JP4209554B2 - Laser light generator and optical amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser light generator and an optical amplifier using an optical fiber, and more particularly to a laser light generator and a light that generate laser light or amplify light by introducing excitation light into a laser active material in the optical fiber. Regarding amplifiers.
[0002]
[Prior art]
In recent years, in the field of optical communication or optical processing technology, it is desired to put into practical use an inexpensive and high-power laser light generator.
[0003]
Under such circumstances, an optical fiber laser oscillator or an optical waveguide type laser oscillator can be easily made into a single oscillation mode by adjusting and adjusting the core diameter and the refractive index difference between the core and the clad, and can emit light. Enhancing the interaction between the laser active substance and light by confining at a high density, and increasing the interaction length by increasing the length, it is possible to generate spatially high-quality laser light with high efficiency. It has been known.
[0004]
Here, in order to achieve high output or high efficiency of the laser beam, how to efficiently introduce the excitation light into the laser active ion or dye or other emission center addition region (usually the core) of the optical fiber or optical waveguide It will be a challenge.
[0005]
However, when the core diameter is usually set in the waveguide mode of single mode, the diameter is limited to less than a dozen μm or less of the addition region (usually the core portion) of the laser active ion or dye or other light emission center. It is generally difficult to introduce excitation light well.
[0006]
Therefore, a second clad portion made of a transparent material having a lower refractive index than the clad portion is provided outside the clad portion, and is introduced from the end face by total reflection due to the refractive index difference between the second clad portion and the clad portion. The pumped light is confined in the first cladding part and the core part, and gradually the laser active ions or dyes pass as the confined pumping light passes through the added region (usually the core part) of the laser active ions or dyes or other emission centers. There is known a method in which excitation light is absorbed by other emission centers and high-power laser light is output. This is a double clad fiber laser. (E. Snitzer, H. Po, FHakimi, R. Tumminelli, and BCMcCllum, in Optical Fiber Sensors, Vol. 2 of 1988 OSA Tecnical Digest Series (Optical Society of America, Washington, DC, 1988), paper PD5.).
[0007]
However, in the case of a double-clad fiber laser, if the cross-sectional shape of the inner cladding part is circular, excitation light that selectively transmits near the active region of the laser-active ion or dye or other emission center (usually the core part) Only the laser active material is efficiently absorbed, and the absorption efficiency of the other part is very low. That is, there is a problem that absorption saturation occurs due to the mode.
[0008]
Therefore, a device has been devised to make the shape of the inner cladding portion rectangular, but it is generally difficult to produce an optical fiber having a cross-sectional shape other than a circle, and the mechanical strength tends to be insufficient. It is.
[0009]
In order to solve these problems, an optical fiber laser device (Japanese Patent Laid-Open No. 10-135548) that introduces excitation light from the side surface into an addition region (usually a core portion) of a laser active ion or dye or other emission center in an optical fiber. ) And a laser device (Japanese Patent Laid-Open No. 10-190097) have been proposed.
[0010]
When excitation light is introduced from the side into the laser active ion or dye or other emission center addition region (usually the core), the laser active ion or dye or other emission center addition region (usually the core portion) ), The waveguide length (L) is very long compared to the diameter (d), and L / d is 10 ⁶ Therefore, much more excitation energy can be introduced into the optical fiber or the waveguide than the method of introducing the excitation light from the cross-sectional direction of the waveguide.
[0011]
In such an optical fiber laser device (Japanese Patent Laid-Open No. 10-135548) and a laser device (Japanese Patent Laid-Open No. 10-190097), the excitation light propagates across the optical fiber. In addition, it is necessary to have a low loss configuration with high quality. Therefore, conventionally, such a low-loss configuration has been realized by adopting a configuration in which the optical fiber is embedded in an optical adhesive or a configuration in which the optical fibers are thermally fused.
[0012]
[Problems to be solved by the invention]
However, in the laser beam generators disclosed in JP-A-10-135548 and JP-A-10-190097, pumping light is introduced in a direction crossing the optical fiber, and pumping light is propagated so as to cross the core row. Therefore, there is a problem that the scattering of the excitation light between the core and the clad is increased, the absorption efficiency of the excitation light is lowered, and as a result, the efficiency of the laser light generator is lowered.
[0013]
Further, in the method of receiving optical fibers disclosed in JP-A-10-135548 and JP-A-10-190097 into an optical adhesive, an optical adhesive that is an organic substance is used, so that light resistance under strong excitation is used. There is also a problem that it is inferior.
[0014]
Further, in the method of thermally fusing optical fibers disclosed in Japanese Patent Laid-Open Nos. 10-135548 and 10-190097, a bundle of optical fibers having a certain height is heat-fused at a high temperature of 1500 ° C. or higher. However, since it is difficult to select a fusion type that can withstand such a high temperature, it is difficult to maintain the shape of the optical fiber bundle after the fusion.
[0015]
Further, in the method of heat-sealing optical fibers disclosed in JP-A-10-135548 and JP-A-10-190097, a bundle of optical fibers having a certain thickness is heat-sealed. There is also a problem that a temperature difference sometimes occurs between the outside and inside of the optical fiber bundle, and uniform heat fusion is difficult.
[0016]
The present invention has been made in view of these points, and an object of the present invention is to provide a laser light generator and an optical amplifier that can efficiently introduce excitation light, have excellent light resistance, and are easy to manufacture. .
