JPH0540287A - Wavelength transforming device - Google Patents

Abstract

PURPOSE:To use the device as a continuous wavelength variable minimum pulse light source by realizing high-efficiency wavelength transformation by generating beams having the two kinds of wavelengths with high wavelength transforming efficiency. CONSTITUTION:This waveform transforming device 11 transforms the wavelength of the laser beam made incident to optical crystal 12 composed of 2- adamantyl.amino/5-nitropyridine (AANP) having a nonlinear optical characteristic. At such a wavelength transforming device, when an angle formed by the azimuth of the incident laser beam and the Z axis of the optical elastic axis of the optical crystal is defined as THETA and an angle formed by the projection of the azimuth of the incident laser beam to a plane formed by the X and Y axes of the optical elastic axis and the X axis is defined as PHI, the optical crystal is arranged so that the laser beam made vertically incident to the optical crystal can obtain a surface with the 35-45 deg. range of the THETA and the 65-90 deg. range of the PHI and can be rotated around the two axes vertical to the laser beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light wavelength conversion device, and more particularly, it is combined with a dye laser or the like which generates a light pulse having a wavelength of about 0.6 μm in a short time width of about 10 ps or less. The present invention relates to a wavelength conversion device for laser light used as a continuous wavelength tunable ultrashort pulse light source that generates an optical pulse in the 1.3 μm wavelength band, which is important for optical communication.

[0002]

2. Description of the Related Art Conventionally, a wavelength conversion device as shown in FIG. 3 is well known as a wavelength conversion device for laser light.

This wavelength conversion device 1 has a KTP (KTiOP) having a nonlinear wavelength conversion characteristic (nonlinear optical characteristic).
The O ₄ ) crystal (optical crystal) 2 and the excitation light are condensed to form the K
A condenser (concave mirror) 3 for making the light incident on the TP crystal 2,
An optical device (concave mirror) 4 for converting the converted light whose wavelength is converted by the KTP crystal 2 into parallel rays, and a rotation mechanism 5 for adjusting the wavelength of the converted light provided in the KTP crystal 2. An optical filter 6 for separating the excitation light from the converted light and a prism 7 for separating the two wavelengths of the converted light are roughly configured.

Next, the operating principle of the wavelength conversion device 1 will be described. In FIG. 3, when the excitation light L _P having the angular frequency ω _p is condensed by the condenser 3 and enters the KTP crystal 2, ω _p = ω _s + ω _i ... (Due to the nonlinear optical effect of the KTP crystal 2. 1) Two types of light having angular frequencies ω _s and ω _i that satisfy the following condition are generated.

The above-mentioned phase matching condition of ω _s and ω _i can be expressed as Δk = k _p −k _s −k _i (2) using the momentum k _x (x = p, s, i). , Ω _s and ω _i are Δ in Equation (2)
It is determined to satisfy k = 0.

Here, the momentum k _x is

[Equation 1] Satisfy the relationship. In equation (3), c is the speed of light and n is K.
The refractive index corresponding to each frequency in the TP crystal 2 is shown.

Generally, two methods are used for frequency tuning. The first method is a method called temperature matching, in which excitation light is incident perpendicularly to the crystal axis of the optical crystal. In this method, tuning the temperature coefficient of the refractive index n _e are different, the angular frequency of the excitation light by changing the temperature to the refractive index n _o and an extraordinary ray with respect to the ordinary ray (o-ray) (e- ray) I can do things.

The second method is a method called angle matching shown in this conventional example, which is a method of changing the incident direction of the excitation light to the KTP crystal 2. K with birefringence
In the TP crystal 2, the refractive index n _e (θ, φ) depends on the angle formed by the light propagation direction and the principal axis (optical elastic axis) of the dielectric constant tensor of the KTP crystal 2, and

[Equation 2] Follow

Here, θ is an angle formed by the light propagation direction with one of the optical elastic axes (Z axis), and φ is a plane (XY plane) formed by the other two optical elastic axes in the light propagating direction. Is the angle with the X axis.

Particularly, in the case of uniaxial crystal, if n _x = n _y = n _e (5) n _z = n _o (6), then from equation (4),

[Equation 3] Is obtained. Here, n _o , n _e , n _x , n _y , and n _z are constants.

