JPWO2006098313A1 - Optical amplifier and laser device - Google Patents

Abstract

In the case of a conventional optical amplifier or fiber laser using an optical fiber, it is necessary to make the diameter of the core the same as the wavelength (about 1 to several μm) in order to propagate single mode light in the optical fiber. Therefore, even if the excitation light is irradiated from the side surface, the diameter of the core is too small, so that the excitation light absorbed by the core is reduced. Since the optical fiber (2) is a photonic crystal fiber, single mode light can be propagated even if the diameter of the light propagation region is about 100 μm, for example. Therefore, the excitation light (E) received from the side surface of the optical fiber (2) is efficiently absorbed in the light propagation region. Therefore, it is possible to provide an optical amplifier and a laser device that can emit high-output light with a small and simple configuration.

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 a photonic crystal 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 structure of a conventional laser apparatus for microfabrication will be described using an LD (Laser Diode) pumped solid state laser and a fiber laser as examples.

  FIG. 14 is a diagram showing a configuration of a resonator of a conventional LD-pumped solid-state laser. Referring to FIG. 14, the laser device 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 pulsed 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 input from the LD array 112 through the lens 114 to one end surface of the crystal 104. 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 excitation light emitted from each of the plurality of LD elements to the lens 114, a plurality of optical fibers 116 corresponding to each of the plurality of LD elements are provided. A plurality of optical fibers 116 are bundled by a fiber coupling 118. Excitation light E transmitted through each of the plurality of optical fibers 116 is emitted 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. 15 is a diagram showing a configuration of a conventional fiber laser. Referring to FIG. 15, the laser device 200 includes a resonator 202. The resonator 202 is a ring resonator composed of an optical fiber. Fiber Bragg gratings (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 has a function 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. Note that the wavelength of the excitation light and the wavelength of the signal light differ depending on the type of rare earth element.

  As in the laser apparatus 100 of FIG. 14, 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.

  FIG. 16 is a diagram showing the connection between the optical fiber 116 and the resonator 202 of FIG. Referring to FIG. 16, the optical fiber 210 constitutes a resonator 202. FIG. 16 shows a cross section of the optical fiber 210. 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 the second cladding 222. 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. 17 is a diagram showing a configuration of a conventional optical fiber amplifier. Referring to FIG. 17, 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. Thus, a solid-state laser oscillator in which an optical means for generating a second harmonic laser beam and suppressing coupling due to generation of a sum frequency between two polarization modes of the fundamental laser beam is provided in the resonator is disclosed. . This solid-state laser oscillator has optical means for oscillating the two polarization modes of the fundamental laser beam in a single longitudinal mode, and the oscillation intensity of the two polarization modes of the fundamental laser beam is the same. Control means for controlling the effective resonator length of the resonator is provided.

  In addition, 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 with their light emitting points in one direction. Disclosed is a laser device comprising: a block fixedly held in an aligned state; and a collimator lens array formed by integrating a plurality of collimator lenses that collimate laser beams emitted from laser diodes in a parallel state. . 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 collimator lens array is fixed to the block in a state in which 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 include a first amplifying fiber on the signal light input end side and a second amplifying fiber on the signal light output end side. The optical fiber amplifier also 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 LD-pumped solid-state laser shown in FIG. 14, since the two reflecting mirrors 106 and 108 are provided, the relative positions of the reflecting mirrors are likely to shift due to vibration and 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. Since the adjustment work is performed manually, 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. 15, 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 pumped laser. . However, the work for connecting the optical fiber 116 to the first cladding 220 of the optical fiber 210 is manually performed. 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.

  In addition, in order to emit high output light (increase the amplification factor) in an optical amplifier using an optical fiber, it is necessary to increase the length of the optical amplification fiber. Since the occupied area becomes larger, the entire apparatus becomes larger. Even if the optical fiber is bent in order to reduce the area occupied by the optical fiber, light escapes from the bent portion. Therefore, there is a problem that the amplification factor decreases when the optical fiber is bent.

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

  In summary, the present invention is an optical amplifier including a photonic crystal fiber that propagates signal light having a predetermined wavelength of light as a main wavelength in a single mode. The photonic crystal fiber includes a signal light propagation region for propagating signal light, and surrounds a central portion of the signal light propagation region. A periodic structure made of a medium is provided, and the signal light propagation region is doped with a light amplification substance that causes stimulated emission when signal light is incident in an excited state. The optical amplifier further includes an excitation unit that irradiates the signal light propagation wavelength from the side surface of the photonic crystal fiber toward the signal light propagation region and excites the optical material, thereby being selected according to the periodic structure. Signal light having a predetermined wavelength of light as a main wavelength is propagated in a single mode, and the signal light is amplified by irradiation with excitation light.

  According to another aspect of the present invention, an optical amplifier is a signal light source that emits signal light having a predetermined wavelength of light as a main wavelength; the signal light is received at one end surface; and the signal light is propagated in a single mode. A photonic crystal fiber emitting from the other end surface. The photonic crystal fiber includes a signal light propagation region for propagating signal light, and surrounds a central portion of the signal light propagation region. A periodic structure made of a medium is provided, and the signal light propagation region is doped with a light amplification substance that causes stimulated emission when signal light is incident in an excited state. The optical amplifier further includes an excitation unit that irradiates excitation light having a wavelength different from that of the signal light from the side surface of the photonic crystal fiber toward the signal light propagation region and excites the optical material. The optical amplifier amplifies signal light propagating through the photonic crystal fiber.

  Preferably, the periodic structure is formed by periodically providing holes in the solid medium constituting the photonic crystal fiber in the cross section of the photonic crystal fiber.

  The pores have no solid medium and air is present. Individual vacancies constituting the periodic structure in the cross section are vacancies in which the same cross-sectional shape is continuously connected from one end face to the other end face of the photonic crystal fiber.

