JP2001015835A - Laser beam generating device and optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a scattering of excitation light in an optical fiber at the time of the introduction of the excitation light into the optical fiber, and also to relax the condition of the constitution of an excitation light reflective part in a laser beam generating device which performs the generation of a laser beam and an amplification of signal light by the introduction of the excitation light into the optical fiber, and an optical amplifier. SOLUTION: One link of an optical fiber 2 using a laser active material as its core is folded back a plurality of times, the parts, which are held between the folded- back parts, of the fiber 2 are respectively arranged on a straight line, these straight line parts are arranged in almost parallel to each other, whereby the plane of the fiber 2 is formed and this plane is pinched in between two glass flat plates 5 to fuse the plane to the flat plates 5. At this time, both ends of the fiber 2 are arranged on the outsides of the flat plates 5 and a reflecting mirror 3 is mounted on the one end on one side of both ends of the fiber, which are arranged on the outsides of the flat plates. Prisms 4a and 4b for introducing excitation light/in the fiber 2 are arranged into the form of the plane of this fiber 2, and the light 7 is introduced in the fiber 2 toward the longitudinal direction of the fiber 2 via these prisms 4a and 4b. The fiber 2 introduced with the light 7 generates a laser beam and the generated laser beam is taken out from the one end on one side of the ends of the fiber 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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 method of generating laser light or amplifying light by introducing excitation light into a laser active substance in the optical fiber. The present invention relates to a laser light generating device and an optical amplifier.

[0002]

2. Description of the Related Art In recent years, in the field of optical communication or optical processing technology, practical use of a low-cost, high-output laser light generator has been desired.

Under such circumstances, an optical fiber laser oscillator or an optical waveguide type laser oscillator can easily have a single oscillation mode by designing and manufacturing by adjusting a core diameter and a refractive index difference between a core and a clad. In addition, by confining the light at high density, the interaction between the laser active substance and the light is enhanced, and by increasing the length, the interaction length can be increased, so that high-efficiency spatially high-quality laser light is generated. It is known that it can.

Here, in order to realize high output or high efficiency of a laser beam, it is necessary to efficiently excite a laser active ion or a dye or other light emitting center added region (usually a core portion) of an optical fiber or an optical waveguide. The challenge is to introduce light.

[0005] However, when the core diameter is set to a single-mode waveguide condition, the diameter is usually several tens of μm in the region where the laser active ions or dyes or other luminescent centers are added (usually the core portion).
It is generally limited to the following, and it is generally difficult to efficiently introduce excitation light into this diameter.

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 the end face is formed by total reflection caused by a difference in refractive index between the second clad portion and the clad portion. The pumping light introduced is confined in the first cladding part and the core part, and the laser light is gradually activated as the confined excitation light passes through the region (usually the core part) where laser active ions or dyes or other luminescent centers are added. 2. Description of the Related Art There is known a method in which excitation light is absorbed by ions, dyes, or other luminescent centers to output high-power laser light. This is a double clad fiber laser. (E.Snitzer, H.Po, FHakimi, R. Tumminelli, an
d BCMcCllum, in Optical Fiber Sensors, Vol.2 of
1988 OSA Tecnical Digest Series (Optical Society of
America, Washington, DC, 1988), paper PD5.).

However, in the case of a double-clad fiber laser, if the cross-sectional shape of the inner cladding is circular, it selectively passes through the vicinity of the area (usually the core) where laser active ions or dyes or other luminescent centers are added. Only the excited excitation light is efficiently absorbed by the laser active material, and the absorption efficiency of the other portions is very low. That is, there is a problem that absorption saturation occurs depending on the mode.

[0008] In order to cope with this, it has been devised to make the shape of the inner cladding rectangular. However, it is generally difficult to produce an optical fiber having a cross-sectional shape other than circular, and the mechanical strength is also insufficient. Tends to be.

[0009] To solve these problems, an optical fiber laser device for introducing excitation light from the side into a region (usually a core portion) to which laser active ions or dyes or other luminescent centers are added in an optical fiber (Japanese Patent Application Laid-Open No. HEI 9-163572). 10-1
35548) and a laser device (Japanese Unexamined Patent Application Publication No. 10-19909).
7) has been proposed.

When the excitation light is introduced from the side surface into the region (usually the core portion) where laser active ions or dyes or other luminescent centers are added, the region where laser active ions or dyes or other luminescent centers are added (usually the core portion) ), The waveguide length (L) is much longer than the diameter (d), and L / d is 10 ⁶ or more, so that the pumping energy is much larger than the method of introducing the pumping light from the cross-sectional direction of the waveguide. Can be introduced into an optical fiber or a waveguide.

