JPH081504B2 - 1.3 μm band optical amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical fiber type 1.3 μm
The present invention relates to an optical amplifier.

[0002]

2. Description of the Related Art Recently, for application to the field of optical communication in the 1.3 μm band, research on functional fibers such as fiber amplifiers and fiber lasers has been conducted using optical fibers doped with neodymium (Nd) which is a rare earth element. Has been done. For example,
Neodymium ion (N
There has been reported a report in which a glass doped with d ³⁺ ) was prepared and the optical amplification characteristics of an optical fiber formed from this glass were evaluated (New Glass Forum, announced in January 1990). In this report, regarding the characteristics of the optical fiber, the fluorescence peak wavelength is 1.323 μm, and the ESA (Excitin
g State Absorption) The peak wavelength is 1.310 μm and the amplification peak wavelength is 1.360 μm.
In addition, the document “Electronics Letters, 1990, Vol. 26, pp 194
~ 195 ", it was reported that an amplification gain of 10 dB was obtained for a minute signal at a wavelength of 1.33 µm.

[0003]

However, according to the above-mentioned report, the wavelength range in which the amplification gain is obtained is 1.31 to 1.36 μm as shown in FIG. 4, and in the wavelength range shorter than 1.31 μm. It will be a negative gain. This is considered to be due to the absorption of the signal due to the ESA transition.

Therefore, in order to solve the above problem, it is necessary to use an optical fiber doped with another rare earth element, which has a fluorescence characteristic in the 1.3 μm band and which hardly causes ESA transition, as an amplification medium. Then, the present inventors have concluded that praseodymium is promising as such a rare earth. However, examination of the absorption characteristics of praseodymium is as shown in FIG. That is, as an exciting laser, around 1.0 μm, around 0.6 μm, or 0.5 μm
Only wavelengths in the vicinity can be used, and these are all wavelength bands that have not yet been developed.

In view of such a situation, the present invention is 1.3 μm
It is an object of the present invention to provide a 1.3 μm band optical amplifier capable of amplifying in all wavelength bands used in band communication.

[0006]

In a 1.3 μm band optical amplifier according to the present invention which achieves the above object, an optical fiber having a rare earth element praseodymium added to at least a core is used as an amplification medium, and the optical fiber has a wavelength of An optical amplifier in which a pumping light is incident together with a signal light near 1.3 μm, and the light is directly amplified by utilizing the stimulated emission effect of praseodymium and the signal light, and an excitation light source is an optical fiber doped with neodymium. It is characterized by being constituted by.

[0007]

[Function] An optical fiber doped with neodymium used as an excitation light source has, for example, a reflective film coated on both end surfaces. For example, when 0.8 μm band light is introduced, it is 1.05 μm.
The laser oscillation light of m can be obtained, which is unprecedented. This 1.05 μm light coincides with the absorption wavelength region of praseodymium in the 1 μm band, and can be used as an excitation light source for at least an optical fiber in which praseodymium is added to the core. Therefore, when the laser oscillation light described above is introduced as excitation light together with the signal light in the vicinity of 1.3 μm into the optical fiber doped with praseodymium, the signal light is excited by the dielectric emission effect. That is, by using the above-mentioned optical fiber as the excitation light source, the praseodymium-doped optical fiber was excited by the 0.8 μm semiconductor laser.

[0008]

EXAMPLES The present invention will be described below based on examples.

FIG. 1 conceptually shows the structure of a 1.3 μm band optical amplifier according to an embodiment. In the figure, 1 is a neodymium (Nd) -doped optical fiber, and mirrors 2A and 2B are abutted on both ends of the Nd-doped optical fiber 1 so as to be orthogonal to the optical axis. Then, on the opposite side of the mirrors 2A and 2B, a 0.8 μm band semiconductor laser 3 and a dichroic mirror 4 are arranged so as to be optically coupled to the Nd-doped optical fiber 1 via lenses 5A and 5B, respectively. .

On the other hand, 6 in FIG. 1 indicates praseodymium (P
r) A doped fiber, which is arranged so as to be optically coupled to the opposite side of the dichroic mirror 4 from the Nd-doped optical fiber 1 via the lens 5C. On the side opposite to the Nd-doped optical fiber 1 of the dichroic mirror 4, P
A signal light source 7 is optically coupled to the opposite side of the r-doped optical fiber 6 via a lens 5D.

Here, the mirror 2A on the semiconductor laser 3 side
Has a reflectance of 100% at a wavelength of 1.06 μm and a wavelength of 0.8 μm.
The transmittance at 100 m is 100%, while the mirror 2B on the opposite side has a reflectance of 90% at a wavelength of 1.06 μm and a transmittance of 100% at a wavelength of 0.8 μm. Therefore, in such a configuration, the output light from the semiconductor laser 3 in the 0.8 μm band is condensed by the lens 5A, then transmitted through the mirror 2A, and is incident on the Nd-doped optical fiber 1.
The d-doped optical fiber 1 oscillates at a wavelength of 1.06 μm. In this embodiment, the length of the Nd-doped optical fiber 1 is set to 1
m and neodymium were added to 2000 ppm. The output of the semiconductor laser 3 is 0.85 μm and the maximum output is 10
It is 0 mW. At this time, the input power to the Nd-doped optical fiber 1 was 55 mW, and the output power of 1.06 μm was 35 mW.