  According to still another aspect of the present invention, a laser apparatus includes an optical amplifier. The optical amplifier includes a photonic crystal fiber that propagates signal light whose main wavelength is light of a predetermined wavelength in a single mode. A photonic crystal fiber has a signal light propagation region for propagating signal light, and has a plurality of refractive indexes that satisfy Bragg reflection conditions for light of a predetermined wavelength so as to surround a central portion of the signal light propagation region. And a light amplifying substance that induces stimulated emission when signal light is incident in an excited state in the signal light propagation region. The optical amplifier further includes a pumping unit that irradiates pumping light having a wavelength different from that of the signal light from the side surface of the photonic crystal fiber toward the signal light propagation region, thereby exciting the optical material, and is thereby selected by the periodic structure Signal light having a predetermined wavelength of light as a main wavelength is propagated in a single mode, and the signal light is amplified by irradiation with excitation light. The laser device further includes a reflection part that reflects the signal light on each end face of the photonic crystal fiber.

  According to still another aspect of the present invention, a laser apparatus includes an optical amplifier. The optical amplifier includes a photonic crystal fiber that propagates signal light whose main wavelength is light of a predetermined wavelength in a single mode. The photonic crystal fiber has a signal light propagation region for propagating signal light, and has a plurality of refractive indexes different from each other so as to satisfy the Bragg reflection condition for light of a predetermined wavelength so as to surround the central portion of the signal light propagation region. And a light amplifying substance that induces stimulated emission when signal light is incident in an excited state in the signal light propagation region. The optical amplifier further includes a pumping unit that irradiates pumping light having a wavelength different from that of the signal light from the side surface of the photonic crystal fiber toward the signal light propagation region, thereby exciting the optical material, and is thereby selected by the periodic structure Signal light having a predetermined wavelength of light as a main wavelength is propagated in a single mode, and the signal light is amplified by irradiation with excitation light. The laser device further includes a return portion for returning the signal light reaching the one end surface of the photonic crystal fiber to the other end surface of the photonic crystal fiber.

  More preferably, the photonic crystal fiber is installed such that the one end face and the other end face are close to each other, and the return portion reflects a part of the signal light emitted from the other end face and enters the one end face, It is a reflecting mirror that transmits part of the signal light emitted from the other end surface.

  More preferably, the laser device further includes a first reflection unit that is provided on the opposite side of the excitation unit with respect to the photonic crystal fiber and reflects the excitation light toward the photonic crystal fiber.

  More preferably, the laser device further includes a second reflection unit provided between the photonic crystal fiber and the excitation unit, and the second reflection unit transmits the excitation light emitted from the excitation unit, The excitation light reflected by the reflecting portion of the light is reflected toward the photonic crystal fiber.

  More preferably, the outer shape of the first reflecting portion is at least a part of an ellipse, and the photonic crystal fiber is arranged so that the position of the light propagation region is the position of the focal point of the ellipse.

  More preferably, the photonic crystal fiber has a shape in which a cross section perpendicular to the propagation direction of the signal light is at least a part of an ellipse, and the light propagation region is disposed at the focal point of the ellipse.

  More preferably, the photonic crystal fiber generates signal light by itself by spontaneous emission generated in the light amplification material in response to excitation light emitted from any one of the plurality of excitation light sources, and the generated signal light This causes stimulated emission in the light amplification substance.

  More preferably, the excitation unit irradiates the photonic crystal fiber with excitation light so that the incident angle becomes a Brewster angle.

More preferably, the excitation unit includes a plurality of excitation light sources that continuously emit excitation light.
More preferably, the return portion is optically coupled to the one end surface and returns the signal light reaching the one end surface toward the other end surface, and is optically coupled to the other end surface, and the other end surface. And a second fiber grating structure that returns the signal light that has reached to one end surface.

  More preferably, the laser device further includes an optical waveguide unit provided between the excitation unit and the photonic crystal fiber to guide the excitation light to a side surface of the photonic crystal fiber, and the optical waveguide unit provides the excitation light in a planar shape. The photonic crystal fiber is provided along the light emitting surface.

More preferably, the optical waveguide unit is made of a foldable material.
More preferably, the laser device is provided on the side opposite to the light emitting surface with respect to the photonic crystal fiber, and includes a reflecting portion that reflects the excitation light toward the photonic crystal fiber, and the light emitting surface and the photonic crystal fiber. And a transmissive portion that is provided between them and transmits the excitation light.

  More preferably, the transmission unit is a dichroic mirror that transmits light having a wavelength for exciting the light amplification substance in the excitation light.

More preferably, the transmission unit is a microlens array including a plurality of microlenses that collect excitation light.
More preferably, the photonic crystal fiber has a shape in which a cross section perpendicular to the propagation direction of the signal light is a parabola, and the light propagation region is disposed at the focal point of the parabola.

  More preferably, inside the light propagation region, in the cross section, another hole different from the holes forming the periodic structure is provided in the light propagation region.

  More preferably, the laser device further includes a cooling unit that circulates cooling water that immerses and cools the photonic crystal fiber.

  Preferably, the optical amplifier further includes an optical waveguide provided between the pumping unit and the photonic crystal fiber to guide the pumping light to the side surface of the photonic crystal fiber. The optical waveguide unit includes a light emitting surface for emitting excitation light in a planar shape. The photonic crystal fiber is provided along the light emitting surface.

  According to the optical amplifier of the present invention, the adjustment for inputting the excitation light to the core is simple by irradiating the side surface of the photonic crystal fiber that propagates the single mode light and performs optical amplification. In addition, it is possible to emit high output light while being small.

