JP2000224116A - Optical repeater amplifier - Google Patents

Abstract

(57) [Problem] To provide an optical repeater with a reduced noise figure. SOLUTION: An optical circulator 22 that operates so that an input from a terminal 22a is output from a terminal 22b and an input from the terminal 22b is output from a terminal 22c, and fiber Bragg grating that reflects light having a wavelength of monitoring light 25, a fiber amplifier 26, an optical filter 23 for blocking spontaneous emission light of the fiber amplifier, and an OE element 24 for monitoring light, and a terminal 22a of the optical circulator is used as an input of the optical repeater amplifier, The terminal 22b of the optical circulator is connected to the input terminal of the fiber Bragg grating 25, the output terminal of the fiber Bragg grating 25 is connected to the input terminal of the fiber amplifier 26, and the output terminal of the fiber amplifier 26 is connected to the optical repeater. The output terminal of the amplifying device, the terminal 22c of the optical circulator is connected to the input terminal of the optical filter 23, the optical filter Optical repeater amplifier device, characterized in the output terminal 23 being connected to the OE element 24 for the monitoring light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical repeater and, more particularly, to an optical repeater transmission system for realizing long-distance transmission by repeating and amplifying an optical signal as it is, and monitoring light and signal light in the repeater. The demultiplexing means.

[0002]

2. Description of the Related Art In an optical transmission system, an erbium-doped fiber amplifier is used.
: EDFA) can reduce the cost of the system significantly by applying a rare earth doped fiber amplifier as an optical repeater. In order to realize an optical repeater transmission system including an optical repeater amplifying device, not only an optical repeater technology but also a supervisory signal transfer technology for realizing operation, management and maintenance of the optical repeater amplifying device is required. There are several types of supervisory signal transfer methods. Currently, a method in which light having a wavelength different from that of a transmission signal is used as supervisory light, and supervisory light is wavelength-multiplexed with signal light and transmitted between relay amplifiers is currently used. It has become.

For example, Shinji Oka, Kazuyuki Matsumura, Yukio Kobayashi,
A paper by Kazuo Hagimoto and colleagues, "Study on monitoring method for large-capacity optical transmission system" (IEICE 1996)
Technical report OCS-95-122) outlines the method. This prior art example will be described below with reference to FIG. FIG. 1 shows a conventional configuration of an optical repeater / amplifier in a case where a method of wavelength multiplexing monitoring light and transmission light is used. For simplicity of description, the monitoring light transmitting unit is not shown in FIG. The signal light (wavelength λsig) and the monitoring light (wavelength λsv) are wavelength-division multiplexed and transmitted.
Input to the optical repeater. The signal light (λsig) and the monitoring light (λsv) are split by the monitoring light WDM coupler 12, and the monitoring light (λsv) is input to the monitoring light photodiode 13. The signal light (λsig) transmitted through the monitoring light WDM coupler 12 is transmitted through the optical isolator 14, amplified by the fiber amplifier 15, and output from the output terminal 16. The fiber amplifier 15 is a pump light source 15a, a pump light WDM coupler that combines the pump light and the signal light.
15b and a rare-earth-doped fiber 15c. To prevent oscillation of the amplifier, an optical isolator 14 is generally connected to the input and output of the fiber amplifier 15 (only the optical isolator on the input side is shown in FIG. 1). The monitoring light (λsv) input to the monitoring light photodiode 13 is converted into an electric signal, and the monitoring circuit 17 operates, manages, and maintains the fiber amplifier 15 based on the electric signal.

