JPH08283096A - Laser material - Google Patents

Abstract

PURPOSE: To obtain a small-sized, high efficiency and high output laser material which emits light having a 1.03μm wavelength band and is useful as a pumping source for exciting praseodymium fluoride fiber that is employed for amplifying the light having a 1.03μm wavelength band. CONSTITUTION: This laser material is comprised of a single crystal substrate consisting of a compound represented by the formula (Ga1-a Ya )3 Ga5 O12 (wherein (a) is a numerical value within the range of 0<=a<=0.3) and a garnet single crystal which is formed on the substrate by a liquid phase epitaxial method and consists of a compound represented by the formula (Gd1-x-y-z Ybx Ndy Nz )3 (Ga1-q Mq )5 O12 (wherein: N is at least one element selected from Y, La, Lu and Ca; M is at least one element selected from Zr, Mg and Ge; and (x), (y), (z) and (q) are numerical values within the ranges of 0<x<1, 0<y<1, 0<=z<0.3 and 0<=q<0.5 respectively and also, (x), (y) and (z) meet the relational expression 0<x+y+z<1).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a small and inexpensive 1.02 μm to 1.03 μm band solid-state laser pump light source for pumping praseodymium fluoride fiber mainly used for 1.3 μm band optical amplifiers.

[0002]

2. Description of the Related Art Using praseodymium fluoride fiber
A 1.3 μm band optical amplifier (PDFA) has been proposed. For example, the 1994 OPTICAL FIBER COMMUNICATION (OFC'94) Te
The current status of PDFA was introduced in an invited talk by S. Sudo and others on chnical Digest p.199. Also, OFC'94, Technical Dige
In the PDFA report by st p.200, M. Fake, etc., Nd ³⁺ : YLF (YLiF ₄ ) was used as the pump light, and a saturation output of +18 dBm, a gain of 30 dB or more, and a noise figure of 6 dB or less were obtained. Have reported that. In this report, PDFA was further downsized and PD
In order to improve FA characteristics, it is necessary to bring the wavelength of pump light closer to the absorption wavelength of praseodymium (Pr) (1.017 μm) and to make it higher power. As a pump light source for PDFA excitation, Nd ³⁺ : YLF has a high output of 800 mW, but there is a problem that the emission wavelength is 1.047 nm, which is deviated from the absorption center wavelength of Pr.

On the other hand, the emission wavelength of the PDFA pump light source is
It is conceivable to use the emission using the ² F _5/2 → ² F _7/2 transition of Yb ³⁺ , which is 1.02 to 1.03 μm. In recent years, for host crystals
It has been reported that Yb ³⁺ : YAG using YAG (Y ₃ Al ₅ O ₁₂ ) is used and a bulk type or optical waveguide type laser operating at room temperature is used.
(DC Hanna et. Al, Optics Communications 99 (199
3), 211-215, TYFAN, Solid State Lasers; New Devel
opments and Applications, (1993), pp.189-203) However, in Yb ³⁺ : YAG, the excitation wavelength for Yb excitation is
Since it is 0.941 μm or 0.968 μm, which is close to the emission wavelength of 1.03 μm, it is difficult to configure an external resonator when constructing a laser (it is difficult to achieve high reflectance at the emission wavelength and high transmittance at the absorption wavelength). I have a problem. Further, when Ti ³⁺ : Al ₂ O ₃ is used to excite Yb ³⁺ , this pump light source has a problem that it is expensive and has a large size. Therefore, even if LD is used, Yb ³⁺ is excited. There is a problem that the high output 0.94 μm band cannot be easily obtained. Also, InGaAs
A semiconductor laser using a strained superlattice has a problem that it is difficult to achieve a high output of 1.017 μm. Conventionally, Y ₃ Al ₅ O ₁₂
NdYb co-doped laser materials using Gd ₃ Ga ₅ O ₁₂ or Gd ₃ Ga ₅ O ₁₂ as a host crystal are described in AA Kaminskii's Laser Crystals (Springer-Ve
rlag, Berlin Heidelberk NewYork 1981, pp.45-49) describes the emission mechanism. If 0.81 μm pumping with an inexpensive and high-power semiconductor laser is used, this pumping light
Nd ³⁺ absorbs and transits to ⁴ F _5/2 or ² H _9/2 , and further shifts to the ⁴ F _3/2 level by non-radiative transition. The dipole interaction of Nd ³⁺ ions and Yb ³⁺ ions, the energy from the Nd ³⁺ ions to Yb ³⁺ ions are transmitted, Yb ³⁺ ions probability of transition to ² F _5/2 level Get higher Then, when the Yb ³⁺ ion makes a transition to the ground level, it stimulates and emits light of 1.03 μm. Confirmation of this emission mechanism has been verified at 77K, but Nd
Emission at room temperature using Yb co-doped garnet crystal has not been confirmed to date.