It is a conceptual diagram which shows the structure of the optical amplifier of this invention. It is a figure which shows typically the cross section of the optical fiber 2 of FIG. FIG. 5 is a schematic diagram illustrating a configuration of a laser device according to a second embodiment. It is the schematic which shows the structure of the optical amplifier 1 of FIG. FIG. 10 is a diagram illustrating another configuration example of the optical amplifier 1 in the second embodiment. FIG. 10 is a diagram showing still another configuration example of the optical amplifier 1 in the second embodiment. FIG. 6 is a schematic diagram illustrating a configuration of a laser device according to a third embodiment. FIG. 6 is a schematic diagram illustrating a configuration of a laser device according to a fourth embodiment. It is the figure which looked at the laser apparatus 31 of FIG. 8 from upper direction. It is sectional drawing of the line segment XX part of FIG. 6 is a diagram illustrating an example of an optical fiber 2 according to Embodiment 4. FIG. FIG. 10 is a diagram showing another example of the optical fiber 2 in the fourth embodiment. FIG. 6 is a diagram illustrating another configuration example of the transmission unit 45. 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. FIG. 16 is a diagram illustrating a connection between the optical fiber 116 and the resonator 202 in FIG. 15. It is a figure which shows the structure of the conventional optical fiber amplifier. It is a figure which shows the cross section of the optical fiber 2 of FIG. 1 concretely.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical amplifier, 2,2A, 116,210 Optical fiber, 2D hole, 4A excitation light source, 4 excitation part, 6 light source, 8 Signal light propagation area, 9 Periodic structure area, 8A, 9A hole, 11,21 31, 100, 200 Laser device, 12 pulse oscillation LD, 13 reflector, 14A, 14B collimator lens, 15 winding frame, 16, 16A, 16B, 16C reflector, 18 heat sink, 19 LD element, 19A electrode, 22 reflector , 32 Control unit, 34 Light guide, 35 Light emitting surface, 36A, 36B Wavelength selection unit, 36C Radiation surface, 38 Pointer, 40 Driver 42 Cooling unit, 43 Isolator, 44 Heat sink, 45 Transmission unit, 46A, 46B Seal, 50 cylindrical lens, 52 cooling water, 60 microlens, 91-94 boundary line, 102, 02 resonator, 104 crystal, 106, 108 reflector, 110 Q switch, 112 LD array, 114 lens, 118 fiber coupling, 218 core, 220 first clad, 222 second clad, 300 optical fiber amplifier, 301 optical amplification Fiber, 302, 304 light source, 306 fiber branch, 308 fiber coupler, D1 distance, E excitation light, L1, L2, S1, S2, S100 signal light, L3 transmitted light, L4 reflected light, LA laser light, P1 position.

  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 conceptual diagram showing a configuration of an optical amplifier according to the present invention. Referring to FIG. 1, an optical amplifier 1 includes an optical fiber 2, a pumping unit 4 that irradiates pumping light E from a side surface of the optical fiber 2 toward a light propagation region of the optical fiber, and a signal light S1 on one end surface of the optical fiber. And a light source 6 for incident light. The signal light S1 is amplified in the optical fiber 2 and output from the other end surface of the optical fiber 2 as signal light S2.

  The optical fiber 2 is a photonic crystal fiber. 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 period of the crystal is not allowed to exist in the photonic crystal due to the energy band structure (photonic band) due to the periodic structure.

  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.

  In the present invention, the signal light S1 corresponds to light having a photonic bandgap wavelength. The wavelength of the excitation light E is a wavelength in the transmission region of the photonic band. Therefore, the wavelength of the signal light S1 and the wavelength of the excitation light E are different.

  FIG. 2 is a diagram schematically showing a cross section of the optical fiber 2 of FIG. Referring to FIG. 2, the optical fiber 2 includes a signal light propagation region 8 and a periodic structure region 9. The periodic structure region 9 surrounds the central portion of the signal light propagation region 8, and the holes 9A are periodically formed in a transparent material such as glass or plastic so as to satisfy the Bragg reflection condition for the light of the wavelength of the signal light. This is a region having a provided structure. Air is present in the holes.

  In a diffraction grating whose refractive index changes periodically, light of a specific wavelength is strongly reflected and light of other wavelengths is transmitted due to the relationship between the period of the diffraction grating and the wavelength of the light in the direction of incident light. To do. Such reflection is called Bragg reflection. The period of the holes 9A provided in the optical fiber is provided in a transparent material with an interval and size approximately equal to the wavelength of the signal light, and the periodic structure is appropriately arranged so that the signal light propagating in the fiber is Bragged. Reflection can be generated, and the signal light can propagate while being confined in the signal light propagation region 8. If the periodic structure is finite, a wavelength having a certain spread around a specific wavelength satisfies the Bragg reflection condition, but such a case is also included.

  In the periodic structure region 9, the pumping light has a wavelength different from that of the signal light, and the pumping light from the side surface of the fiber is transmitted to the signal light propagation region 8 with high transmittance by designing the periodic structure so as not to satisfy the Bragg reflection condition. Can reach.

  The signal light propagation region 8 is doped with a rare earth element as an optical amplification material. When the excitation light E in FIG. 1 enters the signal light propagation region 8, the rare earth element doped in the signal light propagation region 8 is excited by the excitation light E. Further, when the signal light S1 enters the signal light propagation region 8, stimulated emission occurs in the excited rare earth element, and the signal light S1 is amplified.

  Depending on the type of rare earth element, the wavelengths of the excitation light and stimulated emission light are different. Specific examples of rare earth elements include neodymium (Nd), ytterbium (Yb), erbium (Er), and the like. For example, in the case of neodymium, the wavelength of the excitation light is 808 nm, and the wavelength of the stimulated emission light is 1064 nm. In the case of ytterbium, the wavelengths of excitation light are 940 ± 10 nm and 970 nm, and the wavelength of stimulated emission light is 1030 nm. In the case of erbium, the wavelengths of excitation light are 980 nm and 1480 nm, and the wavelength of stimulated emission light is 1550 nm. Therefore, the optical amplifier 1 can output light of different wavelengths by exchanging the optical fiber 2 according to the required wavelength of the signal light S2.

  Furthermore, by irradiating the entire area of the optical fiber 2 (actually, the region where the rare earth element is added) with the excitation light uniformly, the absorption probability (absorption cross section) of the excitation light caused by excessive irradiation is reduced. By avoiding the influence and maintaining a high absorption probability, it becomes possible to increase the amplification factor of the signal light and emit light from the optical fiber.

