JPH0380635A - Optical communication system - Google Patents

Abstract

PURPOSE:To take a long transmission distance by devising the system such that an excellent eye pattern is obtained in the case of high speed optical communication and a reception section receives an optical pulse with a large extinct ratio. CONSTITUTION:An optical threshold level element 4 arranged at the end of an optical transmission line 2 at the side of an optical reception section 3 applies threshold level processing to an optical pulse having an optical threshold level between received binary levels, resulting that the extinct ratio E' of the converted optical pulse is larger than the extinct ratio E of the optical pulse generated by an optical transmission section 1. That is, the extinct ratio E of the optical pulse of the optical transmission section 1 is set smaller to generate an optical pulse in following to a drive current of an semiconductor laser thereby obtaining an excellent eye pattern, and the extinct ratio E' of the optical pulse inputted to the optical reception section 3 is converted larger to prevent the deterioration in the minimum reception level of the optical reception signal at the optical reception section 3. Thus, the transmission distance of the optical transmission section 2 is taken long.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical communication system in an optical communication system consisting of an optical transmission section using a semiconductor laser as a light source, an optical transmission line, and an optical reception section, the present invention relates to an optical communication method when performing high-speed optical communication. The purpose is to obtain a good eye pattern and to enable the receiver to receive optical pulses with a large extinction ratio. (Has a light intensity value between the two levels of the light pulse, and when there is a light input with a power greater than this light intensity value, an optical output with a large power is output, and a light with a power smaller than this light intensity value is output.) An optical threshold element has a characteristic of outputting an optical output having a small power when there is an input, and also has a characteristic that the ratio of two powers of this optical output is larger than the ratio of the binary levels of the optical input. The optical receiver is
It is configured to receive the optical output of this optical threshold element and convert it into a corresponding electrical signal.

[Industrial Application Field] The present invention relates to an optical communication method in an optical communication system consisting of an optical transmitter, an optical transmission line, and an optical receiver using a semiconductor laser as a light source, and is particularly applicable to high-speed optical communication. The present invention relates to an optical communication system that allows a good eye pattern to be obtained when carrying out the optical communication, and also allows a receiving section to receive optical pulses with a large extinction ratio.

BACKGROUND OF THE INVENTION As the information society becomes more sophisticated, it is desired to achieve higher speed communication in the field of data communication. From now on, even in optical communication systems that use optical fibers as transmission paths, it will be necessary to take new measures to increase the communication speed of optical communication.

[Prior Art] Optical communication systems generally employ a configuration in which a semiconductor laser is used in an optical transmitter. As shown in Fig. 5, this semiconductor laser does not oscillate when the applied drive current is smaller than the dark value current rtb, but oscillates only when the dark value current becomes larger than rtb. It has characteristics. Based on this characteristic, even if the drive current is increased from a current value below the dark value current to a current value above the dark value current, the laser does not oscillate immediately and there is a delay in the laser light output. It turns out.

In order to realize high-speed optical communication from now on, we will use a drive current that has a configuration in which a modulation current (1) is superimposed on a bias current (2), which has a larger current value than the dark value current (2). A method will be adopted in which optical pulses at a binary level are generated. Even if such a drive current is used, if the difference between the bias current 1b and the modulation current 3 is large, the laser oscillation will not be able to follow up, resulting in a laser output with the same duty ratio as the drive current. When implementing even higher speed optical communication, the bias current I and the modulation current 1. By setting the difference between the drive current and the drive current to a smaller value, a laser output having the same duty ratio as the drive current duty ratio can be obtained.

In other words, conventionally, when performing high-speed optical communication, it is necessary to obtain a good eye pattern (a method of superimposing PCM signals with a clock signal period, and the larger the eye opening formed in the center, the more accurate the determination of 110. 1i of the bias current l and the modulation current
The process was carried out to determine the flow value.

[Problem to be solved by the invention]

However, in the conventional technology, the higher the speed of optical communication, the worse the extinction ratio of the optical signal becomes in order to obtain the required eye pattern of the optical signal.
As the difference between the LO level and the LO level becomes smaller, the problem arises that the minimum reception level of the optical reception signal at the optical receiver side deteriorates, and the transmission distance becomes difficult to achieve. Problems will arise.