[0004]

SUMMARY OF THE INVENTION The present invention is a laser material composed of Nd ³⁺ , Yb ³⁺ co-doped garnet, which is free from such drawbacks as 1.03 for pumping praseodymium fluoride fiber.
The purpose of the present invention is to develop a laser material that is useful as a fixed laser in the μm band and is small in size, high in efficiency, and high in output.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a laser material which solves the above-mentioned problems, which is represented by the formula (Gd _1-a Y _a ) ₃ Ga ₅ O ₁₂
(Here, a is represented by the number 0 ≦ a ≦ 0.3) and a formula (Gd _1-xyz Yb _x Nd _y N _z ) ₃ (Ga _1-q M _q ) ₅ O ₁₂ (wherein N is selected from at least one element of Y, La, Lu and Ca, M is selected from at least one element of Zr, Mg and Ge, x, y, z, and q are 0 <x <1 and 0 <y <, respectively.
1, 0 ≦ z <0.3, 0 ≦ q <0.5, where 0 <x + y +
The laser material consists of a garnet single crystal of z <1 (indicated by the number z <1).
The present invention has been completed by finding that light emission specific to codope can be efficiently realized at room temperature.

That is, the above-mentioned laser materials are excellent as praseodymium fluoride pump light sources in the 1.02 μm to 1.03 μm band, and they are economical because they can be used as inexpensive and high-power pumping light sources for the 0.81 μm band. Then again 1.03
It is possible to stably emit light in the μm band. And N
There is no problem that the wavelength of the emitted light deviates from the absorption center wavelength of Pr as in d ³⁺ : YLF, and the excitation wavelength band is 0.941 μm or 0.968 μm as in Yb ³⁺ : YAG, which is 1.03 μm.
There is an advantage that it is not necessary to use a light source for excitation having a size close to μm, and it can be obtained with a small size, high efficiency, and high output.

The present invention relates to a single crystal substrate of the formula (Gd _1-a Y _a ) ₃ Ga ₅ O ₁₂ (where a is a number 0 ≦ a ≦ 0.3),
On top of that, the formula (Gd
_1-xyz Yb _x Nd _y N _z ) ₃ (Ga _1-q M _q ) ₅ O ₁₂ (where N is Y, La, L
selected from at least one element of u and Ca, M is Zr and M
selected from at least one element of g and Ge, x, y,
z and q are 0 <x <1, 0 <y <1, and 0 ≦ z <, respectively.
The present invention is directed to a laser material characterized by comprising a garnet single crystal of 0.3, 0 ≦ q <0.5, where 0 <x + y + z <1. If the emission mechanism uses 0.81 μm excitation light, this excitation light is
³⁺ absorbed by dipolar interactions of Nd ³⁺ ions and Yb ³⁺ ions, the energy from the Nd ³⁺ ions to Yb ³⁺ ions are transmitted, Yb ³⁺ ions ² F _5/2 level The probability of transitioning to becomes higher. It is considered that when the Yb ³⁺ ion makes a transition to the ground level, it efficiently stimulates and emits light in the 1.03 μm band at room temperature.

