JPH04225333A - Wavelength conversion element - Google Patents

Abstract

PURPOSE:To carry out positioning of a wavelength conversion element with excellent workability when the above element is attached to light source equipment. CONSTITUTION:A flange part 5 consisting of high polymer material is installed on the outside surface of an optical fiber type wavelength conversion element 4 having a core 41 and a clad 42. This flange part 5 functions as a positioning projecting part when wavelength conversion element 4 is attached to light source equipment, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is constructed as an optical fiber having a core and a cladding surrounding it, and a fundamental wave such as a laser beam is input into the core, and its second harmonic is converted into a fiber end surface. The present invention relates to a wavelength conversion element that emits light from a wavelength conversion element.

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 in which the above phenomenon occurs are called nonlinear optical materials, and inorganic materials such as KH2 PO4 and LiNbO3 are well known. Furthermore, recently, organic materials such as 2-methyl-4-nitrileaniline (MNA) have also attracted attention because they have large nonlinear optical constants.

[0003] Wavelength conversion elements that use the above-mentioned nonlinear optical materials as constituent materials to halve the wavelength of a low-power laser light source such as a semiconductor laser are being actively researched. This wavelength conversion element is designed to confine the fundamental wave (semiconductor laser light) with high energy density and to lengthen the interaction length with the fundamental wave. Therefore, as the form of the wavelength conversion element, for example, an optical waveguide type is used. This is a method in which 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.
In order to extract the second harmonic, 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. 15, a second harmonic is generated from the light propagating through the optical waveguide 91 at point A and leaks into the substrate 92 and overlayer 93 at an angle α. Then, if the equal phase surface of the second harmonic that is emitted again in the α direction after a unit time and the equal phase surface of the second harmonic match, then the second harmonic is emitted in the direction of this angle α. It is said that it is emitted. When the refractive index of the substrate 92 for the fundamental wave is nS (ω), the refractive index of the waveguide 91 is nG (ω), and the refractive index of the substrate 92 for the second harmonic is nS (2ω), nS (2ω) ＞nG (ω)＞nS (ω)
・・・・・・
As long as condition (1) is satisfied, phase matching can be achieved automatically.
Cerenkov radiation becomes possible.

However, in the optical waveguide type wavelength conversion element,
Because the second harmonic is radiated from the narrow optical waveguide to the substrate, the output beam has a crescent-shaped cross section, making it difficult to condense the emitted light well and making it difficult to condense it into a small spot. The drawback is that it cannot be done. Therefore, it has been difficult to use second harmonics for writing/reading information to/from an optical storage medium having minute pits, such as an optical disk.

On the other hand, in an optical fiber type wavelength conversion element 100 as shown in FIG. 16, in which the refractive index of the core 101 and the cladding 102 satisfies the above equation (1), Since the harmonic wave 103 spreads in a rotationally symmetrical ring shape, it has excellent light focusing characteristics. The ring-shaped second harmonic wave 103 is formed by, for example, a conical prism (Japanese Patent Laid-Open No.
It is possible to easily collimate the light into parallel light by using a Fresnel type lens (see Japanese Unexamined Patent Publication No. 2-186327). By condensing this parallel light with a lens, a diffraction-limited condensed spot can be obtained.

[0007] As described above, the optical fiber type wavelength conversion element has excellent light focusing characteristics, and is small and lightweight, so it can be integrated into a small package together with a semiconductor laser light source, so it is suitable for reading optical discs. It is seen as promising for applications such as light sources.

[0008]

[Problem to be solved by the invention] However, since the core diameter of the optical fiber type wavelength conversion element is small, about 1 to 2 μm,
There is a problem in that it is extremely difficult to align the elements when assembling them together with a semiconductor laser light source into a small package. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a wavelength conversion element that solves the above-mentioned technical problems and can significantly improve the workability of alignment work.

[0009]

[Means for Solving the Problems] A wavelength conversion element according to claim 1 for achieving the above object is constructed in the form of an optical fiber having a core and a cladding surrounding the core, and the wavelength conversion element is configured as an optical fiber having a core and a cladding surrounding the core. A wavelength conversion element configured to emit converted light, which is a second harmonic, from a fiber end face, characterized in that at least one of a positioning convex portion and a concave portion is provided on the outer peripheral surface of the fiber.

