JPH04215621A - Wavelength transforming element - Google Patents

Abstract

PURPOSE:To obtain a wavelength transforming element which is easily machinable and capable of eliminating the need for adjustment after machining and positively protecting the output end part of an optical fiber when manufacturing a structure for transforming a secondary higher harmonic wave outputted from the optical fiber type wavelength transforming element into parallel light beams. CONSTITUTION:With an optical fiber type wavelength transforming element 4, a clad 42 is surrounded by a cylindrical transparent layer 5, and on the end part of the wavelength transforming element 4, a conical surface (circular symmetrical inclined face) 51 for transforming a secondary higher harmonic wave outputted from the wavelength transforming element 4 into parallel light beams is formed to the transparent layer 5. The wavelength transforming element 4 is formed to be embedded in the cylindrical transparent layer 5, and the light beams outputted from the end part of the wavelength transforming element 4 are refracted on the circular symmetrically inclined face 51 formed on the transparent layer 5 to become parallel light beams and outputted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion element capable of generating a second harmonic from an incident laser beam and extracting the second harmonic as a parallel beam.

0002

2. Description of the Related Art A nonlinear optical effect is a phenomenon in which when light enters a medium, polarization occurs in proportion to a higher-order term equal to or higher than the square of the electric field of the light, and this phenomenon generates second-order harmonics. Materials containing the above medium are called nonlinear optical materials,
Inorganic materials such as KH2PO4 and LiNbO3 have been put into practical use. Furthermore, recently, organic materials represented by 2-methyl-4-nitroaniline (MNA) have also attracted attention because they have large nonlinear optical constants.

[0003] A wavelength conversion element that uses the above-mentioned nonlinear optical material as a second harmonic generation element to halve the wavelength of a low-power laser beam such as a semiconductor laser has been put into practical use. This wavelength conversion element is designed to confine the fundamental wave (semiconductor laser light) for harmonics at high energy density and to lengthen the interaction length with the harmonics.

[0004] Therefore, the form of the wavelength conversion element is as follows:
For example, an optical waveguide type is used. In this method, a long and narrow optical waveguide is formed on a substrate to confine and propagate light, and an overlayer is coated on top of it. However, in order to extract the second harmonic generated in the optical waveguide, etc. , the optical waveguide must have a structure that can accommodate the propagation phase velocity of the second harmonic of the wavelength. That is, the fundamental wave and the second harmonic must be phase matched. Various methods can be considered to achieve this phase matching, but the simplest method is to use the Cerenkov radiation method.

In this method, as shown in FIG. 7, a second harmonic is generated from the light propagating through the optical waveguide 11 at point A and leaks into the substrate 12 and overlayer 13 at an angle θ. Then, after unit time, at point B, the equal phase front of the second harmonic that is emitted in the direction again, and the above two
When the equal phase planes of the harmonics match, the second harmonic is emitted in the direction of this angle θ. The refractive index of the substrate for the fundamental wave is ns (ω), the refractive index of the waveguide is nG (ω), and the refractive index of the substrate for the second harmonic is ns
(2ω), as long as the condition ns (2ω)>nG (ω)>ns (ω) is satisfied, phase matching is automatically achieved and Cerenkov radiation becomes possible. This method has been adopted as a method that allows for consistency.

However, in the optical waveguide type wavelength conversion element, the second harmonic is radiated from the narrow width optical waveguide to the substrate.
The characteristics of the light beam are crescent-shaped in cross section, which is not good in terms of focusing. Therefore, this second harmonic has the disadvantage that it cannot be focused on a small spot. Therefore, it has been difficult to use second harmonics for writing and reading from, for example, optical storage media having minute pits, such as optical disks.

On the other hand, since the optical fiber type wavelength conversion element is axially symmetrical, the second harmonic spreads in a ring shape,
It can also be made into parallel rays. Therefore, a light source device has been proposed that includes (1) a collimating lens that has a circularly symmetrical inclined surface (conical surface) and converts the second harmonics emitted from the optical fiber type wavelength conversion element into parallel light beams ( JP-A-1-
(See Publication No. 287531).

