With the rapid growth of network data traffic, in recent years, the relevant standards for multimode fiber and its applications have continued to upgrade. Ethernet rate upgrade from 10GbE / 40 GbE / 100 GbE to 25 GbE / 50 GbE / 200 GbE / 400 GbE, and in the future will be upgraded to higher speed 800 GbE / 1.6 TbE; Fibre Channel rate from 8GFC / 16FC to serial 32GFC / 64GFC and parallel 128GFC / 256GFC, as well as higher-speed serial 128GFC and parallel 512GFC in the future. At the same time, multi-mode optical module technology has gradually evolved from NRZ coding to 4-level PAM4 signal coding; from single-wavelength light sources to multi-wavelength multiplexing, such as 2-wave multiplexing BiDi technology, 4-wave multiplexing SWDM technology, and future Possible 8 wavelength multiplexing. In addition, multimode fiber has the potential for MDM, which increases transmission capacity by taking advantage of multiple available modes in multimode fiber.
1. Current status of cabling applications in data centers
In recent years, the demand for data center networks has continued to grow. According to Cisco statistics and predictions, the overall annual growth rate of global data center traffic from 2015 to 2020 will be a compound annual growth rate of 27%, of which the cloud data center annual growth rate will be 30%. % Stable growth.
At present, most data center wiring schemes use copper, short-distance multimode optical devices, and long-distance single-mode optical devices. Multi-mode SR4 and single-mode PSM4 solutions dominate. One of the most critical indicators of internal cabling selection in the data center is cost, and the solution with the lowest cost is often the most advantageous. Therefore, SR is used for distances of hundreds of meters, and LR is used for long distances of more than 2 kilometers. Alibaba currently uses 100GBASE-SR4 multimode fiber connection in its network and finds that it is more cost-effective than the connection method based on single mode fiber and PSM4 or CWDM4. Given the scale, architecture, network capacity, and storage requirements of the enterprise's local data center, multimode fiber and VCSEL will remain the primary solutions in this important market.
2. OM5 fiber manufacturers and SWDM alliance
OM5 optical fiber extends the bandwidth performance of traditional OM4 optical fiber at 850nm to 953nm, using 4-wavelength short-wavelength division multiplexing (SWDM4) technology to simultaneously transmit four wavelengths on a multimode fiber to increase the transmission capacity of the multimode fiber to the original 4 times, while fully backward compatible.
As a new technology that can greatly increase the transmission capacity of multimode fiber and increase the transmission distance, SWDM is self-evident for the construction of data centers and related fiber, device and equipment manufacturers. At present, the alliance members include optical fiber and wiring manufacturers such as YOFC, Corning, OFS, Prysmian, CommScope, etc., and also include equipment manufacturers such as Dell, Huawei, Huasan, Juniper and module manufacturers such as Finisar and Lumentum. The alliance released the Multi-Source Agreement (MSA) in March 2017, defining the application requirements of 40GE SWDM4 and 100GE SWDM4, and stated that it will further expand to 400Gb / s applications in the future.
3. OM5 fiber related standards update progress
OM5 fiber is built on the basis of OM3 / OM4 fiber, and its performance is extended to support multiple wavelengths. OM5 shows the future of sustainable development of multimode fiber systems. Since 2015, several major international standards organizations have added specifications for OM5 fiber and its applications.
3.1TIA and IEC
The Telecommunications Industry Association (TIA) was the first to officially release the TIA-492AAAE fiber standard in June 2016, which defines a broadband multimode fiber (WBMMF) that can support wavelength division multiplexing technology in the 850 ~ 950nm band. In October 2016, ANSI / TIA-568.3-D optical fiber structured wiring standard was released, and TIA-492AAAE optical fiber was approved for wiring.
The International Electrotechnical Commission (IEC) officially released the IEC 60793-2-10 ed. 6 fiber standard in August 2017, defining WBMMF as A1a.4 fiber type, and received ISO / IEC support for 11801. ed. In November 2017, the ISO / IEC 11801-1 optical fiber wiring standard was officially released, and the name of this optical fiber wiring was determined to be OM5.
3.2 IEEE 802.3
The IEEE 802.3bs standard, drafted in September 2016 and officially released in December 2017, defines the media access control parameters, physical layer and management parameters of 200Gb / s and 400Gb / s Ethernet, which is also formal for broadband multimode fiber wiring It is named "OM5" and specifies the shortest link distance that OM3 / OM4 / OM5 three-type fiber can support in 400GBASE-SR16 system, as shown in Table 1.
