WO2006098313A1

WO2006098313A1 - Optical amplifier and laser device

Info

Publication number: WO2006098313A1
Application number: PCT/JP2006/305001
Authority: WO
Inventors: Takehiko Wada; Eisaku Kojima
Original assignee: Omron Corporation
Priority date: 2005-03-15
Filing date: 2006-03-14
Publication date: 2006-09-21
Also published as: JPWO2006098313A1

Abstract

In the optical amplifier and fiber laser using the conventional optical fiber, the diameter of the core must be equivalent to the wavelength (approximately 1 to several μm) to propagate single mode light in the optical fiber. Therefore, even when an excitation light is applied from a side plane, since the core diameter is too small, a small quantity of excitation light is absorbed in the core. As an optical fiber (2) is a photonic crystal fiber, single mode light can be propagated even when the diameter of a light propagating region is, for instance, approximately 100μm. Therefore, excitation light (E) applied from the side plane of the optical fiber (2) is efficiently absorbed by the light propagating region. An optical amplifier and a laser having the small and simple constitution for emitting high power light are provided.

Description

Specification

Optical amplifier and laser device

Technical field

TECHNICAL FIELD [0001] 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.

Background art

[0002] Laser light can be used in various industrial applications. For example, laser light is used for processing to mark quality information on the surface of a component. Laser light is used for mounting semiconductor chips and repairing defects in liquid crystal pixels.

[0003] In particular, when a lot of information such as the date of manufacture is recorded in a minute area, it must be possible to add accurately. The mode of laser light used for microfabrication is more suitable for single mode (single mode) than for multimode (multimode).

[0004] Laser devices must respond to various requirements, such as being small in size, resistant to impact, and low in cost. In order to satisfy these demands, laser resonators have been individually designed according to the output of the laser beam, the wavelength of the laser beam, and the mode of the beam beam. The laser resonator was adjusted based on know-how accumulated over many years.

[0005] The configuration 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, laser apparatus 100 includes resonator 102. The resonator 102 includes a crystal 104 such as YAG (Yttrium Alu minum Garnet) and YV04, reflecting mirrors 106 and 108 facing each other through the crystal 104, and a Q switch 110 for generating laser oscillation and generating laser light. Including The Q switch 110 is a shirt 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 shatter 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. Further, when the crystal 104 is YV04, a crystal cut along the c-axis direction of the a-axis to c-axis crystal axes is used to output single-mode laser light. 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, laser apparatus 200 includes resonator 202. The resonator 202 is a ring resonator configured by an optical fiber. Fiber Bragg Gratings (FBG) 206, 208 forces S are formed at both ends of the optical fiber. The FBG is a diffraction grating formed in the core of an optical fiber and functions as an optical filter.

An optical fiber used for the resonator 202 is an optical amplification fiber in which a rare earth element is added to a core. When the excitation light enters the core, the rare earth element is excited. Furthermore, when signal light (not shown) enters the core, stimulated emission occurs in the excited rare earth element, so that 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, the 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 a connection between the optical fiber 116 and the resonator 202 in FIG. Referring to FIG. 16, the optical fiber 210 constitutes the resonator 202. In FIG. 16, a cross section of the optical fiber 210 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 the second cladding 222. Through the first cladding 220 The excitation light reflected from the first clad 220 and the second clad 222 is reflected toward the first clad 220. 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 via the fiber branch line 306 and the fiber coupler 308. The signal light incident on one end face of the light amplification fiber 301 from the light source 302 is amplified by the light amplification fiber 301. The signal light S 100 is emitted from the other end of the optical amplification fiber 301 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 passes through a nonlinear optical crystal element provided in a resonator. A solid-state laser provided with optical means in the resonator for generating second harmonic laser light by resonance operation and suppressing coupling due to sum frequency generation between two polarization modes of the fundamental laser light. An oscillator is disclosed. This solid-state laser oscillator has the same optical means for oscillating the two polarization modes of the fundamental laser beam in a single longitudinal mode and the oscillation intensity force S of the two polarization modes of the fundamental laser beam. And a control means for controlling the effective resonator length of the resonator.

