JP2005031574A - High-frequency electromagnetic wave generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and high output high-frequency electromagnetic wave generating device. <P>SOLUTION: In the high-frequency electromagnetic wave generating device which introduces a first electromagnetic wave W1 and a second electromagnetic wave W2 with different frequencies into a nonlinear dielectric with second order nonlinearity and propagates them and consequently generates a third electromagnetic wave W3 with a frequency equal to a difference between the two frequencies, a unimodal dielectric waveguide 1 is equipped with a core part 2 composed of the nonlinear dielectric and a cladding part 3 formed so as to cover a circumference of the core part 2 and composed of a material with a refractive index less than that of the core part 2. Quality of materials of the core part 2 and the cladding part 3 and a cross-sectional dimension of the core part 2 are selected so as to make phase velocity of an electromagnetic beat generated by a synthesis of the electromagnetic waves W1 and W2 nearly coincide with that of the electromagnetic wave W3 propagated through a composite dielectric structure consisting of the core part 2 and the cladding part 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to the structure of a small-sized, high-output high-frequency electromagnetic wave generator mainly in a frequency band of about 0.1 to 10 THz.

Conventionally, as a small high-frequency electromagnetic wave generator in the 0.1 to 10 THz band, electromagnetic waves from two different frequency lasers are simultaneously introduced into a dielectric having a second-order nonlinear effect, and the difference in frequency of the introduced electromagnetic waves is supported. An apparatus that generates an electromagnetic wave is proposed (for example, Non-Patent Document 1). The concept of high frequency electromagnetic wave generation by this high frequency electromagnetic wave generator is shown in FIG. In the high-frequency electromagnetic wave generator shown in FIG. 3, the electromagnetic waves W1 and W2 having _two different frequencies f ₁ and f ₂ from a laser (not shown) are condensed by a bulk optical system 5 such as a lens and then a bulk nonlinear dielectric. 4, an electromagnetic wave W3 having a frequency f ₂ −f ₁ of a difference between the electromagnetic waves W1 and W2 is generated. The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
K.Kawase et al., “Widely tunable THz-wave parametric generator for imaging system”, RIKEN Review, RIKEN, July 2002, No. 47, p. 48-51

  However, in the high-frequency electromagnetic wave generator of Non-Patent Document 1, the spot size of the electromagnetic waves W1 and W2 can be focused only to about 0.1 millimeters at most, and the spot size diameter of the electromagnetic waves W1 and W2 increases as it further propagates. Since it expands rapidly, the energy density does not increase, and as a result, there is a problem that the power conversion efficiency from the laser to the electromagnetic wave W3 is very low. In the high-frequency electromagnetic wave generator of Non-Patent Document 1, the conversion efficiency is improved by increasing the peak power by shortening the pulse of the laser, but the average power becomes very low at the microwatt level because it is pulsed. End up. Moreover, since it is a pulse driving | operation, the use range is restrict | limited largely, such as being unusable as a carrier electromagnetic wave for wireless communications.

  Further, in the high-frequency electromagnetic wave generator of Non-Patent Document 1, the phase velocity of the beat caused by the introduced electromagnetic waves W1 and W2 of two frequencies travels in the nonlinear dielectric 4 and the phase of the high-frequency electromagnetic wave W3 propagating in the same system. A so-called phase matching condition that matches the speed needs to be satisfied. However, in a normal bulk material, the phase matching condition is satisfied only under very special conditions. Specifically, the two electromagnetic waves W1 and W2 to be introduced intersect at a minute angle to establish the phase matching condition. However, since the beams intersect each other diagonally, high-efficiency high-frequency generation is expected. In order to increase the effective interaction length, the beam spot diameter must be increased, and the expansion of the beam spot diameter is a condition contrary to the above-described energy density problem. That is, such a high-frequency electromagnetic wave generator cannot essentially increase the high-frequency electromagnetic wave generation efficiency due to problems of energy density and phase matching, and cannot be a small and high-power device.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a small-sized and high-output high-frequency electromagnetic wave generator.

