JP2007134414A - Light source apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide small laser equipment or an ASE light source with a single mode, sufficient efficiency and stable output. <P>SOLUTION: Laser equipment or the light source uses an excitation LD whose wavelength is longer than light that a wavelength of excitation light generates, a resonator, and a rare earth element addition fiber. The fiber normalization frequency V of the rare earth element addition fiber is 2.4<V<3.9 with respect to the generated wavelength of light. A fiber at the single mode to light generated by a part of fibers except for the rare earth addition fiber is inserted into the resonator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fiber laser device using a rare earth element-doped fiber.

Conventionally, much research has been conducted on optical fiber lasers using rare earth-doped fluoride fibers. Above all, the visible light laser realized by adding rare earth elements such as Nd ³⁺ , Tm ³⁺ , Er ³⁺ , Ho ³⁺ , Pr ³⁺ into the core of the fluoride fiber is the red color characteristic of this material. This is a phenomenon utilizing an up-conversion phenomenon in which light having a shorter wavelength than the excitation light can be obtained from excitation light such as external light.

  Visible fiber lasers are expected to be visible light sources because they have a shorter wavelength than infrared light and also have advantages specific to fiber lasers. (For example, refer to Patent Document 1 and Non-Patent Document 1).

  The normalized frequency V of the fiber is defined as the following equation (1).

V = (2π / λ) ・ NA ・ a (1)
Where λ is the wavelength of light, NA is the numerical aperture of the fiber, and a is the radius of the core of the fiber.

  In particular, the value of λ when V = 2405 in a certain fiber (NA and a are constant) is called a cutoff wavelength λc. When V <2.405, light of a certain wavelength in a certain fiber is propagated in a single mode, and when V> 2.405, it is propagated in a multimode. Therefore, in a certain fiber, the mode changes depending on the length of the wavelength with λc as a boundary, and the mode changes when the NA and a of the fiber change even at the same wavelength.

Conventionally, when obtaining a single mode laser in a fiber laser, a rare earth element-doped fiber that can obtain a single mode with respect to laser light has been designed and selected (see Patent Document 2).
JP 2005-26475 A Japanese Patent Laid-Open No. 1-118184 “Rare-Earth-Doped Fiber Lasers and Amplifiers”; Michel JF Digonnet; MARCEL DEKKER, INC. (1993) 171-242

  However, in the fiber laser using the up-conversion process that is the subject of the present invention, the wavelength of the pumping light is longer than that of the laser beam and the wavelength difference is large, so that, for example, as described in JP-A-1-181588 When the rare earth element-doped fiber is designed and selected so that the laser beam is single mode, the pumping light is lost due to the bending loss of the fiber, or the laser beam becomes multimode if the bending loss of the pumping light is avoided.

  In order to avoid this, it is conceivable to oscillate the laser light in a multimode and then extract the laser light in a single mode. However, it is necessary to couple the laser to a single mode output fiber for the laser light. At this time, there is a problem that the connection loss is increased and the energy conversion efficiency as the laser device is deteriorated. In addition, when a fiber in which a multimode exists is exposed to a temperature change, the intensity distribution of the laser in the fiber changes, and as a result, the laser lacks stability.

  In addition, there is a method using a double-clad fiber, but it is difficult to produce a high-quality double-clad fiber with a fluoride fiber or a chalcogenide fiber, which is prone to an upconversion phenomenon. The structure of the input / output unit has become complicated.

  The present invention has been made in view of the above circumstances, and provides a small laser device or an ASE light source having a single mode and an efficient and stable output.

  In order to solve the above-mentioned problem, the present invention provides a fiber laser device using the up-conversion phenomenon, wherein the normalized frequency V of the rare earth element-doped fiber is 2.4 <V <3.9 with respect to the wavelength of the laser light. It is.

  Further, only a part of the fiber in the resonator is a fiber laser device that is a single mode fiber for the generated laser light.

  In addition, the fiber laser device uses an up-conversion phenomenon in which the wavelength of pumping light is longer than that of laser light and includes a pumping LD, a resonator, and a rare earth-doped fiber.

  Further, the fiber laser device uses any one of fluoride glass, fluorine oxide glass, fluoride crystal-containing glass, and fluorine oxide crystal-containing glass as a rare earth-doped fiber.

  In addition, a fiber laser device in which a fiber that is single mode with respect to generated light is installed in a place other than between the rare earth-doped fiber and the pumping LD in the resonator.

  By setting the normalized frequency V of the rare earth element-doped fiber to 2.4 <V <3.9 with respect to the wavelength of the laser beam, even a laser using an upconversion process in which the laser wavelength is shorter than the pump wavelength, Thus, the bending loss of the fiber becomes small enough to be ignored, and the fiber can be bent and stored, so that the apparatus can be miniaturized.

  In addition, by inserting a single mode fiber for the laser light generated in the resonator, the laser is mainly single mode. Loss due to mode mismatch is minimized.