[0017]
[Means for Solving the Problems]
In the present invention, in order to solve the above-mentioned problem, in a laser beam generator for generating laser beam by supplying excitation light to a laser active substance, Said By having a laser active substance and an outer peripheral portion that covers the laser active substance, and arranging at least some of them substantially parallel to each other Bundles arranged on a plane A single optical fiber, Excitation that introduces excitation light substantially parallel to the optical fiber, the refractive index of light being substantially equal to the outer periphery, two glass flat plates sandwiching a portion other than both ends of the optical fiber, and the glass flat plate A transparent resin having a refractive index smaller than that of the outer peripheral portion covering the light introduction portion and the side of the glass plate that does not contact the optical fiber; There is provided a laser beam generator characterized by comprising:
[0019]
Also, In an optical amplifier that amplifies input light by supplying excitation light to a laser active material, the laser active material has an outer peripheral portion that covers the laser active material, and at least a part thereof is arranged substantially parallel to each other A bundle of optical fibers arranged on a plane, two glass flat plates sandwiching a portion other than both ends of the optical fiber, the refractive index of light being substantially equal to the outer peripheral portion, and the glass flat plate An excitation light introducing portion that introduces excitation light substantially parallel to the optical fiber, and a transparent resin having a refractive index smaller than that of the outer peripheral portion that covers the side of the glass plate that does not contact the optical fiber. Features optical amplifier Is provided.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the first embodiment will be described.
[0022]
FIG. 1 is a plan view of a laser beam generator 1 according to the first embodiment.
The laser beam generator 1 includes a flat optical fiber 2 including a laser active substance, a reflection mirror 3 that reflects the laser beam, prisms 4a and 4b that introduce excitation light 7 into the optical fiber 2, and the optical fiber 2 in a plane. It is comprised by the glass flat plate 5 pinched in the shape.
[0023]
The optical fiber 2 is folded at a plurality of locations, and constitutes a bundle of optical fibers 2 having folded portions at both ends. In the portion sandwiched between the folded portions of the bundle of optical fibers 2, the optical fibers 2 are arranged in a straight line, and the optical fibers 2 arranged in a straight line are arranged substantially parallel to each other, thereby obtaining a planar light. A bundle of fibers 2 is formed. Here, in order to align the optical fibers 2 in a planar shape, first, the optical fibers 2 are tightly wound using an optical fiber winder without overlapping an appropriate-sized winding drum. The winding drum is devised so that the wound optical fiber 2 can be pulled out without disturbing the row. Several peelable adhesive tapes for keeping the row are affixed to the wound optical fiber 2, and the wound optical fiber 2 is pulled out from the winding drum while keeping the row. The optical fibers 2 drawn here are crushed in the lateral direction while keeping the row and gathered into a linear strip shape. This straight line portion retains its shape with a thin quartz plate that is pre-grooved. In this step, in order to prevent the optical fiber 2 from being broken, it is desirable that the optical fiber 2 is coated with a resin coating that can maintain the mechanical strength, and the coating resin used for coating can be easily removed with an organic solvent. desirable. Further, dry removal by plasma treatment is possible as another means for removing the coating resin. The removal of the coating resin is not limited to the whole, but may be a part. For example, it is possible to remove only the excitation light absorbing portion and leave the loop portion as it is with the resin. In this case, if a transparent resin having a refractive index lower than that of the clad is used as the coating resin, it is possible to easily configure a form in which excitation light, which will be described later, is absorbed by the core while circulating inside the optical fiber 2. desirable. Further, the folded portion of the optical fiber 2 is also arranged in a planar shape. At this time, it is desirable that the overlap of the folded portion of the optical fiber 2 is three layers or less.
[0024]
As the optical fiber 2, either a silica-based fiber or a non-quartz-based fiber may be used. However, when a non-silica-based fiber such as fluoride glass, chalcogenite glass, tellurite glass, or the like is used, its low Phenon absorption enables laser oscillation in the mid-infrared region including wavelengths that cannot be realized with silica-based fibers. For example, Ce in non-quartz fiber ³⁺ Is used as the core, it is possible to oscillate laser light having a wavelength of 5 μm. When laser wavelengths when other materials are used as the core in the non-quartz fiber are listed, Pr ³⁺ : 5 μm, 1.3 μm, 2.3 μm / Nd ³⁺ : 5 μm, 2.5 μm / Tb ³⁺ : 5 μm / Dy ³⁺ : 3 μm, 1.34 μm, 1.7 μm / Ho ³⁺ : 5 μm, 4 μm, 3 μm, 2 μm / Er ³⁺ : 3 μm, 3.5 μm, 4 μm / Tm ³⁺ : 5.5 μm, 4 μm, 2 μm, and 1.2 μm. In general, fluoride glass, chalcogenite glass, tellurite glass, etc. also have a higher multiphoton absorption intensity due to ESA (absorption from the excited level), and vibration from a long wavelength to a short wavelength. Frequency up-conversion is possible. In this example, Er as the core ³⁺ Green laser, Pr when used ³⁺ Red, green and blue lasers with Tm ³⁺ There is a blue laser or the like when using. Also, using fluoride glass or chalcogenite glass, Pr ³⁺ In the case where an optical amplifier is configured with the core as a core, it becomes possible to amplify an optical signal having a wavelength band of 1.3 μm, which is difficult to amplify with a silica fiber. In addition, using multi-component aluminosilicate glass or tellurite glass, Er ³⁺ When the optical amplifier is configured with the core as the core, the wavelength dependence of the amplification gain in the optical signal amplification in the 1.5 μm band is flatter than that of the silica-based fiber, and amplification in a very wide band is possible in the multi-wavelength optical communication. Become.
[0025]
The cross-sectional shape of the optical fiber 2 may be any shape such as a circle or a rectangle. However, when the cross-sectional shape of the optical fiber 2 is a circle, excitation at the contact portion between the linear portion of the bundle of optical fibers 2 and the folded portion. The delivery efficiency of the light 7 is as low as about 70 to 90%. Moreover, when the cross-sectional shape of the optical fiber 2 is circular, the excitation light 7 traveling inside the optical fiber 2 at the folded portion is hardly absorbed by the core. For this reason, the cross-sectional shape of the optical fiber 2 is preferably other than a circular shape such as a rectangle.
