JPH04331930A - Light wavelength conversion device - Google Patents

Abstract

PURPOSE:To make a second harmonic completely parallel and to facilitate the manufacture of the device. CONSTITUTION:This light wavelength conversion device consists of a laser light source 1, a double refractive material 2, a waveguide 3 made of a nonlinear optical material provided on the surface of the double refractive material 2 or in it, and a conical lens 7 which converges or diverges the second harmonic generated by converting laser light propagated in the waveguide 3; and the conical lens 7 is composed of a graded index conical lens and the second harmonics from all projeciton surfaces which are projected from the double refractive material 2 are made completely paralle. Further, LiNb2O3 is used for the conic lens and the angle between the axis of rotation of the conical lens and the optical axis of LiNb2O3 is set to nearly 27.3 deg. to make one surface of the conical lens plane, thereby facilitating the manufacture.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength conversion device that is applied to shorten the wavelength of a light source used in a plate-making device, a laser beam printer, an optical information recording device, a spectroscopic analysis device, and the like.

0002

[Background Art] In recent years, the development of shorter wavelength laser beams has been progressing for the purpose of increasing the resolution and speed of plate-making equipment and laser beam printers, and increasing the recording density of optical information recording devices. . Regarding the wavelength of semiconductor lasers, there are no conventional GaAs-based semiconductor lasers that can oscillate at a wavelength of 580 nm or less in principle, so second harmonic generation (second harmonic generation), which extracts the second harmonic with a wavelength half the wavelength of the incident fundamental wave, is used. S
Research on optical wavelength generators using HG) is active.

An example of a conventional optical wavelength conversion device will be described below with reference to the drawings.

In FIG. 4 showing the operation of a conventional optical wavelength conversion device, 1 is a fundamental wave emitted from a laser light source (not shown), and 2 is a birefringent material made of, for example, LiNb2 O3. 3 is a material having a nonlinear optical effect (for example, LiNb2) provided on the surface or inside of the birefringent material 2.
It is a waveguide formed of O3). 4 is the fundamental wave that passed through the waveguide 3, and 5 is the second harmonic.

In FIG. 4, when a fundamental wave 1 propagates through a guided wave 3, a part of the fundamental wave 1 is converted into a second harmonic 5 due to the nonlinear optical effect of the waveguide 3. At this time, if the phase velocity of the second harmonic 5 in the medium is larger than the phase velocity of the fundamental wave 1 in the medium, the second harmonic 5 is radiated into the birefringent material 2 in the form of Cerenkov radiation. Ru. The unconverted fundamental wave 1 is transmitted as the fundamental wave 1, and the Cherenkov-emitted light is emitted as the second harmonic 5. As shown in FIG. 4, this second harmonic wave 5 is a diverging light whose cross section perpendicular to the direction of propagation is crescent-shaped, and since it is difficult to use it as it is, it is necessary to convert it into parallel light.

[0006] Therefore, the present applicant has proposed a means for converting the second harmonic 5, which has been Cherenkov-radiated, into parallel light. The principle will be briefly explained using FIGS. 5 and 6. FIG. 5 is a vertical cross-sectional view showing the principle of parallelization of the second harmonic, and 6 is the emission angle of the second harmonic 5. In FIG. 7 is a conical lens; 8 is a rotation axis of the conical lens 7 coaxial with the waveguide 3; By appropriately selecting the refractive index and apex angle of the conical lens 7 according to the size of the output angle 6, the second harmonic wave 5 can be made parallel to the rotation axis 8 within the cross section shown in FIG. According to the principle of Cerenkov radiation, the second harmonic 5 forms part of a cone that is axially symmetrical about the rotation axis 8, so the cone lens 7 obtained by rotating the cone lens 7 about the rotation axis 8 (See FIG. 6), all the second harmonics 5 become parallel lights.

[0007]

However, with the above configuration, there remains the problem that the second harmonic propagating in the birefringent material cannot be completely parallelized.

