JPH06164021A - Method of monitoring optical amplifier - Google Patents

Abstract

PURPOSE:To realize a monitoring method which monitors the operating state of an optical amplifier by a method wherein excitation light which has been transmitted without being absorbed by a fiber doped with Er is monitored in the optical amplifier. CONSTITUTION:The method is provided with an optical amplifier 10 which amplifies input signal light, at a second wavelength, by being excited by excitation light at a first wavelength, with an excitation-light generation means 20 which generates the excitation light at the first wavelength and with an excitationlight power measuring means 30 which measures the power of- excitation light, at the second wavelength, which has been transmitted without being absorbed by the optical amplifier 10. When the excitation light at the first wavelength is excitated by the optical amplifier 10 and the signal light at the second wavelength is amplified, the power of the excitation light at the first wavelength, which has been transmitted without being absorbed by the optical amplifier 10 is measured by the excitation-light power measuring means 30. Thereby, the title method is constituted so as to monitor the optical amplifier 10 and the excitation-light generation means 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier monitoring method for monitoring the operating state of an optical amplifier. In recent years, optical communication systems using optical fibers have been widely adopted.

Up to now, an amplifier used in an optical communication system has a function of converting an optical signal into an electric signal, amplifying the electric signal, and then returning the optical signal again. However, recently, the optical signal is directly amplified. Optical amplifiers have come to be used, and the development of such optical amplifiers has been rapidly progressing.

The characteristics of the optical amplifier are: small size, high reliability, and low price. -Operation is possible regardless of the transmission speed.

A multi-wavelength optical signal can be collectively amplified. That is. Utilizing these characteristics, optical amplifiers are about to be introduced in a wide range from trunk lines to subscriber lines.

When introducing such an optical communication system, it is essential to monitor the operating state of the optical amplifier in order to maintain high stability of the system. Current,
In the erbium (hereinafter referred to as Er) -doped fiber optical amplifier that is the most practical, the pumping light source is the only active element, so it is necessary to monitor this operating state.

There is a demand for a method of monitoring an optical amplifier which can easily and surely monitor the optical amplifier.

[0007]

2. Description of the Related Art FIG. 8 is a diagram for explaining a conventional example. In the figure, 11 is an Er-doped fiber, F1 and F2 are optical fibers, L1 to L4 are lenses, 41 and 42 are isolators,
Reference numeral 61 is a wavelength multiplexer, and 71 is an optical bandpass filter.

Reference numeral 21A is an excitation light source, 21B is a laser diode, 21C is a photodiode, 22A is a back power monitor, and 22B is a current monitor. In the figure, the signal light input is input from the optical fiber F1 through the lens L1 to the isolator 41, the signal light in the forward direction passes as it is, and is input into the Er-doped fiber 11 through the lens L2.

On the other hand, the pumping light generated by the laser diode 21B of the pumping light source 21A is the wavelength multiplexer 61 and the lens L3.
It is injected into the Er-doped fiber 11 through and the signal light is directly amplified.

The amplified signal light is output to the optical fiber F2 through the lens L3, the wavelength multiplexer 61, the isolator 42, the optical bandpass filter 71, and the lens L4. At this time, the pump light source 21A is monitored by the laser diode 21B.
The back power of is converted into an electric signal by the photodiode 21C and taken out, and its output is monitored by the back power monitor 22A. Alternatively, the operating state of the excitation light source 21A is monitored by monitoring the bias current for exciting the laser diode 21B with the current monitor 22B.

[0011]

In the above-mentioned conventional example, the gain is obtained by inputting the signal light and the pumping light into the Er-doped fiber, but in the conventional back power monitor and bias current monitor, the Er is obtained. The pumping light injected into the doped fiber is not directly monitored.

Further, in order to monitor the input power, the power is divided and extracted by the beam splitter, so that the noise figure (hereinafter referred to as Noise Figure NF) is deteriorated.

The present invention intends to realize a monitoring method for monitoring the operating state of an optical amplifier by monitoring the pumping light that has passed through the optical amplifier without being absorbed by the Er-doped fiber.