  In the case of an optical amplifier or fiber laser using a conventional optical fiber, the diameter of the light propagation region must be approximately the same as the wavelength (about 1 to several μm) in order to propagate single mode light. Therefore, even if the excitation light is irradiated from the side surface of the fiber in the conventional optical amplifier, the diameter of the light propagation region is too small, so that the excitation light absorbed in the light propagation region is reduced. Since the optical fiber 2 is a photonic crystal fiber, single mode light can be propagated even if the diameter of the light propagation region is about ten times that of the optical propagation region. Therefore, even if the excitation unit 4 irradiates the excitation light E from the side surface of the optical fiber 2 toward the signal light propagation region 8, the signal light propagation region 8 can efficiently absorb the excitation light E. Therefore, the optical amplifier 1 can easily adjust the position of the pumping portion with respect to the optical fiber 2 as compared with the conventional optical amplifier.

  Next, a configuration example of the photonic crystal fiber in the embodiment of the present invention will be specifically described with reference to FIG.

FIG. 18 is a diagram specifically showing a cross section of the optical fiber 2 of FIG. 1.
Referring to FIG. 18, in signal light propagation region 8, another hole 8A (core) different from hole 9A constituting periodic structure region 9 is provided. The plurality of holes 9A surround the holes 8A of the signal light propagation region 8 in a multiple manner and are periodically arranged. In other words, the periodic structure region 9 has a structure in which transparent substances such as glass and plastic and holes are stacked in layers around the holes 8A. The boundary lines 91 to 94 are lines shown for convenience as the boundaries between the layers.

  The diameter of the air holes 8A is about 15 μm. Also, the refractive index of the holes is approximately equal to 1. Ytterbium (Yb) is added to the signal light propagation region 8 as a light amplification substance. Ytterbium is added to the first layer (the region between the holes 8A and the boundary line 91).

  In order for the structure of the optical fiber 2 to be a photonic bandgap structure, the above-described layers are required to be about 1 to 6 layers, but in order for the optical fiber 2 to propagate light in a single mode, about 4 layers are required. (FIG. 18 shows an example of four layers).

  When the laser oscillation wavelength is 1064 nm, the pitch Λ between the two holes 9A is about 2 to 3 μm, the diameter d of the holes 9A is about 2 to 3 μm, and the structural parameter d / Λ is about 1. .

  In the structure shown in FIG. 18, ytterbium (Yb) may be added to the first layer, and a laser dopant such as erbium (Er) may be added to the first layer and the second layer. Erbium emits light having a wavelength close to that of ytterbium upon receiving excitation light from the outside of the fiber (on the side of the fiber). The light emitted by erbium excites ytterbium in the center of the fiber. Erbium may be added to the first to sixth layers (or more layers).

  As described above, according to the first embodiment, Bragg is applied to light having a predetermined wavelength so as to have a signal light propagation region to which a rare earth element is added and to surround the central portion of the signal light propagation region. A photonic crystal fiber having a periodic structure composed of transparent materials and vacancies having different refractive indexes that satisfy the reflection conditions, and an excitation unit that emits excitation light from the side surface of the photonic crystal fiber toward the light propagation region With this, it is possible to easily set the arrangement of the excitation unit with respect to the optical fiber, and it is possible to realize a small and high-power optical amplifier.

[Embodiment 2]
FIG. 3 is a schematic diagram showing the configuration of the laser apparatus according to the second embodiment. Referring to FIG. 3, the laser device 11 includes an optical amplifier 1, a reflecting mirror 13, and collimator lenses 14A and 14B. The reflecting mirror 13 reflects a part of the signal light L2 emitted from one end face of the optical fiber 2 and enters the other end face of the optical fiber 2 and transmits a part of the signal light L2. When the amplification of the signal light L2 by the optical amplifier 1 and the loss of the signal light L2 by the reflector, 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 13 The laser beam LA is emitted from the outside. 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 optical amplifier 1 includes an optical fiber 2, a plurality of pumping light sources 4A, a pulse oscillation LD 12, a cylindrical winding frame 15, a reflection unit 16, and a heat sink 18. The optical fiber 2 is installed in a ring shape by being wound along the side surface of the winding frame 15. Since the optical fiber 2 is a photonic crystal fiber, even if it is wound along the winding frame 15, resistance to bending is extremely strong, and light hardly leaks from the bent portion. Therefore, even if the optical fiber 2 is lengthened, the optical amplifier 1 can be prevented from increasing in size, so that the laser device 11 is small and can emit high-power laser light.

  The plurality of excitation light sources 4A constitutes the excitation unit 4 in FIG. Since the optical fiber 2 is wound around the winding frame 15, the excitation light source 4 </ b> A emits excitation light in the radial direction of the winding frame 15. The excitation light source 4A includes an LD element (not shown) that performs continuous oscillation. The oscillation wavelength of the LD element is a wavelength in the transmission region of the photonic band as well as an excitation wavelength of the rare earth element. The oscillation wavelength is appropriately determined according to the rare earth element added to the light propagation region of the optical fiber 2 and the transmission region of the photonic band.

  Although eight excitation light sources 4A are provided, the number of excitation light sources 4A may be different. By providing a plurality of excitation light sources 4A, even if one of the excitation light sources 4A does not emit excitation light due to a failure or the like, another excitation light source 4A emits excitation light, so that the laser device 11 emits laser light LA. it can. Further, the larger the number of excitation light sources 4A included in the laser device 11, the higher the output of the laser light.

  The optical amplifier 1 includes a reflecting portion 16 provided so as to sandwich the optical fiber 2. The reflector 16 is provided so that the excitation light emitted from the excitation light source 4A is efficiently absorbed by the light propagation region of the optical fiber 2.

  The reflection part 16 includes reflection parts 16A and 16B. The reflection portion 16 </ b> A is provided on the side opposite to the excitation light source 4 </ b> A with respect to the optical fiber 2, and reflects the excitation light toward the light propagation region of the optical fiber 2. The reflector 16B is provided along the optical fiber except for the region irradiated with the excitation light from the excitation light source 4A. The reflection part 16B reflects the reflected excitation light toward the optical fiber 2 together with the reflection part 16A. In this way, since the excitation light is repeatedly reflected by the reflecting portions 16A and 16B, the excitation light is efficiently absorbed in the light propagation region. The reflecting portions 16A and 16B are configured by, for example, a prism sheet (diffraction grating sheet), a metal vapor deposition sheet, a sheet with a multilayer dielectric coating, or the like.