[0017] Further, as a conventional technique for adjusting the optical axis of a laser, for example, in Japanese Unexamined Patent Application Publication No. 2004-47650 (Patent Document 2), a plurality of laser diodes and these laser diodes are respectively connected to light emitting points. Are fixedly held in a state in which they are aligned in one direction, and a collimator lens array in which a plurality of collimator lenses that collimate laser beams emitted from the laser diode are integrated in a state in which they are aligned in one direction. A laser device is disclosed. In this laser device, a smooth lens defining surface is formed in front of the portion where the plurality of laser diodes of the block are fixed, at a predetermined distance from the light emitting point of the laser diode and perpendicular to the light emitting axis of the laser diode. 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. [0018] Further, as a conventional example of an optical fiber amplifier, for example, in Japanese Unexamined Patent Application Publication No. 2004-297101 (Patent Document 3), an optical fiber that amplifies signal light by supplying pumping light to a plurality of amplifying optical fibers. An amplifier is disclosed. 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. 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 intensity of the pumping light supplied by the first pumping light supply means, the second pumping light supply means for supplying pumping light to the second amplifying optical fiber, and the first pumping light supply means is constant. Based on the first control means for controlling and the gain detected by the first gain detection means, the second control for controlling the intensity of the pumping light supplied by the second pumping light supply means to be a constant gain. And an isolator disposed between the first amplifying optical fiber and the second amplifying optical fiber.

Patent Document 1: Japanese Patent No. 2893862

Patent Document 2: JP 2004-47650 A

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-297101

Disclosure of the invention

Problems to be solved by the invention

In the LD-pumped solid-state laser shown in FIG. 14, since the two reflecting mirrors 106 and 108 are provided, the relative position of the reflecting mirror is likely to shift due to vibration or temperature change. Therefore, when a laser device is installed, adjustment for outputting laser light is required.

[0020] Further, 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-state laser, it is more susceptible to vibration shock than the LD-solid-pumped laser. In contrast, strong. However, the work for connecting the optical fiber 116 to the first cladding 220 of the optical fiber 210 is performed manually. This work increases the cost of the fiber laser device. In other words, conventional laser devices emit light from LD elements. The cost of the laser device was increasing because a lot of labor was required for the adjustment work to put the excitation light into the core.

[0022] 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, but the optical fiber becomes longer. Since the area occupied by the optical fiber becomes larger, the entire apparatus becomes larger. Even if the optical fiber is bent to reduce the area occupied by the optical fiber, the light escapes from the bent portion, so that the amplification factor decreases when the optical fiber is bent. is there.

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.

Means for solving the problem

In summary, the present invention is an optical amplifier that includes a photonic crystal fiber that propagates signal light having a main wavelength of light having a predetermined wavelength in a single mode. The photonic crystal fiber includes a signal light propagation region for propagating signal light, and has a refractive index different from each other so as to satisfy a Bragg reflection condition for light of a predetermined wavelength so as to surround a central portion of the signal light propagation region. A periodic structure having a plurality of medium forces is provided, and the signal light propagation region is doped with a light amplifying 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 region from the side surface of the photonic crystal fiber with a wavelength different from that of the signal light and excites the optical material, thereby selecting according to the periodic structure. Signal light having a predetermined wavelength as the 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 a 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 transmitted in a single mode. And a photonic crystal fiber that propagates and emits from the other end face. The photonic crystal fiber includes a signal light propagation region for propagating signal light, and has a refractive index different from each other so as to satisfy a Bragg reflection condition for light of a predetermined wavelength so as to surround a central portion of the signal light propagation region. A periodic structure having a plurality of medium forces is provided, and the signal light propagation region is doped with a light amplifying substance that causes stimulated emission when signal light is incident in an excited state. Light increase The width device 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 the signal light propagating through the photonic crystal fiber.

[0026] Preferably, the periodic structure is formed by periodically providing holes in a solid medium constituting the photonic crystal fiber in a cross section of the photonic crystal fiber.

[0027] Air exists in the pores by a solid medium. 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 having a predetermined wavelength of light as a principal wavelength in a single mode. The photonic crystal fiber has a signal light propagation region for propagating signal light, and has a refractive index that satisfies the Bragg reflection condition for light of a predetermined wavelength so as to surround the center of the signal light propagation region. A plurality of different medium force periodic structures are provided, and the signal light propagation region is doped with a light amplifying substance that induces stimulated emission when signal light is incident in an excited state. 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 and excites an optical material, and is thereby selected by a 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 reflecting portion 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 having a predetermined wavelength of light as a principal wavelength in a single mode. A photonic crystal fiber has a signal light propagation region for propagating signal light, and has a refractive index different from each other so as to satisfy the Bragg reflection condition for light of a predetermined wavelength so as to surround the center of the signal light propagation region. A periodic structure composed of a plurality of media is provided, and an optical amplification substance that induces stimulated emission when signal light is incident in an excited state is doped in the signal light propagation region. Optical amplifier side of photonic crystal fiber It further includes an excitation unit that irradiates the signal light propagation region from the signal light with a wavelength different from that of the signal light and excites the optical material, whereby light having a predetermined wavelength selected by the periodic structure is defined as the main wavelength. The signal light propagates in a single mode, and the signal light is amplified by the irradiation of the 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.

