JP4937988B2 - Etching method of optical amplifying medium fiber and manufacturing method of pumping light incident structure to optical amplifying medium fiber - Google Patents

Description

  The present invention relates to a method for etching an optical amplifying medium fiber used in fields such as information communication, laser medicine, and laser processing, and a method for manufacturing an excitation light incident structure on an optical amplifying medium fiber.

  Conventionally, as a kind of optical amplifying medium fiber, as shown in FIG. 12, an inner cladding 102 is provided on the outer periphery of a core 101 to which a rare earth element is added, and a hole layer 103 is provided on the outer periphery of the inner cladding 102. In some cases, an outer cladding 104 is provided, and a coating 105 is provided thereon. The hole layer 103 is configured by alternately forming holes 106 and connecting portions 107 that connect the inner cladding 102 and the outer cladding 104 in the circumferential direction (Non-Patent Document 1).

  Since the optical amplifying medium fiber 110 having such a hole fiber structure has a large refractive index difference between the inner cladding 102 and the hole layer 103, excitation light having a large numerical aperture is incident from the end face of the light amplifying medium fiber 110. There is an advantage that a high-power optical fiber laser can be configured. When this type of optical amplifying medium fiber 110 is optically pumped, if the pumping light is incident from the side of the optical fiber 110, the pumping light is scattered by the hole layer 103 and the incident efficiency is low. The light is incident from the end face of the amplification medium fiber 110.

  FIG. 13 is a schematic view showing an example of a conventional optical excitation method for an optical amplifying medium fiber. In this optical excitation method, the light of the excitation light 124 output from the laser diode 126 (excitation light source) is condensed on the end surface 111 of the optical amplification medium fiber 110 by the condenser lens 127, whereby the excitation light 124 is condensed into the optical amplification medium fiber. 110 enters the inner clad 102 of the optical fiber 110 and excites the rare earth element added to the core 101 of the optical amplifying medium fiber 110.

  FIG. 14 is a schematic configuration diagram showing a first example of a conventional optical fiber amplifier. In this optical fiber amplifier 140A, the signal light 143 output from the end face 142 of the signal light incident optical fiber 141 is collected by the condenser lens 144, passes through the optical filter 145, and the end face of the optical amplifying medium fiber 110. 111 is incident. The excitation light 124 is collected by the condenser lens 127, reflected by the optical filter 145, and incident on the end surface 111 of the optical amplification medium fiber 110. In the optical amplification medium fiber 110, the signal light is amplified by the rare earth element excited by the absorption of the excitation light 124, and is output as the output signal light 146 from the end surface 112 on the opposite side of the optical amplification medium fiber 110.

  FIG. 15 is a schematic configuration diagram showing a second example of a conventional optical fiber amplifier. The optical fiber amplifier 140B uses a plurality of laser diodes (excitation light sources) 126, 126,... To increase the intensity of the excitation light 124 incident on the optical amplification medium fiber 110. Then, the excitation light 124 output from these excitation light sources 126, 126,... Is multiplexed by an optical multiplexing element 128 made of quartz glass or the like, and is optically amplified via a condenser lens 127 and an optical filter 145. It is configured to enter the end surface 111 of the medium fiber 110. Thereby, this optical fiber amplifier 140B can obtain a higher amplification factor than when one pumping light source is used.

  FIG. 16 is a schematic configuration diagram showing a third example of a conventional optical fiber amplifier. In this optical fiber amplifier 140C, a plurality of optical amplifying medium fibers 110a, 110b, and 110c are coupled in series via a condenser lens 144 and an optical filter 145 that combines the excitation light 124 and the signal light 143 and 147. It becomes the composition. That is, the signal light 143 output from the end face 142 of the signal light incident optical fiber 141 is sequentially incident on the first, second, and third optical amplification medium fibers 110a, 110b, and 110c and amplified there. Between the respective optical amplification medium fibers 110a, 110b, and 110c, the signal light propagates through the space as a spatial beam 147, is combined with the excitation light, and enters the next optical amplification medium fibers 110b and 110c. As a result, high-intensity output signal light 146 can be obtained.

  FIG. 17 is a schematic view showing another example of a conventional optical excitation method for an optical amplifying medium fiber. The optical amplifying medium fiber 210 used in this method includes a core 201, an inner clad 202 made of quartz glass or the like, and an outer clad 203 formed on the outer circumference of the inner clad 202. A double clad type optical fiber. The outer cladding 203 has a resin coating whose refractive index is slightly lower than that of the inner cladding 202 (for example, the refractive index of the outer cladding 203 is 1.42 with respect to the refractive index of the inner cladding 202 is 1.45). Thus, waveguide in the inner cladding 202 is possible.

  In this optical excitation method, the outer cladding 203 of the optical amplifying medium fiber 210 is removed in a part in the longitudinal direction, and further, a part of the outer periphery of the inner cladding 202 exposed in the coating removing part 211 is polished. A planar polishing portion 212 is formed. The end face 223 of the excitation light incident optical fiber 220 is cut obliquely and joined to the polishing section 212. Further, a protective resin layer 214 is provided to protect the bonding portion 213 and the polishing portion 212.

