JPH07218941A - Wavelength converting device - Google Patents

Abstract

PURPOSE:To obtain satisfactory monochromaticity, to miniaturize the device and to lower the price by separating fundamental light and SHG light with an optical device on the side of an organic coated fiber outgoing terminal, beam shaping the SHG light and transmitting it without transmitting the fundamental light. CONSTITUTION:This device is provided with a light source element 1 for emitting the fundamental light of first-order light, organic coated fiber 2 as a non- linear optical element on which the first-order light is made incident, and an optical element 3 on which second-order light emitted from this organic coated fiber 2 is made incident. Then, an emitting side terminal 3b at this optical element 3 is provided with a function for mutually separating the fundamental light and SHG light consisting of mixed light made incident from the organic coated fiber 2 based on the difference in polarizing direction, beam-shaping and transmitting the SHG light polarized at 90 deg. but not transmitting the fundamental light separated from the SHG light on the other hand. Namely, the optical element 3 is arranged on the outgoing terminal side of the organic coated fiber 2, and the emitted mixed light is passed inside the optical element 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength converter mainly used for converting a laser beam into a second harmonic of a half wavelength (shortening the wavelength).

[0002]

2. Description of the Related Art In recent years, the shortening of the wavelength of laser light has become an increasingly important elemental technology due to the need for higher density of memory, higher accuracy of measurement, and higher accuracy of display. In order to realize such a short wavelength, a method of shortening the oscillation wavelength of the semiconductor laser itself, which is a light source element, and a non-linear optical element are used to convert the fundamental light emitted from the semiconductor laser into the fundamental light. There is a method to shorten the wavelength,
It is considered that a method using a nonlinear optical element will be put to practical use in the near future.

In this case, the non-linear optical element means an element capable of wavelength conversion utilizing the non-linearity of the crystal, and the wavelength is halved after converting the primary light incident on the crystal. SHG (Seco as second harmonic
nd Hermonic Generation) An element used when obtaining light. And, in the present situation, a Cerenkov radiation type organic core fiber produced by using an organic nonlinear optical material, that is, an organic core fiber having an optical fiber structure in which a core with a high refractive index and a clad with a low refractive index are integrated It is generally used as a nonlinear optical element.

In the organic core fiber here, the incident fundamental light becomes the guided mode and the SHG light as the second harmonic becomes the radiated mode, and then the angle from the core, that is, the wavelength. It utilizes the phenomenon that light is emitted into the clad at an angle that is determined based on the core diameter and the refractive index, and is considered promising as being superior in terms of tolerance to temperature and wavelength, productivity, and price. Is.

[0005]

By the way, from the organic core fiber having the above-mentioned conventional structure, the basic light incident as the primary light and the SHG light obtained in the 90 ° -polarized state are mixed. The mixed light is emitted as secondary light. Therefore, in order to select and obtain only the SHG light, it is necessary to remove the basic light from the mixed light emitted from the organic core fiber.

Then, in order to remove the basic light at a normal experimental level, a polarizing beam splitter for separating the basic light and the SHG light by utilizing the difference in the polarization direction, an absorption filter or a reflection filter having wavelength selectivity, etc. It is generally used to use a separating element. However, if a practical wavelength conversion device is constructed by using such separation elements, the number of parts will increase, and as a result, the wavelength conversion device can be made smaller and less expensive. It will be difficult.

[0007] Also, for this organic core fiber
If the next light is normally incident normally, an incident loss of about several percent will occur, but since the SHG light increases in proportion to the square of the incident fundamental wave, the output of the SHG light is increased. It is necessary to suppress the incident loss as much as possible in order to increase. And as a measure for suppressing such incident loss,
As disclosed in Japanese Patent Application Laid-Open No. 2-254426, a method has been proposed in which the incident light coupling surface of the organic core fiber is covered with a dielectric multilayer film as an antireflection coating film. However, when manufacturing such an antireflective coating film, not only the film forming process using a vacuum apparatus is required, but also the cost becomes high.
The inconvenience of causing the deterioration of the organic core fiber left in the vacuum atmosphere has occurred.

The present invention was devised in view of these inconveniences, and an object thereof is to provide a wavelength conversion device which can realize a miniaturization and a cost reduction of the entire structure.

