JP2010205926A - Optical fiber device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber device which can be manufactured and repaired in expensively, and imparts an optical film or processed surface of more stable quality onto the end of a gain medium fiber. <P>SOLUTION: An optical fiber of ≤500 nm in length is prepared as a terminal fiber 2, and formation of the optical film 4 on one end surface 2a thereof or surface processing is performed. Then the other end surface of the optical fiber is connected to an end surface 1A of the gain medium fiber 1 to obtain an optical fiber device as the terminal fiber 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical fiber device in which a gain medium fiber and an optical film are integrally combined, and a manufacturing method thereof.

An optical fiber in which a rare earth element such as ytterbium (Yb), erbium (Er), thulium (Tm), or neodymium (Nd) is added to the core portion (particularly, a double-clad fiber) has high optical conversion efficiency and is an amplifier for optical communication. Are used to construct various optical amplifiers and industrial laser devices (for example, Patent Documents 1 to 4).
An optical fiber containing a substance capable of wavelength conversion and amplification as described above is called a “gain medium fiber”.
In order to construct a laser using a gain medium fiber, a resonator must be added to the fiber, and a coupling between the mirror and the gain medium fiber is required. Also, when an amplifier is configured using the gain medium fiber, various filters and mirrors are provided for the gain medium fiber, and in this case also, coupling of the filter or mirror and the gain medium fiber is necessary. Become.

For example, when a resonator for laser oscillation is applied to a gain medium fiber, the following two types of arrangement modes of mirrors for constituting the resonator are mainly mentioned.
One is a mode in which a pair of external dichroic mirrors (optical bandpass filters) 201 and 202 are arranged at both ends of a gain medium fiber to constitute an external resonator 200 as shown in FIG. Patent Document 5). However, in such an aspect, since the gain medium fiber and each mirror must be spatially coupled, a certain amount of space is required, and expensive parts such as a mirror and a collimator are required. The size and price of the equipment become a problem.
The other one is a dichroic mirror by directly depositing a highly reflective film 301 on at least one end face of the gain medium fiber (usually the side where the excitation light is input), as shown in FIG. 8B. It is an aspect (for example, patent document 6, 7). A reflection film may be directly formed on the other end face to form a mirror. However, in the example shown in the figure, the low end reflection mirror (Fresnel reflection mirror) 302 on the laser light emission side is obtained by making the fiber end face a flat polished surface. Yes.

  The mode in which the reflection film is directly formed on the end face of the gain medium fiber has fewer parts and a simpler configuration than the mode in which a separate external mirror is used. There is also an effect.

However, the present inventors have studied in detail the process of directly forming the reflection film on the end face of the optical fiber as described above. In the formation process, the film is formed in a high vacuum state such as sputtering or electron beam evaporation. It was found that the following problems occurred.
(I) Since the gain medium fiber is usually a long one having a total length of 20 m or more, when such a long optical fiber is accommodated in a processing chamber and processed, the handling of the optical fiber or the inside of the chamber Therefore, it takes a long time to form the reflective film. Such a problem in handling exists not only in film formation but also in the case of end face polishing.
(Ii) The temperature inside the chamber rises during vapor deposition, gas is released from the polymer layer covering the outside of the fiber, and the properties of the reflective film deteriorate.
(Iii) The reproducibility of the characteristics of the reflective film is low, and the quality of each process varies.
(Iv) Since the gas is released from the polymer layer and it is necessary to increase the volume of the chamber so that a long optical fiber can be accommodated in the chamber, it takes a long time for vacuuming.
It was also found that due to the problem of gas from the polymer layer (ii), the number (or total length) of fibers that can be deposited by one processing is limited.
In addition, in the aspect in which the reflection film or reflection surface is directly formed on the fiber end face, if the reflection film or reflection surface is damaged, the entire fiber must be handled as a processing target for repair. It has also been found that there is a problem of requiring a long time and high costs for the.
The above problems exist not only in the case of reflecting films but also in the case where various optical films are applied to the end face of any gain medium fiber, or when surface processing for forming a mirror surface or the like is performed. It is a problem.

JP 2007-103751 A JP-A-9-205239 JP 2000-503476 A JP 2002-277669 A Japanese Patent Application No. 2007-273842 JP 2007-13181 A JP 2007-250951 A

  An object of the present invention is to solve the above-mentioned problems, to provide an optical film and a processed surface with a more stable quality, which can be manufactured and repaired at a lower cost, and to the end of the gain medium fiber. It is in.