According to this optical pumping method, the pumping light 224 propagating through the pumping light incident optical fiber 220 is incident on the optical amplifying medium fiber 210 from the junction 213, so that the optical amplifying medium fiber 210 is optically pumped.
J. et al. K. Sahu et al., “Jacked air clad cladding pumped ytterbium-doped fiber laser width with tuning range”, Electronics Letters, Vol. 1, United Kingdom, Letters 200, p. 1116-1117 US Pat. No. 6,370,297

  In the case of the optical fiber amplifiers 140A to 140C using the optical fiber amplifying medium fiber 110 having the hole fiber structure described above, the signal light 143 and 147 and the pumping light 124 need to be incident on the optical amplifying medium fiber 110 as a spatial beam. An optical system such as a condenser lens 144 and an optical filter 145 is required, and the signal light incident optical fiber 141 and the excitation light source 126 need to be aligned at the same time. For this reason, very complicated work is required for adjusting the optical axis of the light beam. In addition, even after adjusting the optical axis, there is a problem that the optical axis is shifted due to mechanical disturbances such as vibration and impact, and other disturbances such as temperature changes, and desired amplification characteristics cannot be obtained. .

  Further, when the double clad type optical amplifying medium fiber 210 is used, the difference in refractive index between the inner clad 202 and the outer clad 203 is small, so that among the pumping light 224 incident from the pumping light incident optical fiber 220, Only components having a small incident angle θ can propagate through the optical amplifying medium fiber 210. A component having a large incident angle θ leaks from the inner cladding 202 to the outer side of the optical fiber 210 through the outer cladding 203, resulting in optical loss. That is, there is a problem that the incident efficiency of the excitation light 224 into the optical amplification medium fiber 210 is low and the optical loss is large.

  Accordingly, an object of the present invention is to provide a method for manufacturing a pumping light incident structure on an optical amplifying medium fiber that can enter the optical amplifying medium fiber with high efficiency and obtain excellent amplification characteristics, and the pumping light. It is an object of the present invention to provide an optical amplifying medium fiber etching method suitable for manufacturing an incident structure.

In order to solve the above problems, a core to which a rare earth element is added, an inner cladding provided on the outer periphery of the core, a hole layer formed on the outer periphery of the inner cladding, and an outer periphery of the hole layer An outer clad provided on the outer clad, and a coating provided on an outer periphery of the outer clad, wherein the hole layer includes a hole formed extending in a longitudinal direction, and an outer periphery of the inner clad. An optical amplifying medium fiber etching method comprising a connecting portion connecting the inner periphery of the outer cladding, wherein after removing a part of the coating in the longitudinal direction to form a coating removing portion, the optical amplification In a state where air is pumped from both ends of the medium fiber into the hole and an internal pressure is applied, the coating removal portion is immersed in an etching solution, and a part of the outer cladding of the optical amplification medium fiber is removed in the longitudinal direction. The inner cladding is exposed To provide an etching method of the optical amplification medium fiber which is characterized by forming a side cladding exposure section.
In the optical amplifying medium fiber, the inner cladding has a polygonal cross section, the outer cladding has an annular cross section, and the connecting portion has a ridge line on the outer peripheral surface of the inner cladding on the inner surface of the outer cladding. It is preferable to be joined.

  The present invention also provides a core to which a rare earth element is added, an inner cladding provided on the outer periphery of the core, a hole layer formed on the outer periphery of the inner cladding, and an outer periphery of the hole layer. The outer cladding, and a coating provided on the outer periphery of the outer cladding, wherein the hole layer includes a hole extending in the longitudinal direction, the outer periphery of the inner cladding, and the A method for manufacturing a pumping light incident structure on an optical amplifying medium fiber for making the pumping light incident on an optical amplifying medium fiber comprising a connecting portion that connects the inner periphery of the outer cladding. An inner clad exposed portion formed by removing a portion of the outer clad in the longitudinal direction by the etching method according to claim 1 is formed on a portion of the inner clad exposed portion, and then exposed to the inner clad exposed portion. Inner cladding Circumferentially, to provide a manufacturing method of the excitation light incident structure to the optical amplification medium fiber which is characterized by bonding the end faces of the excitation light incident optical fiber.

The end face of the excitation light incident optical fiber is formed obliquely with respect to the optical axis of the excitation light incident optical fiber, and this end face is inclined with respect to the optical amplification medium fiber at an incident angle. It is preferable to join so that it can inject.
The inner clad exposed portions can be formed at a plurality of locations in the longitudinal direction of the optical amplifying medium fiber, and end faces of different excitation light incident optical fibers can be joined to the plurality of inner clad exposed portions, respectively.

  According to the optical amplifying medium fiber etching method of the present invention, when the outer cladding is removed and the opening of the hole is exposed to the etching solution, it is possible to prevent the etching solution from entering the hole due to the capillary phenomenon. it can.