[0010] At least one of the positioning protrusions and recesses may be formed directly on the outer peripheral surface of the cladding. Alternatively, a cylindrical transparent layer may be provided on the outer periphery of the cladding, and at least one of the positioning protrusions and recesses may be formed on the outer circumferential surface of the transparent layer.

[0011]

[Function] According to the above configuration, at least one of the positioning convex portion and the concave portion is provided on the outer peripheral surface of the fiber, so when the wavelength conversion element is attached to a light source device, etc., the element can be easily aligned. can be done.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples will be explained in detail below with reference to the accompanying drawings showing examples. FIG. 2 is a conceptual diagram showing the basic configuration of a light source device using a wavelength conversion element according to an embodiment of the present invention. This light source device collimates laser light generated from a laser light source 1 such as a semiconductor laser with a spherical lens 2, focuses the collimated light beam with a condensing spherical lens 3, and makes it enter a wavelength conversion element 4. This is how it was done. The semiconductor laser light source 1, the spherical lens 2, the condensing spherical lens 3, and the wavelength conversion element 4 are positioned and fixed with adhesive to holders 51, 52, 53, and 54, respectively, which are integrally formed on the base 50. ing. In this way, the semiconductor laser light source 1 and the wavelength conversion element 4 are integrated into a small package.

The wavelength conversion element 4 is constructed in the form of an optical fiber, as shown in an enlarged view in FIG.
It has a core 41 and a cladding 42, and a flange portion 5 which is a positioning convex portion on the outer periphery of the cladding 42.
It has been established. This flange portion 5 is, for example, P
It is made of a transparent polymer material such as MMA (polymethyl methacrylate). The core 41 and cladding 42 are
A known nonlinear optical material such as MNA (2-methyl-4-nitrile aniline) is applied to one or both of them.

When a laser beam is incident on the core 41 of the wavelength conversion element 4, Cerenkov radiation is generated with the incident laser beam as a fundamental wave, and the generated second harmonic (converted light) is emitted and diffused in a ring shape. radiation. The emitted converted light is, for example, collimated, further condensed, and used for reading an optical disc. FIG. 3 is a perspective view showing the configuration of the holder 54 to which the wavelength conversion element 4 is fixed. This holder 54 is integrally formed with the base 50, and has a V-shaped upper surface 55, and has a V-shaped upper surface 55, so that the holder 54 can be attached to the wavelength conversion element 4 in a direction perpendicular to the optical axis 10 of the wavelength conversion element 4 (see FIG. 2). Efforts are being made to improve the workability of positioning. Furthermore, a groove portion 56 is formed on the upper surface 55 of the holder 54 and extends in a direction intersecting the optical axes of the lenses 2, 3, etc. The width W2 of the groove portion 56 is slightly wider than the width W1 of the flange portion 5 of the wavelength conversion element 4 (see FIG. 1). The wavelength conversion element 4 is attached by fitting the flange portion 5 into the groove portion 56 of the holder 54 .

The holder 54 is arranged so that the incident end surface 4a of the wavelength conversion element 4 is located near the focal point of the laser beam from the lens 3 when the wavelength conversion element 4 is attached. Therefore, by simply fitting the flange portion 5 of the wavelength conversion element 4 into the groove portion 56 of the holder 54, the wavelength conversion element 4 can be roughly aligned. Thereafter, by displacing the wavelength conversion element 4 in the direction of its optical axis 10 within the range of the clearance created between the flange portion 5 and the groove portion 56, alignment is performed on the submicron order. After completion, the wavelength conversion element 4 is bonded to the holder 54 with an adhesive.

As described above, by using the wavelength conversion element 4 of this embodiment, the wavelength conversion element 4 can be approximately aligned simply by fitting the flange portion 5 into the groove portion 56 of the holder 54. Therefore, the alignment work of the wavelength conversion element 4 is greatly simplified, and the adjustment work can be completed in a short time. Note that the alignment of the wavelength conversion element 4 on a submicron order may be performed using a holder 57 separated from the base 50 as shown in FIG. That is, after bonding the wavelength conversion element 4 to the holder 57, the recess 59 formed on the lower surface of the holder 57 is fitted into the positioning projection 58 formed on the base 50, and the gap between the projection 58 and the recess 59 is The position of the holder 57 may be displaced in the direction of the optical axis 10 of the wavelength conversion element 4 within the range of the clearance, and the holder 57 may be bonded to the base 50 when the positioning is completed.

