JP2002368689A - Optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission system that can keep transmission quality high with a simple method. SOLUTION: The optical transmission system interconnects a plurality of communication nodes via a broadcast type optical transmission line. Each communication node is provided with a transmission controller 10. The transmission controller 10 includes an electro-optical conversion section 15 that converts an electrical signal into an optical signal and outputs the optical signal to a broadcast type optical transmission line, a photoelectric conversion section 16 that receives the optical signal from the optical transmission line and converts it into an electrical signal, and a luminous intensity monitor section 19 that monitors the luminous intensity. The photoelectric conversion section 16 receives the optical signal outputted from the electro-optical conversion section 15 and the luminous intensity monitor section 19 controls the electro- optical conversion section 15 on the basis of the reception state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission system in which a plurality of communication nodes are connected via a broadcast type optical transmission line.

[0002]

2. Description of the Related Art With the recent development of information processing technology, the functions and performance of circuit boards used in data processing systems or communication systems have been greatly increased. As the number of signal connections to each circuit board increases as circuit functions increase, data bus boards that connect each circuit board with a bus structure require a backplane-type data bus that requires a large number of connectors and connection lines. Has been adopted. Up to now, the processing speed of the system has been improved by increasing the number of connection lines and increasing the parallelism by miniaturization. However, the bus operation speed, the fan-out, and the bus size are limited by the signal delay caused by the capacitance between connection lines and the connection line resistance, and the processing speed of the system may be limited by the performance of the bus. In addition, electromagnetic noise (EMI: Electromagneti
c Interference) is also a major constraint on improving the processing speed of the system. Therefore, the optical interconnection, which has been spotlighted mainly in the trunk line system,
It is also being applied to electrical wiring between substrates.

[0003] Among the various types of optical interconnection technologies that have been proposed in the past, the most widespread one at present is trunk line communication using a single mode optical fiber. However, the cost of equipment required for these systems is high, and optical interconnection has not yet penetrated the consumer market. Also,
In general, optical interconnection using optical fibers realizes one-to-one communication, and many-to-many connections such as bus connections need to lay many fibers, which is not preferable.

[0004] Therefore, low-cost and highly expandable optical interconnection is known as, for example, “electronics”, 2
October 2000, pp. 49-53, "New Concept Optical Sheet Bus Technology". According to this technology, for example, a so-called broadcast-type transmission path that transmits light output from one point to multiple points by using a low-cost flat light guide path made of resin and providing a reflection-diffusion optical system inside, for example. Can be obtained.

[0005] In optical communication, a signal is transmitted by a change in light intensity. Therefore, in order to maintain signal transmission quality, it is necessary to constantly control the light intensity within a desired range. However, optical elements and optical transmission lines are generally susceptible to the surrounding environment and connection loss of optical components, and the system needs a function to compensate for the change. For example, Japanese Patent Application Laid-Open
JP-93-199199 discloses an "optical transmission / reception level adjustment circuit".
Is disclosed. This technique notifies loss information of an optical signal detected by a reception unit to a transmission unit, and adjusts driving conditions of the light emitting element based on the information.

[0006]

However, in a method of feeding back information detected by a receiving unit distant from a transmitting unit as in the prior art, a system is complicated due to the feedback, and transmission is not performed. There is a problem that it takes time to start.

Further, in order to monitor that a correct signal has been actually transmitted, a certain specific data string is transmitted, and it is checked whether or not the node which has received the specific data string can restore the specific data string. be able to. However, in this case, it is necessary to have a function to create a specific data string or a memory to hold predetermined data, and to confirm these, add this check to the initialization procedure before starting transmission, for example. Is required, and the system tends to be complicated. As another method, it is known to detect an error by adding a parity bit to data or encoding the data. In this case, the data to be transmitted is made redundant, so that the transmission band is narrowed,
The problem is that extra time is required to convert the data.