Such an optical fiber laser device (Japanese Patent Application Laid-Open No. 10-135548) and a laser device (Japanese Patent Application Laid-Open No.
In 90097), since the pumping light propagates across the optical fibers, it is necessary to make the gap between the optical fibers optically high quality and low loss. Therefore, conventionally, such a low-loss configuration has been realized by adopting a configuration in which the optical fibers are embedded in an optical adhesive or a configuration in which the optical fibers are thermally fused.

[0012]

However, Japanese Patent Application Laid-Open No.
In the laser light generating apparatus and the optical amplifier disclosed in 135548 and Japanese Patent Application Laid-Open No. H10-199007, the excitation light is irradiated from the side of the optical fiber, so that the scattering of the excitation light on the optical fiber surface is large. There is.

In the laser light generator and the optical amplifier disclosed in Japanese Patent Application Laid-Open Nos. 10-135548 and 10-190997, the introduced excitation light has a curved surface in the excitation light reflecting portion that houses the optical fiber. Since it was decided to be absorbed by the core of the optical fiber while repeating total reflection on the inner surface, in order to increase the efficiency of pumping light introduction, the surface condition inside the pumping light reflector was kept good and the internal surface There is also a problem that special consideration must be given to the shape.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a laser light generator and an optical amplifier which reduce scattering when pumping light is introduced and alleviate internal configuration conditions of a pumping light reflecting portion. With the goal.

[0015]

According to the present invention, there is provided a laser light generating apparatus for generating a laser beam by supplying excitation light to a laser active material. A continuous optical fiber having an outer peripheral portion covering the optical fiber, an excitation light introducing section for introducing excitation light into the optical fiber, and an excitation light reflecting section for containing at least a part of the optical fiber and confining the excitation light inside And at least a part of the optical fibers is arranged linearly, and the optical fibers arranged linearly are arranged substantially parallel to each other to form a substantially planar bundle, and the excitation light is introduced. The laser light generator is characterized in that the section introduces excitation light into the substantially planar bundle in the longitudinal direction of the optical fiber.

Here, the optical fiber constitutes a substantially planar bundle composed of an array of linear portions, and the pumping light introducing section extends the pumping light in the longitudinal direction of the optical fiber with respect to the substantially planar bundle constituted by the optical fiber. To enhance the efficiency of introducing the excitation light into the optical fiber by confining the excitation light in the excitation light reflector.

In an optical amplifier for amplifying signal light by supplying excitation light to a laser active substance, a continuous optical fiber having a laser active substance and an outer peripheral portion covering the laser active substance; A pumping light introducing section for introducing pumping light into the fiber, and a pumping light reflecting section for containing at least a part of the optical fiber and confining the pumping light therein; at least a part of the optical fiber is linearly formed; Arranged, a substantially planar bundle is formed by arranging the optical fibers arranged in a straight line substantially in parallel with each other, and the excitation light introducing unit is configured to, with respect to the substantially planar bundle, the optical fiber There is provided an optical amplifier characterized by introducing excitation light in a longitudinal direction.

Here, the optical fiber constitutes a substantially planar bundle composed of an array of linear portions, and the pumping light introducing section extends the pumping light in the longitudinal direction of the optical fiber with respect to the substantially planar bundle constituted by the optical fiber. To enhance the efficiency of pump light introduction into the optical fiber by confining the pump light in the pump light reflector.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment will be described.

FIG. 1 is a plan view of a laser light generator 1 according to the first embodiment. The laser light generator 1 includes:
A continuous optical fiber 2 containing a laser active substance, a reflecting mirror 3 for reflecting laser light, prisms 4a and 4b for introducing excitation light 7 into the optical fiber 2, and a glass flat plate 5 for sandwiching the optical fiber 2 in a plane. It is configured.

