WO2007055137A1

WO2007055137A1 - Light source device

Info

Publication number: WO2007055137A1
Application number: PCT/JP2006/321873
Authority: WO
Inventors: Takuya Teshima; Yoshinori Kubota
Original assignee: Central Glass Company, Limited
Priority date: 2005-11-08
Filing date: 2006-11-01
Publication date: 2007-05-18
Also published as: JP2007134414A

Abstract

A laser device or a light source employing a pumping LD emitting excitation light having a wavelength longer than that of the emitting light, a resonator, and a rare earth element-added fiber characterized in that the standardized frequency V of the rare earth element-added fiber is between 2.4 and 3.9 times of the wavelength of the emitting light, and a fiber exhibiting single mode for such a light as generated by a part of fibers other than the rare earth element-added fiber is inserted into the resonator.

Description

Specification

Light source device

Technical field

[0001] The present invention relates to a fiber laser device using a rare earth element-doped fiber.

Background of the Invention

Conventionally, many studies have been made on optical fiber lasers using rare earth-doped fluoride fibers. Above all, visible lasers 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 are characteristic of this material. Excitation light force such as external light This phenomenon utilizes the phenomenon of obtaining light with a shorter wavelength than the excitation light, that is, the upconversion phenomenon.

[0003] Visible fiber lasers are expected to be visible light sources because they have a shorter wavelength than infrared light and have the advantages of fiber lasers. (For example, see Patent Document 1 and Non-Patent Document 1).

[0004] The standard frequency V of the fiber is defined as the following equation (1).

V = (2 / X)-NA- a

Where λ is the wavelength of light, ΝΑ is the numerical aperture of the fiber, and a is the radius of the fiber core.

[0005] In particular, the value of λ at a certain fiber (NA, a constant) V = 2.405 is called the cutoff length c. When V <2.405, light of a certain wavelength in a fiber is propagated in single mode, and when V> 2.405, it is propagated in multimode. Therefore, in a certain fiber, the mode changes depending on the length of wavelength with c as the boundary, and the mode changes when the NA and a of the fiber change even at the same wavelength.

[0006] Conventionally, when obtaining a single mode laser in a fiber laser, a rare earth element-doped fiber capable of obtaining a single mode with respect to a laser beam has been designed and selected (see Patent Document 2).

Patent Document 1: JP 2005-26475 A

Patent Document 2: Japanese Patent Laid-Open No. 11581584

Non-Patent Document 1: “Rare—Earth—Dooed Fiber Lasers and Amp Lif iers”; Mich el JF Digonnet; MARCEL DEKKER, INC. (1993) 171—242 Summary of the Invention

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 light, and the wavelength difference is large. For example, Japanese Patent Application Laid-Open No. 1-181584 If a rare earth element-doped fiber is designed and selected so that the laser light is single mode, the pump light is lost due to the bending loss of the fiber, or the laser light is It became a mode.

[0008] 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 was a problem that the connection loss was increased and the energy conversion efficiency of the laser device was degraded. In addition, when a fiber with multimodes was exposed to temperature changes, the intensity distribution of the laser in the fiber changed, resulting in a laser that lacked stability.

[0009] In addition, there is a method using a double clad fiber. The up-conversion phenomenon is likely to occur! /, And fluoride fiber and chalcogenide fiber! In addition, the structure of the input and output parts of the excitation light and laser light has become complicated.

[0010] The present invention has been made in view of the above circumstances, and provides a small laser device or an ASE light source that is single-mode and has high efficiency and stable output.

[0011] In order to solve the above problems, the present invention provides a fiber laser device using an up-conversion phenomenon. The standard frequency V of the rare earth element-doped fiber is 2. A fiber laser device in which 4 <V <3.9 is provided.

[0012] Further, the present invention is a fiber laser device that is a single mode fiber with respect to laser light generated by a part of the fiber in the resonator.

[0013] Further, the present invention is a fiber laser device using an up-conversion phenomenon that includes an excitation LD, a resonator, and a rare earth-doped fiber in which the wavelength of the excitation light is longer than that of the laser light.

[0014] Further, a fiber laser device using any one of a fluoride glass, a fluoride oxide glass, a fluoride crystal-containing glass, and a fluoride oxide crystal-containing glass as a rare earth-doped fiber. It may be a position.

[0015] In addition, a fiber laser device installed in a place other than between the rare earth doped fiber and the pumping LD in the fiber force resonator that is single mode with respect to the generated light may be used.

FIG. 1 shows one of the cheapest configurations of a fiber laser device according to the present invention.

FIG. 2 is a schematic diagram showing an example of a fiber laser device according to another embodiment of the present invention.

FIG. 3 is a schematic view showing an example of a fiber laser device according to another embodiment of the present invention.

Detailed description

[0017] The present invention can be used not only for communication systems in the field of optical communication but also for application fields of optical transmission such as evaluation and measurement.

[0018] A laser using an upconversion process in which the laser wavelength is shorter than the excitation wavelength by setting the standard 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 so, the bending loss of the fiber with respect to the excitation light is sufficiently small to be negligible, and the fiber can be bent and stored, so that the apparatus can be miniaturized.

[0019] In addition, by inserting a fiber that becomes a single mode with respect to the laser beam generated in the resonator, the laser is mainly single mode, so when outputting the laser, the laser outputs the single mode fiber. Even so, losses due to mode mismatch are minimized.