[0008] This is NdYb by the liquid phase epitaxial method.
When a doped garnet crystal is produced, the ionic radii of Nd ³⁺ and Yb ³⁺ differ greatly from 1.109Å and 0.985Å, respectively, so that regularity occurs in the arrangement of Nd ³⁺ and Yb ³⁺ ions in the film growth direction. Therefore, most problems become concentration quenching by the laser material hardly occurs to regularly arranged without also codoped with Nd ³⁺ and Yb ³⁺ in high concentration to each other of the elements is localized, smoothly Nd ³ Energy transfer between ^{+ −} Yb ³⁺ ions is considered to occur. This means that, as shown in Reference Examples 1 and 2, the laser material is annealed to vibrate the crystal lattice to randomize the arrangement of Nd ³⁺ and Yb ³⁺ ions existing in the dodecahedral position of the garnet crystal. Therefore, it was confirmed that the efficiency of Nd ³⁺ , Yb ³⁺ co-doped emission was significantly reduced.

The single crystal substrate is represented by the formula (Gd _1-a Y _a ) ₃ Ga ₅ O ₁₂ , wherein Y is added for the purpose of lowering the refractive index of the substrate, and a is dislocation when it exceeds 0.3. Since there is a problem that occurs, it is necessary to set the number to 0 ≦ a ≦ 0.3.

The garnet single crystal has the formula (Gd _1-xyz Yb _x Nd
_y N _z ) ₃ (Ga _1-q M _q ) ₅ O ₁₂ , where N is selected from at least one element of Y, La, Lu, and Ca for the purpose of finely adjusting the lattice constant. In order to realize the emission of Nd ³⁺ and Yb ³⁺ , it is necessary that x be 0 <x <1, preferably 0 <x <0.3 and y is 0 <y <1. However, if 0 <y <0.3 and x and y are 1 or more, pits are generated in the crystal. If z is 0.3 or more, there is a problem that pits are generated, so 0 ≦ z <0.3 is necessary, and preferably 0 ≦ z <0.2. However, x, y, and z are numbers of 0 <x + y + z <1.

Regarding M, M is selected from at least one element of Zr, Mg and Ge for the reason of increasing the lattice constant of the substrate without changing the refractive index of the crystal and reducing the coloring of the crystal. However, if q is 0.5 or more, pits may occur, so 0 ≦ q <0.5, preferably 0 ≦ q
The number should be <0.3.

In the liquid phase epitaxial method, a single crystal substrate is dipped in a melt using PbO ₂ as a flux, which is a metal oxide constituting a garnet component as a raw material.
This can be performed by a known method of pulling while rotating and growing a garnet single crystal on the substrate. If this thickness is less than 1 μm, the output of laser oscillation is small, so 1 μm or more is preferable.

If the absolute value of the lattice constant values | Δa | between the single crystal substrate and the garnet single crystal exceeds 0.01Å, cracks are likely to occur in the garnet single crystal, so | Δa | ≦ 0.01Å
It is also necessary that the refractive index of the garnet single crystal is Gd ₃ Ga ₅ O ₁₂ (wavelength 633).
It has the advantage of becoming closer to 1.965) in nm.

[0014] The refractive index of the single crystal substrate n _s, and the refractive index of the garnet single crystal was n _f n _s and n relationship _f is n _s
When <n _f , the light incident on the garnet single crystal layer is reflected at the interface between the single crystal substrate and the garnet single crystal layer and passes through only the garnet single crystal layer, so that the luminous efficiency is improved. If the substrate is used as an under-cladding layer, a garnet single crystal layer is processed into a core layer, and an over-cladding layer having a smaller refractive index than the core layer is formed, it can be used as an optical waveguide.

Further, when n _s = n _f , light is not reflected at the interface between the single crystal substrate and the garnet single crystal layer, and the light passes therethrough. Therefore, light is incident from a direction perpendicular to the surface and perpendicular to the surface. Since a large number of garnet single crystal layers can be passed through because they can be passed in the direction of, the laser material can be small and highly efficient, and can emit high-power pump light.

