JPH04234021A - 1.3mum band optical amplifier - Google Patents

Abstract

PURPOSE:To allow amplification in a full wavelength region used in communication of a 1.3mum band by using a praseodymium-added optical fiber for a medium for amplification and a neodymium-added optical fiber for a exciting light source. CONSTITUTION:The optical fiber 6 formed by adding the praseodymium to at least its core is used for the amplifying medium. The exciting light from a exciting light source constituted of the optical fiber 1 added with the neodymium and signal light are introduced into the praseodymium-added optical fiber, by which the signal light is amplified. The exciting light 1 added with the neodymium to be used as the exciting light source is formed by coating, for example, both end faces with reflection films. A laser oscillated beam of 1.05mum is obtd. if, for example, 0.8mum band light is introduced into this fiber. Then, the signal light is excited by a dielectric release effect by introducing the laser oscillated beam of the signal light about 1.3mum is introduced as the exciting light together with this signal light into the optical fiber added with the praseodymium.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an optical fiber type 1.3μ
This invention relates to an m-band optical amplifier.

0002

[Prior Art] In recent years, research has been carried out on functional fibers such as fiber amplifiers and fiber lasers using optical fibers doped with neodymium (Nd), a rare earth element, for application in the field of optical communication in the 1.3 μm band. being done. For example, neodymium ions (Nd
There has been a report (published by New Glass Forum, January 1990) in which a glass doped with 3+) was prepared and the optical amplification characteristics of an optical fiber formed from this glass were evaluated. In this report, regarding the characteristics of the optical fiber, the fluorescence peak wavelength is 1.323 μm, and the ESA (Ex
(citing State Absorption)
Peak wavelength is 1.310μm, amplification peak wavelength is 1.3
A result of 60 μm has been obtained. In addition, the literature “Electronics Letters
, 1990, Vol. 26, pp. 194-195”
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 amplification gain can be obtained is 1.31 to 1.36 μm, as shown in FIG. This results in a negative gain. This is thought to be due to signal absorption due to ESA transition.

[0004] Therefore, in order to solve the above problem, it is necessary to use as an amplification medium an optical fiber doped with other rare earth elements that have fluorescence characteristics in the 1.3 μm band and are less likely to cause ESA transition. The present inventors have concluded that praseodymium is a promising rare earth element. However, when considering the absorption characteristics of praseodymium, it is as shown in FIG. That is, the excitation laser has a diameter of around 1.0 μm, around 0.6 μm, or around 0.0 μm.
Only wavelengths around 5 μm can be used, and both of these are currently undeveloped wavelength regions.

[0005] In view of these circumstances, the present invention has been developed to
1.3μ that can amplify all wavelength ranges used in m-band communications
The purpose of the present invention is to provide an m-band optical amplifier.

[0006]

[Means for Solving the Problems] A 1.3 μm band optical amplifier according to the present invention that achieves the above object uses an optical fiber doped with the rare earth element praseodymium at least in the core as an amplification medium, and a wavelength This is an optical amplifier that directly amplifies light by inputting excitation light together with a signal light around 1.3 μm and utilizing the stimulated emission effect caused by the optical excitation of praseodymium and the signal light, in which the excitation light source is an optical fiber doped with neodymium. It is characterized by being composed of.

[0007]

[Function] The neodymium-doped optical fiber used as an excitation light source has, for example, a reflective film coated on both end faces, and for example, when 0.8 μm band light is introduced, the
Laser oscillation light of 5 μm can be obtained, which is unprecedented. This 1.05 μm light matches the absorption wavelength range of praseodymium in the 1 μm band, and can be used as an excitation light source for an optical fiber whose core is doped with praseodymium. Therefore, when the above-mentioned laser oscillation light is introduced as excitation light into an optical fiber doped with praseodymium along with a signal light of around 1.3 μm,
Signal light is excited by the dielectric emission effect. That is, by using the above-mentioned optical fiber as an excitation light source,
This means that the praseodymium-doped optical fiber is excited by a 0.8 μm semiconductor laser.

[0008]

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

FIG. 1 conceptually shows the configuration of a 1.3 μm band optical amplifier according to an embodiment. In the figure, reference numeral 1 denotes a neodymium (Nd)-doped optical fiber, and mirrors 2A and 2B are abutted against each other at 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 connected via lenses 5A and 5B, respectively.
It is arranged so as to be optically coupled to the doped optical fiber 1.