Further, as a method of compensating for the deterioration with time and the temperature change of the light emitting element, a method of enclosing a light receiving element for monitoring the amount of light in a package of the light emitting element is well known.
However, this method adjusts the light amount of the light emitting element itself based on a certain initial value, and cannot correct the state after the actual transmission of the optical signal.

Accordingly, an object of the present invention is to provide an optical transmission system capable of maintaining high transmission quality by a simple method.

[0010]

An object of the present invention is to provide a broadcast type optical transmission between a plurality of communication nodes having an optical output unit for converting an electric signal into an optical signal and an optical input unit for converting an optical signal into an electric signal. An optical transmission system connected via a path, wherein at least one of the communication nodes receives an optical signal output by itself via the optical transmission path and monitors a transmission state of the optical signal. Achieved by the system.

Here, the communication node can monitor the transmission state of the optical signal and change the driving condition of the optical output unit so that the received light intensity becomes constant. Further, when an abnormality of the optical signal is detected, the abnormality can be displayed on a transmission error display section. Furthermore, the communication node can monitor the data error by comparing the optical signal output by itself with the optical signal received via the optical transmission line. In this case, when there is an operation period in which a plurality of communication nodes simultaneously transmit optical signals, a function of changing a driving condition of the optical output unit, a function of displaying the abnormality on a transmission error display unit, and an error of the data At least one of the monitoring functions can be canceled.

The optical transmission line is formed of a light-transmitting medium having one end connected to an individual light guide provided for each communication node and the other end provided with an end face for changing a traveling direction of light to a substantially opposite direction. Or, a translucent medium provided with a plurality of steps in one end having an input / output unit for inputting or outputting an optical signal at one end, and an end face at the other end for changing a traveling direction of light to a substantially opposite direction. Can be formed respectively. Here, the end face that changes the traveling direction of the light to a substantially opposite direction may include an optical system that diffuses the light.

A transmission control device according to the present invention converts an electric signal to an optical signal and outputs the signal to a broadcast type optical transmission line, and receives the optical signal from the optical transmission line and converts it into an electric signal. A light intensity monitoring unit that monitors light intensity, wherein the light intensity monitoring unit has a constant intensity of an optical signal received from the light input unit and output from the light output unit. The light output unit is controlled as described above.
Further, it is possible to include a transmission error display unit that displays the abnormality when the optical intensity monitoring unit detects an abnormality in the optical signal received by the optical input unit and output from the optical output unit. Here, the light intensity monitoring unit may stop at least one of a control function of the light output unit and a function of a transmission error display unit that displays the abnormality in response to an external mode signal.

In addition, a transmission control device according to the present invention stores an optical output unit that converts an electric signal into an optical signal and outputs the optical signal to a broadcast-type optical transmission line, and stores signal data output from the optical output unit. A data storage unit, an optical input unit that receives an optical signal from the optical transmission line and converts it into an electrical signal, and compares the stored signal data with the signal data input from the optical input unit to determine whether correct data is present. A data comparing / determining unit for determining whether or not the data is transmitted. Here, the data comparison / judgment unit can stop the signal data comparison / judgment function in response to an external mode signal. With this configuration, light can be transmitted to multiple points using a so-called broadcast-type optical transmission line, and an optical signal output by itself can be monitored, compared, and determined by itself, and transmitted by a simple method. Quality can be kept high.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail, but before that, an optical transmission line used in the present invention will be briefly described. In each of the drawings, the same reference numerals are used to refer to the same components unless otherwise specified.

