Second breath multimode
Along with the increase in the number of devices connected to networks and the volumes of data generated by them, the bandwidth requirements of network infrastructures are also increasing. The main burden of traffic transmission in virtually all networks today are fiber-optic systems. And the most economically attractive, especially for communication over short distances, remain solutions based on high-water fiber (IIM). Recently, along with the development of broadband IIM and SWDM technology, fundamentally new opportunities have emerged to increase the capacity of systems based on IIM.
Recall that a light-carrying core in a multimode fiber has a diameter of approximately six times greater than that in a single-mode fiber (OMV). This facilitates alignment and alignment of the fibers — an important task for connector designers, as well as sources and receivers of light signals. In many ways, this is why IIM became the first type of fiber, which began to be used in communication networks - back in the early 80s of the last century. And only in the late 80s, when it became possible to provide centering with an accuracy of the order of a micron and laser diodes appeared, single-mode fiber became widely used in communication networks.
Typical optical fiber structure
But, despite the advantages of single-mode technology in terms of range and bandwidth, IIM remained the main type of fiber for most networks, including LAN, data center networks, etc. This is due to the cost advantages of multimode technology, due to the already mentioned simpler fiber alignment, the wide availability of low-cost radiation sources and other reasons.
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The multimode has come a long way throughput improvements. It all started with LED emitters (LED) and megabit speeds. In the 90s, when higher speeds were required, LEDs began to give way to new low-cost light sources — VCSEL lasers with a wavelength of 850 nm, which are capable of modulating the signal much faster. This, in turn, led to the transition from an IWM with a core diameter of 62.5 μm (cable systems of class OM1) to fibers with a core of 50 μm (class OM2).
In the late 90s, the era of gigabit speeds. It took a further increase in bandwidth. It was provided by new multimode fibers, which were originally developed optimized for laser transmission (LOMMF). The first standard LOMMF fibers provided about four times the bandwidth than OM2 fibers. This is how a new class of fibers appeared - OM3, which opened the door to 10 Gigabit systems in the early 2000s.
The next stage is the development by the end of the decade of OM4 fiber with an even greater bandwidth ratio. This fiber provided a linear speed of 25 Gbps. In addition to increasing the linear speed, an increase in the number of fibers forming the communication channel was also required to achieve ever higher speeds. So, when using a linear speed of 10 Gbit / s, four fibers are needed to form a 40G channel (eight for duplex), 10 for fiber 100G (20 for duplex). When switching to a linear speed of 25 Gbit / s, the number of fibers for the 100G channel is proportionally reduced (up to eight for the duplex), but for the implementation of advanced 400G systems, 32 fibers are needed.
To simplify the organization and maintenance of multi-fiber systems, MPO group connectors have become increasingly used. The compact MPO design allows you to terminate 8, 12, 16 and more fibers in the space corresponding to the duplex connector LC. The high density of MPO makes it possible to deploy a preterminated cable system with a large number of fibers, eliminating the lengthy process of installing connectors in the field.
However, increasing the capacity of multimode systems by increasing the number of fibers is a path that has many disadvantages. Increasing the number of fibers increases the complexity of the system, imposes increased requirements on cable channels, means of laying fibers in the switching field, etc. At the same time, until recently, multimode technologies did not use an elegant way to increase throughput, which has long been known in the world of single-mode technology. We are talking about spectral compaction (WDM), when in a single fiber a multitude of spectral channels are formed at different wavelengths. Accordingly, the fiber capacity is multiplied by the number of such channels. In single-mode systems, dozens of spectral channels can be used.
Principles of Spectral Compaction (WDM)
Why was this seal not used in multimode technique? Everything is very simple. OM3 and OM4 fibers are optimized for laser transmission at the same wavelength - 850 nm. “Step to the left, step to the right” (according to the spectral scale) - the throughput of such a fiber drops sharply, and it is no longer suitable for transmitting high-speed flows. Therefore, to implement spectral compaction in the IIM, it was necessary to develop a new fiber capable of providing effective bandwidth in a relatively wide “window” of wavelengths.