  According to the pumping light incident structure manufactured by the pumping light incident structure manufacturing method for the optical amplifying medium fiber of the present invention, the connection state between the optical amplifying medium fiber and the pumping light incident optical fiber can be reliably maintained. The optical axis is not shifted by other disturbances such as mechanical disturbances and temperature changes. Since the excitation light incident optical fiber is directly bonded to the optical amplifying medium fiber, a condensing lens is not required, the number of components can be reduced, the cost can be reduced, and the signal light propagates through the space. Loss can be avoided. Moreover, due to the presence of the hole layer, the upper limit of the incident angle of the excitation light becomes larger than before, and the incident efficiency of the excitation light from the excitation light incident optical fiber to the optical amplifying medium fiber can be increased.

  Further, when the inner clad exposed portions are formed at a plurality of locations in the longitudinal direction of the optical amplifying medium fiber, and end faces of different excitation light incident optical fibers are joined to the plurality of inner clad exposed portions, Even when the length of the amplification medium fiber is longer than the length of attenuation of the excitation light, the excitation light can be supplied over the entire length of the optical amplification medium fiber. Therefore, pumping light from a plurality of pumping light sources can be efficiently supplied to the optical amplifying medium fiber, and the optical amplifying medium fiber can be excited with higher efficiency. Moreover, since it is not necessary to take out signal light as a spatial beam in the middle, loss of signal light can be reduced. In addition, since an optical multiplexing element is not required, the number of components can be reduced and the cost can be reduced, and excitation light can be incident from the excitation light source to the optical amplifying medium fiber with low loss.

  Hereinafter, the present invention will be described in detail based on embodiments.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a pumping light incident structure (hereinafter sometimes simply referred to as “pumping light incident structure”) to the optical amplifying medium fiber of the present invention. FIG. 2 is a cross-sectional view showing an optical amplifying medium fiber used in the excitation light incident structure shown in FIG.

As shown in FIG. 2, the optical amplifying medium fiber 10 used in the excitation light incident structure of the present embodiment includes a core 1 to which a rare earth element is added, and an inner cladding 2 provided on the outer periphery of the core 1. A hole layer 3 formed on the outer periphery of the inner cladding 2, an outer cladding 4 provided on the outer periphery of the hole layer 3, and a coating 5 provided on the outer periphery of the outer cladding 4. . Between the inner cladding 2 and the outer cladding 4, a hole 6 having a substantially arcuate cross-sectional shape and a connecting portion 7 that connects the outer periphery of the inner cladding 2 and the inner periphery of the outer cladding 4 are arranged in the circumferential direction. Are formed alternately in four places, and the pore layer 3 is constituted by these. The holes 6 are formed to extend in the longitudinal direction of the optical amplifying medium fiber 10.
Here, the inner cladding 2 has a substantially rectangular cross section, and the outer cladding 4 has an annular cross section. The connecting portion 7 is formed by joining the ridge line of the outer peripheral surface 2 a of the inner cladding 2 to the inner surface 4 a of the outer cladding 4.
Note that the shape of the cross section of the inner cladding 2 is not particularly limited to a quadrangular shape. In order to facilitate the joining with the excitation light incident optical fiber 20, it is preferable that the outer peripheral surface 2 a facing the hole 66 of the inner cladding 2 has a flat portion, for example, a polygon such as a triangle, a pentagon, a hexagon, etc. It is also possible to make the inner cladding 2 having a cross section in shape. However, the outer peripheral surface 2a of the inner cladding 2 may be a curved surface as long as the bonding with the excitation light incident optical fiber 20 is sufficiently performed.

The core 1 can be composed of a rare earth element-added glass obtained by adding a rare earth element to quartz glass. The rare earth element may be any element that is conventionally used in an optical amplifying medium fiber. For example, erbium (Er), thulium (Tm), yttrium (Y), ytterbium (Yb), holmium (Ho), and samarium. (Sm), praseodymium (Pr), neodymium (Nd), and the like.
The inner cladding 2 and the outer cladding 4 can be made of, for example, quartz or quartz glass in which a known dopant such as germanium or fluorine is added to quartz. For example, the rare earth element can be added at a mass ratio of about 100 to 2000 ppm. Further, not only the core 1 but also a portion of the inner cladding 2 adjacent to the core 1 can be added with a rare earth element. In addition, as a material of the optical amplifying medium fiber 10, a material used for a known quartz glass-based optical fiber, a fluoride-based optical fiber, or the like can be used.

FIG. 3 is a cross-sectional view showing an example of a base material used for manufacturing the optical amplifying medium fiber 10. FIG. 4 is a schematic diagram for explaining a process of manufacturing the base material shown in FIG.
The base material 60 shown in FIG. 3 corresponds to the core 1, the inner cladding 2, the hole layer 3, and the outer cladding 4 of the optical amplifying medium fiber 10, and the core part 61, the inner cladding part 62, the hole layer 63, respectively. An outer cladding 64 is provided. The base material manufacturing apparatus 70 shown in FIG. 4 includes at least a pair of glass lathes 71 and 71 including a chuck 72 that holds the glass tube 64, and a burner 73 that heats the glass tube 64.

