JPH06112567A - Optical amplifier - Google Patents

Abstract

PURPOSE:To obtain an optical amplifier which produces no much noise and can respond at a high speed by constituting the optical amplifier of on fiber amplifier cascade-connected in multiple stages and semiconductor laser amplifier and amplifying the optical signal inputted to the optical amplifier by means of the first-stage fiber amplifier. CONSTITUTION:The title optical amplifier is constituted so that the signal light inputted to the title optical amplifier can be first amplified by means of an amplifier 1 composed of a rare-earths doped optical fiber and again amplified by means of a semiconductor laser amplifier 2. A monitor section 7 monitors the gain or signal output of the optical amplifier and a control circuit 8 controls the gain or signal output of the optical amplifier by driving the exciting light source 4 of the amplifier 1 and current device circuit 6 of the amplifier 2 based on monitored values outputted from the section 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier, and more particularly to an optical amplifier used in an optical transmission system or optical signal processing.

[0002]

2. Description of the Related Art As an optical amplifier of this type, a rare earth-doped optical fiber amplifier or a semiconductor laser amplifier has been conventionally known.

FIG. 5A shows a schematic structure of a rare earth-doped optical fiber amplifier, which comprises an amplification section 50, a monitor section 51, and a pumping light source 52, and the monitor section 51 uses the rare earth-doped optical fiber amplifier. Is monitored or the output signal light power is monitored, and the control circuit 53 drives and controls the pumping light source 52 based on this monitor value.

FIG. 2B shows a schematic structure of a semiconductor laser amplifier, which includes an amplifier 54, a monitor 55, and a current drive circuit 56, and the monitor 55 controls the semiconductor laser amplifier. The gain or the output signal light power is monitored, and the control circuit 57 drives the current drive circuit 56 based on this monitor value to perform control.

[0005]

However, in the rare earth-doped optical fiber amplifier having such a structure, the noise figure is low, but the problem that the gain response speed is slow remains. For example, 0.98μ
In the case of an m-pumped erbium-doped optical fiber amplifier, the noise figure was about 4 dB and the response speed was about 1 ms.

On the other hand, in the semiconductor laser amplifier, although the response speed of the gain is high, the problem that the noise figure is high remains. For example, in the case of a quantum well structure semiconductor laser amplifier, the noise figure is about 7 dB and the response speed is 10
It was about 0 ps.

For these reasons, it has been conventionally desired to realize an optical amplifier having low noise and high speed response.

Therefore, the present invention has been made under such circumstances, and an object of the present invention is to provide an optical amplifier with low noise and high speed response.

[0009]

In order to achieve such an object, an optical amplifier according to the present invention basically comprises at least one fiber amplifier and a semiconductor laser amplifier which are cascade-connected in multiple stages. The optical amplifier is equipped with the optical amplifier, and the optical signal input to the optical amplifier is amplified by the fiber amplifier provided in the first stage.

[0010]

In the optical amplifier thus constructed, among the plurality of amplifiers provided therein, the fiber amplifier has excellent noise characteristics, and the semiconductor laser amplifier has excellent light speed response characteristics. Has become.

The fiber amplifier and the semiconductor laser amplifier are cascade-connected in multiple stages to form an optical amplifier. At this time, the first stage amplifier is used as a fiber amplifier, and an optical signal input to the optical amplifier is first By inputting this fiber amplifier, an optical amplifier having excellent noise characteristics can be obtained.

By including the semiconductor laser amplifier in the amplifier of the next stage and thereafter, an optical amplifier having an excellent response speed can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Basic Structure FIG. 1 is an explanatory diagram showing the basic structure of an optical amplifier according to the present invention.

In the figure, first, it is assumed that the signal light propagates from the higher order to the lower order. The optical amplifier has a configuration in which the upper rare-earth-doped optical fiber amplifier 1 and the lower semiconductor laser amplifier 2 are connected to each other and are cascade-connected.

That is, the rare earth-doped optical fiber amplifier 1
Is provided with an amplification unit 3 and a pumping light source 4, and the semiconductor laser amplifier 2 is provided with an amplification unit 5 and a current drive circuit 6, and is common to the rare earth-doped optical fiber amplifier 1 and the semiconductor laser amplifier 2 and is a monitor unit. 5 and a control circuit 8.

As a result, the signal light inputted to the optical amplifier is first amplified by the rare earth-doped optical fiber amplifier 1 and further amplified by the semiconductor laser amplifier 2.

Then, the gain or signal light output in this optical amplifier is monitored by the monitor section 7, and the control circuit 8 is based on the monitor value detected by this monitor section 7.
The control of the gain or the signal light output is performed by driving the pumping light source 4 in the rare earth-doped optical fiber amplifier 1 and the current drive circuit 6 in the semiconductor laser amplifier 2.

Next, the operation of the optical amplifier thus constructed will be described.

Here, in order to better understand the operation of the optical amplifier configured as in this embodiment, the operation of the conventional optical amplifier will be described first before the description thereof.

