JP2008250184A - Fiber light source apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent contamination on an incident end face of a fiber of a fiber light source apparatus which emits light from a light source after transmitting the light through an optical fiber with an inexpensive means. <P>SOLUTION: The fiber light source apparatus comprises: the light source 1; light condensing systems 2 and 3 which condense the light B from the light source 1; the optical fiber 10 which receives the condensed light B from the incident end face 10c and transmits the condensed light B; and a cylindrical holding member 12 bonded at the outer peripheral face close to the incident end face 10c of the optical fiber 10 to hold the optical fiber 10. An optical fiber 14 having a diameter larger than that of the optical fiber 10 is disposed in the holding member 12 while the emitting end face 14d thereof is brought into contact with the incident end face 10c. Further, the respective outer peripheral faces of the optical fibers 10 and 14 and the holding member 12 are bonded by using an adhesive 11 having transmissivity for the light B of 28 %/mm or larger, and a protective film 13 is formed on the emitting end face 10d of the optical fiber 10 to suppress the adhesion of other optical members in contact with the end face 10d. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fiber light source device, and more particularly to a fiber light source device having a structure in which light emitted from a light source is once propagated in an optical fiber and then emitted from the optical fiber.

  Conventionally, optical fibers have been widely used for propagation of light such as laser light in a wide range of fields such as communication. For example, as shown in Patent Document 1, the end of this optical fiber is fixedly held in a cylindrical holding part called a ferrule, and the optical fiber is often handled together with the ferrule. The ferrule is made of glass, metal, or the like, and when the optical fiber end portion is fixed therein, the inner peripheral surface of the ferrule and the outer peripheral surface of the clad of the optical fiber that is in a bare state are bonded and fixed. It is common.

  For example, as described in Patent Document 2, a fiber light source device in which an optical fiber as described above and a light source such as a laser device are combined is known. This fiber light source device basically receives a light source such as a semiconductor laser or a solid-state laser, a condensing optical system that condenses the light emitted from the light source, and receives and propagates the collected light from the incident end face. It is comprised from the optical fiber radiate | emitted from an output end surface.

As in this light source device, when relatively high power light such as laser light is condensed and applied to the incident end face of the optical fiber (more specifically, the incident end face of the core), the light is particularly light in the short wavelength region. In some cases, there is a problem that the incident end face is easily contaminated by organic substances contained in the air. In order to prevent this problem of contamination, it has been proposed that a transparent member generally called a stub is brought into contact with the incident end face of an optical fiber as shown in Patent Document 3. . In such a structure, the power density of light increases on the incident end face of the optical fiber, which is the light convergence position, but the incident end face of the optical fiber is isolated from the air by the stub. On the other hand, since the light having a relatively large beam diameter that is converging passes on the incident end face of the stub that comes into contact with air, the power density of the light on the end face is relatively low. From the above points, both the incident end face of the optical fiber and the incident end face of the stub are hardly contaminated by the organic substance contained in the air.
Japanese Patent Laid-Open No. 2005-300596 Japanese Patent Laid-Open No. 5-288967 JP 2004-253783 A

  As described above, in the structure in which the end portion of the optical fiber is bonded and fixed in the ferrule, there is a problem that the end portion of the optical fiber protrudes from the ferrule during repeated use. This is considered to be due to the deterioration of the adhesive that bonds and fixes the two.

  FIG. 3 shows the above problem in an easy-to-understand manner. As shown here, the peripheral surface of the portion near the one end face (incident end face) 10c of the optical fiber 10 comprising the core 10a and the clad 10b disposed around the core 10a is formed on the inner periphery of the cylindrical ferrule 12 by the adhesive layer 5. It is fixedly held on the surface. The normal state is as shown in FIG. 1 (1). However, if the adhesive layer 5 deteriorates and the optical fiber 10 is allowed to move, the tip of the optical fiber 10 as shown in FIG. Protrudes from the ferrule 12. The deteriorated adhesive layer 5 is recognized as a yellowing portion from the outside when the ferrule 12 is made of transparent glass or the like.

  When such a phenomenon occurs in the above-described fiber light source device having a stub, problems such as a light propagation loss occur between the optical fiber and a stub connected by an optical contact.

  Moreover, in the fiber light source device having the above stub, there is a problem that the cost tends to be high because a special stub is used.

  The present invention has been made in view of the above circumstances, and can prevent deterioration of an adhesive that adheres and fixes a holding member such as a ferrule and an optical fiber, and can also prevent contamination of an incident end face of the optical fiber. And it aims at providing the fiber light source device which can be produced at low cost.

