JPH11204862A - Fiber laser and fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase efficiency and output and permit generating laser beams of a blue region and a green region, by pumping a fiber having a core to which Pr3+ is added by using a GaN based laser diode. SOLUTION: A system is composed of a laser diode 11 generating a laser beam 10 as a pumping light, a condenser lens 12 converging a laser beam 10 as a divergent light, and a fiber 13 having a core to which Pr3+ is added. As the laser diode 11, an InGaN based laser diode is used. The fiber 13 is composed of a core having a circular section, a first clad which is arranged in the outside and has an almost rectangular section, and a second clad which is arranged in the outside and has a circular section. The laser beam 10 converged by the condenser lens 12 is inputted in the core of the fiber 13. Fluorescence is generated by pumping Pr3+ . Fluorescence resonates between both ends 13a, 13b of the fiber 13, and blue and green laser beams 15 are generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber laser in which a fiber having a core doped with Pr ³⁺ is excited by a laser diode (semiconductor laser) to generate a laser beam.

[0002] Further, the present invention provides a method in which a fiber doped with Pr ³⁺ is excited by a laser diode to generate fluorescence,
The present invention relates to a fiber amplifier that amplifies light incident on a fiber by the fluorescence.

[0003]

2. Description of the Related Art For example, IEICE Technical Report, LQE95-30
(1995) p. 30 and Optics communications 86 (1991) p. 337
As shown in (1), there is known a fiber laser in which a fiber having a fluoride-based core to which Pr ³⁺ is added is excited by a laser diode to generate a laser beam.

[0004] Also, as shown in the above-mentioned document,
A fiber amplifier is known in which a fiber having a core doped with Pr ³⁺ is excited by a laser diode to generate fluorescence, and light contained in the wavelength region of the fluorescence is incident on the fiber and amplified by the energy of the fluorescence. ing.

[0005] In particular, the latter document describes a Pr ³⁺ -doped fiber laser excited by an Ar laser.
491nm, 520nm, 605nm, 635n by 6.5nm excitation
m has been confirmed.

On the other hand, for example, Japanese Patent Application No. 9-1 by the present applicant.
No. 10554 describes a solid-state laser in which a solid-state laser crystal to which Pr ³⁺ is added is excited by a laser diode.

The above-mentioned fiber lasers, fiber amplifiers, and solid-state lasers can generate or amplify a laser beam in the blue or green region, so that a color image can be formed on a color photosensitive material. It is also conceivable to configure a light source for writing.

[0008]

However, the above-described Ar laser-excited fiber laser or fiber amplifier is
If an attempt is made to excite with a power of several W to several tens of W for writing a color image or the like, since water cooling means is required, problems such as an increase in the size of the apparatus, a short life, and low efficiency are caused.

On the other hand, a solid laser in which a solid laser crystal doped with Pr ³⁺ is excited by a laser diode has a structure in which heat energy of excitation light is concentrated on a small solid laser crystal. It has been recognized that the beam quality and output stability are impaired by the thermal lens effect. This problem is particularly remarkable when pumping with a power of several W to several tens of W class.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can efficiently generate a high-output laser beam in a blue region or a green region, can be formed in a small size, and can improve the output and beam quality. An object is to provide a fiber laser having high stability.

Another object of the present invention is to provide a fiber amplifier which can efficiently amplify a laser beam in a blue region or a green region, can be formed in a small size, and has high stability in output and beam quality. I do.

[0012]

The fiber laser according to the present invention is characterized in that the fiber having the above-mentioned core doped with Pr ³⁺ is excited by a GaN-based laser diode.

In this fiber laser,
Can either ³ P ₀ → ³ by a transition of H ₄ be oscillated laser beam in the blue region of 465~495 nm, ³ P
₁ → ³ by a transition of H ₅ can also be oscillated laser beam in the green region of 515 ~555 nm.

[0014] Furthermore, ³ P ₀ → ³ F ₂ or ³ P ₀
→ The laser beam in the red region of 600 to 660 nm can be oscillated by the transition of ³ H ₆ .

A GaN-based laser diode as an excitation light source is more specifically, for example, InGaN or InGaN.
A material having an active layer made of GaNAs or GaNAs can be used.

On the other hand, the fiber amplifier according to the present invention
A fiber having a core to which r ³⁺ is added is excited by a GaN-based laser diode, and an incident light having a wavelength included in a wavelength region of fluorescence generated by the excitation is amplified. .