According to the light source device having the above configuration, when the laser light emitted from the laser light source is guided to the optical fiber type second harmonic generation element and the second harmonic is generated, the second harmonic is axially symmetrical and conical. The wave spreads out from the end face of the optical fiber as a wave with an equal phase front. FIG. 8 shows this situation, and the second harmonic is generated by the cladding 42 of the optical fiber 4.
It spreads out into a conical beam B. Therefore, by passing this second harmonic through a collimating lens that at least partially has a circularly symmetrical inclined surface,
Parallel rays of harmonics can be obtained.

(2) As shown in FIG. 9, a structure has also been proposed in which a circularly symmetrical inclined surface 4a is formed at the output end of the optical fiber to convert the second harmonics emitted from the optical fiber into parallel light beams. (See Japanese Unexamined Patent Publication No. 1-293325).

0010

[Problem to be solved by the invention] However, the above (1)
In this case, a conical collimating lens must be manufactured, and its rotational symmetry axis must be precisely aligned with the rotational symmetry axis of the optical fiber. Also, (2
), processing accuracy is required because the minute part called the output end of the optical fiber must be precisely processed. Moreover, when processing the output end of the optical fiber, the end face may be chipped or scratched, resulting in a lower yield.

[0011] The present invention is easy to process when manufacturing a structure for converting second harmonics emitted from an optical fiber type wavelength conversion element into parallel light beams, and does not require adjustment after processing.
It is an object of the present invention to provide a wavelength conversion element that can reliably protect the output end of an optical fiber.

0012

[Means for Solving the Problems] A wavelength conversion element of the present invention for achieving the above object surrounds a cladding with a cylindrical transparent layer, and at an end of the wavelength conversion element, the transparent layer has a A circularly symmetrical inclined surface is formed to convert the second harmonics emitted from the wavelength conversion element into parallel light beams.

[0013]

[Operation] According to the above configuration, the wavelength conversion element is embedded in a cylindrical transparent layer, and the light emitted from the end of the optical fiber type wavelength conversion element is transmitted through the light formed in this transparent layer. It is refracted by a circularly symmetrical inclined surface and exits as parallel rays.

[0014]

Embodiments Next, embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a laser light source 1 such as a semiconductor laser, a spherical lens 2 that collimates the laser light generated from the laser light source 1, a condensing spherical lens 3 that collects the collimated light beam, a core 41, and a cladding 42. A light source device is shown that includes an optical fiber type wavelength conversion element 4 using a nonlinear optical material in one or both of them, and a cylindrical polymer transparent layer 5 surrounding the optical fiber type wavelength conversion element 4. At the output end of the optical fiber type wavelength conversion element 4, a conical surface (apex angle 2α) 51 is formed in the polymer transparent layer 5 to collimate the second harmonic generated from the optical fiber type wavelength conversion element 4. There is. The rotational symmetry axis of the conical surface 51 is formed to coincide with the rotational symmetry axis of the optical fiber type wavelength conversion element 4.

The material for the transparent polymer layer 5 includes plastic materials for optical lenses such as diglycol diallyl carbonate, polymethyl methacrylate, polystyrene, polycarbonate, and polymicrohexyl methacrylate. Further, the refractive index of the cladding 42 for the second harmonic is nc, and the refractive index of the polymer transparent layer 5 for the second harmonic is np. The angle between the cladding 42 and the rotational symmetry axis of the second harmonic is θo, and the angle between the second harmonic and the rotational symmetry axis within the polymer transparent layer 5 is θ.

In the above light source device, the second harmonics emitted from the optical fiber type wavelength conversion element 4 are refracted at the conical surface 51 and emitted parallel to the axis of rotational symmetry, as shown in FIG. 2 which is an enlarged view. To go. The conditions for this are, using Snell's law,

[0017]

[Math 1]

The apex angle 2α of the conical surface 51 is selected so that the following equation is obtained. With the above configuration, a parallel beam can be emitted from the conical surface 51. By condensing this beam with a known condensing means, it is possible to obtain a small spot that almost coincides with the optical wavelength limit. In addition,
The shape of the conical surface 51 described above is not limited to that shown in FIG. For example, as shown in FIG.
The portion 52 at the tip of which the second harmonic does not pass may be cut flat.