That is, the present invention has the following characteristics.
(1) having a structure in which an optical fiber having a length of 500 mm or less is connected as a terminal fiber to at least one end face of the gain medium fiber;
The terminal fiber is formed with an optical film on the end face opposite to the end face side relating to the connection with the gain medium fiber or is subjected to surface processing.
Optical fiber device.
(2) The connection between the gain medium fiber and the terminal fiber is
(I) is a connection formed by contacting and fusing the end faces relating to the connection of the gain medium fiber and the terminal fiber,
(Ii) It is a connection by attaching a connector to the end face related to each connection of the gain medium fiber and the terminal fiber, and connecting the connectors together.
The optical fiber device according to the above (1).
(3) The gain medium fiber is a double clad fiber, and the terminal fiber is a double clad fiber having a cross-sectional structure and the same layer structure as the gain medium fiber,
The connection between the gain medium fiber and the terminal fiber is removed from at least one of the two ends from the end face related to the connection to a predetermined length, and the first cladding is exposed by removing the second cladding and the outer layer; It is a connection made by contacting and fusing the end faces related to the connection between the two,
The optical fiber device according to the above (1).
(4) In the portion where the gain medium fiber and the terminal fiber are connected, the total length of the section in which the second cladding and the outer layer are removed is 2 mm or more. The optical fiber device according to (3), wherein light propagating through one cladding is prevented from entering the first cladding of the terminal fiber.
(5) In the portion where the gain medium fiber and the terminal fiber are connected, the fiber transmitting the pump light is connected to the first cladding exposed by removing the second cladding and the outer layer by the combiner. The optical fiber device according to (3) above.
(6) In the portion where the gain medium fiber and the terminal fiber are connected, the first cladding exposed by removing the second cladding and the outer layer thereof has a higher refractive index than the material of the first cladding. The optical fiber device according to (3), which is covered with
(7) The gain medium fiber is an air hole type double clad fiber having an air hole as a second clad, and the end fiber is an air hole type double clad fiber having the same layer structure as the gain medium fiber in a cross-sectional structure. ,
The terminal fiber has an air hole sealed to a predetermined length from the end surface opposite to the end surface side related to the connection with the gain medium fiber.
The optical fiber device according to the above (1).
(8) The gain medium fiber is a double clad fiber, and the terminal fiber is a double clad fiber having a cross-sectional structure and the same layer structure as the gain medium fiber,
The first cladding of the terminal fiber is added with a substance that absorbs light that propagates through the first cladding of the gain medium fiber and enters the first cladding of the terminal fiber.
The optical fiber device according to any one of (1) to (7).
(9) The method of manufacturing an optical fiber device according to any one of (1) to (8),
An optical fiber having a length of 500 mm or less that can be used as a terminal fiber of the optical fiber device is prepared, and after forming an optical film on one end face or performing surface processing, the other end face of the optical fiber is The manufacturing method according to claim 1, wherein the end fiber is connected to an end face of the gain medium fiber.

In the present invention, the end face of the long gain medium fiber is not directly processed, but the processed part is separated, that is, a short optical fiber having a length of 500 mm or less that can be connected to the gain medium fiber is used as the terminal fiber. The short end fiber is prepared and subjected to surface processing (flat mirror polishing or the like) or optical film formation, and then connected to the gain medium fiber.
With this manufacturing method and the structure obtained thereby, while maintaining the merit of forming an optical film directly on the fiber end face, the problem in handling when processing such as the formation of an optical film, It is possible to eliminate the problem of gas generation and the problem of limiting the number of films that can be formed due to the limitation of the total length of the fiber, thereby improving productivity, reducing costs, and easily replacing parts.

In the present invention, since a short terminal fiber is connected to the gain medium fiber, various functions can be added to the connecting portion and the terminal fiber.
For example, when the gain medium fiber is a double clad fiber, an end fiber having the same clad structure is connected, and at the connection portion, at least one of the two is connected to the predetermined length from the end face related to the connection. If the second cladding (which may include the outer layer in the case of an air hole structure) is removed, the pump light or the like propagating in the first cladding is unnecessarily propagated to the terminal fiber. And only the light in the core can be propagated. As a result, the pump light can be prevented from being output, and the multilayer film can be prevented from being deteriorated by the pump light.
Further, when the gain medium fiber is an air hole type double clad fiber, an end fiber having a similar clad structure is connected, and an air in a section of a predetermined length from the end face on which the optical film of the end fiber is to be formed. If the hole is sealed, the coupling efficiency of pump light input from the outside is not hindered by the air hole.
Further, when the gain medium fiber is a double clad fiber, the terminal fiber is also an optical fiber having the same structure, and the pump light propagating in the first clad of the gain medium fiber is transmitted to the first clad of the terminal fiber. If a substance that absorbs this light is added, pump light that has not been absorbed and propagated to the first cladding is absorbed by the first cladding, and damage to the optical film or the like can be prevented. Such a configuration is useful when pump light is input from a gain medium terminal.
When the gain medium fiber is an air hole type double clad fiber, if the air clad layer is removed and one or more optical fibers for pump light transmission are connected to the exposed first clad by a combiner or the like, Even if the pump light is not section-coupled with a collimator or the like, it can be easily coupled with only the fiber, and the optical coupling loss can be greatly reduced. Further, in order to confine the pump light, it is preferable that the portion of the first cladding connected to the combiner is covered with a polymer having a lower refractive index than the material of the first cladding.