In this fiber amplifier, ³ P ₀
→ The transition of ³ H ₄ can generate fluorescence in the wavelength range of 465 to 495 nm to amplify the incident light of the wavelength included in this range, and the transition of ³ P ₁ → ³ H ₅ can cause the increase of 515 to 555. nm of by generating fluorescence having a wavelength region, can either be used to amplify incident light having a wavelength included in this region, and further, ³ P ₀ → ³ F ₂ or ³ P ₀ → ³ H
_By the transition of 6, fluorescence in the wavelength region of 600 to 660 nm can be generated, and the incident light having the wavelength included in this region can be amplified.

In this fiber amplifier, more specifically, a GaN-based laser diode as an excitation light source having an active layer made of, for example, InGaN, InGaNAs or GNAs can be used.

[0019]

The solid state laser crystal to which Pr ³⁺ has been added can be excited, for example, by excitation light (pumping light) having a wavelength of about 440 nm. On the other hand, an InGaN-based laser diode is free from the problem of deterioration in crystallinity at an oscillation wavelength of 450 nm or less, and thus can be suitably used to obtain excitation light having a wavelength of about 440 nm.

The thermal conductivity of this InGaN-based laser diode is 130 W / m ° C., which is much larger than that of a ZnMgSSe-based laser diode such as 4 W / m ° C. In addition, the mobility of the transition is ZnMgSSe.
Because it is very small compared to the system laser diode,
The COD (catastrophic optical damage) is very high, and a long life and high output can be easily obtained. By using an InGaN-based laser diode that easily obtains a long life and high output as the excitation light source, the fiber laser of the present invention can generate a long-life, high-power laser beam in the blue or green region.

The same applies to the case where an InGaNAs laser diode or a GaNAs laser diode is used.

Further, the fiber having a core doped with Pr ³⁺ used in the present invention can be easily formed to have a length of 0.5 m or more. In such a case, the thermal energy of the excitation light is applied to the fiber. Eliminate local concentration. Therefore, the beam quality and output stability are not impaired by heat, and the output and beam quality are stabilized.

The fiber laser of the present invention is basically composed of one fiber and a laser diode, and does not require water cooling means unlike an Ar laser-excited fiber laser. , High efficiency is realized.

All the effects described above can be similarly obtained in the fiber amplifier of the present invention.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<First Embodiment> FIG. 1 shows a fiber laser according to a first embodiment of the present invention.
This fiber laser is composed of a laser diode 11 that emits a laser beam 10 as excitation light, a condenser lens 12 that collects a laser beam 10 that is divergent light, and a fiber 13 having a core doped with Pr ^3+. Become.

The laser diode 11 has an oscillation wavelength
A 444 nm broad-area InGaN-based laser diode is used.

As shown in FIG. 2, the fiber 13 has a core 20 having a circular cross section, a first cladding 21 having a substantially rectangular cross section disposed outside the core 20, and a circular circular cross section disposed outside the core. Of the second cladding 22. Core 20 is Pr ³⁺
Doped Zr-based fluoride glass such as ZBLAN
_{P (ZrF 4 -BaF 2 -LaF 3} -AlF 3 -AlF 3 -
NaF—PbF ₂ ), and the first cladding 21 is, for example, ZBLAN (ZrF ₄ —BaF ₂ —LaF ₃ —AlF _3).
-NaF), and the second cladding 22 is made of, for example, a polymer.

The core 20 is not limited to the above ZBLANP.
ZBLAN or In / Ga-based fluoride glass such as IG
PZCL, ie, (InF ₃ -GaF ₃ -LaF ₃ )-
It may be formed using (PbF ₂ -ZnF ₂ ) -CdF or the like.

The wavelength 444 n collected by the condenser lens 12
The m laser beam 10 is input to the first cladding 21 of the fiber 13 and propagates therethrough in a guided mode. That is, the first cladding 21 is a laser beam which is an excitation light.
For 10 it acts as a core.

The laser beam 10 also passes through a portion of the core 20 during its propagation. In the core 20, Pr ³⁺ is excited by the incident laser beam 10, and ³ P
The transition from _{0 to} ³ H ₄ produces fluorescence at a wavelength of 491 nm. This fluorescence propagates through the core 20 in a guided mode.

In the core 20 composed of ZBLANP,
Other, wavelength 520nm by a transition ³ P ₁ → ³ H ₅
Fluorescent, ³ P ₀ → ³ fluorescence wavelengths 605nm by a transition F _2, the fluorescence of 635nm can be generated by a transition _³ P ₀ → ³ F ^3.