To set the refractive indexes n _s and n _f as described above, for example, the compositions of the single crystal substrate and the garnet single crystal may be changed.

An example of the amplification mechanism of a praseodymium fluoride fiber using a solid-state laser using the laser material of the present invention as a pump light source will be described with reference to FIG. 4. The surface of the laser material 11 of the present invention is coated with a reflective film 15. After processing, 0.81 μm band semiconductor laser light source 10 is connected to this, and 0.81 μm excitation light is introduced into this laser material 11 to 1.03 μm.
m pump light is generated, and then through the coupler 17 through the optical isolator 12 for 1.03 μm band and the collimator 13.
Introduced into praseodymium fluoride fiber 14, 1.3 μm
The signal light 16 of the band is amplified.

[0018]

According to the present invention, the formula (Gd _1-a Y _a ) ₃ Ga ₅ O ₁₂ (where a is 0
≦ a ≦ 0.3) and a formula (Gd formed by the liquid phase epitaxial method on the single crystal substrate
_1-xyz Yb _x Nd _y N _z ) ₃ (Ga _1-q M _q ) ₅ O ₁₂ (where N is Y, La, L
selected from at least one element of u and Ca, M is Zr and M
selected from at least one element of g and Ge, x, y,
z and q are 0 <x <1, 0 <y <1, and 0 ≦ z <, respectively.
0.3, 0 ≦ q <0.5, where 0 <x + y + z <1), which is a laser material consisting of a garnet single crystal, which is mainly used for the praseodymium fluoride fiber pump used in the 1.3 μm band optical amplifier. Small and inexpensive 1.02
It is useful as a solid-state laser pump light source in the μm to 1.03 μm band.

[0019]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 Gd _2.4 Y _0.6 Ga ₅ O ₁₂ (lattice constant by the Czochralski method
12.367Å) (hereinafter referred to as YOG) was produced, and crystals without dislocations were obtained. The refractive index of this product was measured by the prism coupling method and found to be 1.9407 at a wavelength of 1.52 μm.
(n _s ). This YOG crystal has a diameter of 2 inches and a thickness of 400
After processing to a wafer of μm, the film composition Nd _0.11 Yb _0.19 Gd _2.70 Ga ₅ O was formed on one surface of this YOG substrate by liquid phase epitaxial method.
_Twelve garnet single crystal thin films were grown to a thickness of 4 μm. This has a lattice constant of 12.366Å and a refractive index of 1.52 μm.
Was 1.9455 (n _f ). When the liquid phase epitaxial wafer was irradiated with light having a wavelength of 0.81 μm at room temperature and the generated fluorescence was observed, the results shown in FIG. 1 were obtained. As shown in Fig. 1, the wavelength of Nd ³⁺ is 1.064μ.
m emission did not occur, and emission by Yb ³⁺ ions near the wavelength of 1.03 μm was observed at room temperature. This indicates that the energy conversion from Nd ³⁺ to Yb ³⁺ occurs at room temperature.

Next, Nd _0.11 Yb formed on the YOG substrate
_When 0.81 μm light was incident on the _0.19 Gd _2.70 Ga ₅ O ₁₂ garnet single crystal thin film through the rutile prism as shown in Fig. 2, the refractive index of this thin film was about 0.24% larger than that of the substrate. Light propagated. The emitted light emitted from the emission end of the sample is coupled to an optical fiber through a collimator, and the light is observed by an optical spectrum analyzer. The emission spectrum of 1.02 to 1.03 μm shown in FIG. Was observed.