FIG. 2B is an explanatory diagram showing the operation of a conventional optical amplifier composed of a rare earth-doped optical fiber amplifier or a semiconductor laser device, in which the signal loss from the input end to the input end of the optical amplification medium is L _{Let f be} the gain of the optical amplification medium, and _let L be the signal loss from the output end of the optical amplification medium to the output end of the optical amplifier.

In this case, the effective gain G of the optical amplification medium
_{The net} is given by G _net = L _f × L _r × G.
Further, the effective noise figure F _net is given by F _net = 2 × N _sp / L _f . Here, N _sp is an effective population inversion parameter of the optical amplification medium.

In the case of the numerical examples, among the rare earth-doped optical fiber amplifiers, for example, in the case of an erbium-doped optical fiber amplifier pumped at 0.98 μm, 2 × N _sp -3d.
B, 1 / L _{r to} 1 dB.

Of the semiconductor laser amplifiers, for example, in the case of a semiconductor laser amplifier having a quantum well structure, 2 × N.
_{sp ~4dB,} is a 1 / L _f ~3dB.

[0024] Therefore, the effective noise figure F _{net Non} is a rare earth doped optical fiber amplifier, F _net ~4dB, a semiconductor laser amplifier, F _net ~7dB next, it is higher in the semiconductor laser amplifier is known.

On the other hand, the response speed of the effective gain is determined by the response speed of the optical amplification medium. It is about 1 ms for the rare earth-doped optical fiber amplifier and about 100 ps for the semiconductor laser amplifier, and the response speed of the semiconductor laser amplifier is smaller. It turns out.

FIG. 2 showing an optical amplifier according to the present invention.
In (a), the signal light loss from the input end of the optical amplifier to the input end of the optical amplification medium in the rare earth-doped optical fiber amplifier 1 is L _f-1 , the gain of the optical amplification medium is G _-1 , and the output of the optical amplification medium. The signal loss from the end to the output end of the rare earth-doped optical fiber amplifier 1 is L _r-1 . Further, the signal light loss from the input end of the semiconductor laser amplifier 2 to the input end of the optical amplification medium is L _f-2 , the gain of the optical amplification medium is G _-2 , and the output of the semiconductor laser amplifier 2 from the output end of the optical amplification medium. The signal loss up to the end is L _r-2 . The signal light loss from the output end of the optical amplification medium in the rare earth-doped optical fiber amplifier 1 to the input end of the optical amplification medium in the semiconductor laser amplifier 2 is L _int .

When defined in this way, the effective gain G _net of this optical amplifier is G _net = L _f-1 × L _int × L _r-2 × G _-1
× G _-2 will be given.

The effective noise figure F _net is F _net ˜2 ×
N _sp-1 / L _f-1 + 2 × N _sp-2 / (L _{f -1} × L _int × G _-1 )
Will be given in. Here, N _sp-1 is the effective effective population inversion parameter of the rare earth-doped optical fiber, and N _sp-2
Shows the effective effective population inversion parameter of the semiconductor element.

In the case of numerical examples, among the rare earth-doped optical fiber amplifiers, for example, in the case of an erbium-doped optical fiber amplifier pumped with 0.98 μm, 2 × N _{sp-1 to} 3
dB, 1 / L _f ~1dB, a G _-1 ~20dB.

Of the semiconductor laser amplifiers, for example, in the case of a quantum well structure semiconductor laser amplifier, 2 × N.
_{sp-2 ~4dB, 1 / L} f ~3dB, a G _-2 ~10dB.

At this time, the effective noise figure F _net is
In the case of the erbium-doped optical fiber amplifier and the semiconductor laser amplifier of the quantum well structure, F _net = 4 dB. Also, 1 / L _int = 5 dB.

At this time, the effective noise figure F _net is F _net = 4
It becomes dB, which is almost the same as the effective noise figure of the rare earth-doped fiber amplifier.

On the other hand, the effective gain G _{net Non} is proportional to the G _-1 × G _-2, the response speed T _{net Non} becomes T _{net Non} through T _-2 from the relation T _-1 »T _-2. Here, the response speed T ₋₁ of the erbium-doped optical fiber amplifier is about ₁ ms, and the response speed T ₋₂ of the semiconductor laser amplifier is about 100 ps.

From this, the response speed of the effective gain G _net is almost the same as the response speed of the semiconductor laser amplifier.

Therefore, the optical amplifier having the above-mentioned configuration is
Effective noise figure equivalent to rare earth doped optical fiber amplifier,
It will have a response speed equivalent to that of a semiconductor laser amplifier.

Example 1. FIG. 3 is a block diagram showing an embodiment of the optical amplifier according to the present invention.

In the figure, an erbium-doped optical fiber 30 is used as a rare earth-doped optical fiber, and a 1.5 μm band polarization-independent semiconductor laser 31 is used as a semiconductor laser element.

