JP4779567B2 - Optical amplifier and laser device - Google Patents

Description

  The present invention relates to an optical amplifier and a laser device, and more particularly to an optical amplifier and a laser device including an optical fiber.

  Laser light can be used for various industrial applications. For example, laser light is used for processing for marking quality information on the surface of a component. Laser light is used for mounting semiconductor chips, repairing defects in liquid crystal pixels, and the like.

  In particular, when a large amount of information such as the date of manufacture is recorded in a minute area, it must be possible to perform accurate processing. A single mode (single mode) is more suitable as a mode of laser light used for microfabrication than a multimode (multimode).

  The laser device must meet various requirements such as being small in size, being strong against impacts, and being low in cost. In order to satisfy such a demand, conventionally, laser resonators have been individually designed according to the output of laser light, the wavelength of laser light, the mode of beam light, and the like. In addition, adjustment of the laser resonator has been performed based on know-how accumulated over many years.

  The configuration of a conventional laser apparatus for microfabrication will be described by taking an LD (Laser Diode) pumped solid state laser and a fiber laser as examples.

FIG. 16 is a diagram showing a configuration of a resonator of a conventional LD-pumped solid-state laser.
Referring to FIG. 16, laser apparatus 100 includes a resonator 102. The resonator 102 includes a crystal 104 such as YAG (Yttrium Aluminum Garnet) or YVO4, reflecting mirrors 106 and 108 facing each other through the crystal 104, and a Q switch 110 for generating pulse oscillation and outputting laser light. The Q switch 110 is a shutter such as an acousto-optic element or an electro-optic element.

  Excitation light for exciting the crystal 104 is incident on one end surface of the crystal 104 from the LD array 112 via the lens 114. When the Q switch 110 is turned on in the excited state (the shutter is opened), laser oscillation is performed and the laser beam LA is emitted from the reflecting mirror 108.

  The LD array 112 is provided with a plurality of LD elements (not shown). In order to guide the excitation light emitted from each of the plurality of LD elements to the lens 114, a plurality of optical fibers 116 are provided corresponding to each of the plurality of LD elements. A plurality of optical fibers 116 are bundled by a fiber coupling 118. The excitation light E transmitted through each of the plurality of optical fibers 116 exits from one end face of the fiber coupling 118.

  If the crystal 104 is YAG, an aperture (not shown) is provided between the reflecting mirror 108 and the crystal 104 in order to output single mode laser light. When the crystal 104 is YVO4, a crystal cut along the c-axis direction of the a-axis to c-axis crystal axes is used in order to output a single mode laser beam. The crystal cut along the c-axis is attached to the laser device 100 so that the optical path and the c-axis are in the same direction.

FIG. 17 is a diagram showing a configuration of a conventional fiber laser.
Referring to FIG. 17, the laser device 200 includes a resonator 202. The resonator 202 is a ring resonator composed of an optical fiber. Fiber Bragg gratings (hereinafter referred to as FBG) 206 and 208 are formed at both ends of the optical fiber. FBG is a diffraction grating formed in the core of an optical fiber, and functions as an optical filter.

  The optical fiber used for the resonator 202 is an optical amplification fiber in which a rare earth element is added to the core. When the excitation light enters the core, the rare earth element is excited. Further, when signal light (not shown) enters the core, stimulated emission occurs in the excited rare earth element, and thus the signal light is amplified. The wavelength of excitation light and the wavelength of signal light differ depending on the type of rare earth element.

  As in the laser apparatus 100 of FIG. 16, excitation light enters the resonator 202 from the LD array 112 via the optical fiber 116. However, the optical fiber 116 and the resonator 202 (optical fiber) are directly connected.

18 is a diagram showing the connection between the optical fiber 116 and the resonator 202 in FIG.
Referring to FIG. 18, a cross section of an optical fiber 210 constituting the resonator 202 is shown. The optical fiber 210 is provided with a core 218, and a first cladding 220 is provided so as to surround the core 218. Further, a second cladding 222 is provided so as to surround the first cladding 220.

  The end face of the optical fiber 116 is connected to the end face of 220 in the first cladding. The excitation light passing through the first cladding 220 is reflected toward the first cladding 220 at the boundary between the first cladding 220 and the second cladding 222. Excitation light that enters the core 218 from the first cladding 220 is absorbed by the core 218.

FIG. 19 is a diagram showing a configuration of a conventional optical fiber amplifier.
Referring to FIG. 19, an optical fiber amplifier 300 includes an optical amplification fiber 301, a light source 302 that emits signal light, and a plurality of light sources 304 that emit excitation light. Excitation light emitted from each of the plurality of light sources 304 enters the core of the optical amplification fiber 301 through the fiber branch line 306 and the fiber coupler 308. The signal light incident on one end surface of the light amplification fiber 301 from the light source 302 is amplified by the light amplification fiber 301. From the other end of the optical amplification fiber 301, signal light S100 is emitted as amplified signal light.

  As an example of a conventional solid-state laser, for example, in Japanese Patent No. 2893862 (Patent Document 1), a fundamental laser beam generated in a laser medium is resonated so as to pass through a nonlinear optical crystal element provided in the resonator. The solid state laser oscillator in which the optical means for generating the type II second harmonic laser beam and suppressing the coupling due to the sum frequency generation between the two polarization modes of the fundamental laser beam is provided in the resonator. Is disclosed. The solid-state laser oscillator oscillates two polarization modes of the fundamental laser beam in a single longitudinal mode, and oscillates the two polarization modes of the fundamental laser beam in a single longitudinal mode. Optical means and control means for controlling the effective resonator length of the resonator so that the oscillation intensities of the two polarization modes of the fundamental laser beam are the same are provided.