  A heat sink 18 is provided between each of the plurality of excitation light sources 4A. Since heat emitted from the LD element included in the excitation light source can be released by the heat sink 18, an increase in temperature of the LD element can be suppressed. Therefore, the wavelength of the excitation light is stabilized.

  In FIG. 3, the excitation light source 4 </ b> A is provided inside the winding frame 15 with respect to the optical fiber 2, but may be provided outside the winding frame 15 with respect to the optical fiber 2.

  The reflecting mirror 13 is made of, for example, quartz glass. Quartz glass has the advantage that volume expansion due to temperature is small. In order to reflect the signal light L2, for example, a dielectric multilayer film is laminated on the reflecting surface of the reflecting mirror 13. The reflectivity of the signal light L2 on the reflecting surface can ensure 99% or more when a dielectric multilayer film is used on the reflecting surface. Note that by changing the distance between the optical fiber 2 and the reflecting mirror 13, the oscillation wavelength of the laser light can be finely adjusted.

  Thus, in the laser device of the second embodiment, only one reflecting mirror is provided for the optical fiber 2. Therefore, since the number of reflecting mirrors is smaller than that of a conventional LD-pumped solid-state laser, the position can be easily adjusted even if the positions of the optical amplifier 1 and the reflecting mirror 13 are shifted due to vibration shock.

  The collimator lenses 14A and 14B are provided to make the signal light L2 entering the optical fiber 2 and the signal light L2 exiting the optical fiber 2 into parallel light beams.

  FIG. 4 is a schematic diagram showing the configuration of the optical amplifier 1 of FIG. Referring to FIG. 4, excitation light source 4A is provided with a plurality of LD elements 19 that perform continuous oscillation. The number of LD elements 19 is appropriately determined according to the power of pumping light necessary for pumping the light propagation region. In FIG. 4, the heat sink 18 is not shown in order to avoid making the figure complicated. Similarly, only two excitation light sources 4A are shown in order to avoid the figure from becoming complicated.

  It is particularly preferable that the incident angle A of the excitation light E with respect to the optical fiber 2 is incident with the Brewster angle as the center. The Brewster angle refers to an incident angle at which reflection is zero when linearly polarized light (P-polarized light) having only an electric field component parallel to the incident surface is incident. If the central value of the polarization direction and the incident angle of the LD used for the excitation light is the Brewster angle, the excitation light E efficiently enters the optical fiber 2, and therefore the excitation light is efficiently absorbed in the light propagation region. The Brewster angle in the second embodiment is about 34 °.

  FIG. 5 is a diagram illustrating another configuration example of the optical amplifier 1 according to the second embodiment. Referring to FIG. 5, the optical fiber 2, the reflecting portion 16C, the LD element 19 and the electrode 19A are shown. The electrode 19A is an electrode for applying a drive voltage to the LD element 19 and controlling its operation. FIG. 5 shows a cross section of the main part of the optical amplifier 1 as seen from the propagation direction of the signal light.

  The outer shape of the reflecting portion 16C is at least a part of an ellipse. The ellipse has two focal points. Therefore, if the LD element 19 is regarded as a point light source, the optical fiber 2 is provided so that the position of the light propagation region becomes the first focus of the ellipse, and the light emitting surface of the LD element 19 is provided at the position of the second focus. The pumping light E emitted from the LD element 19 can be collected in the optical fiber 2. In the case of the optical amplifier 1 shown in FIG. 5, since the reflecting portion 16 </ b> C is provided along the optical fiber 2, the length of the reflecting portion 16 </ b> C is required only by the length of the optical fiber 2.

  FIG. 6 is a diagram illustrating still another configuration example of the optical amplifier 1 according to the second embodiment. Referring to FIG. 6, optical fiber 2A, LD element 19 and electrode 19A are shown. Similar to FIG. 5, FIG. 6 shows a cross section of the main part of the optical amplifier 1 as seen from the propagation direction of the signal light.

  In the optical amplifier 1 shown in FIG. 6, the shape of the optical fiber 2A is a part of an ellipse. The signal light propagation region 8 is provided at the position of the first focus of the ellipse, and the light emitting surface of the LD element 19 is provided at the position of the second focus. Similarly to the optical amplifier 1 shown in FIG. 5, the excitation light E emitted from the LD element 19 is collected in the signal light propagation region 8, and therefore, the excitation light E can be efficiently absorbed in the light propagation region. In the case of the optical amplifier shown in FIG. 6, since it is not necessary to provide a reflection part outside the optical fiber, the cost of the laser device can be reduced.

  When a collimator lens is provided between the LD element 19 and the optical fiber, the excitation light incident on the optical fiber becomes a parallel light beam. If the excitation light is a parallel light beam, in the optical amplifier 1 shown in FIG. 5, the outer shape of the reflecting portion 16C is a parabola, and the optical fiber 2 is provided at the focal point of the parabola. Similarly, in the optical amplifier 1 shown in FIG. 6, the outer shape of the optical fiber 2A is a parabola, and the signal light propagation region 8 is provided at the focal point of the parabola.

  As described above, according to the second embodiment, the light emitted from the optical amplifier including the photonic crystal 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 is increased. Therefore, it is possible to realize a laser apparatus that can easily adjust the wavelength and can easily change the wavelength and output of the laser beam.

[Embodiment 3]
FIG. 7 is a schematic diagram showing the configuration of the laser apparatus according to the third embodiment. Referring to FIG. 7, laser device 21 is different from laser device 11 of FIG. 2 in that pulse oscillation LD 12 is not included and reflecting mirror 22 is included. Since the configuration of the other part of laser device 21 is the same as the configuration of the corresponding part of laser device 11, the following description will not be repeated.

