JP2988142B2 - Optical booster amplifier and optical transmission circuit - 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 booster amplifier for amplifying an optical signal in the field of optical fiber communication and the like and an optical transmission circuit including the optical booster amplifier, and more particularly to an improvement in a method of exciting the optical booster amplifier.

[0002]

2. Description of the Related Art Optical fiber communication devices are excellent in high-speed modulation characteristics and long-distance transmission characteristics, and are being rapidly spread and improved in technology as next-generation communication devices. In particular, an optical fiber communication device using an optical amplifier such as an optical fiber amplifier can construct a long-distance communication system by increasing transmission power and receiving sensitivity, and can construct a high-density frequency multiplex communication by wavelength multiplex communication. In the future, it is attracting attention as a very important component of the communication system.

[0003] In the above-mentioned optical fiber communication apparatus, particularly in an apparatus using an optical fiber amplifier as a transmission booster amplifier,
It has been confirmed that an optical signal can be amplified up to about 100 mW, and its application to a long-distance communication system is expected.

In an optical fiber communication apparatus for performing digital communication, a mark rate of a code ("1",
The ratio of occurrence of “1” in the two values of “0” is not necessarily 0.5. For example, in the case of a trunk transmission system, from 0.25 to 0.75 in a short time, such as LAN It is said that the information transmission system fluctuates further. Since the pulse peak value of such an optical signal needs to be constant at the output end of the optical transmitting circuit, the output average value of the optical signal output from the optical booster amplifier is 0.5 to 0.5 at the above-described code mark rate. It will fluctuate up to 1.5 times.

The above-described optical transmission circuit absorbs the average output fluctuation of the optical signal and outputs an optical signal having a constant peak value.
When an optical fiber amplifier is used as the booster amplifier, the pumping light output of the optical fiber amplifier is 0.5 to 1.5.
It is necessary to control the output to double the range. However, the excitation light source that generates the excitation light has a pulse peak value of 1.
Even in the normal operating state of 0 times, it operates with considerable output,
In order to output 1.5 times higher pumping light, the current drive system of the pumping light source needs a considerable operation margin. Therefore, when the pumping light source performs the above-described high-power operation, there is a problem that the life of the pumping light source is greatly shortened.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate the above-mentioned problems of the optical booster amplifier according to the prior art, and to eliminate the above problem even when the optical signal has a mark rate fluctuation.
An object of the present invention is to provide an optical booster amplifier that has a margin of operation of a current drive system of an excitation light source and has little adverse effect on the life of the excitation light source, and an optical transmission circuit using the optical booster amplifier as an amplifier for an optical signal.

[0007]

SUMMARY OF THE INVENTION An optical booster amplifier according to the present invention is an optical amplifier that amplifies an input optical signal whose amplitude has been modulated by a digital signal by pumping light, and supplies the pumping light to the optical amplifier. At least two excitation light sources and an excitation light source control circuit for changing a supply rate of excitation light from the two excitation light sources according to a mark rate of the digital signal are included.

In the optical booster amplifier, the input optical signal may be a plurality of optical signals having different wavelengths.

Further, an optical transmission circuit including an optical booster amplifier comprises: an optical signal generator for generating an optical signal amplitude-modulated by a digital signal; an optical amplifier for exciting the optical signal by exciting it with excitation light; First and second excitation light sources for supplying light to the optical amplifier, a mark ratio detector for detecting a mark ratio of the optical signal generated by the optical signal generator, and excitation light from the first excitation light source Is controlled to an intensity corresponding to the mark rate, and when the mark rate is higher than a predetermined value, the second excitation light source is also operated, and the excitation light from the second excitation light source corresponds to the mark rate. And an excitation light intensity control circuit for controlling the intensity of the excitation light.

[0010]

The present invention focuses on the fact that an optical amplifier used in an optical fiber communication system or the like and requiring high-power pumping light generally has a working (first) and standby (second) pumping light source as a pumping light source. The preliminary pumping light source is operated only at the moment when the mark ratio of the optical signal becomes high, and compensates for the shortage of the pumping output of the working pumping light source at the time of the high mark ratio. When the load is shared between two or more pump light sources as described above, the load required for the current pump light source becomes appropriate even when the mark rate of the optical signal is high, and the current of the current (first) pump light source is reduced. The operating margin of the drive system is increased, and the adverse effect on the life of these excitation light sources is reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of the present invention. FIG. 2 is an explanatory diagram showing the operating range of the working excitation power supply and the standby excitation light source in this embodiment.