[0026]
The bundle of optical fibers 2 configured as described above is sandwiched between the upper and lower sides of the optical fiber 2 by a glass plate 5 having substantially the same refractive index as that of the clad of the optical fiber 2, and the bundle of optical fibers 2 is arranged in a plane. At this time, both end faces of the optical fiber 2 are arranged outside the glass flat plate 5. A reflection mirror 3 is attached to one end face of both end faces of the optical fiber 2 arranged outside the glass flat plate 5.
[0027]
Next, the bundle of optical fibers 2 sandwiched between the glass flat plates 5 is integrated by heat-sealing. Here, the folded portion of the bundle of optical fibers 2 may or may not be heat-sealed, but the heat-sealed folded portion is highly likely to have reduced strength. It is desirable not to heat-seal.
[0028]
After heat fusion, the surface of the glass flat plate 5 is polished with optical accuracy in order to increase the absorption efficiency of excitation light. Here, when the polishing accuracy on the surface of the glass flat plate 5 after polishing is not sufficient, a transparent fluororesin is applied to the surface of the glass flat plate 5 after polishing, or transparent oil having a refractive index lower than that of the cladding is applied to the glass flat plate. It is good also as apply | coating to the surface of 5 or making it flow. If sufficient accuracy can be maintained only by polishing, the surface state after polishing may be left as it is.
[0029]
Prisms 4a and 4b are arranged on the upper surface of the glass flat plate 5 after the surface treatment such as surface polishing and transparent fluororesin application. Here, the prisms 4a and 4b are formed on the upper part of the straight portion of the planar bundle formed by the optical fiber 2. Note that the refractive index of the light of the prisms 4a and 4b is preferably larger than the refractive index of the light of the clad.
[0030]
2 is a cross-sectional view taken along the line AA in FIG.
The optical fiber 2 has a coaxial structure in which the core 2a, which is a laser active material, is centered and surrounded by the clad 2b. The AA cross section of the laser light generator 1 of this embodiment is the same as that of each optical fiber 2. Since the clad 2b is heat-sealed, a plurality of cores 2a are scattered in the heat-sealed clad 2b. The heat-sealed clad 2 b is sandwiched between the glass flat plates 5 from above and below, and the transparent fluororesin layer 6 covers the upper and lower sides of the glass flat plate 5. The case where the bundle of optical fibers is planar has been described above, but the bundle of optical fibers may be curved as long as the excitation light can be confined and the excitation light introducing portion can be provided.
[0031]
Next, the overall operation of the laser beam generator 1 in this embodiment will be described.
Excitation light 7 emitted from an excitation light source (not shown) is converted into parallel light by a cylindrical lens (not shown), and the excitation light 7 converted into parallel light is converted into a prism 4a made of quartz glass or the like. It is introduced into the straight portion of the bundle of optical fibers 2 via 4b. Here, as the excitation light source, an LD (laser diode) having a wavelength of 1.5 μm, 0.98 μm, 0.9 μm, 0.8 μm, 0.67 μm, or the like can be used. In addition, an LD-excited individual laser can be used as an excitation light source. In this case, the wavelength selection range is widened, and excitation light having a wavelength of 1.06 μm, 1.1 μm, 0.53 μm or the like can be selected.
[0032]
By introducing such excitation light 7 under the conditions described later, the introduced excitation light 7 reaches the core 2 a while repeating total reflection inside the glass plate 5. Here, it is preferable that 70% or more of the pumping light 7 to be introduced is absorbed by the core 2a of the optical fiber 2 in this linear portion. Note that the excitation light 7 that could not be absorbed by the straight line portion may be absorbed by the core 2a through the folded portion of the optical fiber 2 while circling to reach the straight line portion again.
[0033]
The core 2a into which the excitation light 7 has been introduced generates laser light. The laser light travels through the core 2a while being totally reflected at the boundary between the core 2a and the clad 2b, and reaches both ends of the optical fiber 2. At this time, the laser light that has reached the side where the reflection mirror 3 is attached at both ends of the optical fiber 2 is reflected by the reflection mirror 3, travels inside the core 2 a of the optical fiber 2, and the reflection mirror 3 is attached. It reaches one end (only Fresnel reflection exists) of the optical fiber 2 that is not. The laser beam reaching one end of the optical fiber 2 to which the reflection mirror 3 is not attached is taken out from the cross section.
[0034]
FIG. 3 is a configuration diagram showing how the excitation light 7 is introduced into the core 2a.
When the refractive index of the light of the prism 4a is larger than the refractive index of the light of the clad 2b, the excitation light 7 incident on the prism 4a has a smaller angle between the traveling direction of the excitation light 7 and the longitudinal direction of the core 2a. Thus, the light is refracted at the boundary between the prism 4a and the clad 2b. In general, the amount of scattering of the excitation light 7 when the excitation light 7 is applied to the core 2a is maximized when the angle formed by the traveling direction of the excitation light 7 and the longitudinal direction of the core 2a is 90 °, and the angle is The smaller the amount, the smaller the amount of scattering. Therefore, the excitation light 7 is refracted in this way and introduced into the core 2a, whereby the scattering of the excitation light 7 at the core 2a can be suppressed to a low level. Further, since the angle formed between the traveling direction of the excitation light 7 and the core 2a is reduced, the distance that the excitation light 7 traverses the core 2a per time becomes longer, whereby the excitation light 7 is more efficiently transmitted to the core 2a. Can be introduced.
[0035]
FIG. 4 is a diagram showing the incident conditions of the excitation light 7.