As described above, the first fiber light source device according to the present invention is as follows.
A light source;
A condensing optical system for condensing the light emitted from the light source;
An optical fiber for receiving and propagating the collected light from the incident end face and emitting from the exit end face;
In a fiber light source device comprising a cylindrical holding member such as a ferrule to which the outer peripheral surface of the portion near the incident end face of the optical fiber is bonded and holding the optical fiber,
An optical fiber having a diameter larger than that of the optical fiber is disposed in the cylindrical holding member in a state in which an exit end face thereof is in contact with the entrance end face,
Each outer peripheral surface of the two optical fibers and the holding member are bonded by an adhesive having a light transmittance of 28% / mm or more,
A protective film body that suppresses adhesion with another optical member that contacts the end face is formed on the exit end face of the optical fiber.

A second fiber light source device according to the present invention is a fiber light source device comprising the same light source as described above, a condensing optical system, an optical fiber, and a holding member.
The optical fiber is disposed in a state where the incident end face is displaced in the optical axis direction with respect to the light convergence position,
The outer peripheral surface of the optical fiber and the holding member are bonded by an adhesive having a light transmittance of 28% / mm or more,
A protective film body that suppresses adhesion with another optical member that contacts the end face is formed on the exit end face of the optical fiber.

  The fiber light source device of the present invention is particularly preferably configured on the assumption that a multi-mode optical fiber is applied as an optical fiber for receiving and propagating the condensed light from the incident end face as described above. .

  Furthermore, the fiber light source device of the present invention is particularly preferably configured on the assumption that a light source that emits light having a wavelength of 450 nm or less is applied.

  The fiber light source device of the present invention is particularly preferably configured on the assumption that the refractive index of the adhesive is larger than the refractive index of the clad of the optical fiber with which the adhesive is in contact.

  According to the inventor's research, the above-mentioned problem that the adhesive that bonds and fixes the optical fiber and the ferrule deteriorates is mainly caused by the light scattered on the end face of the optical fiber being irradiated onto the adhesive portion. It turned out to be happening.

  That is, as the above-mentioned adhesive, a thermosetting type is generally used in many cases, and the thermal stress received during the bonding tends to remain in the cured adhesive layer. In this state, when the fiber light source device is used and the adhesive layer is irradiated with light as described above, heat is also applied at that time, so the residual stress is released by the heat and the adhesive layer moves, As a result, it is considered that the optical fiber protrudes from the holding member. Conventionally, as the adhesive for adhering and fixing the optical fiber and the holding member, those having an absorption rate of 90% or more with respect to the guided light have been often used. . For example, as shown in FIG. 12, the thermosetting adhesive 353ND manufactured by Epotec Co., Ltd., which is used as a standard in communications, absorbs almost 100% of light having a wavelength of about 600 nm or less. Further, as shown in FIG. 13, the company's thermosetting adhesive 314 absorbs almost 100% of light having a wavelength of about 400 nm or less.

  Even when the adhesive is not a thermosetting type, the adhesive is photochemically deteriorated by being irradiated with light as described above, or is deteriorated by heat, leading to the protrusion of the optical fiber. Sometimes.

  The first and second fiber light source devices according to the present invention are obtained based on this new knowledge, and the light is transmitted by an adhesive having a transmittance of 28% / mm or more for light guided through the optical fiber. Since the fiber (particularly, in the first fiber light source device, in addition to the large-diameter optical fiber) and the holding member are bonded to each other, the cured adhesive layer is extremely difficult to absorb light. . Accordingly, it is difficult for the adhesive layer to absorb light and deteriorate due to heat or the like, so that the optical fiber is effectively prevented from moving.

  Note that the deterioration of the adhesive described above is more likely to occur as the energy of the light applied thereto increases. In particular, when the optical fiber is a multimode optical fiber, in general, high-power light is often input compared to a single-mode optical fiber, and light having a relatively short wavelength of 450 nm or less itself has a long wavelength. It is in a higher energy state than light. Therefore, when the present invention is applied to a fiber light source device to which a multimode optical fiber is applied in this way or a fiber light source device in which the wavelength of guided light is 450 nm or less, the effect of preventing the deterioration of the adhesive Becomes more prominent.

  On the other hand, when the refractive index of the adhesive that bonds and fixes the optical fiber and the holding member is larger than the refractive index of the clad that the adhesive contacts, the light scattered on the incident end face of the optical fiber May propagate through the layer in guided mode. In this way, when light is guided through the adhesive layer, the adhesive layer receives more energy than when light is simply irradiated there. Therefore, when the present invention is applied to the fiber light source device in which the refractive index of the adhesive is larger than the refractive index of the cladding in contact with the adhesive, the effect of preventing the deterioration of the adhesive is further improved. It will be remarkable.