In the optical transmission circuit shown in FIG. 1, an optical signal generator 6a generates an optical signal S3a having a wavelength of 1.55 μm, and an optical fiber amplifier 4 amplifies the optical signal S3a and converts the transmission signal S4 into an optical fiber communication system. Output to a transmission path (not shown). The excitation light source 28 supplies the excitation light S7 to the optical fiber amplifier 4 in response to the correction output S5a from the optical signal generator 6a and the monitoring output S6 from the optical fiber amplifier 4.

In the optical signal generator 6a, the distributed feedback semiconductor laser 1 is driven by the pulse signal current from the pulse drive circuit 2 and the DC bias current S1 from the bias current source 3 to generate the optical signal S3a. I do.
A pulse signal current S2 of 2.4 Gb / s is applied to the pulse drive circuit 2 via a mark ratio detector 5. The mark ratio detector 5 detects the appearance ratio (mark ratio) of the logic "1" in the pulse signal current S2, and supplies a correction output S5a proportional to the mark ratio to the excitation light source 28.

The optical fiber amplifier 4 includes an Er-doped optical fiber 20 for amplifying the optical signal S3a, a multiplexing / demultiplexing circuit 24 for introducing the pump light S7 from the pump light source 28 into the Er-doped optical fiber 20, and an Er-doped optical fiber. Optical isolators 25a and 25b arranged before and after 20 to prevent reflection of the optical signal S3a and the transmission signal S4, and a photodetector 10 for monitoring an average output of the transmission signal S4 from a part of the transmission signal S4.
And This optical fiber amplifier 4 has a gain of about 10 dB in a normal operation state and outputs a transmission signal S4 having an average output of 10 mW. Part of this transmission signal S4 is
The detection output S6 is detected by the photodetector 10, ie, the average output level of the optical transmission circuit is monitored.

The excitation light source 28 has a correction output S5a from the optical signal generator 6a and a monitor output S5 from the optical fiber amplifier 4.
6 is input to the arithmetic circuit 9. The arithmetic circuit 9 responds to the correction output S5a and the monitor output S6 by
The first current drive source 12 and the current drive source 12 of the preliminary excitation light source 22 are controlled to keep the peak output of the transmission signal 11 at a constant value. The working pump light source 21 outputs pump light having a wavelength of 1.48 μm, and the preliminary pump light source 22 outputs pump light having the same wavelength. These pump lights are polarization-multiplexed by the optical multiplexing circuit 23 and supplied to the multiplexing / demultiplexing circuit 24 of the optical fiber amplifier 4 as the pump light S7.

As shown in FIG. 2, the working excitation light source 21
In the region where the mark ratio of the optical signal S3a is 0.6 or less, the operation of the optical fiber amplifier 4 is entirely controlled by the output pump light. When the mark ratio exceeds 0.6, the arithmetic circuit 9 also activates the preliminary current drive source 13, so that the preliminary excitation light source 22 also supplies excitation light.

In order to cover the excitation light of the optical fiber amplifier 4 with the current excitation light source 21 alone in the range of the mark ratio of the optical signal S3a from 0.6 to 0.75, the driving capability of the current drive source 12 must be increased. It is necessary to increase from 800 mA to 1 A or more, and to increase the operation output of the working pump light source 21 to 100 mW or more. Then, it becomes necessary to increase the driving capability of the working current drive source 12 by 1.5 times.
2 also needs to be enlarged. In addition, the excitation light source 21 is required to have almost twice the reliability as compared with the case where the auxiliary light source 22 is used together.

In the embodiment shown in FIG. 1, the preliminary excitation light source 22 is used supplementarily when the optical signal S3a has a high mark rate.
Driving ability of current drive sources 12 and 13, excitation light sources 21 and 22
Pump light output level can be kept low, and
It is no longer necessary to request these circuits 12, 13, 21, 22 for high reliability. When the operating current of the working pumping light source 21 rises to 1.5 times the initial set value due to element deterioration or the like, the optical transmitting circuit of this embodiment is switched to the spare pumping light source 22 for use (as described above). A detailed description of the switching mechanism is publicly known, so a detailed description thereof will be omitted.) At the time of this switching, the correction output S5 of the mark ratio described above is used.
The control of the pumping light S7 level by a
Of course, it can be switched to the side. In this case,
When the mark ratio becomes 0.6 or more, the current excitation light source 21 is used when the mark ratio is high.

FIG. 3 is a block diagram of a second embodiment of the present invention.

In this optical transmission circuit, the optical transmission circuit of FIG.
While only one optical signal S3a is handled, a plurality of optical signals S3a to S3c having different wavelengths are handled, and an optical transmission circuit of a so-called frequency multiplex communication system is configured. Optical signal S from optical signal generators 6a, 6b, 6c
3a, S3b, and S3c are multiplexed by the optical multiplexing circuit 26 and supplied to the optical fiber amplifier 4. These multiplexed optical signals S3a, S3b, S3c are commonly amplified by the optical fiber amplifier 4 to become a transmission signal S4. The arithmetic circuit 9a of the excitation light source 28a includes the optical signal generators 6a, 6
Each mark ratio S5 from the mark ratio detection circuit 8 for b, 6c
a, S5b, S5c and optical detector 1 of optical fiber amplifier 4
The monitoring output S6 from 0 is processed to control the working and standby current driving sources 12 and 13 to keep the peak output of the transmission signal S4 at a constant value.