[0004]

As a basic characteristic value of an optical repeater, there is a noise figure (NF).
The noise figure of the fiber amplifier in the optical repeater
(dB), where L0 (dB) is the loss from the input terminal of the optical repeater to the fiber amplifier input, the noise figure of the entire optical repeater is generally given by L0 + NF1 (dB). Is known to. This equation indicates that if a loss exists on the input side of the optical repeater, the noise figure increases by the loss. In the conventional configuration shown in FIG. 1, the noise figure increases by the loss of the monitoring light WDM coupler 12 and the optical isolator 14. Therefore, in order to suppress the increase of the noise figure of the optical repeater amplifier, these input loss,
In particular, it is required to reduce the loss of the monitoring light WDM coupler 12. At present, a dielectric multilayer film type filter is frequently used as the monitoring light WDM coupler 12, but the coupling loss occurs within the device at a minimum of 0.6.
, A loss of about 1.0 dB was generated, and reduction of the noise figure of the optical repeater was limited.

An object of an embodiment of the present invention is to provide an optical repeater amplifying apparatus in which a noise figure is reduced by realizing a monitoring light demultiplexing unit with low loss in consideration of the above problem. .

[0006]

FIG. 2 is a diagram showing a basic configuration of an embodiment of the present invention.

In order to achieve the above object, the present invention provides a configuration in which an input from a first terminal is output from a second terminal,
An optical circulator that operates to output an input from the second terminal to a third terminal, and a fiber Bragg grating 1 that operates to reflect light having a wavelength of monitoring light and transmit light having a wavelength of signal light. And a fiber amplifier for amplifying the signal light, one optical filter that cuts off the spontaneous emission light of the fiber amplifier and operates so as to transmit the wavelength of the monitoring light, and converts the monitoring light into an electric signal. For monitoring light
A first terminal of the optical circulator is used as an input of the optical repeater, and a second terminal of the optical circulator is connected to an input terminal of the fiber Bragg grating. An output terminal connected to the input terminal of the fiber amplifier, an output terminal of the fiber amplifier used as an output terminal of the optical repeater amplifier, a third terminal of the optical circulator connected to an input terminal of the optical filter, An optical repeater amplifying device wherein an output terminal of a filter is connected to the monitoring light OE element.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG.

The monitoring light (wavelength λsv) and the signal light (wavelength λsi
g) is wavelength multiplexed, and the input terminal 2 of the optical repeater
Enter 1 The optical circulator 22 is a device that operates to output the input from the terminal 22a to the terminal 22b and output the input from the terminal 22b to the terminal 22c, and the terminals 22a, 22b,
22c is the input terminal 21 of the optical repeater,
It is connected to a fiber Bragg grating (FBG) 25 and an optical filter 23. The signal light (λsig) and the monitoring light (λsv) are both supplied to the terminal 22b of the optical circulator 22.
And is input to the FBG 25. The FBG 25 is a device that uses the monitoring light wavelength (λsv) as a reflection wavelength (Bragg wavelength). The monitoring light (λsv) is reflected by the FBG 25 and input to the terminal 22 b of the optical circulator 22. On the other hand, the signal light (λsig) passes through the FBG 25 and
Entered in 6.

The fiber amplifier 26 comprises a pump light source 26a, a pump light WDM coupler 26b for multiplexing the pump light and the signal light, and a rare earth doped fiber 26c. I do. Although the forward pump type fiber amplifier is used in the embodiment shown in FIG. 2, it goes without saying that the embodiments of the present invention can be applied to the backward pump type and the bidirectional pump type.

An optical circulator reflected by the FBG 25
The monitoring light (λsv) input to the terminal 22b of the 22 is output from the terminal 22c in accordance with the operation principle of the optical isolator described above.
The optical circulator 22 also has a function of preventing return light (backward propagating light) from the fiber amplifier 26 from being input to the fiber amplifier 26 again, thereby preventing the fiber amplifier 26 from oscillating.

The monitoring light (λsv) output from the terminal 22c of the optical circulator 22 is input to the optical filter 23. The optical filter 23 has a characteristic of blocking spontaneous emission light generated from the fiber amplifier 26 and transmitting a monitoring light wavelength (λsv). The monitoring light (λsv) transmitted through the optical filter 23 is input to the monitoring light photodiode 24. The monitoring light is converted into an electric signal by the photodiode 24 and reaches the monitoring circuit 28.
The monitoring circuit 28 operates, manages, and maintains the optical repeater based on the received monitoring electric signal.

