JP2016212427A - Optical fiber device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber device having such a structure that another optical fiber is joined to the side face of an optical fiber which suppresses the increase of temperature of a joined portion.SOLUTION: An optical fiber device 1 has a first fluoride fiber 3, a second fluoride fiber 4 and sapphire 6. The first fluoride fiber 3 has a core, a first clad, and a second clad which has a smaller refractive index than that of the first clad, is formed of an ultraviolet curable resin, and guides light. The second fluoride fiber 4 makes light incident or emit from a first end, and has an end surface of a second end which is joined diagonally to the side surface of the first fluoride fiber 3. The sapphire 6 is arranged so as to cover the whole circumference of the joined portion between the first fluoride fiber 3 and the second fluoride fiber 4, has thermal conductivity equal to or higher than those of the first and second fibers 3 and 4, and has light transmissivity to light guided by the fiber.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical fiber device.

  A fiber added with a laser active substance (active fiber) is used in a laser oscillator or an optical amplifier. For example, in a laser oscillator or an optical amplifier using an active fiber made of fluoride, excitation light is introduced from the end face of the fiber in order to cause laser oscillation. When the excitation light is guided to the active fiber, the excitation light is absorbed by the core portion to which the laser active substance is added, and thereby output light is emitted. At this time, the core generates heat by the excitation light being absorbed by the core.

  In particular, a fluoride fiber is poor in heat resistance as compared with a general silica fiber, and therefore, when excitation light is strong, deformation or damage occurs due to heat generation, and laser oscillation and amplification cannot be performed. For this reason, in the configuration in which the excitation light is introduced from the fiber end face, the laser output is limited.

  Therefore, it is conceivable to use an optical coupler as disclosed in Patent Document 1. The device of Patent Document 1 has a gain fiber and a pumping optical fiber connected to the side surface of the gain fiber. The pumping optical fiber guides pumping light from the pumping light source to the gain fiber. As described above, if a laser oscillator is configured by connecting a plurality of units each having a pumping optical fiber connected to the side surface of the gain fiber, pumping light can be introduced from a plurality of locations. For this reason, the power of the pumping light that can be introduced can be increased, and the laser output can be increased while suppressing the heat generation of the gain fiber.

JP 2009-129940 A

  When another optical fiber is connected to the side surface of the optical fiber as in Patent Document 1, light leaks at the interface of the joint or light is scattered by irregular reflection, so that the vicinity of the joint becomes high temperature. There is a case.

  As described above, in particular, since the fluoride fiber has low heat resistance, the fiber may be damaged if the temperature near the joint is high.

  SUMMARY OF THE INVENTION An object of the present invention is to suppress a joining portion from becoming high temperature in an optical fiber device having a configuration in which another optical fiber is joined to a side surface of the optical fiber.

  An optical fiber device according to one aspect of the present invention includes a first fiber, a second fiber, and sapphire. The first fiber includes a core, a first cladding covering the outer peripheral surface of the core, and a second cladding formed of an ultraviolet curable resin having a smaller refractive index than the first cladding and covering the outer peripheral surface of the first cladding. And guides light. In the second fiber, light enters or exits from the first end, and the end surface of the second end is obliquely bonded to the side surface of the first fiber. Sapphire is disposed so as to cover the entire circumference of the joint between the first fiber and the second fiber, and has a thermal conductivity equal to or higher than that of the first and second fibers, and is guided by the first fiber and the second fiber. It is light transmissive to the emitted light.

  When this apparatus is used as an optical coupler, excitation light from the excitation light source is introduced into the first fiber through the second fiber. By connecting a plurality of such units including the first fiber and the second fiber, excitation light can be introduced from a plurality of locations. Therefore, high output laser light can be obtained while suppressing heat generation due to introduction of excitation light.

  This device can also be used as a light distributor, in which case the light guided in the first fiber is distributed and emitted from the first end of the second fiber.

  In such a configuration, sapphire is provided at the joint of the two fibers so as to cover the entire circumference of the joint. This sapphire has good thermal conductivity and is light transmissive to excitation light. For this reason, it is possible to release the heat generated in the vicinity of the joint between the two fibers, and to suppress the sapphire from absorbing the excitation light and generating heat.

  Here, “having optical transparency with respect to the excitation light” means that the absorption rate of the excitation light is 1% or less, and sapphire transmits the excitation light because the excitation light is transmitted almost without being absorbed. Absorption does not generate enough heat to damage the fiber. For example, sapphire can radiate heat for excitation light having a wavelength of 0.3 to 4.0 μm.

