JPH08250792A - Direct light amplifier - Google Patents

Abstract

PURPOSE: To provide a direct light amplifier against which the V level of its output light can be controlled without controlling the level of excitation light. CONSTITUTION: Means (branch coupler 16 and PD 17) which monitor the level of the output light of an optical fiber amplifier composed of an Er-doped optical fiber 12 and excitation laser diode module 14 is provided in the poststage of the amplifier and, at the same time, a variable optical attenuator 11 is provided in the preceding stage of the amplifier to adjust the attenuation factor of the attenuator 11 so that the output of the PD 17 can be made to coincide with a reference voltage by means of a control circuit 19 to which the reference voltage is inputted from a reference voltage source 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical direct amplifying device, for example, an optical direct amplifying device used in an optical communication system.

[0002]

2. Description of the Related Art As an optical direct amplifying device used in an optical communication system or the like, one having a structure shown in FIGS. 2 and 3 is known.

The optical direct amplifying device shown in FIG.
In this optical direct amplification device, the pumping light level output from the pumping laser diode module (LD) 14 is monitored by a photodiode (PD) 17 in a control called “Auto Power Control” control. The control circuit 19 controls the excitation light level output from the LD 14 so that the voltage signal from the PD 17 matches the reference voltage from the reference voltage source 18.

The optical direct amplifying device shown in FIG.
In this optical direct amplification device, a part of the optical signal amplified by the erbium-doped optical fiber 12 is processed by the branching coupler 16 in the photodiode module ( PD) 17, the PD 17 outputs a voltage signal corresponding to the level of the input optical signal.

The voltage signal output from the PD 17 is
It is input to the control circuit 19, and the control circuit 19 controls the pumping light level output from the pumping laser diode module (LD) 14 so that the voltage signal thereof matches the reference voltage from the reference voltage source 18.

[0006]

Among the above-mentioned optical direct amplification devices, the one having the configuration shown in FIG. 2 only controls the pumping light level to be constant, so that when the input light level changes. However, in the configuration shown in FIG. 3, the pumping light level is controlled so that the output light level becomes constant. Even when the level changes, the output light level can be controlled to be constant. Therefore, the configuration of FIG. 3 is an optical direct amplification device having a wider application range.

In the optical direct amplifying device having the structure shown in FIG. 3, when the input light level fluctuates, the pumping light level is quickly adjusted so that the output light level becomes constant. Is desired. For this purpose, the current / light output characteristics of the pump laser diode module 14, the pump light level / gain characteristics of the erbium-doped optical fiber 12, etc.
Based on the characteristics of each part, when the input light level changes, the operation content of the control circuit 19 (two inputs can be changed so that the gain in the erbium-doped optical fiber 12 can be changed to a desired gain in the shortest time. It is necessary to determine the procedure for determining the output value).

However, since the current / light output characteristics of the pump laser diode module 14 have a large temperature dependency, the responsiveness of the feedback loop for controlling the pump light level is high regardless of the temperature. However, the conventional optical direct amplification device is a device that is easily affected by temperature changes.

Therefore, an object of the present invention is to provide an optical direct amplifying device capable of controlling the output light level constant without adjusting the pumping light level.

[0010]

According to the first aspect of the present invention,
(A) An optical variable attenuator that inputs an optical signal, attenuates it, and outputs it; (b) a rare earth-doped optical fiber amplifier that directly amplifies the optical signal output by this optical variable attenuator; and (c) this rare earth-doped optical fiber amplifier. Optical branching means for branching a part of the optical signal output from the fiber amplifier as monitor light; (d) Level detecting means for detecting the level of the monitor light branched by the optical branching means; and (e) Level detecting this. Attenuation rate control means for controlling the attenuation rate of the variable optical attenuator so that the level detected by the means becomes a predetermined level.

That is, according to the first aspect of the present invention, a means for monitoring the output light level of the rare earth-doped optical fiber amplifier constituted by the rare earth-doped optical fiber and the pumping light source is provided, and the rare earth-doped optical fiber is provided. A variable optical attenuator is installed in front of the amplifier, and the optical direct amplifying device is configured so that the level of light output to the outside can be controlled to a constant level by adjusting the attenuation factor of the variable optical attenuator. To do.

According to a second aspect of the present invention, (a) a rare earth-doped optical fiber amplifier for directly amplifying an input optical signal,
(B) An optical variable attenuator capable of controlling the attenuation rate, which attenuates and outputs the optical signal output by the rare earth-doped optical fiber amplifier, and (c) a part of the optical signal output by the optical variable attenuator. Optical branching means for branching as monitor light, (d)
Level detecting means for detecting the level of the monitor light branched by the optical branching means, and (e) the attenuation rate of the optical variable attenuator is controlled so that the level detected by the level detecting means becomes a predetermined level. And an attenuation factor control means for

That is, according to the second aspect of the present invention, an optical variable attenuator is provided at the rear stage of the rare earth-doped optical fiber amplifier composed of the rare earth-doped optical fiber and the pumping light source, and at the rear stage of the optical variable attenuator. By providing a means for monitoring the output light level and adjusting the attenuation factor of the variable optical attenuator, the optical direct amplification device is configured so that the level of the light output to the outside is controlled to be constant. .

When a rare earth-doped optical fiber amplifier using an erbium-doped optical fiber is used,
It is possible to obtain an optical direct amplification device that can use the lowest loss wavelength band of the silica optical fiber.

[0015]

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

FIG. 1 shows a schematic configuration of an optical direct amplification device according to an embodiment of the present invention. As shown in the figure, the optical direct amplifying device of the embodiment includes an optical variable attenuator 11, an erbium-doped optical fiber 12, a wavelength division multiplexing coupler 13, a pumping laser diode (LD) 14, an optical isolator 15, and a branch coupler. 16, a photodiode module 17, a reference voltage source 18, and a control circuit 19.

The variable optical attenuator 11 is an optical circuit that attenuates an input optical signal with a certain attenuation rate and outputs the attenuated optical signal. The attenuation rate can be controlled by a control signal from the outside. Then, the optical signal to be amplified is supplied to the erbium-doped optical fiber 12 via the variable optical attenuator 11. The optical signal attenuated by the variable optical attenuator 11 in the erbium-doped optical fiber 12 is L
It is amplified according to the pumping light level output from D14.
The excitation light level is the erbium-doped optical fiber 12
The wavelength division multiplexing coupler 13 introduces the pumping light into the erbium-doped optical fiber 12 so that a relatively high gain is amplified therein.

In the erbium-doped optical fiber 12,
The amplified optical signal passes through the optical isolator 15 and then is branched by the branching coupler 16. One of the branched optical signals is introduced into the PD 17 as monitor light,
The PD 17 outputs an electric signal according to the level of the introduced optical signal. The output of the PD 17 is input to the control circuit 19 together with the output of the reference voltage source 18, and the control circuit 19 outputs the light so that the signal output by the PD 17 matches the reference voltage output by the reference voltage source 18. Variable attenuator 11
Control the decay rate of.

As described above, in the optical direct amplifying device of the embodiment, the output light level is made constant by adjusting the level of the light input to the erbium-doped optical fiber 12 instead of adjusting the pumping light level. Control.

In the optical direct amplifying device of the embodiment, an erbium-doped optical fiber is used for direct optical amplification,
It is also possible to use a rare earth-doped optical fiber using another rare earth such as neodymium or praseodymium. However, when the erbium-doped optical fiber is used, an optical direct amplification device that can amplify an optical signal in the 1.55 μm band, which is the same as the minimum loss wavelength band of the silica optical fiber, is configured.

Further, in the optical direct amplifying device of the embodiment, the optical variable attenuator 11 is provided in front of the erbium-doped optical fiber 12, but it is provided between the wavelength division multiplexing coupler 13 and the optical isolator 15 or the optical isolator 15. Even if it is provided between the isolator 15 and the branch coupler 16, an optical direct amplification device having the same function as the optical direct amplification device of the embodiment can be configured.

[0022]

As described in detail above, claim 1 is as follows.
According to the third aspect of the invention, since the output light level is controlled without adjusting the excitation light level, it is possible to control the output light level at a constant level without being affected by temperature changes. A direct amplification device will be obtained.

When a rare earth-doped optical fiber amplifier using an erbium-doped optical fiber is used as in the third aspect of the invention, an optical fiber that can utilize the lowest loss wavelength band of the silica optical fiber can be used. A direct amplification device will be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical direct amplification device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a conventional optical direct amplification device in which APC control is performed.

FIG. 3 is a block diagram showing a schematic configuration of a conventional optical direct amplification device in which ALC control is performed.

[Explanation of Codes] 11 Optical Variable Attenuator 12 Erbium-Doped Optical Fiber 13 Wavelength Division Multiplexer 14 Excitation Laser Diode Module (LD) 15 Optical Isolator 16 Branch Coupler 17 Photodiode (PD) 18 Reference Voltage Source 19 Control Circuit

Claims (3)

[Claims] 1. An optical variable attenuator for inputting and attenuating an optical signal, outputting the same, a rare earth-doped optical fiber amplifier for directly amplifying an optical signal output by the optical variable attenuator, and an output for the rare earth-doped optical fiber amplifier. Optical branching means for branching a part of the optical signal as monitor light, level detecting means for detecting the level of the monitor light branched by the optical branching means, and the level detected by the level detecting means is a predetermined level. And an attenuation factor control means for controlling the attenuation factor of the variable optical attenuator. 2. A rare earth-doped optical fiber amplifier that directly amplifies an input optical signal, and an optical variable attenuator that attenuates an optical signal output by this rare earth-doped optical fiber amplifier and outputs the attenuated optical signal. Optical branching means for branching a part of the optical signal output from the variable optical attenuator as monitor light; level detecting means for detecting the level of the monitor light branched by the optical branching means; and level detecting means An optical direct amplifying device, comprising: an attenuation factor control means for controlling the attenuation factor of the optical variable attenuator so that the level detected by the device becomes a predetermined level. 3. The optical direct amplifying device according to claim 1 or 2, wherein the rare earth-doped optical fiber amplifier uses an erbium-doped optical fiber.