JPH06303207A - Optical direct amplifier - Google Patents

Abstract

PURPOSE:To transmit digital information of fault information with an optical main signal. CONSTITUTION:Fault information 15 is converted into two kinds of frequencies less than a low pass interruption frequency by a frequency shift keying modulation circuit 16, and an exciting semiconductor laser driving circuit drives an exciting semiconductor laser 19. Exciting light by the laser is inputted to an erbium addition fiber by a wavelength division multiplex coupler 13, and optical direct amplificatior is executed in a form that exciting light is overlapped with the optical main signal. The optical signal which is thus obtained is outputted from an output terminal 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical direct amplifier used in an optical communication device, and more particularly to an optical direct amplifier characterized by a pumping semiconductor laser modulation method.

[0002]

2. Description of the Related Art An optical amplifier is used in an optical intermediate repeater as an amplifier for sending an optical main signal input from one transmission line to the other transmission line. In such an optical amplifier, a direct-current constant current is passed through a pumping semiconductor laser for direct optical amplification. Regarding the optical direct amplifier, for example, "optical fiber amplifier" Yasuo Omura, Masataka Nakazawa,
OPTRONICS (1990) No. 11, pp. Four
7-53.

[0003]

In the optical direct amplifier, since a direct current of constant current is applied to the pumping semiconductor laser for amplification, the optical direct amplifier itself will transmit even if some signal other than the optical main signal is transmitted. Since it does not have the function of converting electrical signals into light, it can only transmit the optical main signal itself. Therefore, even if a failure is detected by the optical intermediate repeater, this failure information cannot be transmitted to the downstream side together with the optical main signal.

Therefore, an object of the present invention is to provide an optical direct amplifier capable of transmitting such digital information as failure information together with an optical main signal.

[0005]

According to a first aspect of the present invention, a rare earth-doped fiber such as an erbium-doped fiber that directly amplifies an optical main signal input from an input terminal by pumping light is superimposed on the optical main signal. FSK modulation circuit for inputting power digital information and frequency-shift keying modulating it, pumping semiconductor laser driven by this modulated frequency, output signal light of rare earth-doped fiber and output light of pumping semiconductor laser The optical direct amplifier is provided with a wavelength division multiplexing coupler for inputting and outputting as a light signal after amplification.

That is, in the optical direct amplifier according to the first aspect, when the optical direct amplification is performed using the rare earth-doped fiber such as the erbium-doped fiber, the pumping semiconductor laser is selected based on the digital information to be superimposed on the optical main signal. Drive,
By inputting the pumping light thus output into the wavelength division multiplexing coupler, digital information is superimposed on the optical main signal.

According to the second aspect of the invention, the erbium-doped fiber for directly amplifying the optical main signal inputted from the input terminal by the pump light and the failure information to be superimposed on the optical main signal are inputted as digital information. FSK modulation circuit for frequency shift keying modulation, pumping semiconductor laser driven at this modulated frequency, optical signal after amplification by inputting output signal light of erbium-doped fiber and output light of pumping semiconductor laser The optical direct amplifier is equipped with a wavelength division multiplexing coupler for outputting as.

That is, according to the second aspect of the present invention, when the optical direct amplification is performed using the erbium-doped fiber, the pumping semiconductor laser is driven based on the failure information to be superimposed on the optical main signal, and output by this. By inputting the pumping light to the wavelength division multiplexing coupler, digital information is superimposed on the optical main signal.

According to the third aspect of the present invention, an erbium-doped fiber that directly amplifies the optical main signal input from the input terminal by pumping light and digital information to be superimposed on the optical main signal are input and erbium-doped. FSK modulation circuit for frequency shift keying modulation at a frequency lower than the low cutoff frequency of the fiber, pumping semiconductor laser driven by this modulated frequency, output signal light of erbium-doped fiber and output of pumping semiconductor laser An optical direct amplifier is provided with a wavelength division multiplexing coupler which inputs light and outputs as an optical signal after amplification.

That is, according to the third aspect of the present invention, when the optical direct amplification is performed using the erbium-doped fiber, the digital information to be superimposed on the optical main signal is generated at a frequency lower than the low cutoff frequency of the erbium-doped fiber. Digital information is superimposed on the optical main signal by performing shift keying modulation, driving the pumping semiconductor laser using the two frequencies obtained by this, and inputting the pumping light output by this into the wavelength division multiplexing coupler. I am trying to let you.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 shows the structure of an optical direct amplifier according to an embodiment of the present invention. One end of an erbium-doped fiber 12 is connected to the input end 11 of the optical signal of the optical direct amplifier, and the other end is connected to the wavelength division multiplexing coupler 1.
3 is connected to the output end 14 of the optical signal. The erbium-doped fiber 12 directly amplifies the signal light input from the input end 11 in the erbium-doped fiber 12 by the excitation light having a wavelength effective for this amplification characteristic.

