JP2888623B2 - Optical amplifier and optical oscillator - Google Patents

Description

The present invention relates to an optical amplifying device and an optical oscillating device used in a wavelength band of 1.5 to 1.7 μm.

[Conventional technology]

For application to the optical communication field in the wavelength range of 1.5 to 1.7 μm,
Using optical fibers doped with rare earth elements, optical amplification and optical amplification of fiber amplifiers, fiber sensors, fiber lasers, etc.
Efforts have been made to fabricate optical oscillators. Among the fibers doped with rare earth elements, there have been many reports on optical fibers containing silica glass as a core doped with erbium ions (Er ³⁺ ), and an optical amplifier using such an optical fiber has been reported. Then, wavelength 1.53 ~ 1.56μm
It is known that an optical gain can be obtained in the band.

[Problems to be solved by the invention]

However, an optical amplifier comprising an optical fiber doped with Er ³⁺ cannot sufficiently cope with a wavelength range of 1.5 to 1.7 μm covered by a semiconductor laser used as a signal light source or the like. In addition, for example, when an optical amplification / oscillation device of a longer wavelength side of 1.65 μm band is required for use in a failure detection system for maintenance of an optical communication system having a wavelength band of 1.55 μm or the like. However, optical amplifiers, optical oscillators, and the like made of optical fibers doped with Er ³⁺ could not always sufficiently cope with the 1.65 μm band.

In view of the above circumstances, the present invention relates to an optical amplifying device and an optical oscillating device including an optical fiber that does not use Er ³⁺ as an active material, and has a sufficient optical amplification and optical oscillation in a wavelength band of 1.5 to 1.7 μm. It is an object to provide an optical amplifier and an optical oscillator having a gain.

[Means for solving the problem]

In order to achieve the above object, an optical amplifying device according to the present invention includes an optical transmission line, an excitation light source, and optical means.
Here, the optical transmission line is configured to include an optical functional glass to which thulium ion (Tm ³⁺ ) is added as an active substance,
The signal light in the wavelength band of 1.5 to 1.7 μm is propagated. The excitation light source generates excitation light in the 1.20 μm wavelength band. Further, the optical means causes the excitation light from the excitation light source to enter the optical transmission path.

The optical transmission line and the like used in the optical amplifier according to the present invention can be applied to an optical oscillator such as a fiber laser.

Specifically, the optical oscillation device is configured to include the optical transmission line, the excitation light source, and the optical unit. Here, the excitation light source generates excitation light in a wavelength band of 1.20 μm, and the optical means causes the excitation light to enter the optical transmission line from the excitation light source. Also,
The resonator structure feeds back emitted light in a wavelength band of 1.5 to 1.7 μm from inside the optical transmission line to the optical transmission line.

[Action]

In the optical amplifying device according to the present invention, the active material Tm ³⁺ is excited by the pumping light having a wavelength of 1.20 μm introduced into the optical transmission line, and efficient three-level emission is achieved. to enable. This is because the wavelength of the excitation light of 1.20 μm corresponds to the transition from the ground level ³ H ₆ to the energy level ³ H ₅ . That is, the atoms at the ground level ³ H ₆ are once pumped to the energy level ³ H ₅ by this excitation, and then transition to the level ³ H ₄ without radiation. By such pumping and non-radiative transition, the population inversion is formed between the level ³ H ₆ and level ³ H _4, it is possible to emission at a wavelength 1.5~1.7μm band.
At this time, the signal light of the wavelength 1.5~1.7μm band excited Tm ³⁺ is incident, Tm ³⁺ is induced in the signal light, the wavelength
Generates light in the 1.5-1.7 μm band. As a result, the wavelength 1.5 to
Optical amplification in the 1.7 μm band becomes possible.

In the optical oscillation device according to the present invention, Tm ³⁺ is excited by the excitation light in the 1.20 μm wavelength band introduced into the optical transmission line by the optical means. Part of the excited Tm ³⁺ is emitted light in the wavelength band of 1.5 to 1.7 μm from the inside of the optical transmission line, and the wavelength 1.
Induced by light in the 5-1.7μm band, wavelength 1.5-1.7μ
Generates m-band emission light. By repeating this,
Optical oscillation in the wavelength band of 1.5 to 1.7 μm is possible.

〔Example〕

Hereinafter, embodiments of the optical amplifying device of the present invention will be described.

FIG. 1 shows a fiber amplifier which is an optical amplifying device in a wavelength band of 1.5 to 1.7 μm.