Moreover, since the 1st and 2nd fiber light source device by this invention is formed with the protective film body which suppresses adhesion | attachment with the other optical member which contacts this end surface in the output end surface of an optical fiber, It is possible to prevent the reaction of oxide (quartz, SiO ₂ ) contained in both of the light emitting end faces, which are generated when optical contact is made with an optical member such as another optical fiber. In particular, when the guided light is light with high energy density or short wavelength light, the optical fiber and the optical member are integrated at the reaction site of the oxide, and the reaction site is damaged when they are separated. However, if the above-mentioned reaction can be prevented by the protective film body, such a problem can be prevented, and a fiber light source device with stable performance can be realized. .

  Further, particularly in the first fiber light source device according to the present invention, the optical fiber having a larger diameter than the optical fiber for light propagation originally provided as described above, and the light emitting end face is incident on the optical fiber for light propagation. Since it is disposed in the cylindrical holding member so as to be in contact with the end face, the large-diameter optical fiber performs the same function as the above-described stub. That is, the power density of light increases on the incident end face of the original optical fiber for light propagation, which is the light convergence position, but the incident end face of this optical fiber is isolated from the air by the large-diameter optical fiber. On the other hand, since light having a relatively large beam diameter that is converging passes on the incident end face of a large-diameter optical fiber that comes into contact with air, the power density of the light on the end face is relatively low. From the above points, the incident end face of any optical fiber is hardly contaminated by the organic substance contained in the air.

  Since the above-mentioned large-diameter fiber can be used by cutting a generally provided fiber, the first fiber light source device according to the present invention is lower than a conventional device using a special stub. It can be manufactured at a low cost.

  Further, particularly in the second fiber light source device according to the present invention, the optical fiber for light propagation is arranged in a state where the incident end face is shifted in the optical axis direction with respect to the converged position of the condensed light. The power density of the light on the incident end face is relatively low as compared with the case where the light converges on the incident end face as in the conventional apparatus. If so, the incident end face of the optical fiber is hardly contaminated by an organic substance contained in the air.

  Since the second fiber light source device according to the present invention does not use any special means such as the stub described above for preventing contamination of the incident end face of the optical fiber, this device is also less expensive than the conventional device. Can be produced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a fiber light source device according to a first embodiment of the present invention. This fiber light source device includes a light source 1 such as a semiconductor laser, a collimator lens 2 that collimates a laser beam B emitted from the light source 1 in a divergent light state, and condenses the laser beam B that has become parallel light. And a pair of cylindrical ferrules 12 that respectively hold both ends of the optical fiber 10.

  The optical fiber 10 used here is a multimode optical fiber composed of a core 10a and a clad 10b disposed around the core 10a. Specifically, the outer peripheral surface of the clad is bonded and fixed to the inner peripheral surface of the cylindrical ferrule 12 by the adhesive layer 11.

  A protective film body 13 to be described in detail later is formed on the right end face (outgoing end face) 10d of the optical fiber 10 in the drawing. A large-diameter optical fiber 14 is in contact with an end face (incident end face) 10c on the left side of the optical fiber 10 in the figure, and this large-diameter optical fiber 14 is also attached to the inner peripheral surface of the cylindrical ferrule 12 by the adhesive layer 11. Bonded and fixed.

  Reference numeral 20 denotes a connector housing for connecting the optical fiber 10 to another optical fiber. The fiber light source device of this embodiment constitutes a pigtail type light source device as an example, and the end of the optical fiber 10 to which the connector housing 20 is attached, that is, the end on the emission end face 10d side is not shown. The end of the optical fiber 10 on the opposite side, that is, the end on the incident end face 10 c side, is housed in the case together with the light source 1 and both lenses 2 and 3.

  As the optical fiber 10, one having a core diameter of about 60 μm is used. On the other hand, as the large-diameter optical fiber 14, a core having a diameter of 105 μm is used as an example. The outer diameter of the cladding 10b of the optical fiber 10 and the outer diameter of the cladding 14b of the large-diameter optical fiber 14 are the same, for example, 125 μm. The incident end face 10c of the optical fiber 10 and the exit end face 14d of the large-diameter optical fiber 14 are connected to each other by an optical contact.

  In this fiber light source device, a laser beam B having a wavelength of 405 nm and an output of 200 mW is emitted from the light source 1 as an example, and this laser beam B converges to a beam diameter of, for example, about 30 μm by the action of both the lenses 2 and 3. The optical fiber 10 is arranged in a state where the incident end face 10 c is at the convergence position of the laser beam B. Therefore, the laser beam B is incident on the core 10a from the incident end face side, is guided there, and is emitted from the right end face 10d, that is, the emission end face in the drawing.

  In the present embodiment, for example, a thermosetting adhesive model 314 manufactured by Epoxy Technology, Inc., is used as the adhesive that becomes the adhesive layer 11. This adhesive has a transmittance of about 28% / mm for the laser beam B having a wavelength of 405 nm.