[0014]

FIG. 1 is a block diagram for explaining the principle of the present invention. In the figure, 10 is an optical amplifier that amplifies the input signal light of the second wavelength by pumping with the pump light of the first wavelength, and 20 is the first wavelength that pumps the signal light of the second wavelength. Is a pumping light generating means for generating the pumping light, and 30 is a pumping light power measuring means for measuring the power of the pumping light of the second wavelength that has passed through the optical amplifier 10 without being absorbed by the optical amplifier 10. When pumping with the pumping light of the first wavelength and amplifying the signal light of the second wavelength, the power of the pumping light of the first wavelength that has passed without being absorbed by the optical amplifier 10 is measured by the pumping light power measuring means 30. Is measured to monitor the operating states of the optical amplifier 10 and the pumping light generator 20.

[0015]

The pumping light of the first wavelength is injected into the optical amplifier 10,
When amplifying the signal light of the second wavelength, the pump light of the first wavelength is absorbed by the optical amplifier 10 and amplifies the signal light of the second wavelength.

Therefore, by measuring the pumping light power measuring means 30 for the power of the pumping light of the first wavelength that has passed through the optical amplifier 10 without being absorbed, the pumping light power measuring means 30 measures the power of the first wavelength absorbed by the optical amplifier 10. It becomes possible to measure the power of the pumping light, and the operating states of the optical amplifier 10 and the pumping light generating means 20 can be monitored.

[0017]

FIG. 2 is a diagram for explaining an embodiment of the present invention.
The figure shows an example of backward pumping in which signal light and pumping light travel in opposite directions. Here, the wavelength of the signal light is 1.55 μm, and the wavelength of the pump light is 1.48 μm.

In the figure, 11 is an Er-doped fiber, F1,
F2 is an optical fiber, L1 to L4 are lenses, 41 and 42 are isolators, 51 is a beam splitter, 61 is a wavelength multiplexer, and 71 is an optical bandpass filter.

Further, 21 is an excitation laser diode for generating laser light having a wavelength of 1.48 μm, and 31 is, for example,
It is a light receiver composed of a pin photodiode.
In the figure, the operation in which the signal light input is input to the Er-doped fiber 11 and is optically amplified by the pumping light generated by the pumping laser diode 21 is the same as in the conventional example.

FIG. 3 is a diagram for explaining the operation of the embodiment of the present invention. (A) shows the progress of the signal light, and the signal light input from the fiber F1 enters the beam splitter 51 through the lens L1 and is input to the isolator 41. In the isolator 41, the light in the forward direction passes as it is,
The signal light passes through the isolator 41 and is input to the Er-doped fiber 11 through the lens L2.

(B) shows the progress of the excitation light in the opposite direction, and E
The excitation light that has not been absorbed among the excitation lights injected into the r-doped fiber 11 is input to the isolator 41 through the lens L2.

In the isolator 41, the light in the opposite direction spreads at a certain angle, so this is taken out by the beam splitter 51, input to the photodetector 31, and the power thereof is monitored to check the operating state of the Er-doped fiber 11. Can be monitored.

At this time, the light receiver 31 has 1.55 μm
Since the spontaneous emission light of the band is also input, by providing an optical filter that reflects light having a wavelength of 1.55 μm and transmits light having a wavelength of 1.48 μm between the beam splitter 51 and the light receiver 31, Even if the level of the excitation light is small, it can be accurately monitored.

FIG. 4 is a diagram (1) for explaining another embodiment of the present invention. The figure shows an example of forward pumping in which signal light and pumping light travel in the same direction. The difference between the forward pumping of FIG. 4 and the backward pumping of FIG. 2 is that a wavelength multiplexer 61 is provided between the lens L1 and the isolator 41, and after the signal light and the pump light are multiplexed, Er doping is performed from the same direction. That is, the input is made to the fiber 11.

In the optical bandpass filter 71 between the isolator 42 and the lens L4, only the signal light is transmitted and the light of other wavelengths is reflected. Therefore, since the excitation light and the spontaneous emission light in the 1.55 μm band are reflected from the optical bandpass filter 71, the optical filter 81 is provided to allow only the excitation light of 1.48 μm to pass and input to the light receiver 31. The power can be monitored and the operating condition of the Er-doped fiber 11 can be monitored.