[0009]

A first wavelength conversion device according to the present invention is an organic core fiber on which a basic light from a light source element is incident, and a mixed light of the basic light and the SHG light which have passed through the organic core fiber. The optical element has a function of separating the basic light and the SHG light, shaping the SHG light into a beam, and transmitting the beam, and not transmitting the basic light. Is characterized by.

Further, the second wavelength conversion device according to the present invention is such that the organic core fiber on which the basic light from the light source element is incident, and the basic light and S which have passed through this organic core fiber.
An optical element having mixed light of HG light incident thereon, and the optical element has a function of separating the basic light and the SHG light, beam-shaping the SHG light and transmitting the same, and not transmitting the basic light. On the other hand, the organic core fiber is characterized in that the angle of the incident light coupling surface with respect to the fundamental light matches the Brewster angle.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 is a structural view showing the overall construction of a wavelength conversion device according to a first embodiment of the present invention, and FIG. 2 is an enlarged structural view showing only its optical element.

The wavelength conversion device according to the present embodiment has a light source element 1 for emitting basic light which is primary light, an organic core fiber 2 as a nonlinear optical element on which the primary light is incident, and this organic core fiber 2. And the optical element 3 on which the secondary light emitted from is incident, and the organic core fiber 2 and the optical element 3 are oriented in the direction along the optical axis L of the light source element 1 which is the incident direction of the basic light. It is arranged.
The light source element 1 in this case has a wavelength of 88
A single-mode semiconductor laser of 0 nm and an output of 100 mW is used. Between the light source element 1 and the incident light coupling surface 2a of the organic core fiber 2, a collimator lens 4 and a condensing lens, which is a commercially available semiconductor laser, are used. Lens 5
Are arranged. The collimator lens 4 here
Has a specification of NA = 0.5, and the condenser lens 5 has a specification of NA = 0.615.

On the other hand, the organic core fiber 2 is similar to the conventional example in that the basic light that has entered from the light source element 1 and the
The mixed light obtained by mixing the SHG light obtained by polarization by 0 ° is emitted as the secondary light. And this organic core fiber 2 is LG16 of Nippon Electric Glass Co., Ltd.
It was produced by using a capillary glass made of high-refractive index glass (1.686 / wavelength: 880 nm), and the core having a high refractive index has a diameter of 1.3 μm.
m, diameter of clad with low refractive index is 1 mm, length is 10
It is set to mm. Further, in this case, DM is used as the core material, that is, the organic nonlinear optical material forming the core.
NP (3,5-dimethyl-1- (4-nitrophenyl)
Pyrazole) is used, and organic core fiber 2
Is a single crystal of the core material filled in the capillary glass by the zone melt method. The symbol P in the figure indicates the fiber axis, and the fiber axis P is aligned with the optical axis L of the light source element 1.

Further, the optical element 3 in this embodiment is B
As shown in FIG. 2, the secondary light emitted from the organic core fiber 2, that is, the incident side portion of the mixed light composed of the fundamental light and the SHG light ( (The left part separated by a virtual line in Fig. 2)
3a has a conical prism shape, while the incident side portion 3a
The emission side portion (the right side portion in FIG. 2) except for 3 has a circular cross-sectional shape. Then, the incident side portion 3a of the optical element 3 has a bottom angle corresponding to the emission angle of SHG light, for example, 13.3 when the emission angle of SHG light is 7 °.
It has a base angle of 4 °. The arrow A in the figure indicates the incident direction of the mixed light.

The output side portion 3b of the optical element 3 has a planar-shaped dielectric multilayer film 6 positioned at an angle of 45 ° with respect to the light collimated by the conical prism-shaped incident side portion 3a. In addition, a pair of glass bodies are bonded together. Then, the emission side portion 3b separates the basic light and the SHG light, which form the mixed light incident from the organic core fiber 2, from each other based on the difference in the polarization direction, and the SHG light polarized by 90 ° is a beam. It is a portion that has a function of shaping and transmitting the light, but not transmitting the basic light separated from the SHG light.

In other words, the dielectric multilayer film 6 here has a property of reflecting the basic light and transmitting the SHG light while the ZnS film having a thickness of 105 nm and the Mg film having a thickness of 95 nm are used.
It is formed by alternately forming 25 layers of F2 films. In addition, on the incident side surface and the output side surface of the optical element 3, S
A coating film 7 made of a MgF2 single layer having a thickness of 94 nm is formed so as to maximize the transmittance for HG light.

