JPH0521874A - Optical active device - Google Patents

Abstract

PURPOSE:To provide a fiber amplifier capable of realizing light amplification in a 1.3mum band of wavelength by means of a simplified pumping source. CONSTITUTION:An optically functional glass used for an optical fiber 30 contains Nd<3+> and Yb<3+> together with Pr<3+> as an active material. The Nd<3+> and Yb<3+> are excited by the pumping light of 0.8mum and 0.98mum of wavelength generated from the first and second laser beam sources 32 and 132. Correspondingly, the Pr<3+> receives the energy transmission from the Nd<3+> and Yb<3+> to be excited as well. The excited Pr<3+> is guided by a signal light to generate a radiation light of 1.3mum band of wavelength corresponding to the transition from <1>G4 to <3>H5. Therefore, when the intensity of excited light becomes over the specified level, the signal light is subject to amplification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical active device, a fiber amplifier, a waveguide element amplifier, a fiber laser and a waveguide element laser used for optical amplification in the 1.3 .mu.m band.

[0002]

2. Description of the Related Art An optical functional glass to which a rare earth element is added as an active substance is a fiber amplifier, a fiber sensor and a fiber amplifier used for optical communication in a wavelength range of 1.3 μm, which is generally performed within a range of 1.310 ± 0.025 μm. Applications to fiber lasers and other optically active devices are being considered. For example,
An optical fiber made of fluoride glass doped with praseodymium ion (Pr ³⁺ ) as an active substance has a wavelength of 1.3.
It has been reported that optical amplification in the μm band can be realized (OFC '90 Post Deadline Papers (PD2-1)). In the Pr ³⁺ -doped optical fiber shown in this report, the pumping light wavelength is 1.017 μm and the input intensity is 180 mW.

[0003]

However, in the present technology, there is no small and simple light source such as a semiconductor laser as an excitation light source capable of supplying such long wavelength and high intensity excitation light, and a large gas laser, There was no choice but to excite Pr ³⁺ in the optical fiber using a solid-state laser or the like. For this reason,
There is a problem in that it is not possible to reduce the size of the optical amplifier or the like.

Therefore, the present invention is an optical active device composed of an optical fiber or a waveguide element using an optical functional glass doped with Pr ^{3+ and} having a wavelength of 1.0 μm or less that can be supplied by a laser diode or the like. It is an object of the present invention to provide an optical active device capable of enhancing the efficiency of light emission, optical amplification, etc. in the wavelength band of 1.3 μm by the excitation light.

The present invention also provides a fiber amplifier, a waveguide element amplifier, a fiber laser, and
An object is to provide a waveguide device laser and the like.

[0006]

The optical active device according to the present invention comprises (a) a host glass containing Pr as an active substance.
^An optical fiber having a core made of optical functional glass in which neodymium ions (Nd ³⁺ ) and ytterbium ions (Yb ³⁺ ) are added together with ³⁺ , and (b) a first wavelength band of 0.8 μm for exciting Nd. A first pumping light source for generating pumping light of (c), a second pumping light source for generating second pumping light of (c) Yb in a wavelength band of 0.98 μm, and (d) first
And pumping light coupling means for causing the second pumping light to enter the optical fiber from each pumping light source. In this case, instead of the above optical fiber, the host glass is made of Pr.
You may use the waveguide element provided with the planar waveguide which consists of optical functional glass which added ³⁺ , Nd3 ^+, and Yb3 ⁺ .

According to the above optical active device, Nd ³⁺ is excited by the first excitation light introduced into the optical fiber by the excitation light coupling means, and Yb ³⁺ is excited by the second excitation light. . Pr existing near the excited Yb ^3+
3+ is excited with a predetermined probability by receiving energy transfer from Yb ³⁺ . Further, Pr ³⁺ existing in the vicinity of the excited Nd ³⁺ is also excited with a predetermined probability by receiving energy transfer from Nd ³⁺ . Further, Pr ³⁺ existing in the vicinity of Yb ³⁺ existing in the vicinity of the excited Nd ³⁺ is also excited with a predetermined probability by energy transfer from Nd ³⁺ via Yb ³⁺ . A part or most of the Pr ³⁺ excited in this way is induced by the signal light in the 1.3 μm wavelength band existing in the optical fiber, and the emitted light corresponding to the transition ¹ G ₄ → ³ H ₅ is emitted. It is possible to generate various functions such as optical amplification function, optical switch function and optical sensor function in this band.