Therefore, by changing the angle of the KTP crystal 2 with respect to the excitation light, the angular frequency of the converted light can be tuned.

When tuning the angular frequency of the converted light, there are first-type phase matching and second-type phase matching.

In the case of the first type phase matching, (a) In the case of a positive crystal

[Equation 4]

(B) In case of negative crystal

[Equation 5] Becomes

Further, in the case of the second kind phase matching, (a) In the case of a positive crystal

[Equation 6]

(B) In case of negative crystal

[Equation 7] Becomes

The converted light thus extracted is sent to the optical filter 6
After being separated from the excitation light by means of the prism 7, the prism 7 spatially separates the two kinds of converted light into two kinds of converted lights L _s and L _i having angular frequencies ω _s and ω _i. To go out.

[0018]

The wavelength conversion device 1 described above.
It is known that in the wavelength conversion of the excitation light using the, the conversion efficiency of the excitation light depends on the effective nonlinear constant of the nonlinear crystal such as the KTP crystal 2, but the conventionally used KTP crystal 2 or the like. The effective nonlinear coefficient of the nonlinear crystal is extremely small, and the conversion efficiency of the pumping light is small.

Therefore, if the intensity of the incident laser light is increased for the purpose of increasing the intensity of the converted light, the nonlinear crystal itself such as the KTP crystal 2 is damaged by the laser light, and the intensity of the converted light is increased. There is a problem that it cannot be increased beyond the current level. Therefore, the use of the wavelength conversion device 1 is extremely limited.

The present invention has been made in view of the above-mentioned circumstances, and has a wavelength of 0.6 ps with a short time width of about 10 ps or less.
It can be combined with a dye laser or the like that generates an optical pulse in the vicinity of μm, and can realize highly efficient wavelength conversion into the 1.3 μm band, which is important for optical communication.
It is an object of the present invention to provide a wavelength conversion device for laser light which can be used as a continuous wavelength variable ultrashort pulse light source for generating optical pulses in the μm band.

[0021]

The present invention employs the following wavelength conversion device.

That is, the wavelength conversion device according to claim 1 comprises an optical crystal having nonlinear optical characteristics, and in the wavelength conversion device for converting the wavelength of laser light incident on the optical crystal, the optical crystal is , 2-adamantylamino-5-nitropyridine (AANP).

The wavelength converter according to a second aspect is the wavelength converter according to the first aspect, wherein an angle between the azimuth of the incident laser light and the Z axis of the optical elastic axis of the optical crystal is Θ. And the angle formed by the projection of the azimuth of the incident laser light on the plane (X-Y plane) formed by the X axis and the Y axis of the optical elastic axis and the X axis is Φ, the optical crystal, The laser light incident vertically on the optical crystal has a Θ range of 3
It has a surface such that the range of 5 to 45 ° and Φ is 65 to 90 °, and is arranged so that it can rotate around two axes perpendicular to the laser light incident on this optical crystal. It has a feature.

Here, the AANP crystal is a nonlinear crystal having a surface perpendicular to the azimuth in the range of Θ = 35 to 45 ° and Φ = 65 to 90 ° with respect to the optical elastic axis.

The AANP crystal, which is an organic crystal, is disclosed by the present inventors (reference: Nonlinear Optical Prope).
rties of 2-Adamantylamino-5-Nitropyridine Cryst
als (Applied Physics Letters Vol.58, No.23,10 Ju
ne 1991), 1.064μ
In second harmonic generation (SHG) at m, the efficiency is 100 times or more higher than that of a conventional KTP crystal or the like.

The present inventors have confirmed that this AANP crystal has a grain size of 0.6.
The wavelength converter was applied to optical parametric wavelength conversion for obtaining an optical pulse from the 17 μm dye laser beam to the 1.3 μm band, and the same high efficiency was obtained and continuous wavelength tunability was possible.

[0027]

In the wavelength converter according to the first aspect of the invention, when laser light is incident on the optical crystal made of 2-adamantylamino-5-nitropyridine (AANP), the nonlinear optical effect of the AANP crystal causes (1) and (2). Light of two wavelengths converted so as to satisfy the formula is generated.

