JP2605578B2 - Optical direct amplifier - Google Patents

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 modulation method of a pumping semiconductor laser.

[0002]

2. Description of the Related Art An optical amplifier is used in an optical intermediate repeater as an amplifier for transmitting an optical main signal input from one transmission line to another transmission line. Conventionally, such an optical amplifier performs direct optical amplification by flowing a DC constant current to a semiconductor laser for excitation. Regarding optical direct amplifiers, for example, "optical fiber amplifiers" Yasuo Omura, Masataka Nakazawa,
OPTRONICS (1990) No. 11, pp. 4
7-53.

[0003]

In the optical direct amplifier, amplification is performed by supplying a DC constant current to the pumping semiconductor laser. Therefore, even if an attempt is made to transmit any signal in addition to the optical main signal, the optical direct amplifier itself is not used. However, there is no function of optically converting an electric signal, and only the transmission of the optical main signal itself can be performed. 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.

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

According to the first aspect of the present invention, a rare earth-doped fiber such as an erbium-doped fiber for directly amplifying an optical main signal inputted from an input terminal by pumping light and digital information to be superimposed on the optical main signal are inputted. This is a rare earth
And FSK modulation circuit for modulating frequency <br/> number shift keying at a frequency lower than the low frequency cutoff of the doped fiber, the F
Excitation semiconductor laser directly driven at the frequency modulated by the SK modulation circuit, and a wavelength division multiplexing coupler that inputs the output signal light of the rare-earth-doped fiber and the output light of the excitation semiconductor laser and outputs the amplified optical signal. Are provided in the optical direct amplifier.

That is, according to the first aspect of the present invention, when direct optical amplification is performed using a rare-earth-doped fiber such as an erbium-doped fiber, digital information to be superimposed on an optical main signal is input to an FSK modulation circuit, and is input to the FSK modulator. Rare earth added phi
Frequency shift key at a frequency lower than the
Modulation, and this output directly outputs the pumping semiconductor laser.
Driven. Then, by inputting this pumping light to the wavelength division multiplex coupler, digital information is superimposed on the optical main signal.

According to the second aspect of the present invention, the rare earth-added
Iva is an erbium-doped fiber with a low cutoff frequency
The lower frequency is less than 1.4KHz
And

In the case of erbium-doped fiber,
By setting the frequency to
The amplification response of the optical direct amplifier is the same for both of the two applied frequencies.
It will be set within the band.

[0009]

[0010]

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows the configuration 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 an optical signal output terminal 14. The erbium-doped fiber 12 directly amplifies the signal light input from the input end 11 in the erbium-doped fiber 12 by pumping light having a wavelength effective for the amplification characteristic.

On the other hand, if any failure occurs in the optical intermediate repeater including the optical direct amplifier, failure information 15 indicating the failure is output from a failure information creation circuit (not shown), and the frequency shift keying (FSK) is performed.
g) Input to the modulation circuit 16. Here, the failure information 15 includes two of H (high) and L (low).
This is a signal represented by a value. The FSK modulation circuit 16 converts this into two kinds of frequencies in accordance with the signal level of the failure information 15 and supplies this converted output 17 to a 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 multiplex coupler 13.

In such an optical direct amplifier, parameters affecting the amplification of the erbium-doped fiber 12 include:
There are an input signal light intensity, an excitation light intensity, a length of the erbium-doped fiber 12 itself, an added concentration of the erbium-doped fiber 12, a mode field diameter, and the like. 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. The wavelength division multiplexing coupler 13 receives 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 optical signal output end 14. Has become.

FIG. 2 shows an example of a waveform obtained by FSK-modulating the failure information using the FSK modulation circuit. It is shown that the signal is converted into two kinds 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 an amplification response frequency characteristic of the optical direct amplifier of this embodiment. As can be seen from this figure, the lower cutoff frequency at which the relative gain drops by 3 dB is 1.
Since the frequency is 4 KHz, the excitation semiconductor laser 19 is driven 2
All kinds of frequencies need to be set to 1.4 KHz or less.

FIG. 4 shows the characteristics of the semiconductor laser for excitation used in this embodiment. The horizontal axis shows the drive current, and the vertical axis shows the intensity of the excitation light.
It can be seen that as the drive 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 amplitude of the optical signal output from the optical signal output terminal 14 changes according to the failure information 15, and the failure information is superimposed on the optical main signal.

[0019]

As described above, claims 1 and 2
According to the invention described in Item 2 , digital information such as failure information is input to the FSK modulation circuit and the digital information is input to the rare earth-doped fiber.
FSK modulated at a frequency lower than the low cut-off frequency of
And the two frequencies output from the FSK modulation circuit are shared.
Is set within the amplification response band of the optical direct amplifier.
You. Therefore, digital information such as failure information can be superimposed on the optical main signal and transmitted with a simple configuration . In addition, FSK modulation is performed and superimposed on the optical main signal.
Since, on the reception side as compared with the case of superposed remains digital means is a baseband signal-to-noise ratio (S /
N) can be improved.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram illustrating an example of a waveform obtained by FSK-modulating failure information using an FSK modulation circuit.

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

FIG. 4 is a characteristic diagram of the semiconductor laser for excitation used in the present embodiment.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Input end 12 Erbium-doped fiber 13 Wavelength division multiplex coupler 14 Output end 15 Failure information 16 Frequency shift keying modulation circuit 18 Pumping semiconductor laser drive circuit 19 Pumping semiconductor laser

Claims (2)

(57) [Claims] 1. A rare earth-doped fiber for amplifying light directly by the excitation light optical main signal input from the input terminal, come enter the digital information to be superimposed on the optical main signal
Frequency lower than the low cut-off frequency of the rare-earth-doped fiber.
An FSK modulation circuit that performs frequency shift keying modulation by a wave number, a pumping semiconductor laser that is directly driven by a frequency modulated by the FSK modulation circuit, an output signal light of the rare-earth-doped fiber, and a pumping semiconductor laser. And a wavelength division multiplexing coupler for inputting the output light and outputting as an amplified optical signal. 2. The rare earth-doped fiber is erbium-doped.
And a lower frequency than the low cutoff frequency.
Claim wherein the number is less than 1.4 kHz 1
An optical direct amplifier as described .