  When the laser beam B enters or exits the core 10a, a part of the laser beam B is scattered on the left end face (incident end face) 10c and the right end face (exit end face) 10c in the figure, and the scattered light is adhesive. The layer 11 may be irradiated. However, in the present embodiment, the adhesive layer 11 is difficult to absorb the scattered light because the adhesive having a low absorption rate is used as described above. Therefore, it is difficult for the adhesive layer 11 to absorb light and deteriorate due to heat or the like, and thus the optical fiber 10 is prevented from moving relative to the ferrule 12. If the optical fiber 10 moves with respect to the ferrule 12 on the incident end face side, the optical contact with the large-diameter optical fiber 14 in contact with the ferrule 12 is impaired, and light propagation between the optical fibers 10 and 14 occurs. Loss may occur.

  In the present embodiment, a multimode optical fiber is applied as the optical fiber 10, and a laser beam B having a high output of 200 mW is input thereto. The laser beam B has a short wavelength of 405 nm and has a higher energy than the laser beam in the infrared region or near infrared region. In such a case, the adhesive layer 11 is inherently easily deteriorated by receiving scattered light with higher energy, and the effect of preventing deterioration becomes particularly remarkable.

  Further, when the laser beam B is input from the optical fiber end face 10c to the core 10a as described above, if the refractive index of the adhesive layer 11 is larger than that of the clad 10b of the optical fiber 10, the light scattered by the end face 10c is The adhesive layer 11 may propagate in the waveguide mode. When light is guided through the adhesive layer 11 in this way, the adhesive layer 11 receives larger energy than when light is simply irradiated there, and thus is inherently susceptible to degradation. ing. Therefore, in such a configuration, if a low-absorbing adhesive is applied as the adhesive to be the adhesive layer 11, the effect of preventing the deterioration of the adhesive layer 11 becomes more remarkable.

  In this embodiment, the above-described thermosetting adhesive model 314 manufactured by Epoxy Technology, Inc. is used to bond the ferrule 12 to the output end side of the optical fiber 10. Therefore, in the present embodiment, the adhesive layer 11 on the emission end side of the optical fiber 10 is also prevented from being deteriorated.

The protective film body 13 is a film body that suppresses a chemical reaction between the optical fiber 10 and another optical fiber (not shown) that is optically contacted with the optical fiber 10. Suppress the reaction. Specific examples of such a film body include a film body containing fluoride (LiF, BaF ₂ , MgF ₂ , CaF ₂ ) and the like. Since the protective film body 13 is formed, when the optical fiber 10 and another optical fiber are separated from each other, reaction sites of oxides contained in both optical fibers are damaged and cannot be reused. It is possible to prevent problems such as an increase in propagation loss.

  Here, the protective film body 13 is formed even if the optical fiber 10 and another optical fiber are pressure-bonded under a load of 1 kg or less (more preferably 500 g or less) and a load of 50 g or more and then the two optical fibers are separated. It is further desirable that the body 13 and both optical fibers be minimally damaged so that both optical fibers can remain reusable.

The protective film body 13 may be either a single layer film or a multilayer film. In the case of a multilayer film, it is desirable that the outermost film (uppermost layer) of the multilayer film does not easily react with quartz or SiO ₂ contained in the optical fiber 10. Moreover, as the protective film body 13, the form demonstrated in detail later is applicable.

  Here, the power density of the laser beam B increases on the incident end face 10 c of the optical fiber 10 at the convergence position of the laser beam B. The incident end face 10 c of the optical fiber is isolated from the air by the large-diameter optical fiber 14. Has been. On the other hand, since the laser beam B having a relatively large beam diameter that is converging passes on the incident end face 14c of the large-diameter optical fiber 14 that comes into contact with air, the power density of the laser beam b on the end face 14c. Is relatively low. From the above points, the incident end faces 10c and 14c of any optical fiber are hardly contaminated by organic substances contained in the air.

  In order to converge the laser beam B on the incident end face 10c of the optical fiber 10 as described above, when the core diameter of the large-diameter optical fiber 14 is D, the length is L, and the incident-side numerical aperture is NA, It is necessary that D ≦ 2 · L · NA.

  Further, as the large-diameter optical fiber 14, what is generally provided can be cut short and used. Therefore, while this fiber light source device can prevent contamination of the incident end face 10c of the optical fiber 10, Compared with a conventional apparatus using a special stub or the like for preventing contamination, it can be manufactured at a low cost.

  Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same elements as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted unless particularly necessary.

  The fiber light source device of FIG. 2 is basically different from that shown in FIG. 1 in that the large-diameter optical fiber 14 is omitted. Instead, in this embodiment, the beam diameter of the laser beam B on the incident end face 10c of the optical fiber 10 is made larger than that in the first embodiment. That is, in the first embodiment, the laser beam B is converged on the incident end face 10c, and the beam diameter on the incident end face 10c is 30 to 50 μm. On the other hand, in this embodiment, the convergence position of the laser beam B is shifted from the incident end face 10c in the optical axis direction, and the beam diameter on the incident end face 10c is about 100 μm.