  The laser device 21 is a laser capable of continuous oscillation. When the output of each of the plurality of excitation light sources 4A is gradually increased, light due to spontaneous emission is generated in the light propagation region of the optical fiber 2. This light becomes signal light and is amplified while propagating through the optical fiber 2. A part of the signal light L2 emitted from one end face of the optical fiber 2 is reflected by the reflecting mirror 13 and enters the other end face of the optical fiber 2, and a part thereof is transmitted through the reflecting mirror 13 and emitted. When the amplification of the signal light L2 by the optical amplifier 1 and the emission of the signal light L2 by the reflecting mirror 13 are balanced, laser oscillation occurs.

  In the second embodiment, the signal light L1 enters from one end face of the optical fiber 2, so that the amplified signal light L2 travels only in one direction (clockwise). In the third embodiment, since the traveling direction of the signal light L2 is not particularly limited, the clockwise direction, the counterclockwise direction, or the clockwise direction and the counterclockwise direction are considered as the traveling directions. In particular, when the traveling direction is both the clockwise direction and the counterclockwise direction, the signal light L <b> 2 is output from both end faces of the optical fiber 2. Therefore, transmitted light L3 is generated as light that passes through the reflecting mirror 13 in addition to the laser light.

  In the third embodiment, a reflecting mirror 22 that reflects the transmitted light L3 is provided. The transmitted light L3 is reflected by the reflecting mirror 22, and the reflected light L4 and the laser light LA are combined at a position P1 on the reflecting mirror 13. Therefore, in Embodiment 3, it can prevent that the output of the laser beam LA falls. In Embodiment 3, since there is no light emitted to the outside other than the laser beam LA, the worker can easily handle the laser device when the worker processes the product using the laser device. it can.

  In order to prevent the output of the laser light LA from being lowered when the reflected light L4 and the laser light LA are combined, the phase of the laser light LA and the phase of the light L4 must be the same at the position P1. For this reason, the distance D1 from the position P1 to the reflecting mirror 22 must be set so as to be an integral multiple of the half length (half wavelength) of the oscillation wavelength.

  Also in the third embodiment, similarly to the second embodiment, a reflecting portion 16C shown in FIG. 5 may be used instead of the reflecting portion 16. In the third embodiment, an optical fiber 2A may be used instead of the optical fiber 2.

  As described above, according to the third embodiment, a laser device that performs continuous oscillation is realized by increasing the output of pumping light output from the pumping light source so that spontaneous emission occurs in the light propagation region of the optical amplification fiber. can do.

[Embodiment 4]
FIG. 8 is a schematic diagram showing the configuration of the laser apparatus according to the fourth embodiment. Referring to FIG. 8, the laser device 31 includes an optical amplifier 1, a heat sink 18, a control unit 32, a light guide 34, and wavelength selection units 36A and 36B.

  Wavelength selection units 36A and 36B are provided at both ends of the optical fiber 2. The wavelength selectors 36A and 36B have a function corresponding to a conventional FBG, and are selectively set to have a high reflectance only for a specific wavelength. Instead of the wavelength selectors 36 </ b> A and 36 </ b> B, both end faces of the optical fiber 2 may be coated with a reflection film for reflecting the signal light at the end face and returning the signal light to the inside of the optical fiber 2.

  In each of the wavelength selectors 36A and 36B, part of the signal light is returned to the optical fiber 2 and part of the signal light is emitted to the outside. When the amplification of the signal light by the optical fiber 2 and the emission of the signal light by each of the wavelength selectors 36A and 36B are balanced, the laser light LA is emitted from the laser device 31. The radiation surface 36C from which the laser light is emitted to the outside is mirror-coated so that most of the light is reflected and part of the light is transmitted.

  The excitation unit 4 includes a plurality of LD elements 19 that are light sources. As in the second and third embodiments, a plurality of LD elements 19 are included in the excitation unit 4, so that even if any one of the LD elements does not emit excitation light due to a failure, the optical fiber 2 is connected by another LD element. Can be excited. In addition to the LD element 19, the light source included in the excitation unit 4 may be an LED (including a light emitting diode) or a lamp.

  The light guide 34 is an optical waveguide unit that is provided between the excitation unit 4 and the optical fiber 2 and guides the excitation light E to the side surface of the optical fiber 2. The excitation light E emitted from the LD element 19 is reflected by the light guide 34 and enters the optical fiber 2 from the side surface of the optical fiber 2. The light guide 34 has a light emitting surface for emitting the excitation light E in a planar shape. The optical fiber 2 is provided on the light emitting surface from which the excitation light E is emitted from the light guide 34. Rather than locally irradiating the optical fiber 2 with the excitation light, the excitation light is uniformly irradiated, so that absorption saturation hardly occurs, and the rare earth element is efficiently excited without increasing loss. Can do.

  The control unit 32 is a pulse generator that generates an arbitrary waveform, for example. The control unit 32 includes an instruction unit 38 that outputs an instruction for controlling the output of laser light and temperature, and a driver 40 that performs a process for controlling the current injected into the pulse oscillation LD 12 based on the instruction sent from the instruction unit 38. including.

  The laser device 31 further includes a cooling unit 42 that cools the optical fiber 2. The optical fiber 2 is immersed in cooling water. The cooling unit 42 circulates cooling water to cool the optical fiber 2.

  In the second embodiment and the third embodiment, the optical fiber is bent in a ring shape, but in the fourth embodiment, the optical fiber 2 is bent along the surface. Since the optical fiber 2 is a photonic crystal fiber, it can be freely provided on the light emitting surface with a predetermined bending radius or less. In addition, it is preferable that an optical fiber is provided so that the whole light emission surface may be covered so that much excitation light can be absorbed.

  FIG. 9 is a view of the laser device 31 of FIG. 8 as viewed from above. Referring to FIG. 9, the light guide 34 has a light emitting surface 35. The optical fiber 2 is provided along the light emitting surface 35. An isolator 43 is provided between the pulse oscillation LD 12 and the wavelength selection unit 36A. The isolator 43 passes the signal light L1 emitted from the pulse oscillation LD12 through the optical fiber 2, but blocks light returning from the optical fiber 2 to the pulse oscillation LD12. Return light does not enter the pulse oscillation LD 12 by the isolator 43. Therefore, the pulse oscillation LD12 is protected. Note that the isolator 43 may not be included in the laser device 31.