The optical fiber 2 is folded at a plurality of places to form a bundle of optical fibers 2 having folded portions at both ends. The optical fibers 2 are arranged linearly in a portion sandwiched between the folded portions of the bundle of optical fibers 2, and the optical fibers 2 arranged linearly are arranged substantially parallel to each other, so that a planar light A bundle of fibers 2 is configured. Here, in order to align the optical fibers 2 in a plane, first, the optical fibers 2 are densely wound on an appropriate size winding drum without overlapping using an optical fiber winding machine.
The winding drum is designed so that the wound optical fiber 2 can be pulled out without disturbing the line. A few peelable adhesive tapes are applied to the wound optical fiber 2 to keep the row, and the wound optical fiber 2 is pulled out from the winding drum while keeping the row. Here, the pulled out optical fibers 2 are held down in the lateral direction while keeping the rows, and are grouped into a linear band.
The shape of the straight portion is maintained by a thin quartz plate having a groove formed in advance. 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 enough to maintain the mechanical strength, and the coating resin used for the coating should be easily removed with an organic solvent. desirable. Further, as another means for removing the coating resin, dry removal by plasma treatment is also possible. The removal of the coating resin may be not only the whole but also a part. For example, it is possible to remove only the excitation light absorbing portion and leave the loop portion with the resin as it is. In this case, when a transparent resin having a lower refractive index than the cladding is used as the coating resin, a configuration in which excitation light described later is absorbed by the core while orbiting the inside of the optical fiber 2 can be easily configured. desirable. Further, the folded portion of the optical fiber 2 is also arranged in a plane, and in this case, it is desirable that the overlap of the optical fiber 2 at the folded portion is three layers or less.

As the optical fiber 2, either a quartz-based or non-quartz-based fiber may be used, but when a non-quartz-based fiber such as fluoride glass, chalcogenite glass or tellurite glass is used, The multi-phenon absorption enables laser oscillation in the mid-infrared region including wavelengths that cannot be realized with a silica-based fiber. For example, when Ce ³⁺ is used as a core in a non-quartz fiber, laser light having a wavelength of 5 μm can be oscillated. The laser wavelengths when other materials are used as the core in the non-quartz fiber are listed as Pr ³⁺ : 5 μm, 1.3 μm.
m, 2.3 μm / Nd ³⁺ : 5 μm, 2.5 μm / T
b 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
m, 4 μm, 2 μm, 1.2 μm. Also,
In general, fluoride glass, chalcogenite glass, tellurite glass, and the like also have a higher multiphoton absorption intensity due to ESA (absorption from an excitation level) than a quartz-based fiber, and have a higher vibration frequency from a long wavelength to a short wavelength. Conversion is possible.
Examples of this include a green laser when using Er ³⁺ as a core, a red, green and blue laser when using Pr ³⁺ , and a T laser.
There is a blue laser or the like when m ³⁺ is used. When an optical amplifier is formed using fluoride glass or chalcogenite glass and Pr ³⁺ as a core, it is possible to amplify an optical signal in the 1.3 μm wavelength band, which is difficult to amplify with a quartz-based fiber. Furthermore, when an optical amplifier is configured using Er3 ⁺ as a core using multi-component aluminosilicate glass or tellurite glass, the wavelength dependence of the amplification gain in the amplification of an optical signal in a 1.5 μm band is higher than that of a silica-based fiber. Flatter, very wide band amplification is possible in multi-wavelength optical communications.

The cross section of the optical fiber 2 is circular,
Any shape such as a rectangle may be used, but when the cross-sectional shape of the optical fiber 2 is circular, the delivery efficiency of the excitation light 7 at the contact point between the straight portion and the folded portion of the bundle of the optical fiber 2 is about 70 to 90%. Low. When the cross-sectional shape of the optical fiber 2 is circular, the optical fiber 2
Is hardly absorbed by the core.
Therefore, it is desirable that the cross-sectional shape of the optical fiber 2 be something other than a circular shape such as a rectangle.

The bundle of optical fibers 2 constructed as described above is sandwiched above and below by a glass flat plate 5 whose refractive index of light is substantially the same as that of the clad of the optical fiber 2, and the bundle of optical fibers 2 is arranged in a plane. I do. At this time, the optical fiber 2
Are disposed outside the glass 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 plate 5.

Next, the bundle of optical fibers 2 sandwiched between the glass plates 5 is integrated by heat fusion.
Here, for the folded portion of the bundle of optical fibers 2,
Although heat fusion may or may not be performed, it is desirable that the heat-sealed folded portion is not heat-fused because the strength is likely to decrease.

After the thermal fusion, the surface of the glass plate 5 is polished with optical precision in order to increase the absorption efficiency of the excitation light. Here, when the polishing accuracy on the surface of the polished glass plate 5 is not sufficient, a transparent fluororesin is applied to the polished surface of the glass plate 5 or a transparent oil having a lower refractive index than the clad is applied to the glass plate 5. 5 may be applied or fluidized. When sufficient accuracy can be maintained only by polishing, the surface state after polishing may be maintained.

