JPH05136511A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To suppress the introduction into optical fibers of noise light of the waveband same as the signal light generating in the light source, and to improve the noise characteristics of the optical fibers by a method wherein a filtering means, with which the light of wavelength band of signal light is shut off, is provided on the light path between an optical means and the light source. CONSTITUTION:Semiconductor lasers 2 and 12 generate an excited light of 1.48mum band. The laser 2 is the light source for excitation in forward direction, and it is made incident on a fiber coupler 6 passing through the filter 4 to be used for prevention of noise. After the above-mentioned laser 2 has been combined with the signal light of 1.55mum band in wavelength which is made incident from an input end, the combined light is made incident on the left end of the Er-doped fibers 10 to be used for light amplification. On the other hand, the laser 12 is the light source for backward excitation, it is made incident on a second optical fiber coupler 16 passing through a second filter 14, and then it is made incident on the right end of the Er-doped fibers 10. As the noise light of the wavelength same as the signal light can be removed from the excitation light which is made incident from both directions of the Er-doped fiber 10 by the presence of the first and the second filters 4 and 14, noise can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier composed of an optical fiber doped with a rare earth element, a transition element and other active substances.

[0002]

2. Description of the Related Art An optical fiber doped with a rare earth element has an amplification function in a specific wavelength band. In particular, an optical fiber (Er-doped fiber) doped with Er (erbium) is
Since silica-based optical fiber has an optical amplification function in the wavelength band of 1.55 μm, which shows low loss, development is being actively pursued and various applications are being considered (Shimada, “Er-doped fiber optical amplifier Impact on communication systems ",
O plus E, No.113, pp75-82). As the wavelength of the pumping light, it was clarified that the wavelength range of 1.48 μm, which enables high-power oscillation by a semiconductor laser, can be applied, and a compact and inexpensive optical fiber amplifier can be constructed (M.N.
agazawa, et al., “Efficient Er ³⁺ -doped optical fib
er amplifier pumped by a 1.48 μm InGaAs laser di
ode ”, Appl. Phys. Lett. 54 (4), 23 Jan 1989).

FIG. 1 shows a configuration example of a conventional optical fiber amplifier. The pumping light from the pumping semiconductor laser having the wavelength of 1.48 μm and the signal light from the signal source are combined by the optical fiber coupler and are incident on the Er-doped fiber. An optical isolator for suppressing oscillation is inserted at both ends of the Er-doped fiber, and an optical filter for removing unnecessary noise light is connected to the output.

[0004]

However, in the case of the conventional optical fiber amplifier, the pumping semiconductor laser has a wavelength of 1.48.
Since not only the μm band but also the light of the wavelength 1.55 μm band is slightly generated, this pumping semiconductor laser itself becomes a noise source. Also, the transmission quality deteriorates due to the signal light being reflected at the end face of the backward pumping semiconductor laser,
Further, there is a problem that the semiconductor laser is damaged. As a method of solving this, it is conceivable to insert an optical isolator between the pumping semiconductor laser and the optical fiber coupler, but the device is generally expensive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical fiber amplifier in which noise caused by the pumping light source is small, the transmission quality is excellent, and the pumping light source is not easily damaged.

[0006]

In order to solve the above problems, an optical fiber amplifier according to the present invention generates an optical fiber doped with an active substance and pumping light for exciting the active substance doped in the optical fiber. A light source and optical means for introducing pumping light from the light source into the optical fiber are provided, and filter means for blocking light in the wavelength band of the signal light is provided on the optical path between the optical means and the light source. There is.

[0007]

In the above optical fiber amplifier, since the filter means for blocking the light in the wavelength band of the signal light is provided on the optical path between the optical means and the light source, the same wavelength band as the signal light generated by the light source is provided. Can be restricted from being introduced into the optical fiber doped with the active substance. As a result, the noise characteristic of the optical fiber amplifier can be improved. On the contrary, since it is possible to restrict the signal light from the optical fiber side from entering the light source, it is possible to prevent the light source from being damaged by the signal light entering the light source side from the optical means.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of an embodiment of the present invention will be briefly described below with reference to FIGS.