The present invention has been made in view of the above circumstances, and is intended to enable a good eye pattern to be obtained when performing high-speed optical communication, and to enable a receiver to receive optical pulses with a large extinction ratio. The aim is to provide a new optical communication method that enables

[Means to solve the problem]

FIG. 1 is a diagram illustrating the principle of the present invention.

In the figure, 1 is an optical transmitter, which uses a semiconductor laser to
2 is an optical transmission line that is composed of an optical fiber and transmits the optical pulses generated by the optical transmitter 1; 3 is an optical A receiving section is composed of an avalanche photodiode or the like and converts the received optical pulse into a corresponding electric signal, and 4 is an optical threshold element disposed at the end of the optical transmission line 2 on the optical receiving section 3 side. It has an optical threshold between the two levels of the input optical pulse, and when there is an optical input with a power greater than this optical threshold, it outputs an optical output with a large power, and this optical threshold It has the characteristic that when there is an optical input with a smaller power, an optical output with a smaller power is output, and the ratio of the two powers of this optical output is larger than the ratio of the binary levels of the optical input. and 5 is an optical transmission means that transmits the optical output of the optical threshold element 4 to the optical receiver 3.

(Operation) In the present invention, when an optical pulse is transmitted from the optical transmitter l, the optical threshold element 4 performs dark value processing on this optical pulse, thereby obtaining the transmitted value expressed by the following formula. The extinction ratio E of the incoming optical pulse is converted into an optical pulse with an extinction ratio E'' expressed by the following formula: E=10j!og where L, a: L○ level of the transmitted optical pulse b: Hl level of the transmitted optical pulse Execute processing.

b' E ' = 10 l og a゛ However, a': L○ level b'' of the converted light pulse, i Hl level of the exchanged light pulse There is a light threshold between the extinction ratio E and the extinction ratio E゛. According to the characteristics of the element 4, the relationship a' a holds true, so the extinction ratio E° of the optical pulse converted by the optical threshold element 4 is lower than the extinction ratio E of the optical pulse generated by the optical transmitter l. It becomes something big.

The optical receiver 3 then converts the optical pulse with the large extinction ratio E' input via the optical transmission means 5 into a corresponding electric signal, which is transmitted from the optical transmitter 1. The light pulses are processed to generate corresponding electrical signals.

As described above, by using the present invention, the extinction ratio E of the optical pulse generated by the semiconductor laser in the optical transmitter 1 can be set to a small value, so that the optical pulse that can follow the drive current of the semiconductor laser can be generated. In addition, a good eye pattern can be obtained by generating
By converting the optical pulse inputted into the optical pulse into one having a large extinction ratio E°, it becomes possible to prevent the minimum reception level of the optical reception signal on the optical receiver 3 side from deteriorating.

As a result, the transmission distance of the optical transmission line 2 can also be increased.

〔Example〕

Hereinafter, the present invention will be explained in detail according to examples.

As explained in FIG. 1, in the present invention, there is an optical threshold between the two levels of the input optical pulse, and when there is an optical input with a power greater than this optical threshold, the optical pulse has a large power. When there is an optical input with a power smaller than this optical threshold, it outputs an optical output with a small power, and the ratio of the two powers of this optical output is the binary level of the optical input. An optical threshold element 4 having a characteristic that the ratio of
According to this optical threshold element 4, the extinction ratio of the optical pulse transmitted from the optical transmitting section 1 is converted into a large one, and TLTE is performed so that the extinction ratio of the optical pulse transmitted from the optical transmitting section 1 is increased and inputted to the optical receiving section 3.

An example of the optical threshold element 4 having such characteristics is an optical bistable laser constituted by a semiconductor laser.

When this optical bistable laser is driven with a fixed bias current, as shown in FIG. 2(a),
When there is an optical input P, , as shown in Fig. 2(b),
When this optical input P, o is small, the optical output P is extremely weak.
When the optical input P and o are large, the optical output P is extremely strong. It operates to output ut. Since this optical bistable laser exhibits hysteresis characteristics in its dark value operation, its application as an optical memory device is currently being widely considered.

FIG. 3 shows an example of a module structure 40 of the optical threshold device 4 using this optical bistable laser. In the figure, 2a
is an optical fiber corresponding to the optical transmission line 2 explained in FIG.
4a is an optical bistable laser, 5a is an optical fiber constituting the light transmission means 5 explained in FIG. 1, and 41 is a temperature control circuit for controlling the inside of the module structure 40 to a constant temperature to stabilize operating conditions. , 42.43 is a rod lens, and 44.45 is a polished glass plate coated with an anti-reflection coating.