  Further, as a conventional technique for adjusting the optical axis of a laser, for example, in Japanese Patent Application Laid-Open No. 2004-47650 (Patent Document 2), a plurality of laser diodes and these laser diodes are arranged so that each light emitting point is in one direction. Disclosed is a laser device comprising a block fixedly held in an aligned state, and a collimator lens array in which a plurality of collimator lenses for collimating laser beams emitted from laser diodes are aligned in one direction. In this laser device, a smooth lens defining surface that is a predetermined distance away from the light emitting point of the laser diode and perpendicular to the light emitting axis of the laser diode is formed in front of the portion where the plurality of laser diodes of the block are fixed. The This laser apparatus is characterized in that the collimator lens array is fixed to the block in a state where one end surface of the collimator lens array is aligned with the lens defining surface.

As a conventional example of an optical fiber amplifier, for example, Japanese Patent Application Laid-Open No. 2004-297101 (Patent Document 3) discloses an optical fiber amplifier that supplies pumping light to a plurality of amplifying optical fibers to optically amplify signal light. . In this optical fiber amplifier, the plurality of amplifying optical fibers have a first amplifying fiber on the signal light input end side and a second amplifying fiber on the signal light output end side. Further, the optical fiber amplifier supplies a first gain detecting means for calculating a signal light amplification gain in the second amplifying optical fiber from the first amplifying fiber and pumping light to the first amplifying optical fiber. The first pumping light supply means, the second pumping light supply means for supplying pumping light to the second amplifying optical fiber, and the intensity of the pumping light supplied by the first pumping light supply means are made constant. Based on the first control means for controlling and the gain detected by the first gain detecting means, the second for controlling the intensity of the pumping light supplied by the second pumping light supplying means to be constant. Control means, and an isolator disposed between the first amplifying optical fiber and the second amplifying optical fiber.
Japanese Patent No. 2893862 JP 2004-47650 A JP 2004-297101 A

  In the case of the LD-pumped solid-state laser shown in FIG. 16, since the two reflecting mirrors 106 and 108 are provided, the relative position of the reflecting mirror tends to shift due to vibration or temperature change. Therefore, when the laser device is installed, adjustment for outputting laser light is necessary.

  In addition, the optical axis of the LD element must be adjusted so that excitation light emitted from a plurality of LD elements included in the LD array 112 enters the core of the optical fiber 116. Adjustment work is performed manually. Therefore, it takes time and the cost of the LD-pumped solid-state laser device increases.

  On the other hand, in the case of the fiber laser shown in FIG. 17, since the optical fiber itself is a resonator and no reflecting mirror is provided unlike the LD-pumped solid laser, it is more resistant to vibration shock than the LD solid-pump laser. . However, the work for connecting the optical fiber 116 shown in FIG. 18 to the first cladding 220 of the optical fiber 210 is performed manually. This work increases the cost of the fiber laser device. That is, in the conventional laser apparatus, since much labor is required for the adjustment work for putting the excitation light emitted from the LD element into the core, the cost of the laser apparatus is high.

  Further, in order to emit high output light (increase the amplification factor) in a conventional fiber laser or an optical amplifier using a conventional optical fiber, it is necessary to increase the length of the optical amplification fiber. However, the longer the optical fiber, the larger the area occupied by the optical fiber, which increases the size of the entire apparatus.

  An object of the present invention is to provide an optical amplifier and a laser device capable of emitting high-power light with a small and simple configuration.

  In summary, the present invention is an optical amplifier that includes a transparent plate, an optical fiber, an excitation light generator, and a reflector. The transparent plate has first and second main surfaces parallel to each other. The optical fiber is wound along a side surface that connects the first and second main surfaces, and amplifies the incident signal light with pumping light. The excitation light generator applies excitation light to the transparent plate so as to be totally reflected by the first and second main surfaces inside the transparent plate. The reflection portion wraps the optical fiber along the side surface from the peripheral portion of the first main surface to the peripheral portion of the second main surface, and the inner surface surrounding the optical fiber becomes a reflection surface that reflects the excitation light.

  Preferably, the wavelength of the excitation light and the transparency of the transparent plate are such that the critical angle of the excitation light on the first and second main surfaces is less than 45 ° with respect to the direction perpendicular to the first and second main surfaces. A refractive index is selected. The side surface is provided perpendicular to the first and second main surfaces, or at an angle equal to or less than the difference between 45 ° and the critical angle from the direction perpendicular to the first and second main surfaces. .

Preferably, the excitation light generation unit emits excitation light toward the side surface.
Preferably, the optical amplifier further includes an introduction portion that is provided on the first main surface and guides the excitation light to the transparent plate. The introducing portion has an incident surface provided with respect to the first main surface at a predetermined angle for the excitation light to be totally reflected by the first and second main surfaces inside the transparent plate.

  More preferably, the excitation light generation unit is configured so that the optical path of the excitation light incident from the excitation light generation unit and the optical path of the reflected light reflected by the reflection unit from the excitation light generation unit are orthogonal to the first main surface. The direction in which the excitation light is emitted is set so as not to overlap when viewed.