This problem will be explained below using FIGS. 7 and 8. FIG. 7 is a cross-sectional view perpendicular to the waveguide of the optical wavelength conversion device, where 9 is a vertical plane including the waveguide 3, and 10 is a plane representative of the plane including the waveguide 3, which will be referred to as an exit surface hereinafter. Reference numeral 11 is an angle formed by the vertical surface 9 and the exit surface 10, and its size will be referred to as α hereinafter. FIG. 8 is a cross-sectional view of the optical wavelength conversion device at the output surface 10, and the magnitude of the output angle 6 at the output surface 10 is assumed to be θ(α). In the birefringent material 2, the second harmonic, which is an extraordinary ray, feels a different refractive index depending on the direction of propagation.
Different for each 0.

FIG. 9 shows an angle 11 formed by the vertical plane 9 and the exit plane 10.
The relationship between the magnitude α of the output angle 6 and the magnitude θ(α) of the output angle 6 is shown in a graph.

As described above, since the magnitude θ(α) of the exit angle 6 differs for each exit surface 10, the conical lens 7 with a constant refractive index
is used, the second harmonic 5 within one output surface 10
Even if it is possible to make parallel light, the second harmonics will gradually deviate from parallel on the other exit surfaces 10, and it will not be possible to make them completely parallel light.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide an optical wavelength conversion device that can completely convert the second harmonic into parallel light and is easy to manufacture.

0012

[Means for Solving the Problems] The optical wavelength conversion device of the present invention includes a laser light source, a birefringent material, a waveguide made of a nonlinear optical material provided on or inside the birefringent material, and a waveguide. The second laser beam generated by converting the propagating laser beam
An optical wavelength conversion device comprising a conical lens that converges or diverges harmonics, characterized in that the conical lens is a gradient index conical lens.

Preferably, the gradient index conical lens is made of a birefringent material, in particular LiNb as the birefringent material.
2O3, the rotation axis of the conical lens and LiNb2
Preferably, the angle formed with the optical axis of O3 is approximately 27.3 degrees.

[0014]

[Operation] According to the above structure of the present invention, by using a gradient index conical lens having a different refractive index for each output surface, each refractive index is adjusted according to the output angle of the second harmonic, which is different for each output surface. By setting, all the second harmonics can be made into parallel light.

[0015] Also, as a gradient index conical lens, LiN
b2 Using O3, the rotation axis of the conical lens and LiNb2
By making the angle formed by O3 with the optical axis approximately 27.3 degrees, one side of the conical lens can be made flat, which facilitates manufacturing.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Optical wavelength conversion devices according to embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sectional view of an optical wavelength conversion device according to a first embodiment of the present invention. In FIG. 1, 1 is a fundamental wave emitted from a laser light source (not shown), 2 is, for example, LiNb2
A birefringent material made of O3, 3 a waveguide formed of a material having a nonlinear optical effect (for example, LiNb2 O3) provided on or inside the birefringent material 2, and 5 a second harmonic. When the fundamental wave 1 propagates through the guided wave 3, a part of the fundamental wave 1 is converted into a second harmonic 5 due to the nonlinear optical effect of the waveguide 3, and this second harmonic 5 is complexed in the form of Cerenkov radiation. The second harmonic wave 5 is emitted into the interior of the refractive material 2 , and is emitted from the birefringent material 2 at an exit angle 6 , and enters a conical lens 7 whose rotation axis 8 is coaxial with the waveguide 3 . The second harmonic wave 5 is made parallel to the rotation axis 8 by appropriately selecting the refractive index and apex angle of the conical lens 7 according to the magnitude of the output angle 6 of the second harmonic wave 5.

Conditions for collimating light in the above basic configuration will be explained.

