JP2746776B2 - Optical preamplifier - 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 preamplifier.
2. Description of the Related Art An optical preamplifier is used in a trunk optical network or a subscriber optical communication system to perform optical amplification before converting a received optical signal into an electric signal to improve a reception level. This type of optical preamplifier is required to have not only high gain but also a wide dynamic range (a range of light intensity in which deterioration of reception sensitivity can be suppressed within an allowable range).

[0002]

2. Description of the Related Art Hitherto, 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 optical amplification medium on a chip as an optical preamplifier. In these conventionally proposed optical preamplifiers, the gain is controlled so that the optical output level becomes constant irrespective of the fluctuation of the input level.

[0004]

As described above, when controlling the gain of the optical preamplifier so that the optical output becomes constant,
When the optical input level increases, the optical output level acts to keep it constant, and the gain of the optical preamplifier decreases. In a general optical amplifier, there is a problem that when the gain is reduced, noise is increased and a dynamic range is narrowed.

The present invention has been made in view of such technical problems, and has as its object to provide an optical preamplifier having a wide dynamic range.

[0006]

A first configuration of the optical preamplifier according to the present invention has a first configuration in which the gain is controlled to be constant.
And a second optical amplifier, the gain of which is controlled so that the output level becomes constant, are connected in series in this order.

A second configuration of the optical preamplifier according to the present invention comprises an optical amplifier whose gain is controlled to be constant and a variable optical attenuator whose attenuation rate is controlled so that its output level is constant. Are connected in series in this order.

[0008]

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

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments 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 from the input port 2 to the optical preamplifier is split by the optical splitter 4, and most of the input light 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 split by the optical splitter 10, and most of the light is split by the second optical amplifier 1
Enter 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 split by the optical splitter 20, and most of the light is output from the output port 26. The other light split by the light splitter 20 is input to the light receiver 22 and is converted into an electric signal according to the light receiving level.

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

Reference numeral 18 denotes a control circuit to which a 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. I do.

Reference numeral 24 denotes a control circuit for the second optical amplifier. This 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 is constant,
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. This embodiment corresponds to the second configuration. The same reference numerals are given to substantially the same portions as those in the previous embodiment, and the description thereof is partially omitted. Note that the first optical amplifier 6 in the previous embodiment does not need to distinguish between the first and second optical amplifiers in the present embodiment. 6 is assumed.

In this embodiment, most of the light from the optical amplifier 6 enters the variable optical attenuator 28 via the optical branching unit 10. The light output from the variable optical amplifier 28 is split by the optical splitter 30, and most of the light is output from the output port 36. The other light branched by the light branching unit 30 is
2 and is converted into an electric signal corresponding to the light receiving level. An attenuation rate control circuit 34 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 control is performed so that the gain of the optical amplifier 6 at the preceding stage is constant, and the attenuation factor of the variable optical attenuator 28 at the subsequent stage is controlled so that the 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 changes the transmittance of the medium in accordance with a control signal using the Franz-Gelish effect or the like can be used. FIG. 3 is a diagram showing a configuration example of an optical amplifier that can be used in the embodiment of the present invention. Reference numeral 38 denotes an input port, 40 denotes an excitation light source for outputting excitation light having a wavelength having a predetermined relationship with the wavelength of the input light, 42 denotes a drive circuit of the excitation light source 40, and 44 denotes input light from the input port 38 and excitation light. This is an optical multiplexer that multiplexes and outputs. The input light and the pump light multiplexed by the optical multiplexer 44 are guided into the rare earth doped fiber 48 via the optical isolator 46. Light that has passed through the rare-earth doped fiber 48 is output from an output port 52 via an optical isolator 50.

According to this configuration, the pumping action in the rare-earth doped fiber 48 based on the pump light causes
The input light is amplified in its amplitude. As the optical multiplexer 44, a fiber fusion type optical coupler or the like adjusted so as to increase the wavelength dependence of the branching ratio can be used.

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

[0022]

As described above, according to the present invention,
There is an effect that an optical preamplifier having a wide dynamic range can be provided.

[Brief description of the 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

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18 H01S 3/10 H04B 10/00 G02F 1/35

Claims (2)

(57) [Claims] 1. A first method in which a gain is controlled to be constant.
, And a second optical amplifier whose gain is controlled so that the output level becomes constant, wherein the first optical amplifier
An optical preamplifier, characterized in that an output of the amplifier is connected to an input of the second optical amplifier. 2. An optical amplifier having a gain controlled to be constant, and a variable optical attenuator having an attenuation rate controlled so that an output level is constant, wherein an output of the optical amplifier is controlled.
An optical preamplifier connected to an input of the optical attenuator .