Shulou(Shulou.com)06/01 Report--

Rosenberg Asia Pacific Electronics Co., Ltd.: Li Ping

Preface

Science and technology change life, and informationization is a major trend in the development of the world today. Internet of things, cloud computing, big data and other emerging network information technology continue to innovate and apply, while in mobile Internet technology, 3G network is becoming more and more mature. 4GLTE network has been in pilot operation throughout the country since last year, and the speed of mobile Internet will step onto a new level. In this era of information industrialization, the city where we work and live is also transforming to a smart city, and all kinds of network applications are closely related to us. Whether it is the application of emerging technologies or the construction of smart cities, applications are inseparable from the basic network. The construction of the basic network is mainly based on the site, active terminals and interconnected equipment, as well as the basic interconnection channel of the network-wiring system. Wiring system needs to be installed on site, which is easily affected by environment, product quality, installation technology and other factors, which is the most important link to determine the quality of network transmission. The reliability of the wiring system not only depends on the quality supervision in the project, but also requires strict control of the last level and on-site acceptance testing.

The urgency of testing Technology Development

At present, most small and medium-sized cabling projects still use 10 gigabit as the backbone to achieve gigabit to desktop network architecture. However, with the rapid development of 3G/4G and Internet services, bandwidth has been unable to meet the needs of applications. 40G/100G for backbone links has become an inevitable trend for large-scale cabling projects, especially for enterprise data centers and Internet IDC data center projects. According to the IDC market report, it is expected that 40G/100G will gradually become the mainstream port speed after 2015.

Since the 40G/100G standard of 802.3ba was issued by IEEE in June 2010, the network of 40G/100G is mainly based on experimental network and has low requirements for field testing. After more than two years of system development and testing, the transmission technology of 40G/100G is becoming more and more mature, and major manufacturers have launched 40G/100G switching and routing equipment. Telecom long-distance backbone links use single-mode optical fiber system, while the integrated cabling system of buildings and data centers is mainly multimode OM3/OM4 optical fiber system for short-distance transmission, using 12-core MPO connectors and four-channel / ten-channel pre-connected optical cables. The pre-connected optical cable greatly reduces the installation time and labor cost, but how to quickly identify the optical fiber polarity and quickly and accurately test the attenuation of the link has become the primary problem of field testing.

Traditional optical fiber testing technology

First of all, let's review the original testing technology of gigabit and 10 gigabit optical fiber links. In 2003, TIA-526-14Mui A multimode cable installation optical intensity loss test standard officially defined the CPR (CoupledPowerRatio) optical coupling rate detection method, the light source is divided into five levels (as shown below), LED light source is a level 1 light source, VCSEL vertical cavity surface emitting laser light source is between level 3 and level 4, FP laser light source is equivalent to level 5 light source. At the same time, the test limit of optical loss is further improved. The maximum loss value of 1000BASE-SX applied to OM1 fiber is 2.6 dB and the maximum loss value of 10GBASE OM3 SR applied to OM3 fiber is 2.6dB. As a general standard for optical fiber link testing, this standard does not aim at specific network applications and emphasizes the detection of the normal state of optical signal transmission. It is recommended to use LED light source to test multimode optical fiber links, which can detect the worst case of optical fiber links. On the other hand, the laser-optimized VCSEL light source is used to detect the links of specific network applications, such as active devices using VCSEL light sources or the current network is ready to upgrade to use VCSEL light sources, the tested optical fiber loss value is closer to the real loss value of network applications.

The TIA-526-14Mura standard is cited by many related testing standards, such as ANSI/TIA/EIA-568-B,ISO/IEC11801,ISO/IEC14763-3 and so on. And ANSI/TIA/EIA568-B.1.7.1 and ISO/IEC14763-36.22 also specify the size and usage of 50/62.5um multimode fiber reels. The reel acts as a mode filter by winding the optical fiber, which reduces the high-order mode produced by the light source in the optical cable, reduces the difference of test results caused by different light sources, and improves the stability and repeatability of multimode fiber testing.