FIG. 1 is a cross-sectional view of the optical wavelength conversion device taken along an output plane forming an angle α with the vertical plane (the plane of symmetry of the second harmonic 5), and the output angle 6 of the second harmonic 5 in this cross section is Let the magnitude of be θ(α). Also, the size of the half angle 11 of the front apex angle of the conical lens 7 is γ, and the half angle 1 of the rear apex angle of the conical lens 7 is γ.
2 is β, and the refraction angle 13 at the first surface of the conical lens 7 is
The magnitude of is θ1, and the angle of incidence 14 on the second surface of the conical lens 7 is
The magnitude of is θ2, and the refraction angle 15 at the second surface of the conical lens 7 is
Let the magnitude of be θ3. Further, the refractive index of the conical lens 7 in this cross section is set as n(α), and the condition under which the second harmonic wave 16 transmitted through the conical lens 7 is parallel to the rotation axis 8 is determined.

According to Snell's law in refraction at the first surface,

[0021]

[Math 3]

[0022] Similarly, on the second side,

[0023]

[Math 4]

Furthermore, since the sum of the interior angles of a quadrilateral is 2*π, the following equation holds.

[0025]

[Math 5]

Furthermore, since the second harmonic wave 16 transmitted through the conical lens 7 is parallel to the rotation axis 8,

[0027]

[Math 6]

[0028] Therefore, β obtained from equation (5) is
After substituting into equation (6) to find θ3, substituting it into equation (4) and transforming it into the form of the product of trigonometric functions of θ2, cosθ
By dividing by, the condition to find is

[0029]

[Math 7]

It is given by

This condition is transformed into equations regarding θ(α), γ, β, and n(α). That is, by transforming equation (7) using trigonometric formulas and removing the π/2 term, we obtain equation (4) and
From equation (6), θ2 is expressed by β and n(α), and from equation (3), θ1 is expressed by θ(α), γ, and n(α), and these are (
7) By substituting and rearranging the equation, the following equation is obtained as stated in claim 2.

[0032]

[Math. 8]

[0033] Furthermore, when equation (1) is solved for β, the following equation is obtained.

[0034]

[Math. 9]

[0035] Thus, θ(α), the refractive index n(0) in the plane of symmetry of the second harmonic of the gradient index conical lens, and the half angle γ of the apex angle on the incident side of the second harmonic are given. Then, the refractive index n for each exit surface of the gradient index conical lens is
(α) and the half angle β of the apex angle on the output side, the above equation (1) is used.
By giving Equation (2), all the second harmonics can be made into parallel light.

Here, we will further consider manufacturing the gradient index conical lens 7 using LiNb2 O3, which is generally easily available, as a birefringent material. The conditions for this are that the refractive index of the ordinary ray of LiNb2O3 is no, the refractive index of the extraordinary ray is ne,

[0037]

[Math. 10]

[0038]

[Math. 11]

What is necessary is to find the shape of a conical lens that has a refractive index distribution as follows. As an example, when the wavelength of semiconductor laser light is 830 nm, the wavelength of the second harmonic is 415 nm.
nm, θ(0)=52.6049°, n(0)=
Since no=2.418 and ne=2.311, solving the conditional expression numerically and finding γ, β, and n(α) yields γ=118.92° and β=30.69°. becomes. Therefore, the size γ of the half angle 11 of the front side apex angle of the conical lens 7 is 118.92°, the size β of the half angle 12 of the rear side apex angle of the conical lens 7 is 30.69°, and the material of the conical lens is L.
When iNb2 O3 is used, all light rays passing through the conical lens 7 become parallel lights.

Next, an optical wavelength conversion device according to a second embodiment of the present invention will be explained with reference to FIG. In FIG. 3, the same reference numerals are given to the same components as those shown in FIG. 1, and the description thereof will be omitted. 18 is the optical axis of LiNb2O3. 19 is the optical axis 18 and the rotation axis 8 of the conical lens
It is the angle formed by , and its size is 27.3°. At this time, the size of the half angle 11 of the front apex angle of the conical lens is 66
．． If it is 3 degrees, the light rays 16 that pass through all the conical lenses become parallel lights when the rear apex angle is 180 degrees, as will be explained next.

In this way, the rotation axis 8 of the conical lens 7 and the L
The angle formed with the optical axis of iNb2 O3 is approximately 27.3°.
The reason why β=90° in FIG. 1 is explained below. Figure 2 shows the ray vector and LiNb2 when α=90°.
It is a diagram showing a refractive index ellipsoid cut along a plane including the optical axis of O3, and 17 is a light ray that passes through LiNb2O3.