On the other hand, when some kind of failure occurs in the optical intermediate repeater including the optical direct amplifier, failure information 15 indicating the failure is output from a failure information creating circuit (not shown), and frequency shift keying (FSK) is performed.
g) Input to the modulation circuit 16. Here, the failure information 15 is 2 of H (high) and L (low).
It is a signal represented by a value. The FSK modulation circuit 16 converts this into two types of frequencies according to the signal level of the failure information 15, and supplies the converted output 17 to the pumping semiconductor laser drive circuit (LDD) 18. The pumping semiconductor laser drive circuit 18 drives the pumping semiconductor laser 19 connected to the wavelength division multiplexing coupler 13.

In such an optical direct amplifier, the parameters affecting the amplification of the erbium-doped fiber 12 are:
There are the input signal light intensity, the excitation light intensity, the length of the erbium-doped fiber 12 itself, the doping concentration of the erbium-doped fiber 12 or the mode field diameter. However, if the input signal intensity and the parameters of the erbium-doped fiber 12 are fixed, the degree of amplification is determined only by the intensity of the pump light. Further, the wavelength division multiplexing coupler 13 inputs the output signal light of the erbium-doped fiber 12 and the output light of the pumping semiconductor laser 19, and outputs the amplified signal light to the output end 14 side of the optical signal. Has become.

FIG. 2 shows an example of a waveform obtained by FSK-modulating failure information using an FSK modulation circuit. It is shown that the signals are converted into two types of frequencies f ₁ and f ₀ corresponding to the signal “1” (H) and the signal “0” (L).
The two types of frequencies f ₁ and f ₀ are set within the amplification response band of the optical direct amplifier. This will be specifically described below.

FIG. 3 shows the amplification response frequency characteristic of the optical direct amplifier of this embodiment. As can be seen from this figure, the low cutoff frequency at which the relative gain decreases by 3 dB is 1.
Since it is 4 KHz, it drives the pumping semiconductor laser 2.
It is necessary to set the frequency of each type to 1.4 KHz or less.

FIG. 4 shows the characteristics of the pumping semiconductor laser used in this embodiment. The horizontal axis represents the drive current, and the vertical axis represents the intensity of the excitation light.
It can be seen that as the driving current for the pumping semiconductor laser 19 increases, the pumping light intensity for amplifying the erbium-doped fiber 12 also increases.

FIG. 5 shows the amplification characteristics of the optical direct amplifier of this embodiment. As the intensity of the excitation light increases, the intensity of the output light also increases accordingly. As a result, as shown in FIG. 1, the optical signal output from the optical signal output terminal 14 has its amplitude changed according to the failure information 15, and the failure information is superimposed on the optical main signal.

[0019]

As described above, claims 1 to 3 are as described above.
According to the described invention, the digital information such as the failure information is F
Since the optical direct amplification is performed by the SK modulation and the pumping light output from the pumping semiconductor laser driven by the SK modulation, digital information such as failure information can be superimposed on the optical main signal to be transmitted. Further, since the FSK modulation is performed and superimposed on the optical main signal, the signal-to-noise ratio (S / N) is improved on the receiving side as compared with the case where the digital means as the base band is used for superimposing. be able to.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of an optical direct amplifier according to an exemplary embodiment of the present invention.

FIG. 2 is a waveform diagram showing an example of a waveform in which failure information is FSK-modulated using an FSK modulation circuit.

FIG. 3 is a characteristic diagram showing amplification response frequency characteristics of the optical direct amplifier of the present embodiment.

FIG. 4 is a characteristic diagram of a pumping semiconductor laser used in this example.

FIG. 5 is a characteristic diagram showing the amplification characteristic of the optical direct amplifier of the present embodiment.

[Explanation of symbols]

 11 Input Terminal 12 Erbium Doped Fiber 13 Wavelength Division Multiplexer 14 Output Terminal 15 Failure Information 16 Frequency Shift Keying Modulator 18 Pumping Semiconductor Laser Drive Circuit 19 Pumping Semiconductor Laser

Claims (3)

[Claims] 1. A rare earth-doped fiber for directly amplifying an optical main signal input from an input terminal by pumping light, and an FSK modulation for inputting digital information to be superimposed on the optical main signal and performing frequency shift keying modulation on the digital information. A circuit, a pumping semiconductor laser driven at this modulated frequency, and a wavelength division multiplexing coupler for inputting the output signal light of the rare earth-doped fiber and the output light of the pumping semiconductor laser and outputting it as an optical signal after amplification. An optical direct amplifier comprising: 2. An erbium-doped fiber that directly amplifies an optical main signal input from an input terminal by pumping light, and fault information to be superimposed on the optical main signal is input as digital information and frequency shift keying modulation is performed. Do F
SK modulation circuit, pumping semiconductor laser driven by this modulated frequency, wavelength division in which the output signal light of the erbium-doped fiber and the output light of the pumping semiconductor laser are input and output as an optical signal after amplification An optical direct amplifier comprising a multiple coupler. 3. An erbium-doped fiber that directly amplifies an optical main signal input from an input terminal by pumping light, and digital information to be superimposed on the optical main signal, which is input to the erbium-doped fiber for low-frequency cutoff. An FSK modulation circuit that performs frequency shift keying modulation at a frequency lower than the frequency, a pumping semiconductor laser that is driven at this modulated frequency, and the output signal light of the erbium-doped fiber and the output light of the pumping semiconductor laser are input. And a wavelength division multiplexing coupler which outputs the amplified optical signal as an optical signal.