The first samples of the new fiber appeared a few years ago. In the spring of 2015, at the Optical Fiber Communications (OFC) conference, Finisar and CommScope demonstrated the work of the WDM technology on the new IIM, known as broadband (BMS-IIM). The transmission of four spectral channels was shown (at lengths of 850, 880, 910 and 940 nm), each of which provided a throughput of 25 Gbit / s, and in the aggregate, 100 Gbit / s. The corresponding spectral compaction technology is called SWDM - Short Wavelength Division Division Multiplexing.
Even earlier, in the fall of 2014, CommScope, together with the same Finisar and a number of other companies, initiated in the TIA Association a project to develop a standard for new fiber. In June 2016, the subcommittee TR-42.12, which is responsible for the TIA Association for optical fibers and cables, approved the ANSI / TIA-492AAAE standard, which specifies WB-MMF. The document describes fiber optimized for laser sources, designed to transmit signals at one wavelength or at several wavelengths in the range from 850 to 953 nm. And a little later, in October 2016, at a joint meeting of the relevant committees of the ISO and IEC organizations, it was decided to classify BMS-IIM to the OM5 class.
The efforts of the cable cutters were picked up by the active network equipment manufacturers. The SWDM Alliance industrial consortium was jointly formed to develop specifications and promote the Shortwave Wavelength Division Multiplexing technology. (The founders of the SWDM Alliance were Commscope, Corning, Dell, Finisar, H3C, Huawei, Juniper, Lumentum and OFS.) The SWDM Alliance has already published two specifications for 40- and 100-gigabit Ethernet transmissions (40 GE SWDM4 and 100 GE SWDM4, respectively) . SWDM technology allows high-speed 40G and 100G channels to be implemented using just a pair of OM5 fibers. It also opens up the possibility of efficient implementation of 200G, 400G and 800G Ethernet channels based on multimode fiber.
Various options for the transmission of high-speed streams, including the use of SHP-MMV and spectral compaction (WDM)
So, the emergence of BF-IIM, or fiber class OM5, marks a significant breakthrough in the development of multimode technology. Now, high transmission rates (for example, 100G) can be realized with a significantly smaller number of fibers. In addition, the possibility of switching to higher speeds without the need to use additional fibers. In general, the technical progress is impressive, thanks to which the throughput of multimode fiber has increased 160,000 times, from 10 Mbit / s to potentially 1600 Gbit / s, while maintaining the main advantages of multimode - low cost.
Recall that a light-carrying core in a multimode fiber has a diameter of approximately six times greater than that in a single-mode fiber (OMV). This facilitates alignment and alignment of the fibers — an important task for connector designers, as well as sources and receivers of light signals. In many ways, this is why IIM became the first type of fiber, which began to be used in communication networks - back in the early 80s of the last century. And only in the late 80s, when it became possible to provide centering with an accuracy of the order of a micron and laser diodes appeared, single-mode fiber became widely used in communication networks.
Typical optical fiber structure
But, despite the advantages of single-mode technology in terms of range and bandwidth, IIM remained the main type of fiber for most networks, including LAN, data center networks, etc. This is due to the cost advantages of multimode technology, due to the already mentioned simpler fiber alignment, the wide availability of low-cost radiation sources and other reasons.
')
The multimode has come a long way throughput improvements. It all started with LED emitters (LED) and megabit speeds. In the 90s, when higher speeds were required, LEDs began to give way to new low-cost light sources — VCSEL lasers with a wavelength of 850 nm, which are capable of modulating the signal much faster. This, in turn, led to the transition from an IWM with a core diameter of 62.5 μm (cable systems of class OM1) to fibers with a core of 50 μm (class OM2).
In the late 90s, the era of gigabit speeds. It took a further increase in bandwidth. It was provided by new multimode fibers, which were originally developed optimized for laser transmission (LOMMF). The first standard LOMMF fibers provided about four times the bandwidth than OM2 fibers. This is how a new class of fibers appeared - OM3, which opened the door to 10 Gigabit systems in the early 2000s.
The next stage is the development by the end of the decade of OM4 fiber with an even greater bandwidth ratio. This fiber provided a linear speed of 25 Gbps. In addition to increasing the linear speed, an increase in the number of fibers forming the communication channel was also required to achieve ever higher speeds. So, when using a linear speed of 10 Gbit / s, four fibers are needed to form a 40G channel (eight for duplex), 10 for fiber 100G (20 for duplex). When switching to a linear speed of 25 Gbit / s, the number of fibers for the 100G channel is proportionally reduced (up to eight for the duplex), but for the implementation of advanced 400G systems, 32 fibers are needed.