  More preferably, the direction in which the excitation light generation unit emits the excitation light is set so that the optical axis of the excitation light does not pass through the center of the first main surface when viewed from a direction orthogonal to the first main surface. Is done.

Preferably, the reflecting portion is in close contact with each of the first and second peripheral portions.
Preferably, the first and second main surfaces have the same shape in which at least a part of the outer periphery is a curve.

  More preferably, the shape of each of the first and second main surfaces is one of a circle and an ellipse.

  Preferably, the excitation light generation unit includes a plurality of excitation light sources that emit excitation light. The optical amplifier further includes a plurality of introduction portions that are provided on the first or second main surface corresponding to each of the plurality of excitation light sources and guide the excitation light to the transparent plate. Each of the plurality of excitation light sources has a direction of emitting the excitation light so that the excitation light emitted by itself does not enter the introduction portion provided corresponding to the other excitation light sources before reaching the reflection portion. Is set.

  Preferably, the excitation light generation unit is configured such that the spread of the excitation light in the first direction perpendicular to the optical axis of the excitation light and parallel to the first main surface is perpendicular to the optical axis of the excitation light and perpendicular to the first direction. The excitation light is emitted so as to be larger than the spread of the excitation light in the second direction.

  More preferably, the laser device includes any one of the optical amplifiers described above, a signal light source, and a reflecting mirror. The signal light source emits signal light incident on one end of the optical fiber. The reflecting mirror reflects a part of the signal light emitted from the other end of the optical fiber, re-enters the one end, and transmits a part of the signal light emitted from the other end.

  According to the optical amplifier and the laser device of the present invention, high-power light can be emitted while being a small and simple device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

[Embodiment 1]
FIG. 1 is a top view of the optical amplifier according to the first embodiment.

2 is a cross-sectional view taken along the line II-II in FIG.
Referring to FIGS. 1 and 2, the optical amplifier 1 includes a transparent plate 2, an optical fiber 4, an excitation light source 6, a reflection unit 8, and a signal light source 10.

  Transparent plate 2 is made of glass or acrylic resin, for example, and has main surfaces 2A and 2B parallel to each other. The transparent plate 2 has a side surface 2C that connects the main surfaces 2A and 2B. The optical fiber 4 is wound along the side surface 2C. By winding the optical fiber 4 along the side surface 2C, the optical amplifier 1 can be downsized even if the total length of the optical fiber 4 is long.

  As shown in FIG. 1, the main surfaces 2 </ b> A and 2 </ b> B have the same shape in which at least a part of the outer periphery is a curve. Specifically, the main surfaces 2A and 2B have a circular shape. When the shapes of the main surfaces 2A and 2B are polygons, if the optical fiber 4 is bent at the apex portion of the polygon, the stress concentrates on the portion, so that the optical fiber 4 is easily broken. It is possible to prevent the optical fiber 4 from being broken because at least a part of the outer periphery of the main surfaces 2A and 2B is curved. However, the main surfaces 2A and 2B may be oval in shape.

  In FIG. 1, the main surfaces 2A and 2B have a diameter (circle diameter) of about 100 mm. In addition, the thickness of the transparent plate 2 is about 3 mm, for example.

  The optical fiber 4 amplifies the signal light S1 with the pumping light E. Specifically, the optical fiber 4 is an optical amplification fiber in which a rare earth element is added to the core portion. In this embodiment, ytterbium (Yb) is used as the rare earth element. However, the rare earth element added to the core may be neodymium (Nd) or erbium (Er). Details of the optical fiber 4 will be described later.

  The excitation light source 6 corresponds to the “excitation light generation unit” of the present invention and emits excitation light E. Specifically, the excitation light source 6 is a semiconductor laser. As will be described later, the excitation light source 6 gives excitation light E to the transparent plate 2 so as to be totally reflected by the main surfaces 2A and 2B inside the transparent plate 2.

  The power of the excitation light E is 5 to 20 W, for example. The center wavelength of the excitation light E is set to 915 nm or 975 nm, which is the excitation wavelength of ytterbium. The excitation light E passes through the transparent plate 2 while spreading in the direction along the main surface 2A. As a result, it is possible to prevent high-power light from concentrating on one place where the optical fiber 4 is located, so that damage to the optical fiber 4 can be prevented.

  The reflecting portion 8 wraps the optical fiber 4 together with the side surface 2C from the peripheral portion 2D of the main surface 2A to the peripheral portion 2E of the main surface 2A. In the reflecting portion 8, the inner surface that wraps the optical fiber 4 is a reflecting surface that reflects the excitation light E emitted from the side surface 2 C to the outside of the transparent plate 2. For example, the reflecting portion 8 is a metal ring attached to the transparent plate 2. A metal film having a high light reflectivity such as aluminum or silver is deposited on the reflecting surface of the reflecting portion 8. When the reflective portion 8 has a wavelength selection function, a dielectric multilayer film is used instead of the metal film. Further, the reflection surface facing the side surface 2C may be a flat surface or a curved surface.

  1 and 2, the reflecting portion 8 is shown to cover the optical fiber 4 over the entire periphery of the peripheral portion 2D and the entire periphery of the peripheral portion 2E, but a part of the peripheral portions 2D and 2E (for example, an excitation light source) It may be provided only in the range in which the excitation light E emitted from E reaches. Further, the reflecting portion 8 is not limited to be provided without interruption, and a gap or a cut may be provided as long as optical amplification is substantially possible.