In this figure, d is the thickness of the bundle of optical fibers 2 sandwiched between the glass flat plates 5, n1 is the refractive index of the light of the prism 4a, n2 is the refractive index of the light of the clad 2b, and n3 is the glass flat plate 5. Refractive index is shown. Θ0 is the angle formed by the excitation light 7 incident on the prisms 4a and 4b with the bundle of optical fibers 2, θ1 is the angle formed by the refracted excitation light 7 with the bundle of optical fibers 2, and Δx1 is inside the cladding 2b. The longitudinal component of the optical fiber 2 at which the reflected excitation light 7 travels from one reflection to the next is shown, and Δx0 represents the distance from the incident point of the excitation light 7 to the cladding 2b to the edge portion of the prism 4a. ing.
[0036]
The relational expressions for θ0, θ1, n1, n2, n3, d and the total reflection angle θmax at the glass flat plate 5 are shown below.
[0037]
[Expression 1]
θ1 = cos ^-1 (N2 · (cos θ0) / n1)
[0038]
[Expression 2]
Δx1 = d / tan θ1
[0039]
[Equation 3]
θmax = 90 ° -sin ^-1 (N3 / n2)
Here, in order for the excitation light 7 to proceed while being totally reflected inside the glass flat plate 5, the condition of θ1 <θmax must be satisfied. Further, the condition of 2Δx1> Δx0 must be satisfied so that the excitation light 7 introduced from the prism 4a is reflected by the glass flat plate 5 and does not leak out from the prism 4a again. As a specific example, when d = 0.125 mm, n1 = n2 = 1.458, n3 = 1.33, θ0 = 5 °, θ1 = 5 °, θmax = 24.2 °, 2Δx0≈2.9 mm, The condition is satisfied by setting Δx0 <2.9 mm.
[0040]
As described above, in this embodiment, the optical fiber 2 connected to the optical fiber 2 is folded a plurality of times to form a bundle having a flat surface arranged so that a part of the optical fibers 2 are substantially parallel to each other. Since the pumping light 7 is introduced substantially in parallel with the optical fiber 2, the scattering of the pumping light 7 in the optical fiber 2 can be reduced, and the introduction efficiency of the pumping light 7 is improved.
[0041]
Further, in this embodiment, since the optical fiber 2 connected in a plurality of times is folded back to form a planar bundle, and this bundle is heat-sealed to constitute the laser light generating device 1, the bundle of optical fibers 2 is formed. Can be easily heat-sealed, and the laser light generator 1 having high light resistance can be easily configured.
[0042]
Furthermore, since the optical fiber 2 is a flat bundle, the optical fiber 2 has a high cooling capacity and does not require a special cooling device.
In this embodiment, the bundle of optical fibers 2 is heat-sealed. However, an inorganic or organic transparent adhesive may be applied to bond the optical fibers 2 together.
[0043]
Further, in this embodiment, only one bundle of the planar optical fibers 2 is configured. However, a planar bundle of a plurality of optical fibers 2 is configured, and at least two of the planar bundles are coupled in series. It is good as well.
[0044]
Furthermore, in the present embodiment, this configuration is used as the laser light generating device 1, but the reflection mirror 3 may be removed and used as an optical amplifier.
[0045]
[Example 1]
In the first embodiment, as an optical fiber, 0.5 at% Nd is formed inside the core of a silica glass fiber having a continuous core diameter of 50 μm, a cladding diameter of 125 μm, and a numerical aperture of 0.2. ³⁺ What doped ion was used. A plurality of optical fibers were folded back and closely arranged on a quartz thin plate having a thickness of 0.15 mm so that the central portion sandwiched between the folded portions became a plate shape of 200 × 15 mm. The optical fiber is sandwiched between two thin quartz plates and is subjected to reduced pressure (10 ^-Four The heat treatment was performed at 1550 ° C. for 30 minutes. Here, in order to prevent the optical fiber from being scattered on the side of the quartz thin plate, a quartz strip jig having a thickness of 0.10 mm was installed to hold the side of the quartz thin plate.
[0046]
As a result, an all glass type flat plate laser structure was produced. This flat structure was etched with a 30 wt% HF aqueous solution to reduce the thickness to 0.12 mm. Thereafter, the surface of the structure was fire polished with an oxyhydrogen burner to prepare a mirror surface. A quartz prism was attached to the flat structure with a heat-resistant optical adhesive, and a transparent fluorine resin having a refractive index of 1.33 was coated on the portion other than the prism. Further, a gold film was deposited leaving the prism portion.
[0047]
A total of 40 W of excitation light with an oscillation wavelength of 0.8 μm formed into parallel light was input from the prism. One end face of the optical fiber was pressed with a reflection mirror having a reflectance of 99%, and the other end face was left as a broken surface. As a result, it was possible to confirm laser oscillation of 8 W wavelength in the 1.06 μm band. As described above, the scattering loss of excitation light at the boundary between the core and the clad of the optical fiber can be reduced.
[0048]
Next, a second embodiment will be described.
FIG. 5 is a plan view showing the configuration of the laser beam generator 10 in this embodiment. The laser beam generator 10 includes an optical fiber 12, a glass flat plate 13, and a prism 15.
[0049]
The optical fiber 12 is tightly wound without overlapping an appropriate size winding drum using the optical fiber winder described in the first embodiment, and is taken out while maintaining its shape. The extracted optical fiber 12 has a cylindrical shape, and the optical fiber 12 is arranged in a planar shape by pushing down the cylinder obliquely.
[0050]
The optical fiber 12 arranged in a flat shape in this way is sandwiched between the glass flat plates 13 and is heat-sealed as it is. At this time, both ends of the optical fiber 12 are arranged in a state of being drawn out of the glass flat plate 13.