The present invention introduces a first electromagnetic wave and a second electromagnetic wave having two different frequencies into a nonlinear dielectric having a second-order nonlinearity, and propagates them to obtain a third frequency difference between the two frequencies. In the high-frequency electromagnetic wave generating device for generating an electromagnetic wave, the core part made of the nonlinear dielectric material into which the first electromagnetic wave and the second electromagnetic wave are introduced, and the core part formed to cover the periphery of the core part A single-mode dielectric waveguide having a cladding portion made of a material having a lower refractive index, and a phase velocity of an electromagnetic wave beat generated by the synthesis of the first electromagnetic wave and the second electromagnetic wave is The material of the core part and the clad part and the cross-sectional dimension of the core part are selected so that the electromagnetic wave substantially matches the phase velocity propagating through the composite dielectric structure composed of the core part and the clad part. It is those that have been.
Also, one configuration example of the high-frequency electromagnetic wave generation device of the present invention is that the phase velocity of the electromagnetic wave beat generated by the synthesis of the first electromagnetic wave and the second electromagnetic wave, and the third electromagnetic wave propagates through the composite dielectric structure. The phase velocity is substantially matched with an accuracy of 2.5% or less.
In one configuration example of the high-frequency electromagnetic wave generator of the present invention, the core portion is made of an inorganic nonlinear material or an organic nonlinear material, and the cladding portion is made of Al ₂ O ₃ , SiO ₂ , MgO, diamond-like carbon, epoxy It consists of either a polymer or a polyimide polymer.
Moreover, in one structural example of the high frequency electromagnetic wave generator of this invention, the cross-sectional shape of the said core part is a square.
Moreover, in one structural example of the high frequency electromagnetic wave generator of this invention, the said core part has a cross-sectional dimension which is 1.0 micrometer or less in both width and height, and larger than 0.2 micrometer.

  According to the present invention, a high energy density state can be realized by introducing the first electromagnetic wave and the second electromagnetic wave into the minute core portion. Further, the phase velocity of the electromagnetic wave beat generated by the synthesis of the first electromagnetic wave and the second electromagnetic wave substantially coincides with the phase velocity at which the third electromagnetic wave propagates through the composite dielectric structure composed of the core portion and the cladding portion. By selecting the material of the core part and the clad part and the cross-sectional dimensions of the core part, the phase matching condition can be established. As a result, the high frequency in the high frequency electromagnetic wave generator which introduce | transduces the 1st electromagnetic wave and 2nd electromagnetic wave of two different frequencies into the nonlinear dielectric material which has a 2nd order nonlinearity, and generate | occur | produces the 3rd electromagnetic wave of the frequency of the difference of two frequencies. Electromagnetic wave generation efficiency can be dramatically improved. As a result, the high-frequency electromagnetic wave generator in the 0.1 to 10 THz region can be reduced in size and increased in output, and the high-frequency electromagnetic wave generator that is small and easy to operate can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A is a cross-sectional view of a single-mode dielectric waveguide used in a high-frequency electromagnetic wave generator according to an embodiment of the present invention, cut along a plane perpendicular to the propagation direction of the electromagnetic wave, and FIG. FIG. 2 is a view showing a concept of high-frequency electromagnetic wave generation by the high-frequency electromagnetic wave generator of the present embodiment, in which the one-mode dielectric waveguide is cut along a plane parallel to the propagation direction of the electromagnetic wave. The high-frequency electromagnetic wave generator of the present embodiment is composed of a single mode dielectric waveguide 1 and two lasers (not shown) having different frequencies. The single mode dielectric waveguide 1 is made of a core portion 2 made of a nonlinear dielectric material having second-order nonlinearity, and a material having a refractive index smaller than that of the core portion 2 formed so as to cover the periphery of the core portion 2. It is comprised from the cladding part 3 which becomes.

In the present embodiment, a high energy density is realized by the small core portion 2 of the single-mode dielectric waveguide 1, and the first electromagnetic wave W1 having _two different frequencies f ₁ and f ₂ introduced into the core portion 2 The third electromagnetic wave W3 having the frequency f _out (= f ₂ −f ₁ ) corresponding to the difference between the _two frequencies f ₁ and f ₂ is the core of the phase velocity V _pBEAT of the electromagnetic wave beat generated by the synthesis with the second electromagnetic wave W2. The material of the core part 2 and the clad part 3 and the cross-sectional dimension of the core part 2 are selected so as to substantially coincide with the phase velocity V _pOUT propagating through the composite dielectric structure composed of the part 2 and the clad part 3. Yes.

