JP3248174B2 - Optical communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system for converting an electric signal into an optical signal by an electric / optical converter and transmitting the optical signal through an optical fiber. The present invention relates to an optical communication system for improving the transmission quality when intensity-modulating an optical converter.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of a conventional optical communication system.

On the transmitting side 1, electric signals are inputted to input terminals 1 to N, each electric signal is frequency-multiplexed by a combiner 10, converted into an optical signal by an electric / optical converter 5, and received by an optical fiber 3. Transmitted to side 2.

The bias current of the electric / optical converter 5 is set to a constant value by a fixed bias circuit 15.

On the receiving side 2, the received optical signal is converted back to an electrical signal by the optical / electrical converter 6, and output from the electrical signal output terminals 1 ′ to N ′ by the distributor 11.

In the conventional optical communication system, as described above, when a frequency-multiplexed or one electric signal is converted into an optical signal by an electric / optical converter and transmitted by an optical fiber, the bias of the electric / optical converter is used. The current was set to a fixed value.

[0007]

However, in the conventional method of setting the bias current of the electric / optical converter to a fixed value, intermodulation distortion from a plurality of high-level electric signals interferes with a low-level electric signal. However, there is a problem that the communication quality of the low-level electric signal is significantly deteriorated.

Further, even when transmitting one electric signal, if the input level to the electric / optical converter is high, there is a problem that the electric signal is distorted and the communication quality is deteriorated.

In view of the above, the present invention has been made in view of the above points, and has been made in view of the above circumstances, and is an optical communication system capable of transmitting a frequency-multiplexed or single electric signal of varying level economically and with high quality through an optical fiber. The aim is to provide a scheme.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a transmitting side converts one or a plurality of electric signals having different frequencies into an optical signal and transmits it to a receiving side, and the receiving side converts the optical signal into an electric signal. In a communication system, in order to reduce power consumption of an electrical / optical converter and reduce intermodulation distortion generated between the electrical signals due to non-linearity of the electrical / optical converter, a plurality of electrical signals are transmitted. It is characterized in that the bias current of the electric / optical converter is made variable in accordance with the frequency relationship and the level.

[0011]

More specifically, in a communication system in which a plurality of electrical signals having different frequencies are converted into optical signals on a transmitting side, the optical signals are transmitted to a receiving side, and the optical signals are converted into electrical signals on a receiving side. Level detecting means for detecting the level of each electric signal on the transmitting side, frequency detecting means for detecting the frequency of each electric signal on the transmitting side, and converting each electric signal on the transmitting side into an optical signal Converting electricity /
Bias current varying means for varying the bias current of the optical converter, and based on the level relationship of each electric signal by the level detecting means and the frequency relationship of each electric signal by the frequency detecting means, at a low level. An optical communication system characterized in that a bias current of the electric / optical converter is set by the bias current varying means so that an electric signal affected by intermodulation distortion satisfies a desired quality.

[0013]

According to the present invention constructed as described above, a plurality of high-level electric signals are converted to a low-level electric signal by utilizing the fact that the intermodulation distortion characteristic changes depending on the bias current value of the electric / optical converter. If intermodulation distortion from the signal interferes,
To reduce the intermodulation distortion, the bias current is increased to prevent quality deterioration.

On the other hand, in other cases, the bias current is set to a small value in order to reduce the power consumption of the electric / optical converter.

This makes it possible to transmit an electric signal economically and with high quality through an optical fiber.

The same applies to the case where one electric signal is transmitted. When the input level to the electric / optical converter is high, the bias current is reduced to improve the quality.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of the present invention.
This embodiment shows a configuration in which signal transmission between a transmitting side 1 and a receiving side 2 in an optical communication system is transmitted through an optical fiber 3.

On the transmitting side 1, an electric signal is inputted to an input terminal, and one of the electric signals is inputted to a level detecting circuit 7 by a distributor 4.

The other output of the distributor 4 is an electric / optical converter 5
Is input to

The bias control circuit 8 includes a level detection circuit 7
Is input, and the bias current of the electro-optical converter 5 is set so that the electric signal satisfies the desired quality.

On the receiving side 2, the optical signal from the transmitting side 1 is converted back to an electric signal by the optical / electrical converter 6, and then output to an output terminal.

FIG. 2 is a block diagram of a second embodiment of the present invention.

On the transmitting side 1, a plurality of electric signals having different frequencies are input to input terminals 1 to N.

These electric signals are input to a level detecting circuit 4 for detecting each level and a frequency detecting circuit 9 for detecting each frequency.

However, the order of the level detection circuit 7 and the frequency detection circuit 9 is not limited to this.

Level detection circuit 7 and frequency detection circuit 9
Is input to the synthesizer 10, where it is frequency-multiplexed.

The composite current of the frequency-multiplexed electric signal is injected into the electric / optical converter 5 with the bias current as the center.

That is, the magnitude of the light output changes according to the magnitude of the injection current.

