JPH0227325A - Light wavelength converter - Google Patents

Abstract

PURPOSE:To reduce the size and cost of the above converter and to facilitate optical axis adjustment by providing a circular conical lens provided coaxially with a light guide to the exit end of an SHG element. CONSTITUTION:SH light 31 is obtd. in the direction coaxial with the SHG element 4 by providing the circular conical lens 41 the central axis of which is aligned to the central axis of a waveguide 2 provided to the SHG element 4. Since a cylindrical part 42 is provided to the circular conical lens 41, the alignment to align the optical axis centers at the time of assembling the circular conical lens 41 together with lenses 6, 7 and a semiconductor laser 5 to a housing is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical wavelength conversion device that uses semiconductor laser light and is used in optical memory devices, laser printers, and the like.

Conventional technology Conventionally, second harmonic generation (
It is known to convert the wavelength of a laser beam into % by using SHG (hereinafter abbreviated as SHG) (for example, Japanese Patent Application Laid-open No. 72222/1983).

7, 8, and 9 show conventional optical wavelength conversion devices, in which 1 is a nonlinear optical crystal substrate, 2 is an optical waveguide provided on the nonlinear optical crystal substrate 1, and 3 is a light input. Department. 4
is an optical wavelength conversion element (hereinafter referred to as SHG element), which is composed of a nonlinear optical crystal substrate 1 and an optical waveguide 2. Also 5
is a semiconductor laser, e is a collimating lens, and 7 is a focus lens. When the light 8 that has been focused from the semiconductor laser 6 through the collimating lens 6 and the focus lens 7 is introduced into the light incidence section 3, the A second harmonic (hereinafter abbreviated as SH light) 9 whose wavelength is converted by the nonlinear optical effect is obtained. Note that 18 is the primary light that has passed through the optical waveguide 2.

Here, SHHO2 is called Cherenkov radiation, and becomes a crescent-shaped diffused light 1o as shown in FIG. As shown in FIG. 9, this SHHO2 is emitted while making an angle A with the waveguide 2 in the y direction, and! It has an extent of angle B in the direction. Note that the crescent moon light is almost parallel light in the thickness direction.

However, the SHHO with such diffused light 10
2 is difficult to use, so conventionally parallel light has been obtained by adding all the beam shaping means shown in FIG. 1o.

In Figure 10, 12.14 is a cylindrical convex lens, 1
3 is a cylindrical concave lens.

The operation will be explained below. SHG that does not expose prisoners first
SHHO2 from the element, cylindrical convex lens 12
This is shown in Figure 9. The spread in the X direction in FIG. 10 is collimated to become a light beam 15. Next, the cylindrical concave lens 13
As a result, the thickness direction of the crescent moon light is expanded to obtain a diffused light beam 16 in the Y direction.

Next, the beam 9 in the Y direction is collimated by the cylindrical convex lens 14 to obtain parallel light 17.

Problems to be Solved by the Invention However, the above configuration requires three cylindrical lenses, and when trying to obtain parallel light with the cylindrical convex lenses 12 and 14, it is necessary to adjust the focal length of each lens. There is.

Furthermore, the above configuration is originally effective for point light sources, but has the problem that it is only approximately effective for linear light sources such as Cherenkov synchrotron radiation, where the light source is the length of a waveguide. had.

In view of the above-mentioned problems, the present invention provides an optical wavelength conversion device that converts Cerenkov radiation obtained by a waveguide type SHG element into parallel light with better parallelism, and is equipped with a beam shaping means that is more compact and inexpensive than conventional ones. This is what we provide.

Means for Solving the Problems In order to achieve the above objects, the optical wavelength conversion device of the present invention comprises:
Semiconductor laser and the light of the semiconductor laser are focused and SH
means for inputting the light into the optical waveguide provided in the G element;
At the output end of the element, a beam shaping means is provided, which comprises a conical lens provided coaxially with the 0M optical waveguide.

Operation The present invention can extract crescent-shaped Cerenkov radiation light as ring-shaped parallel light with the above-described configuration.

Embodiments Before describing specific embodiments of the present invention, the principle of operation thereof will be explained in detail.