The circuit operation of the individual components in the embodiment of FIG. 3 is the same as in the first embodiment, and a description thereof will be omitted.
Also in this embodiment, a transmission signal S4 having a constant peak light output is obtained irrespective of a change in the mark ratio of each of the optical signals S3a to S3c, as in the embodiment of FIG.
Moreover, in this embodiment, even if any of the optical signal generators 6a to 6c stops transmitting the optical signal S3, the peak value of the transmission signal S4 by the other optical signal generators 6 is always a constant output. Will be kept.

The present invention is not limited to the above embodiment, and it is of course possible to modify the above embodiment. FIG.
In the embodiment of FIG. 3, the Er-doped optical fiber 20 is used as an amplifier (optical amplifier) for the optical signal S3.
This optical amplifier may use another kind of rare earth-doped optical fiber amplifier, or may be a waveguide amplifier. The wavelength of the light is 1.55 μm of the optical signal S3 and 1.48 μm of the pump light.
It is natural that it is not limited to m. The excitation light sources 21 and 22 are classified into active and standby, but do not necessarily mean a redundant configuration, and may be configured based on the concept of an active light source and a compensation light source. Only the working light source may be used at all times. Although the operation threshold of the preliminary excitation light source 22 is set to the mark ratio 0.6 of the optical signal S3, this threshold may be freely selected. For example, if the threshold value is set to 0.48, the preliminary excitation light source 22 will always perform a small operation. The pumping light S7 is pumped from the signal output side of the Er-doped optical fiber 20 in each of the embodiments of FIGS. 1 and 3, but is pumped from the signal input side or from both the input and output. You may. Although the number of excitation light sources is two in this embodiment, it goes without saying that more excitation light sources may be used.

[0024]

As described above, according to the present invention, when the mark ratio of the optical signal input to the optical booster amplifier varies, the intensity of the excitation light supplied to the optical booster amplifier is changed according to the mark ratio. Since each of the two or more excitation light sources is set, not only the operation margin of the current drive system of the excitation light source is properly maintained, but also the effect of reducing the adverse effect on the life of the excitation light source is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation range of a working excitation light source and a standby excitation light source in the embodiment of FIG.

FIG. 3 is a block diagram of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Pulse drive circuit 4 Optical fiber amplifier 5 Mark ratio detector 6a, 6b, 6c Optical signal generator 9, 9a Operation circuit 10 Photodetector 12 Working current drive source 13 Reserve current drive source 20 Er-doped optical fiber 21 Active pumping light source 22 Preliminary pumping light source 23 Optical multiplexing circuit 24 Multiplexing / demultiplexing circuit 25a, 25b Optical isolator 26 Optical multiplexing circuit 28, 28a Pumping light source

Continuation of front page (56) References JP-A-1-135085 (JP, A) JP-A-3-206746 (JP, A) JP-A-4-92483 (JP, A) Taga, et al., "459 km, 2.4 Gbit / s four wavelengths multiple multiplexing optical fiber transmission, transmission, electronic distribution, electronic distribution, electronic distribution, and electronic distribution. 26, No. 8, p 500-501 (58) Fields investigated (Int. Cl. ⁶ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 H01S 3/10

Claims (3)

(57) [Claims] 1. An optical amplifier which amplifies an input optical signal whose amplitude has been modulated by a digital signal by being pumped by pumping light;
At least two excitation light sources that supply the excitation light to the optical amplifier, and an excitation light source control circuit that changes a supply rate of the excitation light from the two excitation light sources according to a mark rate of the digital signal. Characteristic optical booster amplifier. 2. The optical booster amplifier according to claim 1, wherein said input optical signal is a plurality of optical signals having different wavelengths. 3. An optical signal generator for generating an optical signal amplitude-modulated by a digital signal, an optical amplifier for amplifying the optical signal by exciting it with excitation light, and a first amplifier for supplying the excitation light to the optical amplifier. And a second excitation light source; a mark ratio detector for detecting a mark ratio of the optical signal generated by the optical signal generator; and controlling the excitation light from the first excitation light source to an intensity corresponding to the mark ratio. When the mark ratio is higher than a predetermined value, the second excitation light source is also operated to control the excitation light from the second excitation light source to an intensity corresponding to the mark ratio. An optical transmission circuit comprising: