JPH01229549A - Digital signal light transmission system - Google Patents

Abstract

PURPOSE:To heighten a light transmitting level by obtaining at least one modulated digital signal composed of a pulse train having a pulse width narrower than its bit width for every bit period from an original digital signal composed of a binary digit string to be transmitted, converting the modulated digital signal into a light signal, and transmitting the light signal. CONSTITUTION:The duty ratio of a modulated digital signal TM becomes considerably smaller compared with that of an original digital signal TX, and the duty ratio and the mark ratio of a light signal TO to be transmitted become considerably smaller compared with that when the original digital signal TX is directly converted into the light signal. Consequently, even when the peak value of a current applied to a light emitting element 21 is heightened, the mean value becomes considerably lower compared with that when the original digital signal TX is directly converted into the light signal. Thus, even when the light emitting element 21 is a light emitting diode, etc., having small light emitting ability, the light signal TO having high peak power can be obtained, and the light transmitting level can be heightened.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a digital signal optical transmission system that converts a digital signal having a bit string structure, such as a data signal, into an optical signal and transmits the optical signal.

"Prior Art" When converting a digital signal with a bit string structure such as a data signal into an optical signal and transmitting it, conventionally, the digital signal to be transmitted directly turns on and off a light emitting element.
A direct intensity modulation method is used in which the digital signal to be turned off, ie, to be transmitted, is directly converted into an optical signal.

That is, as shown in FIG. 3, the digital signal TX to be transmitted, which has a bit string configuration with a bit width of BW as shown in FIG. 4, obtained from the transmitting device 10, is directly transmitted.
A current is supplied to the drive circuit 22 of the light emitting element 21, and during the high level period of the digital signal TX, a current flows through the light emitting element 21 and light is emitted from the light emitting element 21. That is, the digital signal TX becomes an optical signal as shown in FIG. converted to TP,
The optical signal TP is transmitted over, for example, an optical fiber 30, and on the receiving side, the light from the optical fiber 30 enters a light receiving element 41, a current flows through the light receiving element 41, and the current is transmitted to an amplifying and shaping circuit 42. In other words, the optical signal RP from the optical fiber 30 as shown in FIG. A digital signal RX that is the same as the digital signal TX is obtained, and the digital signal RX is supplied to the receiving device 50.

[Problem to be solved by the invention] By the way, in the above-mentioned digital signal optical transmission system, when increasing the transmission distance or branching the transmission path, it is necessary to increase the optical transmission level and to increase the optical reception level. The scope needs to be widened.

However, in the conventional digital signal optical transmission system shown in FIG.
is directly converted into an optical signal TP, so if the peak value of the current flowing through the light emitting element 21 is increased in order to increase the optical transmission level, its average value will also become considerably high, and the light emitting element 21
In addition, if the amount of light incident on the light receiving element 41 fluctuates greatly, the pulse width distortion of the current flowing through the light receiving element 41 increases, causing the signal to be transmitted as a digital signal RX. It becomes difficult to obtain the same digital signal TX on the side.
There is a disadvantage that it is difficult to widen the light receiving level range.

Therefore, the present invention aims to increase the optical transmission level without using expensive light emitting elements with large light emitting capacity in a digital signal optical transmission system that converts a digital signal with a bit string structure such as a data signal into an optical signal and transmits it. In addition, the original digital signal can be reliably reproduced on the receiving side regardless of the amount of light incident on the light-receiving element, and the light-receiving level range can be widened.

"Means for Solving the Problem" In the present invention, from an original digital signal having a bit string configuration to be transmitted, at least one beat/bit signal is transmitted for each bit period in the high level period or the low level period. A modulated digital signal consisting of a train of pulses with a pulse width narrower than the pulse width is obtained, the modulated digital signal is converted to an optical signal and transmitted, and the receiving side converts the received optical signal to a modulated digital signal that is an electrical signal. , the original digital signal is reproduced from the modulated digital signal.

"Function" In the digital signal optical transmission system of the present invention having the above configuration, the duty ratio of the modulated digital signal on the transmitting side is smaller than that of the original digital signal, and the duty ratio of the optical signal to be transmitted becomes smaller than that of the original digital signal. The mark rate is smaller than when converting the original digital signal directly into an optical signal, so even if the peak value of the current flowing through the light emitting element is set to a high value, the average value will be lower than when converting the original digital signal directly into an optical signal. It is possible to reduce the cost by using an inexpensive light-emitting element such as a light-emitting diode, which has a small light-emitting capacity, without using an expensive light-emitting element such as a semiconductor laser with a large light-emitting capacity. An optical signal with peak power can be obtained, and the optical transmission level can be increased.

Furthermore, on the receiving side, it is only necessary to accurately detect only the rising edge of the modulated digital signal on the transmitting side, that is, only the rising edge of the current flowing through the light receiving element, and the modulated digital signal on the transmitting side is a string of discrete pulses. Because of this, the rise of the current flowing through the light receiving element can be accurately detected regardless of the pulse width distortion of the current flowing through the light receiving element, so the original digital signal can be reliably reproduced regardless of the amount of light incident on the light receiving element. , the light receiving level range can be widened.

Furthermore, since the optical signal to be transmitted is a train of discrete pulses, there is almost no interference between bits during transmission.

Embodiment FIG. 1 shows an example of the digital signal optical transmission system of the present invention.