FIG. 5 is a perspective view showing the structure of another embodiment of the present invention. In this embodiment, an annular positioning recess 61 is directly formed on the outer peripheral surface of the cladding 42 using a diamond grindstone or the like. With this configuration, for example, if a holder having a convex portion that fits into the concave portion 61 is used, the wavelength conversion element 4 can be positioned in a short time and with good workability. Note that instead of forming the annular recess 61, as shown in FIG. 6, a positioning recess 62 having a straight cutout shape may be formed.

FIG. 7(a) is a perspective view showing the structure of still another embodiment of the present invention, and FIG. 7(b) is a longitudinal sectional view thereof. In this embodiment, the wavelength conversion element 4 is made of PMMA.
It is surrounded by a cylindrical transparent polymer layer 65 made of a transparent polymer material such as, and a flange portion 66, which is a convex portion for positioning, is formed on the side surface of this transparent polymer layer 65.

With such a configuration, the wavelength conversion element 4
positioning can be performed satisfactorily. Also, since the overall diameter is thicker, handling becomes easier. Furthermore, since the wavelength conversion element 4 is protected by the polymer transparent layer 65, the wavelength conversion element 4 is prevented from being damaged. Furthermore, if the distance D between the incident end surface 65a of the polymer transparent layer 65, into which the laser beam is incident, and the incident end surface 4 of the wavelength conversion element 4 is made sufficiently long, even if the incident end surface 65a is somewhat damaged, The laser beam focused on the core 41 of the incident end surface 4a can have a sufficient amount of light.

Note that instead of forming the flange portion 66 as shown in FIG. 8, an annular positioning recess 67 may be formed. Further, as shown in FIG. 9, a polymer transparent layer 65
An annular positioning recess 69 and a flange 70 are provided on the side surface of the
You may form both. With the configuration shown in FIG. 9,
The input end face 4a of the wavelength conversion element 4 and the output end face 4b from which the converted light is output can be clearly distinguished, and confusion between the input side and the output side can be prevented.

Furthermore, the positioning protrusions and recesses do not need to be formed in an annular shape, and may be one or more protrusions and/or recesses divided in the circumferential direction of the outer peripheral surface of the polymer transparent layer 65. may be formed. FIGS. 10 and 11 show still other modifications of the configuration shown in FIG. 7, respectively. That is, in the configuration of FIG.
The output side end 71 of the polymer transparent layer 65 is formed into a conical shape, and in the configuration of FIG. 11, a diffraction grating is formed at the output side end 72. With this configuration, the converted light (second harmonic) that is emitted from the output end surface 4b of the wavelength conversion element 4 and diffused in a ring shape is collimated into parallel light, and is emitted from the end 71 of the transparent polymer layer 65. will be done. According to these configurations, a lens for collimating the converted light from the wavelength conversion element 4 into parallel light becomes unnecessary. Next, an example of manufacturing the device will be described. Here, an example of manufacturing an element having the configuration shown in FIG. 10 will be described.

SF1 with an inner diameter of 0.8 μm and an outer diameter of 1.0 mm
After sucking up the melt of 3,5-dimethyl-1-(4-nitrophenyl)pyrazole into a 5-glass capillary tube (manufactured by Hoya Glass) using capillary action, crystals were grown from the end using the Bridgman method. , we fabricated an optical fiber type wavelength conversion device. This optical fiber type wavelength conversion element was cut into a length of 5 mm, and one end face was polished to form an output end, thereby producing a wavelength conversion element 4. 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 fiber output end at an output angle of 12 degrees. Here, the output angle is the angle formed between the optical axis of the wavelength conversion element 4 and the traveling direction of the output light.

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 degrees. Next, as shown in FIG. 12, a cylindrical mold 80 ( For example, the wavelength conversion element 4 described above was inserted into the tube (with an inner diameter of 2 mm) and held therein. At this time, the optical axis of the wavelength conversion element 4 and
The axes of the cylindrical mold 80 were made to coincide with each other, and the polished output end was directed toward the bottom surface of the mold 80. mold 80
The lid 80a has a circular hole 82 located on the axis of the mold 80.
is formed, and by inserting the wavelength conversion element 4 into this hole 82, the optical axis of the wavelength conversion element 4 and the axis of the mold can be aligned. Note that the mold 80 can be divided at the annular recess 81.