On the upper surface of the glass plate 5 which has been subjected to surface treatment such as surface polishing and application of a transparent fluororesin, a prism 4 is provided.
a and 4b are arranged. Here, the prisms 4a, 4b
Is formed above the linear portion of the planar bundle formed by the optical fiber 2. It is desirable that the refractive index of the light of the prisms 4a and 4b is larger than the refractive index of the light of the cladding.

FIG. 2 is a sectional view taken along line AA of FIG. The optical fiber 2 has a coaxial structure around a core 2a, which is a laser active substance, and a clad 2b surrounding the core 2a.
Since the clad 2b of each optical fiber 2 is thermally fused,
A plurality of cores 2a are scattered in the thermally fused clad 2b. The thermally fused clad 2b is sandwiched between glass plates 5 from above and below, and the transparent fluororesin layer 6 covers the glass plate 5 from above and below. Although the case where the bundle of optical fibers is planar has been described above, the bundle of optical fibers may be curved as long as the excitation light can be confined and the excitation light introduction section can be provided.

Next, the laser light generator 1 according to this embodiment
Will be described. The excitation light 7 emitted from an excitation light source (not shown) is converted into parallel light by a cylindrical lens or the like (not shown), and the excitation light 7 converted into parallel light is converted into a prism 4a made of quartz glass or the like. The optical fiber 2 is introduced into the linear portion of the bundle of the optical fibers 2 via the optical fiber 4b. Here, the excitation light source has a wavelength of 1.5.
μm, 0.98 μm, 0.9 μm, 0.8 μm, 0.6
An LD (laser diode) of 7 μm or the like can be used. Further, an LD-excited solid laser can be used as an excitation light source. In this case, the wavelength selection range is widened and 1.0
Excitation light having a wavelength of 6 μm, 1.1 μm, 0.53 μm or the like can be selected.

By introducing such excitation light 7 under the conditions described later, the introduced excitation light 7 reaches the core 2a 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. The excitation light 7 that could not be absorbed by the linear portion may be absorbed by the core 2a while circulating through the folded portion of the optical fiber 2 to reach the linear portion again.

The core 2a into which the pumping light 7 is introduced generates laser light, and the laser light travels inside the core 2a while being totally reflected at the boundary between the core 2a and the clad 2b.
Reach both ends. At this time, the laser light that has reached the side of the optical fiber 2 to which the reflection mirror 3 is attached 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. To one end of the optical fiber 2 (only Fresnel reflection exists). Optical fiber 2 without reflecting mirror 3 attached
The laser light reaching one end of the laser beam is extracted from the cross section.

FIG. 3 is a configuration diagram showing a state in which 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 cladding 2b, the angle of the excitation light 7 incident on the prism 4a between the traveling direction of the excitation light 7 and the longitudinal direction of the core 2a becomes smaller. Thus, the light is refracted at the boundary between the prism 4a and the cladding 2b. In general, the amount of scattering of the excitation light 7 when the excitation light 7 is irradiated on the core 2a is maximized when the angle between the traveling direction of the excitation light 7 and the longitudinal direction of the core 2a is 90 °, and the angle becomes The smaller the size, the smaller the scattering amount. Thus, the excitation light 7 is refracted in this way and introduced into the core 2a, so that the scattering of the excitation light 7 on the core 2a can be suppressed. 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 becomes longer each time, whereby the excitation light 7 is more efficiently transferred to the core 2a. Can be introduced.

FIG. 4 is a diagram showing the conditions under which the excitation light 7 is incident. In this figure, d is the thickness of the bundle of optical fibers 2 sandwiched between the glass plates 5, n1 is the refractive index of the light of the prism 4a, n2 is the refractive index of the light of the cladding 2b, and n3 is the refractive index of the glass plate 5. Shows the refractive index. Also, θ0 is the prism 4
a, the angle of the excitation light 7 incident on the bundle of optical fibers 2, θ1 is the angle of the excitation light 7 after refraction forms the bundle of optical fibers 2, and Δx1 is the excitation light 7 reflected inside the cladding 2 b. Represents the longitudinal component of the optical fiber 2 that travels from one reflection to the next, and Δx0 represents the distance from the point of incidence of the excitation light 7 on the cladding 2b to the edge of the prism 4a.

In the following, θ0, θ1, n1, n2, n3,
d and a relational expression regarding the total reflection angle θmax at the glass plate 5.

