JP2904445B2 - Optical transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-speed optical transmission system,
The present invention relates to an optical transmission device required in a long repeater transmission system.

[0002]

2. Description of the Related Art In realizing a high-speed and long-relay digital optical transmission system, there has been a serious problem of waveform distortion due to dispersion of an optical fiber as a transmission path and spread of spectrum of transmitted signal light. The most effective way to solve this is to make the dispersion of the fiber zero. However, the dispersion of the fibers when there fiber given, in some only becomes zero at a specific wavelength (zero-dispersion wavelength), is the sign of the dispersion on both sides of the zero-dispersion wavelength is inverted, it shifted from the zero dispersion wavelength So it gets bigger. In a real system, considering the dispersion of the wavelength characteristics of the fiber and the light source, even in a system using the zero dispersion wavelength of the fiber, the wavelength of the light source and the zero dispersion wavelength of the installed fiber are completely the same. Without having a finite variance σ. Therefore, as shown in FIG. 4, by connecting a dispersion medium (for example, fiber) having a dispersion (−σ) just opposite to the dispersion of the fiber which is the transmission line and setting the total dispersion to zero, waveform deterioration due to dispersion is reduced. After removal, the light can be converted into an electric signal by the light receiving element.

[0003]

However, the above prior art has the following problems. In general, a direct detection system that converts the intensity of an optical signal into an electric signal is widely used as a practical device because it is simple and has excellent characteristics. However, since the S / N ratio of an electric signal demodulated by the direct detection method is determined by the noise characteristics of the O / E converter and the input optical signal power, when a dispersion medium is added, the reception sensitivity is reduced by the loss of the medium. Causes a decrease. The same can be said for the transmitting side. That is, the transmission output is reduced by the loss of the dispersion medium, and the allowable loss that can be allocated to the transmission path as the transmission reception level difference is reduced. That is,
Since the reduction of the transmission / reception level difference occurs at the same time in order to compensate for the waveform deterioration due to dispersion, it cannot be said that it is a practically effective method.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides an optical transmission apparatus capable of providing a configuration in which a loss of the dispersion medium does not cause deterioration of reception sensitivity while adding a dispersion medium for compensating dispersion of a transmission line. With the goal.

[0005]

SUMMARY OF THE INVENTION The present invention provides one or more devices.
Optical receiving circuit having an optical amplifier and a photoelectric conversion unit of
Is an optical transmitter having one or more optical amplifiers and an electro-optical converter.
In optical transmission equipment using communication circuits or both
Therefore, at least one of the optical receiving circuit and the optical transmitting circuit
In another circuit, an optical amplifier and the photoelectric or
A component that compensates for the dispersion characteristics of the transmission line between the
It is characterized by having a dispersive medium .

[0006]

According to the present invention, the combination of the optical amplifier and the dispersion medium suitable for the device can compensate for the dispersion of the transmission line without lowering the performance of the transmission device due to the loss of the dispersion medium.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, second, third and fourth embodiments of the present invention will be described below.
An embodiment will be described with reference to the drawings. In the present invention, by the combination of the optical amplifier and the dispersion medium suitable for the device, without reducing the performance of the transmission device due to the loss of the dispersion medium,
The dispersion of the transmission path can be compensated. That is, in the direct detection method, the S / N is determined by the photoelectric conversion unit, and the signal is converted into a baseband electric signal. Therefore, the influence of the dispersion of the transmission line cannot be equalized after the photoelectric conversion. Therefore, S /
Since there is no other way than to insert a dispersion medium before the circuit for determining N, the loss is sensitive to the reduction in the difference between the transmission and reception levels. In order to solve such a problem, in the receiving apparatus including the optical amplifier OA and the O / E converter of FIG. 5 according to the present invention, the S / N as the receiver is determined by the optical amplifier OA at the first stage, and the O / E alone Higher sensitivity than receiving. Moreover, after being optically amplified, the level itself of the optical signal is not sensitive to S / N. Therefore, by setting the output level of the OA to be sufficiently higher than the reception sensitivity of the O / E,
Even if a dispersion medium is inserted between A and OE, a configuration can be achieved in which dispersion can be compensated without affecting reception sensitivity.

First embodiment. FIG. 1 shows a case where an optical receiving unit is configured using the above principle. C is a coaxial cable, O /
E is an optical / electrical conversion circuit, D is a dispersion medium, OA1 and O
A2 is an optical amplifier and F is an optical fiber. OA2 is required when the loss of the dispersion medium is large.