As the signal light source 11, a laser diode is used. One end of an optical fiber 18a is optically connected to the output side of the signal light source 11, and the other end of the optical fiber 18a is connected to the input side of the coupler 13. Further, a laser diode is used as the laser light source 12, which is an excitation light source. One end of an optical fiber 19a is optically connected to the output side of the laser light source 12, and the other end of the optical fiber 19a is connected to the input side of the coupler 13.

Two optical fibers 18b and 19b extend from the output side of the coupler 13, and one end of the optical fiber 19b is immersed in a matching oil 17 for preventing return light, and the other optical fiber
The end of 18b is connected to one end of the optical fiber 10 as an optical transmission line via a connector or the like. An optical spectrum analyzer 15 is provided on the output side at the other end of the optical fiber 10, and a filter 16 is interposed between them.

Here, the coupler 13 is produced by fusion-splicing of two optical fibers 18, 19, and the coupler 13 and the fibers 18a, 18b, 19a, 19b constitute optical means.

The optical fiber 10 is a 2 m long SM fiber, and has a Tm
^It has a core made of quartz glass to which ³⁺ has been added.

Hereinafter, the operation of the fiber amplifier of FIG. 1 will be briefly described.

The laser light source 12 outputs excitation light in a wavelength band of 1.20 μm. This excitation light enters the coupler 13 via the optical fiber 19a, and further enters the optical fiber 10 via the optical fiber 18b. Since the excitation light Tm ³⁺ is added as active substance in the core of the optical fiber 10 to be incident, Tm ³⁺ excited in a predetermined state by this excitation light, the wavelength 1.5~1.7μ
The m-band emission becomes possible.

The signal light in the wavelength band of 1.5 to 1.7 μm output from the signal light source 11 enters the fiber coupler 13 via the optical fiber 18a. The signal light that has entered the coupler 13 is combined with the excitation light from the laser light source 12 and enters the optical fiber 10. The signal light incident on the optical fiber 10 induces the pumped Tm ³⁺ to generate stimulated emission light in a wavelength band of 1.5 to 1.7 μm.

From the output side of the optical fiber 10, the pumping light and the amplified signal light are output. Of these, the pumping light is cut by the filter 16. Therefore, only the amplified signal light is incident on the optical spectrum analyzer 15, and the gain of optical amplification by the optical fiber doped with Tm ³⁺ can be measured.

Regarding the principle of increasing the gain of the fiber amplifier of FIG.
A brief description will be given with reference to FIG.

FIG. 2 shows Tm added to a glass sample such as quartz glass.
FIG. 3 is a diagram schematically showing a ³⁺ energy level.

The Tm ³⁺ in the core is excited by the 1.20 μm pumping light introduced into the optical fiber, and the atom at the ground level ³ H ₆ temporarily transitions to the level ³ H ₅ . After that, the excited electrons emit energy such as phonons and are relaxed to a level of ³ H ₄
Transitions to. Such pumping, the population inversion is formed between the level ³ H ₆ and level ³ H _4, wavelength 1.5 to.
Light emission of a three-level system with a peak in the 7 μm band becomes possible.
As a result, effective stimulated emission in the wavelength band of 1.5 to 1.7 μm becomes possible.

The measurement result of the optical amplification gain obtained for the fiber amplifier of FIG. 1 will be described.

The wavelength of the excitation light incident on the optical fiber from the laser light source 12 was 1.21 μm, and the output was 30 mW. Also, the wavelength of the signal light incident on the optical fiber from the signal light source 11 is 1.65 μm.
And the output was 1 μW. From the measurement result by the optical spectrum analyzer 15, it was found that the optical amplification gain of the fiber amplifier of the example was about 6 dB.

For comparison, the same experiment was conducted by changing the pumping light source from 1.21 μm to 0.8 μm band.
It was about B. This is mitigated to level ³ H ₆ not only level ³ H ₄ atoms pumped from the level ³ H ₆ to level ³ F ₄ by the excitation light of wavelength 0.8μm band in non-radiative transition process For example, it is considered that the population inversion between the levels ³ H ₆ and ³ H ₄ is not effectively formed.

FIG. 3 shows the structure of an optical fiber 10 used in the fiber amplifier of FIG. 1 for reference.

The optical fiber 10 includes a core obtained by adding Tm to quartz and a clad obtained by adding fluorine (F) to quartz. Its core diameter is 6 μm and its outer diameter is 125 μm. The relative refractive index difference の between the core and the clad is about 0.7%.

Hereinafter, a brief description will be given of the production of the optical fiber of FIG.