FIG. 1 is a cross-sectional view showing an example of the configuration of the optical fiber device. The dimensional relationship of each part is exaggerated for the sake of explanation. Further, the loop in the center of the gain medium fiber 1 in the figure is an expression that suggests that the gain medium fiber 1 is an optical fiber that is sufficiently long or bent. FIG. 2 is a schematic diagram illustrating an example of an arrangement configuration of the fiber amplifier. FIG. 3 is a diagram illustrating a structure example of an air hole type double clad fiber. FIG. 4 is a perspective view sequentially illustrating a preferred process for the outermost end surface of the terminal fiber. FIG. 5 is a diagram showing an example of connection when the gain medium fiber and the terminal fiber are both double-clad fibers. FIG. 6 is a diagram showing an example of connection when the gain medium fiber and the terminal fiber are both air-hole type double clad fibers. FIG. 7 is a perspective view showing a state in which the second cladding at the end is removed, taking a fiber air hole type double cladding fiber as an example. FIG. 8 is a diagram showing a configuration example of a mirror when a resonator is added to the gain medium fiber.

Hereinafter, embodiments of the optical fiber device of the present invention will be described in detail with reference to the manufacturing method of the present invention. Specific applications of the present invention include a fiber laser device and a fiber amplifier. The fiber laser device and the fiber amplifier are different from each other in the detailed configuration (part of the known technology) such as the optical film. . In the following description, the fiber laser device is taken as a typical example, but the description also serves as an explanation of the main configuration of the fiber amplifier. Additional details regarding the specific configuration of the fiber amplifier will be mentioned.
FIG. 1 is a cross-sectional view illustrating an example of the configuration of the optical fiber device, and illustrates an aspect in which the optical fiber device is an optical fiber laser device including a resonator.
As shown in FIG. 1, the optical fiber device has a structure in which an optical fiber having a length of 500 mm or less is connected to at least one end face 1 </ b> A of the gain medium fiber 1 as a terminal fiber 2. The terminal fiber 2 is subjected to flat mirror polishing on an end surface (hereinafter, outermost end surface) 2a opposite to the end surface related to the connection with the gain medium fiber 1, and then a multilayer film (high reflection mirror) is optically provided. It is formed as a film 4.
In the example of the figure, another optical fiber having a length of 500 mm or less is also connected as the terminal fiber 3 on the other end face 1B side of the gain medium fiber 1, and its outermost end face is polished as surface processing. A flat mirror surface (Fresnel reflection mirror) is formed by processing, and the low reflection mirror 3a is formed. The resonator is constituted by mirrors (4, 3a) at the final end surfaces of the two terminal fibers 2, 3, and the pump light L1 is input into the gain medium fiber through the terminal fiber 2, and the laser light generated in the gain medium fiber. L2 is emitted through the terminal fiber 3. Such an input / output configuration is called a forward excitation system.
In addition to the forward excitation method as described above, a backward excitation method and a bidirectional excitation method may be employed. In the backward pumping method, pump light is input into the gain medium fiber 1 from the mirror on the terminal fiber 3 side, and the mirror on the terminal fiber 2 side is used as a high reflection mirror to cause laser oscillation between the two mirrors. A configuration example in which the light is emitted through the terminal fiber 3 again is given. Further, in the bidirectional pumping method, in order to make the light distribution of the pump light uniform, the pump light is simultaneously input into the gain medium fiber 1 from both the end fibers 2 and 3, and the light generated in the fiber 1 is transmitted to the fiber. A configuration example in which light is emitted through 3 is given. Appropriate mirrors at both ends constituting the resonator may be selected and combined in accordance with each excitation method.
In addition, in FIG. 1, although the aspect which connects a terminal fiber to both of a gain medium fiber is shown as a preferable example of a resonator, an external optical apparatus is used instead of one terminal fiber as needed. May be.

In the method of manufacturing the optical fiber device, first, a terminal fiber 2 is prepared, and an optical film 4 is formed on one end surface 2a thereof. Prior to the formation of the optical film, the end surface is preferably subjected to flat mirror polishing. Since the Fresnel reflectivity of glass is 3 to 4%, surface processing to the outermost end surface may be used instead of forming the optical film.
Hereinafter, "optical film" and "end surface subjected to surface processing" are also collectively referred to as "optical film etc.", and the formation of optical film and surface processing are collectively referred to as "formation of optical film etc." Also called.
When connecting a terminal fiber to both ends of the gain medium fiber as in the example of FIG. 1, a necessary optical film or the like is also formed on the end surface 3 a of the other terminal fiber 3.
Next, as shown in FIG. 1, the end fibers (both end fibers 2 and 3 in the example shown) formed with an optical film or the like are connected to the end faces 1A and 1B of the gain medium fiber 1, An optical fiber device is obtained.