A fiber amplifier according to the present invention comprises the above-mentioned optical active device and a signal light coupling means such as a coupler for guiding the signal light in the wavelength band of 1.3 μm into the above optical fiber. in this case,
Instead of the above optical fiber, Pr ³⁺ in the host glass,
A part of the optically active device may be configured by using a waveguide element having a planar waveguide made of optical functional glass doped with Nd ³⁺ and Yb ³⁺ .

According to the above fiber amplifier, Pr ³⁺ is indirectly excited by the relatively short wavelength first and second pumping lights introduced into the optical fiber by the pumping light coupling means. A part or most of this excited Pr ³⁺ is simultaneously induced by the signal light coupling means into the signal light in the 1.3 μm wavelength band introduced into the optical fiber to generate radiated light. Optical amplification is possible in the 3 μm band.

The fiber laser of the present invention comprises the above-mentioned photoactive device and a resonator structure for feeding back the light in the 1.3 μm wavelength band or in the vicinity thereof from the inside of the optical fiber to the optical fiber. In this case, instead of optical fiber,
A part of the optical active device may be configured by using a waveguide element having a planar waveguide made of an optical functional glass in which Pr ³⁺ , Nd ³⁺ and Yb ³⁺ are added to the host glass.

According to the above fiber laser, Pr ³⁺ is indirectly pumped by the first and second pumping lights having relatively short wavelengths introduced into the fiber by the pumping light coupling means. A part or most of the excited Pr ³⁺ is induced by spontaneous emission light having a wavelength of 1.3 μm band existing in the optical fiber to generate radiated light and emit laser light in the wavelength 1.3 μm band. Will be possible.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Explanation of the Principle of the Present Invention] Before explaining the embodiments, a hypothesis which is the basis of the present invention will be briefly explained. FIG. 1 is an energy level diagram for explaining this hypothesis.

Nd ³⁺ and Y together with the active substance Pr ³⁺
Wavelength 0.8 introduced into optical functional glass with b ³⁺ added
The first excitation light in the μm band excites Nd ³⁺ to generate a level ⁴ I
_The electronic transition corresponding to the level ⁴ F _3/2 is generated from _9/2 . As a result, inversion between the level ⁴ F _3/2 and level ⁴ I _9/2 of Nd ³⁺ are formed. These two levels ⁴ F _3/2 , ⁴
The energy difference between I _9/2 is the two levels of Pr ^{3+ 1} G ₄ , ³
Since it substantially corresponds to the energy difference between H ₄ , the excitation energy of Nd ³⁺ is transferred to Pr ³⁺ existing in the vicinity thereof, and apparently the level of Nd ^{3+ 4} F _3/2 To P
An electron transits to the level ¹ G ₄ of r ³⁺ . Also, the energy difference between the excited two levels ⁴ F _3/2 and ⁴ I _9/2 of Nd ³⁺ is the energy between the two levels ² F _5/2 and ² F _{7/2 of} Yb ^3+. because it substantially corresponds to the difference, the excitation energy of Nd ³⁺ is transmitted to the Yb ³⁺ present in near, then the excitation energy of the excited Yb ³⁺ is present near the Pr
Transmitted to ³⁺ . In other words, apparently Nd ³⁺ level ⁴ F
_{3/2 level} to Yb ³⁺ level ² F _5/2 to Pr ³⁺ level ¹ G
_The electron transits to ₄ .

On the other hand, the second excitation light of wavelength 0.98 μm band introduced into the above-mentioned optical functional glass excites Yb ³⁺ to change from level ² F _7/2 to level ² F _5/2 . Generate a corresponding electronic transition. As a result, level ² F _5/2 and level ² F of Yb ³⁺
_The population inversion is formed between _7/2 and. This 2 level ² F
Energy difference between _5/2 and ² F _7/2 is Pr ³⁺ 2 level ¹ G
_4, ³ since the substantially corresponds to the energy difference between H _4, Y
The excitation energy of b ³⁺ is transferred to Pr ³⁺ existing near it, and apparently the level of Yb ³⁺ is ² F _5/2.
Electron transits to Pr ³⁺ level ¹ G ₄ .

As described above, a part or most of Pr ³⁺ indirectly pumped by the first and second pumping lights is guided to the signal light in the 1.3 μm wavelength band existing in the optical fiber. , Emits radiated light corresponding to transition ¹ G ₄ → ³ H ₅ , and enables various functions such as optical amplification function, optical switch function, and optical sensor function in this band.

In the above-mentioned optical functional glass, as a host glass (matrix glass) to which Pr ³⁺ or the like should be added, fluorophosphate glass, phosphate glass, silicate glass,
Chalcogenide glass, fluoride glass, quartz glass, etc. can be used.