FIGS. 1A and 1B are diagrams showing an example of a broadcast type optical transmission line used in the present invention, wherein FIG. 1A is a perspective view and FIG. 1B is a side view. In the figure, a light-transmitting medium can be used for the core 4 of the optical transmission line 1, and a clad 5 having a smaller refractive index than the light-transmitting medium of the core is disposed on the upper and lower surfaces and left and right side surfaces of the core 4. It is desirable to do. As the translucent medium, a plastic material such as polymethyl methacrylate, polycarbonate, amorphous polyolefin, or inorganic glass can be used. The optical signal travels in the core 4 molded into a flat plate. Optical transmission line 1
Has a role of reflecting an optical signal. Therefore, the end face 3 is provided with a reflection / diffusion optical system for polishing the surface or reflecting and further diffusing light. The end face facing the reflection surface is machined stepwise as shown in FIG. 1 (a), and the end face is machined into a 45 ° face 7 with respect to the upper and lower faces of the flat plate as shown in FIG. 1 (b). Polish so that light is easily reflected. In some cases, a metal film or the like may be deposited on this end face.

It is desirable that the light incident / exit portion 2 is subjected to a process such as mirror polishing so that there is no loss when light enters / exits. Thus, the optical signal 6 input from the light input / output unit 2 is reflected by the 45-degree surface 7, propagates through the core 4, is reflected by the reflection surface 3 on the other end surface, and is again reflected by the 45-degree surface 7. The light is reflected and emitted from the light input / output unit 2. At this time, since the light returns while being widely diffused, the same optical signal can be extracted not only from the optical input / output unit to which the optical signal 6 has been input but also from other optical input / output units. That is, a broadcast-type optical transmission path is configured, and signals can be transmitted and received between arbitrary light input / output units 2. With this function, a plurality of communication nodes can be connected to this optical transmission line to form a backplane type optical bus. One layer of the optical transmission line corresponds to one bit of the electric wiring, and in order to realize multi-bit, it is necessary to arrange the optical transmission lines in parallel as described below.

FIG. 2 is a diagram showing an example of an optical transmission system in which a communication node is connected to the optical transmission line of FIG. 1, wherein (a) is a plan view and (b) is a side view. The communication node 8 can transmit and receive signals using the optical transmission line 1, and has functions such as a CPU, a memory, an image processing board, and an external interface. The communication node 8 has a photoelectric conversion unit 9 and can transmit and receive an optical signal through the optical transmission line 1 shown in FIG. The photoelectric conversion unit includes a light output unit (electric-light conversion unit) including a light emitting element such as an LED or a laser diode that converts an electric signal into an optical signal, and an optical input unit including a light receiving element such as a photodiode that converts an optical signal into an electric signal. (Optical-electrical conversion unit). This example shows a state in which four layers of the optical transmission line 1 are arranged, and as shown in FIG. 2A, the light transmission / reception portions of the respective layers are arranged so as not to overlap. FIG. 2 shows a configuration in which communication between four daughter boards is performed using four layers of optical transmission lines, and the bit width of the optical signal at this time corresponds to 4 bits.

FIGS. 6A and 6B are diagrams showing another example of an optical transmission line usable in the present invention, wherein FIG. 6A is a perspective view and FIG. 6B is a side view. The same material as shown in FIGS. 1 and 2 can be used for the optical transmission line. Also in the present embodiment, the one end face 3 of the optical transmission line 1 has a role of reflecting an optical signal, and is provided with a reflection / diffusion optical system which polishes the surface or reflects and further diffuses light. I have. On the other hand, as shown in FIG. 6A, an individual light guide path 31 to which each communication node is connected is connected to the end face facing the reflection surface. A commercially available optical connector can be used for this connection, and the connection may be performed using an optical adhesive, or may be performed by heat fusion. An optical fiber made of glass or various plastics is suitable as the individual light guide.

FIG. 7 is a diagram showing an example of an optical transmission system in which a communication node is connected to the optical transmission line of FIG. Each communication node 8 is provided with a photoelectric conversion unit 9, and transmits an optical signal into the optical transmission line 1 via the individual light guide path 31. The light guided into the optical transmission path is reflected by the reflection surface 3 as in FIGS. 1 and 2, and is guided to the individual light guide paths 31 in different directions. In this figure, the optical transmission line is shown as a substantially rectangular shape, but the shape is not limited to this, and other shapes may be used as long as the input unit and the reflection unit face each other.