FIG. 2 is a diagram showing the configuration of the optical fiber amplifier according to the embodiment. First and second semiconductor lasers 2,
Both 12 generate excitation light in the wavelength band of 1.48 μm. The first semiconductor laser 2 is a light source for forward pumping, and the pumping light generated from the first semiconductor laser 2 passes through the first filter 4 to produce the first laser light.
It is incident on the optical fiber coupler 6. The pumping light that has entered the first optical fiber coupler 6 has a wavelength of 1.5 that has entered from the input end.
After being multiplexed with the signal light in the 5 μm band, it passes through the first optical isolator 8 for suppressing oscillation and enters the Er-doped fiber 10 for optical amplification at the left end of the drawing. On the other hand, the second semiconductor laser 12 is a light source for backward pumping, and pumping light generated from the second semiconductor laser 12 passes through the second filter 14 and enters the second optical fiber coupler 16 and enters the right end of the Er-doped fiber 10 in the drawing. To do. The signal light incident on the left end of the Er-doped fiber 10 in the drawing and passing therethrough is the second optical fiber coupler 16 provided at the other end of the Er-doped fiber 10.
And passes through the second optical isolator 18 and exits from the output end.

FIG. 3 shows the first and second filters 4, 14
3 is a graph showing the light transmission characteristics of Most of the light in the wavelength band of 1.48 μm incident on each filter is transmitted, but the light in the wavelength band of 1.55 μm incident on each filter is hardly transmitted. That is, noise light having the same wavelength as the signal light included in the pumping light does not pass through these filters.

The operation of the optical fiber amplifier shown in FIG. 2 will be briefly described. The pumping light entering one end of the Er-doped fiber 10 via the first optical fiber coupler 6 and the pumping light entering the other end of the Er-doped fiber 10 via the second optical fiber coupler 16 enter the Er-doped fiber 10. The added Er is excited bidirectionally. The signal light incident on one end of the Er-doped fiber 10 via the first optical fiber coupler 6 is amplified by stimulated emission of excited Er. The amplified signal light is extracted at the output end via the second optical fiber coupler 16. In this case, due to the presence of the first and second filters 4, 14, the Er-doped fiber 1
Since the noise light having the same wavelength as the signal light is removed from the pumping light that is incident from both directions of 0, the noise of the optical fiber amplifier can be reduced. Further, since the signal light is not guided to the second semiconductor laser 12 for backward pumping, the transmission quality is not impaired due to the signal light being reflected by the end face of the semiconductor laser, and further the semiconductor laser is used. Can be prevented from being damaged.

The present invention is not limited to the above embodiment. For example, a rare earth element Nd or the like can be used as the active substance other than Er. Further, as the first and second filters, a fusion splicing type optical fiber coupler or the like can be used in addition to the dielectric multilayer film. Further, although the first and second filters do not have to completely block the transmission of the light of the signal light wavelength, it is desirable that the first and second filters hardly prevent the transmission of the light of the excitation light wavelength. further,
Either one of the first and second semiconductor lasers 2 and 12 can be removed to form a unidirectional pumping type optical fiber amplifier.

[0013]

As described above, according to the optical fiber amplifier of the present invention, the filter means for blocking the light in the wavelength band of the signal light is provided on the optical path between the optical means and the light source. It is possible to restrict the introduction of noise light in the same wavelength band as the signal light generated by the light source into the optical fiber doped with the active substance. As a result, the noise characteristic of the optical fiber amplifier can be improved. On the contrary, since it is possible to restrict the signal light from the optical fiber from entering the light source, it is possible to prevent the light source from being damaged by the signal light entering the light source side from the optical means.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional optical fiber amplifier.

FIG. 2 is a diagram showing an optical fiber amplifier according to an embodiment.

FIG. 3 is a diagram showing wavelength dependence of transmittance of an optical filter inserted between an excitation light source and an optical fiber coupler.

[Explanation of symbols]

2, 12 ... Light source for generating excitation light, 4, 14 ... Filter means, 6, 16 ... Optical means, 10 ... Optical fiber

Claims (1)

[Claims] 1. An optical fiber added with an active substance, a light source for generating excitation light for exciting the active substance added to the optical fiber, and an optical means for introducing the excitation light from the light source into the optical fiber. An optical fiber amplifier comprising: filter means for blocking light in a wavelength band of signal light provided on an optical path between the optical means and the light source.