To construct an optical active device from the above optical functional glass, this optical functional glass is used as a material for an optical transmission line. For example, although it may be formed in a waveguide element having a planar waveguide formed of this glass, it is possible to produce an optical fiber having a core made of the above-mentioned optical functional glass to produce an optical fiber having a wavelength of 1.3 μm band. Desirable for obtaining active devices.

As a concrete manufacturing method of the above optical fiber, 2
Known manufacturing methods such as a melting crucible method, a built-in casting method, and a rod-in-tube method can be used. Furthermore, when quartz glass is used as a host glass of Pr ³⁺ which is an active material, VAD method, MCVD method, OVD method and the like can be used.

As a concrete structure of the above optical fiber, it is desirable to use a single mode fiber, and it is desirable that the core diameter is 5 μm or less and the relative refractive index difference is 1% or more. However, even a multimode fiber can be used depending on the application. Further, considering the connection with the existing fiber, it is possible to set the core diameter to about 8 μm and the relative refractive index difference to about 0.3%.

The optical active device of the present invention comprises the above optical fiber, a laser for generating pumping light of wavelength 0.8 μm and wavelength 0.98 μm for pumping Nd ³⁺ and / or Yb ³⁺ , and the like. Of the first and second pumping light sources, and pumping light coupling means such as a coupler that causes these pumping lights to enter the optical fiber from the respective pumping light sources.

According to the above-mentioned optically active device, Nd ³⁺ is excited by the first pumping light having a wavelength of 0.8 μm introduced into the optical fiber by the pumping light coupling means, and Pr ^{3 which} has received energy from this is excited. ⁺ Is also excited. The wavelength of 0.98 μm introduced into the optical fiber by the excitation light coupling means.
Yb ³⁺ is excited by the second excitation light of m, and Pr ³⁺ that has undergone energy transfer from this is also excited. A part or most of the Pr ³⁺ excited in this way is induced by the signal light in the 1.3 μm wavelength band existing in the optical fiber, and the emitted light corresponding to the transition ¹ G ₄ → ³ H ₅ is emitted. It is possible to generate various functions such as optical amplification function, optical switch function and optical sensor function in this band.

[Description of Specific Examples] (1) Fabrication of Optical Fiber First, composition 53.5ZrF ₄ -20BaF ₂ -3.5L.
Raw materials for aF ₃ -3.0AlF ₃ -20NaF (mol%) fluoride glass were prepared, and Pr ³⁺ and Nd were prepared together with them.
Predetermined amounts of ³⁺ and Yb ³⁺ compounds were mixed. The mixed raw materials were melted in a platinum crucible under an inert atmosphere and then vitrified by quenching. For comparison, Pr
A fluoride glass containing only ³⁺ was also prepared.

In order to manufacture an optical active device from this optical functional glass, a fiber was manufactured as follows. First, the above-mentioned optical functional glass is formed into a rod shape to obtain a glass rod for a core. Further, a glass pipe for cladding, which has a composition lower in refractive index than the glass rod for core and does not contain Pr ³⁺ etc., is prepared. Then, these glass rods and glass pipes were formed into a preform and drawn into an optical fiber. As a result, a single mode fiber having a core diameter of 3 μm, an outer diameter of 125 μm and a relative refractive index difference of 1.0% was obtained. This single mode fiber was cut to a length of 10 m.

(2) Fabrication Example of Fiber Amplifier FIG. 2 shows a fabrication example of the fiber amplifier in the 1.3 μm wavelength band using the above optical fiber. The illustrated fiber amplifier has a bidirectional two-wavelength pumping type configuration, and includes an optical fiber 30 containing rare earth ions for amplifying a signal light having a wavelength of 1.3 μm and a first pumping light having a wavelength of 0.8 μm. A first laser diode light source 32 for generating light and a wavelength of 0.
A second laser diode light source 132 that generates a second excitation light in the 98 μm band, and first and second laser diodes that emit the first and second excitation lights from the respective excitation light sources 32 and 132 into the optical fiber 30. And a multiplexing / demultiplexing coupler 33, 133.