  The signal light S <b> 1 emitted from the signal light source 10 enters one end face of the optical fiber 4. Specifically, the signal light source 10 is a semiconductor laser. The power of the signal light S1 is, for example, 100 mW, and the center wavelength is 1035 nm or 1064 nm. When light of these wavelengths enters the ytterbium in the excited state, stimulated emission occurs, and the signal light S1 is amplified. The signal light S2 emitted from the other end surface of the optical fiber 4 is the amplified signal light S1.

  A triangular prism 21 is provided on the main surface 2A as an “introducing portion” for guiding the excitation light E to the transparent plate 2. The triangular prism 21 is made of the same material as the transparent plate 2 so that a difference in refractive index from that of the transparent plate 2 does not occur. The triangular prism 21 may be integrally formed with the transparent plate 2 or may be fixed to the main surface 2A with a transparent adhesive. However, when an adhesive is used, a material that makes the difference in refractive index as small as possible from the triangular prism 21 and the transparent plate 2 is used.

  Excitation light E from the excitation light source 6 enters the transparent plate 2 via the triangular prism 21 and is totally reflected by the main surfaces 2A and 2B. Therefore, the excitation light E is not lost while traveling through the transparent plate 2. The excitation light E enters the core portion from the side surface of the optical fiber 4 wound along the side surface of the transparent plate 2. In the optical amplifier 1, it is not necessary to adjust the optical axis for entering the pumping light from the end face of the optical fiber, which is necessary in the conventional optical fiber amplifier. Further, by using the reflecting portion 8, the excitation light that has passed through the optical fiber 4 can be returned to the optical fiber 4. Therefore, the optical fiber can be excited efficiently. Further, a laser device can be realized by combining the optical amplifier 1 and the resonator.

  Next, the conditions under which the excitation light E is totally reflected inside the transparent plate 2 will be described with reference to the drawings.

  FIG. 3 is a diagram showing the traveling direction of the excitation light E when the triangular prism 21 is not provided on the main surface 2A.

  Referring to FIG. 3, excitation light E that enters transparent plate 2 (for example, a glass plate) from the air is refracted at main surfaces 2A and 2B and exits again into the air. Without the triangular prism 21, total reflection of the excitation light E does not occur in the transparent plate 2, and the excitation light E cannot be confined.

  FIG. 4 is a diagram showing the traveling direction of the excitation light E when the triangular prism 21 is provided on the main surface 2A.

  Referring to FIG. 4, since the triangular prism 21 and the transparent plate 2 are made of the same material, the refractive indexes are equal. Therefore, the excitation light E travels straight through the triangular prism 21 and the transparent plate 2 and reaches the main surface 2B at an incident angle θ1. Here, if the refraction angle θ2 becomes 90 °, the excitation light E travels inside the transparent plate 2 without coming into the air. The incident angle θ1 at this time is referred to as a “critical angle”. When the refractive index of air is 1, and the refractive index of the transparent plate 2 is n, the incident angle θ1 that satisfies n × sin θ1 = 1 is the critical angle according to Snell's law.

  If the incident angle θ1 is larger than the critical angle, the excitation light E is totally reflected by the main surface 2B. In addition, even on the main surface 2A parallel to the main surface 2B, the incident angle of the excitation light E is θ1, so that the excitation light E is totally reflected. In this way, the total reflection can be caused by making the excitation light E incident through the triangular prism 21.

  An angle formed by the slope A (incident surface) of the triangular prism 21 with respect to the main surface 2A is defined as θ. The angle θ corresponds to the “predetermined angle” in the present invention. If the excitation light source 6 is in contact with the inclined surface A as shown in FIG. 4 and the excitation light E does not spread, θ = θ1. However, in actuality, if static electricity is generated on the surface of the triangular prism 21, the excitation light source 6 may be damaged by the static electricity, so the excitation light source 6 is provided away from the inclined surface A. The excitation light E travels while spreading. Considering these points, the angle θ is determined as follows.

FIG. 5 is a diagram for explaining the angle θ when the spread of the excitation light E is taken into consideration.
Referring to FIG. 5, let J be the optical axis of excitation light E. The optical axis J is perpendicular to the slope A. In addition, a straight line parallel to the optical axis J (that is, a perpendicular to the slope A) is defined as B1. Since the angle (spreading angle) formed by the excitation light E with respect to the optical axis J is ψ1, the angle formed by the excitation light E and the perpendicular B1 is also ψ1. The excitation light E is refracted when entering the triangular prism 21. The refraction angle is angle ψ2. The excitation light E is totally reflected by the main surface 2B. The perpendicular of main surface 2B is defined as B2. The angle formed by the excitation light E with respect to the perpendicular B2 is ψ3. Here, the angle ψ3 is a critical angle.

Regarding the angles θ, ψ2, and ψ3, the relationship of the following formula (1) is established.
θ = ψ2 + ψ3 (1)
The refractive indexes of the triangular prism 21 and the transparent plate 2 are n. According to Snell's law, the relations of the following expressions (2) and (3) are established for the angles ψ1 to ψ3.

sinψ1 = n × sinψ2 (2)
n × sin ψ3 = 1 (3)
From the equations (1) to (3), the relationship shown in the following equation (4) is established for the angles θ and ψ1.

θ = sin ⁻¹ (sin ψ1 / n) + sin ⁻¹ (1 / n) (4)
For example, when the material of the transparent plate 2 is an acrylic resin, n is about 1.482. For example, when ψ1 = 12.5 °, the angle θ is about 50 ° from the equation (4). Therefore, if θ ≧ 50 ° is set, total reflection of the excitation light E occurs on the main surfaces 2A and 2B. The angle ψ3 at this time is about 42.4 °.

FIG. 6 is a cross-sectional view of the optical fiber 4 of FIG.
With reference to FIG. 6, the optical fiber 4 includes a core part 12, a clad part 14 provided around the core part 12, and a covering part 16 provided around the clad part 14. The diameters of the core portion 12, the cladding portion 14, and the covering portion 16 are 5 μm, 125 μm, and 245 μm, respectively. The NA (numerical aperture) indicating the maximum light receiving angle of the optical fiber 4 is 0.13.

  Since the optical fiber 4 is a single mode fiber, the diameter of the core portion 12 is small. Therefore, if the excitation light E is to be entered from the cross section of the optical fiber 4, it is necessary to adjust the optical axis J of the excitation light source with high accuracy. However, in the present embodiment, excitation light enters the core portion from the side surface direction of the optical fiber. Therefore, since the diameter of the core part 12 is small, even if the excitation light E emitted from the transparent plate 2 passes through the optical fiber 4, the amount of excitation light absorbed by the core part 12 is increased by repeating reflection at the reflection part 8. be able to. Therefore, it is not necessary to adjust the optical axis of the excitation light E with high accuracy. Further, the light emitted from the optical fiber has a small beam diameter and high power.

  The covering portion 16 is a transparent resin such as acrylic. The covering portion disperses the stress when the optical fiber 4 is bent. When the excitation light E is concentrated on one side of the side surface of the optical fiber 4, the covering portion of that portion is melted. As a result, the optical fiber 4 is easily broken due to stress concentration in the melted portion of the coating. Therefore, it is preferable that the excitation light E spreads as much as possible.

FIG. 7 is a schematic diagram showing a light emitting part of an LD chip used for the excitation light source 6.
With reference to FIG. 7, the state which looked at the light emission part 61 of the excitation light source 6 (LD chip) from the opposite side of the slope A is shown. The slope A is a plane perpendicular to the optical axis of the excitation light E as shown in FIG. The length of the light emitting portion 61 in the direction parallel to the main surface 2A (C1-C2 axis direction in FIG. 7) is the length of the slope A in the direction perpendicular to the axis C1-C2 direction (C3-C4 axis direction in FIG. 7). Shorter than that. Specifically, for example, the length of the side a1 of the light emitting unit 61 is 100 μm, and the length of the side a2 is 1 μm.

  The light emitted from the narrow slit is diffracted more greatly, but the same phenomenon occurs in the excitation light E emitted from the excitation light source 6. Therefore, as shown in FIG. 7, on the slope A perpendicular to the optical axis of the excitation light E, the spread of the excitation light E in the first direction (C1-C2 axis direction) parallel to the main surface 2A is C1 on the slope A. It becomes larger than the spread of the excitation light E in the second direction (C3-C4 axis direction) perpendicular to the -C2 axis direction.

  In the present embodiment, the excitation light E can be efficiently put into the transparent plate 2 by suppressing the excitation light E from spreading in the C3-C4 axis direction of FIG. Further, the optical fiber 4 can be prevented from being damaged by greatly spreading the excitation light E in the direction along the main surface 2A.

FIG. 8 is a diagram showing in detail the configuration of the reflection unit 8 in FIG. 1 and the surroundings.
With reference to FIG. 8, the excitation light emitted from the transparent plate 2 is reflected by the reflecting portion 8, and the light that has not been absorbed by the core portion of the optical fiber 4 reenters the transparent plate 2. The reflecting portion 8 is in close contact with the peripheral portion 2D of the main surface 2A and the peripheral portion 2E of the main surface 2B so that no gap is generated. As a result, the excitation light (reflected light) re-incident on the transparent plate 2 can be confined in the transparent plate 2. If there is a gap, the light incident on the transparent plate 2 will eventually escape to the outside of the transparent plate 2 when the reflected light enters the gap. The main surfaces 2A and 2B are preferably as flat as possible in order to bring the reflecting portion 8 into close contact with the peripheral portions 2D and 2E.

  FIG. 9 is a diagram for explaining a problem when a gap is generated between the reflecting portion 8 and the main surface 2A.

  Referring to FIG. 9, excitation light E emitted from side surface 2 </ b> C is repeatedly reflected by reflection portion 8 and enters transparent plate 2 through a gap between reflection portion 8 and main surface 2 </ b> A. In the transparent plate 2, the excitation light E is repeatedly reflected by the reflecting portion 8, but finally escapes to the outside of the transparent plate 2 at a portion where the reflecting portion 8 does not exist. This phenomenon is the same as the light refraction shown in FIG.

  A description will be given with reference to FIG. 8 again. The wavelength of the excitation light E and the refractive index n of the transparent plate 2 are such that the critical angle of the excitation light E on the main surfaces 2A and 2B of the transparent plate 2 (angle ψ3 in the figure) is perpendicular to the main surfaces 2A and 2B. The angle is set to be less than 45 °. At this time, the side surface 2C is provided perpendicular to the main surfaces 2A and 2B as shown in FIG. 8, or an angle of (45-critical angle) or less from the direction perpendicular to the main surfaces 2A and 2B. It is provided so that it may become the inclination of.