Next, in the above, it was produced on a YOG substrate.
A Nd _0.11 Yb _0.19 Gd _2.70 Ga ₅ O ₁₂ garnet single crystal thin film was dry-etched to form a 4 μm square core ridge. Furthermore, a buried optical waveguide was formed by epitaxially growing a 6 μm thick Gd _2.4 Y _0.6 Ga ₅ O ₁₂ [refractive index 1.9407 (wavelength 1.52 μm)] on the top of the core ridge by liquid phase epitaxial method as an overclad. Was produced. This embedded optical waveguide was cut into a length of 1 cm and the end face was optically polished. Then from the optical fiber
When 0.81 μm of light was made incident on the above optical waveguide and the emitted light was coupled with an optical fiber and the emitted light was observed by an optical spectrum analyzer, the emission spectrum of 1.02 to 1.03 μm shown in FIG. 1 was observed.

[0022] Example 2 1-inch diameter, (hereinafter referred to as GGG) Gd ₃ Ga ₅ O ₁₂ having a thickness of 400 [mu] m (lattice constant 12.383A, refractive index 1.9454 (n _s) (wavelength 1.52 .mu.m)) on the crystal substrate A garnet single crystal film having a film composition of Nd _0.11 Yb _0.19 Gd _2.70 Ga ₅ O ₁₂ was grown to a thickness of 1.5 mm on both surfaces by a liquid phase epitaxial method. This product had no cracks, the lattice constant was 12.383Å, and the refractive index at a wavelength of 1.52 μm was 1.9454 (n _f ). Next, after the surface of the epitaxial thick film was optically polished, 0.8 m of output power of 50 mW was obtained.
The garnet single crystal film is inserted into an optical system in which a 1 μm laser is spatially propagated, condensed by a collimator and coupled with an optical fiber (FIG. 3 (b)) and not (FIG. 3).
The optical spectrum of (a)) was observed with an optical spectrum analyzer. As a result, in FIG. 3 (b), Yb ³⁺ 1.02 to 1.03
Emission at μm was observed at room temperature.

Next, it was prepared on both sides of this GGG substrate.
Nd _0.11 Yb _0.19 Gd _2.70 Ga ₅ O ₁₂ Garnet single crystal film on both sides of which 0.81 μm and 1.03 μm were formed by using ion assisted deposition method.
In the high reflectance in the transmittance is larger other wavelengths TiO ₂ -Si
A laser material was prepared by forming a reflective film composed of an O ₂ multilayer film. Next, as shown in FIG. 4, the 0.81 μm semiconductor laser light source 1, the laser material 11 and the 1.03 μm band optical isolator 12 are used.
Further, the collimator 13 was coupled with the praseodymium fluoride fiber 14 via the signal light 16 and the coupler 17 to form a solid-state laser unit. When the emission intensity of the laser light by the pumping light of the 0.81 μm laser light of this laser material was measured, a laser output of 1.2 W was obtained at the center wavelength of 1.03 μm.

Example 3 By the liquid phase epitaxial method, a film thickness of 1. was formed on both sides of a GGG crystal substrate having the same 1-inch diameter and 400 μm thickness as in Example 2.
A 5 mm Nd _0.2 Yb _0.4 Gd _2.4 Ga ₅ O ₁₂ garnet single crystal film was grown. The lattice constant of this garnet single crystal film is 12.383.
Å, the refractive index at a wavelength of 1.52 μm was 1.9454 (n _f ). Next, this substrate was cut into a 3 mm square, and chips of a laser material were produced in which the same reflective films as in Example 2 were formed on both surfaces of the chips. Next, a wavelength of 0.81 as shown in Fig. 4
μm semiconductor laser light source 1, chip of the above laser material, 1.03 μm band optical isolator 12, and collimator
The solid-state laser unit was formed by coupling 13 with the signal light 16 and the praseodymium fluoride fiber 14 via the coupler 17. When the emission intensity of laser light due to this laser material was measured, a laser output of 1.4 W was obtained at a center wavelength of 1.03 μm. Further, when this solid-state laser unit was used in the amplifier for signal light in the 1.3 μm band shown in FIG. 4, good results were obtained.