Applications of the optical fiber device include, for example, an optical fiber type laser device, an optical fiber type amplifier, a wavelength converter such as an ASE (Amplified Spontaneous Emission) light source, a laser guide (in this case, the optical film is not a mirror but an antireflection film) For example).
Cross section structure of gain medium fiber (core diameter, clad structure, refractive index profile from the center to the outside) used for constructing the optical fiber device, base material of each part, added substance, cross section of terminal fiber The characteristics of the structure (core diameter, cladding structure, refractive index profile from the center to the outside), optical film applied to the outermost end surface of the end fiber, etc. are configured by the laser device and amplifier according to these applications To be determined and combined.

  FIG. 2 is a schematic diagram showing an example of the arrangement configuration of the fiber amplifier. In the example of the figure, the end fiber 3 is connected to only one side (right side) of the gain medium fiber 1, and the end face on the other side (left side in the figure) It has become. The oblique polished surface reduces the reflectivity due to Fresnel reflection, thereby obtaining the effect of suppressing the return light. The end face of the terminal fiber 3 may be an obliquely polished face, but in the example of FIG. 2, a multilayer film 5 having optical characteristics of increasing the coupling efficiency between incident light and the fiber by setting the Fresnel reflectivity to approximately 0% is formed. ing. 2, when the pump light L20 and the signal light (seed light) L10 are input to the gain medium fiber 1, the signal light L30 amplified in the gain medium fiber is output.

As described in the description of the background art, a double-clad fiber is preferable as a gain medium fiber for constituting a laser device or an optical amplifier, and a rare earth such as Yb, Er, Tm, or Nd is used as a core portion. An element and one or more elements selected from Al, Ge, P, and the like are added.
Among the double-clad fibers, as shown schematically in FIG. 3 which is a cross-sectional view perpendicular to the optical axis, an air-hole type double-clad fiber in which a large number of air holes 12h are gathered to form the second clad 12 is Compared to polymer clad type double clad fiber, it has features such as easy to increase NA (numerical aperture), high heat resistance, and reduced skew light, and is preferably used as the structure of gain medium fiber. it can.
For the cross-sectional structure, dimensions, materials of each part, etc. of air-hole type double clad fiber in which rare earth elements are added to the core part, reference may be made to the prior art (Optics Communication, Vol.186 (2003), p.311-317). , Quantum Electronics Vol.13 (2007), p.573-578).
An example of the structure of the air hole type double clad fiber shown in FIG. 3 is given below.
Core 10: Yb-doped quartz glass (outer diameter 5 μm to 60 μm)
First clad 11 (for pump light guide): pure quartz glass (layer thickness: 60 μm to 600 μm)
Second clad 12: air hole structure (layer thickness of about 5 μm to about 50 μm)
Support layer 13: pure quartz glass (layer thickness: 150 μm to 500 μm)
A plurality of protective layers (a layer made of a low-refractive silicone resin, a fluororesin layer on the outside thereof, etc.) are further formed on the outside of the support layer, but illustration and explanation are omitted.
The outer diameter of the entire fiber including the protective layer is about 800 μm to 1700 μm.

  The total length of the gain medium fiber used in the optical fiber device varies depending on the application and the core absorption coefficient, but is about 0.5 m to 50 m, and 5 m to 30 m is a preferable range. Since the overall length varies depending on the coefficient, it is preferable to adjust the total absorption coefficient of the pump guide to 10 dB. As described in the description of the background art, such a long optical fiber has various problems in forming an optical film directly on its end face, so that the advantages of the configuration of the present invention are remarkable. Become.

The cross-sectional structure of the terminal fiber is preferably matched with the cross-sectional structure of the gain medium fiber from the viewpoint that the entire optical fiber device is in the form of one continuous optical fiber. For example, if the gain medium fiber is an air hole type double clad fiber, it is preferable that the terminal fiber be an air hole type double clad fiber having a core structure and a numerical aperture NA of the same dimensions. If the core size or the core NA is different, scattering (reflection) may occur from the connected portion and the loss may increase. Therefore, the error of the core diameter or the core NA is preferably within ± 10%.
The core of the terminal fiber does not necessarily need to be added with a substance that becomes a gain medium such as rare earth elements. The terminal fiber may be a simple transmission optical fiber that preferably connects the outermost end surface of the terminal fiber and the gain medium fiber.
In addition, the structure of the terminal fiber may be such that at least the core outer diameter and the outermost diameter of the entire fiber coincide with those of the gain medium fiber, and the other clad structure is the same as that of the gain medium fiber. It may be different from the structure.
The numerical aperture NA of the terminal fiber on the output side is preferably controlled by a material selected from the group consisting of Al, P, Ge, F, and B.