A signal light source 31 having a wavelength band of 1.3 μm is connected to the optical fiber 38a provided in the first multiplexing / demultiplexing coupler 33 formed by fusion-spreading the optical fibers 38 and 39. The input side of the optical fiber 30 is coupled to the optical fiber 38b facing this, and the signal light is made incident on the inside of the optical fiber 30. An optical fiber 39a extending from the first multiplexing / demultiplexing coupler 33 is connected to a first laser diode 32 that generates excitation light having a wavelength band of 0.8 μm. Therefore, the pumping light of the wavelength 0.98 μm band from the laser diode 32 is also introduced into the optical fiber 30 together with the signal light. On the other hand, to the optical fiber 139a provided in the second multiplexing / demultiplexing coupler 133, the second laser diode 132 that generates the excitation light in the wavelength band of 0.98 μm is connected. Further, the fiber 138 a provided in the second multiplexing / demultiplexing coupler 133 is coupled to the output side of the optical fiber 30. Therefore, the excitation light in the wavelength band of 0.98 μm from the laser diode 132 is also included in the second multiplexing / demultiplexing coupler 133.
It is introduced into the optical fiber 30 via.

The output light from the output side of the optical fiber 30 is
A fiber 138a, a second multiplexing / demultiplexing coupler 133,
Fiber 138b and optical filter 3 that cuts the excitation light
6 and is guided to the photodetector 35. Photodetector 35
Detects the intensity and the like of the amplified signal light. The first
And the remaining optical fibers 39b and 139b extending from the second multiplexing / demultiplexing couplers 33 and 133 are dipped in matching oil 37 to prevent returning light.

The operation of the fiber amplifier shown in FIG. 3 will be briefly described. The signal light in the wavelength band of 1.3 μm from the signal light source 31 passes through the first multiplexing / demultiplexing coupler 33 to the optical fiber 3
It is incident within 0. At the same time, the first and second excitation light sources 3
The pumping lights of wavelengths 0.8 μm band and 0.98 μm band from 2, 132 also enter the optical fiber 30 through the first and second multiplexing / demultiplexing couplers 33. These excitation lights are Nd ³⁺
And Yb ³⁺ are also excited, and Pr ³⁺ to which energy is transferred from this is also indirectly excited. The excited Pr ³⁺ is induced by the signal light to generate radiation light having a wavelength band of 1.3 μm corresponding to the transition ¹ G ₄ → ³ H ₅ . When the excitation light exceeds a predetermined intensity, the signal light is amplified.

The measurement results obtained with the fiber amplifier of FIG. 3 will be described.

(Example 1) As the optical fiber 30, the core 30a contains Pr ³⁺ of 5000 ppm and Nd ³⁺ of 5000 p.
A single mode fiber containing 5000 ppm of pm, Yb ³⁺ was prepared. A laser diode was used as the signal light source 31, the wavelength was 1.32 μm, and the signal light input was −30 dB. First and second excitation light sources 32, 1
As 32, a laser diode was used, the wavelength was 0.8 μm and 0.98 μm, and the pumping light input was 30 mW. The gain for the signal light of wavelength 1.32 μm was 30 dB.

(Example 2) As the optical fiber 30, the core 30a has Pr ³⁺ of 5000 ppm and Nd ³⁺ of 5000 p.
A single mode fiber doped with pm was prepared. As the signal light source 31, the same one as the laser diode of (Example 1) was used. As the first pumping light source 132, the same one as the laser diode of (Example 1) was used, and the pumping light input was set to 50 mW. No excitation light was generated from the second excitation light source 32. The gain for signal light having a wavelength of 1.30 μm was 20 dB.

(3) Manufacturing Example of Waveguide Element Amplifier FIG. 3 is a diagram showing an example of the waveguide element amplifier.
A planar waveguide 130a that bifurcates on the substrate 120,
Form 130b and 130c. A second rare earth ion such as Nd ³⁺ is added to the planar waveguide 130a together with Pr ³⁺ . A filter 136 made of a grating is formed at the other end of the planar waveguide 130a. Signal light having a wavelength band of 1.3 μm is incident on the planar waveguide 130b. In addition, the planar waveguide 130c has a wavelength of 0.8 μm.
m, a wavelength of 0.98 μm, or other excitation light is incident. As the laser light source for generating the excitation light, the same laser light source as that shown in FIG. 32 is used.

The operation of the fiber amplifier 100 shown in FIG. 3 will be briefly described. The signal light in the wavelength band of 1.3 μm enters the planar waveguide 130a through the planar waveguide 130b, and the excitation light of wavelengths 0.8 μm and 0.98 μm from the excitation light source such as a laser diode is also transmitted to the planar waveguide 130c. To enter the planar waveguide 130a. These excitation lights are
Excites Nd ³⁺ and Yb ³⁺ , and further excites Pr ³⁺ .
The excited Pr ³⁺ is induced by the signal light, and the transition ¹ G ₄ →
^It emits radiation in the 1.3 μm wavelength band corresponding to ³ H ₅ . When the excitation light exceeds a predetermined intensity, the signal light will be amplified.