Reference Example 1 Nd _0.11 Yb _0.19 Gd _2.70 Ga produced on the YOG substrate of Example 1
_{The 5} O ₁₂ garnet single crystal thin film was annealed in the air at 1,500 ° C. for 48 hours, irradiated with 0.81 μm of light, and the emitted light was observed. The emission of 1.02 to 1.03 μm seen in FIG. 1 disappeared. However, a weak emission of 1.064 μm was observed.

Reference Example 2 Nd _0.11 prepared on the GGG substrates of Example 2 and Example 3
Yb _0.19 Gd _2.70 Ga ₅ O ₁₂ Garnet single crystal film, and Nd _0.2 Yb
_0.4 Gd _2.40 Ga ₅ O ₁₂ Garnet single crystal film in air at 1,500 ℃
Anneal for 48 hours, irradiate this with 0.81 μm light,
When the generated light emission was observed, the light emission of 1.02 to 1.03 μm observed in FIG. 3B disappeared and the weak light emission of 1.064 μm was observed. A solid-state laser unit similar to that of Example 2 was constructed using this annealed laser material, but no laser oscillation of 1.03 μm occurred.

[0027]

INDUSTRIAL APPLICABILITY The laser material of the present invention is a compact, high-efficiency, high-output pump light source for the praseodymium fluoride fiber in the 1.03 μm band, and is inexpensive as an excitation light source.
It is economical because a semiconductor laser of 0.81 μm band can be used.

[Brief description of drawings]

FIG. 1 is a diagram showing emission characteristics near 1.03 μm when a laser material of the present invention is used.

FIG. 2 is a diagram showing a measurement system for evaluating the emission characteristics of the laser material of the present invention.

FIG. 3A is a diagram showing an optical spectrum of transmitted light when the laser material of the present invention is not inserted in an optical path. (B) The figure which shows the optical spectrum of the transmitted light when the laser material of this invention is inserted in an optical path.

FIG. 4 is a diagram showing the configuration of a 0.81 μm band semiconductor laser pumped 1.03 μm band solid state laser incorporating the laser material of the present invention.

[Explanation of symbols]

1 ... Laser light having a wavelength of 0.81 μm 2 ... Rutile prism 3, 11 ... Laser material 4 ... Polished end face 5 ... Guided light 6 ... Emitted light 7 ... Collimator 8 ... Optical fiber 9, 14 ... Optical spectrum analyzer 10 ... 0.81 μm band light emission For semiconductor laser light source 12 ... 1.03μm band optical isolator 13 ... Collimator 14 ... Praseodymium fluoride fiber 15 ... Reflective film 16 ... Signal light 17 ... Coupler

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Naoto Sugimoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Masayuki Tanno 2-13-1 Isobe, Annaka-shi, Gunma Issue Shin-Etsu Chemical Co., Ltd., Precision Materials Research Laboratory (72) Inventor Satoru Fukuda 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Industry Co., Ltd. Precision Materials Research Laboratory (72) Inventor Toshihiko Nagao 2-13-1 Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory

Claims (4)

[Claims] 1. The formula (Gd _1-a Y _a ) ₃ Ga ₅ O ₁₂ (where a is 0 ≦ a
≤ 0.3) and a formula (Gd _1-xyz) formed on it by the liquid phase epitaxial method.
Yb _x Nd _y N _z ) ₃ (Ga _1-q M _q ) ₅ O ₁₂ (where N is selected from at least one element of Y, La, Lu, and Ca, and M is Zr, Mg, or Ge). X, y, z, q selected from at least one or more elements
Are respectively 0 <x <1, 0 <y <1, 0 ≦ z <0.3,
0 ≦ q <0.5, where 0 <x + y + z <1). 2. The laser material according to claim 1, wherein an absolute value | Δa | of a lattice constant difference between the substrate and the garnet single crystal is | Δa | ≦ 0.01Å. The laser material according to claim 1 wherein is the refractive index of the substrate is n _s, and the refractive index of the garnet single crystal was n _f n _s ≦ n _f. 4. A solid-state laser comprising the laser material according to any one of claims 1 to 3.