[0030] More preferably, the photonic crystal fiber is disposed so that 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 to the one end face. It is a reflecting mirror that enters and transmits part of the signal light emitted from the other end surface.

[0031] 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.

[0032] 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 excitation light emitted from the excitation unit. The excitation light reflected by the first reflecting part is reflected toward the photonic crystal fiber.

[0033] More preferably, the outer shape of the first reflecting portion is at least a part of an ellipse, and the photonic crystal fiber is disposed such that the position of the light propagation region is the position of the focal point of the ellipse.

[0034] 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 a position of the focal point of the ellipse. .

[0035] More preferably, the photonic crystal fiber generates signal light by itself generated by spontaneous emission generated in the light amplification material in response to excitation light emitted from any one of a plurality of excitation light sources. The signal amplification causes stimulated emission in the light amplification substance.

[0036] More preferably, the excitation unit irradiates the photonic crystal fiber with excitation light so that the incident angle becomes a Brewster angle.

[0037] 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 one end surface and optically coupled to the first fiber grating structure for returning the signal light reaching the one end surface toward the other end surface, and the other end surface. And a second fiber grating structure for returning the signal light reaching the other end surface toward the one end surface.

[0038] 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 includes the excitation unit The photonic crystal fiber includes a light emitting surface for emitting light in a planar shape, and the photonic crystal fiber is provided along the light emitting surface.

[0039] More preferably, the optical waveguide section is made of a foldable material.

More preferably, the laser device is provided on the opposite side of 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.

[0040] More preferably, the transmission part is a dichroic mirror that transmits light having a wavelength for exciting the light amplification substance in the excitation light.

[0041] More preferably, the transmission part is a microphone aperture lens 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 arranged at the focal point of the parabola.

[0042] More preferably, inside the light propagation region, in the cross section, another hole different from the holes constituting the periodic structure is provided in the light propagation region.

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

[0044] 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.

The invention's effect

According to the optical amplifier of the present invention, single-mode light is propagated and optical amplification is performed. Excitation light is input to the core by irradiating the side surface of the photonic crystal fiber with the excitation light. This makes it easy to make adjustments to achieve high light output while being compact.

Brief Description of Drawings

FIG. 1 is a conceptual diagram showing a configuration of an optical amplifier according to the present invention.

2 is a diagram schematically showing a cross section of the optical fiber 2 in FIG.

FIG. 3 is a schematic diagram showing a configuration of a laser apparatus according to a second embodiment.

FIG. 4 is a schematic diagram showing the configuration of the optical amplifier 1 of FIG.

FIG. 5 is a diagram showing another configuration example of the optical amplifier 1 in the second embodiment.

FIG. 6 is a diagram showing still another configuration example of the optical amplifier 1 in the second embodiment.

FIG. 7 is a schematic diagram showing a configuration of a laser apparatus according to a third embodiment.

FIG. 8 is a schematic diagram showing a configuration of a laser apparatus according to a fourth embodiment.

FIG. 9 is a view of the laser device 31 of FIG. 8 as viewed from above.

10 is a cross-sectional view taken along line XX in FIG.

FIG. 11 is a diagram showing an example of an optical fiber 2 in a fourth embodiment.

FIG. 12 is a diagram showing another example of the optical fiber 2 in the fourth embodiment.

FIG. 13 is a diagram showing another configuration example of the transmission unit 45.

FIG. 14 is a diagram showing a configuration of a resonator of a conventional LD-pumped solid-state laser.

FIG. 15 is a diagram showing a configuration of a conventional fiber laser.

16 is a diagram showing a connection between the optical fiber 116 and the resonator 202 in FIG.

FIG. 17 is a diagram showing a configuration of a conventional optical fiber amplifier.

FIG. 18 is a diagram specifically showing a cross section of the optical fiber 2 of FIG.