As described above, the mixed light composed of the basic light incident as the primary light and the SHG light polarized by 90 ° from the organic light from the organic core fiber 2 which constitutes the wavelength conversion element of this embodiment. Is emitted as in the conventional example. However, in this embodiment,
An optical element 3 that separates the basic light and the SHG light forming the mixed light from each other based on the difference in polarization direction is arranged on the emission end side of the organic core fiber 2, and the emitted mixed light is inside the optical element 3. Since the structure that passes through S is used, the basic light is separated from the optical element 3 and then collimated S
Only the HG light will be emitted. The inventor of the present invention conducted an experiment after incorporating the optical element 3 having the above-described configuration into a wavelength conversion element, and found that the transmission ratio of basic light to SHG light was 1/1000.
It has been confirmed that it is below the level.

Second Embodiment FIG. 3 is a structural view showing the overall construction of a wavelength conversion device according to a second embodiment of the present invention, and FIG. 4 is an enlarged structural view showing only its optical element. The entire structure of the wavelength conversion device according to the second embodiment is different from that of the optical element, except that
Since this is basically the same as that of the first embodiment, parts and portions which are the same as or correspond to those in FIGS. 1 and 2 are denoted by the same reference numerals in FIGS. 3 and 4, and detailed description thereof is omitted here.

The wavelength conversion device according to the present embodiment comprises a light source element 1 which is a semiconductor laser, an organic core fiber 2 and an optical element 8 which are sequentially arranged along the optical axis L of the light source element 1. The collimator lens 4 and the condenser lens 5 are arranged between the light source element 1 and the incident light coupling surface 2 a of the organic core fiber 2.

The optical element 8 here is arranged on the emission end side of the organic core fiber 2 and after absorbing the basic light in the mixed light emitted from the organic core fiber 2 as the secondary light. It has a function of beam-shaping only SHG light and transmitting it, that is, a function of separating the basic light and the SHG light based on the difference in absorption.
Using glass called CM500 made by YA, S
It is manufactured as a conical prism shape having a base angle corresponding to the emission angle of HG light. A coating film 7 made of a MgF 2 single layer is formed on the entrance side surface and the exit side surface of the optical element 8 to enhance the transmittance for SHG light.

Therefore, in the wavelength conversion element in which the optical element 8 is incorporated, the basic light and the SHG light forming the mixed light emitted from the organic core fiber 2 are separated based on the difference in absorption. As a result, only the SHG light is emitted from the optical element 8. According to the experiments conducted by the inventor, it has been confirmed that the transmission ratio of the basic light to the SHG light is about 1/1000 or less.

Third Embodiment FIG. 5 is a structural diagram showing the overall structure of a wavelength conversion device according to a third embodiment of the present invention, and FIG. 6 is an enlarged structural diagram showing only its optical element. The overall structure of the wavelength conversion device according to the third embodiment is basically the same as that of each of the first and second embodiments except that it is related to the optical element, and therefore, in FIGS. The same or corresponding parts and portions as those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted here.

The wavelength converter according to this embodiment comprises a light source element 1 which is a semiconductor laser, an organic core fiber 2 and an optical element 9 which are arranged in a direction along the optical axis L of the light source element 1. A collimator lens 4 and a condenser lens 5 are arranged between the light source element 1 and the incident light coupling surface 2 a of the organic core fiber 2. The optical element 9 used here is glass called BK7 and has a bottom angle corresponding to the emission angle of SHG light, for example, 13.
It is manufactured as a conical prism shape having a base angle of 4 ° and is arranged on the emission end side of the organic core fiber 2.

Further, 11 is provided on the exit side surface of the optical element 9.
A coating film 10 is formed by alternately forming 9 layers of a ZnS film having a thickness of 0 nm and a MgF 2 film having a thickness of 110 nm.
A coating film 7 composed of two single layers is formed. That is, the coating film 10 here functions as a selective transmission film that separates the basic light and the SHG light in the mixed light that have been emitted from the organic core fiber 2 and then entered the optical element 9, from each other. Has become. In addition,
It is possible to form the coating film 10 serving as a selective transmission film on the incident side surface of the optical element 9, but since the incident side surface has a curved shape, it is difficult to design and the cost is increased. In the embodiment, the coating film 10 is provided only on the emission side surface of the optical element 9 having a planar shape.
Is to be formed.