The bias control circuit 8 includes a level detection circuit 7
And the frequency relationship of the electrical signal obtained from the frequency detection circuit 5 are input, and the electrical / optical conversion is performed so that the electrical signal at a low level and affected by the intermodulation distortion satisfies the desired quality. The bias current of the device 5 is set.

On the receiving side 2, after the optical signal from the transmitting side 1 is converted into an electric signal by the optical / electrical converter 6, the distributor 11
And the signals are output to output terminals 1 'to N', respectively.

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

A frequency-multiplexed electric signal is input to an input terminal of the transmission side 1, and one of the frequency-multiplexed signals is input to a level detection circuit 12 and a frequency detection circuit 13 by a distributor 14.

The other output of the distributor 14 is input to the electric / optical converter 5.

The bias control circuit 8 includes a level detection circuit 1
2 and the level detection circuit 1
3 is input, and the bias current of the electric / optical converter 5 is set so that the electric signal at a low level and affected by the intermodulation distortion satisfies the desired quality.

On the receiving side 2, the optical signal from the transmitting side 1 is converted into an electric signal by the optical / electrical converter 6,
And the signals are output to output terminals 1 'to N', respectively.

FIG. 4 is a diagram showing the relationship between the injection current and the light output. The average of the light output is proportional to the bias current.

When a radio frequency signal modulated as an electric signal is injected into the electric / optical converter, the injected current changes around the bias current.

FIG. 5 is a diagram showing the relationship between the bias current and the intermodulation distortion.

Intermodulation distortion is, for example, a third-order distortion.
Frequency f ₁ and passes the signal common nonlinear elements f ₂ (amplification, modulation) when a phenomenon in which distortion component is generated in the position of the _{2f 1 -f 2, 2f 2 -f} 1.

It is known that when the bias current is changed from A to B in FIG. 4, the intermodulation distortion is reduced from U ₁ to U ₂ .

FIGS. 6 (a) and 6 (b) are conceptual diagrams showing deterioration of transmission quality due to intermodulation distortion. FIG. 6 (a) shows the case where the number of input electric signals is 3, and the frequency relation is equal at each interval. (B) is a diagram showing a spectrum when only the signal level of frequency 3 is low, with the same relationship between the number of input electric signals and the frequency as in (a).

As a specific example, when the bias current is set to A in FIG. 4, a ratio D between the intermodulation distortion U ₁ generated from the electric signals of frequencies 1 and 2 and the maximum level D of the electric signal of frequency 3 is obtained.
Assume that / U ₁ is the lower limit of the bias current that satisfies the desired D / U ratio.

The bias current value A at this time is the most economical value with the minimum power consumption of the electric / optical converter.

On the other hand, in the case of (b), since the level of the electric signal of frequency 3 is low, the desired D / D
Does not satisfy U ratio.

In this case, the bias current value is increased to B and the intermodulation distortion is reduced to U ₂ so that the desired D / U ratio is satisfied.

The setting of the bias current may be either continuous variable or stepwise (stepwise) variable.

[0048]

As described above, according to the present invention, in an electric / optical conversion technique for converting a plurality of or one electric signal having different frequencies into an optical signal and transmitting the same, a reduction in distortion and a reduction in power consumption are achieved. Since power consumption can be realized at the same time, an economical and high-quality optical communication system can be provided.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a third embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between current and light output.

FIG. 5 is a diagram showing a relationship between a bias current and intermodulation distortion.

FIG. 6 is a diagram showing a relationship between intermodulation distortion and a signal level.

FIG. 7 is a conventional configuration diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transmission side, 2 ... Reception side, 3 ... Optical fiber, 4,11,
14: distributor, 5: electric / optical converter, 6: optical / electrical conversion circuit, 7, 12: level detection circuit, 8: bias control circuit, 9, 13: frequency detection circuit, 10: synthesizer, 15 ...
Fixed bias circuit.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H04J 14/02 (56) References JP-A-2-148929 (JP, A) JP-B-61-42976 (JP, B2) JP 61-42459 (JP, B2) JP 3-29211 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04J 14/00-14/08 H04B 10/00- 10/28

Claims (1)

(57) [Claims] 1. A communication system for converting a plurality of electric signals having different frequencies into an optical signal on a transmitting side, transmitting the optical signal to a receiving side, and converting the optical signal into an electric signal on a receiving side, wherein: Level detecting means for detecting the level of each electric signal on the transmitting side; frequency detecting means for detecting the frequency of each electric signal on the transmitting side; and electricity for converting each electric signal on the transmitting side into an optical signal. A bias current varying means for varying a bias current of the optical converter, wherein a low level is set based on a level relationship between the respective electric signals by the level detecting means and a frequency relationship between the respective electric signals by the frequency detecting means. The bias current varying means controls the electric / optical converter so that the electric signal affected by the intermodulation distortion satisfies a desired quality. Optical communication system and sets the scan current.