While holding the wavelength conversion element 4, the MMA
(methyl methacrylate) and 1-hydroxycyclohexyl phenyl ketone, a photopolymerization initiator, in a weight percent of 99%.
．． A solution mixed at a ratio of 9%:0.1% was poured, and MMA was polymerized by irradiation with ultraviolet rays to form PMMA (polymethyl methacrylate) 83. PMMA at this time
The refractive index of is 1.5 for light with a wavelength of 0.442 μm.
It was 5.

[0025] 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. After this, as shown in FIG.
One end of the wavelength conversion element 4 was cut to have a total length of 1 mm. Then, as shown in Figure 14, MMA is added again to polymerize and P
PMM that constitutes the polymer transparent layer 65 together with MMA 83
Make A84, take out the whole thing, and make a PMM that will be the input end.
The surface of A84 was optically polished.

When a semiconductor laser beam with a wavelength of 0.884 μm was incident on the core of the wavelength conversion element 4 of the device thus manufactured, a wavelength of 0. The converted light of .442 μm was emitted as parallel light. When the element produced in this way was attached to the light source device shown in FIG. 2, the alignment could be completed in about 1 minute.

On the other hand, when a conventional element having no positioning protrusions or recesses was attached to the light source device shown in FIG. 2, it took about 5 minutes to align it.

[0028]

As described above, according to the wavelength conversion element of the present invention, at least one of the protrusion and the recess for positioning is provided on the outer peripheral surface of the fiber, so that the wavelength conversion element can be attached to a light source device, etc. At the same time, the workability of the element positioning work is improved, and the element positioning can be completed in a short time.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the basic configuration of a wavelength conversion element according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing the basic configuration of a light source device to which the wavelength conversion element is applied.

FIG. 3 is a perspective view showing the configuration of a holder to which a wavelength conversion element is fixed.

FIG. 4 is a conceptual diagram showing another configuration example for positioning a wavelength conversion element.

FIG. 5 is a perspective view showing the basic configuration of a wavelength conversion element according to another embodiment of the present invention.

FIG. 6 is a perspective view showing the basic configuration of a wavelength conversion element according to another embodiment of the present invention.

FIG. 7 is a diagram showing the basic configuration of a wavelength conversion element according to another embodiment of the present invention.

FIG. 8 is a perspective view showing the basic configuration of a wavelength conversion element according to another embodiment of the present invention.

FIG. 9 is a perspective view showing the basic configuration of a wavelength conversion element according to another embodiment of the present invention.

FIG. 10 is a sectional view showing the basic configuration of a wavelength conversion element according to another embodiment of the present invention.

FIG. 11 is a sectional view showing the basic configuration of a wavelength conversion element according to another embodiment of the present invention.

FIG. 12 is a cross-sectional view for explaining a method of manufacturing a wavelength conversion element using a mold.

FIG. 13 is a cross-sectional view for explaining a method of manufacturing a wavelength conversion element using a mold.

FIG. 14 is a cross-sectional view for explaining a method of manufacturing a wavelength conversion element using a mold.

FIG. 15 is an explanatory diagram showing the Cerenkov radiation method.

FIG. 16 is a perspective view showing an output beam of an optical fiber type wavelength conversion element.

[Explanation of symbols]

4 Wavelength conversion element 41 Core 42 Clad 5 Flange part 61 Positioning recess 62 Positioning recess 65 Polymer transparent layer 66 Flange part 67 Positioning recess 69 Positioning recess 70 Flange part

Claims (3)

[Claims] 1. A wavelength conversion element configured as an optical fiber having a core and a cladding surrounding the core, and configured to emit converted light, which is a second harmonic of a fundamental wave incident on the core, from an end face of the fiber, A wavelength conversion element characterized in that at least one of a positioning convex part and a concave part is provided on the outer peripheral surface of a fiber. 2. The wavelength conversion element according to claim 1, wherein at least one of the positioning projections and recesses is formed directly on the outer peripheral surface of the cladding. 3. A cylindrical transparent layer is provided on the outer periphery of the cladding, and at least one of the positioning protrusions and recesses is formed on the outer periphery of the transparent layer. The wavelength conversion element according to claim 1.