  As a result, when the excitation light E once exiting the side surface 2C and reflected by the reflecting surface enters the transparent plate 2 again from the side surface 2C, it is totally reflected by the main surfaces 2A and 2B no matter what angle it enters. Loss can be reduced. In particular, since the optical fiber 4 is wound around the side surface 2C, the excitation light E emitted outside the transparent plate 2E is scattered in various directions. According to such a configuration, the side plate 2C is transparent to the transparent plate. The excitation light incident on the inside of the main surface 2A, 2B will not escape.

  The excitation light source may be installed on the main surface 2B side, or may be installed to face the side surface of the transparent plate 2.

FIG. 10 is a diagram illustrating a modification of the first embodiment.
Referring to FIG. 10, excitation light source 6 emits excitation light E toward side surface 2C. The reflection portion 8A is different from the reflection portion 8 of FIG. 1 in that the reflection portion 8A includes a transparent light guide portion 8B through which excitation light E passes. The direction of the excitation light E (the direction of the optical axis) at the excitation light source 6 is adjusted so that the refraction angle ψ4 of the excitation light E is smaller than the above-mentioned critical angle (42.4 °). Thereby, the excitation light E incident on the inside of the transparent plate 2 from the side surface 2C is totally reflected by the main surfaces 2A and 2B.

  As described above, according to the first embodiment, a small and high output optical amplifier can be realized.

  Further, according to the first embodiment, the labor required for adjusting the optical axis for entering the excitation light into the core of the optical amplification fiber is reduced.

[Embodiment 2]
FIG. 11 is a top view of the optical amplifier according to the second embodiment.

  Referring to FIG. 11, optical amplifier 1A is different from optical amplifier 1 in FIG. 1 in that pumping light sources 6A and 6B are further provided. The pumping light sources 6A and 6B are semiconductor lasers that emit pumping light E similarly to the pumping light source 6. Further, the optical amplifier 1A differs from the optical amplifier 1 in that triangular prisms 22 and 23 are provided on the main surface 2A corresponding to the excitation light sources 6A and 6B, respectively. Since other parts of optical amplifier 1A have the same configuration as optical amplifier 1, the following description will not be repeated.

  In the second embodiment, a plurality of excitation light sources are provided. These excitation light sources constitute the “excitation light generator” of the present invention. In the second embodiment, the number of excitation light sources is variable. Therefore, according to the second embodiment, the power of the excitation light can be adjusted.

  In addition, when the excitation light emitted from a certain excitation light source is reflected and returns to the excitation light source again, there is a possibility that the light emitting portion of the excitation light source (light emitting end face of the LD element) is damaged. Therefore, in each of the excitation light sources 6, 6 </ b> A, 6 </ b> B, the direction in which the excitation light E is emitted is adjusted so that the optical axis of the excitation light does not pass through the center of the transparent plate 2 (the center M of the circle). Specifically, the optical path of the excitation light that has entered the transparent plate 2 from the excitation light source and the optical path of the reflected light that is reflected by the reflecting portion 8 of the incident excitation light E are orthogonal to the main surface 2A (in FIG. 11). The direction in which the excitation light E is emitted is adjusted so as not to overlap when viewed from a direction perpendicular to the paper surface. Thereby, since reflected light does not return to an excitation light source, damage to an excitation light source can be prevented.

FIG. 12 is a diagram showing an arrangement example of the excitation light sources 6, 6A, 6B.
Referring to FIG. 12, excitation light sources 6, 6A, 6B are provided on main surface 2A at the same positions as excitation light sources 6, 6A, 6B shown in FIG. 11, but in a direction orthogonal to main surface 2A (FIG. 12). The direction in which the excitation light E is emitted is set so that the optical axis of the excitation light E does not pass through the center M of the circle when viewed from the direction perpendicular to the paper surface in FIG. For example, the excitation light E from the excitation light source 6 reaches the reflection part 8 through the optical path PT1. The reflected light passes through the optical path PT2.

FIG. 13 is a diagram showing another arrangement example of the excitation light sources 6, 6A, 6B.
Referring to FIG. 13, positions P1 to P3 indicate the positions of excitation light sources 6, 6A and 6B in FIG. 11, respectively. In the arrangement shown in FIG. 13, the excitation light sources 6, 6A, 6B are provided at positions shifted from the positions P1 to P3 in the + Y direction, the + Y direction, and the −X direction, respectively. The triangular prisms 21 to 23 are also provided at positions corresponding to the excitation light sources 6, 6A and 6B, respectively. As a result, the optical axis of the excitation light E emitted from each of the excitation light sources 6, 6A, 6B does not pass through the center M of the circle.

  Moreover, it is necessary not only to prevent damage due to excitation light emitted from a certain excitation light source itself, but also to prevent damage due to excitation light emitted from other excitation light sources.

  FIG. 14 is a diagram showing an example in which the excitation light sources 6 and 6A are arranged so as not to be affected by the excitation light.

