JPH04361583A - Light amplification stabilizing system - Google Patents

Abstract

PURPOSE:To provide a light amplification stabilizing system which is prevented from varying in amplification degree and outputs signals of stable power. CONSTITUTION:In a light amplification device which employs a rearward excitation method where an erbium-doped optical fiber 15 is used, a wavelength division multiplex optical branching device or an optical coupler 12 used for separating exciting light 14 which passes through the erbium-doped optical fiber 15 from signal light is provided, the optical power of exciting light is monitored so as to control the drive current of an exciting light source 17 through a feedback method to make exciting light constant in optical power.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an erbium-doped optical fiber amplifier, and more particularly to an optical amplification stabilization method suitable for stabilizing optical amplification.

0002

2. Description of the Related Art Conventionally, as an optical fiber, an erbium-doped optical fiber is known, which is formed by adding erbium (doping) and forming the fiber into a fiber. Unlike a semiconductor laser, this erbium-doped optical fiber forms a population inversion by optical excitation, so it can achieve high excitation density even with a small input, and has low loss, so it can be used from several tens of centimeters to several kilometres.
It has excellent characteristics as an amplification medium, such as having a long interaction length of m.

[0003] An erbium-doped optical fiber amplifier using an erbium-doped optical fiber having such characteristics has been developed (Reference: "Optical Fiber Amplifier" by Kimura et al., Optronics, 1990, No. 11, p. 4)
7-p53).

FIG. 4 is a diagram for explaining a conventional optical amplification stabilization method using backward pumping. This shows the construction of an erbium-doped optical fiber amplifier. In FIG. 4, 41 is an input signal light, 42 is an erbium-doped optical fiber (EDF), 43 is an optical coupler such as an optical multiplexer/demultiplexer for wavelength division multiplexing or an optical coupler, 44 is a pumping light source such as a semiconductor laser, and 45 is an optical coupler. Excitation light emitted from the excitation light source 44,
46 is APC (Automatic Power
47 is an output signal light.

FIG. 5 is a diagram for explaining a conventional optical amplification stabilization method using forward pumping. This shows the construction of an erbium-doped optical fiber amplifier. In FIG. 5, 51 is an input signal light, 52 is an optical coupler such as an optical multiplexer/demultiplexer for wavelength division multiplexing or an optical coupler, 53 is an erbium-doped optical fiber (EDF), 54 is an optical multiplexer/demultiplexer for wavelength division multiplexing, 55 is an excitation light source such as a semiconductor laser, 56 is excitation light emitted from the excitation light source 55, 57 is an APC circuit,
58 is an output signal light.

First, in optical amplification by backward pumping, as shown in FIG. 4, the pumping light 45 emitted from the pumping light source 44 is
Erbium-doped optical fiber 42 via optical coupler 43
incident on . For the optical coupler 43, an optical multiplexer/demultiplexer for wavelength division multiplexing or an optical coupler is used. Thereby, the input signal light 41 is combined with the excitation light 45 within the erbium-doped optical fiber 42, and is amplified by stimulated emission of erbium electrons excited by the excitation light 45. This amplified light is separated from the pumping light by an optical multiplexer/demultiplexer for wavelength division multiplexing of the optical coupler 43 and taken out as an output signal light 47.

On the other hand, in optical amplification by forward pumping, input signal light 51 and pumping light 56 are in the same direction, as shown in FIG. Therefore, the wavelength division multiplexing optical multiplexer/demultiplexer 54 separates the input signal light and the pump light, and extracts the output signal light 58.

By the way, the degree of amplification expressed by the ratio of the input signal light power and the output signal light power is as shown in FIG.
It depends on the pumping light power incident on the erbium-doped optical fiber. In order to keep the amplification level stable, it is necessary to keep the pumping light power stable. For this purpose, an APC circuit 46 or 57 is used to keep the output power of the excitation light source stable. This APC circuit 46 or 57, when the excitation light source 44 or 55 is a semiconductor laser (LD) light source,
A method is adopted in which the rear output optical power of the LD is monitored and the LD drive current is feedback-controlled.

[0009]

However, in the above conventional method, if the loss between the pumping light source and the erbium-doped optical fiber changes, even if the optical power emitted from the pumping light source is stable, the amplification degree will change. The problem was that it was unstable.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical amplification stabilization method that can solve the above-mentioned conventional problems, prevent fluctuations in amplification, and obtain stable output signal power.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the optical amplification stabilization method of the present invention provides an optical amplification device using backward pumping using an erbium-doped optical fiber.
It has an optical multiplexer/demultiplexer or optical coupler for wavelength division multiplexing to separate the pumping light that has passed through the erbium-doped optical fiber from the signal light, and monitors the optical power of the pumping light so that the optical power remains at a constant value. The feature is that the drive current of the excitation light source is feedback-controlled so as to achieve the following.