FIG. 3 is a diagram showing an example of a transmission control device in the photoelectric conversion unit 9. In the figure, a transmission control device 1
Numeral 0 is a circuit function part for performing control relating to transmission / reception of an optical signal, which receives an electric signal 11 to be transmitted to another node, converts it into an optical signal 12, transmits the signal to a transmission line, and receives the signal from the optical transmission line. It plays a role of returning the optical signal 13 to the electric signal 11.

Hereinafter, the transmission control operation of the present invention will be described in more detail with reference to FIG. When transmitting a signal to another node, the transmission control device 10 transmits the received electric signal to the data encoding unit 1 by the input / output control unit 18.
Send to 4. The input / output control unit 18 has a function of distinguishing transmission data and reception data and distributing signals. The data encoding unit 14 converts the electric signal into an electric signal suitable for optical transmission. For example, a plurality of parallel signals can be converted into a serial signal, or a control code can be added. The encoded electric signal is sent to the electric-optical converter 15. The electro-optical converter 15 includes a light emitting element and a driving unit for driving the light emitting element. The transmitted electric signal is converted into an optical signal 12 there and output to an optical transmission line.

On the other hand, when receiving a signal, the optical-electrical conversion unit 16 first converts the received optical signal 13 into an electric signal having a desired amplitude. This part will be described with reference to FIG. FIG. 4 is a diagram illustrating a configuration example of the optical-electrical conversion unit 16. First, the optical signal 13 entering the optical-electrical converter 16 is converted by the photodiode 22 as a photodetector into a minute current 25 proportional to the light intensity. The change in the minute current 25 is converted into a change in a voltage signal 26 by a preamplifier 23 that performs current-voltage conversion, and is further converted into a desired amplitude level of an electric signal 27 by a post amplifier 24 that amplifies the voltage change. Here, the amplitude level of the desired electric signal is an amplitude change corresponding to the level of the electric signal used in the system.

Returning to FIG. 3, the electric signal converted by the optical-electrical converter 16 is converted into a serial-parallel signal and a control code by a data decoder 17 via a light intensity monitor 19 to be described later. Is removed and returned to the original electric signal. Here, it goes without saying that data encoding and decoding methods are unified in all communication nodes. The restored electric signal is sent to the upper layer by the input / output control unit 18. As described with reference to FIG. 4, since the amplitude of the electric signal output from the optical-electrical conversion unit 16 depends on the light intensity, the correct electric signal cannot be restored unless a sufficient amount of the optical signal is received.

Here, the operation of the light intensity monitoring unit 19 will be described. As described above, the optical transmission path in the present invention is of a broadcast type, and an optical signal transmitted from one communication node uniformly reaches another communication node through the optical transmission path. Also, due to the characteristic of light that light traveling in opposite directions does not interfere with each other, even when the own node is a transmitting node, if the own node has both a transmitting unit and a receiving unit, FIG. 2 or the light transmitted inside the light guide path shown in FIGS. 6 and 7 can be received by the own node. That is, the transmission result of the optical signal transmitted by itself can be confirmed by the own node. The light intensity monitoring unit 19 shown in FIG. 3 uses this characteristic to sequentially monitor the light intensity after transmission. Therefore, it is possible to monitor the transmission state in real time, even during a special operation such as initial setting before communication.

In the first embodiment of the present invention, when the light intensity monitoring unit 19 observes that the light emission intensity on the transmitting side has dropped during communication, as shown in FIG. The error information 21 is output from the unit 19 to the electro-optical conversion unit 15, whereby the driving conditions of the electro-optical conversion unit 15 are changed, so that the appropriate light intensity is always maintained. Alternatively, more simply, when it is detected that the optical signal is abnormal, for example, there is a defect in the light intensity, it can be displayed on the error display section 20. The monitoring of the light intensity according to the present invention is different from the conventional method of feeding back the information of the monitor light receiver installed near the light emitting element, and can feed back the state of the light actually propagated in the optical transmission path. Therefore, more strict failure analysis can be performed.