That is, in this embodiment, since the optical element 9 is incorporated in the wavelength conversion element, the mixed light emitted from the organic core fiber 2 is the basic light and the SHG light based on the difference in reflection. As a result, only SHG light is emitted from the optical element 9.
According to experiments conducted by the inventor, it has been confirmed that the transmission ratio of the basic light to the SHG light is about 1/1000 or less.

Fourth Embodiment FIG. 7 shows the entire structure of a wavelength conversion device according to a fourth embodiment of the present invention. This wavelength conversion element is the same as the first to third embodiments except for the arrangement state of each component. It is basically common with. Therefore, in FIG. 7, parts and portions that are the same as or correspond to those in FIGS.
Detailed description here is omitted.

The wavelength conversion device according to the present embodiment has a light source element 1 for emitting basic light which is primary light, an organic core fiber 2 as a nonlinear optical element for incidence of primary light, and this organic core fiber 2. An optical element 3 into which the secondary light emitted from the light source is incident, a collimating lens 4 for collimating the basic light emitted from the light source element 1, and an organic core after condensing the collimated basic light. It is provided with a condenser lens 5 which is incident on the incident light coupling surface 2a of the fiber 2. The light source element 1 in this case has a wavelength of 880 nm and an output of 100 mW.
While a single mode semiconductor laser is used, the collimator lens 4 has NA = 0.5, and the condenser lens 5 has NA.
= 0.615, and the collimator lens 4 and the condenser lens 5 follow the direction along the optical axis L of the light source element 1 which is the incident direction of the basic light emitted from the light source element 1. It is arranged.

The organic core fiber 2 here is
As in the first embodiment, DMNP as a core material is provided in a capillary glass made of LG16 high refractive index glass (1.686 / wavelength: 880 nm) manufactured by Nippon Electric Glass Co., Ltd.
(3,5-dimethyl-1- (4-nitrophenyl) pyrazole) was filled and then monocrystallized by the zone melt method, and the core diameter was 1.3 μm.
m, the clad diameter is 1 mm, and the length is 10 mm. The organic core fiber 2 has an incident light coupling surface 2a having a plane shape orthogonal to the fiber axis P direction.
Is arranged so that the angle with respect to the basic light coincides with the Brewster angle, and the optical element 3 is also arranged on the emission end side of the organic core fiber 2 along the fiber axis P. At this time, the emission end face of the organic core fiber 2 also has a planar shape orthogonal to the fiber axis P direction, and the smoothness of the emission end face and the incident light coupling surface 2a is set to about λ / 10. .

The Brewster angle (Br) is tan (Br) = n2 / n1 where n1 is the refractive index of air and n2 is the refractive index of the core of the organic core fiber.
When applied to this embodiment, n1 = 1 and n2 = 1.6998, resulting in Br.
A value of = 59.5 ° is obtained. Therefore, the organic core fiber 2 in the present embodiment is arranged after selecting the direction in which the angle of the incident light coupling surface 2a with respect to the basic light has the Brewster angle of 59.5 °.

By adopting the above configuration, in the wavelength conversion device of this embodiment, the incident loss when the primary light is coupled to the organic core fiber 2 is 1% or less, which is the measurement limit. It has been confirmed by an experiment conducted by the inventor that Further, according to this wavelength conversion device, the SH emitted from the optical element 3 is
The output of G light is 8 compared with the case of vertical incidence in the conventional example.
It is also clear that it will be improved by about%.

Fifth Embodiment FIG. 8 is a structural diagram showing the overall construction of a wavelength conversion device according to a fifth embodiment of the present invention. The wavelength conversion device according to this example is basically the same as the first to fourth examples except for the shape of the organic core fiber itself. Therefore, in FIG. Corresponding parts and portions are designated by the same reference numerals, and detailed description thereof will be omitted.

The wavelength converter according to this embodiment comprises a light source element 1, an organic core fiber 2, an optical element 3 and a collimator lens 4 arranged along the optical axis L of the light source element 1.
The organic core fiber 2 in this case is such that the angle of the incident light coupling surface 2a with respect to the fundamental light matches the Brewster angle. That is, the incident light coupling surface 2a of the organic core fiber 2 is oriented so that the angle with respect to the basic light incident from the optical element 1 matches a Brewster angle, for example, a predetermined Brewster angle of 59.5 °. It has a planar shape that is inclined along.