FIG. 5 is a diagram (2) explaining another embodiment of the present invention. The figure shows a configuration in which forward pumping and backward pumping are performed simultaneously, and pumping laser diodes 21 and 22 that generate pumping light to be injected into the Er-doped fiber 11, wavelength multiplexers 61 and 62 that multiplex signal light and pumping light, The optical receiver 31 is configured to monitor the pumping light power that has passed through the Er-doped fiber 11 without being absorbed, and the pumping light power is monitored from the output of the light receiver 31 to monitor the operating state.

FIG. 6 is a diagram for explaining the output characteristics of the light receiver according to the embodiment of the present invention. In (A), the input power is monitored by the output of the light receiver. In the optical amplification, the excitation light is E
The gain is obtained by being absorbed by the r-doped fiber 11. Therefore, even if the gain is constant, the power of the pumping light that is absorbed differs depending on whether the input signal light is strong or weak.

That is, in the case of amplifying a strong signal light, the pumping light is largely absorbed and the transmitted power becomes small. On the contrary, when the weak signal light is amplified, the absorption of the pumping light becomes small and the transmitted power becomes large.
By applying this relationship, the input signal power can be monitored by measuring the transmitted pumping light power monitor output voltage when the pumping light power is constant.

In (B), the Er-doped fiber 11 is controlled so that the output level is constant (Automatic Level Control).
l Hereinafter, referred to as ALC) is performed by increasing or decreasing the power of the excitation light. The relationship between the power of the transmitted pumping light and the input power in this case is as shown in the figure. In (B), the inclination is larger than that in (A) because control is performed so as to reduce the power of the excitation light.

If the Er-doped fiber 11 is used in a saturated state, the fluctuation of the output power with respect to the fluctuation of the input power can be suppressed to some extent. Therefore, ALC is possible even when the pump light power is constant.

FIG. 7 is a diagram (3) for explaining another embodiment of the present invention. In the embodiment of the invention of FIG. 2, for example,
Although the beam splitter 51 with a branching ratio of about 10: 1 is used, insertion of the beam splitter 51 inevitably causes insertion loss, which leads to deterioration of the noise figure NF.

Therefore, as shown in FIG. 7, in the case of backward pumping, by using the reflecting mirror 91 instead of the beam splitter 51, the deterioration of the noise figure NF can be prevented.

The reflecting mirror 91 has a small hole at the center through which the signal light passes, and the isolator 4 is provided with the signal light as it is through the hole of the reflecting mirror 91.
Since it passes 1, the insertion loss does not occur and the noise figure does not deteriorate. The excitation light is monitored by inputting the excitation light reflected by the reflection mirror 91 to the light receiver 31.

[0034]

According to the present invention, by monitoring the pumping light power that has passed through the optical amplifier without being absorbed,
The operating state of the optical amplifier can be monitored.

Further, by using a reflecting mirror having a hole for passing the signal light at the center, it is possible to monitor the operating state of the optical amplifier without degrading the noise figure.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the principle of the present invention.

FIG. 2 is a diagram illustrating an embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the embodiment of the present invention.

FIG. 4 is a diagram (1) illustrating another embodiment of the present invention.

FIG. 5 is a diagram (2) illustrating another embodiment of the present invention.

FIG. 6 is a diagram for explaining output characteristics of a light receiver according to an embodiment of the present invention.

FIG. 7 is a diagram (3) for explaining another embodiment of the present invention.

FIG. 8 is a diagram illustrating a conventional example.