To simplify the organization and maintenance of multi-fiber systems, MPO group connectors have become increasingly used. The compact MPO design allows you to terminate 8, 12, 16 and more fibers in the space corresponding to the duplex connector LC. The high density of MPO makes it possible to deploy a preterminated cable system with a large number of fibers, eliminating the lengthy process of installing connectors in the field.
However, increasing the capacity of multimode systems by increasing the number of fibers is a path that has many disadvantages. Increasing the number of fibers increases the complexity of the system, imposes increased requirements on cable channels, means of laying fibers in the switching field, etc. At the same time, until recently, multimode technologies did not use an elegant way to increase throughput, which has long been known in the world of single-mode technology. We are talking about spectral compaction (WDM), when in a single fiber a multitude of spectral channels are formed at different wavelengths. Accordingly, the fiber capacity is multiplied by the number of such channels. In single-mode systems, dozens of spectral channels can be used.
Principles of Spectral Compaction (WDM)
Why was this seal not used in multimode technique? Everything is very simple. OM3 and OM4 fibers are optimized for laser transmission at the same wavelength - 850 nm. “Step to the left, step to the right” (according to the spectral scale) - the throughput of such a fiber drops sharply, and it is no longer suitable for transmitting high-speed flows. Therefore, to implement spectral compaction in the IIM, it was necessary to develop a new fiber capable of providing effective bandwidth in a relatively wide “window” of wavelengths.
The first samples of the new fiber appeared a few years ago. In the spring of 2015, at the Optical Fiber Communications (OFC) conference, Finisar and CommScope demonstrated the work of the WDM technology on the new IIM, known as broadband (BMS-IIM). The transmission of four spectral channels was shown (at lengths of 850, 880, 910 and 940 nm), each of which provided a throughput of 25 Gbit / s, and in the aggregate, 100 Gbit / s. The corresponding spectral compaction technology is called SWDM - Short Wavelength Division Division Multiplexing.
Even earlier, in the fall of 2014, CommScope, together with the same Finisar and a number of other companies, initiated in the TIA Association a project to develop a standard for new fiber. In June 2016, the subcommittee TR-42.12, which is responsible for the TIA Association for optical fibers and cables, approved the ANSI / TIA-492AAAE standard, which specifies WB-MMF. The document describes fiber optimized for laser sources, designed to transmit signals at one wavelength or at several wavelengths in the range from 850 to 953 nm. And a little later, in October 2016, at a joint meeting of the relevant committees of the ISO and IEC organizations, it was decided to classify BMS-IIM to the OM5 class.
The efforts of the cable cutters were picked up by the active network equipment manufacturers. The SWDM Alliance industrial consortium was jointly formed to develop specifications and promote the Shortwave Wavelength Division Multiplexing technology. (The founders of the SWDM Alliance were Commscope, Corning, Dell, Finisar, H3C, Huawei, Juniper, Lumentum and OFS.) The SWDM Alliance has already published two specifications for 40- and 100-gigabit Ethernet transmissions (40 GE SWDM4 and 100 GE SWDM4, respectively) . SWDM technology allows high-speed 40G and 100G channels to be implemented using just a pair of OM5 fibers. It also opens up the possibility of efficient implementation of 200G, 400G and 800G Ethernet channels based on multimode fiber.
Various options for the transmission of high-speed streams, including the use of SHP-MMV and spectral compaction (WDM)
So, the emergence of BF-IIM, or fiber class OM5, marks a significant breakthrough in the development of multimode technology. Now, high transmission rates (for example, 100G) can be realized with a significantly smaller number of fibers. In addition, the possibility of switching to higher speeds without the need to use additional fibers. In general, the technical progress is impressive, thanks to which the throughput of multimode fiber has increased 160,000 times, from 10 Mbit / s to potentially 1600 Gbit / s, while maintaining the main advantages of multimode - low cost.
Source: https://habr.com/ru/post/350098/
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