Explanation of symbols

[0047] 1 optical amplifier, 2, 2A, 116, 210 optical fiber, 2D hole, 4A pumping light source, 4 pumping unit, 6 light source, 8 signal light propagation region, 9 periodic structure region, 8A, 9A hole, 11 , 21, 31, 100, 200 Laser device, 12-pulse oscillation LD, 13 reflector, 14A, 14B collimator lens, 15 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 Indicator unit, 40 Driver 42 Cooling unit, 43 Isolation , 44 heat sink, 45 transmission plate, 46A, 46B Cinole, 50 Cylindrical lens, 52 cooling water, 60 microlens, 91-94 boundary, 102, 202 resonator, 104 crystal, 106, 108 reflection Mirror, 110 Q Switch, 112 LD Array, 114 Lens, 118 Fino Coupling, 218 Core, 220 1st Clad, 222 2nd Clad, 300 Optical Fiber Amplifier, 301 ί 曾 Fino, 302, 304 306 Fino ¾, 308 Fiber force plastic, D1 distance, E excitation light, LI, L2, SI, S2, S100 signal light, L3 transmitted light, L4 reflected light, LA laser light, P1 position.

BEST MODE FOR CARRYING OUT THE INVENTION

[0048] 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.

[0049] [Embodiment 1]

FIG. 1 is a conceptual diagram showing the configuration of the optical amplifier of 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 face of the optical fiber 2 as signal light S2.

[0050] The optical fiber 2 is a photonic crystal fiber. A photonic crystal is an artificial crystal in which two types of substances with different refractive indices are arranged periodically with a size and spacing equivalent to the wavelength of light. A photonic crystal has wavelength selectivity and reflects only light having a wavelength corresponding to the period of the crystal at the interface. The reason for this is that due to the energy band structure (photonic band) due to the periodic structure, the wavelength according to the period of the crystal is not allowed to exist in the photonic crystal.

[0051] The light of the wavelength selected by the periodic structure cannot penetrate into the photonic crystal. Therefore, light propagates through the 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 band gap 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 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, 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 signal light wavelength. This area has the structure provided in Air is present in the holes.

[0054] In a diffraction grating in which the refractive index changes periodically, the light of a specific wavelength is strongly reflected from the relationship between the period of the diffraction grating in the direction of the incident light and the wavelength of the light. Transmits light. Such reflection is called Bragg reflection. With respect to signal light propagating in the fiber, the period of holes 9 A 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. Bragg reflection can be generated, and signal light can propagate while being confined in the signal light propagation region 8. In addition, 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 excitation light has a wavelength different from that of the signal light, and the excitation light from the side surface of the fiber is transmitted with high transmittance by designing the periodic structure so as not to satisfy the Bragg reflection condition. Can reach propagation area 8.

[0056] The signal light propagation region 8 is doped with a rare earth element as an optical amplification substance. 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.

[0057] The wavelengths of the excitation light and the stimulated emission light differ depending on the type of rare earth element. Specific examples of rare earth elements include neodymium (Nd), ytterbium (Yb), and erbium (Er). For example, in the case of neodymium, the excitation light wavelength is 808 nm and the stimulated emission light wavelength is 1064 ηm. 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 wavelength of the excitation light is 980η m and 1480 nm, and the wavelength of the 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.

[0058] Further, by uniformly irradiating the entire area of the optical fiber 2 (in practice, the region to which the rare earth element is added) with the excitation light uniformly, the absorption probability (absorption cross-sectional area) of the excitation light caused by excessive irradiation is increased. It is possible to increase the amplification factor of the signal light and to emit light from the optical fiber by avoiding the effect of the decrease in () and maintaining a high absorption probability.

[0059] In the case of an optical amplifier or fiber laser using a conventional optical fiber, the diameter of the light propagation region must be the same as the wavelength (about 1 to several μm) in order to propagate single mode light. Nare ,. Therefore, even if the conventional optical amplifier is irradiated with excitation light from the side surface of the fiber, the diameter of the light propagation region is too small, so that the excitation light absorbed in the light propagation region is reduced. Since optical fiber 2 is a photonic crystal fiber, it can propagate single-mode light even if the diameter of the light propagation region is about 10 times that diameter. Therefore, even if the excitation unit 4 emits 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.

[0060] Next, a configuration example of the photonic crystal fiber in the embodiment of the present invention will be specifically described with reference to FIG.

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 surrounds the holes 8A of the signal light propagation region 8 in multiple layers 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. Boundary lines 9:! To 94 are lines shown for convenience as boundaries between layers.