When the difference between the frequencies of the two electromagnetic waves W1 and W2 introduced into the core portion 2 is sufficiently smaller than the frequencies of the electromagnetic waves W1 and W2, the phase velocity V of the electromagnetic wave beat generated by the synthesis of the electromagnetic waves W1 and W2 _pBEAT is consistent with group velocity V _GLN electromagnetic W1, W2. Therefore, “the phase velocity V _{pBEAT of the} electromagnetic wave beat” under such conditions may be rephrased as “the group velocity V _glN of the electromagnetic waves W1 and W2”.

Similarly, when the frequency difference between the two electromagnetic waves W1 and W2 introduced into the core portion 2 is sufficiently smaller than the frequencies of the electromagnetic waves W1 and W2, the size of the core portion 2 is the size of the generated high-frequency electromagnetic wave W3. Since it is sufficiently small with respect to the wavelength, it is only necessary to consider the material of the cladding part 3 for the generated high-frequency electromagnetic wave W3. Therefore, under such conditions, “the phase velocity V _pOUT at which the high-frequency electromagnetic wave W3 propagates through the composite dielectric structure including the core portion 2 and the cladding portion 3” is “the phase velocity at which the high-frequency electromagnetic wave W3 propagates through the cladding portion 3”. In other _words, “V _pOUT ”. The single-mode dielectric waveguide 1 satisfies the single-mode condition for the electromagnetic waves W1 and W2, but may not satisfy the single-mode condition for the generated high-frequency electromagnetic wave W3. is there. Therefore, for the high-frequency electromagnetic wave W3, the propagating structure is not a single-mode dielectric waveguide but a composite dielectric structure including the core portion 2 and the cladding portion 3.

The material of the core part 2 is preferably a substance having a large second-order nonlinearity, specifically, an inorganic nonlinear material such as LiNbO ₃ , LiTaO ₃ , KTiOPO ₄ , KNbO ₃ , BaB ₂ O ₃ , MMONS, DIVA, An organic nonlinear material called DMNP, APDA, ABSA, NPNa, DAST, LAP or the like is used. The electromagnetic waves W1 and W2 introduced into the core part 2 are generally electromagnetic waves from a laser from the infrared region to the visible light region, and the refractive index of these nonlinear substances in the frequency band of the electromagnetic waves W1 and W2 is 1.6 to. The value is about 2.3.

The material of the clad part 3 is an electromagnetic wave W3 to be generated with the refractive index in the frequency band of the electromagnetic waves W1 and W2 introduced into the core part 2 being lower than the refractive index of the core part 2 in the same frequency band and the frequency bands of the electromagnetic waves W1 and W2. It is necessary to use a material with a low loss in the frequency band. Specifically, Al ₂ O ₃ , SiO ₂ , diamond-like carbon, epoxy polymer, polyimide polymer and the like can be mentioned. The refractive index of the cladding part 3 in the frequency band of the electromagnetic waves W1 and W2 introduced into the core part 2 is about 1.5 to 1.8.

Here, let us consider a case where infrared light in the vicinity of 200 THz is introduced into a rectangular single-mode dielectric waveguide 1 composed of a core portion 2 made of LiNbO ₃ and a cladding portion 3 made of crystalline SiO ₂ . In this case, the refractive index of the core part 2 with respect to the electromagnetic waves W1 and W2 near 200 THz is about 2.2, and the refractive index of the cladding part 3 is about 1.5. In such a combination of materials, the dimension of the core portion 2 of the rectangular single-mode dielectric waveguide 1 that satisfies the single-mode condition is, for example, in the case of the core portion 2 having a square cross section, one side of the square is 0.8. It is below micrometer.