Therefore, the incident end face 13a of the fiber 13 has an HR (high reflection) and a wavelength of 520 nm for a wavelength of 491 nm.
m, 605 nm, 635 nm and an excitation light wavelength of 444 nm are coated with an AR (non-reflection) characteristic. Have been.

As a result, the fluorescence having the wavelength of 491 nm resonates between both end surfaces 13a and 13b of the fiber 13 to cause laser oscillation. Thus, a blue-green laser beam 15 having a wavelength of 491 nm is generated, and the laser beam 15 is emitted forward from the emission end face 13b of the fiber 13.

In this embodiment, the laser beam 15 is
In the first embodiment, the laser beam 10 as the excitation light propagates in the first cladding 21 in the multimode. Thereby, applying the high-power broad-area laser diode 11 to the pump light source,
The laser beam 10 can be input to the fiber 13 with high coupling efficiency.

In addition, since the cross-sectional shape of the first cladding 21 is substantially rectangular, the probability that the laser beam 10 follows an irregular reflection path in the cladding cross-section and is incident on the core 20 is increased. .

As described above, high oscillation efficiency is secured, and a high-power laser beam 15 can be obtained. In this embodiment, when the length of the fiber 13 is 0.5 m and the output of the laser diode 11 is 1 W, a laser beam 15 having an output of 100 mW was obtained.

<Second Embodiment> FIG. 3 shows a fiber laser according to a second embodiment of the present invention.
This fiber laser is basically different from the fiber laser in FIG. 1 in that a fiber 33 having a different coating on both end surfaces is used instead of the fiber 13.

That is, in the fiber laser shown in FIG.
HR (high reflection), wavelength 491 nm, 605 nm, 63
AR (non-reflective) for 5 nm and excitation light wavelength of 444 nm
Outgoing end face of fiber 33
33b is coated with 2% of light having a wavelength of 520 nm.

As a result, the fluorescence having the wavelength of 520 nm resonates between both end surfaces 33a and 33b of the fiber 33 to cause laser oscillation. Thus, a green laser beam 35 having a wavelength of 520 nm is generated, and this laser beam 35 is emitted forward from the emission end face 33 b of the fiber 33. In this embodiment, when the length of the fiber 33 is 1 m and the output of the laser diode 11 is 1 W, a laser beam 35 having an output of 200 mW is obtained.

<Third Embodiment> FIG. 4 shows a fiber laser according to a third embodiment of the present invention.
This fiber laser is basically different from the fiber laser of FIG. 1 in that a fiber 43 having a different coating on both end surfaces is used instead of the fiber 13.

That is, in the fiber laser shown in FIG. 4, the incident end face 43a of the fiber 43 has a wavelength of 635 nm.
HR (high reflection), wavelength 491 nm, 520 nm, 60
AR (non-reflective) for 5 nm and excitation light wavelength of 444 nm
Outgoing end face of fiber 43
43b is coated with 3.5% of light having a wavelength of 635 nm.

As a result, the fluorescence having the wavelength of 635 nm resonates between both end faces 43a and 43b of the fiber 43 to cause laser oscillation. Thus, a red laser beam 45 having a wavelength of 635 nm is generated, and the laser beam 45 is emitted forward from the emission end face 43b of the fiber 43. In the present embodiment, when the length of the fiber 43 is 1 m and the output of the laser diode 11 is 1 W, a laser beam 45 having an output of 300 mW was obtained.

<Fourth Embodiment> FIG. 5 shows a fiber amplifier according to a fourth embodiment of the present invention. This fiber amplifier collects a laser diode 11 that emits a laser beam 10 having a wavelength of 444 nm as excitation light, a collimator lens 50 that parallelizes the laser beam 10 that is divergent light, and a laser beam 10 that has become parallel light. It has a light-collecting lens 51 and a fiber 53 having a core doped with Pr ³⁺ .

The collimator lens 50 and the condenser lens 51
A beam splitter 52 is arranged between the two. Below the beam splitter 52 in FIG.
An SHG (second harmonic generation) laser 56 that emits m laser beams 55 is provided. This laser beam
55 is collimated by a collimator lens 57, and the collimated laser beam 55 is applied to the beam splitter 52.
Incident on.

The fiber 53 has basically the same structure as that shown in FIG. 1, but has end faces 53a and 53a.
b is provided with a coat having characteristics of AR (non-reflection) for each wavelength described above.