The length of the terminal fiber varies depending on the thickness thereof, but is preferably 500 mm or less from the viewpoint of achieving the object of the present invention and from the viewpoint of conversion efficiency of the resonator. The upper limit value of the length of the end fiber is not a critical value such that the handleability of the fiber and the film forming processability on the end face change abruptly, but the present inventors etc. It is an appropriate value set as being able to achieve the object of the present invention.
When the length of the terminal fiber exceeds 500 mm, the problem to be solved by the present invention (that is, a problem when a long gain medium fiber is accommodated in the chamber and processed) also appears in the processing of the terminal fiber. In addition, the optical loss in the terminal fiber also appears remarkably.
On the other hand, the lower limit of the length of the terminal fiber is not particularly limited, but about 10 mm is an appropriate lower limit. If the length of the terminal fiber is less than the lower limit of 10 mm, it is too short and the handleability is poor, and there is also a problem that the optical film is thermally damaged when connected.
From the above, a preferable length range of the terminal fiber is a lower limit value of 10 mm to an upper limit value of 500 mm, and of these, a preferable length is 20 mm to 100 mm.

The optical film or the like formed on the outermost end surface of the terminal fiber is one or more films added to the outermost end surface or the surface processed surface itself. The surface processed surface is altered in the surface layer including the surface of the outermost end surface as well as the uneven surface and curved surface formed by the surface itself, such as flat mirror surface and lens surface with a root mean square roughness (RMS) of 0.1 μm or less It may be what you did. The optical film may include a surface processed on the base.
Examples of the function of the optical film include various reflection functions, antireflection functions, and filter functions necessary for configuring a laser device and an amplifier.

The optical film can be a multilayer film made of a metal oxide, an inorganic oxide, a semiconductor material, a dielectric material, etc. (that is, a multilayer high reflection film, a multilayer antireflection film, a selective filter, etc.), or a single film made of various materials. One film or a multilayer film may be used, and publicly known techniques may be referred to for the configuration, spectral characteristics, and film formation method.
Examples structure of the multilayer _{film, SiO 2, TaO x, Ta} 2 O 5, TiO 2, Si, ZrO 2, HfO 2, GaN, SiN x, ITO (Indium Tin Oxide), Al 2 O 3, and, SiC There is a mode in which two materials are selected from the group consisting of, and films made of these materials are alternately laminated on the fiber end face.
In the case of forming a multilayer film on the end face of the glass fiber, it is preferable that the SiO ₂ film and the TaO _x film are alternately laminated from the viewpoint of film resistance, glass adhesion, and spectral characteristics. The layer in contact with the end face of the glass fiber may be either a SiO ₂ film or a TaO _x film, but by making the SiO ₂ film a layer in contact with the end face of the glass fiber, the adhesion to the end face is good. Become.
A sputtering method, a CVD method, an electron beam evaporation method, or the like can be used for forming the multilayer film, but the electron beam evaporation method is a preferable method from the viewpoint of productivity and film thickness accuracy.

FIG. 4 schematically shows a preferable method for treating the outermost end face when the terminal fiber is an air hole type double clad fiber. The terminal fiber 2 in the figure has a core 20, a first cladding 21, a second cladding 22 having an air hole structure, and a support layer 23. The outer layer is not shown.
As described in the description of the effect of the invention, when the terminal fiber is an air hole type double clad fiber, each of the second clad (air hole structure) 22 is formed on the outermost end surface 2a as shown in FIG. If the air hole is open, dust, dust, water droplets, etc. may enter the air hole during polishing to deteriorate fiber characteristics.
Therefore, as shown in FIG. 4B, after the air hole is sealed from the outermost end surface to a specific length, the optical film 4 and the like are applied as shown in FIG. 4C.
The length of the sealed section of the air hole varies depending on the diameter of the optical fiber and the wavelength of the pump light, but is approximately 50 mm or less, particularly 0.1 mm to 5 mm, which is an effective and preferable length.
In addition, when pump light is input from the outermost end surface of the terminal fiber, if the air hole is opened at the outermost end surface, the pump light leaks to the opening of the air hole. descend. Therefore, it is preferable to seal from the outermost end surface to a specific length, but when the outer diameter of the support layer is 1 mm and the outer diameter of the second cladding is 600 μm, the preferable sealing section of the air hole is sinθ. = From NA, 0.2 mm to 0.3 mm is preferable.
In the cross section of the terminal fiber 2 shown in FIGS. 6A to 6C, the air hole is sealed, and the air hole 22 does not reach the outermost end surface.
When the length of the terminal fiber is 50 mm or less, the air hole may be sealed over the entire length of the terminal fiber. Moreover, although the air hole of a connection part may be removed for a fixed area, you may connect as it is.
The air holes are preferably sealed by heating the fiber with a burner torch, discharge, laser, or the like.