In Fig. 6, 9 is a crescent-shaped SH light (Cherenkov cone), 21 is a conical lens, and SH
The rotational symmetry axes of the HO2 conical lens 21 are aligned. The operation of the light beam shaping means configured as described above will be explained. In FIG. 5, angle a is the Cherenkov radiation angle, which is a constant determined by the Cherenkov radiation mechanism. The angle β is the angle of incidence of the Cherenkov radiation 9 entering the bottom surface of the conical lens 21, the angle γ is the corresponding output angle, the angle δ is the angle of incidence on the side surface of the conical lens 21, and the angle ε corresponds to this. The exit angle, corner 4, is the conical lens 2.
The angle between the Cherenkov radiation beam refracted by the side surface of the conical lens 21 and the side surface, and the angle () are half angles of the apex angle of the conical lens 21.

Here, if the refractive index of the medium through which the Cherenkov radiation is transmitted is 1 in air, and the refractive index of the conical V-lens 21 is n, then from Fig. 6, the simple geometric theorem, and the law of refraction, α −β Slnβ=nsin7 n Sinδ=SlnE ε+ζ=− Using these equations, the SH light 11 emitted from the conical lens 21 is
Solving for α and η under the condition that they are parallel to the axis of rotational symmetry of the conical lens 21, that is, γ+δ=ε ζ=η, gives the following equation.

Therefore, when a Cherenkov cone with an apex angle of 2α is given, if n and η exist that satisfy the relationship of equation (1), all the Cherenkov radiation 9 in FIG. As a result, even in the three-dimensional structure of Fig. 6 obtained by rotating the figure in Fig. 6 around the axis of rotational symmetry, all the Cherenkov radiation is parallel to the axis of rotational symmetry, i.e. It becomes parallel light. As an example of n and η, in the case of our experiments, lithium niobate (L z Nb
O5) When a laser beam with a wavelength of 860 nm is incident on a waveguide formed on the substrate surface, the radiation angle is 63°, where α is taken as α. At this time, for example, the glass material LaK14 (n=1,71
6at wavelength = 430 nm), η-33° is obtained. Now, since the parallel light obtained here is a ring-shaped parallel light, in order to expand or reduce the diameter of the luminous flux, as in the conventional example, a pair of spherical concave and convex lenses is set at the confocal position, and the The optical axis may be made to coincide with the axis of rotational symmetry of the conical lens 21 shown in FIG.

As described above, by aligning the rotational symmetry axis of the conical lens with the apex angle determined by the apex angle of the Cerenkov cone and the refractive index of the glass material to the rotational symmetry axis of the Cerenkov cone, the Cherenkov radiation light is made into parallel light. can do.

An optical wavelength conversion device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the invention. In this figure, the same parts as in FIG. 7 are given the same numbers and their explanations will be omitted.

First, by providing the conical lens 41 with its central axis aligned with the optical waveguide 2 provided in the SHG element 4, the SH
SH light 31 is obtained coaxially with the G element 4.

The reason why the cylindrical portion 42 is provided on the conical lens 41 is to facilitate alignment of the optical axis centers when assembling the conical lens 41 together with the semiconductor laser 6 and lens 6.7 in a housing (not shown). This is what I did.

Next, a second embodiment will be described with reference to FIG. 2.

Components that are the same as those in FIG. 7 are given the same numbers and their explanations will be omitted. 4
3 is a conical lens cut along a cross section passing through the central axis of the conical shape to form a flat surface; 44 is a substrate to which the conical lens 43 is fixed together with the SHG element 4; υ is made of any material such as glass, ceramic, metal, etc. So, the surface should be plain.

The optical waveguide surface of the SHG element 4 is bonded to the substrate 44, and the optical axes of the leading waveguide 2 and the conical lens 43 are aligned. As is clear from Fig. 5, the conical lens is divided into two parts by the cross section passing through the central axis, but it can function sufficiently, and the SH light 3
1 can be obtained.

In the second embodiment, since the conical lens 43 is cut along the cross section passing through the optical axis, there is an effect that alignment of the SHG element 4 with the optical waveguide 2 is facilitated. Furthermore, since the SHG element 4 and the conical lens 43 are integrally fixed, there is also the effect that the deviation of the optical axis due to temperature, vibration, etc. is reduced.

FIG. 3 is a block diagram of the third embodiment. In this figure, the same parts as those in FIG. 7 are given the same numbers and their explanations will be omitted. In this embodiment, a conical lens 45 is fixed to the output end of the SHG element 4 with an optically transparent adhesive, and parallel light 46 is obtained.