  In order to solve the above problems, the present invention provides a fiber laser device using an upconversion phenomenon, wherein the normalized frequency V of the rare earth element-doped fiber is 2.4 <V <3.9 with respect to the wavelength of the laser beam, and resonance Only a portion of the fiber in the chamber is a single mode fiber for the generated laser light. The bending loss of the fiber is reduced with respect to the pumping light, the pumping light can be used efficiently, and a pseudo or intrinsic single mode laser is obtained, and the laser beam loss is small even if it is guided to the single mode fiber. As a result, an efficient fiber laser device can be obtained.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing an example of a fiber laser device of the present invention. The fiber laser includes an excitation light source 101, a 550 nm band broadband filter 102, a rare earth element doped fiber 103, a single mode fiber 105, and a fiber Bragg grating 106.

  Since the excitation light source 101 is for activating the rare earth element in the rare earth element doped fiber 103, it is not limited to the type or wavelength of the laser. Depending on the type of rare earth element and the wavelength of the laser beam to be obtained, it is necessary to replace it with an appropriate one.

  A Fabry-Perot type resonator is formed by using the broadband filter 102 and the fiber Bragg grating 106.

  In fabricating the resonator, it is only necessary to reflect light of a specific wavelength among the ASE light. Unlike the figure, both may be mirrors, both may be fiber Bragg gratings, or other methods may be used. Absent.

  The resonator may be a ring resonator.

  As the rare earth element-doped fiber 103, an erbium-doped fluoride fiber or the like can be used. The rare earth element may be other excited active elements that are not erbium. An example is shown in Table 1.

  Further, ZBLAN or the like can be used as the base material to be added, but quartz glass, chalcogenide glass, or the like may be used as long as gain can be obtained substantially at the upconversion emission wavelength. These may be in any combination as necessary.

  The V value of the rare earth element-doped fiber 103 needs to be 2.4 <V <3.9 with respect to the wavelength of the generated laser light. In the case of V ≦ 2.4, a bending loss of the fiber occurs in the pumping light, so that efficient pumping cannot be performed, or the rare earth element-doped fiber 103 cannot be bent at a desired radius, and the apparatus cannot be downsized.

  In the case of V ≧ 3.9, the laser is induced in the multi-mode, so that when the laser is to be taken out in the single mode from now on, the loss becomes large, and as a result, the laser device is not efficient.

  The single mode fiber 105 needs to satisfy V <2.405 with respect to the laser light.

  The insertion position of the single mode fiber is most preferably a place other than between the pumping LD and the rare earth doped fiber in the resonator. When inserted between the pumping LD and the rare earth doped fiber, the bending loss to the pumping light by the single mode fiber may increase, and it becomes impossible to provide a stable and efficient fiber laser device.

  In addition, an optical isolator, a polarization controller, a band pass filter, a coupler, a lens, and the like may be incorporated inside and outside the resonator.

  Hereinafter, the present invention will be described with reference to examples.

  FIG. 1 is a schematic diagram showing an example of a fiber laser device of the present invention.

  The fiber laser includes an excitation light source 101, a 550 nm band broadband filter 102, a rare earth element doped fiber 103, an optical coupler 104, a single mode fiber 105, and a fiber Bragg grating 106.

  As the excitation light source 101, a semiconductor laser having a wavelength of 974 nm was used. A 200 cm erbium-doped fluoride fiber was used as the rare earth element-doped fiber 103. A Fabry-Perot type resonator was formed using a 550 nm band broadband filter 102 and a fiber Bragg grating 106. The 550 nm band broadband filter 102 had a reflectivity of 99.9% in the wavelength range of 538 nm to 546 nm, and the fiber Bragg grating 106 had a reflectivity of 80% at a wavelength of 543 nm.

As the fiber Bragg grating 106, a fiber having a V _FBG of 2.53 and a grating is used with respect to a laser beam of 543 nm. The rare earth element-doped fiber 103 was wound in a ring shape with a diameter of 45 mm. The V _RDF for the light of 543 nm of the rare earth element-doped fiber 103 in this example was 3.52. The single mode fiber 105, V _SM to light of a laser beam 543nm is 1.9, using a fiber of V _SM <2.4.

  Excitation light emitted from the excitation light source 101 excites erbium in the erbium-doped fluoride fiber, which is the rare earth element-doped fiber 103, in two stages, and the erbium-doped fluoride fiber generates ASE light near 543 nm. Of the ASE light, light having a wavelength of 543 nm is folded back by the 550 nm band broadband filter 102 and the fiber Bragg grating 106.

  The rare earth element-doped fiber 103 gradually gains by the input of excitation light, and laser oscillation occurs between the 550 nm band broadband filter 102 and the fiber Bragg grating 106. Laser light with a wavelength of 543 nm was output from the fiber Bragg grating 106 side. At this time, the laser beam output from the fiber Bragg grating 106 was emitted almost in a single mode.