As shown in FIG. 2, from the transmitting device IO, the original digital signal TX to be transmitted has a bit string configuration with a bit width of BW, and the ring digital signal TX at the beginning of each bit period of the original digital signal TX. A bit synchronization signal TB consisting of a train of pulses with a pulse width sufficiently narrower than the bit width BW of is obtained, and the ring digital signal TX and the bit synchronization signal TB are supplied to the OR gate 23. Thus, a modulated digital signal TM is obtained which is composed of a train of pulses each having a pulse width sufficiently narrower than the bit width BW of the ring digital signal TX at the beginning of each bit period in the high level period of the ring digital signal TX.

This modulated digital signal TM is supplied to the drive circuit 22 of the light emitting element 21, and a current flows through the light emitting element 21 during the high level period of the modulated digital signal TM.
The modulated digital signal TM emits light from the second
The optical signal To is converted into the optical signal To as shown in the figure.
is transmitted, for example, through an optical fiber 30.

In this case, the duty ratio of the modulated digital signal TM is considerably smaller than that of the ring digital signal TX, and the duty ratio or mark rate of the optical signal To to be transmitted is such that the ring digital signal TX is directly converted into an optical signal. Therefore, even if the peak value of the current flowing through the light emitting element 21 is increased, its average value will be considerably lower than when the ring digital signal TX is directly converted into an optical signal. Even if the light-emitting element 21 is a light-emitting diode or the like with low light-emitting ability, the light signal T is still generated.

As a result, a high peak power can be obtained, and the optical transmission level can be increased. Furthermore, since the optical signal To to be transmitted is a train of discrete pulses, there is almost no interference between bits during transmission.

On the receiving side, light from the optical fiber 3o enters the light receiving element 41, a current flows through the light receiving element 41, and the current is converted into voltage and shaped by the amplifying and shaping circuit 42, that is, the light is transmitted from the optical fiber 30. The optical signal RO as shown in FIG. 2 is converted into an electrical signal, and a modulated digital signal RM similar to the modulated digital signal TM on the transmitting side is obtained from the amplifying and shaping circuit 42 as shown in FIG.

In this case, since the modulated digital signal TM on the transmitting side is a train of discrete pulses, in the amplification shaping circuit 42, the rise of the current flowing through the light receiving element 41, regardless of the pulse width distortion of the current flowing through the light receiving element 41, That is, the rising edge of the modulated digital signal TM on the transmitting side is accurately detected. The pulse width of each pulse of the modulated digital signal RM obtained from the amplification and shaping circuit 42 does not necessarily have to be the same as that of the modulated digital signal TM on the transmitting side.

This modulated digital signal RM is supplied to the bit synchronous signal reproducing circuit 43, and from the bit synchronous signal reproducing circuit 43,
As shown in FIG. 2, each bit period of the modulated digital signal RM consists of a train of pulses each having a pulse width sufficiently narrower than the bit width BW of the modulated digital signal RM, and the rising edge of the pulse train corresponds to the rising edge of the modulated digital signal RM. As a result, a beat/beat synchronization signal RB delayed by a time shorter than the pulse width of each pulse of the modulated digital signal RM is obtained.

The modulated digital signal RM obtained from the amplification and shaping circuit 42 is supplied to the data terminal of the D flip-flop 44, and the bit synchronization signal RB obtained from the bit synchronization signal reproduction circuit 43 is supplied to the trigger terminal T of the D flip-flop 44. By reading the level state of the modulated digital signal RM by the rise of the bit synchronization signal RB, the output terminal Q of the D clip-flop 44 reproduces the same signal as the ring digital signal TX on the transmitting side as shown in FIG. A digital signal RX is obtained, and the reproduced digital signal RX is supplied to the receiving side device 50. Further, the bit synchronization signal RB is also supplied to the receiving side device 50 as necessary.

As described above, the rising edge of the modulated digital signal TM on the transmitting side is accurately detected regardless of the pulse width distortion of the current flowing through the light receiving element 41, and the ring digital signal TXfJ is reliably reproduced regardless of the amount of light incident on the light receiving element 41. Therefore, the light receiving level range can be widened.

It should be noted that various circuits other than those shown in FIG. 1 are conceivable for the circuit that obtains the modulated digital signal TM from the ring digital signal TX on the transmitting side and the circuit that obtains the reproduced digital signal RX from the modulated digital signal RM at the time of debt/debt. .

Furthermore, the present invention can be applied to cases where something other than optical fiber is used as the transmission path.

[Effect of the Invention J As described above, according to the present invention, it is possible to increase the optical transmission level without using an expensive light-emitting element with a large light-emitting capacity, and it is possible to increase the optical transmission level (irrespective of the amount of light incident on the light-receiving element). The original digital signal can be reliably reproduced on the receiving side, and the range of light reception levels can be widened.

[Brief explanation of the drawing]

FIG. 1 is a system block diagram showing an example of the digital signal optical transmission system of the present invention, FIG. The system block diagram shown in FIG. 4 is a diagram showing an example of the form of signals obtained in each part.

Claims (1)

[Claims] (1) Modulating digital signal consisting of at least one pulse train for each bit period in the high level period or low level period, each pulse width narrower than the bit width, from the original digital signal of the bit string configuration to be transmitted. Obtain a signal, convert the modulated digital signal into an optical signal, and transmit it. On the receiving side, convert the received optical signal into a modulated digital signal that is an electrical signal, and reproduce the original digital signal from the modulated digital signal. ,
Digital signal optical transmission method.