  10 is a cross-sectional view taken along line XX in FIG. Referring to FIG. 10, optical fiber 2 is sandwiched between reflecting portion 16 </ b> A and transmitting portion 45. The reflecting portion 16 </ b> A is a metal film laminated on the surface of the heat radiating plate 44. The reflection portion 16 </ b> A is provided on the side opposite to the light emitting surface 35 with respect to the optical fiber 2, and reflects the excitation light E toward the optical fiber 2. The transmission unit 45 transmits light having a wavelength that excites the light amplification substance doped in the light propagation region, among the excitation light E emitted from the excitation unit 4. The transmission part 45 is, for example, a dichroic mirror.

  The angle of the upper surface of the heat sink 18 (the reflection surface of the light guide 34) and the angle of the lower surface of the heat dissipation plate 44 are preferably set so that the excitation light reflected by the reflecting portion 16A does not return to the LD element. .

  Excitation light E emitted from the excitation light source is converted into parallel rays by the cylindrical lens 50. The light guide 34 is provided with an inclination. The excitation light E is reflected by the inclined surface of the light guide 34 and enters the optical fiber 2 through the transmission part 45.

  The light guide 34 is a transparent material that transmits the excitation light E. The light guide 34 is made of, for example, glass or resin, but is preferably made of a material that can be bent to reduce the size of the laser device 31. A specific example of the material of the light guide 34 is, for example, PET (polyethylene terephthalate).

  The seals 46A and 46B are used to seal the cooling water 52 between the optical fibers 2. In order to release the heat of the cooling water 52 to the outside, it is preferable that the material of the seals 46A and 46B has high thermal conductivity. Further, the surface of each of the seals 46A and 46B facing the optical fiber 2 is coated with a reflection film (not shown) that reflects the excitation light E.

  As in the second and third embodiments, in the fourth embodiment as well, in order to increase the amplification factor in the optical amplifier 1, it is preferable to efficiently collect the pumping light E in the light propagation region of the optical fiber. Hereinafter, the shape and configuration of the photonic crystal fiber capable of efficiently collecting the excitation light in the light propagation region will be described.

  FIG. 11 is a diagram illustrating an example of the optical fiber 2 according to the fourth embodiment. Referring to FIG. 11, a cross section of the optical fiber 2 is shown. The cross section shown in FIG. 11 is perpendicular to the propagation direction of the signal light. The shape of the cross section becomes a parabola. Since the excitation light E sent from the light guide 34 to the optical fiber 2 is a parallel ray, the excitation light E can be efficiently collected in the signal light propagation region 8 by providing the signal light propagation region 8 at the focal point of the parabola. It becomes possible.

  FIG. 12 is a diagram illustrating another example of the optical fiber 2 according to the fourth embodiment. Referring to FIG. 12, the shape of the optical fiber 2 is a parabola. However, a hole 2D is provided in the signal light propagation region 8 in the cross section. In particular, when high-power laser light is output, such a hole is provided in the signal light propagation region 8, thereby avoiding an increase in absorption coefficient due to the presence of light at high density and suppressing output loss. It becomes possible.

  FIG. 13 is a diagram illustrating another configuration example of the transmission unit 45. Referring to FIG. 13, a microlens array including a microlens 60 is formed on the light emitting surface 35 as a transmission part 45. The optical fiber 2 is provided on the microlens array. Since the excitation light is collected by the microlens 60 and enters the optical fiber 2, it is possible to efficiently collect the light in the light propagation region.

  As described above, according to the fourth embodiment, it is possible to output single mode laser light while being small in size by making excitation light incident on the side surface of the photonic crystal fiber from the light emitting surface. .

  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.

Claims (23)