  The rare earth element-doped fiber 103 was wound with a diameter of 45 mm, but there was almost no bending loss of the excitation light. The single mode fiber 105 attached according to the present invention also served as a pumping light removing filter that diverges pumping light that the rare earth element doped fiber 103 could not absorb.

  In the fiber laser device having such a configuration, an excitation power of 500 mW was input from the excitation light source 101. As a result, an output of 5 mW was obtained. Furthermore, when a fiber having the same characteristics as the single mode fiber 105 was attached to the laser output end, the connection loss was 0.2 dB, and the laser output was 4.8 mW.

(Comparative Example 1)
The same configuration as that of Example 1 except that there is no single mode fiber 103 is referred to as Comparative Example 1. The laser beam output from the fiber Bragg grating 106 was emitted in multimode. Furthermore, when a fiber having the same characteristics as the single mode fiber 105 was attached to the output end of the laser, the splice loss was 5 dB.

  FIG. 2 is a schematic view showing an example of the fiber laser device of the present invention.

  The fiber laser includes an excitation light source 101, a 550 nm band broadband filter 102, a rare earth element doped fiber 103, an optical coupler 104, a single mode fiber 105, and a loop mirror 201.

  As the excitation light source 101, a semiconductor laser having a wavelength of 974 nm was used. As the rare earth element-doped fiber 103, a 100 cm erbium-doped fluoride fiber was used. A resonator is formed using a loop mirror 201 using a 550 nm band broadband filter 102 and an optical coupler. The 550 nm band broadband filter 102 had a reflectance of 99.9% in the wavelength range of 538 nm to 546 nm.

  As the loop mirror 201, a 2 × 2 coupler having a branching ratio of 12% was used. The rare earth element-doped fiber 103 was wound in a ring shape with a diameter of 45 mm.

The V _RDF for the light of 543 nm of the rare earth element-doped fiber 103 in this example was 3.52. The single mode fiber 105, V _SM to light of a laser beam 543nm is 1.9, using a fiber of V _SM <2.4. The single mode fiber 105 was inserted between the rare earth doped fiber 103 and the 550 nm band broadband filter 102 as shown in the figure.

  An excitation power of 500 mW was input from the excitation light source 101. As a result, laser oscillation was confirmed and an output of 15 mW was obtained. Furthermore, when a fiber having the same characteristics as the single mode fiber 105 was attached to the laser output end, the connection loss was 0.2 dB, and the laser output was 14 mW.

  FIG. 3 is a schematic diagram showing an example of the fiber laser device of the present invention.

  The fiber laser includes an excitation light source 101, a rare earth element-doped fiber 103, a single mode fiber 105, two optical couplers 301 and 302, and an isolator 303.

As the excitation light source 101, a semiconductor laser having a wavelength of 974 nm was used. As the rare earth element-doped fiber 103, a 100 cm erbium-doped fluoride fiber was used. A ring resonator was formed, and the optical coupler 302 had a branching ratio of 50%. The V _RDF for the light of 543 nm of the rare earth element-doped fiber 103 in this example was 3.52. The single mode fiber 105, V _SM to light of a laser beam 543nm is 1.9, using a fiber of V _SM <2.4. The single mode fiber 105 was inserted at the position shown in the figure.

  An excitation power of 500 mW was input from the excitation light source 101. As a result, laser oscillation was confirmed and an output of 10 mW was obtained. Furthermore, when a fiber having the same characteristics as the single mode fiber 105 was attached to the laser output end, the connection loss was 0.2 dB, and the laser output was 9.5 mW.

  When the insertion position of the single mode fiber 106 was changed and the laser output was measured, the same output was obtained at any place other than between the optical coupler 301 and the rare earth element doped fiber 103 in the ring resonator.

  The present invention can be used not only in a communication system in the field of optical communication but also in an application field of optical transmission such as evaluation and measurement.

1 shows one of the cheapest configurations of a fiber laser device according to the present invention. It is a schematic diagram which shows an example of the fiber laser apparatus of the other form of this invention. It is a schematic diagram which shows an example of the fiber laser apparatus of the other form of this invention.

Explanation of symbols

101 Excitation light source
102 550nm wideband filter
103 rare earth-doped fiber
104 Optical coupler
105 single-mode fiber
106 Fiber Bragg grating
201 Loop mirror
301 optical coupler
302 Optical coupler
303 Isolator

Claims (3)

In a laser device or light source using a pumping LD, a resonator, and a rare earth element-doped fiber, the wavelength of the pumping light is longer than that of the generated light. On the other hand, a laser device characterized in that 2.4 <V <3.9, and a single-mode fiber is inserted into light generated by a part of the fiber other than the rare-earth doped fiber in the resonator. The laser device according to claim 1, wherein the rare earth-doped fiber is any one of fluoride glass, fluorine oxide glass, fluoride crystal-containing glass, fluorine oxide crystal-containing glass, and chalcogenide glass. The laser device according to claim 1, wherein a fiber that is single mode with respect to the generated light is inserted in a place other than between the rare earth-doped fiber and the pumping LD in the resonator.

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