[0062] The diameter of the air hole 8A is about 15 μm. The refractive index of the holes is almost equal to 1. In the signal light propagation region 8, ytterbium (Yb) is added as a light amplification substance. Ytteripium is added to the first layer (the area between the hole 8A and the boundary 91).

[0063] For the structure of the optical fiber 2 to be a photonic bandgap structure, the above-described layers are About 6 to 6 layers are required, but about 4 layers are required for optical fiber 2 to propagate light in a single mode (FIG. 18 shows an example of 4 layers).

[0064] When the laser oscillation wavelength is 1064 nm, the pitch Λ between the two holes 9A is about 2 to 3, the diameter d of the holes 9A is about 2 to 3 zm, and the structural parameter d / Λ is about 1

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

[0066] As described above, according to Embodiment 1, light having a predetermined wavelength is provided 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. On the other hand, a photonic crystal fiber having a periodic structure consisting of transparent materials and vacancies having different refractive indexes that satisfy the Bragg reflection condition, and from the side surface of the photonic crystal fiber toward the light propagation region By providing the pumping unit that irradiates the pumping light, the arrangement of the pumping unit with respect to the optical fiber can be easily set, and a small and high-power optical amplifier can be realized.

[0067] [Embodiment 2]

FIG. 3 is a schematic diagram showing the configuration of the laser apparatus of 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. Amplification of signal light L2 by optical amplifier 1 and signal light L2 by reflector, loss in fiber, extinction due to dopant concentration, and extinction that occurs depending on fiber length cause laser oscillation, which causes reflection mirror Laser light LA is emitted from 13 to the outside. Quenching is a phenomenon in which light energy is lost as heat by phonon emission, etc., because it absorbs light at the oscillation wavelength and stores it again.

[0068] The optical amplifier 1 includes an optical fiber 2, a plurality of pumping light sources 4A, a pulse oscillation LD12, and a cylindrical The frame 15, the reflector 16, and the heat sink 18 are configured. The optical fiber 2 is installed in a ring shape by being wound along the side surface of the separating frame 15. Since the optical fiber 2 is a photonic crystal fiber, even if it is twisted along the whirling frame 15, almost no light leaks from the bent part that is extremely resistant to bending. 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.

[0069] The plurality of excitation light sources 4A constitute the excitation unit 4 in FIG. Since the optical fiber 2 is wound around the perimeter 15, the excitation light source 4 A emits excitation light in the radial direction of the reel 15. The excitation light source 4A includes an LD element (not shown) that performs continuous oscillation. The oscillation wavelength of the LD element is the wavelength in the transmission region of the photonic band as well as the 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.

[0070] 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, the other excitation light source 4A emits excitation light. Can be emitted. Further, as the number of excitation light sources 4A included in the laser device 11 increases, the output of the laser light can be increased.

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

[0072] The reflecting portion 16 includes reflecting portions 16A and 16B. The reflecting portion 16A is provided on the side opposite to the pumping light source 4A with respect to the optical fiber 2, and reflects the pumping light toward the light propagation region of the optical fiber 2. The reflecting portion 16B is provided along the optical fiber except for the region where the excitation light source 4A force is irradiated with the excitation light. The reflection unit 16B reflects the reflected excitation light toward the optical fiber 2 together with the reflection unit 16A. As described above, 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 constituted by, for example, a prism sheet (diffraction grating sheet), a metal vapor deposition sheet, a sheet with a multilayer dielectric coating, or the like. [0073] A heat sink 18 is provided between each of the plurality of excitation light sources 4A. Since the heat from the LD element included in the excitation light source can be released by the heat sink 18, an increase in the 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 A is provided inside the firing frame 15 with respect to the optical fiber 2, while the excitation light source 4 A is provided outside the firing frame 15 with respect to the optical fiber 2. It ’s okay.

[0075] The reflecting mirror 13 is made of, for example, quartz glass. Quartz glass has the advantage of small volume expansion with temperature. 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 be ensured to be 99% or more when a dielectric multilayer film is used on the reflecting surface. Note that the oscillation wavelength of the laser beam can be finely adjusted by changing the distance between the optical fiber 2 and the reflecting mirror 13.

Thus, in the laser device of Embodiment 2, only one reflecting mirror is provided for optical fiber 2. Therefore, since the number of reflecting mirrors is smaller than that of a conventional LD-pumped solid-state laser, the position S can be easily adjusted even if the optical amplifier 1 and the reflecting mirror 13 are displaced 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 rays.