Further, in the wavelength converter according to claim 2,
When laser light is incident on the AANP crystal, light of two types of wavelengths converted so as to satisfy the expressions (1) and (2) is generated due to the nonlinear optical effect of the AANP crystal. (2)
The phase matching condition of the equation is satisfied by the angle matching, and the angular velocity of the optical crystal is adjusted so that light having an angular frequency matching the condition is generated.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wavelength converter according to the present invention will be described below with reference to FIG.

The wavelength conversion device 11 is an improvement of the wavelength conversion device 1 described in the conventional example. The same components as those of the wavelength conversion device 1 are designated by the same reference numerals and the description thereof will be omitted.

This wavelength conversion device 11 condenses the optical crystal (AANP crystal) 12 made of 2-adamantylamino-5-nitropyridine (AANP) and the excitation light, and
Condenser (concave mirror) 3 for making the light incident on the ANP crystal 12
An optical device (concave mirror) 4 for converting the converted light whose wavelength has been converted by the AANP crystal 12 into parallel rays, and a rotation mechanism 5 provided on the AANP crystal 12 for adjusting the wavelength of the converted light. A wavelength conversion mechanism comprising an optical filter 6 for separating the excitation light from the converted light and a prism 7 for separating two wavelengths of the converted light,
A mode-locking dye laser (dye laser) 13 that emits an ultrashort optical pulse having a wavelength of 0.617 μm and a YAG excitation dye amplifier light source (dye amplifier) 14 are roughly configured.

The AANP crystal 12 has θ = 36 ° and φ = 9.
The surface of this AANP crystal 12 is Θ =, so that the incident light in the 0 ° azimuth is just perpendicular to this AANP crystal 12.
It is cut so that it is perpendicular to the azimuth of 36 ° and Φ = 90 °. Here, they are arranged so as to achieve the first type phase matching at the angle.

Next, the operation of the wavelength converter 11 will be described. Wavelength 0.6 emitted from dye laser 13
The 17 μm dye laser beam L _p is amplified by the dye amplifier 14 and then converged by the condenser 3 to enter the AANP crystal 12. The characteristics of the dye laser light L _p are as follows.
Wavelength 0.617μm, pulse width 1ps, repetition frequency 1
The output is 0 Hz and the spire output is 10 GW / cm ² .

The incident dye laser light L _p is AA
In the NP crystal 12, due to the non-linear optical effect of the AANP crystal 12, two kinds of converted light having wavelengths of 1.38 and 1.12 μm that satisfy the expressions (1) and (2) are generated.

Here, the phase matching condition of the equation (2) is AA
It can be tuned by the rotating mechanism 5 so that light having an angular frequency satisfying the conditions, which is satisfied by the angle matching of the NP crystal 12, is generated. The wavelength of the converted light is AA of the excitation light.
The incident angle with respect to the NP crystal 12 can be changed by adjusting the rotation mechanism 5 of the AANP crystal 12.

The converted light thus extracted is separated from the excitation light by the optical filter 6, and then the converted light of two kinds of wavelengths is spatially separated by the prism 7 into two kinds of converted lights L _s and L _i. And emits to the outside.

FIG. 2 is a graph showing the tuning characteristics of the converted light wavelength, that is, the relationship between the converted wavelength and the adjustment angle of the AANP crystal.

In the figure, black circles represent the wavelength conversion device 1 of the above embodiment.
The effect when 1 is used is shown, and the solid line shows the calculated value using the value of the refractive index in the above-mentioned reference.

As is apparent from the graph, the wavelength conversion efficiency in the case of using the wavelength conversion device 11 of this embodiment is a value 36 times larger than that of the wavelength conversion device 1 of the conventional example, and has a very high conversion efficiency. I understand.

As described above, this wavelength conversion device 1
1, the AANP crystal 12 is provided so that the incident light in the azimuths of θ = 36 ° and φ = 90 ° is incident on the AANP crystal 12 just perpendicularly. Is cut so that the surface of is perpendicular to the azimuth of Θ = 36 ° and Φ = 90 °.
Since No. 2 is arranged so as to achieve the first-type phase matching at the above-mentioned angle, it is possible to generate light of two types of wavelengths, which are more excellent in wavelength conversion efficiency than conventional ones.

