JPH0548207A - Optical preamplifier - Google Patents

Abstract

PURPOSE:To provide an optical preamplifier having a wide dynamic range. CONSTITUTION:For example, a first optical amplifier 6 is so formed as to make its gain constant, and the gain of a second optical amplifier 12 is so controlled as to make its output level constant. Then, the first optical amplifier 6 is connected in series with the second optical amplifier 12 in this order. In this manner, a optical preamplifier is configured.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an optical preamplifier.
The optical preamplifier is used in a trunk line or subscriber optical communication system to perform optical amplification before converting a received optical signal into an electric signal to improve a reception level. In this type of optical preamplifier, not only high gain but also wide dynamic range (a range of light intensity capable of suppressing deterioration of reception sensitivity within an allowable range) is required.

[0002]

2. Description of the Related Art Conventionally, it has been proposed to use an optical fiber amplifier having an optical fiber (rare earth doped fiber) doped with a rare earth element such as Er (erbium) in a core as an optical preamplifier.

It has also been proposed to use a semiconductor laser type semiconductor optical amplifier having an on-chip optical amplification medium as an optical preamplifier. In these conventionally proposed optical preamplifiers, the gain is controlled so that the optical output level becomes constant regardless of the fluctuation of the input level.

[0004]

When the gain of the optical preamplifier is controlled so that the optical output becomes constant as described above,
It acts to keep the optical output level constant when the optical input level increases, reducing the gain of the optical preamplifier. In a general optical amplifier, there is a problem that noise decreases as the gain decreases and the dynamic range narrows.

The present invention was created in view of the above technical problems, and an object thereof is to provide an optical preamplifier having a wide dynamic range.

[0006]

The first configuration of the optical preamplifier according to the present invention is the first configuration in which the gain is controlled to be constant.
And an optical amplifier whose gain is controlled so that the output level becomes constant are connected in series in this order.

The second structure of the optical preamplifier of the present invention is an optical amplifier whose gain is controlled to be constant, and a variable optical attenuator whose attenuation rate is controlled to be constant to output level. And are connected in series in this order.

[0008]

According to the first or second structure of the present invention, since the optical amplifier in the preceding stage is controlled so that its gain is constant, the noise generated is constant regardless of the optical input level. .. Therefore, a wide dynamic range can be secured without deterioration of the receiving sensitivity due to the fluctuation of the optical input level.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an optical preamplifier showing a first embodiment of the present invention, and this embodiment corresponds to the first configuration.

The input light input to the optical preamplifier from the input port 2 is split by the optical splitter 4 and most of it is input to the first optical amplifier 6. The other light branched by the light branching unit 4 is input to the light receiver 8 and converted into an electric signal according to the light receiving level.

The light output from the first optical amplifier 6 is branched by the optical branching unit 10, most of which is the second optical amplifier 1.
Enter in 2. The other light branched by the light branching unit 10 is input to the light receiver 14 and converted into an electric signal according to the light receiving level.

The light output from the second optical amplifier 12 is branched by the optical branching section 20, and most of it is output from the output port 26. The other light branched by the light branching unit 20 is input to the light receiver 22 and converted into an electric signal according to the light receiving level.

Reference numeral 16 is a gain detection circuit to which the signals from the photodetectors 8 and 14 are input. The gain detection circuit 16 detects the ratio of the input and output levels of the first optical amplifier 6 and responds to the gain. Output a signal of different level.

Reference numeral 18 is a control circuit to which the signal from the gain detection circuit 16 is input. The control circuit 18 controls the gain of the first optical amplifier 6 so that the signal level from the gain detection circuit 16 becomes constant. To do.

Reference numeral 24 is a control circuit for the second optical amplifier. The control circuit 24 controls the gain of the second optical amplifier 12 so that the light receiving level of the light receiver 22 becomes constant. According to the configuration of this embodiment, the first optical amplifier 6 is controlled so that its gain becomes constant, and
The optical amplifier is controlled so that its output level becomes constant, so that the first configuration of the present invention is realized.

FIG. 2 is a block diagram of an optical preamplifier showing a second embodiment of the present invention, and this embodiment corresponds to the second configuration. The parts substantially the same as those in the previous embodiment are designated by the same reference numerals, and the description thereof will be partially omitted. Regarding the first optical amplifier 6 in the previous embodiment, since it is not necessary to distinguish the first and second optical amplifiers in this embodiment, the word "first" is omitted and the optical amplifier is omitted. 6

In this embodiment, most of the light from the optical amplifier 6 is input to the variable optical attenuator 28 via the optical branching section 10. The light output from the variable optical amplifier 28 is branched by the optical branching unit 30, and most of it is output from the output port 36. The other light split by the light splitting unit 30 is the light receiver 3
2 and is converted into an electric signal corresponding to the received light level. Reference numeral 34 denotes an attenuation rate control circuit that controls the attenuation rate of the variable optical attenuator 28 so that the light receiving level of the light receiver 32 becomes constant.

According to this embodiment, the optical amplifier 6 in the front stage is controlled so that its gain is constant, and the variable optical attenuator 28 in the rear stage is controlled so that its output level is constant. Therefore, the second configuration of the present invention is realized.

As the variable optical attenuator 28, a variable optical attenuator that can change the transmittance of the medium according to a control signal by using the Franz-Gerdish effect or the like can be used. FIG. 3 is a diagram showing a configuration example of an optical amplifier which can be used in the embodiment of the present invention. 38 is an input port, 40 is a pumping light source that outputs pumping light having a wavelength having a predetermined relationship with the wavelength of input light, 42 is a drive circuit for the pumping light source 40, and 44 is input light and pumping light from the input port 38. An optical multiplexer that multiplexes and outputs. The input light and the excitation light multiplexed by the optical multiplexer 44 are guided into the rare earth-doped fiber 48 via the optical isolator 46. The light that has passed through the rare earth-doped fiber 48 is output from the output port 52 via the optical isolator 50.

According to this configuration, the pumping action in the rare earth-doped fiber 48 based on the pumping light causes
The input light has its amplitude amplified. As the optical multiplexer 44, it is possible to use a fiber fusion type optical coupler or the like adjusted so that the wavelength dependence of the branching ratio becomes large.

In order to control the gain of the optical amplifier in the case of implementing the present invention, for example, the output level of the pumping light source may be electrically controlled.

[0022]

As described above, according to the present invention,
It is possible to provide an optical preamplifier having a wide dynamic range.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical preamplifier showing a first embodiment of the present invention.

FIG. 2 is a block diagram of an optical preamplifier showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example of an optical amplifier that can be used for implementing the present invention.

[Explanation of symbols]

 6 First Optical Amplifier (Optical Amplifier) 12 Second Optical Amplifier 28 Variable Optical Attenuator

Claims (2)

[Claims] 1. A first control for controlling a gain to be constant
2. An optical preamplifier comprising an optical amplifier (6) and a second optical amplifier (12) whose gain is controlled so that the output level is constant, which are connected in series in this order. 2. An optical amplifier (6) whose gain is controlled to be constant and a variable optical attenuator (28) whose attenuation factor is controlled to keep its output level constant are serially connected in this order. An optical preamplifier characterized by being connected.