, d ₃₂ is a non-linear optical constant when a Y-polarized fundamental wave is entered and a Z-polarized wavelength converted wave is taken out. A constant, d ₃₃ is a non-linear optical constant when the Z-polarized fundamental wave is incident to take out the Z-polarized wavelength converted wave, and d ₂₄ is the Y and Z-polarized fundamental wave is incident to take out the Y-polarized wavelength converted wave. In this case, d ₁₅ is a nonlinear optical constant when the fundamental waves of X and Z polarization are made incident and the wavelength conversion wave of X polarization is extracted. The size of each nonlinear optical constant is shown in the table below.

In the above table, the values obtained by X-ray crystal structure analysis,
Is the value measured by the Maker Frige method (both values for the fundamental wave with a wavelength of 1.064 μm), and the unit is [x10 ^-9 es
u].

The clad 12 is made of SG8 glass and its outer diameter is about 5 mm
It is said that. On the other hand, the diameter of the core 11 is 1 μm.

Here, a method for producing the light wavelength conversion element 10 will be described. First, a hollow glass fiber 1 that becomes the clad 12.
2'is prepared. This glass fiber 12 'is S
Made of F8 glass with an outer diameter of about 5 mm and a hollow diameter of 1
μm. Then, as shown in FIG. 3, the PRA is kept in a molten state in a furnace or the like, and one end portion of the glass fiber 12 'is immersed in the melt 11'. Then, due to the capillary phenomenon, the melted PRA enters into the hollow portion of the glass fiber 12 '. The temperature of the melt 11 'is slightly higher than its melting point (102 ° C) in order to prevent the decomposition of PRA. Then, when the glass fiber 12 'is rapidly cooled, the PRA that has entered the hollow portion is polycrystallized.

Next, by gradually pulling out the optical fiber 12 'from the inside of the furnace maintained at a temperature higher than the melting point of PRA (for example, 102.5 ° C) to the outside of the furnace maintained at a temperature lower than the melting point,
The melted PRA is single-crystallized from the part drawn out of the furnace. As a result, the core 11 is formed in a single crystal state over a long range of 50 mm or more, and the crystal orientation is also uniform, and the light wavelength conversion element 10 can be made sufficiently long.
As is well known, the wavelength conversion efficiency of this type of optical wavelength conversion element is proportional to the length of the element, so the longer the optical wavelength conversion element, the higher the practical value.

When the PRA is filled in the glass fiber 12 'in a single crystal state as described above, the crystal orientation state is such that the c-axis (optical axis is the X-axis) extends in the core axis direction as shown in FIG. Becomes

In order to single crystallize PRA as described above,
For example, a method using a Bridgman furnace as shown in Japanese Patent Application No. 61-075078 by the applicant of the present application can be used. Further, the drawing speed of the glass fiber 12 'may be, for example, about 5 mm / h.

After the core 11 was filled as described above, both ends of the glass fiber 12 'were cut with a fiber cutter to form a light wavelength conversion element 10 having a length of 10 mm.

The light wavelength conversion element 10 is used as shown in FIG. Wavelength λ emitted from the first semiconductor laser 20
A laser beam (first fundamental wave) 21 of ₁ = 1300 nm is collimated by a collimating lens 22 and then passed through a beam splitter 25, and a second semiconductor laser 30
The laser beam (second fundamental wave) 31 having a wavelength λ ₂ = 800 nm emitted from the laser beam is also collimated by the collimator lens 32 and then passed through the beam splitter 25. Thus, the first and second fundamental waves are emitted. 21 and 31 are combined into one beam. The fundamental waves 21 and 31 can be combined by using a dichroic mirror or the like. The combined fundamental waves 21 and 31 are focused into a small beam spot by the condenser 32 and are radiated to the end surface 11a of the core 11. As a result, both fundamental waves 21 and 31 enter the core 11. As an example, the first semiconductor laser 20 has an output 10 for optical communication.
A laser having an output of 80 mW for an optical disc was used as the second semiconductor laser 30.