When a highly reflective film is formed by a multilayer film and a fiber resonator is configured, the spectral characteristics may be designed according to the purpose. For example, the gain medium fiber is a Yb-doped fiber, and the pump light wavelength is 915 nm or In the case of 976 nm, spectral characteristics such as a reflectance of almost 100% in the wavelength region from 1000 nm to 1150 nm and a transmittance of almost 100% in the wavelength region from 850 nm to 990 nm can be mentioned.
In the case of forming a partial reflection film, the reflectance is preferably 5% to 60% in order to increase the conversion efficiency of the laser, but attention should be paid to the generation of self-excited pulses and nonlinear characteristics.

  The surface processing applied to the outermost end surface of the end fiber varies depending on the purpose, but flat mirror processing by mechanical polishing, oblique mirror processing, lens surface processing, and method of cutting the fiber so that the end surface is mirrored from the beginning Includes diamond blade cutting, laser cutting, diamond pen cutting, and the like.

The method for connecting the gain medium fiber and the terminal fiber is not particularly limited as long as light can propagate between the two.
For example, as shown in FIG. 5 (a), the end surfaces related to the connection of the gain medium fiber 1 and the terminal fiber 2 are brought into full contact with each other, and are joined by fusion, as shown in FIG. 5 (b). As shown in FIG. 5 (c), the end faces relating to the connection between the two are partially brought into contact with each other and fused to join the connectors. And a method of connecting the connectors to each other.
For fusion between the end faces of the optical fibers, a known fusion technique may be referred to, and a burner torch or discharge can be used.
By adopting a configuration in which the connectors are connected, the terminal fibers can be easily attached and detached, and if the terminal fibers are held as replacement parts, the maintenance becomes easy.

As described in the description of the effect of the present invention, when the gain medium fiber and the terminal fiber are double clad fibers having the same cross-sectional structure, at a connection portion, at least one of the two has a predetermined length. If the second clad (which may include the outer layer in the case of an air hole structure) is removed only in this section, pump light or the like propagating through the first clad propagates unnecessarily to the terminal fiber. Can be suppressed.
FIG. 6 is a cross-sectional view showing a mode in which the second clad and its outer layer are removed by taking an air clad double clad fiber as an example. The terminal fiber 2 shown in FIG. 6 is an air clad type double clad fiber having the same cross-sectional structure as the gain medium fiber 1. The reference numerals of the respective parts are the same as those in FIGS. FIG. 7A is a perspective view showing the end surface 1A of the gain medium fiber 1, and FIG. 7B is a perspective view showing a state in which the second cladding and the outer layer are removed therefrom. The reference numerals of the respective parts are the same as those in FIGS.
In the example of FIG. 6A, the gain medium fiber 1 and the terminal fiber 2 are both removed from the second cladding and its outer layer. Reference numeral J denotes a connection interface (fused surface) between the two. Such an embodiment also has an advantage that alignment for bonding is easy because both first clads are exposed.
In the example of FIG. 6B, only the gain medium fiber 1 has the second cladding and outer layer removed, and in the example of FIG. 6C, only the end fiber 2 has the second cladding and outer layer. Has been removed.
6A to 6C, the total length x of the removed second cladding is the same, and there is a length x suitable for peeling. The length x may be at least a value that makes it difficult for light that has propagated through the first cladding of the gain medium fiber to propagate to the terminal fiber. For example, as an example of general fiber specifications, when the core diameter is 40 μm, the numerical aperture NA = 0.08, the outer diameter of the support layer is 1 mm, and the outer diameter of the second cladding is 600 μm, the length x is 2 mm or more. In particular, 10 mm to 100 mm is a preferred range.
The larger the total length x of the removed second cladding x, the more effective it is from the point of suppressing light propagation. However, if x is too large (if the removal interval is too long), the fiber will break. It becomes easy and handling becomes difficult.

In the connecting portion shown in FIG. 6, the first cladding is exposed by removing the second cladding and the outer layer. In order to effectively remove the pump light propagating through the first cladding of the gain medium fiber using this connection, or to direct it toward the outside, the refractive index of the first cladding material is higher than that of the first cladding material. The exposed first cladding may be covered with a high material (resin, oil, etc.).
In addition, if one or more pump optical fibers are connected to the first cladding exposed at the connecting portion using a combiner for coupling pump light, it is easily coupled with only the fiber without coupling the pump light. it can. According to this configuration, since the pump light does not propagate to the optical film, the optical film is not damaged, and the fiber device can be stably operated.

As described in the description of the effect of the present invention, when the gain medium fiber and the terminal fiber are double clad fibers having the same cross-sectional structure, light propagating in the first clad of the gain medium fiber (pump light) It is a preferable aspect that a substance that absorbs the above is added as a dopant to the first cladding of the terminal fiber.
Examples of such a substance include one or more materials selected from the group consisting of Yb, Nd, Er, Tm, and Nd according to the wavelength of the pump light.