The base material 60 can be manufactured, for example, as shown in FIG.
First, a rectangular columnar glass rod 68 that becomes the core portion 61 and the inner cladding portion 62 is inserted into the glass tube 64 that becomes the outer cladding portion of the base material 60. As this glass rod 68, for example, based on a cylindrical quartz glass rod in which a rare earth element for optical amplification and germanium for increasing the refractive index are added to the central portion that becomes the core portion 61, The outer periphery can be cut and polished into a prismatic shape.
Next, both ends of the glass tube 64 in which the glass rod 68 is inserted are gripped by the chuck 72 of the glass lathe 71. Further, the glass tube 64 is heated by the flame 73 a of the burner 73 disposed outside the glass tube 64 while the glass tube 64 is rotated around the central axis by the glass lathe 71. During the heating, the burner 73 is traversed in the longitudinal direction of the glass tube 64 (the left-right direction in FIG. 4). As the outer glass tube 64 is heated and softened by the oxyhydrogen flame 73a, the inner and outer diameters of the glass tube 64 shrink, and the inner surface 64a of the glass tube 64 (outer cladding portion) becomes the side surface (inner cladding) of the glass rod 68. Are attached to and integrated with the ridge line 68a.
In this way, the portion where the glass tube 64 and the glass rod 68 are attached becomes the connecting portion 67, and the inner surface 64a of the glass tube 64 and the outer peripheral surface 62a of the glass rod 68 that is not attached to the inner surface of the glass tube 64. The base material 60 having the hole layer 63 can be obtained with the gap 66 therebetween.
The base material 60 having the hole layer 63 is heated and drawn using a drawing device used for drawing an ordinary optical fiber, and the diameter is reduced to the diameter of the optical fiber 10. At the time of drawing, the spun optical fiber is coated with a resin to provide a resin coating 5. As described above, the optical amplifying medium fiber 10 as shown in FIG. 2 can be obtained.

As shown in FIG. 1, in the excitation light incident structure 13 of the present embodiment, the optical amplifying medium fiber 10 has the coating 5 and the outer cladding 4 removed in a part in the longitudinal direction, and this inner cladding exposed portion. 14 shows the inner cladding 2 exposed. The hole layer 3 and the outer cladding 4 are left on both sides of the inner cladding exposed portion 14. The end face 23 of the excitation light incident optical fiber 20 is joined to the joint 16 that is a part of the outer periphery 15 of the exposed inner cladding 2.
In the inner cladding exposed portion 14, the connecting portion 7 and the portion of the outer cladding 4 in the vicinity thereof are exposed to the inner cladding as long as they do not adversely affect the joining with the optical fiber 20 for excitation light incidence and the incidence of the excitation light 24. It may partially remain in the portion 14, or may be completely removed from the inner cladding exposed portion 14.
Although not particularly shown, the excitation light incident structure 13 protects the inner cladding exposed portion 14 and the joint portion 16 so that a flexible protective material such as sponge or rubber is adhered and adhered, or plastic or metal is used. It is also possible to provide a cover with a housing or a casing made of the above. In this case, the mechanical stability and durability of the excitation light incident structure 13 can be improved.

Here, the pumping light incident optical fiber 20 is an optical fiber for propagating pumping light output from a pumping light source (for example, a laser diode) and causing the pumping light to enter the optical amplifying medium fiber 10. As the excitation light incident optical fiber 20, for example, a normal silica-based single-mode optical fiber core in which a resin coating 22 is provided on the outer periphery of the bare optical fiber 21 can be used. Examples of the resin for the resin coating 22 include ultraviolet curable resins such as acrylic resins.
The end face 23 of the pumping light incident optical fiber 20 is formed obliquely with respect to the optical axis of the optical fiber 20 so that the pumping light can enter the optical amplification medium fiber 10 obliquely at an incident angle θ. It has become.

Next, an example of a manufacturing method of this excitation light incident structure will be described.
FIG. 5 is a perspective view showing an example of a state in which the inner cladding exposed portion 14 is formed in the optical amplifying medium fiber 10, and FIG. 6 is an etching apparatus for forming the inner cladding exposed portion 14 in the optical amplifying medium fiber 10. It is a schematic block diagram which shows an example.
The etching apparatus 30 shown in FIG. 6 includes a water tank 33 in which an etching solution 34 such as an aqueous hydrogen fluoride solution is accommodated, and two air pumps 31 and 31.
The water tank 33 is made of a material that is not affected by the etching solution 34. For example, when the etching solution 34 is an aqueous hydrogen fluoride solution, polytetrafluoroethylene (PTFE) or the like is preferable.
Although not particularly illustrated, the water tank 33 can be provided with a temperature regulator for keeping the temperature of the etching solution 34 constant.