  The optical fiber device according to another aspect of the present invention further includes a third fiber connected to at least one end of the first fiber and having a core to which a laser active material is added. Then, excitation light corresponding to the laser active substance is incident on the second fiber.

  Here, the pumping light can be guided into the third fiber by connecting the third fiber to the first fiber. In this case, since it is not necessary to dope a laser active substance into the core of the first fiber, heat generation due to absorption of excitation light can be avoided in the first fiber.

  In the optical fiber device according to still another aspect of the present invention, sapphire covers the joint between the first fiber and the third fiber together with the joint between the first fiber and the second fiber.

  In the configuration in which the third fiber is joined to the end face of the first fiber, heat may be generated at the interface between these joints as well as the interface between the first fiber and the second fiber.

  Therefore, in the present invention, the sapphire covering the joint between the first fiber and the second fiber is also covered with the sapphire between the first fiber and the third fiber. Thereby, the heat generated at each joint can be released by one member.

  In the optical fiber device according to yet another aspect of the present invention, sapphire has a first heat radiating plate and a second heat radiating plate arranged so as to sandwich the joint portion between the first fiber and the second fiber. In this case, the structure of sapphire and the manufacture of the entire optical fiber device are facilitated.

  In the optical fiber device according to still another aspect of the present invention, the second fiber is bonded to the side surface of the first fiber by fusion. The second cladding of the first fiber is formed after the second fiber is fused to the first fiber.

  When the first fiber has a double clad structure having a first clad and a second clad, the second clad is generally formed of a resin. Since the resin clad is poor in heat resistance, it is necessary to remove the resin second clad when the second fiber is bonded to the first fiber by fusion.

  Therefore, in the present invention, after the two fibers are fused, the second cladding removed at the time of fusion is formed again.

  In the optical fiber device according to still another aspect of the present invention, the first fiber and the second fiber are fluoride fibers.

  In the optical fiber device according to still another aspect of the present invention, the first fiber and the second fiber are made of ZBLAN glass.

  In the present invention as described above, in the optical fiber device having a configuration in which another optical fiber is bonded to the side surface of the optical fiber, it is possible to prevent the bonding portion from becoming high temperature.

The block diagram of the optical fiber apparatus by one Embodiment of this invention. The exploded view which expands and shows the junction part of FIG. The exploded view which shows a thermal radiation member and a fiber junction part. The block diagram of the laser oscillator obtained by connecting the apparatus of FIG. The figure which shows the junction part by other embodiment.

  FIG. 1 shows an optical fiber device according to an embodiment of the present invention. The optical fiber device 1 is one unit constituting a laser oscillator, and includes an excitation light source 2, a first fluoride fiber 3, a second fluoride fiber 4, a third fluoride fiber 5, and a heat dissipation member 6. ,have. A fiber laser oscillator can be configured by adding a reflecting mirror and an output mirror to the optical fiber device 1.

  The excitation light source 2 oscillates excitation light having a wavelength for exciting the laser active substance, and can be constituted by, for example, a semiconductor laser. Excitation light oscillated by the excitation light source 2 is introduced into the third fluoride fiber 5 through the second fluoride fiber 4 and the first fluoride fiber 3.

  The first fluoride fiber 3 is a double clad fiber, and has a core 30, a first clad 31, and a second clad 32 as shown in FIG. FIG. 2 is an exploded view of part of the heat dissipation member 6 and the first fluoride fiber 3. The first cladding 31 is formed so as to cover the outer peripheral surface of the core 30. The second cladding 32 is formed so as to cover the outer peripheral surface of the first cladding 31.

The core 30 of the first fluoride fiber 3 is made of fluoride glass that is not doped with a laser active material, and is preferably made of ZBLAN (ZrF ₄ —BaF ₂ —LaF ₃ —AlF ₃ —NaF) glass. ing. Since the core 30 is not doped with a laser active substance, no laser light is generated in the core 30, but heat generation due to absorption of excitation light can be avoided. The first cladding 31 is made of fluoride glass, and is preferably made of ZBLAN glass. The second cladding 32 is made of an ultraviolet curable resin or a thermosetting resin. The first cladding 31 has a lower refractive index than the core 30, and the second cladding 32 has a lower refractive index than the first cladding 31. Further, the first clad 31 and the second clad 32 are not doped with a laser active material.