First and second fundamental waves incident on the core 11 as described above
Reference numerals 21 and 31 are non-linear optical materials forming the core 11.
PRA allows each second harmonic 21 ', 31' and sum frequency 4
Converted to 1. Here, the first semiconductor laser 20 is arranged so that the direction of the linearly polarized light of the first fundamental wave 21 is the Y-axis direction, while the second semiconductor laser 30 is the second
Are arranged so that the direction of the linearly polarized light of the fundamental wave 31 is in the Z-axis direction. The first fundamental wave 21 therefore, the second harmonic of the red wavelength lambda _1/2 = 650 nm under the nonlinear optical constant d ₃₂
Is converted to 21 ', while the second fundamental wave 31, the second harmonic 3 of a blue wavelength lambda _2/2 = 400 nm under the nonlinear optical constant d ₃₃
Converted to 1 '. Further, the fundamental waves 21 and 31 have a wavelength λ ₃ = 495 nm (1 / λ ₃ = 1 / λ ₁ +1/1) under the nonlinear optical constant d _24.
λ ₂ ) is converted to the green sum frequency 41. That is, the electric field strength of the first fundamental wave 21 of Y-polarized light is set to ▲ E ^ω1 _Y ▼,
^Assuming that the electric field strength of the Z-polarized second fundamental wave 31 is ▲ E ^ω2 _Z ▼, the polarization of the Z-polarized second harmonic wave 31 '▲ P
^2ω1 _Z ▼, polarization of the Z-polarized second harmonic wave 31 ′ ▲ P ^2ω2
The polarization ▲ P ^{ω1 + ω2} _Y ▼ of the sum frequency 41 of _Z ▼ and Y polarization is respectively Becomes

Next, the phase matching between the above-mentioned converted waves and the fundamental wave before being converted into them will be described. First, the first fundamental wave 21 of PRA constituting the core 11: refractive index for (lambda _{1 =} 1300 nm Y ^{polarization)} ▲ n ω1 _Y ▼, the second fundamental wave 31 (lambda _{2 =} 800 nm:
Refractive index with respect to the ^{Z-polarization)} ▲ n ω2 _Z ▼, and the clad 1
Refractive index ▲ n ^2ω1 _clad ▼ for the second harmonic wave 21 'of SF8 glass constituting 2 and refractive index ▲ n for the second harmonic wave 31'
^2ω2 _clad ▼, refractive index for sum frequency 41 ▲ ^{nω1 + ω2}
_{The clad} ▼ is as follows.

As mentioned above, the core diameter is 1 μm and the clad diameter is about 5 mm.
Then, the effective refractive indices ▲ n ^ω1 _eff ▼ and ▲ n ^ω2 _eff ▼ of the core 11 with respect to the first fundamental wave 21 and the second fundamental wave 31 are both 1.68.

Under the above conditions, the above equation (1) holds when θ ^{ω1 + ω2} = about 10 °, the equation (3) holds θ ^2ω1 = about 3 °, and the equation (4) holds when θ ^2ω2 = about 14 °. As mentioned above, since the radiation mode of the wavelength converted wave to the cladding has a continuous spectrum,
The radiation angles θ ^{ω1 + ω2} , θ ^2ω1 , θ as described above
^2ω2 are all realized, so (1), (3),
All the phase matching conditions of (4) are satisfied.

From the above, the wavelength of 650n which is the second harmonic of the first fundamental wave 21
a red light beam 21 ′ of m, a green light beam 41 of wavelength 495 nm which is the sum frequency of the first fundamental wave 21 and the second fundamental wave 31, and a second harmonic of the second fundamental wave 31. When the blue light beam 31 'with a wavelength of 400 nm is high in intensity, the device end face 10
can be retrieved from b. These three color light beams 21 ', 3
Although 1'and 41 are emitted from the element end face 10b in a mixed state, they can be separated into monochromatic beams by passing through a filter or the like. In particular, by using light with wavelengths of 1300 nm and 900 nm as the first fundamental wave and the second fundamental wave, respectively, 650 nm and 4
It is also possible to obtain wavelength conversion waves of the three primary colors of red, blue and green of 50 nm and 532 nm.

In the above embodiment, both the first fundamental wave 21 having a wavelength of 1300 nm and the second fundamental wave 31 having a wavelength of 800 nm are guided in a single mode. The mode field diameters of the first fundamental wave 21 and the second fundamental wave 31 are 2 μm and 3 μm, respectively, which are sufficiently larger than the respective wavelengths. It is easy to reduce the fundamental waves 21 and 31 to this extent by the condenser lens 26 described above, and therefore the fundamental waves 21 and 31 can be easily input to the element 10.

In the embodiment described above, a total of three types of wavelength-converted waves, that is, the second harmonics of two types of fundamental waves having different wavelengths and the sum frequency are obtained at the same time. In the optical wavelength conversion element of, since the clad is made of an amorphous material having a very wide selectivity of the refractive index and the wavelength dispersion of the refractive index, an arbitrary nonlinear constant (for example, d ₃₂ , d ₃₃ , d ₃₁ etc.) can be used, and the phase matching conditions (1) to (4) can be easily satisfied. Therefore, it is easy to selectively satisfy one or more of these phase matching conditions (1) to (4), and thereby a desired wavelength-converted wave can be obtained at any time. Becomes Examples of the fundamental wavelength, the cladding material, the cladding refractive index, the effective refractive index of the core, the core diameter, etc. in each case are shown below.