  In order to form the inner cladding exposed portion 14 in the optical amplifying medium fiber 10 using the etching apparatus 30 shown in FIG. 6, first, the coating 5 in the portion that becomes the inner cladding exposed portion 14 is removed and the coating removing portion 17 is formed. After the formation, air pumps 31 are connected to both ends of the optical amplifying medium fiber 10 via connecting tubes 32, respectively, and air is pumped into the air holes 6 of the optical amplifying medium fiber 10 to apply an internal pressure. In this state, the coating removal unit 17 is immersed in the etching solution 34. Thereby, the outer cladding 4 of the optical amplifying medium fiber 10 is etched and removed, and the inner cladding exposed portion 14 is formed. At this time, since the internal pressure is applied to the holes 6, when the outer cladding is removed and the opening of the holes 6 is exposed to the etching solution 34, the etching solution 34 is applied to the holes 6 by capillary action. Intrusion is prevented.

  As a method of joining the end face 23 of the excitation light incident optical fiber 20 to the inner cladding exposed portion 14, for example, the coating 5 on the end face 23 side of the excitation light incident optical fiber 20 is removed to expose the bare optical fiber 21. There is a method in which the end face 23 is cut obliquely and then fused and connected to the inner cladding exposed portion 14. Further, instead of fusion splicing, adhesion using an adhesive may be used. The pumping light incident optical fiber 20 is bonded so that the pumping light 24 (see FIG. 1) enters the inner cladding 2 of the optical amplifying medium fiber 10 and is guided by the hole layer 3. Here, when the inner cladding 2 has a prismatic shape, the joint 16 where the inner cladding 2 is bonded to the end face 23 of the excitation light incident optical fiber 20 becomes a flat surface. The operation of joining the optical fiber 20 is simplified, and the joining strength is easily secured.

Next, a method for performing optical excitation of the optical amplifying medium fiber 10 using the excitation light incident structure 13 of the present embodiment will be described.
As shown in FIG. 1, a pumping light source (not shown) such as a laser diode is connected to an end face (not shown) opposite to the end face 23 of the pumping light incident optical fiber 20 joined to the optical amplifying medium fiber 10. Then, the excitation light 24 output from the excitation light source is propagated to the excitation light incident optical fiber 20 and emitted from the end face 23 of the excitation light incident optical fiber 20. As a result, the excitation light 24 is incident on the inner cladding 2 of the optical amplifying medium fiber 10.
Since the hole layer 3 exists on the outer periphery of the inner cladding 2, the refractive index difference between the inner cladding 2 and the hole layer 3 is sufficiently large as compared with the conventional case shown in FIG. 17. Therefore, the upper limit of the incident angle θ of the excitation light 24 that can propagate through the inner cladding 2 becomes larger than before, and more components can be propagated to the inner cladding 2. Therefore, the incident efficiency of the pumping light from the pumping light incident optical fiber 20 to the optical amplifying medium fiber 10 can be increased.

  Compared with the optical pumping method shown in FIG. 13, according to the optical pumping method of the present embodiment, the optical fiber 20 for pumping light incident and the optical amplifying medium fiber 10 are directly joined, so that the optical loss is small. . Since a condensing lens becomes unnecessary, the number of parts can be reduced and cost can be reduced. Further, the optical axis is not easily displaced by mechanical disturbances such as vibration and impact, and other disturbances such as temperature changes, and desired characteristics can be reliably maintained.

FIG. 7 is a schematic configuration diagram showing a first embodiment of an optical fiber amplifier (hereinafter, simply referred to as “optical fiber amplifier”) of the present invention.
This optical fiber amplifier 40A includes an outer periphery 15 of an inner cladding exposed portion 14 formed in a part of the optical amplification medium fiber 10 in the longitudinal direction, one end face 23 of the bare optical fiber 21 of the optical fiber 20 for exciting light incident, Has the excitation light incident structure 13 as described above.
An excitation light source 26 is connected to the other end face 25 opposite to the one end face 23 of the excitation light incident optical fiber 20.

Further, the end face 42 of the signal light incident optical fiber 41 is fusion-bonded to the input end 11 of the optical amplifying medium fiber 10 to form a fusion-bonding portion 44.
The fusion splicing of the optical amplifying medium fiber 10 and the signal light incident optical fiber 41 is performed, for example, in a state where the signal light is propagated to the optical fiber 41 for signal light incident, and the signal light is transmitted to the core 1 of the optical amplifying medium fiber 10. The optical fibers 10 and 41 are aligned so as to be input, and the end faces 11 and 42 of the optical fibers 10 and 41 are heated and fused while maintaining the aligned state. .

According to such an optical fiber amplifier 40A, the rare earth added to the core 1 of the optical amplifying medium fiber 10 by the pumping light incident on the optical amplifying medium fiber 10 from the pumping light source 26 via the pumping light incident structure 13. The element light is excited, and the excited rare earth element amplifies the signal light input from the signal light incident optical fiber 41 to the optical amplifying medium fiber 10, and the other end (output terminal) 12 of the optical amplifying medium fiber 10. The output signal light 43 amplified from can be obtained.
That is, for the manufacture of the optical fiber amplifier 40A, the alignment of the optical fiber may be performed only for the optical fiber 41 for signal light incidence, and labor during manufacturing can be significantly reduced. Once the fusion-splicing is performed, the signal light incident optical fiber 41 and the pumping light incident optical fiber 20 can reliably maintain the connection state with the optical amplifying medium fiber 10, and mechanical disturbance or The optical axis is not shifted by other disturbances such as temperature changes. In addition, as described above, due to the presence of the hole layer 3, the incident efficiency of the excitation light from the excitation light incident optical fiber 20 to the optical amplifying medium fiber 10 can be increased. Therefore, an optical fiber amplifier with high amplification characteristics and reliability is obtained.