Next, a method of processing the conical surface 51 will be explained. This processing method is a method of integrally forming the polymer transparent layer 5 having a conical surface with the wavelength conversion element 4 using a mold. A molten solution of 3,5-dimethyl-1-(4-nitrophenyl)pyrazole was sucked up using capillary action into a SF15 glass capillary tube with an inner diameter of 0.8 μm and an outer diameter of 1.0 mm, and then drawn up using the Bridgman method. A single crystal was grown from the end to create an optical fiber type wavelength conversion element 4. Thereafter, a 5.0 mm piece of the wavelength conversion element 4 was cut out, and one end was optically polished to form an output end. When semiconductor laser light with a wavelength of 0.884 μm was incident on the core of this wavelength conversion element 4, converted light with a wavelength of 0.442 μm was emitted into the air from the output end at an output angle of 12°.

Note that the refractive index of SF15 glass (cladding) is 1.727 for light with a wavelength of 0.442 μm.
, and the radiation angle inside the cladding is 6.9°. Next, the rotational symmetry axis of the wavelength conversion element 4 and the rotational symmetry axis of the mold 6 are set by inserting the wavelength conversion element 4 into a cylindrical mold 6 having a conical surface with an apex angle of 2α = 133.7° at the tip. In addition, with this wavelength conversion element 4 fixed, M
MA (methyl methacrylate) and photopolymerization initiator 1
A solution containing hydroxyl and cyclohexyl phenyl ketone in a weight ratio of 99.9:0.1 was poured into the tube, and MMA was polymerized by irradiation with ultraviolet rays to form PMMA5 (polymethyl methacrylate). The refractive index of PMMA at this time is 1.50 for light with a wavelength of 0.442 μm.
Met. The mold 6 has a lid 6a, and when the wavelength conversion element 4 is inserted into the hole in the center of the lid 6a, the rotational symmetry axis of the wavelength conversion element 4 automatically matches the rotational symmetry axis of the mold. It looks like this.

[0021] During polymerization, it is also effective to add about 1% by weight of diethoxydivinylsilane, which is a silane coupling agent, in order to improve the adhesion between PMMA and clad glass. Thereafter, as shown in FIG. 5, one end of the wavelength conversion element 4 was cut to have a total length of 1 mm. Then, as shown in Figure 6, MMA is added again and polymerized to form PMMA5a, and the whole is taken out and the PMM at the entrance end is
A was optically polished. When a semiconductor laser beam with a wavelength of 0.884 μm was incident on the core, the wavelength was 0.442 μm.
The converted light was emitted from the conical surface of PMMA as parallel light rays.

[0022]

As described above, according to the wavelength conversion element of the present invention, light emitted from the end of the optical fiber type wavelength conversion element embedded in the cylindrical transparent layer is formed in the transparent layer. Since the light is refracted by a circularly symmetrical inclined surface and exits as parallel light, parallel light can be easily obtained without the need for externally attaching and aligning a collimating lens as in the past.

Further, the circularly symmetrical inclined surface can be formed by processing the transparent layer integrated with the wavelength conversion element, and there is no need to directly process the small end face of the cladding of the optical fiber type wavelength conversion element as in the conventional method. good. Therefore, processing becomes easy, and the output end face can be protected with a transparent layer even after processing.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing how a wavelength conversion element is used.

FIG. 2 is an enlarged view of the tip of the wavelength conversion element.

FIG. 3 is an enlarged view showing a modification example of the tip of the wavelength conversion element.

FIG. 4 is a diagram illustrating a method of manufacturing a wavelength conversion element using a mold.

FIG. 5 is a diagram illustrating a method of manufacturing a wavelength conversion element using a mold.

FIG. 6 is a diagram illustrating a method of manufacturing a wavelength conversion element using a mold.

FIG. 7 is an explanatory diagram showing the Cerenkov radiation method.

FIG. 8 is a perspective view showing a beam emitted in a conical wavefront shape.

FIG. 9 is a diagram showing a conventional wavelength conversion element in which the cladding is directly processed.

[Explanation of symbols]

1 Laser light source 4 Optical fiber type wavelength conversion element 41 Core 42 Clad 5 Polymer transparent layer 51 Conical surface

Claims (1)

[Claims] Claim 1: An optical fiber type wavelength conversion element in which either one or both of the core and the cladding is formed of a nonlinear optical material, in which the cladding is surrounded by a cylindrical transparent layer, and the output end of the wavelength conversion element is 2. A wavelength conversion element characterized in that the transparent layer is provided with a circularly symmetrical inclined surface that converts second harmonics emitted from the wavelength conversion element into parallel light beams.