  As described above, the power density of the laser beam B on the incident end face 10c that comes into contact with air is relatively low compared to the case where the laser beam B converges on the incident end face 10c as in the conventional apparatus. If so, the incident end face 10c of the optical fiber 10 is hardly contaminated by organic substances contained in the air.

  The fiber light source device according to the second embodiment does not use any special means such as the above-mentioned stub for preventing contamination of the incident end face 10c of the optical fiber 10, and is manufactured at a lower cost than the conventional device. It becomes possible.

[Connection structure and protective film body]
Next, an example of a structure for connecting the fiber light source device of the present invention to another optical device will be described. FIG. 4 shows an example of this type of connection structure. In the connection structure 50 shown here, for example, as shown in FIGS. 1 and 2, a connection part in which a ferrule 12 as a holding member is bonded and fixed to an optical fiber 10 is optically connected to a similar connection part of another optical device. Connected. The connecting portion of this other optical device is basically composed of the optical fiber 10 and the ferrule 12 similar to those described so far, but for the sake of distinction, they are denoted as 10 'and 12', respectively. Show. Here, the case where the ends of the ferrules 12 and 12 'are polished into a hemispherical shape will be described. However, these ends are perpendicular to the optical fiber axis as shown in FIGS. It may be formed.

The protective film 13 as described above is formed on the end face 12 c of the ferrule 12 and the end face 10 c of the optical fiber 10. The material of the protective film 13 is a material having high transparency in a short wavelength region (190 to 530 nm). For example, fluoride (YF ₃ , LiF, MgF ₂ , NaF, LaF ₃ , BaF ₂ , CaF ₂ and A film body containing AlF ₃ ) or the like is preferable. The tip shape of the ferrules 12 and 12 'has a radius of curvature of 7 to 25 mm and an outer diameter of 1.25 mm or 2.5 mm. The contact pressure at the contact portion between the ferrules 12 and 12 'is preferably about 4.9N to 11.8N.

  The ferrule 12 and the ferrule 12 ′ having the protective film body 13 formed on the end face 12 c are inserted into the sleeve 51 so that the outermost surface of the protective film body 13 and the ferrule 12 ′ (optical fiber 10 ′) are in contact with each other. .

  Conventionally, an optical contact has been used to optically connect optical fibers in such a structure. It is known that when the light to be guided is light in a long wavelength band or when the energy density is not so high, the optical propagation efficiency is improved by employing an optical contact.

  However, when the light to be guided is light with high energy density or short wavelength light, the oxide at the contact portion between the optical fibers reacts and the reaction portion is integrated, and after the reaction, the ferrule is removed from the sleeve. When it is pulled out, there has been a problem that the part that has caused the reaction is damaged and it cannot be reused as an optical connector, or the optical loss increases. In particular, when the light to be guided has a short wavelength, when UV cleaning is performed to prevent the end of the optical fiber from being contaminated by the reaction of the organic substance with the light to be guided, the optical fibers are bonded to each other. The applicant has confirmed that this is a problem as follows.

  FIG. 6 schematically shows a contact surface of the optical fiber 90 when the optical fiber and the glass are UV-cleaned, and the cross section of the optical fiber is brought into contact with the glass with a load of about 500 g and left for about 100 hours. . Here, 91 is a clad, and 92 is a core. 99, the optical fiber 90 and the glass (not shown) are brought into contact with each other after being cleaned and bonded, so that quartz or oxide contained in the optical fiber 90 reacts with the glass so that the optical fiber 90 and the glass are brought into contact with each other. The integrated part is shown.

  When the reaction sites are integrated in this way, it is found that the reaction sites are greatly damaged when the optical fiber 90 and the glass are separated from each other, or the reaction sites adhere to the cross section of the optical fiber 90 or the glass. It was. Note that the surface roughness of the fiber before contact is Ra = 2 nm. Such a phenomenon has occurred even when optical fibers are brought into contact with each other by an optical contact. The above phenomenon is likely to occur when the surface roughness Ra is 5 nm or less, and also when short wavelength light with high energy density is guided through the optical fiber.

On the other hand, as in the connection structure 50 shown in FIG. 4, by forming a protective film body 13 having high transparency in the short wavelength region on the end surfaces of the ferrule 12 and the optical fiber 10, the optical fibers 10 and 10 'are formed. Come into contact with each other through the protective film body 13 without directly contacting. Therefore, it is possible to prevent the reaction of oxide (quartz, SiO _2, etc.) at the contact portion between the optical fibers 10 and 10 ′, eliminate the damage of the contact portion, and realize the connection structure 50 having stable performance. .