  FIG. 8 is a schematic configuration diagram showing an optical fiber amplifier according to the second embodiment of the present invention. In this optical fiber amplifier 40B, the length of the optical amplifying medium fiber 10 is increased in order to increase the amplification factor. The pumping light incident from the pumping light incident optical fiber 20 is attenuated as it propagates through the optical amplifying medium fiber 10, so that the pumping light is not significantly attenuated in the longitudinal direction of the optical amplifying medium fiber 10. A plurality of excitation light incident structures 13 and 13 (here, two locations) are provided. The configuration of each pumping light incident structure 13 is the same as that of the optical fiber amplifier of the first embodiment described above, and a pumping light source 26 is provided for each pumping light incident structure 13.

According to the optical fiber amplifier 40B of the present embodiment, even when the length of the optical amplifying medium fiber 10 is longer than the length of attenuation of the pumping light, the pumping light is supplied over the entire length of the optical amplifying medium fiber 10. Can do. Therefore, the pumping light from the plurality of pumping light sources 26 can be efficiently supplied to the optical amplifying medium fiber 10, and an optical fiber amplifier having a large amplification factor can be configured.
In addition, since the excitation light is dispersed and input from a plurality of locations, the heat generated due to absorption of the excitation light is also dispersed, and the optical amplification medium fiber 10 can be prevented from being overheated locally.

  When the optical fiber amplifier 40B of the present embodiment is compared with the conventional optical fiber amplifiers 140B and 140C as shown in FIGS. 15 and 16, the signal light needs to be extracted as a spatial beam in the middle of the optical fiber amplifier 40B of the present embodiment. And loss of signal light can be reduced. Further, since an optical multiplexing element for multiplexing the pumping light is not required, the number of parts can be reduced and the pumping light can be incident on the optical amplifying medium fiber 10 from the pumping light source 26 with low loss. There are also advantages.

Next, the optical fiber laser of the present invention will be described.
FIG. 9 is a schematic configuration diagram showing the optical fiber laser according to the first embodiment of the present invention. As described above, the optical fiber laser 50A is formed by joining the inner cladding exposed portion 14 formed on the optical amplifying medium fiber 10 and one end face 23 of the bare optical fiber 21 of the optical fiber 20 for excitation light incidence. The excitation light incident structure 13 is provided.
An excitation light source 26 is connected to the other end face 25 opposite to the one end face 23 of the excitation light incident optical fiber 20.

  Further, a total reflection mirror 51 is disposed on one end face 11 of the optical amplifying medium fiber 10. An output mirror 52 that transmits part of the light is disposed on the other end surface 12 opposite to the end surface 11. The total reflection mirror 51 and the output mirror 52 are fixed to the end surfaces 11 and 12 of the optical amplifying medium fiber 10 by, for example, an adhesive. As these mirrors 51 and 52, a mirror suitable for the wavelength of the pumping light and the light emitted from the optical amplifying medium fiber 10 among the mirrors used in known laser transmitters is appropriately selected and used. Can do.

  In FIG. 9, the excitation light incident structure 13 is formed near the end face 11 on the total reflection mirror 51 side, and the excitation light incident optical fiber 20 is directed to the output mirror 52 side (rightward in FIG. 9). It is joined to. However, the optical fiber laser of the present invention is not particularly limited to this, and conversely, the pumping light incident structure 13 is formed near the end face 12 on the output mirror 52 side, and the pumping light incident optical fiber 20 is formed. You may join in the direction (left direction of FIG. 9) which faced the total reflection mirror 51 side.

According to such an optical fiber laser 50 </ b> A, the pumping light incident on the optical amplifying medium fiber 10 from the pumping light incident optical fiber 20 excites the rare earth element of the core 1 of the optical amplifying medium fiber 10. The excited rare earth element spontaneously emits light having a predetermined wavelength corresponding to the energy level, and this spontaneously emitted light is optically amplified while being repeatedly reflected between the total reflection mirror 51 and the output mirror 52. Since it propagates through the medium fiber 10 and is repeatedly amplified, laser oscillation occurs. By outputting a part of the laser light oscillated in this way from the output mirror 52, the output of the laser light 53 can be obtained.
In this way, a highly efficient optical fiber laser can be configured with a relatively simple configuration by using the pumping light incident structure 13 that allows the pumping light to enter the optical amplifying medium fiber 10 with high coupling efficiency. Can do.