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 complication of the figure.

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 is the angle of incidence where the 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 center value of the polarization direction and incident angle of the LD used for the excitation light is the Brewster angle, the excitation light E efficiently enters the optical fiber 2, so that 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 showing another configuration example of the optical amplifier 1 in the second embodiment. See Figure 5 The optical fiber 2, the reflection part 16C, the LD element 19 and the electrode 19A are shown. The electrode 19 A is an electrode for applying a drive voltage to the LD element 19 and controlling its operation. 5 shows a cross section of the main part of the optical amplifier 1 as seen from the propagation direction of the signal light.

[0081] The external 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. Thus, the excitation 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, the reflecting portion 16C is provided along the optical fiber 2, so that the length of the reflecting portion 16C is only the length of the optical fiber 2.

FIG. 6 is a diagram showing still another configuration example of the optical amplifier 1 in the second embodiment. Referring to FIG. 6, optical fiber A, 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. Similar to the optical amplifier 1 shown in FIG. 5, since the pumping light E emitted from the LD element 19 is collected in the signal light propagation region 8, the pumping light E can be efficiently absorbed in the light propagation region. In the case of the optical amplifier shown in FIG. 6, it is not necessary to provide a reflection part outside the optical fiber, so that the cost of the laser device can be reduced.

[0084] 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 ray, 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 a signal light propagation region 8 is provided at the focal point of the parabola.

[0085] 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 a single reflecting mirror, whereby the reflecting mirror and the optical amplifier are It becomes possible to realize a laser apparatus that can easily adjust the relative position and can easily change the wavelength and output of the laser beam. [0086] [Embodiment 3]

FIG. 7 is a schematic diagram showing the configuration of the laser apparatus of the third embodiment. Referring to FIG. 7, laser device 21 is different from laser device 11 of FIG. 2 in that it includes a pulse oscillation LD 12 and includes a mirror, a dot, and a reflecting mirror 22. Since the configuration of other parts of laser device 21 is the same as the configuration of the corresponding portion 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 pumping 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 Embodiment 2, 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 L2 is output from both end faces of the optical fiber 2. Therefore, transmitted light L3 is generated as light passing through the reflecting mirror 13 in addition to the laser light.

In Embodiment 3, a reflecting mirror 22 that reflects the transmitted light L3 is provided. The transmitted light L 3 is reflected by the reflecting mirror 22, and the reflected light L 4 and the laser light LA are combined at a position P 1 on the reflecting mirror 13. Therefore, in Embodiment 3, it is possible to prevent the output of the laser beam LA from being lowered. In Embodiment 3, since there is no light emitted to the outside other than the laser beam LA, when the operator processes the product using the laser apparatus, the operator can easily perform the laser. The device can be handled.

[0090] In order to prevent the output of the laser beam LA from decreasing when the reflected light L4 and the laser beam LA are combined, the phase of the laser beam LA and the phase of the light L4 must be the same at the position P1. Don't be. For this reason, the distance D1 from the position P1 to the reflecting mirror 22 must be set to be an integral multiple of half the oscillation wavelength (half wavelength). In the third embodiment, as in the second embodiment, a reflecting portion 16C shown in FIG. 5 may be used instead of the reflecting portion 16. In the third embodiment, optical fiber 2A may be used instead of optical fiber 2.

As described above, according to the third embodiment, the output of the pumping light output from the pumping light source is increased so that spontaneous emission occurs in the light propagation region of the optical amplifying fiber, thereby performing continuous oscillation. An apparatus can be realized.

[0093] [Embodiment 4]

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

[0094] Wavelength selectors 36A and 36B are provided at both ends of the optical fiber 2. Wavelength selector 36A,

36B has a function equivalent to the conventional FBG, and the reflectance is set selectively high only for a specific wavelength. Instead of the wavelength selectors 36A and 36B, 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 is coated on the both end faces of the optical fiber 2. Moyore.

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 balance, 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 to reflect most of the light and transmit part of the light.

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 one of the LD elements no longer emits excitation light due to a failure, the other LD element may cause the optical fiber to fail. 2 can be excited. In addition to the LD element 19, the light source included in the excitation unit 4 may be an LED (Light Emitting Diode; including an LED backlight) 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. Light guide 34 is excitation light It has a light emitting surface for emitting 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. Since the excitation light is uniformly irradiated rather than irradiating the optical fiber 2 locally, absorption saturation is less likely to occur, and the rare earth element can be efficiently excited without increasing loss. .