Here, the protective film body 13 is a film body that suppresses a chemical reaction between the optical fibers 10 and 10 'at the contact portion, and more specifically, the optical fibers 10 and 10 under physical contact at room temperature. It suppresses the chemical reaction between ′. Specifically, a film body containing the above-described fluoride (LiF, BaF ₂ , MgF ₂ , CaF ₂ ) or the like can be given.

  More preferably, the protective film body 13 is bonded to the contact portion of the optical fibers 10 and 10 'with a load of 1 kg or less (more preferably 500 g or less) and a load of 50 g or more, and then the ferrule 12 and / or Even when the ferrule 12 ′ is pulled out from the sleeve 51, the protective film body 13 and / or the optical fibers 10, 10 ′ are minimally damaged, and the optical fiber 10, 10 ′ maintains a reusable state. Is desirable. With the above configuration, when the ferrules 12 and 12 'are inserted and connected to the sleeve 51, they may be crimped with a load of 1 kg or less (more preferably 500 g or less) and 50 g or more. However, it is possible to prevent damage at the contact portion between the optical fibers 10 and 10 '.

The protective film body 13 may be either a single layer film or a multilayer film. In the case of a multilayer film, it is desirable that the outermost film (uppermost layer) of the multilayer film does not easily react with quartz or SiO ₂ contained in the optical fiber. The protective film body 13 may be formed directly on the end face 12c of the ferrule 12 and the end face 10c of the optical fiber 10, or after the assist film is formed on the end faces 12c and 10c, the protective film body 13 is formed. May be.

The film thickness of the protective film body 13 is set so as not to cause a large light loss. Since the refractive index of the optical fiber 10 and the refractive index of the protective film body 13 are different, the relationship between the film thickness d1 of the protective film body 13 in the optical waveguide direction, the refractive index N of the protective film body, and the guided light wavelength λ is
d1 × N = (λ / 2) × n (1)
(Where n is an integer greater than or equal to 1)
It is desirable that

Further, as in the connection structure 60 shown in FIG. 5, the protective film body 13 described above is provided, and the protective film body 13 'is further formed on the end face 12c of the ferrule 12' (of course, including the end face of the optical fiber 10 '). A film may be formed. In this case, it is desirable that the outermost films are made of different materials that do not easily react so that reaction and integration do not occur at the contact portions of the protective film bodies 13 and 13 '. Further, it is desirable that the total film thickness of the protective film bodies 13 and 13 ′ satisfies the above formula (1). That is, for example, when the film thicknesses of the protective film bodies 13 and 13 'are equal to d2 and the refractive indexes of the respective film bodies are also equal to N, the relationship with the waveguide wavelength λ is
d2 × N = (λ / 4) × n (2)
(Where n is an integer greater than or equal to 1)
It is desirable to satisfy On the other hand, when the film thicknesses of the protective film bodies 13 and 13 'are different from each other and they are made of different materials and have different refractive indexes, the film thickness of the protective film body 13 is d2a, the refractive index is Na, and the protective film body 13 When the film thickness of ′ is d2b and the refractive index is Nb, the relationship with the waveguide light wavelength λ is
(D2a × Na) + (d2b × Nb) = (λ / 2) × n (3)
It is desirable to satisfy

In addition to setting the film thickness of each protective film body by the above method, the change in film quality over time can be reduced by using a fluoride film with a film thickness of the protective film body of less than λ / 2. The applicant has confirmed that an increase in optical loss when laser light is incident on can be suppressed. Hereinafter, this point will be described in detail. Three types of connection structures 50 (see FIG. 4) were prepared by depositing MgF ₂ films having film thicknesses λ / 2, λ / 4, and λ / 6 on the ferrule end face 12c by vapor deposition. FIG. 7 shows the result of measuring the time change of the optical output of the light emitted from another optical fiber 10 ′ when a laser beam having an optical output = 160 mW and a wavelength λ = 405 nm is incident on the optical fiber 10. In this case, the laser light passes through a region of the protective film 13 having a diameter of about 30 μm.

  Here, g1, g2, and g3 are characteristics when the film thicknesses are λ / 2, λ / 4, and λ / 6, respectively. The vertical axis of the graph in FIG. 7 indicates the relative output of the emitted light when the incident light output is 1. That is, the smaller this light output, the greater the optical loss. As shown here, it can be seen that the smaller the film thickness, the less the output power of the emitted light decreases, that is, the less the optical loss.

  Further, when each of the protective film bodies 13 after the experiment was observed with a microscope, almost no change in the appearance of the film having the film thickness λ / 6 was observed, but the films having the film thicknesses λ / 4 and λ / 2 were observed by the laser beam. The discoloration of the area considered to be a passing part was confirmed. Furthermore, the film having a film thickness of λ / 2 was confirmed to have cracks around the discolored portion. The discoloration observed in the films having the film thicknesses λ / 2 and λ / 4 is considered to be because the film was melted by the heat of the laser beam. From this result, it is considered that as the film thickness of the protective film body 13 is larger, the energy absorption of the laser beam by the film is larger, the film quality is changed by this absorption, and the light loss is increased.