[0035]

Equation ¹ θ1 = cos ⁻¹ (n2 · (cos θ0) / n1)

[0036]

## EQU2 ## Δx1 = d / tan θ1

[0037]

Here, θmax = 90 ° −sin ⁻¹ (n3 / n2) Here, in order for the excitation light 7 to travel while totally reflecting inside the glass plate 5, the condition of θ1 <θmax must be satisfied. No. Further, the condition 2Δx1> Δx0 must be satisfied so that the excitation light 7 introduced from the prism 4a is not reflected by the glass plate 5 and leaks out again from the prism 4a. As a specific example, d =
0.125 mm, n1 = n2 = 1.458, n3 = 1.
33, when θ0 = 5 °, θ1 = 5 °, θmax = 2
4.2 °, 2Δx0 ≒ 2.9 mm, and Δx0 <2.
The condition of 9 mm is satisfied.

As described above, in the present embodiment, a bundle of optical fibers 2 is bent 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. From the pump light 7 substantially parallel to the optical fiber 2
And the pump light 7 in the optical fiber 2
Can be reduced, and the introduction efficiency of the excitation light 7 is improved.

Further, in this embodiment, the continuous optical fiber 2 is bent a plurality of times to form a planar bundle, and the bundle is heat-sealed to constitute the laser light generator 1. 2 can be easily heat-sealed, and the laser light generator 1 with high light resistance can be easily configured.

Further, since the optical fiber 2 is formed into a flat bundle, the cooling capacity of the optical fiber 2 is high, and no special cooling device is required. In this embodiment, the bundle of the optical fibers 2 is thermally fused. However, the optical fibers 2 may be bonded to each other by applying an inorganic or organic transparent adhesive.

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 or more planar bundles are connected in series. May be combined.

Further, in this embodiment, this configuration is used as the laser light generator 1, but the reflection mirror 3 may be removed and used as an optical amplifier.

[0043]

Embodiment 1 In the first embodiment, as the optical fiber, a continuous core diameter of 50 μm and a clad diameter of 125 were used.
A quartz glass fiber having a numerical aperture of 0.2 μm and a core thereof doped with 0.5 at% of Nd ³⁺ ions inside the core was used. The optical fibers were bent a plurality of times, and densely 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 flat plate of 200 × 15 mm. The optical fiber is sandwiched between two thin quartz plates, and under reduced pressure (10 ⁻⁴ Pa).
The following heat treatment was performed at 1550 ° C. for 30 minutes. Here, in order to prevent the optical fiber from scattering on the side of the quartz thin plate, a quartz band jig having a thickness of 0.10 mm is installed,
The sides of the quartz sheet were held.

As a result, an all-glass flat laser structure was manufactured. 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 this flat structure with a heat-resistant optical adhesive, and portions other than the prism were coated with a transparent fluororesin having a refractive index of 1.33. Further, a gold film was deposited except for the prism portion.

From the prism, a total of 40 W of excitation light having an oscillation wavelength of 0.8 μm formed into parallel light was supplied. One end face of the optical fiber presses a reflection mirror with a reflectance of 99%,
The other end face was left torn. As a result, 8 W laser oscillation in a wavelength of 1.06 μm was 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.

Next, a second embodiment will be described. FIG. 5 is a plan view showing the configuration of the laser light generator 20 in the present embodiment. The laser light generator 20 includes an optical fiber 21, a reflection mirror 22, and glass flat plates 23a and 23.
b, and a tape-shaped glass plate 24 for introducing excitation light into the optical fiber 21.

The optical fiber 21 is wound tightly without overlapping the winding drum of an appropriate size using the optical fiber winding machine described in the first embodiment, and is taken out while maintaining its shape. . The extracted optical fiber 21 has a cylindrical shape, and is held down 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, opposing side surfaces of the cylinder positioned in the pressing direction are arranged so as not to overlap with each other, and the optical fibers 21 positioned in these portions are not overlapped.
Are arranged in a straight line. The linear portion of the optical fiber 21 thus arranged is sandwiched between the glass flat plates 23a and 23b, and is directly heat-sealed. At this time, a second clad is provided on a portion of the optical fiber 21 that is not sandwiched between the glass flat plates 23a and 23b. Also, one end of the linear portion of the optical fiber 21 has an excitation light 25
A tape-shaped glass plate 24 for introduction is attached.
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 linear portion of the optical fiber 21. Is done. In addition, 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 ends of the optical fiber 21 disposed outside. The glass flat plates 23a and 23b may be on the same plane or may not be on the same plane.