  The second fluoride fiber 4 is a multimode fiber, and has a thick core 40 and a reflective cladding layer 41 formed so as to cover the outer peripheral surface of the core 40 as shown in FIG. Yes. The core 40 and the reflective cladding layer 41 are made of fluoride glass, and are preferably made of ZBLAN glass. The reflective cladding layer 41 has a refractive index smaller than that of the core 40. Further, the refractive index of the core 40 is preferably equal to or lower than the refractive index of the first cladding 31 of the first fluoride fiber 3, and more preferably the same as the refractive index of the first cladding of the first fluoride fiber 3.

  Excitation light from the excitation light source 2 is incident on one end of the second fluoride fiber 4 through the lens 7. The tip of the second fluoride fiber 4 (the end connected to the side surface of the first fluoride fiber 3) is polished obliquely so as to have a predetermined angle. A method for joining the second fluoride fiber 4 to the side surface of the first fluoride fiber 3 will be described later.

  The third fluoride fiber 5 is fused and connected to one end face of the first fluoride fiber 3. The third fluoride fiber 5 is a double clad fiber, and has a core 50, a first clad 51, and a second clad (not shown), like the first fluoride fiber 3. The third fluoride fiber 5 is different from the first fluoride fiber 3 only in the specific configuration of the core 50. That is, the core 50 of the third fluoride fiber 5 is made of fluoride glass, and this fluoride glass is doped with a rare earth element as a laser active material. Specifically, the core 50 is made of ZBLAN glass doped with erbium.

  The heat radiating member 6 has a first heat radiating plate 61 and a second heat radiating plate 62 as shown in FIGS. The 1st and 2nd heat sinks 61 and 62 are the same structures. That is, the first and second heat radiating plates 61 and 62 are formed of rectangular sapphire having good thermal conductivity and light transmittance. Each of the heat sinks 61 and 62 is formed with semicircular grooves 61 a and 62 a that can accommodate the first fluoride fiber 3, the second fluoride fiber 4, and a portion including the joint portion. And the part containing the junction part of the 1st and 2nd fluoride fibers 3 and 4 is inserted | pinched by both the heat sinks 61 and 62, the circumference of the junction part of both the fibers 3 and 4 and the part of the vicinity are 1st and Covered by the second heat sinks 61 and 62.

  Although not shown, a heat sink is provided in contact with both or one of the first and second heat radiating plates 61 and 62.

  In the optical fiber device 1 configured as described above, the excitation light from the excitation light source 2 is incident on the second fluoride fiber 4 through the lens 7. The second fluoride fiber 4 can guide the excitation light within the core 40 and introduce the excitation light into the first cladding 31 of the first fluoride fiber 3 via the joint. At this time, by setting the refractive index of the core 40 to be equal to or lower than the refractive index of the first cladding 31 of the first fluoride fiber 3, reflection of excitation light at the interface between the core 40 and the first cladding 31 can be suppressed.

  The first fluoride fiber 3 and the third fluoride fiber 5 guide the excitation light through the first claddings 31 and 51, respectively. In the third fluoride fiber 5, the excitation light pumps the laser active material of the core 50 while being guided through the first cladding 51, and the laser light is emitted from the laser active material. When erbium is used as the laser active substance and excitation light having a wavelength of 975 nm is introduced, laser light having a wavelength of about 2.8 μm can be obtained. Laser light emitted from the laser active material is guided in the core 50 of the third fluoride fiber 5 and the core 30 of the first fluoride fiber 3.

[Joint method]
A method of bonding the second fluoride fiber 4 to the side surface of the first fluoride fiber 3 will be described.

  First, a part of the second clad 32 including the joint portion of the first fluoride fiber 3 is removed. This is because the second clad 32 is made of resin, has poor heat resistance, and is damaged during fusion. On the other hand, the front end surface of the second fluoride fiber 4 is polished obliquely. At this time, when the protective resin layer is formed on the surface of the second fluoride fiber 4, the resin layer at the tip portion joined to the first fluoride fiber 3 is removed. Then, the tip of the second fluoride fiber 4 is pressed against the side surface of the first fluoride fiber 3, and the two are fused by irradiating laser light, for example.

  After the first fluoride fiber 3 and the second fluoride fiber 4 are fused as described above, the resin-made second clad 32 is again applied to the portion of the first fluoride fiber 3 from which the second clad 32 has been removed. Form.