Further, the present applicant has confirmed that the light loss can be further reduced by the film formed by the ion assist method than by the vapor deposition method. Hereinafter, this point will be described in detail. Two types of connection structures 50 (see FIG. 4) in which a MgF ₂ film having a film thickness of λ / 6 is formed on the ferrule end face 12c by the vapor deposition method and the ion assist method are prepared, light output = 160 mW, wavelength λ = Laser light of 405 nm was made incident on the optical fiber 10, and the temporal change in the optical output of the light emitted from another optical fiber 10 'at that time was measured. FIG. 8 is a graph showing the measurement results, and shows the measurement results when g4 is formed by the vapor deposition method and g5 is formed by the ion assist method.

  From FIG. 8, it can be seen that the decrease in light output is less when the film formed by the ion assist method is used than by the vapor deposition method. In addition, since the slope of the curve g5 is slightly smaller than that of the curve g4, although not shown, it is assumed that the difference in light output between the two film forming methods will increase after 1000 hours or more. The

  In the case of the ion assist method, the target (the end face of the optical fiber 10) can be cleaned with an ion beam or the like before film formation. For this reason, it is considered that the loss at the interface between the target and the film can be reduced, and the optical loss can be reduced as compared with the vapor deposition method. Furthermore, the ion assist method can form a finer film quality than the vapor deposition method. Therefore, it is considered that the film by the ion assist method has less change in film quality due to energy absorption of the laser beam, and light loss can be reduced. Examples of a method capable of cleaning the target before the film formation and forming a film having a finer film quality than the vapor deposition method include an ion plating method and a sputtering method in addition to the ion assist method.

Also, two types of connection structures 50 (see FIG. 4) in which MgF ₂ films having film thicknesses of λ / 6 and λ / 12 are respectively formed on the ferrule end surface 12c by an ion assist method are prepared, light output = 160 mW, wavelength λ = 405 nm laser light was incident on the optical fiber 10. At that time, the time change of the light output of the light emitted from the optical fiber 10 'was measured. FIG. 9 shows the measurement results at that time, and shows a case where g6 is a film thickness λ / 6 and g7 is a film thickness λ / 12. From FIG. 9, it can be seen that the change in the optical output is almost the same between the film thickness λ / 6 and the film thickness λ / 12. Therefore, if the laser light conditions are optical output = 160 mW, λ = 405 nm, and the film thickness is λ / 6 or less, the output change characteristics of the emitted light over time are considered to be substantially the same.

In addition, the present applicant has confirmed that a film using a material having a low absorption coefficient can reduce light loss. FIG. 10 is a graph showing the relationship between the absorption coefficient of a film by a pulse laser with a wavelength of 248 nm and the damage threshold (“High damage threshold fluoride UV mirrors made by Ion Beam Sputtering”, J. Dijion, et., Al., SPIE). (Quoted from Vol.3244, pp406-418, 1998). From this graph, it can be seen that the fluoride film has a higher damage threshold, and among the fluoride films, YF ₃ 3 and LiF have a higher damage threshold than MgF ₂ .

Therefore, two types of connection structures 50 (see FIG. 4) in which an MgF ₂ film and a YF ₃ film having a film thickness of λ / 6 are respectively formed on the ferrule end face 12c by vapor deposition are prepared, light output = 160 mW, wavelength λ = A laser beam of 405 nm was made incident on the optical fiber 10, and the temporal change in the optical output of the light emitted from the optical fiber 10 'at that time was measured. The measurement results are shown in FIG. In this graph, the characteristics when g8 is an MgF ₂ film and g9 is a YF ₃ film are shown. From FIG. 11, it can be seen that the decrease in light output is less in the YF ₃ film than in the MgF ₂ film. In the case of the MgF ₂ film, the slope of the graph is slightly smaller in the case of the YF ₃ film, so it is not shown in the figure, but after 1000 hours or more, the difference in the optical output between the two films has increased. I guess it will be. Therefore, in order to reduce optical loss, it is preferable to use a fluoride film (for example, any one of YF ₃ , LiF, MgF ₂ , NaF, LaF ₃ , BaF ₂ , CaF ₂ and AlF ₃ ), and further absorption. It is more preferable to use YF ₃ or the like having a small coefficient.

  As described above, when laser light having a light output of 160 mW and a wavelength of 405 nm is incident on the optical fiber 10 for 1000 hours or more, the light output of the emitted light after 1000 hours is decreased with respect to the light output of the emitted light immediately after the incidence. In order to suppress the rate to less than 10%, the film thickness of the film formed on the end face of the optical fiber 10 is desirably λ / 6 or less. Further, it is desirable to use a film forming method such as an ion assist method, an ion plating method, or a sputtering method that can clean the target before film formation and can form a dense film. Furthermore, it is desirable that the film has little energy absorption of laser light.

