Optical Loss Testing - Why It Is Important

The Concept of Optical Loss Testing

Optical loss testing is very necessary to evaluate the performance of fiber optic components, cable plants and systems. As the components like fiber, connectors, splices, LED or laser sources, detectors and receivers are being developed, testing confirms their performance specifications and helps understand how they will work together. Designers of fiber optic cable plants and networks depend on these specifications to determine if networks will work for the planned applications.

Providing an accurate method for optical loss testing of multimode fiber is becoming a lot more important for higher data rate applications that place more stringent requirements on the maximum allowable loss for a channel between an optical transmitter and an optical receiver. The higher the data rate, the tighter the loss budget for a channel. The maximum allowable loss for a 10Gb/s Ethernet channel over OM3 multimode fiber is 2.6 dB. The maximum allowable loss for a 40 Gb/s and a 100 Gb/s Ethernet channel is 1.9 dB over OM3 fiber and 1.5 dB over OM4 fiber.

Ethernet	OM3 IL max.(dB)	OM4 IL max.(dB)
1000BASE-SX	4.5	4.8*
10GBASE-SR	2.6	3.1*
40GBASE-SR4	1.9	1.5
100GBASE-SR10	1.9	1.5

Factors That Affect The Accuracy of Optical Loss Testing

Optical loss testing of multimode fiber can be affected by many factors, among which there are several major factors that can affect the testing accuracy for optical loss measurements. These include:

1.The type and quality of the “test reference cords”
The type and quality of the “test reference cord” is critical for accurate optical loss measurements in the field. The end-face geometry of the polished ferrule on the cord connector can have a significant effect on the test results and must meet precise parameters such as radius of curvature, apex and fiber protrusion.

2.Fiber mismatch between the test reference cords and the link under test
Fiber mismatches are the result of inherent fiber characteristics and are independent of the techniques used to join the two optical fibers. The intrinsic coupling loss due to fiber mismatch include core diameter differences, core/cladding concentricity error, numerical aperture differences.

3.The characteristics of light source and how light is coupled into the fiber
The launch conditions and how light is coupled into the fiber can have the greatest effect on optical loss measurements. For multimode fiber, different distributions of launch power (launch conditions) can result in different attenuation measurements.

Testing Tools

Various types of testing equipment are available on the market, such as a fiber visual fault locator (VFL), a fiber power meter, a network cable tester or an optical time-domain reflectometer (OTDR).

Fiber optic cable testing needs special tools and instruments. And they must be appropriate for the components or cable plants being tested. The following five kinds of fiber testing tools are needed for the testing work.

• OLTS—Optical loss test set (OLTS) with optical ratings matching the specifications of the installed system (fiber type and transmitter wavelength and type) and proper connector adapters. Power meter and source are also needed for testing transmitter and receiver power for the system testing.
• Reference test cable—This cable should be with proper sized fiber and connectors and compatible mating adapters of known good quality. And the connector loss is less than 0.5 dB.
• VFL—Visual fiber tracer or visual fault locator (VFL)
• Microscope—Connector inspection microscope with magnification of 100-200X, video microscopes recommended.
• Cleaning Materials—Cleaning materials intended specifically for the cleaning of fiber optic connectors, such as dry cleaning kits or lint free cleaning wipes and pure alcohol.

Conclusion

Optical loss testing is not as simple as it seems and can be affected by many variables, including fiber mismatch, the type and quality of the test reference cords and the launch conditions (OFL/Mandrel wrap versus Encircled Flux). The more stringent optical loss requirements for high speed applications necessitate an accurate test method for testing links in the field. FS.COM offers a wide selection of fiber testers & tools to fit any fiber optic cable lineman or powerline worker jobs. We stock top high quality test equipment for the communications applications. In the fiber optic installation and maintenance works, Optical Power Meters, Fiber Light Sources, Fiber Scopes and OTDR are commonly used for fiber optic testing. And Splicing fiber tools, termination tool kits and cleaning tools, like strippers, cable cutters, splice protective sleeves help work easier. Besides, high quality fiber cables, such as MPO cable, Push-Pull LC cable and so on are also available for your choice.

Reference: http://kellyzeng.inube.com/blog/4748262/optical-fiber-loss-testing/

24-fiber MPO/MTP Solution for 40/100G Migration

Since IEEE 802.3ba 40GBASE-SR4 and 100GBASE-SR10 were ratified in 2010, 24-fiber connectivity has been adopted as the ideal migration solution in the data center. Using 24-fiber cabling throughout an entire channel provides extra flexibility, as users can easily migrate from 10G to 40G or 100G by simply swapping out the connectivity at the end of the channel. Pre-terminated cabling using 24-fiber connectors provides double the density of 12-fiber cabling in the same footprint, reducing the cabling required, allowing for fewer cable pathways, and improving airflow in data centers. Next we will take a closer look at the advantages of 24-fiber MPO/MTP solution in 10G to 40/100G migration.