  The second cladding 32 is made of an ultraviolet curable resin or a thermosetting resin. In the case of the ultraviolet curable resin, the ultraviolet curable resin is applied to the portions covered by the grooves 61a and 62a of the first and second radiator plates 61 and 62 or both the radiator plates 61 and 62 of the first and second fluoride fibers 3 and 4. In the applied state, the first and second fluoride fibers 3 and 4 are sandwiched between the heat radiating plates 61 and 62, and cured by being irradiated with ultraviolet rays from the outside of the transparent sapphire (through the heat radiating member 6). it can. In the case of a thermosetting resin, the resin can be cured and bonded by heating through the heat dissipating member 6 having good thermal conductivity.

  When the second fluoride fiber 4 is fused to the first fluoride fiber 3 and the second clad 32 made of resin is formed on the first fluoride fiber 3 as described above, defects or resin in the fused portion are formed. Excitation light scattering occurs due to peeling or the like due to change with time, and heat is generated. However, since the joining portion is covered with the heat radiating member 6, it is possible to suppress the joining portion from becoming high temperature. Further, the joint portion between the first fluoride fiber 3 and the second fluoride fiber 4 is reinforced by the heat dissipation member 6.

  As shown in FIG. 4, a plurality of optical fiber devices 1 obtained as described above are connected in series, and a reflecting mirror 10 is arranged on one end side, and a lens 11 and an output mirror 12 are arranged on the other end side. Thus, a laser oscillator can be configured. Here, since the excitation light can be introduced from a plurality of locations other than the end face of the fiber, a high-power laser oscillator can be obtained within a range in which the ZBLAN fiber is not thermally damaged.

[Reference example]
In the embodiment, in the first fluoride fiber 3, the resin-made second clad 32 at the joint is removed, and the second clad is formed again after the joining. However, in this example, after the first fluoride fiber 3 and the second fluoride fiber 4 are joined, the second cladding is formed on the portion of the first fluoride fiber 3 covered with the first and second heat radiation plates. Not done.

  If the second cladding 32 of the first fluoride fiber 3 is removed, the excitation light leaks out from the first fluoride fiber 3, so that the introduction efficiency of the excitation light is deteriorated. Further, when the leaked excitation light is irradiated to surrounding members or dust, heat is generated.

  Therefore, when the second clad is not formed after joining both the fluoride fibers 3 and 4, the junction part where the second clad is removed and the vicinity thereof are covered with a member having a refractive index smaller than that of the first clad 31, and excited. It is necessary to prevent light from leaking outside.

In order to realize this, in this example, the first and second heat radiating plates are formed of a CaF ₂ substrate having a refractive index smaller than that of ZBLAN. Here, both heat sinks function as the second cladding of the first fluoride fiber, and the excitation light can be guided in the fiber. Further, by forming the first and second heat radiating plates with members that are transparent to the excitation light, both heat radiating plates can absorb the scattered light even if the scattered light of the excitation light is emitted outside the fiber. Therefore, heat generation can be avoided. Since CaF ₂ has a wider wavelength range of light that can be transmitted than ZBLAN, it is transparent to light that can be guided by the ZBLAN fiber. Furthermore, since the CaF ₂ substrate has higher thermal conductivity than ZBLAN or resin clad, it can be effectively cooled by mounting a heat sink on the CaF ₂ substrate.

  In this example, the heat radiation efficiency is further improved by fusing the first fluoride fiber 3 and the heat radiating member and joining them together without any gap. In this case, by heating the first cladding 31 of the first fluoride fiber 3 in a state where the first cladding 31 of the first fluoride fiber 3 is sandwiched between the first heat sink and the second heat sink, the first hook 31 is heated. The chemical fiber 3, the first heat radiating plate, and the second heat radiating plate can be fused. For example, the first cladding 31 of the first fluoride fiber 3 is heated by a heater, laser irradiation, or the like via a heat dissipation member. The heating temperature at this time is preferably set to be higher than the softening point of the first cladding 31 of the first fluoride fiber 3, and is preferably set to be lower than the crystallization start temperature. Further, when the first fluoride fiber 3 and the heat radiating member are fused, the first heat radiating plate of the second fluoride fiber 4 and the portion covered with the second heat radiating plate may be fused simultaneously with the heat radiating member. Good.

  Note that the first and second heat radiating plates in this example are different from each other in the material, and the other configurations are the same as those in the above embodiment.