When the wavelength of the guided light is in the short wavelength region (190 to 530 nm), the end face of the ferrule 12 'in which the protective film body 13 is not formed in the configuration of FIG. And / or UV cleaning may be applied to the end face 12 c of the ferrule 12. A film body containing the above-described fluoride (any one of YF ₃ , LiF, MgF ₂ , NaF, LaF ₃ , BaF ₂ , CaF ₂ and AlF ₃ ) is inactive to light in the UV region (190 to 410 nm), since the protective film 13 to the ferrule 12 made of the fluoride is deposited, oxide in the contact portion between the optical fiber 10 10 '(quartz, SiO _2, etc.) prevents reactions, the contact portion Damage can be suppressed. Further, in order to prevent contamination by organic matter in the configuration of FIG. 5, even when UV cleaning is performed on the end face 12c of the ferrule 12 'and / or 12, the chemical reaction at the contact portion between the optical fibers 10 and 10' is suppressed. Can do.

The schematic side view which shows the fiber light source device by the 1st Embodiment of this invention The schematic side view which shows the fiber light source device by the 2nd Embodiment of this invention Diagram explaining problems in the prior art The schematic sectional side view which shows an example of the structure which connects the fiber light source device of this invention with another optical device The schematic sectional side view which shows another example of the structure which connects the fiber light source device of this invention with another optical device Schematic sectional view showing an optical fiber with a damaged contact part Evaporation to a film thickness λ / 2, λ / 4, a graph showing the time change of the light power of the light emitted when the deposited lambda / 6 of the MgF ₂ film, respectively Graph showing temporal changes of the optical output of the emitted light when forming the MgF ₂ film having a film thickness of lambda / 6 in each of the methods of deposition and ion assisted deposition Graph showing the time change of the light power of the light emitted when the film thickness λ / 6, λ / 12 of MgF ₂ films were deposited respectively by ion assisted deposition The graph which shows the relationship between the absorption coefficient of a film | membrane by the pulse laser of wavelength 248nm, and a damage threshold value Graph showing the time change of the light power of the light emitted when the film thickness lambda / 6 MgF ₂ film, YF ₃ film were respectively formed by vapor deposition Graph showing an example of absorption characteristics of thermosetting adhesive Graph showing another example of absorption characteristics of thermosetting adhesive

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Condensing lens 10 Optical fiber 10a Optical fiber core 10b Optical fiber cladding 10c Optical fiber incident end face 10d Optical fiber outgoing end face 11 Adhesive layer 12 Ferrule 13 Protective film body 14 Large diameter optical fiber 14a Large-diameter optical fiber core 14b Large-diameter optical fiber clad 14c Large-diameter optical fiber entrance end face 14d Large-diameter optical fiber exit end face 20 Connector housing B Laser beam

Claims (5)

A light source;
A condensing optical system for condensing the light emitted from the light source;
An optical fiber for receiving and propagating the collected light from the incident end face and emitting from the exit end face;
In a fiber light source device comprising a cylindrical holding member that holds the optical fiber by bonding an outer peripheral surface of a portion near the incident end face of the optical fiber,
An optical fiber having a diameter larger than that of the optical fiber is disposed in the cylindrical holding member in a state in which an exit end face thereof is in contact with the entrance end face,
Each outer peripheral surface of the two optical fibers and the holding member are bonded by an adhesive having a light transmittance of 28% / mm or more,
A fiber light source device characterized in that a protective film body that suppresses adhesion with another optical member that contacts the end face is formed on the exit end face of the optical fiber. A light source;
A condensing optical system for condensing the light emitted from the light source;
An optical fiber for receiving and propagating the collected light from the incident end face and emitting from the exit end face;
In a fiber light source device comprising a cylindrical holding member that holds the optical fiber by bonding an outer peripheral surface of a portion near the incident end face of the optical fiber,
The optical fiber is disposed in a state where the incident end face is displaced in the optical axis direction with respect to the light convergence position,
The outer peripheral surface of the optical fiber and the holding member are bonded by an adhesive having a light transmittance of 28% / mm or more,
A fiber light source device characterized in that a protective film body that suppresses adhesion with another optical member that contacts the end face is formed on the exit end face of the optical fiber.   3. The fiber light source device according to claim 1, wherein the optical fiber that receives and propagates the collected light from the incident end face is a multimode optical fiber.   The fiber light source device according to any one of claims 1 to 3, wherein the light source emits light having a wavelength of 450 nm or less.   5. The fiber light source device according to claim 1, wherein a refractive index of the adhesive is larger than a refractive index of a clad of an optical fiber with which the adhesive is in contact.

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