The control unit 32 is a pulse generator that generates an arbitrary waveform, for example. The control unit 3 2 controls the current injected into the pulse oscillation LD 12 based on the instruction sent from the instruction unit 38 and the instruction unit 38 that outputs an instruction for controlling the output and temperature of the laser beam. And driver 40 that performs processing.

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 cools the optical fiber 2 by circulating cooling water.

[0100] In the second and third embodiments, 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. Note that an optical fiber is preferably provided so as to cover the entire light emitting surface so that a large amount of 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. An optical fiber 2 is provided along the light emitting surface 35. Note that an isolator 43 is provided between the pulse oscillation LD 12 and the wavelength selector 36A. The isolator 43 blocks the light S that passes the signal light L1 emitted from the pulse oscillation LD12 through the optical fiber 2 and the light that returns from the optical fiber 2 to the pulse oscillation LD12. The isolator 43 prevents the return light from entering the pulse oscillation LD 12. Therefore, the pulse oscillation LD12 is protected. The isolator 43 may not be included in the laser device 31.

FIG. 10 is a cross-sectional view taken along line XX in FIG. Referring to FIG. 10, optical fiber 2 is sandwiched between reflecting part 16 A and transmitting part 45. The reflecting portion 16 A is a metal film laminated on the surface of the heat sink 44. The reflecting portion 16A 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. [0103] The angle of the upper surface of the heat sink 18 (the reflecting surface of the light guide 34) and the angle of the lower surface of the heat sink 44 are set so that the excitation light reflected by the reflecting portion 16A does not return to the LD element. It is preferable.

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 via the transmission part 45.

[0105] The light guide 34 is a transparent substance 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 terephthaiate).

The seals 46A and 46B are used to seal the cooling water 52 between the optical fibers 2. Cooling water

Since the heat of 52 is released 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 reflective film (not shown) that reflects the excitation light E.

It is to be noted that, in the same way as in the second and third embodiments, the optical amplifier is used in the fourth embodiment.

In order to increase the amplification factor at 1, it is preferable to efficiently collect the excitation light E in the light propagation region of the optical fiber. Hereinafter, the shape and configuration of the photonic crystal fiber that can efficiently collect the excitation light in the light propagation region will be described.

FIG. 11 is a diagram showing an example of the optical fiber 2 in 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 light beam, the excitation light E is efficiently collected in the signal light propagation region 8 by providing the signal light propagation region 8 at the focal point of the parabola. Is possible.

FIG. 12 is a diagram showing another example of the optical fiber 2 in the fourth embodiment. Referring to FIG. 12, the shape of optical fiber 2 is a parabola. However, the hole 2D is provided in the signal light propagation region 8 in the cross section. In particular, when outputting high-power laser light, these holes are provided in the signal light propagation region 8 to avoid an increase in the absorption coefficient due to the presence of high-density light and to reduce output loss. It becomes possible to suppress. FIG. 13 is a diagram illustrating another configuration example of the transmission unit 45. Referring to FIG. 13, a microlens array including microlenses 60 as transmissive portions 45 is formed on light emitting surface 35. 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, light can be efficiently collected in the light propagation region.

As described above, according to the fourth embodiment, the excitation light is incident on the side surface of the photonic crystal fiber from the light emitting surface, so that a single mode laser beam can be output while being small. It becomes possible.

[0112] The embodiments 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

The scope of the claims

[1] A photonic crystal fiber (2) that propagates a single-mode signal light with a predetermined wavelength of light as the main wavelength.

The photonic crystal fiber (2)

Including a signal light propagation region (8) for propagating the signal light,

A periodic structure (9) composed of a plurality of media having different refractive indexes satisfying the Bragg reflection condition for the light of the predetermined wavelength is provided 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 induces stimulated emission when the signal light is incident in an excited state,

Excitation light having a wavelength different from that of the signal light is irradiated from the side surface of the photonic crystal fiber (2) toward the signal light propagation region (8), and an excitation unit (4) for exciting the optical material is further provided. Prepared,

Thereby, an optical amplifier that propagates in a single mode 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 of the excitation light.

[2] 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 it from the other end surface;

The photonic crystal fiber (2)

Excitation light having a wavelength different from that of the signal light is irradiated from the side surface of the photonic crystal fiber (2) toward the signal light propagation region (8), and the excitation part (4) for exciting the optical material is further exposed. To prepare for,

An optical amplifier for amplifying the signal light propagating through the photonic crystal fiber (2).

