Intelligent multi-channel fiber optic connections

High Speed ​​Data Transfer Issues

With the increase in the volume of information transmitted over the network, the problem of high-speed data transmission becomes more and more urgent. High-speed data transfer, as a rule, assumes the presence of a high-bandwidth communication channel between network nodes. When developing a channel with high throughput, both solutions based on copper electrical conductors and solutions based on optical connections can be used. Any connection consists of a transmitter that transmits a signal and a receiver that receives a signal. The signal through the connection can be transmitted both in one or in two directions. Thus, an optical connection may consist, for example, of an optical transmitter, an optical channel, and an optical receiver. In duplex mode, the optical transceiver provides, as signal transmission,

To date, channels are widely used that provide communication at a speed of more than 1 gigabit per second (1 Gb / s), the so-called "1G connections." 1G connections are well standardized (for example, there is a publicly available Gigabit Ethernet standard). Optical 1G connections are typically used to transmit data over long distances (more than 100 meters).

For high-speed data transmission, channels are used that provide communication at a speed of the order of 10 gigabits per second (10 Gb / s), the so-called “10G connections”. When solving complex technical problems, high demands are placed on data transmission channels, which are becoming increasingly difficult to satisfy, especially with the help of copper electrical conductors. However, 10G connections based on copper electrical conductors are used (for example, the 10GBASE-CX4 standard). 10GBASE-CX4 provides data transmission over four shielded twisted pairs in each direction (a total of eight twisted pairs). Such a cable turns out to be rather bulky (about 10 mm in diameter) and expensive to manufacture. In addition, 10GBASE-CX4 can only be used for data transfer no further than 15 meters. A common drawback for all 10G connections, based on copper conductors, is a high level of energy consumption. For example, the 10GBASE-T standard provides data transfer over distances from 55 to 100 meters, but because of the complex signal processing it consumes from 8 to 15 watts per port. If we consider a standard that provides data transmission over distances of about 30 meters, then such a connection will consume at least 4 watts per port. The use of such standards with high energy consumption leads to a significant increase in the cost of servicing connections, and also forces developers to reduce the density of ports on the front panels of the interfaces. For example, energy consumption of the order of 8-15 watts per port limits the density of ports to 8 pieces (or even less) in the same area on which you can place up to 48 ports,

Thus, studies of the electronics market show that when developing channels with high throughput (10G), solutions based on optical connections are increasingly being used. So in the figure below is a graph from a Luxtera report showing the change in time of the dependence of range and data rate on the physical data channel used. The graph shows that by 2014 there will be a complete rejection of solutions based on copper conductors in favor of solutions based on optical and hybrid compounds.

Multichannel Fiber Connections

To build high-performance data transfer systems, it is proposed to use multi-channel fiber optic connections. They provide the necessary low density of optical fibers, acceptable cable sizes and solve the problem of "channel congestion" (duct congestion problem), characteristic of single-channel connections.

Developers of multichannel fiber optic connections seek high channel density with low loss and crosstalk. Crosstalk Level, i.e. the maximum influence of the channels on each other is determined by the characteristics of the optical fibers, as well as the distances between them (fibers). Obviously, the greater the distance between the optical fibers, the lower the density of the multi-channel fiber optic connection. The level of loss depends on the characteristics of the optical fibers and the transmission distance of the signal. Thus, when designing a multi-channel fiber optic connection, it is important to consider and optimize all of the above parameters.

Of the existing means of transmitting data via multichannel fiber-optic connections, one can single out an active optical cable as the most common means.

Active optical cable

AOC, Electrical-optical active optical cable, US Patent No. 2007/0237464 A1 (October 11, 2007).

Active optical cable (AOK) includes, on the one hand, an integrated electrical connector, and on the other, an optical connector. Between them are several optical fibers that provide communication within the optical cable. Communication can be carried out either in one or in two directions.