[0051]
A prism 15 for introducing excitation light 14 is disposed on the upper surface of the glass flat plate 13 with the optical fiber 12 interposed therebetween. The prism 15 is arranged at a position where the central axis in the longitudinal direction intersects with all the optical fibers 12 perpendicularly, and introduces the excitation light 14 substantially parallel to the optical fiber 12 located immediately below the prism 15.
[0052]
The optical fiber 12 into which the excitation light 14 has been introduced generates laser light as in the first embodiment, and the generated laser light travels inside the core of the optical fiber 12 and is extracted from both cross sections of the optical fiber 12.
[0053]
As described above, even when the optical fiber 12 is arranged as in the present embodiment, the same effect as in the first embodiment can be obtained.
In the present embodiment, this configuration is used as the laser beam generator 10, but the same configuration may be used as an optical amplifier.
[0054]
[Example 2]
In the second embodiment, 0.5 at% Nd is contained in the core of a silica glass fiber having a core diameter of 50 μm, a cladding diameter of 125 μm, and a numerical aperture of 0.2. ³⁺ A series of optical fibers doped with ions was used. After placing the optical fiber as shown in FIG. 5 described above, the optical fiber was sandwiched between two borosilicate glass plates (refractive index: 1.47) having a diameter of 250 mmφ and a thickness of 0.5 mm. This is reduced pressure (10 ^-Four Pa or less), and heated at 900 ° C. for 30 minutes to create an integrated structure without bubbles. This was ground and polished from both sides, and the thickness was adjusted to 130 μm (hereinafter referred to as planar structure).
[0055]
A quartz prism having a length of 240 mm was installed at the center of the flat plate structure. This prism has excitation light input surfaces (oblique surfaces) on both sides. Thereafter, a transparent fluororesin having a refractive index of 1.33 was coated except for the prism portion, and gold was further evaporated.
[0056]
Then, a total of 100 W of excitation light from a laser diode having an oscillation wavelength of 0.8 μm was input from both sides of the prism installed at the installed center. Both end faces of the laser fiber were left as fractured surfaces. As a result, a total of 40 W of laser oscillation in a wavelength 1.06 μm band could be confirmed. As described above, the scattering loss of the excitation light at the boundary between the core and the clad of the optical fiber can be reduced.
[0057]
Next, a third embodiment will be described.
FIG. 6 is a plan view showing the configuration of the laser beam generator 20 in this embodiment.
The laser beam generator 20 includes an optical fiber 21, a reflection mirror 22, glass flat plates 23 a and 23 b, and a tape-shaped glass plate 24 that introduces excitation light into the optical fiber 21.
[0058]
The optical fiber 21 is tightly wound without overlapping an appropriate size winding drum using the optical fiber winder described in the first embodiment, and is taken out while maintaining its shape. The extracted optical fiber 21 forms a cylindrical shape, and is pressed and arranged from the side of the cylinder while maintaining the arrangement of the bundle of optical fibers 21 on the side of the cylinder. At this time, the opposite side surfaces of the cylinder located in the pressing direction are arranged so as not to overlap each other, and the optical fibers 21 located in these portions are arranged in a straight line. The straight portion of the optical fiber 21 arranged in this manner is sandwiched between the glass flat plates 23a and 23b and is heat-sealed as it is. At this time, in the optical fiber 21, a second cladding is provided in a portion not sandwiched between the glass flat plates 23a and 23b. A tape-like glass plate 24 for introducing the excitation light 25 is attached to one end of the linear portion of the optical fiber 21. The tape-shaped glass plate 24 has a clad layer outside thereof, and the excitation light 25 travels inside the tape-shaped glass plate 24 while being totally reflected inside the clad layer, and is introduced into a straight portion of the optical fiber 21. Is done. Further, both end portions of the optical fiber 21 are disposed outside the glass flat plates 23a and 23b, and a reflection mirror 22 is attached to one end of both end portions of the optical fiber 21 disposed outside. The glass flat plates 23a and 23b may be on the same plane or not on the same plane.
[0059]
FIG. 7 is a cross-sectional view showing an incident condition of the excitation light 25 introduced into the optical fiber 21.
Here, L is the thickness of the tape-shaped glass plate 24, d is the thickness of the optical fiber 21 arranged linearly, and θ0 is the angle formed by the tape-shaped glass plate and the optical fiber 21 arranged linearly. , Θ1 is the maximum introduction angle of the excitation light 25 introduced into the linear portion of the optical fiber 21, x0 is the length of the contact portion between the tape-like glass plate 24 and the optical fiber 21, and x1 is introduced into the optical fiber 21. The distance from the incident position of the excitation light 25 to the optical fiber 21 to the second reflection position is shown. N1, n2, and n3 are the refractive index of the cladding layer of the tape-shaped glass plate 24 and the optical fiber 21, respectively. The refractive index of the cladding and the refractive indexes of the glass flat plates 23a and 23b are shown. Θmaxf represents the critical reflection angle of the excitation light inside the tape-shaped glass plate 24. Below, the relational expression of L, d, θ0, θ1, x0, x1, n1, n2, n3, θmaxf and the excitation light critical reflection angle θmaxs in the linear portion of the optical fiber 21 sandwiched between the glass flat plates 23a is shown. Show.