As shown in FIG. 1, a specific example is shown in which a terminal device 2 and 3 are connected to both ends of a gain medium fiber 1 by fusion to form a backward pumping laser device.
The wavelength of the pump light to be input is 915 nm, and the center wavelength of the laser light to be oscillated is 1080 nm.
The gain medium fiber 1 and the two terminal fibers 2 and 3 are air hole type double clad fibers having the same structure in which Yb and Al are added to the core. On the outermost end surface of the terminal fiber 2 on the side where the pump light L1 is input, a multilayer film (high reflection film) made of SiO ₂ / Ta ₂ O ₅ is formed after flat mirror polishing, and on the output side of the laser light L2 The outermost end surface of the terminal fiber 2 was a mirror surface (Fresnel reflection mirror) by polishing.

[Processing of optical film, etc. on the outermost end surface of terminal fiber]
The total length of the gain medium fiber 1 is 15 m, and the lengths of the two terminal fibers 2 and 3 are each 50 mm.
Even if the outermost end surface of the terminal fiber is covered with a multilayer film, if the air hole (second clad) is open, the coupling efficiency of the input pump light decreases. After peeling off the fiber coating layer, the air hole was heated with a banner torch (which may be a discharge) from the end face to a length of 300 μm and sealed.
After that, both the two end fibers are subjected to mechanical polishing on the outermost end surface to form a flat end surface with a sealing length of 250 μm, and then treated with hydrofluoric acid (HF) for 1 minute to eliminate surface scratches. went.
As the outermost end face of the terminal fiber 3 on the output side, the obtained flat end face was used as it is as a reflecting face. Further, a multilayer film made of SiO ₂ / Ta ₂ O ₅ was further formed on the outermost end surface on the signal light reflection side by an electron beam evaporation method.
Regarding the spectral characteristics of the multilayer film, the reflectance was almost 100% in the wavelength region from 1000 nm to 1150 nm, and the transmittance was almost 100% in the wavelength region from 850 nm to 990 nm.

[Fusion of terminal fiber to both ends of gain medium fiber]
Thereafter, for the Yb-doped fiber (gain medium fiber) 1, the air holes are sealed over a length of about 2 mm from the connection surfaces at both ends thereof. The air hole is sealed over a length of about 2 mm from the connection surface and cut so that a clean cross section (smooth planar shape) is obtained. As shown in FIG. 1, the two end fibers 2 and 3 are connected to the gain medium fiber. A fiber laser was obtained as a resonator by bonding to both end faces by fusion.

In this embodiment, in the fiber type laser having the configuration shown in FIG. 1, the gain medium fiber 1 and the surface related to the connection of the terminal fiber 2 on which the optical film 4 is formed, as shown in FIG. After the resin coating was peeled over a section of 20 mm from the connection surface, an air hole sealing section having a length of about 1 mm was formed at a position 15 mm from the connection surface. For the terminal fiber 3 on the output side, the second cladding and its outer layer were not removed.
The purpose of forming the air hole sealing section at a position of 15 mm from the connection surface is that when the air hole of the fiber is etched with a hydrofluoric acid solution, which will be described later, the hydrofluoric acid solution penetrates deep into the air hole and the fiber characteristics are reduced. This is to prevent deterioration. That is, the air hole sealing section is used as an air hole etching stopper.
Next, in order to etch the air hole and easily remove the second clad and its outer layer, the part where the resin coat is peeled is etched with a hydrofluoric acid solution for 1 hour, and then a diamond blade, a diamond pen, a laser, etc. The quartz glass was scratched using a quartz cutter, the second cladding and its outer layer were removed, the first cladding was exposed, and the tip portion was cut so that the length of the exposed portion of the first cladding was 10 mm.
Finally, the gain medium fiber 1 and the two terminal fibers 2 and 3 were fused together with the first claddings attached to each other.
Other processing is the same as in the first embodiment.
The length x of the removal section of each second cladding in each connection portion is 10 mm × 2 = 20 mm.
It has been found that, by removing the air hole portion, on the pump light input side, it is possible to reduce the propagation of the pump light propagating through the second cladding to the multilayer film and to suppress the deterioration of the highly reflective film.
Further, the first clad is coated with a resin having a higher refractive index on the outside of the first clad exposed at the connecting portion in order to remove or direct the pump light propagating from the first clad to the outside. It has been found that almost all propagating pump light can be removed.

In this embodiment, as the terminal fiber 2 on the side where the optical film is formed in the embodiment of FIG. 1, the core that does not contain Yb is used in the core, and the pump light is absorbed in the first cladding of the terminal fiber 2. Therefore, the laser apparatus was the same as in Example 1 except that Yb was added as a dopant, Yb and Al were added as dopants in the core of the output-side end fiber 3, and the numerical aperture NA was 0.08. Configured.
The obtained laser device has an oscillation center wavelength of 1080 nm with respect to a pump wavelength of 915 nm, high slope efficiency of 70%, and stable operation without breaking the optical film even when the oscillation power exceeds 500 W. I knew I would get it.