In choosing the migration path from 10G to 40/100 G, there are generally two options: the 12-fiber MPO/MTP solution or 24-fiber MPO/MTP solution. A 12-fiber MPO/MTP connector is used for 40 GbE (data rate up to 40Gbps, 4 x 10 Gbps). But among the 12 fibers, only 8 optical fibers are required—4 for Tx and 4 for Rx, and each channel has a transmission rate of 10 Gbps (usually use the 4 left and 4 right optical fibers, and the inner 4 optical fibers are left unused). And for 100 GbE (data rate up to 100 Gbps, 10 x 10 Gbps or 4 x 25 Gbps), there are two solutions. One is to use two 12-fiber MPO/MTP connectors, one transmitting 10 Gbps on 10 fibers and the other receiving 10 Gbps on 10 fibers. The other is to use a 24-fiber MPO/MTP connector. Among the 24 fibers, only 20 fibers in the middle of the connector are used to transmit and receive at 10 Gbps and the 2 top and bottom fibers on the left and right are unused. Why the 24-fiber is superior to 24-fiber? We’ll see the advantages from the following aspects.

Maximum Fiber Utilization

Using 24-fiber trunk cables with 24-fiber MPO/MTP connectors on both ends to connect from the back of the switch panel to the equipment distribution area can maximum the fiber utilization. For 10G applications, each of the 24 fibers can be used to transmit 10 Gbps, for a total of 12 links. For 40G applications, which requires 8 fibers (4 Tx and 4 Rx), a 24-fiber trunk cable provides a total of three 40G links. For 100 GbE, which requires 20 fibers (10 Tx and 10 Rx), a 24-fiber trunk cable provides a single 100G link (24-fiber solution is the more recommended configuration to used for 100 GbE than 12-fiber solution). This recoups 33% of the fibers that would be lost with 12-fiber trunk cables, providing a much better return on investment.

Reduced Cable Congestion

24-fiber trunk cables provide more amount of fiber in less space. For instance, it takes three 12-fiber trunk cables to provide the same number of links as a single 24-fiber trunk cable—or about 1-1/2 times more pathway space for a 40G application.

Increase Fiber Density

Density in fiber switch panels is critical as today’s large core switches occupying upwards of 1/3 of an entire rack. 24-fiber MPO connectors offer a small footprint which can ultimately provide increased density in fiber panels at the switch location. In addition, with fanout technology, a 24-fiber MPO cable can be designed with a 24-fiber MPO on one end and 12 duplex LCs on the other end which is an ideal solution for high density 40/100 GbE migration.  

Simple and Cost-effective

24-fiber MPO/MTP solution is a simple and cost effective migration path from 10G to 40/100G Ethernet. It effectively supports all three applications—10, 40 and 100 GbE. Data center managers can easily migrate to higher speeds, with less time and complexity, as 24-fiber solution offers guaranteed performance for 10, 40 and 100G applications, upgrading the cabling infrastructure is as simple as upgrading the fan-out cables or cassettes and fiber patch cords to the equipment.

24-fiber MPO/MTP solution provides an efficient way to migrate your network from 10 to 40 and 100 GbE. Choosing the right migration path not only helps you reach maximum benefit but also cut down the expenditures. Of course, choosing a good vendor is also a must. Fiberstore (FS.COM) may be your good choice. For more information, please contact us via sales@fs.com.

Connectivity Options for 10 Gigabit Ethernet

Since March 1999, the Ethernet industry has been working on providing solutions to increase the speed of Ethernet from 1 to 10 gigabits per second. For enterprise LAN applications, 10 Gigabit Ethernet enables network managers to scale their Ethernet networks from 10 Mbps to 10,000 Mbps, while leveraging their investments in Ethernet as they increase their network performance. There are various types of cables and transceivers available for making Ethernet connections at speeds of 10 Gigabit per second. This article will illustrate both the copper and fiber connectivity options for 10 Gigabit Ethernet.

Transceivers

Standards bodies initially offered several options for the 10-Gigabit transceiver. The one that ultimately evolved as most popular in commercial data center usage was the XFP transceiver. In recent years an extension of the SFP transceiver was standardized for use with 10 Gigabit Ethernet and named SFP+. SFP+ has three outstanding advantages. First of all, it was smaller than the XFP form factor allowing for much more dense packaging of ports on (primarily) switches. Secondly, a new type of very short distance copper cable was developed which uses the same mechanical form factor as the optical transceiver and is capable of carrying 10Gbps Ethernet data. This cable type is called direct attach copper cable which will be introduced later. SFP+ has now become the predominant 10G Ethernet connector type.

Fiber Cables

Fiber cables consist of the cable itself and the connectors on the ends. There are multiple choices for cable type and for connector type. The difference in cable choices come from the distance limitations encountered with the various types of optical transmission. The commonly available types of fiber cables include: SR for connections of up to 300 m in length, LR for connections of up to 2 km in length and ER for connections of up to 10 km in length.