[0060]
[Expression 4]
θ1 = θmaxf + θ0
[0061]
[Equation 5]
x0 = L / sin θ0
[0062]
[Formula 6]
x1 = 2d / tan θ1
[0063]
[Expression 7]
θmaxf = cos ^-1 (N1 / n2)
[0064]
[Equation 8]
θmaxs = cos ^-1 (N3 / n2)
Here, in order for the excitation light 25 introduced from the tape-shaped glass plate 24 to travel while totally reflecting the linear portion of the optical fiber 21 sandwiched between the glass flat plates 23a, the condition of θ1 <θmaxs must be satisfied. I must. Further, the excitation light 25 once introduced into the optical fiber 21 from the tape-shaped glass plate 24 is reflected by the glass flat plate 23a, and does not leak from the contact portion between the tape-shaped glass plate 24 and the optical fiber 21. The condition of x0 must be satisfied. As a specific example, when L = 152 μm, d = 125 μm, θ0 = 15.9 °, n1 = 1.4428, n2 = 1.458, n3 = 1.33, θmaxf = 8.3 °, θ1 = 24. 18 °, θmaxs = 24.19 °, x0 = 555 μm, and x1 = 557 μm, satisfying the conditions of θ1 <θmaxs and x1> x0.
[0065]
The pumping light 25 introduced in this way reaches the core inside the optical fiber 21, and the optical fiber 21 that has reached the pumping light 25 generates laser light. The generated laser light reaches both ends of the optical fiber 21, and the laser light reaching one end on the side where the reflection mirror 22 is attached is reflected by the reflection mirror 22. Thereby, the generated laser light is concentrated and extracted from one end side where the reflection mirror 22 is not attached.
[0066]
Thus, even when the laser beam generator 20 is configured as in the present embodiment, the same effects as those of the first embodiment can be obtained.
In the present embodiment, this configuration is used as the laser beam generator 20, but the reflection mirror 22 may be removed and used as an optical amplifier.
[0067]
[Example 3]
In the third embodiment, a quartz glass fiber having a numerical aperture of 0.2 having a square cross section with a core diameter of 40 μm and a cladding diameter of 125 × 125 μm is used as the optical fiber, and 0.4 at% Nd is provided inside the core. ³⁺ Doped with ions. The surface of the optical fiber was coated with an ultraviolet curable resin having a refractive index of 1.38. Two borosilicate glass plates of 0.1 mm are formed so that two portions where the optical fibers are arranged in a straight line are formed, and the size of the plane formed by each straight line portion is a flat plate of 100 × 12 mm. I sandwiched the straight line.
[0068]
The loop portions at both ends were solidified with a heat-resistant adhesive together with the coating, the linear portions were immersed in an organic solvent to remove the coating, and rearranged on a borosilicate glass plate. Then, the whole was put into a vacuum vessel, and only a straight portion was heated to 900 ° C. using a flat heater, and the quartz fiber was sandwiched in a borosilicate glass plate by pressing with a heater from above and below. At this time, an adhesive was applied again to the portion of the optical fiber protruding from the borosilicate glass and having no adhesive or adhesive. Thereafter, this flat plate structure is etched with a 30 wt% HF aqueous solution to reduce the thickness to 0.12 mm, and a thin optical transparent adhesive having a refractive index of 1.47 is applied to the surface of the glass portion. Unevenness was lost.
[0069]
A tape-shaped glass plate of borosilicate glass having a thickness of 0.12 mm, a length of 150 mm, and a width of 12 mm was bonded to the flat plate-type structure. At this time, the bonded portion of the tape-shaped glass plate was obliquely polished at an angle of 10 °. Further, a transparent ultraviolet curable resin was applied to the side surface of the tape-shaped glass plate with an excitation light wavelength of a refractive index of 1.46.
[0070]
Thereafter, a transparent fluororesin having a refractive index of 1.33 was coated on a portion of the structure other than the glass plate for introducing excitation light, and a gold film was further deposited. A total of 20 W of excitation light having an oscillation wavelength of 0.8 μm was input from the end surfaces of the two tape-like glass plates for introducing excitation light. It was observed that the excitation light could not be absorbed by the straight line portion alone, but 90% of the excitation light that could not be absorbed was input to the other straight line portion through the loop portion.
[0071]
One end face of the optical fiber was pressed with a reflection mirror having a reflectance of 99%, and the other end face was left as a broken surface. As a result, it was possible to confirm laser oscillation in a 4 W wavelength band of 1.06 μm. As described above, the scattering loss of excitation light at the boundary between the core and the clad of the optical fiber can be reduced.
[0072]
[Example 4]
In the third embodiment, a quartz glass fiber having a numerical aperture of 0.2 having a square cross-sectional shape with a core diameter of 40 μm and a cladding diameter of 125 × 125 μm is used as the optical fiber, and 0.4 at% Yb is provided inside the core. ³⁺ Doped with ions. The surface of the optical fiber was coated with an ultraviolet curable resin having a refractive index of 1.38. Two pieces of 0.1 mm borosilicate glass plates are formed so that two portions where the optical fibers are arranged in a straight line are formed, and the size of the plane formed by each straight line portion is a flat plate of 100 × 12 mm. I sandwiched the straight line.
[0073]
The loop portions at both ends were solidified with a heat-resistant adhesive together with the coating, the linear portions were immersed in an organic solvent to remove the coating, and rearranged on a borosilicate glass plate. Then, the whole was put into a vacuum atmosphere, and only the straight portion was heated to 900 ° C. using a flat heater, and the quartz fiber was sandwiched between borosilicate glass plates by pressing from above and below with the heater. At this time, an adhesive was applied again to the portion of the optical fiber protruding from the borosilicate glass and having no adhesive or adhesive. Thereafter, this flat plate structure is etched with a 30 wt% HF aqueous solution to reduce the thickness to 0.12 mm, and a thin optical transparent adhesive having a refractive index of 1.47 is applied to the surface of the glass portion. Unevenness was lost.
[0074]
A tape-shaped glass plate of borosilicate glass having a thickness of 0.12 mm, a length of 150 mm, and a width of 12 mm was bonded to the flat plate-type structure. At this time, the bonded portion of the tape-shaped glass plate was obliquely polished at an angle of 10 °. Further, a transparent ultraviolet curable resin was applied to the side surface of the tape-shaped glass plate with an excitation light wavelength of a refractive index of 1.46.