  Referring to FIG. 14, a cross section of the optical amplifier 1A is shown. The direction of emitting the excitation light E is set so that the excitation light emitted by itself does not enter the triangular prism 22 provided corresponding to the excitation light source 6A until the excitation light emitted from itself reaches the reflecting portion 8. The The same applies to the direction in which the excitation light source 6A emits the excitation light E. Thereby, since the excitation light emitted from one of the excitation light sources 6 and 6A does not enter the other, damage to the excitation light sources 6 and 6A can be prevented. The arrangement of the excitation light source 6B is the same as the arrangement of the excitation light sources 6 and 6A in FIG. As described above, in the second embodiment, the plurality of excitation light sources are arranged so that the optical paths do not overlap each other.

  A plurality of excitation light sources and triangular prisms may be provided on the main surface 2B side or on both sides of the main surfaces 2A and 2B. In this case as well, each of the plurality of excitation light sources does not overlap when the optical path of the excitation light emitted by itself and the optical path of the reflected light reflected by the reflection portion are viewed from a direction perpendicular to the main surface. The direction in which the excitation light is emitted is adjusted so that the excitation light emitted by itself does not enter the triangular prism provided corresponding to the other excitation light source while it reaches the reflecting portion. It needs to be adjusted.

  As described above, according to the second embodiment, the power of the excitation light can be changed by changing the number of excitation light sources.

Further, according to the second embodiment, the excitation light source can be prevented from being damaged.
[Embodiment 3]
FIG. 15 is a schematic diagram showing the configuration of the laser apparatus according to the third embodiment.

  Referring to FIG. 15, the laser device 31 includes an optical amplifier 1A, a reflecting mirror 32, collimator lenses 34A and 34B, condensing lenses 36A and 36B, and fiber aligners 38A and 38B. The laser device 31 may include the optical amplifier 1 shown in FIG. 1 instead of the optical amplifier 1A.

  The reflecting mirror 32 reflects a part of the signal light S2 emitted from the other end of the optical fiber 4 to re-enter the surface F1 at one end of the optical fiber 4, and the signal light S2 emitted from the surface F2 at the other end. Part of. When the amplification of the signal light S2 by the optical amplifier 1 and the loss of the signal light S2 by the reflecting mirror, the loss in the fiber, the quenching due to the dopant concentration, and the quenching that occurs depending on the fiber length are balanced, laser oscillation occurs, and the reflecting mirror 32 The signal light S2 that passes through becomes laser light. Note that quenching generally refers to a phenomenon in which light energy is lost as heat due to phonon emission or the like because light of an oscillation wavelength is absorbed and stored again.

The collimator lens 34A makes the signal light S1 a parallel light beam. The condensing lens 36 </ b> A condenses the signal light S <b> 1 that has become a parallel light beam in order to put the signal light S <b> 1 into one end face of the optical fiber 4.
Further, the collimator lens 34B turns the signal light S2 emitted from the optical fiber 4 into parallel light beams. The condensing lens 36B condenses the signal light S2 that has become parallel rays. The focused signal light S2 (laser light) is used for fine processing, for example. The fiber aligner 38 </ b> A is used for finely adjusting the position of the end face of the optical fiber 4.

  As shown in FIG. 15, the laser device 31 is provided with only one reflecting mirror for the optical fiber 4. Therefore, the number of reflecting mirrors is reduced as compared with a conventional LD-pumped solid-state laser, and adjustment can be easily performed even if the relative position between the optical amplifier and the reflecting mirror is shifted due to vibration shock.

  As described above, according to the third embodiment, the light emitted from the optical amplifier including the optical fiber is fed back to the optical amplifier by one reflecting mirror, so that the relative position between the reflecting mirror and the optical amplifier can be easily set. An adjustable laser device can be realized.

  The optical fibers shown in the first to third embodiments may be photonic crystal fibers. The photonic crystal is an artificial crystal in which two kinds of substances having different refractive indexes are periodically arranged with a size and an interval about the wavelength of light. Photonic crystals have wavelength selectivity, and have the property that only light having a wavelength corresponding to the period of the crystal is reflected at the interface. This is because the wavelength corresponding to the crystal period is not allowed to exist in the photonic crystal due to the energy band structure (photonic band) due to the periodic structure of the holes.

  Light having a wavelength selected by the periodic structure cannot penetrate into the photonic crystal. Therefore, light propagates through a light propagation region surrounded by the photonic crystal. The photonic crystal fiber is not subject to the various limitations that conventional optical waveguides have. For example, even if the bending radius is reduced, the amount of light leaking out of the optical fiber can be reduced. Thereby, the power of excitation light can be efficiently converted into light emitted from the fiber.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

FIG. 3 is a top view of the optical amplifier according to the first embodiment. It is sectional drawing between II-II of FIG. It is a figure which shows the advancing direction of the excitation light E in case the triangular prism 21 is not provided in the main surface 2A. It is a figure which shows the advancing direction of the excitation light E when the triangular prism 21 is provided in the main surface 2A. It is a figure explaining angle (theta) when the breadth of excitation light E is considered. It is sectional drawing of the optical fiber 4 of FIG. 4 is a schematic diagram showing a light emitting portion of an LD chip used for an excitation light source 6. FIG. It is a figure which shows the reflection part 8 of FIG. 1, and the surrounding structure in detail. It is a figure explaining the problem when a clearance gap arises between the reflection part 8 and 2 A of main surfaces. 6 is a diagram showing a modification of the first embodiment. FIG. 6 is a top view of an optical amplifier according to a second embodiment. FIG. It is a figure which shows the example of arrangement | positioning of the excitation light sources 6, 6A, 6B. It is a figure which shows another example of arrangement | positioning of the excitation light sources 6, 6A, 6B. It is a figure which shows the example which has arrange | positioned the excitation light sources 6 and 6A so that it may not receive the influence of excitation light mutually. FIG. 6 is a schematic diagram illustrating a configuration of a laser device according to a third embodiment. It is a figure which shows the structure of the resonator of the conventional LD excitation solid-state laser. It is a figure which shows the structure of the conventional fiber laser. It is a figure which shows the connection of the optical fiber 116 of FIG. 17, and the resonator 202. FIG. It is a figure which shows the structure of the conventional optical fiber amplifier.