Copper Cables

• 10GBASE-T
  For 10-Gigabit Ethernet cabling, the standards body determined that even enhanced Cat5e UTP traditional Ethernet cable would not be able to carry the signal reliably for any significant distance. So a new specification which still uses RJ45 connectors was introduced and is commonly referred to by its standards name 10GBASE-T. It calls for a 4-wire twisted pair cable with even more strinent limitations on cross-talk.
• CX4
  CX4 is a cable type generally associated with an alternative networking technology called InfiniBand. CX4 cable can also be used in 10Gigabit Ethernet connections. It uses a coaxial copper cable and can support cable lengths of up to 15m.
• SFP+
  As discussed above, one of the advantages of the SFP+ connector type was that a new type of very-short-distance copper cable was developed which uses the same mechanical form factor as the optical transceiver and is capable of carrying 10Gbps Ethernet data. This cable type namely SFP+ direct attach copper cable is a fixed assembly that is purchased at a given length, with the SFP+ connector modules permanently attached to each end of the cable. It provides high performance in 10 Gigabit Ethernet network applications, using an enhanced SFP+ connector to send 10 Gbps data through one paired transmitters and receivers over a thin twinax cable.

To conclude, 10 Gigabit Ethernet has become the technology of choice for enterprise, metropolitan, and wide area networks. Choosing the right kind of connectivity options helps you ensure the proper and efficient performance of your networks. Fiberstore offers various kinds of fiber optical transceivers for 10 Gigabit Ethernet, such as the HP J9151A, NETGEAR AXM761 SFP+ transceiver and so on. Besides, cables for 10 Gigabit Ethernet can be customized according to your special requirements. 

QSFP+ Optics for High-Density 40GE Connectivity

With the development of the SFF-8436 Multi Source Agreement, many vendor are now offering a variety of IEEE- and MSA-compliant Quad Small Form-Factor Pluggable Plus (QSFP+) devices for fiber networks. And there are basic three 40G QSFP+ optics for this standard: 40G LR4 QSFP+ transceiver, 40G SR4 QSFP+ transceiver and 40G LR4 parallel single mode (PSM) transceiver. This article will take a close look at these 40G QSFP+ optics for high-density 40 GE connectivity.

40G LR4 QSFP+ Transceiver

Conforming to the 802.3ba (40GBASE-LR4) standard, the 40G LR4 QSFP+ transceiver together with the LC connector can support an optical link length up to 10 kilometers over single mode fiber. For example, the following Juniper JNP-QSFP-40G-LR4 compatible 40GBASE-LR4 QSFP+ transceiver offers 4 independent transmit and receive channels, supporting link distance of 10 km over single mode fiber. In the process of transmitting, this kind of transceiver has to introduce MUX/DEMUX to multiplex/de-multiplex optical signals.

The working principle of this kind of QSFP+ transceiver is : in the transmit side, four 10 Gbp/s serial data streams are passed to laser drivers. The laser drivers control directly modulated lasers (DMLs) with wavelengths. the output of the four DMLs are optically multiplexed to a single-mode fiber through an industry-standard LC connector. In the receive side, the four 10 Gbp/s optical data streams are optically de-multiplexed by the integrated optical demultiplexer; then, each data steam is recovered by a PIN photodetector/transimpedance amplifier and passed to an output driver.

40G SR4 QSFP+ Transceiver

The 40G SR4 QSFP+ transceiver, conforming to the 802.3ba (40GBASE-SR4) standard, provides a 40G optical connection using MPO/MTP fiber ribbon connectors. Unlike the 40G LR4 QSFP+ transceiver, this kind of transceiver are used together with multi-mode fiber, supporting with a link length up to 100 meters on OM3 cable and 150 meters on OM4 cable.

The operating principle of the 40G SR4 QSFP+ Transceiver is : the transmitter convertsparallel electrical input signals into parallel optical signals through the use of a laser array. Then the parallel optical signals are transmitted parallelly through the multi-mode fiber ribbon. Reversely, the receiver converts parallel optical input signals via a photo detector array into parallel electrical output signals.

40G LR4 Parallel Single Mode (PSM) Transceiver

40G PSM transceivers are used to provide support for up to four 10Gb Ethernet connections on a QSFP+ port over single mode fiber. These transceivers support distance of up to 10 kilometers over single mode fiber using an 8 parallel fiber MPO interface. Each fiber pair can be broken out to a 10Gb Ethernet connection, compatible with up to four 10GBASE-LR interfaces. The MPO to 4 x LC single mode fiber patch cord can be used to breakout the 4 fiber pair of the MPO parallel connector to 4 separate fiber pairs.

Summary

To sum up, 40G SR4 QSFP+ transceivers are suitable for short-distance transmissions. So they are often used in data centers to interconnect two Ethernet switches with 12 lane ribbon OM3/OM4 cables. while 40G LR4 QSFP+ transceivers and 40G LR4 PSM transceivers are often used in long-distance transmission applications. Fiberstore offers a wide range of 40G QSFP+ transceivers, like 40GBASE-SR4, 40GBASE-LR4, 40GBASE-CR4 QSFP+ transceivers, etc. Besides, we also provide 40G direct attach cables, such as Juniper QFX-QSFP-DAC-1M, Cisco QSFP-4X10G-AOC3M and so on.

Reference:http://www.fiber-optic-transceiver-module.com/basic-40g-qsfp-optics-for-40g-transmission.html