First, as a core material of an optical fiber which is an optical transmission line, quartz glass to which thulium ions are added in an oxide state is melted and formed into a rod shape to obtain a core glass rod. The concentration of Tm ³⁺ as an active substance added to the quartz glass is 300 ppm by weight. Next, quartz glass to which fluorine is added is melted and formed to form a clad pipe. No Tm ³⁺ was added to the clad pipe. These core rod and clad pipe are formed into a preform by a rod-in-tube method. The preform is set in a known drawing device and drawn into an optical fiber. As a result, as described above, an SM fiber having a core diameter of 6 μm and an outer diameter of 125 μm is obtained. This SM fiber is cut into a sample having a length of 2 m for measurement, and is used as an optical fiber 10 for a fiber amplifier.

Hereinafter, embodiments of the light oscillation device of the present invention will be described.

FIG. 4 shows a fiber laser which is an optical oscillation device in a wavelength band of 1.5 to 1.7 μm.

The laser light source 12 is used for the fiber amplifier of FIG. 1, and is a laser diode (LD) having a wavelength of 1.21 μm. The optical fiber 10 doped with Tm ³⁺ is also used in the above fiber amplifier.

Excitation light having a wavelength of 1.21 μm from the LD is introduced into the optical fiber 28 by an appropriate means such as a lens or an optical connector. The pump light enters the optical fiber 10 doped with Tm ³⁺ from the end of the optical fiber 28. Tm ³⁺ in the optical fiber is excited to a predetermined state by this excitation light, and has a wavelength of 1.5 to 1.7.
Light emission in the μm band becomes possible. Here, since the output end of the optical fiber 10 is finished to a mirror surface, the output end and the end face of the laser diode constitute a resonator. As a result, when the output of the pump light exceeds a predetermined value, laser oscillation occurs at any wavelength in the 1.5 to 1.7 μm band.

In the optical fiber of the present embodiment, quartz glass is used as the matrix glass used for the core, but the composition of the matrix glass is not limited to this. For example, silicate glass, phosphate glass, fluoride glass, or the like may be used. By changing the composition of the matrix glass in this way, the wavelength of light emission or stimulated emission can be adjusted in the wavelength range of 1.5 to 1.7 μm.

Further, the optical transmission line of the present invention is not limited to the above optical fiber. For example, the Tm ³⁺ -added glass may be formed on a planar waveguide or the like. However, it is desirable to form an optical fiber from the viewpoint of obtaining a long optical transmission path. This is because the inversion distribution can be generated in Tm ³⁺ at a low threshold value by utilizing the fact that the optical loss is small.

Further, the resonator used for the fiber laser may be of a type using a dielectric mirror or the like.

〔The invention's effect〕

As described above, according to the optical amplifying device or the optical oscillating device according to the present invention, the wavelength of the excitation light in the 1.20 μm band that enables Tm ³⁺ emission in the 1.5 to 1.7 μm band is increased.
Optical amplification or optical oscillation in the 1.5 to 1.7 μm band becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical amplifier according to the present invention,
FIG. 2 is a diagram for explaining Tm ³⁺ pumping by pumping light in a wavelength band of 1.20 μm, FIG. 3 is a diagram showing the structure of an optical fiber used in the optical amplifier of FIG. 1, and FIG. FIG. 3 is a diagram showing an embodiment of the light oscillation device according to the present invention. 10: Optical fiber that is an optical transmission line, 12: 1.20 μm wavelength
Band excitation light source, 13, 18, 19, 28 ... optical means.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Izumi Mikawa Nippon Telegraph and Telephone Corporation, 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo (56) References JP-A-63-184386 (JP, A) 63-502067 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) H01S 3/07 H01S 3/10 H01S 3/17 G02F 1/35 501 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. An optical transmission line configured to have an optical functional glass doped with Tm ³⁺ as an active substance and transmitting signal light in a wavelength band of 1.5 to 1.7 μm, and an excitation light in a wavelength of 1.20 μm. An optical amplifying device comprising: an excitation light source that is generated; and an optical unit that causes the excitation light from the excitation light source to enter the optical transmission path. 2. An optical transmission line for transmitting light in a wavelength band of 1.5 to 1.7 μm, comprising an optical functional glass doped with Tm ³⁺ as an active substance, and generating an excitation light in a wavelength of 1.20 μm band. An excitation light source, and optical means for causing the excitation light to enter the optical transmission line from the excitation light source, and radiated light in a wavelength band of 1.5 to 1.7 μm from within the optical transmission line to the optical transmission line. An optical oscillation device, wherein a resonator structure for feedback is formed.