FIG. 10 is a schematic configuration diagram showing a second embodiment of the optical fiber laser of the present invention. This optical fiber laser 50B is an optical amplifying medium fiber 10 having a total reflection mirror 51 on one end face 11 and an output mirror 52 on the other end face 12 in the same manner as the optical fiber laser 50A of the first embodiment. It has.
The length of the optical amplifying medium fiber 10 is relatively long in order to obtain high-intensity laser light. The pumping light incident from the pumping light incident optical fiber 20 is attenuated as it propagates through the optical amplifying medium fiber 10, so that the pumping light is not significantly attenuated in the longitudinal direction of the optical amplifying medium fiber 10. A plurality of excitation light incidence structures 13 and 13 are provided.
The configuration of each excitation light incident structure 13 is the same as that of the above-described excitation light incident structure, and the excitation light source 26 is provided for each excitation light incident structure 13.

  According to the optical fiber laser 50B of the present embodiment, even when the length of the optical amplifying medium fiber 10 is longer than the length at which the pumping light is attenuated in the optical amplifying medium fiber 10, the pumping light is optically amplified. Can be supplied over the entire length. Therefore, high-intensity laser light 53 can be obtained.

FIG. 11 is a schematic configuration diagram showing a third embodiment of the optical fiber laser of the present invention. This optical fiber laser 50C is an optical amplifying medium fiber 10 having a total reflection mirror 51 on one end face 11 and an output mirror 52 on the other end face 12 in the same manner as the optical fiber laser 50A of the first embodiment. It has.
The optical amplifying medium fiber 10 has an inner clad exposed portion 14 formed at an intermediate portion in the longitudinal direction. The optical amplifying medium fiber 10 has a length sufficient for optical excitation on both sides of the inner cladding exposed portion 14.

  Two optical fibers 20 and 20 for exciting light incidence are joined to the inner cladding exposed portion 14 and are joined in directions facing the output mirror 52 side and the total reflection mirror 51 side, respectively. A pumping light source 26 is coupled to the end face 25 opposite to the end face 23 joined to the optical amplifying medium fiber 10 of the pumping light incident optical fiber 20.

  According to the optical fiber laser 50C of the present embodiment, the two excitation light incident optical fibers 20 can be joined to the inner clad exposed portion 14 at one location, so that the output mirror 52 side is closer to the inner clad exposed portion. It is possible to excite both the portion of the optical amplification medium fiber 10 and the portion of the optical amplification medium fiber 10 that is closer to the total reflection mirror 51 than the exposed inner cladding portion, so that a high-intensity laser beam 53 can be obtained. it can.

Although the present invention has been described based on the preferred embodiment, the present invention is not limited to this embodiment, and various modifications can be made without departing from the gist of the present invention.
The number of pumping light incident structures provided on one optical amplifying medium fiber and the number of pumping light incident optical fibers bonded to one pumping light incident structure are not particularly limited as long as the number is one or more. Two or more may be sufficient.
Further, the optical amplifying medium fiber having a hole layer in the clad used in the present invention is not limited to the structure shown in FIG. 2, and an optical amplifying medium fiber as shown in FIG. Good. The cross-sectional shape of the holes and the number of holes are not particularly limited. However, when the outer cladding is removed by etching or the like, the connection portion between the inner cladding and the outer cladding so that the outer periphery of the inner cladding is easily exposed. The width (dimension in the circumferential direction of the cross section) is preferably relatively small.

The optical amplifying medium fiber may have two or more hole layers (for example, inside and outside) in the radial direction of the cladding. In this case, the cladding is removed up to any one of the hole layers in the inner cladding exposed portion. The outer clad is a portion of the clad that is located outside the hole layer and is removed at the inner clad exposed portion. The inner clad is located inside the hole layer and is exposed at the inner clad exposed portion. In Fig. 1, the cladding is exposed at the outer periphery. That is, in addition to the hole layer serving as a boundary for removing the clad in the inner clad exposed portion, another hole layer may be provided in one or both of the inner cladding and the outer cladding.
In addition, it is preferable that the optical amplifying medium fiber has a resin coating because it protects the optical fiber against external force or impact from the outside and can suppress damage. However, the coating is not necessarily required when used in an environment that prevents external damage. When the outer cladding is exposed without providing the coating, there is an advantage that the step of removing the coating can be omitted when the inner cladding exposed portion is formed.

Hereinafter, the present invention will be described by way of examples.
[Manufacture of optical amplification medium fiber]
A round bar made of quartz glass having a core part diameter of 2 mm and a cladding part outer diameter of 40 mm was prepared. The core of this glass rod is quartz glass to which 1500 ppm (mass ratio) erbium and about 10 mol% germanium are added, and the cladding is quartz glass.
This round bar was processed by cutting and polishing to produce a glass bar having a square cross section and a length of one side of the square of about 25 mm.

The obtained prismatic glass rod is inserted into a quartz tube having an outer diameter of 44 mm and a wall thickness of 4 mm, and the glass rod and the quartz tube are integrated using the base material manufacturing apparatus 70 shown in FIG. A base material 60 having a cross section as shown in FIG.
The obtained base material 60 is drawn by a drawing device used for drawing an ordinary optical fiber, spun so that the clad diameter is 300 μm, coated with an ultraviolet curable resin, and further irradiated with ultraviolet rays to form a resin coating. By forming, the optical amplification medium optical fiber of the present invention could be manufactured.
The obtained optical amplifying medium optical fiber had a cross section as shown in FIG. 2 and had a favorable hole layer.

