JP2004363188A - Optical fiber laser and method of oscillating laser beam of 2.8 micro meter band - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber laser which is excellent in oscillation efficiency and capable of outputting a laser beam of high power, and to provide a method of oscillating a laser beam having a wavelength of 2.8 μm band. <P>SOLUTION: An erbium-loaded glass fiber 3 is used as a gain medium in the optical fiber laser 1 of 2.8 μm band, and an excitation optical source 2 oscillating excitation light 4 having a wavelength of above 980 nm is also used. It is preferable that the wavelength of the excitation light 4 is 985 to 1000 nm. The method of oscillating a laser beam 6 having a wavelength of 2.8 μm band comprises a process of making the excitation light 4 impinge on the erbium-loaded glass fiber 3 as a gain medium to oscillate the laser beam 6 of 2.8 μm band, wherein the excitation light 4 longer than 980 nm in wavelength is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber laser using an erbium-doped glass fiber as a gain medium, and more particularly to an optical fiber laser that oscillates a 2.8 μm band laser beam with high output.
[0002]
[Prior art]
A laser having an oscillation wavelength of 2.9 μm, which is an absorption band of water, is mainly used for medical applications. An optical fiber laser using an erbium-doped glass fiber (hereinafter sometimes referred to as EDF) as a gain medium has been proposed as a laser in the 2.9 μ band. Generally, in an optical fiber laser, in order to increase the output of laser light, it is necessary to lengthen an optical fiber serving as a gain medium. However, since the length of the optical fiber becomes longer and the length of the resonator becomes longer, the spectrum shape of the laser beam has a smaller peak power and a wider half-width at time.
Therefore, it is necessary to increase the oscillation efficiency of the laser so as to obtain a high laser output with a relatively short length.
[0003]
FIG. 3 is an energy level diagram of the erbium-doped glass fiber. When excitation light in the 980 nm band is incident on the EDF, ground level absorption (hereinafter, referred to as GSA) occurs, and electrons in the ground state ( ⁴ I _15/2 ) are excited to the excited state ( ⁴ I _11/2 ). You. Then, when transitioning from the excited state ( ⁴ I _11/2 ) to the ground state ( ⁴ I _13/2 ), 2.8 μm laser light is emitted.
In the excited state ( ⁴ I _11/2 ), when excited level absorption (hereinafter, referred to as ESA) occurs, electrons are excited to the upper level of the laser ( ⁴ F _7/2 ), resulting in 2.8 μm of electrons. The oscillation efficiency of the laser light is reduced.
[0004]
In recent years, absorption spectra of GSA and ESA in the 980 nm band of the EDF have been reported (see Non-Patent Document 1). By reducing the ESA, excellent oscillation efficiency can be obtained, and the laser output of the optical fiber laser can be increased without lengthening the optical fiber. At present, knowledge about the optimum wavelength of the excitation light has not been obtained even in Document 1.
[0005]
[Non-patent document 1]
Richard Quimby, Proceedings of the Meeting: Fiber laser sources and amplifiers, The International Engineering (The International Society for Optical Engineering), 1991, Vol. 1581, p. 72-79
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide an optical fiber laser capable of obtaining a high laser output with excellent oscillation efficiency and a method of oscillating laser light in the 2.8 μm band.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 is an 2.8 μm band optical fiber laser using an erbium-doped glass fiber as a gain medium, wherein an excitation light source oscillating excitation light having a wavelength longer than 980 nm is used. An optical fiber laser.
The invention according to a second aspect is the optical fiber laser according to the first aspect, wherein the wavelength of the excitation light is 980 to 1000 nm.
According to a third aspect of the present invention, there is provided a method of oscillating a laser beam in a 2.8 μm band by causing excitation light to enter an erbium-doped glass fiber as a gain medium, wherein excitation light having a wavelength longer than 980 nm is used. 2.8 μm band laser light oscillation method.
The invention according to claim 4 is the method for oscillating laser light in the 2.8 μm band according to claim 3, wherein pump light having a wavelength of 980 to 1000 nm is used.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating an example of the optical fiber laser according to the present embodiment. The optical fiber laser 1 has an excitation light source 2 and an erbium-doped glass fiber (hereinafter, also referred to as EDF) 3 as a gain medium.
The excitation light source 2 includes a semiconductor laser module 21 that can emit a laser beam 4 having a wavelength longer than 980 nm. The condenser lens 5 is provided so as to face the laser emission port 21a of the semiconductor laser module 21. The condenser lens 5 functions to collect the excitation laser light 4 emitted from the semiconductor laser module 21 and to couple the excitation laser light 4 to the incident end face 31 of the EDF 3 on which a rear mirror 71 described later is deposited. Is what you do.
[0009]
The EDF 3 is made of a glass material in which erbium is added to fluoride glass, quartz glass, or the like, and can be used as a gain medium. The EDF 3 is adjusted so as to oscillate the laser light 6 in the 2.8 μm band.
For example, the EDF 3 is a single mode fiber that is made of fluoride glass to which erbium is added and that employs a cladding pump method having a double cladding structure. The double clad structure is a structure in which a double clad is provided around a core. The excitation laser light propagates through the first clad surrounding the core, and the oscillation laser light can propagate through the core.
The EDF 3 is arranged such that one end face (hereinafter, also referred to as an incident end face) 31 faces the condenser lens 5.
[0010]