The optical isolator 14 connected to the input side of the fiber amplifier in the conventional configuration (FIG. 1) is for preventing backward propagating light to prevent oscillation of the amplifier. In the configuration of this embodiment (FIG. 2), the optical circulator 22 provided for demultiplexing the monitoring light separates the backward propagating light to prevent the oscillation of the amplifier. Can be omitted.
Since the physical configuration between the two terminals inside the optical circulator is the optical isolator itself, the loss between the two terminals of the optical circulator 22 can be made equal to the loss of the optical isolator 14 in principle.

Therefore, assuming that the loss of the optical circulator 22 and the loss of the optical isolator 14 are equal, the input-side loss of the fiber amplifier when comparing the configuration of this embodiment (FIG. 2) with the configuration of the conventional example (FIG. 1). Is the difference between the loss of FBG25 in this embodiment and the monitoring light in the conventional example.
This is the difference between the losses of the WDM coupler 12. FBGs are inherently low loss because they are fiber type devices. For example, FBG
Assuming a transmittance of 90% or 95% as a feasible value, the transmission loss in this case is 0.46 dB or 0.22 dB, respectively.
Becomes At present, at least 0.6 dB in the dielectric multilayer curtain type filter that is frequently used in the monitoring light WDM coupler 22 in the conventional example
Since there is a loss of 1.0 to 1.0 dB, the input-side loss of about 0.1 dB to 0.4 dB or more can be reduced by the configuration of the embodiment.

The noise figure (dB) of the entire repeater is represented by the sum of the noise figure (dB) of the EDFA section and the input side loss (dB).
According to the configuration of the present embodiment, the noise figure can be reduced (in the above-described numerical example, the reduction is from about 0.1 dB to 0.4 dB or more).

[0016]

As described above, according to the embodiment of the present invention, it is possible to reduce the noise figure of the optical repeater amplifier by reducing the loss of the monitoring light demultiplexing means, and as a result, Extension of the total transmission distance of the relay transmission system,
Effects such as extension of the relay span distance and expansion of the span margin can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional configuration.

FIG. 2 is a diagram showing a configuration of an example of the present invention.

[Explanation of symbols]

11: Input terminal of the optical repeater amplifier 12: WDM coupler for monitoring light 13: Photodiode for monitoring light 14: Optical isolator 15: Fiber amplifier 15a: Pump light source 15b: WDM coupler for pump light 15c: Rare earth doped fiber 16: Optical Output terminal of repeater amplifier 17: Monitoring circuit 21: Input terminal 21 of optical repeater amplifier 22: Optical circulator 22a, 22b, 22c: Input / output terminal of optical circulator 23: Optical filter 24: Photodiode for monitoring light 25: Fiber Bragg grating (FBG) 26: Fiber amplifier 26a: Pump light source 26b: WDM coupler for pump light 26c: Rare earth doped fiber 27: Output terminal 28: Monitoring circuit.

Claims (1)

[Claims] An optical repeater amplifying an optical signal in which a monitor light and a signal light having at least one wavelength or more are wavelength-multiplexed, wherein an input from a first terminal is output from a second terminal, and An optical circulator that operates to output an input from two terminals to a third terminal, a fiber Bragg grating that operates to reflect light having a wavelength of monitoring light and transmit light having a wavelength of signal light, A fiber amplifier that amplifies light, an optical filter that operates to block spontaneous emission light of the fiber amplifier and transmits a wavelength of the monitoring light, and a monitoring light OE element that converts the monitoring light into an electric signal. Having the first terminal as an input of the optical repeater amplifier, connecting the second terminal to an input terminal of the fiber Bragg grating, and an output terminal of the fiber Bragg grating Is connected to the input terminal of the fiber amplifier, the output terminal of the fiber amplifier is the output terminal of the optical repeater, the third terminal is connected to the input terminal of the optical filter, and the output terminal of the optical filter is the An optical repeater amplifying device connected to an OE element for monitoring light.