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

Here, the mirror 2A on the side of the semiconductor laser 3 has a reflectance of 100% at a wavelength of 1.06 μm and a reflectance of 0.8 μm.
The transmittance at μm is 100%, while the mirror 2B on the opposite side has a reflectance of 90% at a wavelength of 1.06 μm.
, the transmittance at a wavelength of 0.8 μm is 100%. Therefore, in this configuration, the output light from the semiconductor laser 3 in the 0.8 μm band is focused by the lens 5A, and then transmitted through the mirror 2A and enters the Nd-doped optical fiber 1. emits laser oscillation at a wavelength of 1.06 μm. In this example, the length of the Nd-doped optical fiber 1 was 1 m, and the amount of neodymium added was 2000 ppm. Moreover, the output of the semiconductor laser 3 is 0.805 μm
The maximum power is 100mW. At this time, the input power to the Nd-doped optical fiber 1 was 55 mW, and the output power at 1.06 μm was 35 mW.

The output of 1.06 μm thus obtained is transmitted through the lens 5B, the dichroic mirror 4, and the lens 5C, and enters the Pr-doped optical fiber 6 as excitation light. When such excitation light and the signal light of around 1.3 μm from the signal light source 7 are combined by the dichroic mirror 4 and input into the Pr-doped optical fiber 6, Pr
In the doped optical fiber 6, praseodymium ions are brought into an excited state by the 1.06 μm excitation light. When photons of the 1.3 μm signal light act on this, a transition to a lower level occurs due to stimulated emission, and the 1.3 μm signal light is amplified.

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

[0014] Here, the fiber coupler 10 is used in place of the dichroic mirror 4 described above.
They have similar wavelength dependence. That is, this fiber coupler 10 has a characteristic in which light with a pumping wavelength of 1.06 μm travels straight, and signal light with a wavelength of 1.3 μm moves to the opposite port. A signal light source 7 is coupled to the other port on the same input side as the Nd-doped optical fiber 1 of the fiber coupler 10, and a Pr-doped light source 7 is coupled to the output port on the input port side to which the Nd-doped optical fiber 1 is coupled. Fiber 6 is coupled. As a result, the excitation light from the Nd-doped optical fiber 1 and the signal light from the signal light source 7 are connected to the fiber coupler 1.
0 and introduced into the Pr-doped optical fiber 6,
Similarly to the above embodiment, a 1.3 μm signal light is amplified.

[0015] Here, the characteristics of praseodymium (Pr) will be explained. The absorption characteristics of Pr are as shown in FIG. 5, and FIG. 3 shows an energy level diagram. The 1.3 μm amplification characteristic is caused by the 1G4 to 3H5 transition. Since the energy level of 1G4 is equivalent to photon energy in the wavelength band of 1.06 μm, excitation at this wavelength is possible.

The amplification characteristics of the optical amplifier of the present invention are as follows: The amplification fiber is a fluoride optical fiber doped with 2000 ppm of Pr (core diameter: 6 μm, cladding diameter: 125 μm).
, relative refractive index difference: 0.5%), excitation power 3
The maximum gain was 4 dB at 5 mW. Also, the range in which this gain was obtained was from 1.29 μm to 1.34 μm,
The effect of ESA seen in the Nd-doped optical fiber was clearly not observed.

Note that in the Nd-doped optical fiber 1 and the Pr-doped optical fiber 6 used in the above embodiments, Nd and P
It is sufficient that r is added at least to the core, but the effect can be further improved by adding Nd or Pr to the cladding around the core, that is, the portion from which the guided light seeps out.

[0018]

As explained above, the optical amplifier according to the present invention uses a praseodymium-doped optical fiber as the amplification medium and a neodymium-doped optical fiber as the excitation light source, so that the wavelength range is 1.29 μm to 1.2 μm. .34μm
Amplification is possible in In other words, the amplification wavelength range is not limited by ESA, which is a problem with neodymium-doped optical fibers, and the entire wavelength range used in communication in the 1.3 μm band is amplified. In addition, since a neodymium-doped optical fiber laser is used as the excitation light source, the excitation can be performed with a 0.8 μm band semiconductor laser, and since semiconductor lasers in this wavelength range are low cost, the price of the amplifier is also low. Also plays.

[Brief explanation of the drawing]

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] Claim 1: An optical fiber doped with the rare earth element praseodymium at least in the core is used as an amplification medium, and excitation light is input into the optical fiber together with a signal light having a wavelength of around 1.3 μm, thereby optically excitation of praseodymium and signal light. 1. A 1.3 μm band optical amplifier that performs direct amplification of light by utilizing the stimulated emission effect caused by the 1.3 μm band optical amplifier, characterized in that the excitation light source is constituted by an optical fiber doped with neodymium. 2. In claim 1, the excitation light source has a wavelength-dependent reflector at both ends of an optical fiber whose core is doped with neodymium, and the light source is optically coupled to one end of the optical fiber. A 1.3 μm band optical amplifier characterized in that it has a configuration in which light incident from one end side is lased and emitted from the other end side.