Therefore, it can be combined with a dye laser or the like that generates an optical pulse having a wavelength of about 0.6 μm in a short time width of about 10 ps or less, and highly efficient wavelength conversion into the 1.3 μm band, which is important for optical communication. It can be realized, and can be used as a continuous wavelength variable ultrashort pulse light source that generates an optical pulse in the 1.3 μm band.

In the present embodiment, the surface has Θ = 36.
Although the AANP crystal 12 cut to Φ and Φ = 90 ° was used, the cut surface of the AANP crystal 12 does not necessarily have to be the above value, and in the range of Θ = 35 to 45 ° and Φ = 65 to 90 °. If so, the completely similar effect can be obtained by rotating the AANP crystal 12 around two axes perpendicular to the incident laser beam.

[0043]

As described above, according to the first aspect of the present invention.
According to the wavelength converter described in the above, in the wavelength converter which comprises an optical crystal having nonlinear optical characteristics and converts the wavelength of the laser beam incident on the optical crystal, the optical crystal is made of AANP. Therefore, due to the non-linear optical effect of this AANP crystal, it is possible to generate light of two types of wavelengths with excellent wavelength conversion efficiency. Therefore, a highly efficient continuous wavelength variable wavelength ultrashort pulse light source can be realized.

According to the wavelength conversion device of the first aspect, in the wavelength conversion device of the first aspect, the angle formed by the direction of the incident laser beam and the Z axis of the optical elastic axis of the optical crystal. Is .THETA., And the angle between the X axis and the projection of the azimuth of the incident laser light on the plane (X-Y plane) formed by the X and Y axes of the optical elastic axis is .PHI. Has a surface such that the laser light which is vertically incident on the optical crystal is in the range of Θ of 35 to 45 ° and Φ is of the range of 65 to 90 °, and is perpendicular to the laser light incident on the optical crystal. Since it is arranged so as to be able to rotate around these two axes, it is possible to generate light of two types of wavelengths, which are more excellent in wavelength conversion efficiency than conventional ones.

Therefore, it can be combined with a dye laser or the like that generates an optical pulse having a wavelength of about 0.6 μm in a short time width of about 10 ps or less, and highly efficient wavelength conversion into the 1.3 μm band, which is important for optical communication. It can be realized, and can be used as a continuous wavelength variable ultrashort pulse light source that generates an optical pulse in the 1.3 μm band.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a wavelength conversion device that is an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the conversion wavelength and the adjustment angle of the AANP crystal.

FIG. 3 is a schematic configuration diagram of a conventional wavelength conversion device.

[Explanation of symbols]

11 Wavelength conversion device 12 Optical crystal (AANP crystal) made of 2-adamantylamino-5-nitropyridine (AANP) 3 Concentrator (concave mirror) 4 Optical device (concave mirror) 5 Rotation mechanism 6 Optical filter 7 Prism 13 Mode-locking dye laser ( Dye laser) 14 YAG excitation dye amplifier light source (dye amplifier) L _p Dye laser light L _s , L _i converted light

Front page continuation (72) Inventor Kenichi Kuboji 1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Akira Tomaru 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihonhon (72) Inventor Toshikuni Kaino 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (2)

[Claims] 1. A wavelength conversion device comprising an optical crystal having non-linear optical characteristics and converting the wavelength of a laser beam incident on the optical crystal, wherein the optical crystal is 2-adamantylamino-5-nitropyridine (AANP). ) Is comprised of a wavelength converter. 2. The wavelength conversion device according to claim 1, wherein the angle between the azimuth of the incident laser light and the Z axis of the optical elastic axis of the optical crystal is Θ, and the azimuth of the incident laser light is A plane formed by the X axis and the Y axis of the optical elastic axis (X-Y
When the angle formed by the projection onto the plane and the X-axis is Φ, the optical crystal is such that the laser light perpendicularly incident on the optical crystal has a Θ range of 35 to 45 ° and a Φ range of 65 to 65. 90
A wavelength conversion device having a surface such that the optical crystal has an angle of 0 °, and is arranged so as to be rotatable around two axes perpendicular to the laser light incident on the optical crystal.