Test Model of 10GMPO Multi-core Optical Fiber

Compared with the traditional dual-core optical fiber using connectors such as LC,SC,ST, the MPO connector can support at least 12-core optical fiber, and the MPO connector is mainly used for pre-connected optical cables. Because there are 12-core channels in MPO fiber, TIA-568-C.0-2009B.4 analyzes the channel polarity in detail. For duplex transmission, there are mainly three kinds of polarity connection methods. All three methods are for a common goal-to create an end-to-end optical transceiver channel, but the three methods are not compatible, using different polarity connectors and adapters. For the compatibility and consistency of the whole link, consider using connectors and adapters with the same polarity as far as possible. for example, the polarity of the jumpers used is Amurb, and the type of adapters is KEYUP-KEYUP, otherwise different polarity will cause confusion in use, easy to make installation errors, and cause link failure. Therefore, in 10G fiber channel, the polarity of MPO backbone link mainly adopts class C mode (see figure below). The two ports intercommunicate with each other according to the corresponding number, and the optical channel adopts a pair of groups, cross-connection, such as 1m / m / m, forming a full-duplex transceiver channel. The left and right ends are converted to LC interface through the module box of MPO to LC, and then connect the equipment through LC jumper, which is mainly used in data center high-density cabling system.

Link under test:

Both ends are the schematic diagram of the backbone link of the MPO-LCA module (MPO1-12 ports correspond to LC1-12 ports).

1) set the benchmark: connect the light source output (LC) and the power meter input (LC) of the tester with a LC-LC test jumper.

2) unplug the optical power meter input jumper and connect it to another test jumper.

3) connect the tested optical fiber (the MTP-LC module box at both ends and the MTP-MTP pre-connected optical cable in the middle), and connect the LC test jumper to A module at both ends, one port at one end and two ports at the other.

4) record and save the loss value of the fiber channel currently being tested, then change the LC jumper of the light source end to 2 ports of A module, and the LC jumper of the optical power meter side to 1 port of A module on the other side, record and save until the loss test of 12 channels is completed.

Testing Technology of 40G/100GMPO Multi-core Optical Fiber

In 2010, the link standards of 40G/100G issued by 802.3ba are 40GBASE-SR4 and 100GBASEMAE SR10; connectors and adapters using MPO; the maximum transmission distance of OM3 fiber is 100m, and the maximum loss value is 1.9dB. The maximum transmission distance of OM4 fiber is 150m, and the maximum loss value is 1.5dB. 40G/100G links are mainly used for high-traffic data transmission in data centers. According to third-party statistics, 88% of the backbone links in data centers are no longer than 100m. Therefore, MPO pre-connected optical cable based on OM3/OM4 will become the first choice of 40G/100G link. Previously defined thresholds for 10G fiber link tests, such as 0.75dB for LC connectors, allow multiple connectors (greater than two), and 0.3dB for fusion points is no longer applicable. The new 40G/100G optical fiber backbone link will use pre-connected optical cable, and there are no fusion points and connectors in the link. We only need to consider the loss of the MPO connector at both ends and the loss of the optical cable itself, so as to reduce the loss of the connector as much as possible and ensure that the attenuation of the whole link is within the requirements of the new standard.

The two key factors affecting 40G/100G transmission are light source and optical fiber link loss. The more stringent loss requirements pose a challenge to the traditional testing methods of LED light source. The original LED light source has low output power, large divergence angle and large connector loss, so it adopts the method of overfull injection (OFL-OverFilledLaunch). However, using the finite injection method (UFL-UnderFilledLaunch) of VCSEL light source, the optical channel of near-field intensity is concentrated in the central range, the transmission mode in the center of optical fiber is less, and the divergence angle is small, which effectively solves the disadvantages of LED light source. However, the original standards such as IEEE802.3,ANSI/TIA and ISO/IEC only define the LED light source, taking into account the price factors, and the optical power distribution of VCSEL from different manufacturers is quite different, so the new standard for 40G/100G testing does not use VCSEL light source to define. Similarly, ISO/IEC14763-3 issued in 2006 defines the power distribution method of MPD (ModalPowerDistribution) mode. Although the coupling strength is improved by waveguide array, it can not meet the needs of 40G/100G transmission.

In October 2010, ANSI/TIA-526-14Mel B replaced ANSI/TIA-526-14Mel An and defined the test method of annular flux of EF (EncircledFlux) light source. This method is also defined in IEC61280-4-1 standard. EF restricts the emission conditions of the multimode light source through the mode regulator, filters the optical signal of the higher mode, and uses the jumper of the alternative EF controller to replace the normal test jumper that uses the multimode reel (see figure below). When the tested optical fiber connector and the test equipment connector are the same, one or three test jumpers can be used; when the tested optical fiber connector and the test equipment connector are different, use three test jumpers; the test jumper is at least 2 meters, no more than 10 meters. The annular flux can reduce the measurement deviation of the loss from ±40% to ±10%, thereby reducing the uncertainty of the measurement and improving the repeatability of each measurement.