FIG. 5 is a diagram showing another example of the transmission control device in the photoelectric conversion unit 9. In this example, the data transmission node temporarily stores all or a part of the data transmitted by itself in the data holding memory 29. Then, the signal received via the transmission path and the signal stored in the memory are compared by the data comparing / determining unit 28, thereby determining whether correct data is transmitted. If a data error is found, a procedure for retransmitting the correct data can be taken, or the data error can be corrected by an appropriate method. At this time, it is also effective to simultaneously use the method described in the above embodiment, such as changing the driving conditions of the electro-optical converter. The causes of transmission data bit errors during transmission include electrical-optical conversion units, transmission lines, and optical-
It can be considered in each of the electrical converters and cannot be statistically zeroed out. However, by using this embodiment, the bit error rate can be reduced by a simple method.

FIG. 8 is a diagram showing still another example of the transmission control device in the photoelectric conversion unit 9. In this example, the data comparison / determination unit 28 shown in FIG.
Accordingly, the function of the data comparison / judgment unit 28 can be canceled. Among widely known general-purpose bus protocols, there is a possibility that signals are transmitted from a plurality of communication nodes at the same time, for example, in an arbitration mode in which a plurality of communication nodes take a right to use a bus. When this function is to be realized in the optical bus, the signal received by the own node becomes "1" because the other node transmits "1" while the own node outputs the signal "0". It may appear that a transmission error has occurred. In order not to change the driving condition of the light emitting unit by determining this as an error or to display an error, a signal of a bus operation mode is obtained from a higher-order protocol layer, and an error determination is performed when unnecessary. It is not done. In the operation mode in which a plurality of nodes may emit light at the same time, there is a possibility that the signal “0” is transmitted and the signal “1” is returned. Since "1" should be received irrespective of the operation state of the node, control can be performed so that error detection is performed only when the own node transmits "0". Also in the above example, the control function of the light output unit and the transmission error display function by the light intensity monitoring unit can be stopped according to this kind of external mode signal.

[0029]

According to the present invention, it is possible to sequentially monitor the transmission state during communication, which cannot be realized by the prior art, and it is possible to obtain an optical transmission system with higher transmission quality.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a broadcast type optical transmission line used in the present invention, where (a) is a perspective view and (b) is a side view.

FIG. 2 is a diagram showing an example of an optical transmission system in which a communication node is connected to the optical transmission line in FIG. 1, (a) is a plan view,
(B) is a side view.

FIG. 3 is a diagram illustrating an example of a transmission control device in a photoelectric conversion unit.

FIG. 4 is a diagram illustrating a configuration example of an optical-electrical converter.

FIG. 5 is a diagram illustrating another example of the transmission control device in the photoelectric conversion unit.

FIGS. 6A and 6B are diagrams showing another example of an optical transmission line usable in the present invention, wherein FIG. 6A is a perspective view and FIG. 6B is a side view.

FIG. 7 is a diagram illustrating an example of an optical transmission system in which a communication node is connected to the optical transmission line in FIG.

FIG. 8 is a diagram illustrating still another example of the transmission control device in the photoelectric conversion unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical transmission line 2 Light input / output part 3 Reflection surface 4 Core part 5 Cladding part 6, 12, 13 Optical signal 7 45 degree surface 8 Communication node 9 Photoelectric conversion part 10, 30 Transmission control device 11, 25, 26, 27 Electricity Signal 14 Data encoding unit 15 Electric-to-optical conversion unit 16 Optical-to-electric conversion unit 17 Data decoding unit 18 Input / output control unit 19 Light intensity monitoring unit 20 Error display unit 21 Error information 22 Photodiode 23 Preamplifier 24 Postamplifier 25 Microcurrent 28 Data comparison / judgment unit 29 Data holding memory 31 Individual light guide 32 Mode signal