On the other hand, the SHG laser 56 causes a laser beam having a wavelength of 1040 nm emitted from a DBR (distributed Bragg reflection type) laser diode as a fundamental wave light source to enter an optical waveguide made of a nonlinear optical material having a periodic domain inversion structure. Thus, a laser beam 55 having a half wavelength, that is, 520 nm is obtained.

This laser beam 55 is a beam splitter
Reflects at 52 and fiber 53 with laser beam 10
Incident on. In the fiber 53, as described in the first embodiment, the wavelength
520 nm fluorescence is generated. The laser beam 55 is amplified by receiving energy from the fluorescence having the same wavelength as the laser beam 55 and is emitted forward from the emission end face 53 b of the fiber 53.

In this embodiment, when the output of the SHG laser 56 is 10 mW, a laser beam 55 having an output of 200 mW can be extracted from the fiber 53.

By adding a modulation function to the DBR laser diode, which is the fundamental light source of the SHG laser 56, the laser beam 55 amplified and taken out from the fiber 53 can be modulated.

The embodiment using the InGaN-based laser diode as the excitation light source has been described above.
A laser diode having an active layer made of a NAs-based material or a GaNAs-based material can be used as an excitation light source. In particular, when the absorption band of the fiber core is shifted to the longer wavelength side, InGaNAs that can easily realize a longer wavelength than the InGaN-based laser diode.
It is desirable to use a laser diode based on GaN or a GaNAs laser, so that the absorption efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a fiber laser according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a fiber used in the fiber laser of FIG. 1;

FIG. 3 is a schematic side view showing a fiber laser according to a second embodiment of the present invention.

FIG. 4 is a schematic side view showing a fiber laser according to a third embodiment of the present invention.

FIG. 5 is a schematic side view showing a fiber amplifier according to a fourth embodiment of the present invention.

[Explanation of symbols]

 10 Laser beam (excitation light) 11 InGaN laser diode 12 Condenser lens 13 Fiber 13a, 13b Fiber end face 15 Laser beam 20 Core 21 First clad 22 Second clad 33 Fiber 33a, 33b Fiber end face 35 Laser beam 43 Fiber 43a, 43b Fiber end face 45 Laser beam 50 Collimator lens 51 Focusing lens 52 Beam splitter 53 Fiber 53a, 53b Fiber end face 55 Laser beam 56 SHG laser 57 Collimator lens

Claims (10)

[Claims] 1. A fiber laser having a configuration in which a fiber having a core to which Pr ³⁺ is added is excited by a GaN-based laser diode. By a transition wherein _{^{3 P 0 → 3 H 4 465}} ~49
2. The fiber laser according to claim 1, wherein a laser beam in a wavelength range of 5 nm is oscillated. 3. A ³ P ₁ → ³ transition by 515-55 of H ₅
2. The fiber laser according to claim 1, wherein a laser beam in a wavelength range of 5 nm is oscillated. 4. A ³ P ₀ → ³ F ₂ or ³ P ₀ → ³ H ₆
2. The fiber laser according to claim 1, wherein a laser beam in a wavelength region of 600 to 660 nm is oscillated by the transition. 5. The GaN-based laser diode according to claim 1, wherein
The fiber laser according to any one of claims 1 to 4, wherein the fiber laser has an active layer made of nGaN, InGaNAs, or GNAs. 6. A structure in which a fiber having a core doped with Pr ³⁺ is excited by a GaN-based laser diode to amplify incident light having a wavelength included in a wavelength region of fluorescence generated by the excitation. And fiber amplifier. By a transition 7. _{^{3 P 0 → 3 H 4 465}} ~49
7. The method according to claim 6, wherein fluorescence in a wavelength region of 5 nm is generated to amplify incident light having a wavelength included in this region.
The described fiber amplifier. 8. The transition from ³ P _{1 to} ³ H ₅ causes the transition from 515 to 55.
7. The method according to claim 6, wherein fluorescence in a wavelength region of 5 nm is generated to amplify incident light having a wavelength included in this region.
The described fiber amplifier. 9. ³ P ₀ → ³ F ₂ or ³ P ₀ → ³ H ₆
7. The fiber amplifier according to claim 6, wherein the fluorescence of the wavelength range of 600 to 660 nm is generated by the transition of the above, and the incident light of the wavelength included in this range is amplified. 10. The GaN-based laser diode,
7. A semiconductor device having an active layer made of InGaN, InGaNAs or GNAs.
10. The fiber amplifier according to any one of items 1 to 9.