FIG. 6 is a cross-sectional view showing the conditions under which the excitation light 25 introduced into the optical fiber 21 is incident. 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 between the tape-shaped glass plate and the optical fiber 21 arranged linearly. , Θ
1 is an excitation light 25 introduced into a linear portion of the optical fiber 21.
, X0 is the length of the contact portion between the tape-shaped glass plate 24 and the optical fiber 21, and x1 is the optical fiber 21.
Indicates the distance from the incident position of the excitation light 25 introduced into the optical fiber 21 to the second reflection position, where n1, n1,
n2 and n3 indicate the refractive index of the cladding layer of the tape-shaped glass plate 24, the refractive index of the cladding of the optical fiber 21, and the refractive indexes of the glass flat plates 23a and 23b, respectively. Also,
θmaxf indicates the critical reflection angle of the excitation light inside the tape-shaped glass plate 24. Below, L, d, θ0, θ1, x
The relational expressions of 0, x1, n1, n2, n3, θmaxf and θmaxs, which is the pump light critical reflection angle in the linear portion of the optical fiber 21 sandwiched between the glass plates 23a, are shown.

[0049]

## EQU4 ## θ1 = θmaxf + θ0

[0050]

X0 = L / sin θ0

[0051]

X1 = 2d / tan θ1

[0052]

[Mathematical formula-see original document] θmaxf = cos ^-1 (n1 / n2)

[0053]

## EQU8 ## where θmaxs = cos ⁻¹ (n3 / n2) where the excitation light 2 introduced from the tape-shaped glass plate 24
In order for the laser beam 5 to travel while totally reflecting the linear portion of the optical fiber 21 sandwiched between the glass plates 23a, θ1 <θ
maxs condition must be satisfied. Also, x1> so that the excitation light 25 once introduced into the optical fiber 21 from the tape-shaped glass plate 24a is reflected by the glass flat plate 23a and does not leak from the contact portion between the tape-shaped glass plate 24a and the optical fiber 21. The condition of x0 must be satisfied. As a specific example, L = 152 μm, d = 125
μm, θ0 = 15.9 °, n1 = 1.42828, n2 =
When 1.458 and n3 = 1.33, θmaxf = 8.
3 °, θ1 = 24.18 °, θmaxs = 24.19
°, x0 = 555 μm, x1 = 557 μm, and θ1
It satisfies the condition of <θmaxs and x1> x0.

The pumping light 25 thus introduced reaches the core inside the optical fiber 21, and the optical fiber 21 to which the pumping light 25 reaches 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. As a result, the generated laser light is concentrated and extracted from one end where the reflection mirror 22 is not attached.

As described above, the same effects as those of the first embodiment can be obtained by configuring the laser light generator 20 as in the present embodiment. In this embodiment, this configuration is used as the laser light generator 20, but the reflection mirror 22 may be removed and used as an optical amplifier.

[0056]

Embodiment 2 In the second embodiment, as the optical fiber, the core diameter is 40 μm and the cladding diameter is 125 × 125 μm.
The core was doped with 0.4 at% of Nd ³⁺ ions using a quartz glass fiber having a numerical aperture of 0.2 and a square cross section. Further, the surface of the optical fiber has a refractive index of 1.3.
8 with an ultraviolet curable resin. Two portions where optical fibers are linearly arranged are formed, and a 0.1 mm borosilicate glass plate 2 is formed so that the plane formed by each linear portion has a flat shape of 100 × 12 mm.
The straight part was sandwiched between the sheets.

The loop portions at both ends were hardened together with the coating with a heat-resistant adhesive, the linear portions were immersed in an organic solvent to remove the coatings, and rearranged on a borosilicate glass plate. Then, the whole was put in a decompression container, and only the linear portion was heated to 900 ° C. using a flat heater, and pressed with a heater from above and below, and the quartz fiber was sandwiched between borosilicate glass plates. At this time, an adhesive was applied again to the portion of the optical fiber protruding from the borosilicate glass, which had no coating or adhesive. Thereafter, the flat structure was 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 was applied to the surface of the glass portion to form a thin film. Unevenness has been eliminated.

A tape-like 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-shaped structure. At this time, the bonded portion of the tape-shaped glass plate was subjected to oblique polishing at an angle of 10 °. Further, a transparent ultraviolet curable resin having a wavelength of excitation light having a refractive index of 1.46 was applied to a side surface of the tape-shaped glass plate.

Then, a transparent fluororesin having a refractive index of 1.33 was coated on portions of the structure other than the excitation light introducing glass plate, and a gold film was further evaporated. A total of 20 W of excitation light having an oscillation wavelength of 0.8 μm was injected from the end faces of the two excitation light introduction tape-shaped glass plates. The excitation light could not be completely absorbed only by the linear portion, but 90% of the excitation light could not be absorbed.
It was observed that% was injected into the other linear part via the loop part.