Claims (16)

[Claims] 1. An optical transmission system in which a plurality of communication nodes having an optical output unit for converting an electric signal into an optical signal and an optical input unit for converting an optical signal into an electric signal are connected via a broadcast-type optical transmission line. An optical transmission system, wherein at least one of the communication nodes receives an optical signal output by itself via the optical transmission line and monitors a transmission state of the optical signal. 2. The optical device according to claim 1, wherein the communication node monitors a transmission state of the optical signal and changes a driving condition of the optical output unit so that a received light intensity becomes constant. Transmission system. 3. The optical transmission system according to claim 1, wherein when an abnormality of the optical signal is detected, the abnormality is displayed on a transmission error display unit. 4. The communication node according to claim 1, wherein the communication node compares an optical signal output by the communication node with the optical signal received via the optical transmission line and monitors a data error. An optical transmission system according to item 1. 5. The optical transmission system according to claim 2, wherein a function of changing a driving condition of the optical output unit is canceled when there is an operation period in which the plurality of communication nodes simultaneously transmit optical signals. . 6. The optical transmission according to claim 3, wherein a function of displaying the abnormality on a transmission error display unit is canceled when there is an operation period in which the plurality of communication nodes simultaneously transmit optical signals. system. 7. The optical transmission system according to claim 4, wherein the function of monitoring the data error is canceled when there is an operation period in which the plurality of communication nodes simultaneously transmit optical signals. 8. The optical transmission line is formed by a translucent medium having one end connected to an individual light guide provided for each communication node and the other end provided with an end face for changing a traveling direction of light to a substantially opposite direction. The optical transmission system according to any one of claims 1 to 7, wherein the optical transmission system is formed. 9. An end face of the optical transmission path, wherein a plurality of steps having an input / output section for inputting or outputting an optical signal are provided at one end, and a step of changing the traveling direction of light to a substantially opposite direction is provided at the other end. The optical transmission system according to any one of claims 1 to 7, wherein the optical transmission system is formed of a light-transmitting medium provided with (1). 10. The optical transmission system according to claim 8, wherein the end face that changes the traveling direction of the light to a substantially opposite direction includes an optical system that diffuses the light. 11. An optical output unit for converting an electric signal into an optical signal and outputting the signal to a broadcast type optical transmission line, an optical input unit for receiving an optical signal from the optical transmission line and converting the signal into an electric signal, Light intensity monitoring unit for monitoring the intensity, the light intensity monitoring unit, the light output unit so that the intensity of the optical signal received from the optical input unit and output from the optical output unit is constant. A transmission control device characterized by controlling. 12. A transmission error display unit for displaying the abnormality when the optical intensity monitoring unit detects an abnormality in an optical signal received by the optical input unit and output from the optical output unit. The transmission control device according to claim 11, wherein: 13. The transmission control device according to claim 11, wherein the light intensity monitoring unit can stop a control function of the light output unit in response to a mode signal from the outside. 14. The transmission intensity display unit according to claim 1, wherein the light intensity monitoring unit can stop a function of a transmission error display unit that displays the abnormality in response to an external mode signal.
3. The transmission control device according to 2. 15. An optical output unit that converts an electric signal into an optical signal and outputs the signal to a broadcast-type optical transmission line, a data storage unit that stores signal data output from the optical output unit, and the optical transmission line. An optical input unit for receiving an optical signal from the optical input unit and converting the signal data into an electrical signal; and comparing the signal data input from the optical input unit with the stored signal data to determine whether correct data is transmitted. A transmission control device comprising a comparison / determination unit. 16. The transmission control device according to claim 15, wherein said data comparison / judgment unit can stop a signal data comparison / judgment function according to an external mode signal.