Since the refractive index felt by the light ray 17 is expressed by the length of the vector n, if the angle between n and the optical axis is θ, then

[0043]

[Math. 12]

The following formula holds true. Solving this equation (10) for θ, we get

[0045]

[Math. 13]

Here, if θ=27.3°, ne=
2.311, no=2.418, so equation (11)
Solving, we get n=2.376.

When γ=66.3°, (1), (2
) From the formula, β=90°. Therefore, the conical lens 7
The rear apex angle of is 180°, that is, a plane.

As described above, according to this embodiment, LiNb2 O3 is used as the material of the conical lens, and by setting the angle between the rotation axis of the conical lens and the optical axis of LiNb2 O3 to be approximately 27.3°, the conical Since the rear apex angle of the lens is 180°, that is, a flat surface, a conical lens suitable for processing can be obtained.

[0049]

Effects of the Invention According to the optical wavelength conversion device of the present invention, since the conical lens that converts the second harmonic into parallel light is a gradient index conical lens, it is possible to A completely parallel second harmonic can be obtained.

Further, the conical lens is a gradient index conical lens using a birefringent material, and LiNb2O3 is used as the birefringent material, and the axis of rotation of the conical lens and Li
By setting the angle between the Nb2 O3 and the optical axis to be approximately 27.3 degrees, one side of the conical lens becomes flat, which facilitates manufacturing.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an optical wavelength conversion device in a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an index ellipsoid.

FIG. 3 is a sectional view of an optical wavelength conversion device in a second embodiment of the present invention.

FIG. 4 is a perspective view illustrating the operation of a conventional light conversion device.

FIG. 5 is a vertical cross-sectional view showing the principle of parallelization of second harmonics in a conventional optical wavelength conversion device.

FIG. 6 is a partial perspective view of a conventional optical wavelength conversion device.

FIG. 7 is a cross-sectional view perpendicular to a waveguide of a conventional optical wavelength conversion device.

FIG. 8 is a cross-sectional view of a conventional optical wavelength conversion device taken along a plane including an output surface.

FIG. 9 is a graph showing the relationship between the angle of the exit surface with respect to the plane of symmetry and the exit angle.

[Explanation of symbols]

1 Fundamental wave emitted from a laser light source 2 Birefringent material 3 Waveguide 5 Second harmonic 7 Conical lens 8 Rotation axis

Claims (4)

[Claims] Claim 1: A laser light source, a birefringent material, a waveguide made of a nonlinear optical material provided on or inside the birefringent material, and a second waveguide generated by converting the laser light propagating through the waveguide. An optical wavelength conversion device comprising a conical lens that converges or diverges harmonics, wherein the conical lens is a gradient index conical lens. 2. The half angle of the apex angle on the second harmonic incident side of the gradient index conical lens is γ, and the half angle of the apex angle on the output side is β, and the symmetry plane of the second harmonic and the second harmonic are Let the angle formed with the output surface be α, and the output angle of the second harmonic at the output surface be θ(α)
The refractive index of the gradient index conical lens is a function n(
α), and when θ(α), n(0), and γ are given, n(α) and β are given by [Formula 1] and [Formula 2] Item 1. The optical wavelength conversion device according to item 1. 3. The optical wavelength conversion device according to claim 1, wherein the gradient index conical lens is made of a birefringent material. 4. A laser light source, a birefringent material, a waveguide made of a nonlinear optical material provided on or inside the birefringent material, and a second waveguide generated by converting the laser light propagating through the waveguide. In an optical wavelength conversion device comprising a conical lens that converges or diverges harmonics, the conical lens is a gradient index conical lens using a birefringent material, LiNb2O3 is used as the birefringent material, and rotation of the conical lens is performed. An optical wavelength conversion device characterized in that the angle formed between the axis and the optical axis of LiNb2O3 is approximately 27.3 degrees.