Another optical amplification stabilization method of the present invention is a forward pumping optical amplification device using an erbium-doped optical fiber, in which the pumping light that has passed through the erbium-doped optical fiber is separated from the signal light. It is characterized in that it has an optical multiplexer/demultiplexer for wavelength division multiplexing, monitors the optical power of the excitation light, and feedback-controls the drive current of the excitation light source so that the optical power becomes a constant value.

[0013]

In the present invention, the optical power of the excitation light generated by backward pumping or forward pumping is monitored, and the driving current of the excitation light source is feedback-controlled so that the optical power is kept at a constant value. This prevents the influence of loss fluctuations between the excitation light source and the erbium-doped optical fiber, and provides stable output signal light power.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram for explaining an optical amplification stabilization method using backward pumping, which shows a first embodiment of the present invention. This shows the construction of an erbium-doped optical fiber amplifier with backward pumping.

In FIG. 1, 11 is an input signal light, 12 is an optical coupler such as an optical multiplexer/demultiplexer for wavelength division multiplexing or an optical coupler, 13 is a pumping light power monitor characteristic of the present invention, and 14 is a post-optical amplification signal. excitation light (residual excitation light), 15 is an erbium-doped optical fiber (EDF), 16 is an optical coupler such as an optical multiplexer/demultiplexer for wavelength division multiplexing or an optical coupler, 17 is an excitation light source such as a semiconductor laser, and 18 is an excitation light source. Excitation light is emitted from a light source 17, 19 is an APC circuit, and 20 is output signal light.

The optical amplification system in the first embodiment includes an erbium-doped optical fiber 15 and two optical couplers 12 and 1.
6, a pumping light source 17, an APC circuit 19, and a pumping light power monitor 13. The optical couplers 12 and 16 use optical multiplexers/demultiplexers for wavelength division multiplexing or optical couplers. The excitation light 18 emitted from the excitation light source 17 is transmitted to the optical coupler 1
6 into the erbium-doped optical fiber 15,
Excite erbium electrons. On the other hand, the input signal light 11 is
Erbium doped optical fiber 15 via optical coupler 12
and is amplified by the stimulated emission of the excited erbium electrons mentioned above. The amplified signal light is sent to the optical coupler 16
The light is separated from the excitation light 18 and taken out as an output signal light 20. Further, among the excitation light 18, light that does not contribute to optical amplification by the erbium-doped optical fiber 15 is excitation light (residual excitation light) 14 after optical amplification. The residual pumping light 14 is separated from the signal light by the optical coupler 12, and its optical power is monitored by the pumping light power monitor 13. This residual pumping light power fluctuation information is passed to the APC circuit 19 which is the drive section of the pumping light source 17, and the pumping light power monitor 13
The drive current of the excitation light source 17 is feedback-controlled so that the optical power of the residual excitation light 14 detected in the step is constant.

FIG. 2 is a diagram for explaining an optical amplification stabilization method using forward pumping, showing a second embodiment of the present invention. This shows the construction of an erbium-doped optical fiber amplifier with forward pumping.

In FIG. 2, 21 is an input signal light, 22 is an optical coupler such as an optical multiplexer/demultiplexer for wavelength division multiplexing or an optical coupler, 23 is a pumping light source such as a semiconductor laser, and 24 is the pumping light source 2.
Pumping light emitted from 3, 25 an APC circuit, 26 an erbium-doped optical fiber (EDF), 27 an optical multiplexer/demultiplexer for wavelength division multiplexing, 28 a pumping light power monitor characteristic of the present invention, and 29 an optical Excitation light after amplification (residual excitation light), 3
0 is the output signal light.

The optical amplification system in the second embodiment includes an erbium-doped optical fiber 26, an optical coupler 22, an optical multiplexer/demultiplexer 27 for wavelength division multiplexing, a pumping light source 23, and an APC circuit 25.
and a pump light power monitor 28. The optical coupler 22 uses an optical multiplexer/demultiplexer for wavelength division multiplexing or an optical coupler. The excitation light 24 emitted from the excitation light source 23 is connected to the erbium-doped optical fiber 2 via the optical coupler 22.
6 and excites erbium electrons. The input signal light 21 also enters the erbium-doped optical fiber 26 via the optical coupler 22, and is amplified by stimulated emission of the excited erbium electrons. The amplified signal light is
It is separated from the pumping light 24 by an optical multiplexer/demultiplexer 27 for wavelength division multiplexing, and an output signal light 30 is taken out. In addition, among the pumping light 24, the light that did not contribute to the optical amplification by the erbium-doped optical fiber 26 is the pumping light (residual pumping light) 2 after optical amplification.
It is 9. The residual pumping light 29 is separated from the signal light by the optical multiplexer/demultiplexer 27 for wavelength division multiplexing, and the pumping light power monitor 2
8 monitors the optical power. This fluctuation information of the residual pumping light power is passed to the APC circuit 25 which is the driving part of the pumping light source 23, and the pumping light source 23 is changed so that the optical power of the residual pumping light 29 detected by the pumping light power monitor 28 is constant. Feedback control of drive current.