Table 1 The shortest link distance that OM3 / OM4 / OM5 three types of optical fiber can support in 400GBASE-SR16 system
In November 2016, the draft of the IEEE 802.3cd standard disclosed media access control parameters, physical layer, and management parameters for 50Gb / s, 100Gb / s, and 200Gb / s Ethernet, and stipulated that OM5 fiber can support more than 100 meters. 50GBASE-SR, 100GBASE-SR2 and 200GBASE-SR4. Its official standards are still under discussion and are scheduled to be released in 2018.
In November 2017, IEEE 802.3 established the next-generation 200Gb / s and 400Gb / s multimode fiber physical layer research group, which aims to use less multimode fiber than existing Ethernet to achieve 200Gb / s and 400Gb / s systems. Transmission, referred to as "NGMMF Study Group". At the first formal meeting of the study group held in January 2018, two options of 400GBASE-SR8 or 400GBASE-SR4.2 were proposed to replace 400GBASE-SR16 to support 400G Ethernet. The 400GBASE-SR8 solution uses 8 pairs of optical fibers, which can make full use of the advantages of the existing technology (using VCSELs that are more friendly to PAM4). The target wavelength is 850nm. There are currently several optical module packages for QSFP-DD, OSFP, and COBO 8-Lane. The 400GBASE-SR4.2 solution uses 4 pairs of optical fibers and maintains the same wiring method as the existing 100 GBASE-SR4 solution. Each fiber transmits 2 wavelengths. The PAM4 modulation technology is also used. The target wavelength is 850nm and a longer wavelength. Light source. The 400GBASE-SR4.2 solution is more suitable for wiring using OM5 fiber that can support multiple wavelengths.
4. Application and future development of OM5 fiber
The original intention of OM5 fiber design is to meet the wavelength division multiplexing (WDM) requirements of multimode transmission systems. Therefore, its most valuable application is in the field of shortwave wavelength division multiplexing. Currently, single-wavelength 50Gb / s multi-wavelength optical modules based on multimode fiber are mostly still in the research and development stage. Only a few optical module manufacturers can provide a small number of samples, but only for internal experiments. PAM4 modulation can provide a single-wave rate of 50Gb / s based on the existing 25Gb / s VCSEL. Two-wavelength bidirectional (BiDi) technology and four-wavelength multiplexing (SWDM4) technology reduce the amount of fiber used by one-half and three-quarters for high-speed Ethernet links above 100Gb / s, respectively.
The researchers found that by incorporating appropriate fluorine elements in the core layer of the optical fiber, the difference in optimal alpha value corresponding to different wavelengths can be reduced, so that the bandwidth of the "ultra-wideband multimode fiber" in the entire wavelength range of 850 ~ 1050nm can be improved. This result proves that "Ultra-Broadband Multimode Fiber" has the ability to support 8 wavelength-division multiplexing channels with an interval of 30nm in the 850 ~ 1050nm window.
In the past three years, various optical fiber manufacturers and optical module manufacturers have reported the latest transmission results of OM5 and "ultra-wideband multimode optical fiber" under the support of PAM4 modulation technology and wavelength division multiplexing technology, as shown in Table 2. From the reported experimental results, OM5 fiber is sufficient to support 100Gb / s, 200Gb / s and 400Gb / s multi-wavelength transmission systems over 150 meters.
In addition, through optimized design, the 50μm core diameter multimode fiber can obtain a lower differential mode group delay (DMGD) than the low mode fiber in the 1550nm window for multiple input-multiple output (MIMO) mode division multiplexing (MDM) ) In the system, thereby increasing the capacity of the optical fiber several times, which proves the potential of multi-mode optical fiber for modular division multiplexing in the future.
Latest reported PAM4 transmission experiment progress
Conclusion
Multimode fiber has always been an efficient and flexible transmission medium, and the continuous development of new application potential of multimode fiber can adapt it to higher speed transmission networks. Multimode fiber with VCSEL has the advantages of low link cost, low power consumption, and higher availability, making it the most cost-effective data center solution for most enterprise customers. The continuous and stable growth of demand for cloud data centers and enterprise local data centers provides a broad market prospect for cost-effective multimode fiber solutions. The OM5 fiber solution defined by the new industry standard is optimized for multi-wavelength SWDM and BiDi transceivers, providing longer transmission links and network upgrade margins for high-speed transmission networks above 100Gb / s.