It is assumed that at least one of the ends of the active optical cable has an electrical connector, but the signal is transmitted through the remaining part of the cable through the optical fiber. Thus, the network designer is not required to pre-select between the copper conductor connection and the optical connection. Instead, it is enough for the network nodes to have special ports that support either copper-conductor connections or optical connections.
Duplex data transfer mode is implemented by placing on both ends of the cable transmitting optical components (TOSA, transmit optical sub-assembly) and receiving optical components (ROSA, receive optical sub-assembly). Chips are responsible for controlling the transmitting and receiving optical components. Microcircuits can be placed inside the TOSA and ROSA cases or can be taken out of their limits. If necessary, duplex mode can be disabled. In this case, data transmission will be carried out in only one direction (only transmitters will be placed at one end of the cable, only receivers at the other end).

When an electrical signal is supplied to the corresponding terminals of the electrical connector (via the electrical port), it is converted by the laser driver and the TOSA Optoelectronic Converter into an optical signal. The optical signal is transmitted via optical fiber to ROSA, where it is converted by the ROSA optoelectronic converter into the corresponding electrical signal. The received electrical signal is fed to the corresponding terminal of the electrical connector and then to the electrical port.

The recommended signal transmission range over the active optical cable is 30 meters. Increasing the range to 100 meters leads to a significant increase in the cost of the cable.

A feature of AOK is the need for high-precision installation and alignment of signal transmitters (lasers) and signal receivers (photosensitive photodiodes) relative to physical channels (optical fibers). The developers of such compounds solve mainly technological problems of high-precision installation, trying to place as many channels as possible in small enclosures. As an alternative to AOK, a technology for transmitting data over an intelligent multi-channel fiber optic connection (IMKS) is proposed.

Intelligent multi-channel fiber optic connections

RF patent No. 2270493, 2007. The

use of IMC technology suggests that in case of partial damage to several optical fibers or the displacement of optical fibers relative to the connector, the connection can be quickly restored without violating data integrity. Thus, a compound built on the basis of IMCS technology has the property of regeneration (self-healing).



1 - activated light source; 2 - inactive light source; 3 - matrix of emitters; 4 - unused fiber optoshina; 5 - involved fibers optoshina; 6 — opto-fiber fibers into which several rays of light were directed; 7 - activated photodiodes; 8 - inactive photodiodes; 9 - activated photo-diodes that have received the signal and fibers 6; 10 - photodetector array.

Electric pulses from the control source microcircuit, which modulate the laser radiation, are fed to the inputs of the laser matrix — the information source. This radiation through optocoupler enters the photodiode array located in the information receiver and activates part of the photodiodes. Activated photodiodes generate a stream of electrical pulses to the receiver control chip.

When connecting, the optocoupler is connected to the matrices of the transmitter and receiver rather randomly, combining only the optical regions of the matrices and optocouplers by installing the ends of the optocouplers in the optical connectors of the receiver and transmitter microcircuits. Therefore, knowing only the many activated photodiodes of the receiver matrix, it is impossible to determine which laser emitted the signal that activated these photodiodes. One of the basic principles of IMC operation is to establish a correspondence between each laser and the photodiodes activated by this laser before starting data transfer. An appropriate switching procedure should be implemented in the data link protocol. During the switching, channels for data transmission are determined, i.e. a correspondence is established between the laser and the many photodiodes activated by it.

The channel switching procedure is performed once before the start of data transfer and does not affect the transmission rate in the future. In the event of a communication failure (partial damage to part of the optical fibers or displacement of the optical bus relative to the matrices of the receiver and transmitter), it is necessary to quickly detect this violation and carry out a repeated channel switching procedure. In this case, the number of channels can be reduced, i.e. The bandwidth of the connection will decrease, but the connection will be restored.

Conclusion

This article is an attempt to talk about the problem of high-speed data transfer and about possible ways to solve it, in particular about multi-channel fiber-optic connections.

To make it clear my place in this story, I will say that I am a member of a group of developers engaged in the implementation of the IMKS technology presented here. If this topic will be interesting to readers, I’m ready to tell you more about our work, plus prepare notes on the topics:

• hardware
• software part
• development, modeling and verification of data transfer protocols

Thank you for your attention, I hope it was interesting.