[Explanation of symbols]

 10 optical amplifier 11 Er-doped fiber 20 pumping light generating means 21, 22 pumping laser diode 21A pumping light source 21B laser diode 21C photodiode 22A back power monitor 22B current monitor 30 pumping light power measuring means 31 photodetector 41, 42 isolator 51 beam splitter 61 , 62 wavelength multiplexer 71 optical bandpass filter 81 optical filter 91 reflection mirror F1, F2 optical fiber L1 to L4 lens

Claims (5)

[Claims] 1. A method of monitoring the output of an optical amplifier, comprising: inputting by exciting with an exciting light of a first wavelength;
An optical amplifier (10) for amplifying a signal light having a wavelength of, a pumping light generating means (20) for generating a pumping light having a first wavelength for pumping a signal light having a second wavelength, and the optical amplifier (10) The first that has passed without being absorbed by
And a pumping light power measuring means (30) for measuring the power of the pumping light of the second wavelength, the optical amplifier (10) pumps the pumping light of the first wavelength, and amplifies the signal light of the second wavelength. At this time, the pumping light power measuring means (30) measures the power of the pumping light of the first wavelength that has passed through the optical amplifier (10) without being absorbed by the pumping light amplifier (10) and the pumping light. A method of monitoring an optical amplifier, characterized in that the operating state of the light generating means (20) is monitored. 2. An erbium-doped fiber (11) for optical amplification, and a beam splitter (51) for splitting signal light and pumping light.
And an input isolator (4) that allows the input forward transmitted light to pass through and reversely transmits the transmitted light by expanding the beam diameter at a constant angle to prevent coupling of the backward transmitted light to the input side fiber.
1) and a pump laser diode (2) that generates pumping light for pumping
1), a wavelength multiplexer (61) for multiplexing pumping light for pumping generated by the pumping laser diode (21) and signal light, and an isolator for passing the output of the wavelength multiplexer (61) (42) and a backward pumping light amplification system in which the traveling directions of the pumping light and the signal light are opposite to each other, which comprises an optical bandpass filter (71) that passes only the wavelength of the signal light output from the isolator (42), An optical receiver (3) for measuring the power of the excitation light that has passed through the erbium-doped optical fiber (11) without being absorbed.
1) is provided, the pump light that has passed through the optical isolator (41) in the reverse direction and has a beam spread is received by the photodetector (31), and the power of the pump light is monitored to monitor the operating state of the optical amplifier. A method of monitoring an optical amplifier, comprising: 3. A pump laser diode (21) for generating a light output for pumping and the pump laser diode (21).
Wavelength multiplexer (6) that combines the optical output for pumping and the signal light
1), an erbium-doped fiber (11) that optically amplifies the input signal light, and the input signal light is the erbium-doped fiber (1).
1), an isolator (41) for inputting into the 1), an isolator (42) for passing the output of the erbium-doped fiber (11), and an optical bandpass filter (for passing only the wavelength of the signal light of the output of the isolator (42) ( 71) and an optical filter (81) that passes only the wavelength of the pumping light in the output reflected by the optical bandpass filter (71), and the pumping light and the signal light travel in the same direction. In the amplification system, a photodetector (31) for measuring the power of pumping light that has passed through the erbium-doped fiber (11) without being absorbed.
Is provided, the reflected light reflected by the optical bandpass filter (71) is received by the light receiver (31), and the pumping light power is monitored to monitor the operating state of the optical amplifier. How to monitor. 4. Two pump laser diodes (21, 22) for generating a pumping light output, and a pumping light for pumping and a signal light generated by the two pump laser diodes (21, 22) are combined. Equipped with two wavelength multiplexers (61, 62) that oscillate, and an erbium-doped fiber (11) that optically amplifies the signal light by the pump light, the traveling directions of the pump light and the signal light are the same and opposite directions. In the bidirectional pumping light amplification system, a photodetector (31) for measuring the power of pumping light that has passed through the erbium-doped fiber (11) without being absorbed.
Is provided, the pumping light that has been transmitted without being absorbed by the erbium-doped fiber (11) is received by the photodetector (31), and the pumping light power is monitored to monitor the operating state of the optical amplifier. Optical amplifier monitoring method. 5. The beam splitter (51) according to claim 1 or 2, wherein the beam splitter (51) comprises a reflection mirror (91) having a hole through which a beam of signal light passes, and is reflected by the reflection mirror (91). A method of monitoring an optical amplifier, characterized in that pumping light is received by the photodetector (31) and the pumping light power is monitored to monitor the operating state of the optical amplifier.