This produces the effect that the optical wavelength conversion device can be made much smaller in diameter. Furthermore, similar to the second embodiment, there is also the effect that deviation of the optical axis due to temperature, vibration, etc. is reduced.

FIG. 4 is a configuration diagram showing a fourth embodiment.

In this figure, the same parts as in FIG. 7 are given the same numbers, and their explanations will be omitted. In this embodiment, the tip 47 of the SHG element 4 is formed into a semi-conical shape and a conical lens is integrated therein, so that four parallel lights can be obtained. This conical shape is based on the same idea as described in the explanation of the action, and although detailed calculations are omitted, the apex angle of the Cherenkov cone is
α, the apex angle of the beam shaping unit 47 is 2θ, and the refractive index of the optical crystal is n. When the following relationship holds true, the Cerenkov cone generated with the waveguide 2 as the axis of rotational symmetry is output to the outside as parallel light. It's coming.

As described above, by cutting out the beam shaping part 47 from the optical crystal substrate 1, there is no need to adjust the alignment of the rotational symmetry axis, the number of parts is reduced, and the second to third
The same effects on temperature and vibration as in the embodiment can be obtained.

In the first embodiment, the conical lens 41 is provided with the cylindrical portion 42, but the cylindrical portion may be omitted by using other optical axis alignment means.

Further, there is no problem even if the portion where light does not actually pass, such as the apex angle of the cone, is cut off.

Further, in the second embodiment, the conical lens 43 is cut along a plane passing through the central axis, but it is not necessary to cut through the central axis.
The central axis may be a parallel plane.

In addition, in all examples, the light of the semiconductor laser is focused,
Although we used a collimating lens and a focus lens to input the light into the optical waveguide, it is not necessary to use two lenses; it is also possible to condense and introduce the light into the waveguide with a single lens, as is conventionally known. It is possible. Furthermore, although the purpose of the above explanation was to obtain parallel light, it is also possible to converge or diffuse the Cherenkov radiation by changing the angle between the rotationally symmetric plane through which the Cherenkov radiation passes and the Cherenkov radiation. It is possible. Further, in the fourth embodiment, the waveguide 2 is formed on the surface of the optical crystal 1, but it may be formed inside the optical crystal 1.

In that case, the beam shaping section 47 does not have a semi-conical shape but a conical shape.

Effects of the Invention As described above, the present invention includes a semiconductor laser, a means for condensing the light of the semiconductor laser and inputting it into an optical waveguide provided in an SHG element, and a means for coaxially disposing the optical waveguide at the output end of the SHG element. By providing the conical lens, the crescent-shaped diffused light emitted from the waveguide type SHG element can be shaped into parallel light, convergent light, or diffused light that is coaxial with the waveguide. In addition, in order to obtain parallel light, three cylindrical lenses are required in the conventional example, but the conventional example requires only one conical lens, so it is compact.

It also has the effect of reducing costs and making optical axis adjustment easier.

[Brief explanation of the drawing]

W, Fig. 1 is a block diagram of an optical wavelength conversion device according to a first embodiment of the present invention, Fig. 2 is a block diagram of a second embodiment of the present invention, and Fig. 3 is a block diagram of a third embodiment of the present invention. FIG. 4 is a block diagram of a fourth embodiment of the present invention, and FIG. 5 is a block diagram of the fourth embodiment of the present invention. Fig. 6 is an explanatory diagram explaining the operation of a conical lens, Fig. 7 is a configuration diagram of a conventional optical wavelength conversion device, Fig. 8 is a cross-sectional view of a waveguide type SHG element, and Fig. 9 is a waveguide type SHG element. Explanation of the shape of SH light from an SHG element FIG. 1 FIG. 10 is a block diagram for obtaining conventional parallel light. 1... Nonlinear optical crystal substrate, 2... Optical waveguide, 4... SHG element, 5... Semiconductor laser, 6... Collimating lens, 7.
...Focus lens, 41.43, 45.47
・・・・・・Conical lens. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1st
Figure 2 - Kusen Hamaka + E-Yen 9-cho” missing, 4th figure, 4th figure, 4th figure, 2nd figure

Claims (1)

[Claims] A light beam consisting of a semiconductor laser, a means for condensing the light and introducing it into an optical waveguide provided in a wavelength conversion element, and a conical lens provided coaxially with the optical waveguide at the output end of the wavelength conversion element. Wavelength conversion device.