The output of 1.06 μm thus obtained is obtained by the lens 5B, the dichroic mirror 4 and the lens 5.
The light is transmitted through C and is incident on the Pr-doped optical fiber 6 as excitation light. When the excitation light and the signal light in the vicinity of 1.3 μm from the signal light source 7 are combined by the dichroic mirror 4 and incident on the Pr-doped optical fiber 6, the excitation light of 1.06 μm is generated in the Pr-doped optical fiber 6. The praseodymium ion becomes excited. And to this 1.3
When photons of the signal light of μm act, a transition to a lower level occurs due to stimulated emission, and the signal light of 1.3 μm is amplified.

FIG. 2 conceptually shows the structure of a 1.3 .mu.m band optical amplifier according to another embodiment. The members having the same functions as those in FIG. Omit it. In this embodiment, both ends of the Nd-doped optical fiber 1 are polished on the surfaces orthogonal to the optical axis, and the dielectric thin films are directly coated in multiple layers to form the dielectric multilayer films 8A and 8B. The same effect as that of the mirrors 2A and 2B of the embodiment described above is obtained. The semiconductor laser 3 is coupled to the dielectric multilayer film 8A side of the Nd-doped optical fiber 1 via the lens 5A, while the dielectric multilayer film 8 on the opposite side is coupled.
A fiber coupler 10 is coupled to the B side via a connector 9.

Here, the fiber coupler 10 is used in place of the above-mentioned dichroic mirror 4,
It has the same wavelength dependence. That is, the fiber coupler 10 has a characteristic that light having an excitation wavelength of 1.06 μm goes straight and signal light of 1.3 μm moves to the opposite port. The signal light source 7 is coupled to the other port on the same incident side as the Nd-doped optical fiber 1 of the fiber coupler 10, and the Pr-doped light is coupled to the exit port on the incident port side to which the Nd-doped optical fiber 1 is coupled. Fiber 6 is coupled. As a result, the pumping light from the Nd-doped optical fiber 1 and the signal light from the signal light source 7 are connected to the fiber coupler 10
Are combined by the above and introduced into the Pr-doped optical fiber 6, and the signal light of 1.3 μm is amplified as in the above embodiment.

The characteristics of praseodymium (Pr) will be described below. The absorption characteristics of Pr are as shown in FIG. 5, and the energy level diagram is shown in FIG. The 1.3 μm amplification characteristic is caused by the transition from ¹ G ₄ to ³ H ₅ . Since the energy level of ¹ G ₄ is equivalent to the photon energy in the wavelength band of 1.06 μm, excitation at this wavelength is possible.

The amplification characteristic of the optical amplifier of the present invention is obtained when a fluoride optical fiber (core diameter: 6 μm, cladding diameter: 125 μm, relative refractive index difference: 0.5%) doped with Pr2000 ppm is used as an amplification fiber. , Excitation power 35mW
The maximum gain was 4 dB. The range in which this gain was obtained was 1.29 μm to 1.34 μm, and the effect of ESA observed in the Nd-doped optical fiber was not clearly recognized.

In the Nd-doped optical fiber 1 and the Pr-doped optical fiber 6 used in the above embodiments, Nd and P
r may be added at least to the core, but the effect can be further improved by adding Nd or Pr to the clad around the core, that is, the portion where the guided light exudes.

[0018]

As described above, since the optical amplifier according to the present invention uses the praseodymium-doped optical fiber as the amplification medium and the neodymium-doped optical fiber as the pumping light source, it has a wavelength range of 1.29 μm to 1 μm. Amplification is possible at 0.34 μm. That is, the limitation of the amplification wavelength range due to ESA, which is a problem in the neodymium-doped optical fiber, does not occur, and the amplification is performed in the entire wavelength range used in the 1.3 μm band communication. Further, since the neodymium-doped optical fiber laser is used as the pumping light source, the pumping can be performed by the 0.8 μm band semiconductor laser, and the semiconductor laser in this wavelength range is low in cost, so that the amplifier price is also low. Also plays.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a 1.3 μm optical amplifier according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a 1.3 μm optical amplifier according to another embodiment.

FIG. 3 is an energy level diagram of praseodymium.

FIG. 4 is a graph showing the wavelength dependence of the amplification gain of a neodymium-doped optical fiber.

FIG. 5 is an absorption characteristic diagram of a praseodymium-doped fiber.

[Explanation of symbols]

 1 Nd-doped optical fiber 2A, 2B mirror 3 0.8 μm band semiconductor laser 4 Dichroic mirror 6 Pr-doped optical fiber 7 Signal light source 8A, 8B Dielectric multilayer film 10 Fiber coupler

Claims (2)

[Claims] 1. An optical fiber having at least a core containing praseodymium as a rare earth element is used as a medium for amplification, and pumping light is incident on the optical fiber together with signal light having a wavelength of about 1.3 μm. An optical amplifier that directly amplifies light by utilizing the stimulated emission effect of and a pumping light source is composed of an optical fiber doped with neodymium, which is a 1.3 μm band optical amplifier. 2. The pumping light source according to claim 1, wherein at least both ends of an optical fiber doped with neodymium in the core have reflectors having wavelength dependence, and the light source is optically coupled to one end side thereof. A 1.3 μm band optical amplifier characterized in that light incident from one end side is oscillated and emitted from the other end side.