  Depending on the cross-sectional shape of the waveguide 1 and the combination of materials, the maximum value of the waveguide dimension that satisfies the single mode condition changes. For example, in the same material system as the waveguide 1 having the core section 2 having the square cross section, in the case of the core section 2 having a rectangular section having a ratio of the long side to the short side of 2: 1, the length satisfying the single mode condition is satisfied. The length of the side is 1.0 micrometer or less. The shape dimension that satisfies the single mode condition is inversely proportional to the frequency of the electromagnetic waves W1 and W2 introduced into the core portion 2, and therefore, when visible light having a frequency of several hundred THz is introduced, it is further smaller than the above dimension.

  The reason why the waveguide structure must satisfy the single mode condition is that the generation efficiency of the high frequency electromagnetic wave is remarkably lowered when the multimode waveguide is used. In other words, in the multimode waveguide, there are many beat modes generated by the electromagnetic wave introduced into the core portion, but only one of the modes can be phase-matched, and the other modes generate high-frequency electromagnetic waves. It does not contribute.

In the present embodiment, most of the power of the electromagnetic waves W1 and W2 introduced into the core part 2 is confined in the core part 2 having a cross section with a side of about 1 micrometer. The size is about 1/10000 of the electromagnetic wave beam spot condensed using the bulk optical system 5. Therefore, in the present embodiment, an energy density of about TW / m ² that could not be obtained without pulsing the laser in the conventional high-frequency electromagnetic wave generator shown in FIG. It is possible to easily realize the high frequency generation with high efficiency and high average output.

However, if the cross-sectional dimension of the core part 2 becomes too small, the confinement state of the introduced electromagnetic waves W1 and W2 deteriorates on the contrary, and most of the power leaks to the cladding part 3. In such a state, a high energy density state cannot be maintained. When the electromagnetic waves W1 and W2 near 200 THz are introduced into the single-mode dielectric waveguide 1 composed of the above-described core portion 2 made of LiNbO ₃ and the clad portion 3 made of crystalline SiO ₂ , for example, a core portion having a square cross section When the size of one side of 2 is 0.2 micrometers, 90% or more of the electromagnetic wave power leaks to the clad part 3 and it becomes difficult to generate a high frequency.

For example, a single mode dielectric waveguide 1 composed of a core portion 2 made of LiNbO ₃ having a cross-sectional dimension of 0.8 × 0.4 micrometers and a clad portion 3 made of crystalline SiO ₂ is close to 200 THz. When the phase matching condition is calculated in detail when the electromagnetic waves W1 and W2 having the two frequencies are introduced and the high frequency electromagnetic wave W3 of 1 THz is generated, the group velocity V _glN of the introduced electromagnetic waves W1 and W2 near _{200 THz} is 0. 43 times. Since the frequencies of the two electromagnetic waves W1 and W2 are close to each other with a difference of about 0.5%, the group velocity V _glN coincides with the phase velocity V _pBEAT of the beat wave generated by the synthesis of the electromagnetic waves W1 and W2. The refractive index of the material LiNbO ₃ of the core 2 with respect to the 1 THz electromagnetic wave W3 generated from the beat wave is about 6, unlike the case of 200 THz, and the refractive index of the material SiO ₂ of the cladding 3 is about 2. 1 The phase velocity V _{pOUT at which} the 1 THz electromagnetic wave W3 propagates through the composite dielectric structure composed of the core portion 2 and the cladding portion 3 is 0.42 times the speed of light according to detailed calculation. This is the phase velocity V of the beat wave. _It almost agrees with _{pBEAT with} an error of about 2%.

  Here, the length of the single-mode dielectric waveguide 1 necessary for the present embodiment to sufficiently function as a high-frequency electromagnetic wave generator, that is, the interaction length is the same as the phase matching type high-frequency as in the present embodiment. It can be determined with reference to a traveling wave tube that is an electromagnetic wave generator. The interaction length of a normal traveling wave tube is 10 to 100 times the in-tube wavelength of the generated high-frequency electromagnetic wave. Similarly, also in this embodiment, if an interaction length for at least 10 wavelengths is required, the phase difference between the beat wave and the electromagnetic wave W3 generated between these 10 wavelengths is within ¼ wavelength. Is required. Therefore, the required phase matching accuracy is (1/4 wavelength) / (10 wavelengths) = 0.025, that is, 2.5% or less. The accuracy of this phase matching varies depending on the wavelengths of the electromagnetic waves W1 and W2 to be introduced and the propagation loss thereof, the wavelength of the generated high-frequency electromagnetic wave W3 and the propagation loss thereof, etc. Is done.