[0020] In order to solve the above-mentioned problems, the present invention provides a fiber laser device using an up-conversion phenomenon. The standard frequency V of the rare earth element-doped fiber is 2 with respect to the wavelength of the laser light. 4 <V <3.9, and a single mode fiber is used for the laser beam generated by only a part of the fiber in the resonator. The bending loss of the fiber with respect to the pumping light is reduced, the pumping light can be used efficiently, and a pseudo or intrinsic single-mode laser is obtained, and the loss of the laser light 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. Fiber laser Consists of a pump 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.

Using a broadband filter 102 and a fiber Bragg grating 106, a Fabry-Perot resonator is formed.

[0025] Unlike the figure in which the resonator can be manufactured as long as it can reflect light of a specific wavelength in the ASE light, both may be mirrors or both may be fiber Bragg gratings. It doesn't matter.

[0026] The resonator may be a ring resonator.

For 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.

[table 1]

The glass used as the base material to be added can be used by ZBLAN, etc. If a gain can be obtained at an upconversion emission wavelength, quartz glass, chalcogenide glass, etc. It doesn't matter. These may be in any combination as necessary.

[0029] 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.

[0030] When V ≥ 3.9, the laser is induced in multimode, so when attempting to take out the laser in single mode from now on, the loss increases, and as a result, an efficient laser device cannot be obtained.

[0031] The single mode fiber 105 needs to satisfy V <2.405 with respect to the laser beam.

[0032] The insertion position of the single mode fiber is most preferably a place other than between the pumping LD force rare earth doped fiber in the resonator. If the pumping LD force is also inserted between the rare-earth doped fibers, the bending loss of the pumping light by the single mode fiber may increase, making it impossible to provide a stable and efficient fiber laser device.

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

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

Example 1

FIG. 1 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 550 nm band broadband filter 102, a rare earth element-added calophino plate 103, an optical power plastic 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 for the rare earth element-doped fiber 103. A Fabry-Perot 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.

[0038] The fiber Bragg grating 106 has a V of 2.53 for a laser beam of 543 nm. A fiber with a grating is used. The rare earth element-doped fiber 103 was wound in a ring shape with a diameter of 45 mm. The V for 543 nm light of the rare earth element-added Fino 103 in this example was 3.52. Single mode fiber 105

RDF

For the laser beam of 543nm, V is 1.9 and V is 2.4.

SM SM

Was used.

[0039] The 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, 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 η m-band broadband filter 102 and the fiber Bragg grating 106.

[0040] The rare earth element-doped fiber 103 gradually gains when the excitation light is input, and oscillates 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 single mode.

[0041] The rare earth element-doped fiber 103 had almost all the bending loss of the force-excited light with a diameter of 45 mm. The single mode fiber 105 attached according to the present invention also served as a pumping light removal 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, 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 splice loss was 0.2 dB and the laser output was 4.8 mW.

[0043] (Comparative Example 1)

Comparative Example 1 is the same as Example 1 except that no single mode fiber 103 is used. 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.

Example 2 FIG. 2 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 550 nm band broadband filter 102, a rare earth element-added calo fiber 103, a light power plastic 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. The rare earth element-doped fiber 103 was a 100 cm erbium-doped fluorinated fiber. A resonator was formed using a loop mirror 201 using a 550 nm band broadband filter 102 and an optical power bra. The 550 nm wide band filter 102 had a reflectivity of 99.9% in the wavelength range of 538 nm to 546 nm.

As the loop mirror 201, a 2 × 2 force plastic having a branching ratio of 12% was used. Rare earth element doped fiber

103 was wound in a ring shape with a diameter of 45 mm.

[0048] V of the rare earth element-doped fiber 103 in this example with respect to 543 nm light is 3.

DF

52. For the single mode fiber 105, V was 1.9 for the laser light of 543 nm, and a fiber of V <2.4 was used. Single mode fiber 105 is shown

S S

As shown in Fig. 2, the optical fiber was inserted between the rare earth doped fiber 103 and the 550nm band broadband filter 102.

[0049] 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 splice loss was 0.2 dB, and the laser output was 14 mW.

Example 3

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

[0051] The fiber laser includes an excitation light source 101, a rare earth element-doped fiber 103, a single mode fiin 105, two optical power plastics 301 and 302, and an isolator 303 force.

As the excitation light source 101, a semiconductor laser having a wavelength of 974 nm was used. The rare earth element-doped fiber 103 was a 100 cm erbium-doped fluoride fiber. A ring-type resonator was constructed, and the optical power bra 302 had a branching ratio of 50%. In this example, V for the light of 543 nm of the rare earth element-doped fiber 103 was 3.52. Single mode fiber 105 V is 1.9 for the laser light of 543nm, and V is 2.4.

SM SM

It was. Single mode fiber 105 was inserted at the position shown in the figure.

[0053] 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 splice loss was 0.2 dB and the laser output was 9.5 mW.

[0054] When the insertion position of the single mode fiber 105 was changed and the laser output was measured, the same output was obtained at a place other than between the optical power bra 301 in the ring resonator and the rare earth element doped fiber 103. It was.

Claims

The scope of the claims

[1] In a laser device or a light source using a pumping LD, a resonator, and a rare earth element-added fiber, the wavelength V of the pump light is longer than that of the generated light, the standard frequency V of the rare earth element-doped fiber is A fiber that is 2.4 <V <3.9 with respect to the wavelength of the generated light and that is a single mode is inserted into the light generated by a part of the fiber other than the rare-earth doped fiber in the resonator. A laser device characterized by comprising:

[2] According to claim 1, wherein the rare earth-doped fiber is any one of fluoride glass, fluorinated glass, glass containing fluoride crystal, glass containing fluorinated glass, and chalcogenide glass. The laser apparatus described.

[3] The laser device according to [1], wherein the pumping LD force in the single-mode fiber force resonator is also inserted at a place other than between the rare earth doped fibers.