Second embodiment. FIG. 2 shows an embodiment in which an optical amplifier is used as an optical repeater. The dispersion of the transmission line is compensated by inserting a dispersion medium that gives the dispersion opposite to the dispersion of the fiber of the transmission line in advance between the two optical amplifiers. In FIG. 2, F1 and F2 are optical fibers, D is a dispersion medium, and OA1 and OA2 are optical amplifiers. After amplifying the optical signal attenuated in the transmission line by the first-stage optical amplifier OA1, the dispersion of the transmission line can be compensated for by the same principle and configuration as in the first embodiment without impairing the output characteristics of the optical signal. In the case of the device, OA1 first amplifies the arrived optical signal and S
Since / N is determined, the subsequent stage dispersion medium can compensate for the dispersion without deteriorating the S / N ratio. However, when the optical output of the first-stage optical amplifier is sufficiently high or when the loss of the dispersion medium can be neglected, OA2 can be omitted.

Third embodiment. FIG. 3 shows an embodiment of the transmission unit. The transmission unit is composed of a dispersion medium that gives reverse dispersion to the fiber dispersion of the transmission line in advance and an optical amplifier that compensates for optical loss due to the dispersion medium. In FIG. 3, C is a coaxial cable, E / O is an electric / optical conversion circuit, D is a dispersion medium, OA is an optical amplifier, and F is an optical fiber. The electro-optical converter E / O is directly connected to the optical amplifier OA without using the dispersion medium D.
In a configuration for inputting an output, Er is used as the optical amplifier OA.
When a doped optical fiber amplifier is used, the optical output power P0 of the electro-optical converter E / O is amplified by the gain of the optical amplifier OA, but the input of the optical amplifier OA becomes equal to or more than the 3 dB saturation output of the optical amplifier OA. Even if it increases more than power Pin,
The output of the optical amplifier OA is saturated, and the optical output power hardly increases. As shown in FIG. 3, the dispersion medium D is converted into an electro-optical converter E / O.
And the optical amplifier OA, the dispersion medium D
Not only can be compensated for by the optical amplifier OA, but also can be further amplified. In particular, under the condition where the saturation occurs, the loss of the dispersion medium D does not affect the output power of the optical amplifier OA at all by the amount reduced from the unsaturated gain of the optical amplifier OA. For example, when 10 dB gain compression occurs due to the saturation of the optical amplifier OA, if the loss of the dispersion medium D is 10 dB or less, the transmission unit optical output power becomes equivalent to that in which the dispersion medium D is not inserted. Output performance does not deteriorate due to loss.

Fourth embodiment. FIG. 6 shows an embodiment in which an optical fiber is specifically used as a dispersion medium. This is an example in which a fiber amplifier doped with rare earth ions (erbium) is used as an optical amplifier. The chromatic dispersion in the dispersion-shifted fiber 150 km (F1) used as a transmission line is a dispersion medium (optical fiber F2; where F1 is the chromatic dispersion) inserted between the optical amplifier (OA) and the photoelectric converter (O / E). (The sign is opposite and the value is large). That is,
As shown in FIGS. 7 and 8, the effect of dispersion compensation could be confirmed by experiments.

[0012]

As described above, according to the present invention, the light
The dispersion of the fiber in each transmission line can be compensated for in the receiving circuit and / or the optical transmission circuit without compromising the characteristics due to the loss of the dispersion medium for compensation. No light signal can be obtained.

[Brief description of the drawings]

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

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

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

FIG. 4 is a diagram showing a conventional configuration.

FIG. 5 is a diagram illustrating a configuration example of a receiving circuit using the optical amplifier of the present invention.

FIG. 6 is a diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a 15th embodiment of the present invention without a dispersion medium;
It is a wave form diagram after transmitting 0 km.

FIG. 8 shows a diagram of a fourth embodiment of the present invention when a dispersion medium is present;
It is a wave form diagram after transmitting 0 km.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/00 H04B 9/00

Claims (1)

(57) [Claims] 1. An optical amplifier and a plurality of optical amplifiers
Optical receiver circuit, or one or more optical amplifiers
And an optical transmission circuit having an electro-optical converter, or both
In the optical transmission device using, at least one of the optical receiving circuit or the optical transmitting circuit is used.
In one circuit, an optical amplifier and the opto-electric or electric
Between the light converting portion, having a dispersive medium to compensate for the dispersion characteristics of the transmission path, the optical transmission apparatus according to claim.