A single mode dielectric waveguide 1 composed of a core portion 2 made of LiNbO ₃ having a cross-sectional dimension of 0.8 × 0.4 micrometers and a clad portion 3 made of crystalline SiO ₂ is provided with an electromagnetic wave W1, near 200 THz. In the above-described calculation with W2 introduced, the phase velocity V _pBEAT of the beat wave (group velocity V _glN of the electromagnetic waves W1 and W2) and the generated electromagnetic wave W3 propagate through the composite dielectric structure composed of the core portion 2 and the cladding portion 3. The error from the speed V _pOUT is 2%. Therefore, since the allowable range is 2.5%, the phase matching condition is satisfied here, and high-efficiency high-frequency electromagnetic wave generation is expected.

If a longer waveguide structure is allowed, the effective interaction length can be increased by reducing the error in the phase matching condition by selecting the material or adjusting the shape of the single mode dielectric waveguide 1. Further high-efficiency high-frequency electromagnetic wave generation is expected.
The basic concept of the present invention is the realization of a high energy density state by the minute core portion 2 and the phase matching depending on the material and dimensions of the single mode dielectric waveguide 1, so that the shape of the core portion 2 is square. Obviously any shape other than can be used.

  The present invention is mainly applicable to generation of electromagnetic waves in a frequency band of about 0.1 to 10 THz.

It is sectional drawing which shows the structure of the single mode dielectric waveguide used for the high frequency electromagnetic wave generator which becomes embodiment of this invention. It is a figure which shows the concept of the high frequency electromagnetic wave generation by the high frequency electromagnetic wave generator of embodiment of this invention. It is a figure which shows the concept of the high frequency electromagnetic wave generation by the conventional high frequency electromagnetic wave generator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Single mode dielectric waveguide, 2 ... Core part, 3 ... Cladding part, W1, W2 ... Introduction electromagnetic wave, W3 ... Generated electromagnetic wave.

Claims (5)

A first electromagnetic wave and a second electromagnetic wave having two different frequencies are introduced into a nonlinear dielectric having second-order nonlinearity and propagated to generate a third electromagnetic wave having a frequency that is the difference between the two frequencies. In high frequency electromagnetic wave generator,
A core portion made of the nonlinear dielectric material into which the first electromagnetic wave and the second electromagnetic wave are introduced, and a clad portion made of a material having a refractive index smaller than that of the core portion so as to cover the periphery of the core portion A single mode dielectric waveguide with
The phase velocity of the electromagnetic wave beat generated by the combination of the first electromagnetic wave and the second electromagnetic wave is substantially the same as the phase velocity at which the third electromagnetic wave propagates through the composite dielectric structure composed of the core portion and the cladding portion. Thus, the material of the core part and the clad part and the cross-sectional dimension of the core part are selected. In the high frequency electromagnetic wave generator of Claim 1,
The phase velocity of the electromagnetic wave beat generated by the synthesis of the first electromagnetic wave and the second electromagnetic wave substantially coincides with the phase velocity at which the third electromagnetic wave propagates through the composite dielectric structure with an accuracy of 2.5% or less. The high frequency electromagnetic wave generator characterized by the above-mentioned. In the high frequency electromagnetic wave generator of Claim 1 or 2,
The core portion is made of an inorganic nonlinear material or an organic nonlinear material,
The high-frequency electromagnetic wave generator according to claim 1, wherein the clad portion is made of any one of Al ₂ O ₃ , SiO ₂ , MgO, diamond-like carbon, an epoxy polymer, and a polyimide polymer. In the high frequency electromagnetic wave generator of Claim 1 or 2,
The high-frequency electromagnetic wave generator according to claim 1, wherein a cross-sectional shape of the core portion is a square. In the high frequency electromagnetic wave generator of any one of Claims 1 thru | or 4,
The high-frequency electromagnetic wave generator according to claim 1, wherein both the width and the height of the cross section of the core portion are 1.0 micrometers or less and are larger than 0.2 micrometers.

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