When two types of second harmonics are extracted while satisfying the phase matching conditions (3) and (4).

The fundamental wavelength is λ ₁ = 1300 nm and λ ₂ = 800 nm. SF15 glass is used for the clad, and the clad diameter is set to 2 mm, and the above-mentioned PRA is used for the core, and the core diameter is set to 1.0 μm. PRA
The non-linear constant of is only d ₃₂ , and its refractive index is Is. When both fundamental waves are input as Y-polarized light, two types of second high frequencies can be simultaneously extracted with Z-polarized light.

When the phase matching conditions (1) and (3) or (1) and (4) are satisfied and the sum frequency and one second harmonic are taken out.

The fundamental wavelength is λ ₁ = 1300 nm and λ ₂ = 800 nm. SF5 glass is used for the clad, and the clad diameter is set to 5 mm, and the above-mentioned PRA is used for the core, and the core diameter is set to 1.1 μm. As the nonlinear constant of PRA, d ₃₃ is used to convert the fundamental wave of wavelength λ ₂ into the second harmonic, and d ₂₄ is used to generate the sum frequency.
The refractive index of PRA is Is. When the fundamental wave of wavelength λ ₁ is Y-polarized and the fundamental wave of wavelength λ ₂ is Z-polarized, the second harmonic can be extracted as Z-polarized light and the sum frequency can be extracted as Y-polarized light. In this case, the power of the fundamental wave of λ ₁ = 1300 nm is maximized, while the power of the fundamental wave of λ ₂ = 800 nm is minimized to reduce the power of the second harmonic and increase the sum frequency only. You can also take it out.

In the case of extracting the sum frequency, the difference frequency and one second harmonic by satisfying the phase matching conditions (1), (2) and (3) or (1), (2) and (4).

The fundamental wavelength is λ ₁ = 1300 nm and λ ₂ = 800 nm. SF8 glass is used for the clad, and the clad diameter is set to 5 mm, and the above-mentioned PRA is used for the core, and the core diameter is set to 1.4 μm. As the non-linear constant of the PRA, only d ₃₃ is used to convert the fundamental wave of wavelength λ ₂ into the second harmonic, and d ₂₄ is used to generate the sum difference frequency. The refractive index of PRA is Is. When the fundamental wave of wavelength λ ₁ is Y-polarized and the fundamental wave of wavelength λ ₂ is Z-polarized, both second harmonics can be extracted as Z-polarized light and the sum difference frequency can be extracted as Y-polarized light. In this case, the sum frequency wavelength is 495 nm and the difference frequency wavelength is 2080 nm.
Is.

When the phase matching conditions (1), (2), (3), and (4) are satisfied and a sum frequency, a difference frequency, and two types of second harmonics are extracted.

The fundamental wavelength is λ ₁ = 1300 nm and λ ₂ = 800 nm. SF8 glass is used for the clad, and the clad diameter is set to 5 mm, and the above-mentioned PRA is used for the core, and the core diameter is set to 1.8 μm. The non-linear constant of PRA uses d ₃₂ to convert the fundamental wave of wavelength λ ₁ to the second harmonic, and d ₃₃ to convert the fundamental wave of wavelength λ ₂ to the second harmonic, D ₂₄ for sum and difference frequency generation
To use. The refractive index of PRA is Is. When the fundamental wave of wavelength λ ₁ is Y-polarized and the fundamental wave of wavelength λ ₂ is Z-polarized, both second harmonics can be extracted as Z-polarized light and the sum difference frequency can be extracted as Y-polarized light. In this case, the guided mode of the fundamental wave having the wavelength λ ₁ is the primary mode.

In the present invention, it is preferable to use an organic non-linear optical material having a large non-linear optical constant as the non-linear optical material forming the core.
In addition to PRA, for example, the following molecular formula The nonlinear optical material (3,5-dimethyl-1 (4-
Nitrophenyl) -1,2,4-triazole) can be preferably used.