[0075]
Thereafter, a transparent fluororesin having a refractive index of 1.33 was coated on a portion of the structure other than the glass plate for introducing excitation light, and a gold film was further deposited. A total of 20 W of excitation light having an oscillation wavelength of 0.9 μm was input from the end face of the tape-like glass plate for introducing excitation light. It was observed that the excitation light could not be absorbed by the straight line portion alone, but 90% of the excitation light that could not be absorbed was input to the other straight line portion through the loop portion.
[0076]
One end face of the optical fiber was pressed with a mirror having a reflectance of 99%, and the other end face was left as a broken surface. As a result, it was possible to confirm laser oscillation in a 10 W wavelength band of 1.03 μm. As described above, the scattering loss of excitation light at the boundary between the core and the clad of the optical fiber can be reduced.
[0077]
[Example 5]
In the third embodiment, an AlF3-ZrF4 glass fiber with a numerical aperture of 0.2 having a square cross-sectional shape with a core diameter of 450 μm and a cladding diameter of 500 × 500 μm is used as the optical fiber, and Er of 15 at% is contained in the core. ³⁺ Doped with ions. The surface of the optical fiber was coated with an ultraviolet curable resin having a refractive index of 1.38. Two portions where the optical fibers are arranged in a straight line are formed, and the flat surfaces formed by the respective straight portions are arranged in a flat plate shape of 50 × 12 mm.
[0078]
The loop portions at both ends of the coated fiber were hardened with a heat-resistant adhesive together with the coating, and the straight portions were immersed in an organic solvent to remove the coating and rearranged. Thereafter, the whole was put in a container (glove box) capable of controlling the atmosphere, and only the straight portion of the optical fiber was pressed with a flat heater at 400 ° C., and the fluoride fibers were fused. At this time, the resin was applied again to the portion of the optical fiber that protruded from the fused portion and that did not have a coating or adhesive. Thereafter, the surface of the flat structure was etched by about 5 μm using 5N nitric acid containing 20 wt% aluminum nitrate and 5 wt% boric acid to remove crystal grains generated on the surface. Thereafter, an optical transparent resin having a refractive index of 1.44 was thinly applied to the glass portion of the flat plate structure to eliminate surface irregularities. Then, an AlF3-ZrF4 tape-shaped plate having the same composition as the cladding of the optical fiber and having a thickness of 0.12 mm, a length of 150 mm, and a width of 12 mm was bonded to the surface. Here, the side surface of the tape-like plate is coated with an ultraviolet curable resin having a refractive index of 1.43, which is transparent at the excitation light wavelength. Further, the bonded portion of the tape-like plate was subjected to oblique polishing at an angle of 10 °. Thereafter, the portion other than the tape-like plate in the flat plate structure was coated with a transparent fluorine resin having a refractive index of 1.33.
[0079]
A total of 1 W of excitation light oscillated from the laser diode was introduced in a pulse manner from the end face of the tape-shaped plate of the laser generator thus configured (10 pps, pulse width 500 μs). A mirror having a reflectance of 99% with respect to light having a wavelength of 2.8 μm was attached to one end face of the optical fiber, and the other end face was left as a broken surface. As a result, a pulse laser with a wavelength of 2.8 μm at 0.1 W (10 mJ / puls, 10 pps) was confirmed. As described above, the scattering loss of excitation light at the boundary between the core and the clad of the optical fiber can be reduced.
[0080]
[Example 6]
In this example, a quartz glass fiber having a core diameter of 8 μm, a cladding diameter of 125 μm, and a numerical aperture of 0.1 was used as the optical fiber, and 0.5 at% Nd3 + ions were doped inside the core. The surface of the optical fiber was coated with an ultraviolet curable resin having a refractive index of 1.38. Two borosilicate glass plates of 0.1 mm are formed so that two portions where the optical fibers are arranged in a straight line are formed, and the size of the plane formed by each straight line portion is a flat plate of 1000 × 12 mm. I sandwiched the straight line. Subsequent production steps are the same as in Example 3.
[0081]
A total of 10 W of excitation light having an oscillation wavelength of 0.8 μm was input from the end face of the glass plate for introducing excitation light. Signal light (0 dBm) having a wavelength of 1.06 μm was introduced from one end face of the optical fiber. When the output signal from the other end surface was measured with a power meter, the signal light was amplified to 30 dBm. As described above, the scattering loss of excitation light at the boundary between the core and the clad of the optical fiber can be reduced.
[0082]
Next, a fourth embodiment will be described.
FIG. 8 is a plan view showing the configuration of the laser beam generator 30 in the fourth embodiment.
[0083]
The laser beam generator 30 includes a prism 31, an optical fiber 32, and a glass flat plate 33. The optical fiber 32 is arranged in a plane and spiral shape from the center toward the outside, and is sandwiched and fused by a glass flat plate 33. Here, one end of the optical fiber 32 arranged at the outermost part of the spiral is arranged outside the glass flat plate 33.
[0084]
A prism 31 for introducing the excitation light 34 is disposed on the glass flat plate 33. At this time, the prism 31 is arranged so that a part of the prism 31 is located above the center of the spiral formed by the optical fiber 32.
[0085]
The excitation light 34 introduced through the prism 31 is introduced into the optical fiber 32 in a direction substantially parallel to the optical fiber 32 forming a spiral. The optical fiber 32 into which the excitation light 34 is introduced generates laser light, and the generated laser light is extracted from one end of the optical fiber 32 disposed outside the glass plate 33.
[0086]
Thus, even when the laser beam generator 30 is configured as in the present embodiment, the same effect as in the first embodiment can be obtained.