Optical isolators 32 and 33 are arranged at both ends of the erbium-doped optical fiber 30, and the signal light emitted from the erbium-doped optical fiber 30 is polarized by using an optical lens 34 in a 1.5 μm band polarization-independent semiconductor laser 31. It is supposed to lead to.

Here, the signal light wavelength is 1.55 μm, and the erbium-doped optical fiber 30 is set to agitate with a 0.98 μm semiconductor laser.

Then, the output signal light is monitored by a photodiode (not shown) in the branching device 35, and the control circuit 3
The constant output is controlled by the control unit 6.

The control here is performed by changing the drive current of the 0.98 μm semiconductor pumping light source 37 and the 1.5 μm band polarization dependent semiconductor laser 31 via the current drive circuit 38.

The optical amplifier configured as described above has a gain of 25 dB and a noise figure of 4 d in the constant output control.
B, it was confirmed that the gain response speed was 100 ps.

When this constant output control is performed only by the 1.5 μm band polarization independent type semiconductor laser 31,
The gain was 25 dB, the noise figure was 7 dB, and the gain response speed was 100 ps.

From this, it becomes possible to operate with low noise and to perform constant output control at high speed.

Example 2. FIG. 4 is a block diagram showing another embodiment of the optical amplifier according to the present invention.

In the figure, an erbium-doped optical fiber 30 is used as a rare earth-doped optical fiber, a 1.5 μm band polarization independent semiconductor laser 31 is used as a semiconductor laser element, and optical isolators 32 and 33 are provided at both ends of the erbium-doped optical fiber 30. Erbium-doped optical fiber 30
The signal light emitted from the
This leads to the m-band polarization-independent semiconductor laser 31. The signal light wavelength is 1.55 μm, and the erbium-doped optical fiber is excited by a 0.98 μm semiconductor laser.

Each of the input signal light and the output signal light is monitored by using a photodiode (not shown) in the splitters 35A and 35B, the gain is calculated from these monitor values, and the gain is switched at high speed via the control circuit 36. Are doing.

The control here is performed by changing the drive current of the polarization-dependent semiconductor laser 31 of the 1.5 μm band via the 0.98 μm semiconductor pumping light source 37 and the current drive circuit 38. The drive speed of the polarization-dependent semiconductor laser of the 1.5 μm band is 100 ps.

The optical amplifier thus constructed has a gain of 25 dB and a noise figure of 4 d in the constant output control.
B, it was confirmed that the gain response speed was 100 ps.

When the constant output control is performed only by the 1.5 μm band polarization independent semiconductor laser, the gain is 25 dB, the noise figure is 7 dB, and the gain response speed is 1 dB.
It was 00 ps.

From this, it becomes possible to operate with low noise and to control the gain at high speed.

According to the optical amplifier configured as in the above-described embodiment, of the fiber amplifier and the semiconductor laser amplifier provided therein, the fiber amplifier has excellent noise characteristics, and the semiconductor laser amplifier is also excellent. Has excellent light speed response characteristics.

Such a fiber amplifier and a semiconductor laser amplifier are cascade-connected to form an optical amplifier. At this time, the first stage amplifier is used as a fiber amplifier, and an optical signal input to the optical amplifier is first fed to this fiber amplifier. By inputting it to the optical amplifier, an optical amplifier with excellent noise characteristics can be obtained.

By using a semiconductor laser amplifier in the next stage amplifier, an optical amplifier excellent in response speed can be obtained.

In each of the above-described embodiments, the case where one fiber amplifier and one semiconductor laser amplifier are connected has been described.
It is not limited to this. That is, it goes without saying that either one of the fiber amplifier and the semiconductor laser amplifier, or a plurality of both of them may be configured to be cascade-connected. In this case, a similar effect can be obtained by configuring the optical signal input to the optical amplifier to be amplified by the fiber amplifier provided in the first stage.

[0056]

As is apparent from the above description,
According to the optical amplifier of the present invention, a low noise and high speed response can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a basic configuration of an optical amplifier according to the present invention.

FIG. 2 (a) is an explanatory diagram showing the reason why the object of the optical amplifier according to the present invention can be achieved, and FIG. 2 (b) is a description of the case of the conventional optical amplifier, which is shown for easy understanding. It is a figure.

FIG. 3 is an explanatory diagram showing an embodiment of an optical amplifier according to the present invention.

FIG. 4 is an explanatory diagram showing another embodiment of the optical amplifier according to the present invention.

5A and 5B are configuration diagrams showing examples of conventional optical amplifiers.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Rare earth doped optical fiber amplifier, 2 ... Semiconductor laser amplifier, 3, 5 ... Amplification part, 4 ... Emergent light source, 6 ... Current drive circuit, 7 ... Monitor part, 8 ... Control circuit.

Claims (1)

[Claims] 1. A fiber comprising an optical amplifier having at least one fiber amplifier and a semiconductor laser amplifier connected in a multistage cascade, and an optical signal input to the optical amplifier provided in the first stage. An optical amplifier characterized by being configured to be amplified by an amplifier.