In the wavelength conversion device according to this embodiment, the incident light coupling surface 2a of the organic core fiber 2 needs to be processed so as to have a predetermined Brewster angle. Equipped with a rotating mechanism and a polishing angle adjusting mechanism after confirming the angle at which the output of the SHG light was highest after the pre-polarized basic light was incident to confirm the orientation of the crystal in the core. The organic core fiber 2 is processed using a polishing processing device. At this time, the emission end surface of the organic core fiber 2 has a planar shape orthogonal to the fiber axis P direction, and both the emission end surface and the incident light coupling surface 2a have a smoothness of about λ / 10. Have

As a result, even when the structure according to this embodiment is adopted, the incident loss at the incident light coupling surface 2a of the organic core fiber 2 is about 1% or less, and the SHG emitted from the optical element 3 is also reduced. The light output is also improved by about 8% as compared with the case of vertical incidence in the conventional example.

By the way, in the fourth and fifth embodiments described above, the optical element 3 described in the first embodiment is used, but the present invention is not limited to this, and the second or third embodiment is used. It goes without saying that the wavelength conversion device may be constructed using the optical elements 8 and 9 related to the example.

[0037]

As described above, according to the first wavelength conversion device of the present invention, the optical element arranged on the emission end side of the organic core fiber separates the basic light and the SHG light from each other. The SHG light is shaped and transmitted and the basic light is not transmitted, so it is extremely easy to remove the basic light from the mixed light emitted from the organic core fiber. Can be obtained. As a result, it has excellent monochromaticity,
Moreover, there is an effect that it is possible to easily configure a wavelength conversion device that can be downsized and reduced in cost.

Further, according to the second wavelength conversion device, since the angle of the incident light coupling surface of the organic core fiber with respect to the basic light is matched with the Brewster angle, the primary light incident from the light source element is It is possible to improve the coupling state with the organic core fiber and reduce the incident loss. Therefore, it is not necessary to form an antireflection coating film composed of a dielectric multilayer film as in the conventional example, and it is not necessary to use a vacuum device for forming this film, resulting in cost reduction and organic The deterioration of the core fiber can be prevented.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an overall configuration of a wavelength conversion device according to a first embodiment.

FIG. 2 is an enlarged structural view showing the optical element.

FIG. 3 is a structural diagram showing an overall configuration of a wavelength conversion device according to a second embodiment.

FIG. 4 is an enlarged structural view showing the optical element.

FIG. 5 is a structural diagram showing an overall configuration of a wavelength conversion device according to a third embodiment.

FIG. 6 is an enlarged structural view showing the optical element.

FIG. 7 is a structural diagram showing an overall configuration of a wavelength conversion device according to a fourth embodiment.

FIG. 8 is a structural diagram showing an overall configuration of a wavelength conversion device according to a fifth embodiment.

[Explanation of symbols]

 1 Light source element 2 Organic core fiber 3 Optical element

Claims (7)

[Claims] 1. A wavelength conversion device comprising an organic core fiber on which a fundamental light from a light source element is incident, and an optical element on which a mixed light of the fundamental light and SHG light passing through the organic core fiber is incident. The optical element separates the basic light and the SHG light and
A wavelength conversion device having a function of beam-shaping G light and transmitting it, and not transmitting basic light. 2. The wavelength conversion device according to claim 1, wherein the optical element separates the basic light and the SHG light based on the difference in polarization direction. 3. The wavelength conversion device according to claim 1, wherein the optical element separates the basic light and the SHG light based on the difference in absorption. 4. The wavelength conversion device according to claim 1, wherein the optical element separates the basic light and the SHG light based on the difference in reflection. 5. The wavelength conversion device according to claim 1, wherein the organic core fiber is such that the angle of the incident light coupling surface with respect to the fundamental light matches the Brewster angle. 6. The incident light coupling surface of the organic core fiber has a plane shape orthogonal to the axial direction of the fiber, and in this organic core fiber, the angle of the incident light coupling surface with respect to the fundamental light coincides with the Brewster angle. The wavelength conversion device according to claim 5, wherein the wavelength conversion device is arranged along the direction. 7. The incident light coupling surface of the organic core fiber has a plane shape inclined along a direction in which the angle with respect to the fundamental light coincides with the Brewster's angle. The wavelength conversion device according to claim 5, wherein the wavelength conversion device is arranged in a direction along a light incident direction.