FIG. 3 is a diagram showing a circuit example of the pumping light power monitor in FIG. 1 or 2. In FIG. In Figure 3, 3
2 is a photodiode, 33 is excitation light after optical amplification, 34
is a differential amplifier, and 35 and 36 are resistors.

First, the excitation light (residual excitation light) 3 after optical amplification
3 is detected by the photodiode 32. The detected output voltage is compared with a reference voltage by a differential amplifier 34, and the reference voltage of the APC circuit 19 or 25 is changed by feedback control so that the difference is always zero. That is, the pumping light power monitor monitors the optical power of the pumping light by monitoring the optical power of the residual pumping light, and controls the pumping light source (laser diode) 17 or 23 so that the optical power becomes a constant value. Feedback control of drive current.

In this way, in the first and second embodiments, stable optical amplification can be obtained even if the loss between the excitation light source and the erbium-doped optical fiber varies. The following two factors can be cited as factors that cause the loss between the excitation light source and the erbium-doped optical fiber to vary. (1) When a semiconductor laser (LD) is used as the excitation light source, L
The loss in the coupling system between D and the optical fiber has temperature fluctuation and aging characteristics. The amount of deterioration due to temperature (0 to 60° C.) and the amount of deterioration over time of this loss are usually about 1 dB each. (2) The loss of the optical coupler used to couple the excitation light to the erbium-doped optical fiber is subject to temperature fluctuations and deterioration over time. The temperature of this loss (0 to 60
The amount of deterioration caused by temperature (°C) and the amount of deterioration over time are usually 0.
It is about 5 dB.

[0023] From this, it is considered that the loss that the excitation light emitted from the excitation light source undergoes before it enters the erbium-doped optical fiber increases by about 3 dB. Therefore, if there is no feedback control to keep the pumping light power constant according to this embodiment, the pumping light power incident on the erbium-doped optical fiber may deteriorate by about 3 dB. From the relationship between pump light power and amplification degree shown in Figure 6,
For example, when the power of the pumping light incident on the erbium-doped optical fiber is 40 mW, the amplification degree is about 20 dB. At this time, if the loss of the pumping light received before entering the erbium-doped optical fiber increases by 3 dB, the power of the pumping light entering the erbium-doped optical fiber becomes 20 mW, and the amplification degree becomes about 10 dB. The amplification degree varies by about 10 dB due to variations in loss between the pumping light source and the erbium-doped optical fiber. The first embodiment and the second embodiment of the above book
According to the embodiment, a stable amplification degree can be obtained regardless of loss fluctuations between the excitation light source and the erbium-doped optical fiber.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
Even if the loss between the excitation light source and the erbium-doped optical fiber fluctuates, stable amplification can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an optical amplification stabilization method showing a first embodiment of the present invention.

FIG. 2 is a diagram for explaining an optical amplification stabilization method showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a circuit example of the pumping light power monitor in FIG. 1 or 2;

FIG. 4 is an explanatory diagram of a conventional optical amplification stabilization method using backward pumping.

FIG. 5 is an explanatory diagram of a conventional optical amplification stabilization method using forward pumping.

FIG. 6 is a diagram showing the relationship between pumping light power and amplification degree.

[Explanation of symbols]

11 Input signal light 12 Optical coupler 13 Pumping light power monitor 14 Pumping light after optical amplification (residual pumping light) 15 Erbium-doped optical fiber 16 Optical coupler 17 Pumping light source 18 Pumping light 19 APC circuit 20 Output signal light 21 Input signal Light 22 Optical coupler 23 Pumping light source 24 Pumping light 25 APC circuit 26 Erbium-doped optical fiber 27 Optical multiplexer/demultiplexer for wavelength division multiplexing 28 Pumping light power monitor 29 Pumping light after optical amplification (residual pumping light) 30 Output signal light 32 Photodiode 33 Pumping light after optical amplification 34 Differential amplifier

Claims (2)

[Claims] Claim 1: An optical amplification device using backward pumping using an erbium-doped optical fiber, comprising an optical multiplexer/demultiplexer or an optical coupler for wavelength division multiplexing to separate the pumping light that has passed through the erbium-doped optical fiber from the signal light. An optical amplification stabilization method characterized in that the optical power of the excitation light is monitored, and the drive current of the excitation light source is feedback-controlled so that the optical power becomes a constant value. 2. An optical amplification device using forward pumping using an erbium-doped optical fiber, comprising an optical multiplexer/demultiplexer for wavelength division multiplexing for separating pumping light that has passed through the erbium-doped optical fiber from signal light; An optical amplification stabilization method characterized by monitoring the optical power of excitation light and feedback-controlling the drive current of the excitation light source so that the optical power becomes a constant value.