Explanation of symbols

  1, 1A optical amplifier, 2 transparent plate, 2A, 2B main surface, 2C side surface, 2D, 2E peripheral part, 4, 116, 210 optical fiber, 6, 6A, 6B excitation light source, 8, 8A reflection part, 8B light guide Part, 10 signal light source, 12 core part, 14 clad part, 16 covering part, 21-23 triangular prism, 31, 100, 200 laser device, 32, 106, 108 reflector, 34A, 34B collimator lens, 36A, 36B Optical lens, 38A, 38B fiber aligner, 61 light emitting section, 102, 202 resonator, 104 crystal, 110 Q switch, 112 LD array, 114 lens, 118 fiber coupling, 206, 208 fiber Bragg grating, 218 core, 220 1st 1 clad, 222 second clad, 300 optical fiber array 301, optical amplification fiber, 302, 304 light source, 306 fiber branch, 308 fiber coupler, A slope, B1 to B3 perpendicular, E excitation light, F1, F2 plane, J optical axis, LA laser light, M center, P1 P3 position, PT1 to PT4 optical path, S1, S2, S100 signal light, θ, ψ1 to ψ4 angles, θ1 incident angle, θ2 refraction angle.

Claims (11)

A transparent plate having first and second main surfaces parallel to each other;
An optical fiber wound along a side surface connecting the first and second main surfaces and amplifying the incident signal light with pumping light;
An excitation light generating unit that applies the excitation light to the transparent plate so as to be totally reflected by the first and second main surfaces inside the transparent plate;
A reflective surface that wraps the optical fiber together with the side surfaces from a peripheral portion of the first main surface to a peripheral portion of the second main surface, and an inner surface that wraps the optical fiber reflects the excitation light. and a reflecting portion composed,
The wavelength of the excitation light and the transparency so that the critical angle of the excitation light on the first and second main surfaces is less than 45 ° with respect to the direction perpendicular to the first and second main surfaces. The refractive index of the plate is selected,
The side surface is provided perpendicular to the first and second main surfaces, or less than a difference between 45 ° and the critical angle from a direction perpendicular to the first and second main surfaces. An optical amplifier provided at an angle .   The optical amplifier according to claim 1, wherein the excitation light generation unit emits the excitation light toward the side surface. The optical amplifier is
An introduction part provided on the first main surface for guiding the excitation light to the transparent plate;
The introduction part is
2. The incident surface provided to the first main surface at a predetermined angle for the excitation light to be totally reflected by the first and second main surfaces inside the transparent plate. Optical amplifier. The excitation light generation unit has a direction in which an optical path of excitation light incident from the excitation light generation unit and an optical path of reflected light reflected by the reflection unit of the incident excitation light are orthogonal to the first main surface The optical amplifier according to claim 3 , wherein a direction in which the excitation light is emitted is set so as not to overlap when viewed from above. When viewed from a direction orthogonal to the first main surface, the excitation light generator has a direction to emit the excitation light so that the optical axis of the excitation light does not pass through the center of the first main surface. The optical amplifier according to claim 4 , wherein the optical amplifier is set.   The optical amplifier according to claim 1, wherein the reflection portion is in close contact with each of the first and second peripheral portions.   2. The optical amplifier according to claim 1, wherein the first and second main surfaces have the same shape in which at least a part of an outer periphery is a curve. The optical amplifier according to claim 7 , wherein each of the first and second main surfaces has one of a circle and an ellipse. The excitation light generator is
A plurality of excitation light sources emitting the excitation light,
The optical amplifier is
Provided on the first or second main surface corresponding to each of a plurality of excitation light sources, further comprising a plurality of introduction portions for guiding the excitation light to the transparent plate;
Each of the plurality of excitation light sources is configured so that the excitation light emitted from the plurality of excitation light sources does not enter the introduction portion provided corresponding to another excitation light source before reaching the reflection portion. The optical amplifier according to claim 1, wherein a direction of emitting light is set.   The excitation light generation unit is configured such that a spread of the excitation light in a first direction perpendicular to the optical axis of the excitation light and parallel to the first main surface is perpendicular to the optical axis of the excitation light and the first The optical amplifier according to claim 1, wherein the excitation light is emitted so as to be larger than a spread of the excitation light in a second direction perpendicular to the direction. An optical amplifier according to any one of claims 1 to 10 ,
A signal light source that emits the signal light incident on one end of the optical fiber;
A laser device comprising: a reflecting mirror that reflects part of the signal light emitted from the other end of the optical fiber and re-enters the one end and transmits part of the signal light emitted from the other end .

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