(4) Fabrication Example of Fiber Laser FIG. 4 is a diagram showing an embodiment of the fiber laser.
The fiber laser includes an optical fiber 30, a laser light source 32 including a laser diode and the like, and an excitation light coupling device 43 including a lens and the like. The laser light source 32 generates excitation light having a wavelength of 0.8 μm and a wavelength of 0.98 μm.
The pumping light coupling device 43 outputs these pumping lights to the laser light source 32.
To enter the optical fiber 30. In this case, the input and output ends of the optical fiber are finished into an appropriate mirror surface to form a resonator structure. The resonator structure may be of a normal type using a dielectric mirror or the like. Further, it is possible to form a ring racer having a ring-shaped resonator.

In the above fiber laser, the pumping light of wavelength 0.8 μm and wavelength 0.98 μm from the laser light source 32 is introduced into the optical fiber 30 by the pumping light coupling device 38. These excitation lights excite Nd ³⁺ and Ybd ³⁺ in the optical fiber 30, and further excite Pr ³⁺ . The excited Pr ³⁺ is guided by 1.3 μm spontaneous emission light, and the wavelength corresponding to the transition ¹ G ₄ → ³ H ₅ is 1.3 μm.
Generates synchrotron radiation. When the output of pumping light exceeds a predetermined value, laser oscillation occurs in the 1.3 μm wavelength band.

[0035]

As described above, according to the optical functional glass of the present invention, due to the presence of Nd ³⁺ and Yb ³⁺ ,
It is possible to excite Pr ³⁺ with a simple excitation light source that generates excitation light having a wavelength of 1.0 μm or less. The presence of Pr ³⁺ thus excited enables light emission / optical amplification in the 1.3 μm band or enhances the amplification efficiency. Further, by forming this in a waveguide, an optical fiber or the like, it can be applied to an optical amplifier, an optical functional device such as a laser. In particular, when formed into a fiber, a low threshold and high gain fiber amplifier can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an energy level diagram of a rare earth element such as Pr ³⁺ .

FIG. 2 is a diagram showing an example of a fiber amplifier.

FIG. 3 is a diagram showing an example of a waveguide element amplifier.

FIG. 4 is a diagram showing an example of a fiber laser.

[Explanation of symbols]

30 ... Optical fiber 32, 132 ... Excitation light source 33, 133 ... Multiplexing / demultiplexing coupler as pumping light coupling means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G02B 6/00 376 B 7036-2K G02F 1/35 501 7246-2K H01S 3/07 7630-4M 3 / 17 7630-4M (72) Inventor Takashi Mugo 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Yoshiaki Miyajima 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. A host glass containing Pr ³⁺ , Nd ³⁺ and Yb.
^An optical fiber having a core made of optical functional glass co-doped with ³⁺ , a first pumping light source for generating first pumping light having a wavelength of 0.8 μm band for pumping Nd ³⁺ , and Yb ³⁺ A second pumping light source for generating a second pumping light having a wavelength of 0.98 μm for exciting the
And an excitation light coupling means for allowing the second excitation light source to enter the optical fiber. 2. A fiber amplifier comprising: the optical active device according to claim 1; and a signal light coupling means for guiding a signal light having a wavelength band of 1.3 μm into the optical fiber. 3. A fiber laser comprising the optical active device according to claim 1, and a resonator structure for feeding back light in the 1.3 μm wavelength band or in the vicinity thereof from inside the optical fiber to the optical fiber. 4. A host glass containing Pr ³⁺ , Nd ³⁺ and Yb.
³⁺ a waveguide device having a planar waveguide made of the co-added optical functional glass, a wavelength to excite the Nd ³⁺ 0.8 micron
a first pumping light source for generating a first pumping light in the m band, and Yb
^A second pumping light source for generating a second pumping light having a wavelength of 0.98 μm for pumping ³⁺ , and a first and second pumping light from the first and second pumping light sources to the waveguide element. And an excitation light coupling means to be incident on the inside of the optically active device. 5. A waveguide device amplifier comprising: the optical active device according to claim 4; and a signal light coupling means for guiding signal light in a 1.3 μm wavelength band into the waveguide device. 6. A waveguide element comprising the photoactive device according to claim 4, and a resonator structure for feeding back light in the 1.3 μm wavelength band or in the vicinity thereof from the inside of the waveguide element to the waveguide element. laser.