One end face of the optical fiber was pressed against a reflecting mirror having a reflectivity of 99%, and the other end face was left as a broken surface.
As a result, laser oscillation in a wavelength of 1.06 μm at 40 W was 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.

[0061]

Embodiment 3 In the second embodiment, as the optical fiber, the core diameter is 40 μm and the cladding diameter is 125 × 125 μm.
The core was doped with 0.4 at% of Yb ³⁺ ions using a quartz glass fiber having a numerical aperture of 0.2 and a square cross section. Further, the surface of the optical fiber has a refractive index of 1.3.
8 with an ultraviolet curable resin. Two portions where optical fibers are linearly arranged are formed, and a 0.1 mm borosilicate glass plate 2 is formed so that the plane formed by each linear portion has a flat shape of 100 × 12 mm.
The straight part was sandwiched between the sheets.

The loop portions at both ends were hardened together with the coating with a heat-resistant adhesive, the linear portions were immersed in an organic solvent to remove the coatings, and rearranged on a borosilicate glass plate. Then, the whole was put in a depressurizing air, only the straight portion was heated to 900 ° C. using a flat heater, and pressed with a heater from above and below to sandwich the quartz fiber in a borosilicate glass plate. At this time, an adhesive was applied again to the portion of the optical fiber protruding from the borosilicate glass, which had no coating or adhesive. Thereafter, the flat structure was 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 was applied to the surface of the glass portion to form a thin film. Unevenness has been eliminated.

A tape-like 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-shaped structure. At this time, the bonded portion of the tape-shaped glass plate was subjected to oblique polishing at an angle of 10 °. Further, a transparent ultraviolet curable resin having a wavelength of excitation light having a refractive index of 1.46 was applied to a side surface of the tape-shaped glass plate.

Then, a transparent fluororesin having a refractive index of 1.33 was coated on portions of the structure other than the excitation light introducing glass plate, and a gold film was further deposited. A total of 20 W of excitation light having an oscillation wavelength of 0.9 μm was injected from the end face of the excitation light introduction tape-shaped glass plate. The excitation light could not be absorbed only by the linear portion, but 90% of the excitation light that could not be absorbed was:
It was observed that it was injected into the other straight part via the loop part.

One end face of the optical fiber was pressed against a mirror having a reflectivity of 99%, and the other end face was kept as a broken surface. As a result, laser oscillation in a 1.0 W wavelength band of 1.03 μm was 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.

[0066]

Embodiment 4 In the second embodiment, a core diameter of 450 μm and a cladding diameter of 500 × 500 μm were used as optical fibers.
AlF3-Z having a numerical aperture of 0.2 and a square cross-sectional shape of m
15 at% inside core using rF4 glass fiber
Was doped with Er ³⁺ ions. The surface of the optical fiber was coated with an ultraviolet curable resin having a refractive index of 1.38. Two portions where optical fibers are linearly arranged are formed, and the size of the plane formed by each linear portion is 50
It arrange | positioned so that it might be set to the flat shape of x12mm.

The loop portions at both ends of the coated fiber were hardened together with the coating with a heat-resistant adhesive, and the linear portion was immersed in an organic solvent to remove the coating and rearranged. After that, a container (glove box) whose entire atmosphere can be controlled
Then, only the linear portion of the optical fiber was pressed by a flat heater at 400 ° C. to fuse the fluoride fibers together. At this time, the resin was applied again to the portion of the optical fiber that protruded from the fused portion, to which no coating or adhesive was attached. Thereafter, the surface of the plate-shaped structure was etched by about 5 μm using 5 N nitric acid containing 20 wt% of aluminum nitrate and 5 wt% of 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 structure to eliminate surface irregularities. Then, on the surface thereof, the same composition as the cladding of the optical fiber, the thickness is 0.12 mm,
An AlF3-ZrF4 tape-like plate having a length of 150 mm and a width of 12 mm was bonded. Here, an ultraviolet curable resin transparent at the excitation light wavelength and having a refractive index of 1.43 is applied to the side surface of the tape-shaped plate. Also, an angle of 10
° oblique polishing. Thereafter, portions other than the tape-shaped plate in the flat structure were coated with a transparent fluororesin having a refractive index of 1.33.