[0087]
[Example 7]
In the fourth embodiment, a quartz glass fiber having a core diameter of 50 μm, a cladding diameter of 125 μm, and a numerical aperture of 0.2 is used as the optical fiber, and 0.5 at% Nd is formed inside the core. ³⁺ Doped with ions. The optical fibers were arranged in a spiral shape and sandwiched between two borosilicate glass plates (refractive index: 1.47) having a diameter of 250 mm and a thickness of 0.5 mm. This is reduced pressure (10 ^-Four Pa or less), and heated at 900 ° C. for 30 minutes to create an integrated structure without bubbles. This was ground and polished from both sides to adjust the thickness to 130 μm (hereinafter referred to as flat plate circular structure).
[0088]
A quartz prism having a length of 240 mm was installed at the center of the flat plate structure. This prism has excitation light input surfaces (oblique surfaces) on both sides. Thereafter, a transparent fluororesin having a refractive index of 1.33 was coated except for the prism portion, and gold was further evaporated. Then, a total of 100 W of excitation light having an oscillation wavelength of 0.8 μm was input from both sides of the prism installed at the center. Both end faces of the optical fiber were left as fractured surfaces. As a result, a total of 40 W of laser oscillation in a wavelength 1.06 μm band could be confirmed. As described above, the scattering loss of excitation light at the boundary between the core and the clad of the optical fiber can be reduced.
[0089]
【The invention's effect】
As described above, in the laser light generating apparatus of the present invention, a bundle of optical fibers is folded back multiple times, a bundle having a flat surface arranged so that parts of the optical fibers are substantially parallel to each other is formed, Since the excitation light is introduced from the upper surface or the lower surface, the scattering of the excitation light in the optical fiber can be reduced, and the introduction efficiency of the excitation light is improved.
[0090]
In addition, a series of optical fibers are folded back multiple times to form a flat bundle, and the bundle is heat-sealed to constitute a laser light generator, so that a laser light generator with high light resistance can be easily formed. It can be configured.
[0091]
Furthermore, since the optical fiber is a flat bundle, it is possible to configure a laser light generator that has a high cooling capacity of the optical fiber and does not require a special cooling device. In the optical amplifier according to the present invention, a bundle of optical fibers is folded back multiple times to form a bundle having a flat surface arranged so that parts of the optical fibers are substantially parallel to each other. Therefore, it is possible to reduce the scattering of the excitation light in the optical fiber, and the introduction efficiency of the excitation light is improved.
[0092]
Furthermore, since a series of optical fibers are folded back multiple times to form a planar bundle, and the bundle is thermally fused to form an optical amplifier, an optical amplifier with high light resistance can be easily configured. It becomes possible.
[0093]
In addition, since the optical fiber is a flat bundle, it is possible to configure an optical amplifier that has a high cooling capacity of the optical fiber and does not require a special cooling device.
[Brief description of the drawings]
FIG. 1 is a plan view of a laser beam generator according to a first embodiment.
FIG. 2 is a cross-sectional view taken along the line AA of FIG.
FIG. 3 is a configuration diagram illustrating how excitation light is introduced into a core.
FIG. 4 is a diagram showing an incident condition of excitation light.
FIG. 5 is a plan view showing a configuration of a laser beam generator according to a second embodiment.
FIG. 6 is a plan view showing a configuration of a laser beam generator according to a third embodiment.
FIG. 7 is a cross-sectional view showing an incident condition of excitation light introduced into an optical fiber.
FIG. 8 is a plan view showing a configuration of a laser beam generator according to a fourth embodiment.
[Explanation of symbols]
1 Laser beam generator
2 Optical fiber
3 Reflection mirror
4a prism
4b prism
5 Glass flat plate
7 Excitation light

Claims (7)

In a laser light generator for generating laser light by supplying excitation light to a laser active substance,
And a peripheral portion that covers the laser active material as the laser active material, and an optical fiber bundle of a stretch disposed on a plane by arranging substantially parallel to each other at least partially,
Two glass flat plates sandwiching a portion other than both ends of the optical fiber, the refractive index of light being substantially equal to the outer peripheral portion;
An excitation light introduction unit that is provided on the glass plate and introduces excitation light substantially parallel to the optical fiber;
A transparent resin having a smaller refractive index than the outer peripheral portion covering the side of the glass plate that does not contact the optical fiber;
A laser light generator characterized by comprising:   2. The laser light generator according to claim 1, further comprising a reflection mirror that is disposed on one end side of the optical fiber and reflects the generated laser light.   2. The laser beam generator according to claim 1, wherein the outer peripheral portions of a portion forming the bundle of optical fibers are fused to each other.   2. The laser beam generator according to claim 1, wherein the excitation light introducing unit is a prism having a refractive index of light larger than that of the optical fiber.   In an optical amplifier that amplifies input light by supplying excitation light to a laser active substance,
  A continuous optical fiber having a bundle shape arranged on a plane by arranging the laser active material and an outer peripheral portion covering the laser active material, and arranging at least a part thereof substantially parallel to each other;
  Two glass flat plates sandwiching a portion other than both ends of the optical fiber, the refractive index of light being substantially equal to the outer peripheral portion;
  An excitation light introduction unit that is provided on the glass plate and introduces excitation light substantially parallel to the optical fiber;
  A transparent resin having a smaller refractive index than the outer peripheral portion covering the side of the glass plate that does not contact the optical fiber;
  An optical amplifier comprising:   The optical amplifier according to claim 5, wherein the outer peripheral portions of the portion forming the bundle of optical fibers are fused to each other.   The optical amplifier according to claim 5, wherein the excitation light introducing unit is a prism having a refractive index of light larger than that of the optical fiber.

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