[3] The periodic structure (9) is formed by periodically providing holes in the solid medium constituting the photonic crystal fiber in the cross section of the photonic crystal fiber (2). The optical amplifier according to claim 1 or 2.

[4] A laser device (31) comprising:

With optical amplifier (1)

The optical amplifier (1)

It includes a photonic crystal fiber (2) that propagates signal light whose main wavelength is light of a predetermined wavelength in a single mode,

The photonic crystal fiber (2)

A signal light propagation region (8) for propagating the signal light;

The optical amplifier (1)

Excitation light having a wavelength different from that of the signal light is irradiated from the side surface of the photonic crystal fiber (2) toward the signal light propagation region (8), and an excitation unit (4) for exciting the optical material is further provided. Including

Accordingly, the signal light having the light of the predetermined wavelength selected by the periodic structure (9) as a main wavelength is propagated in a single mode, the signal light is amplified by the irradiation of the excitation light, and the laser device (31) is

The laser device further comprising a reflection part that reflects the signal light on each end face of the photonic crystal fiber (2).

[5] A laser device (11) comprising:

With optical amplifier (1) The optical amplifier (1)

The photonic crystal fiber (2)

A signal light propagation region (8) for propagating the signal light;

The optical amplifier (1)

Accordingly, the signal light having the light of the predetermined wavelength selected by the periodic structure (9) as a main wavelength is propagated in a single mode, the signal light is amplified by the irradiation of the excitation light, and the laser device (11)

A laser apparatus, 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.

[6] 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. 6. The laser device according to claim 5, wherein

[7] A first reflecting section (provided on the side opposite to the excitation section (4A) with respect to the photonic crystal fiber (2) and reflecting the excitation light toward the photonic crystal fiber (2) ( 16

The laser device according to claim 6, further comprising A).

[8] The laser device (11) includes the photonic crystal fiber (2) and the excitation unit (4A). A second reflecting portion (16B) provided between

The second reflecting part (16B) transmits the excitation light emitted from the excitation part (4A) and transmits the excitation light reflected by the first reflection part (16A) to the photonic crystal fiber ( The laser device according to claim 7, which reflects toward 2).

[9] 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.

[10] 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 disposed at a focal point of the ellipse.

[11] The photonic crystal fiber (2) includes the signal light by spontaneous emission generated in the light amplification substance in response to excitation light emitted from any excitation light source power of the plurality of excitation light sources (19). 7. The laser device according to claim 6, wherein the laser light is generated by itself and stimulated emission is caused in the light amplification substance by the generated signal light.

12. 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.

13. 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.

[14] 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;

The laser device according to claim 5, further comprising: a second fiber grating structure (36B) optically coupled to the other end surface and returning the signal light reaching the other end surface toward the one end surface.

[15] The laser device (31) is an optical device that 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). The wave section (34) is further provided, The optical waveguide (34) includes a light emitting surface (35) for emitting the excitation light in a planar shape, and the photonic crystal fiber (2) is provided along the light emitting surface (35). The laser device according to claim 14.

16. The laser device according to claim 15, wherein the optical waveguide section (34) is made of a foldable material.

[17] The laser device (31) includes:

A reflection portion (16A) that is provided on the opposite side of the light emitting surface (35) with respect to the photonic crystal fiber (2) and reflects the excitation light toward the photonic crystal fiber (2); The laser device according to claim 15, further comprising a transmission part (45) provided between a surface (35) and the photonic crystal fiber (2) and transmitting the excitation light.

18. The laser device according to claim 17, wherein the transmission unit (45) is a dichroic mirror that transmits light having a wavelength that excites the light amplification substance in the excitation light.

[19] The laser device according to [17], wherein the transmission section (45) is a microlens array including a plurality of microlenses (60) that collect the excitation light.

[20] 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. The laser device according to claim 15.

[21] 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. The laser apparatus according to 20.

[22] The laser according to claim 14, wherein the laser device (31) further includes a cooling unit (42) for circulating cooling water (52) for immersing and cooling the photonic crystal fiber (2). Equipment

[23] An optical waveguide (34) provided between the pumping section (4) and the photonic crystal fiber (2) and guiding the pumping light to a side surface of the photonic crystal fiber (2). The optical waveguide (34) includes a light emitting surface (35) for emitting the excitation light in a planar shape, and the photonic crystal fiber (2) is provided along the light emitting surface (35). , Claims An optical amplifier according to 1.