A photonic crystal fiber (2) that propagates signal light having a predetermined wavelength of light as a main wavelength in a single mode;
The photonic crystal fiber (2)
A signal light propagation region (8) for propagating the signal light,
A periodic structure (9) comprising a plurality of media having different refractive indexes satisfying the Bragg reflection condition for the light of the predetermined wavelength so as to surround the central portion of the signal light propagation region (8); and ,
The signal light propagation region (8) is doped with a light amplification substance that causes stimulated emission when the signal light is incident in an excited state;
An excitation unit (4) for irradiating excitation light having a wavelength different from that of the signal light from the side surface of the photonic crystal fiber (2) toward the signal light propagation region (8), and exciting the optical material;
Accordingly, an optical amplifier that propagates in a single mode the signal light having the predetermined wavelength of light selected by the periodic structure (9) in a single mode, and amplifies the signal light by irradiation with the excitation light. A signal light source (6) that emits signal light having a predetermined wavelength of light as a main wavelength;
A photonic crystal fiber (2) that receives the signal light at one end surface, propagates the signal light in a single mode, and emits the signal light from the other end surface;
The photonic crystal fiber (2)
A signal light propagation region (8) for propagating the signal light,
A periodic structure (9) comprising a plurality of media having different refractive indexes satisfying the Bragg reflection condition for the light of the predetermined wavelength so as to surround the central portion of the signal light propagation region (8); and ,
The signal light propagation region (8) is doped with a light amplification substance that causes stimulated emission when the signal light is incident in an excited state;
An excitation unit (4) for irradiating excitation light having a wavelength different from that of the signal light from the side surface of the photonic crystal fiber (2) toward the signal light propagation region (8) to excite the optical material;
An optical amplifier for amplifying the signal light propagating through the photonic crystal fiber (2).   The periodic structure (9) is formed by periodically providing holes in a solid medium constituting the photonic crystal fiber in a cross section of the photonic crystal fiber (2). 2. The optical amplifier according to 2. A laser device (31) comprising:
An optical amplifier (1),
The optical amplifier (1)
Including a photonic crystal fiber (2) that propagates signal light having a predetermined wavelength of light as a main wavelength in a single mode;
The photonic crystal fiber (2)
A signal light propagation region (8) for propagating the signal light;
A periodic structure (9) comprising a plurality of media having different refractive indexes satisfying the Bragg reflection condition for the light of the predetermined wavelength so as to surround the central portion of the signal light propagation region (8); and ,
The signal light propagation region (8) is doped with a light amplification substance that causes stimulated emission when the signal light is incident in an excited state;
The optical amplifier (1)
An excitation unit (4) for irradiating excitation light having a wavelength different from that of the signal light toward the signal light propagation region (8) from a side surface of the photonic crystal fiber (2), and exciting the optical material;
Thereby, the signal light having the light of the predetermined wavelength selected by the periodic structure (9) as a main wavelength propagates in a single mode, and the signal light is amplified by the irradiation of the excitation light,
The laser device (31)
The laser apparatus further provided with the reflection part which reflects the said signal light in each end surface of the said photonic crystal fiber (2). A laser device (11) comprising:
An optical amplifier (1),
The optical amplifier (1)
Including a photonic crystal fiber (2) that propagates signal light having a predetermined wavelength of light as a main wavelength in a single mode;
The photonic crystal fiber (2)
A signal light propagation region (8) for propagating the signal light;
A periodic structure (9) comprising a plurality of media having different refractive indexes satisfying the Bragg reflection condition for the light of the predetermined wavelength so as to surround the central portion of the signal light propagation region (8); and ,
The signal light propagation region (8) is doped with a light amplification substance that causes stimulated emission when the signal light is incident in an excited state;
The optical amplifier (1)
An excitation unit (4) for irradiating excitation light having a wavelength different from that of the signal light toward the signal light propagation region (8) from a side surface of the photonic crystal fiber (2), and exciting the optical material;
Thereby, the signal light having the light of the predetermined wavelength selected by the periodic structure (9) as a main wavelength propagates in a single mode, and the signal light is amplified by the irradiation of the excitation light,
The laser device (11)
A laser device further comprising a return portion for returning the signal light reaching one end surface of the photonic crystal fiber (2) to the other end surface of the photonic crystal fiber. The photonic crystal fiber (2) is installed such that the one end face and the other end face are close to each other,
The return portion reflects a part of the signal light emitted from the other end surface and enters the one end surface, and transmits a part of the signal light emitted from the other end surface (13 The laser device according to claim 5, wherein   A first reflecting portion (16A) provided on the opposite side of the excitation portion (4A) with respect to the photonic crystal fiber (2) and reflecting the excitation light toward the photonic crystal fiber (2). The laser device according to claim 6, further comprising: The laser device (11) further includes a second reflecting section (16B) provided between the photonic crystal fiber (2) and the excitation section (4A),
The second reflection unit (16B) transmits the excitation light emitted from the excitation unit (4A) and transmits the excitation light reflected by the first reflection unit (16A) to the photonic crystal fiber ( The laser device according to claim 7, which reflects toward 2). The outer shape of the first reflecting portion (16C) is at least a part of an ellipse,
The laser device according to claim 7, wherein the photonic crystal fiber (2) is arranged so that the position of the light propagation region (8) is the position of the focal point of the ellipse. The photonic crystal fiber (2A) has a shape in which a cross section perpendicular to the propagation direction of the signal light is at least part of an ellipse,
The laser device according to claim 6, wherein the light propagation region (8) is arranged at a focal point of the ellipse.   The photonic crystal fiber (2) itself generates the signal light by spontaneous emission generated in the light amplification material in response to excitation light emitted from any one of the plurality of excitation light sources (19). The laser apparatus according to claim 6, wherein stimulated emission is caused in the light amplification substance by the generated signal light.   The laser device according to claim 6, wherein the excitation unit (4A) irradiates the photonic crystal fiber with the excitation light so that an incident angle becomes a Brewster angle.   The laser device according to claim 12, wherein the excitation unit (4A) includes a plurality of excitation light sources (19) that continuously emit the excitation light. The return part is
A first fiber grating structure (36A) optically coupled to the one end face and returning the signal light reaching the one end face toward the other end face;
6. The laser device according to claim 5, further comprising: a second fiber grating structure (36 </ b> B) optically coupled to the other end surface and returning the signal light reaching the other end surface toward the one end surface. The laser device (31) is provided between the excitation unit (4) and the photonic crystal fiber (2), and guides the excitation light to a side surface of the photonic crystal fiber (2) ( 34),
The optical waveguide section (34) includes a light emitting surface (35) for emitting the excitation light in a planar shape,
The laser device according to claim 14, wherein the photonic crystal fiber (2) is provided along the light emitting surface (35).   The laser device according to claim 15, wherein the optical waveguide section (34) is made of a foldable material. The laser device (31)
A reflection part (16A) provided on the opposite side of the light emitting surface (35) with respect to the photonic crystal fiber (2) and reflecting the excitation light toward the photonic crystal fiber (2);
The laser device according to claim 15, further comprising a transmission portion (45) provided between the light emitting surface (35) and the photonic crystal fiber (2) and transmitting the excitation light.   The laser device according to claim 17, wherein the transmission unit (45) is a dichroic mirror that transmits light of a wavelength that excites the light amplification substance in the excitation light.   The laser device according to claim 17, wherein the transmission unit (45) is a microlens array including a plurality of microlenses (60) that collect the excitation light.   The photonic crystal fiber (2) has a shape in which a cross section perpendicular to the propagation direction of the signal light is a parabola, and the light propagation region is disposed at a focal point of the parabola. Laser equipment.   The inside of the light propagation region is provided with another hole (8A) different from the hole (9A) constituting the periodic structure in the light propagation region in a cross section in the cross section. Laser equipment.   The laser apparatus according to claim 14, wherein the laser apparatus (31) further includes a cooling unit (42) for circulating cooling water (52) for immersing and cooling the photonic crystal fiber (2). An optical waveguide (34) provided between the excitation unit (4) and the photonic crystal fiber (2) and guiding the excitation light to a side surface of the photonic crystal fiber (2);
The optical waveguide section (34) includes a light emitting surface (35) for emitting the excitation light in a planar shape,
The optical amplifier according to claim 1, wherein the photonic crystal fiber (2) is provided along the light emitting surface (35).

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