  Also by this example, the same effect as the said embodiment can be acquired.

[Other Embodiments]
The present invention is not limited to the above-described embodiments, and various changes or modifications can be made without departing from the scope of the present invention.

  (A) In the present invention, the heat radiating member is formed of sapphire, but any material can be used as the heat radiating member as long as the thermal conductivity is equal to or higher than that of the fiber and the material has optical transparency to excitation light. it can.

(B) In the reference example, the first and second heat radiating plates are formed of a CaF ₂ substrate having a small refractive index so as not to leak the excitation light to the outside. However, the configuration for preventing the excitation light from leaking to the outside is provided here. It is not limited. For example, a reflective layer may be coated on the side surface of the fiber.

  (C) Although the ZBLAN fiber not doped with the laser active material is used as the first fluoride fiber in the embodiment, a ZBLAN fiber doped with the laser active material may be used. In this case, the third fluoride fiber becomes unnecessary.

  In addition, when both the first fluoride fiber and the third fluoride fiber are fibers doped with a laser active material, it is not necessary to fuse both fibers.

  (D) The heat dissipating member is not limited to the joint between the first fluoride fiber 3 and the second fluoride fiber 4, but the first fluoride fiber 3 and the third fluoride as in the heat dissipating member 6 'shown in FIG. You may form so that a junction part with the fiber 5 may also be covered. In this case, the heat generated at the two joints can be released by one heat radiating member 6 '.

  (E) In the above embodiment, the present invention is used as a laser oscillator. However, the present invention can also be applied to other apparatuses.

  (F) In the said embodiment, although the 2nd fluoride fiber which has a core was used as the 2nd fiber of this invention, you may use the 2nd fluoride fiber without a core as a 2nd fiber.

  (G) The present invention can also be used as a light distributor that distributes the light guided in the first and third fluoride fibers to the second fluoride fiber and emits the light.

  (H) In the above embodiment, a fiber having a circular cross section has been described as an example. However, a fiber having a rectangular cross section may be used. In this case, the second fiber can be easily joined to the first fiber.

  (I) Although the laser active material has been described as erbium in the above-described embodiment, other laser active materials such as thulium and holmium may be used. Depending on the combination of the wavelength of the laser active substance and the excitation light, laser light of various wavelengths can be generated.

  (J) In the above embodiment, the first fluoride fiber 3 and the second fluoride fiber 4 are fused and joined, but may be joined using another method such as an adhesive. .

DESCRIPTION OF SYMBOLS 1 Optical fiber apparatus 2 Excitation light source 3 1st fluoride fiber 30 Core 31 1st clad 32 2nd clad 4 2nd fluoride fiber 5 3rd fluoride fiber 6,6 'Heat radiation member 61 1st heat sink 62 2nd heat dissipation Board

Claims (7)

A core, a first cladding covering the outer peripheral surface of the core, and a second cladding formed of an ultraviolet curable resin having a refractive index smaller than that of the first cladding and covering the outer peripheral surface of the first cladding. A first fiber for guiding light;
A second fiber in which light is incident or emitted from the first end, and an end surface of the second end is obliquely bonded to a side surface of the first fiber;
The first fiber and the second fiber are arranged so as to cover the entire circumference of the joint between the first fiber and the second fiber, and the thermal conductivity is equal to or higher than that of the first and second fibers, and the first fiber and the second fiber. Sapphire having optical transparency with respect to the light guided;
An optical fiber device comprising: A third fiber connected to at least one end of the first fiber and having a core doped with a laser active material;
Excitation light corresponding to the laser active material is incident on the second fiber.
The optical fiber device according to claim 1.   3. The optical fiber device according to claim 2, wherein the sapphire covers the joint between the first fiber and the third fiber together with the joint between the first fiber and the second fiber.   The optical fiber device according to any one of claims 1 to 3, wherein the sapphire has a first heat radiating plate and a second heat radiating plate arranged so as to sandwich a joint portion between the first fiber and the second fiber. The second fiber is bonded to the side surface of the first fiber by fusion,
The second cladding of the first fiber is formed after fusing the second fiber to the first fiber.
The optical fiber device according to claim 1.   The optical fiber device according to claim 1, wherein the first fiber and the second fiber are fluoride fibers.   The optical fiber device according to claim 6, wherein the first fiber and the second fiber are made of ZBLAN glass.

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