From the end face of the tape-shaped plate of the laser generator configured as described above, a total of 1 W of excitation light oscillated from the laser diode was introduced as a pulse (10 pps, pulse width 500 μs). One end face of the optical fiber has a wavelength of 2.
A mirror having a reflectivity of 99% with respect to light of 8 μm was attached, and the other end face was left as a fractured surface. As a result, 0.1W
(10 mJ / pulss, 10 pps) wavelength 2.8 μm
The pulse laser in the band was 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.

[0069]

Embodiment 5 In this embodiment, 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 an optical fiber, and 0.5 at% N
Doped with d3 + ions. The surface of the optical fiber was coated with an ultraviolet curable resin having a refractive index of 1.38.
Forming two portions where optical fibers are arranged in a straight line,
The size of the plane formed by each straight line portion is 1000
The linear portion was sandwiched between two 0.1 mm borosilicate glass plates (trade name: Pyrex) so as to form a × 12 mm flat plate. Subsequent fabrication steps are the same as in the third embodiment.

A total of 10 W of excitation light having an oscillation wavelength of 0.8 μm was injected from the end face of the glass plate for introducing excitation light. Signal light (0 dBm) with a wavelength of 1.06 μm from one end of the optical fiber
Was introduced. When the output signal from the other end was measured with a power meter, the signal light was amplified to 30 dBm. 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.

[0071]

As described above, in the laser light generating apparatus according to the present invention, at least a part of the continuous optical fibers 2 is linearly arranged, and is formed by the arrangement of the optical fibers arranged linearly. Since the excitation light is introduced into the flat bundle in the longitudinal direction of the optical fiber, scattering of the excitation light in the optical fiber can be suppressed.

In the laser light generator of the present invention, since the pumping light is introduced into the linear portion of the optical fiber in the longitudinal direction of the optical fiber, most of the pumping light is reflected by the pumping light reflecting portion. The light is absorbed by the optical fiber before being reflected by the optical fiber, and the internal configuration conditions of the excitation light reflecting portion can be reduced.

Further, in the optical amplifier of the present invention, at least a part of the continuous optical fiber 2 is linearly arranged,
The pump light is introduced in the longitudinal direction of the optical fiber to the planar bundle formed by the arrangement of the optical fibers arranged in a straight line, so that the scattering of the pump light in the optical fiber can be reduced. It becomes possible.

In the optical amplifier of the present invention, since the pumping light is introduced into the linear portion of the optical fiber in the longitudinal direction of the optical fiber, most of the pumping light is reflected by the pumping light reflecting portion. Before the light is absorbed by the optical fiber, the internal configuration conditions of the excitation light reflecting portion can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a laser light generator according to a first embodiment.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a configuration diagram showing a state in which 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 light generator according to a second embodiment.

FIG. 6 is a cross-sectional view showing the conditions of incidence of the excitation light introduced into the optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light generator 2 Optical fiber 3 Reflection mirror 4a Prism 4b Prism 5 Glass plate 7 Excitation light

Claims (4)

[Claims] 1. A laser light generator for generating laser light by supplying excitation light to a laser active substance, comprising: a continuous optical fiber having a laser active substance and an outer peripheral portion covering the laser active substance; An excitation light introduction unit for introducing excitation light into the optical fiber; and an excitation light reflection unit for containing at least a part of the optical fiber and confining the excitation light therein, and at least a part of the optical fiber is linear. Placed in
A substantially planar bundle is formed by arranging the optical fibers arranged in a straight line substantially parallel to each other, and the excitation light introducing unit is arranged in the longitudinal direction of the optical fiber with respect to the substantially planar bundle. A laser light generator characterized by introducing excitation light toward the laser beam. 2. The laser light generator according to claim 1, wherein the substantially planar bundle is formed by fusing outer peripheral portions of the optical fibers to each other. 3. An optical amplifier for amplifying signal light by supplying excitation light to a laser active substance, comprising: a continuous optical fiber having a laser active substance and an outer peripheral portion covering the laser active substance; A pumping light introducing unit that introduces pumping light into the fiber, and a pumping light reflecting unit that accommodates at least a part of the optical fiber and confine the pumping light therein; and at least a part of the optical fiber is linear. Placed,
A substantially planar bundle is formed by arranging the optical fibers arranged in a straight line substantially parallel to each other, and the excitation light introducing unit is arranged in the longitudinal direction of the optical fiber with respect to the substantially planar bundle. An optical amplifier characterized by introducing excitation light toward the optical amplifier. 4. The optical amplifier according to claim 3, wherein said substantially planar bundle is formed by fusing outer peripheral portions of said optical fibers to each other.