40G/100GMPO Optical Fiber Test Model

A standard MPO/MTP link consists of two MPO jumpers at both ends, two MPO adapters and MPO's pre-connected backbone fiber optic cable. In TIA-568-C.0-2009B.4, two modes An and B are given for parallel multichannel transmission (see figure below, Table5).

In order to ensure the compatibility and singleness of the link, the construction and maintenance is more convenient, especially the MPO jumper which is often plugged and replaced, in the 40G/100G cabling system, mode B will be more adopted. The number of channels of 40G and 100G is different, but their transmission link model is the same, both use MPO/MTP interface for end-to-end transmission. Therefore, we take the 40G single-channel transmission as an example, we should pay attention to the port types of pre-connected optical cables and jumpers-with guide pin (male) and without guide pin (female).

Tested MPO link (mother-to-mother):

Traditional MPO multi-core fiber test model-light source and optical power meter with LC interface

1) setting datum: use 3-segment optical fiber jumper and 2 LC adapters for reference setting, and the light source output port uses multi-mode reel, as shown in the following figure.

2) remove the LC short jumpers between the middle two LC adapters, add two LC-MPO (male) multi-core short jumpers respectively, and connect the first pair of LC to test the first and second ports of MPO, as shown in the following figure.

3) the optical fiber link of the tested MPO is connected, tested, and the attenuation values of the first and second ports of MPO are obtained and saved.

4) disconnect both ends of the LC adapter and the multicore LC-MPO (male) jumper, and test the attenuation of the remaining 5 pairs of links according to Class B polarity.

It can be seen that the link test of 40G/100G using the light source and optical power of the LC interface requires the sector jumper from the MPO to the LC, the jumper at the output end of the light source must be equipped with a multi-mode scroll, and each test channel needs to be benchmark set. Therefore, the operation of this method is complicated, each MPO link needs to be tested 12 times, and it takes a lot of time in large-scale testing.

The latest test model of MPO multi-core optical fiber-light source and optical power meter with MPO interface

At present, there is optical fiber field test equipment with MPO interface on the market, with EF control light source, which can better meet the field test of MPO optical fiber link. By using the MPO interface adapter and the MPO reference jumper and setting the corresponding link attenuation gate threshold, the benchmark setting and attenuation test of 12 links can be carried out at one time, and the polarity of MPO optical fiber can be detected and reported automatically. You need to pay attention to whether the MPO link connector under test has a guide pin (male / female), that is, there are no guide pins at both ends (female-female), there are guide pins at both ends (male-female), and there are guide pins at one end and no guide pin at the other end (male-female). Select the appropriate benchmark jumper to set the benchmark. The following is tested with the most common MPO fiber link model with no guide pins at both ends, that is, with female heads at both ends.

Tested MPO link (mother-to-mother):

1) setting benchmark: use 1 MPO (male-male) test jumper to connect the light source and the optical power meter to conduct the benchmark test.

2) disconnect the jumper at the end of the optical power meter, and then connect to a MPO test jumper.

3) access the tested type B optical fiber link, test the optical fiber polarity and the loss of 12 channels, and save the test results.

4) repeat steps 2) through 3) to test the next MPO (mother-to-mother) fiber link.

Concluding remarks

The original 10GMPO testing model is no longer suitable for future 40G/100G testing needs. The light source and optical power meter of LC interface greatly increase the testing times and time of MPO optical fiber link. A complete test of a 12-core MPO backbone link takes nearly ten minutes, and the test stability is poor. Therefore, it is necessary to use the test instrument with MPO interface for testing. At the same time, EF loop flux control replaces multi-mode reel, which increases the stability and reliability of optical fiber link test. The mode of 100G transmission using ten-channel transceiver and ten-channel transmission is more complex. The IEEEP802.3bm40G/100G working group will improve the 100G transmission mode, and the original ten-channel transceiver mode will be replaced by four channels. As the next generation of 40G/100G, the Ethernet transmission standard of up to 400G will be launched next year and is expected to use OM4 optical fiber. The optical fiber link of MPO interface will be deployed more and more widely in the future, which is no longer limited to high-end users such as telecom operators and data centers. Understanding the transmission model and testing technology of MPO optical fiber link will help us to better control the future 40G/100G high-speed communication transmission channel.

References:

[1] TheneedforEncircledFlux,realorimaginaryAdrianYoung

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