Next, according to FIG. 4, the operational processing of the present invention configured as described above will be explained. Here, (A) in Figure 4
(B) is a diagrammatic representation of the threshold characteristic of the optical bistable laser 4a (the hysteresis characteristic is omitted for convenience of explanation), and (B) is a diagram showing the laser output characteristic of the semiconductor laser of the optical transmitter 1. It is shown diagrammatically, (C)
is a diagrammatic representation of the optical output characteristics of the optical bistable laser 4a.

As shown in FIG. 4 (B), the semiconductor laser of the optical transmitter l changes the optical output with the power "a" to the L○ level and the optical output with the power "b" according to the driving current. As explained in the [Prior Art] section, in order to perform high-speed optical communication under a good eye pattern, these optical outputs are (The bias current (2) having a current value larger than the IIF current 1tk is generated according to the modulation current I, and its extinction ratio E E =104!og is set to the smallest possible value.

The optical bistable laser 4a is connected to this (
When receiving the light pulse shown in B), it converts the manually input LO level "a" into a light output having a power of "a°" as shown in (C) according to the dark value characteristic shown in (A), and It operates to convert the input Hl level "b" into an optical output having a power of "b". At this time,
As can be seen from FIG. 2(b), the optical bistable laser 4a
Since the conversion operation of the optical pulse is performed so that a' a, the extinction ratio of the optical pulse output from the optical bistable laser 4a is Extinction ratio E of the optical pulse transmitted from I
becomes something bigger than.

From now on, the optical receiver 3 that receives the optical pulse having the extinction ratio E° via the optical fiber 5a can perform conversion processing into a corresponding electrical signal by detecting this optical pulse with high detection accuracy. It becomes like this.

Although the illustrated embodiments have been described above, the present invention is not limited thereto. For example, the optical threshold element 4 is not limited to the optical bistable laser 4a, and the optical threshold element 4 is not limited to the optical bistable laser 4a.
Any device may be used as long as it has the dark value characteristic shown in (1), and it is also possible to use other optical bistable devices such as semiconductor thin film etalons, multiple quantum well 5EEDs, and other optical functional devices.

〔Effect of the invention〕

As explained above, according to the present invention, the extinction ratio of the optical pulses generated by the semiconductor laser in the optical transmitter can be set to a small value, thereby generating optical pulses that can follow the driving current of the semiconductor laser. In addition, the optical pulse input to the optical receiver is converted into one with a large extinction ratio, which reduces the minimum reception of the optical reception signal on the optical receiver side. Prevents level deterioration. from now,
Not only will optical communications become faster, but the transmission distance of optical transmission lines will also be longer.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of the present invention, Fig. 2 is an explanatory diagram of an optical bistable laser, Fig. 3 is an example of the module structure of an optical threshold element, and Fig. 4 is an explanation of the operation processing of the present invention. FIG. 5 is an explanatory diagram of the laser output characteristics of a semiconductor laser. In the figure, 1 is an optical transmitter, 2 is an optical transmission line, 3 is an optical receiver, and 4
5 is a light threshold element, and 5 is a light transmission means.

Claims (1)

[Claims] An optical transmitter (1) comprising a semiconductor laser and generating binary-level optical pulses corresponding to a driving current; an optical transmission line (2) that transmits optical pulses; and an optical receiver (3) connected to the optical transmission line (2) that receives the transmitted optical pulses and converts them into corresponding electrical signals. In the optical communication system consisting of the optical receiving section (3) of the optical transmission line (2),
) side has an optical threshold between the two levels of the transmitted optical pulse, and when there is an optical input with a power greater than the optical threshold, an optical output with a large power is output, It has the characteristic of outputting an optical output with a small power when there is an optical input with a power smaller than the optical threshold, and the ratio of the two powers of the optical output is larger than the ratio of the binary levels of the optical input. An optical threshold element (4) having a characteristic is disposed, and the optical receiver (3) receives the optical output of the optical threshold element (4) and processes it so as to convert it into a corresponding electrical signal. An optical communication system, characterized in that the optical communication system is configured to generate an electrical signal corresponding to an optical pulse transmitted from the optical transmitter (1).