(Effect of the invention) As described in detail above, the optical wavelength conversion element of the present invention is formed as a Cherenkov radiation type in which the radiation mode of the wavelength-converted wave to the clad has a continuous spectrum, and then the clad is formed. , The refractive index and the wavelength dispersion of the refractive index are made of an amorphous material having a high degree of freedom in selection, so that two types of fundamental waves having different wavelengths can be guided in a single mode, and a wavelength conversion wave can be obtained. The phase matching condition between the fundamental wave and the fundamental wave is easily satisfied. Therefore, according to the optical wavelength conversion element of the present invention, the sum frequency or the difference frequency of the two types of fundamental waves, the sum frequency and the difference frequency, or the two types of the second harmonics, and further the second harmonic and the sum frequency, The second harmonic and the difference frequency can be extracted at any time.

Further, since the optical wavelength conversion element of the present invention is of fiber type, the power density of the two types of fundamental waves to be incident is increased,
Since the interaction length can be made sufficiently long, a high wavelength conversion efficiency can be realized.

Further, in the optical wavelength conversion element of the present invention, since the clad is made of an amorphous material having a very high degree of freedom in selecting the refractive index and the wavelength dispersion of the refractive index as described above,
The degree of freedom in setting the mode field diameter is increased, so that the mode field diameter can be set large to facilitate the input of the fundamental wave.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention, FIG. 2 is a schematic view showing a bulk crystal structure of the core material of the above embodiment, and FIG. 3 is a method for producing the light wavelength conversion element of the above embodiment. FIG. 4 is a schematic view showing the crystal orientation of the core in the optical wavelength conversion element of the above embodiment, FIG. 5 is a graph showing the relationship between the refractive index wavelength dispersion of the core and the clad according to the present invention, FIG. 6 is a graph showing the mode dispersion of the optical fiber according to the present invention. 10 ... Optical wavelength conversion element, 10b ... Element end face 11 ... Core, 11a ... Core end face 12 ... Clad, 20 ... First semiconductor laser 21 ... First fundamental wave 21 '... Second harmonic of first fundamental wave 30 ... Second semiconductor laser, 31 ... Second fundamental wave 31 '... Second harmonic of second fundamental wave, 41 ... Sum frequency

Claims (6)

[Claims] 1. A fiber in which a core of a nonlinear optical material is filled in a cladding of an amorphous material having a lower refractive index than that, and a first and second fundamental waves having different wavelengths are incident on the core. Are converted to their sum frequency and radiated into the cladding, whereupon a nonlinear polarization wave in the core is created by the sum frequency radiation mode in the cladding and the guided modes of the first and second fundamental waves in the core. An optical wavelength conversion element configured to achieve phase matching between the optical wavelength conversion elements. 2. A fiber having a core of a non-linear optical material filled in a cladding of an amorphous material having a lower refractive index than the core, wherein the first and second fundamental waves having different wavelengths are incident on the core. Are converted into their difference frequency and radiated into the cladding, whereupon the nonlinear polarization wave in the core is created by the radiation mode of the difference frequency in the cladding and the guided modes of the first and second fundamental waves in the core. An optical wavelength conversion element configured to achieve phase matching between the optical wavelength conversion elements. 3. A fiber in which a core of a nonlinear optical material is filled in a clad of an amorphous material having a lower refractive index than that, and the first and second fundamental waves having different wavelengths are incident on the core. Are converted into their sum and difference frequencies and radiated into the cladding, where the sum and difference radiation modes in the cladding and the guided modes of the first and second fundamental waves in the core create
An optical wavelength conversion device configured to achieve phase matching with a nonlinear polarization wave in a core. 4. A fiber in which a core of a nonlinear optical material is filled in a cladding of an amorphous material having a lower refractive index than the core, and the first and second fundamental waves having different wavelengths are incident on the core. Are converted into their respective second harmonics to be radiated into the clad, and at that time, phase matching is performed between the radiating mode of the second harmonic in the clad and the guided mode of the fundamental wave in the core. Optical wavelength conversion element. 5. In addition to the sum frequency and / or the difference frequency, one of the first and second fundamental waves is converted into its second harmonic and radiated into the cladding, the second harmonic in the cladding being then radiated. 4. The optical wavelength conversion element according to claim 1, wherein the optical wavelength conversion element is configured to have a phase matching between a radiation mode of a harmonic wave and a guided mode of a fundamental wave in the core. 6. In addition to the sum frequency and / or the difference frequency, the first fundamental wave and the second fundamental wave are respectively added to the second frequency wave.
It is characterized in that it is configured so as to be converted into a higher harmonic wave and radiated into the cladding, and at that time, a phase matching is performed between the radiation mode of the second higher harmonic wave in the cladding and the guided mode of the fundamental wave in the core. The optical wavelength conversion element according to claim 1, 2 or 3.