It is a schematic block diagram which shows one Embodiment of the excitation light incident structure to the optical amplification medium fiber of this invention. It is sectional drawing which shows the optical amplification medium fiber used for the excitation light incident structure shown in FIG. It is sectional drawing which shows an example of the preform | base_material used for manufacture of the optical amplification medium fiber shown in FIG. It is the schematic explaining an example of the manufacturing apparatus which manufactures the base material shown in FIG. FIG. 3 is a perspective view showing an example of a state in which an inner cladding exposed portion is formed on the optical amplifying medium fiber shown in FIG. 2. It is a schematic block diagram which shows an example of the apparatus which forms an inner clad exposure part in the optical amplification medium fiber shown in FIG. It is a schematic block diagram which shows the optical fiber amplifier of 1st Embodiment. It is a schematic block diagram which shows the optical fiber amplifier of 2nd Embodiment. It is a schematic block diagram which shows the optical fiber laser of 1st Embodiment. It is a schematic block diagram which shows the optical fiber laser of 2nd Embodiment. It is a schematic block diagram which shows the optical fiber laser of 3rd Embodiment. It is sectional drawing which shows an example of an optical amplification medium fiber. It is the schematic which shows an example of the optical excitation method of the conventional optical amplification medium fiber. It is a schematic block diagram which shows the 1st example of the conventional optical fiber amplifier. It is a schematic block diagram which shows the 2nd example of the conventional optical fiber amplifier. It is a schematic block diagram which shows the 3rd example of the conventional optical fiber amplifier. It is the schematic which shows the other example of the optical excitation method of the conventional optical amplification medium fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Inner clad, 3 ... Hole layer, 4 ... Outer clad, 5 ... Cover, 6 ... Hole, 7 ... Connection part, 10 ... Optical amplification medium fiber, 13 ... Excitation light incident structure, 14 ... Inner clad exposed portion, 15 ... exposed outer clad outer periphery, 17 ... cover removal portion, 20 ... excitation light incident optical fiber, 23 ... excitation light incident optical fiber end face, 24 ... excitation light, 34 ... etching solution 40A, 40B ... optical fiber amplifiers, 50A-50C ... optical fiber lasers.

Claims (5)

A core to which a rare earth element is added, an inner cladding provided on the outer periphery of the core, a hole layer formed on the outer periphery of the inner cladding, and an outer cladding provided on the outer periphery of the hole layer And a coating provided on the outer periphery of the outer cladding, wherein the hole layer includes holes formed extending in a longitudinal direction, an outer periphery of the inner cladding, and an inner periphery of the outer cladding. An optical amplifying medium fiber etching method comprising:
After removing a portion of the coating in the longitudinal direction to form a coating removal portion, the coating removal portion is etched in a state where air is pumped from both ends of the optical amplifying medium fiber into the hole and an internal pressure is applied. A method for etching an optical amplifying medium fiber, comprising: dipping in a liquid and removing a part of the outer cladding of the optical amplifying medium fiber in a longitudinal direction to form an exposed inner clad portion.   In the optical amplifying medium fiber, the inner cladding has a polygonal cross section, the outer cladding has an annular cross section, and the connecting portion has a ridge line on the outer peripheral surface of the inner cladding on the inner surface of the outer cladding. The optical amplification medium fiber etching method according to claim 1, wherein the optical amplification medium fiber is bonded. A core to which a rare earth element is added, an inner cladding provided on the outer periphery of the core, a hole layer formed on the outer periphery of the inner cladding, and an outer cladding provided on the outer periphery of the hole layer And a coating provided on the outer periphery of the outer cladding, wherein the hole layer includes holes formed extending in a longitudinal direction, an outer periphery of the inner cladding, and an inner periphery of the outer cladding. And a pumping light incident structure manufacturing method for an optical amplifying medium fiber for making the pumping light incident on an optical amplifying medium fiber composed of a connecting part for connecting
An inner cladding exposed portion formed by removing a portion of the outer cladding in the longitudinal direction by the etching method according to claim 1 or 2 is formed on a portion of the optical amplification medium fiber in the longitudinal direction. A method for producing a pumping light incident structure for an optical amplifying medium fiber, comprising bonding an end face of the pumping light incident optical fiber to the outer periphery of the inner cladding exposed at the portion.   The end face of the excitation light incident optical fiber is formed obliquely with respect to the optical axis of the excitation light incident optical fiber, and this end face is inclined with respect to the optical amplification medium fiber at an incident angle. The method for producing a pumping light incident structure on an optical amplifying medium fiber according to claim 3, wherein bonding is performed so that the light can be incident.   The inner clad exposed portion is formed at a plurality of locations in the longitudinal direction of the optical amplifying medium fiber, and end faces of different excitation light incident optical fibers are joined to the plurality of inner clad exposed portions, respectively. The manufacturing method of the excitation light incident structure to the optical amplification medium fiber of Claim 3 or 4.

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