A rear mirror 71 is vapor-deposited on the incident end face 31 of the EDF 3, and an output coupler 72 is provided on the other end face (hereinafter also referred to as an output end face) 32. Examples of the output coupler 72 include a coupler that functions as a reflecting mirror using Fresnel reflection, and a coupler that includes a multilayer mirror. The output coupler 72 may be formed on the emission end face 32 of the EDF 3 by a vapor deposition method or the like.
The rear mirror 71 and the output coupler 72 are reflection mirrors, are disposed to face each other via the EDF 3, and function as the resonator 7.
Further, a long wave pass filter 8 formed by stacking a plurality of oxides having different refractive indexes on the emission end face 32 side of the EDF 3 is provided. Of the oscillation laser light 6 emitted from the EDF 3, For example, only light in the long wavelength range of 2.56 μm or more is transmitted and output.
[0011]
When the excitation light source 2 emits the excitation laser light 4 having a wavelength longer than 980 nm, the excitation laser light 4 is condensed by the condenser lens 5 and coupled to the incident end face 31 of the EDF 3 on which the rear mirror 71 is deposited. You. The EDF 3 is excited by the incident excitation laser light 4, and the 2.8 μm-band laser light 6 is emitted from the emission end face 32.
[0012]
FIG. 2 shows the light output of the oscillation laser light 6 in the 2.8 μm band emitted from the EDF 3 when the wavelength of the excitation laser light 4 is changed in the range of 966 nm to 1011 nm, and the wavelength of the excitation laser light 4. FIG.
Here, FIG. 2 shows the result of using a single-mode fiber having a double clad structure, which is made of erbium-doped fluoride glass as the EDF 3. The EDF 3 is made of a Zr—Ba—La—Al—Na-based fluoride (hereinafter, also referred to as ZBLAN), has a core diameter of 10 μm, and has a first clad having a rectangular cross section of 100 μm × 200 μm. is there. The output of the excitation laser beam 4 incident on the EDF 3 was kept constant at 2 W.
[0013]
When the wavelength of the excitation laser beam 4 is in the range of 965 nm to 985 nm, the longer the wavelength of the excitation laser beam 4 is, the higher the light intensity of the obtained oscillation laser beam 6 becomes, and when the wavelength of the excitation laser beam 4 is 985 nm. The light intensity of the oscillation laser light 6 is maximized.
When the wavelength of the excitation laser beam 4 is 980 to 1000 nm, the light intensity of the oscillation laser beam 6 is 240 mW or more, and the oscillation laser beam 6 having a higher intensity than when the wavelength of the excitation laser beam 4 is 980 nm is used. It can be seen that it can be obtained.
[0014]
In this embodiment, by setting the wavelength of the excitation laser beam 4 to be longer than 980 nm, the 2.8 μm band laser beam 6 can be oscillated with high oscillation efficiency. The wavelength of the pumping laser beam 4 is preferably 985 to 1000 nm, whereby the high-output laser beam 6 can be obtained with a higher oscillation efficiency than in the case where the conventional pumping laser beam of about 980 nm is used. .
[0015]
In addition, the EDF 3 made of fluoride glass has almost no light absorption in the 2.8 μm band and can suppress the propagation loss of the 2.8 μm band oscillating laser light 6, thereby efficiently and efficiently producing a high output 2. A laser beam 6 in the .8 μm band can be oscillated.
Further, the EDF 3 has a double clad structure, and the first clad surrounding the core is the excitation laser light 4 serving as an excitation region. Therefore, the excitation laser light 4 is wide in the incident end face 31 of the EDF 3 including the first clad. The area can be irradiated, and for example, a high-output semiconductor laser can be used as the excitation light source 2. Thus, high-output 2.8 μm-band laser light 6 can be realized relatively easily.
[0016]
Note that the technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention.
For example, as the pumping light source 2, a tapping fiber is provided at the output port, and a pumping light is emitted from the tapping fiber. May be.
Further, the core radius, the refractive index distribution shape, the erbium concentration distribution, and the like of the EDF 3 are not particularly limited. For example, the DEF 3 is a multimode fiber or a cross section of the EDF 3 in which the outer periphery of the first cladding is square or circular. It does not matter.
Further, a configuration may be employed in which a Q switch or the like is provided on the incident end face 31 side or the output end face 32 side of the EDF 3 so that the laser beam 6 can oscillate in pulses.
[0017]
【The invention's effect】
As described above in detail, the optical fiber laser of the present invention can efficiently oscillate a 2.8 μm band laser beam with a high output by setting the excitation light wavelength to be longer than 980 nm.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of an optical fiber laser according to an embodiment.
FIG. 2 is a diagram showing the relationship between the optical output of a 2.8 μm-band oscillation laser beam emitted from an erbium-doped glass fiber and the wavelength of an excitation laser beam.
FIG. 3 is an energy level diagram of an erbium-doped glass fiber.
[Explanation of symbols]
1 ‥‥ optical fiber laser, 2 ‥‥ excitation light source, 3 ‥‥ erbium-doped glass fiber, 4 ‥‥ excitation light, 6 ‥‥ 2.8 μm band laser light

Claims (4)

An 2.8 μm band optical fiber laser using an erbium-doped glass fiber as a gain medium,
An optical fiber laser using an excitation light source that oscillates excitation light having a wavelength longer than 980 nm. 2. The optical fiber laser according to claim 1, wherein the wavelength of the excitation light is 980 to 1000 nm. A method of oscillating 2.8 μm-band laser light by injecting excitation light into an erbium-doped glass fiber as a gain medium,
A method of oscillating 2.8 μm band laser light, characterized in that pump light having a wavelength longer than 980 nm is used. The method for oscillating 2.8 μm band laser light according to claim 3, wherein excitation light having a wavelength of 98 to 1000 nm is used.

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