In this example, the SiO ₂ / Ta ₂ O ₅ multilayer film was formed on the outermost end face of the terminal fiber on the pump light input side so that the reflectance with respect to the oscillation light of 1080 nm was almost 100%, and A SiO ₂ / Ta ₂ O ₅ multilayer film was formed on the outermost end surface of the terminal fiber on the laser beam emission side so as to have a partial reflectance of 30% with respect to the laser beam after flattening the end surface. Except for the above, a laser apparatus was configured in the same manner as in Example 1.
The obtained laser device has an oscillation center wavelength of 1080 nm and a high slope efficiency of 75% with respect to the pump wavelength of 915 nm, and is stable without breaking the optical film even when the oscillation power is 500 W or more. It was found that it can be operated automatically.

In this embodiment, a laser device is provided in the same manner as in Embodiment 4 except that a detachable fiber connector is attached to each connection end of the two terminal fibers and the gain medium fiber to thereby connect them. Configured.
By attaching a fiber connector to the side opposite to the end portion with the highly reflective film, it has become possible to easily construct a resonator without fusing. In addition, because the fiber connector can be attached and detached, even if the multilayer film is damaged, the end face of the gain medium fiber is not required to be processed directly and can be easily replaced, reducing the repair time. I also found out that
The application of the amplification fiber device is the same as that described above except that the optical film is changed from a highly reflective film to an antireflective film, and the same effect can be obtained.

  According to the present invention, in an optical fiber type laser device or amplifier, the optical film or the like directly formed on the end face of the gain medium fiber can be easily manufactured at low cost while maintaining the advantages of the optical film and processing surface. Repairs can now be made, and the quality of the optical film has become more stable.

DESCRIPTION OF SYMBOLS 1 Gain medium fiber 1A End surface of one side (pump light input side) 1B End surface of the other side (laser light output side) 2 One end fiber 2a Outermost end surface 3 Other end fiber 3a Outermost end surface 4 Optical film L1 Pump light L2 laser light

Claims (9)

An optical fiber having a length of 500 mm or less is connected to at least one end face of the gain medium fiber as a terminal fiber;
The terminal fiber is formed with an optical film on the end face opposite to the end face side relating to the connection with the gain medium fiber or is subjected to surface processing.
Optical fiber device. The connection between the gain medium fiber and the terminal fiber is
(I) is a connection formed by contacting and fusing the end faces relating to the connection of the gain medium fiber and the terminal fiber,
(Ii) It is a connection by attaching a connector to the end face related to each connection of the gain medium fiber and the terminal fiber, and connecting the connectors together.
The optical fiber device according to claim 1. The gain medium fiber is a double clad fiber, and the end fiber is a double clad fiber having the same layer structure as the gain medium fiber in a cross-sectional structure;
The connection between the gain medium fiber and the terminal fiber is removed from at least one of the two ends from the end face related to the connection to a predetermined length, and the first cladding is exposed by removing the second cladding and the outer layer; It is a connection made by contacting and fusing the end faces related to the connection between the two,
The optical fiber device according to claim 1.   In the portion where the gain medium fiber and the terminal fiber are connected, the total length of the section where the second cladding and the outer layer thereof are removed is 2 mm or more, whereby the first cladding of the gain medium fiber is The optical fiber device according to claim 3, wherein the propagating light is prevented from entering the first cladding of the terminal fiber.   A fiber for transmitting pump light is connected by a combiner to the first cladding exposed by removing the second cladding and the outer layer in the portion where the gain medium fiber and the terminal fiber are connected. Item 4. The optical fiber device according to Item 3.   In the portion where the gain medium fiber and the terminal fiber are connected, the first cladding exposed by removing the second cladding and the outer layer is covered with a material having a higher refractive index than the material of the first cladding. The optical fiber device according to claim 3. The gain medium fiber is an air hole type double clad fiber having an air hole as a second clad, and the end fiber is an air hole type double clad fiber having the same layer structure as the gain medium fiber in a cross-sectional structure;
The terminal fiber has an air hole sealed to a predetermined length from the end surface opposite to the end surface side related to the connection with the gain medium fiber.
The optical fiber device according to claim 1. The gain medium fiber is a double clad fiber, and the end fiber is a double clad fiber having the same layer structure as the gain medium fiber in a cross-sectional structure;
The first cladding of the terminal fiber is added with a substance that absorbs light that propagates through the first cladding of the gain medium fiber and enters the first cladding of the terminal fiber.
The optical fiber device according to any one of claims 1 to 7. It is a manufacturing method of the optical fiber device according to any one of claims 1 to 8,
An optical fiber having a length of 500 mm or less that can be used as a terminal fiber of the optical fiber device is prepared, and after forming an optical film on one end face or performing surface processing, the other end face of the optical fiber is The manufacturing method according to claim 1, wherein the end fiber is connected to an end face of the gain medium fiber.

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