Multi-mode or Single-mode Optics for 40GbE Network

To back the changing and fast-growing bandwidth demands of data center, in 2010, the IEEE ratified 40 Gigabit and 100 Gigabit standards, known as IEEE 802.3ba. 40G and 100G Ethernet can be deployed using the same cabling systems today. Both single-mode (SMF) and multi-mode (OM3,OM4) were approved to be utilized in the standard. Multi-mode deploys parallel optics with MPO/MTP interconnects while single-mode fiber will employ serial transmission and use LC or SC connectors. Which cabling options designers should choose for their infrastructure. This article today will provide some practical suggestions to help you make a wise selection. Table 1 shows the comparison between SMF and MMF for 40/100 GbE Implementations.

40GbE Over Multi-mode Fiber
40GbE and 100GbE over multi-mode optics use parallel optics at 10Gbps lasers, simultaneously transmitting across multiple fiber strands to achieve high data rates. Because of the multi-lane nature of these optics, 40GbE multi-mode optics use a different style of fiber cabling, known as MPO or MTP cabling. An MPO/MTP cable presents 12 separate strands of multi-mode fiber in a single ribbon cable. Just as 10GbE optics over multi-mode fiber, an OM3 or OM4 grade MMF is needed to cover longer distances for 40G network.

OM3 and OM4 MMF are laser-optimized fiber with a core size of 50/125 micron. These 50-micron fibers are optimized for the 850nm transmission of VCSEL-based transceivers. These two fibers have different bandwidths, which results in different achievable lengths for the same transceivers. OM4 fibers, according to the TIA-492AAAD, have higher network reliability and increased design flexibility allowing links with a reach of 150 meters. The IEEE 802.3ba standard specified OM3 fiber with a maximum reach of 100 meters. Take Cisco QSFP-40G-SR4 QSFP+ as an example, it can support a distance of 100m and 150m over OM3 and OM4, respectively. The following image shows a 40G-SR4 and 40GBASE-LR4 QSFP+.

Since we can deploy both OM3 and OM4 MMF for our 40G infrastructure, which one is more suitable? In fact, some senior engineers say that installing either OM3 or OM4 cabling in the data center largely depend on length requirements. They determined that OM4 fiber would substantially extend the reach of next generation networking within the data center and it is able to achieve this greater reach because of its greater EMB over OM3 fiber. OM4 optical fiber enables 40/100G Ethernet to reach an additional 60% of the links in the core-to-distribution and in the access-to-distribution channels when compared to OM3. This should lead to faster market acceptance of 40G/100G Ethernet and OM4 fiber.

40GbE Over Single-mode Fiber
40GBase-LR4 optics use the same multi-lane technology as SR4 optics using four strands for transmit and four strands for receive. But with one exception. Instead of using a single fiber strand for each lane, WDM technology is used to multiplex all four transmit lanes onto one strand of fiber and all four receive lanes onto another single strand of fiber, allowing any existing single-mode fiber installation to be used. Because of this, standard LC (for QSFP modules) or SC (for CFP modules) connections are used, allowing for an easy upgrade from a 10GbE connection. The channel cost for 40GBASE-LR4 is much higher than SR4 optics, which is the main factor that limits its popularity. However, 40GBASE-LR4 like Cisco QSFP-40G-LR4 can reach up to 10km.

Conclusion
After going through this article, do you have any idea of choosing which cabling for your 40G network. If you have tight budget and cover a short transmission distance, laser-optimized multi-mode cabling would be the prefect choice. But if you prefer to deploy a high-density long-reach network, single-mode cabling will suit you better. Fiberstore manufactures a large variety of 40G transceivers and cables. You can find what you need here. Please contact us if you are interested.

How to Minimize the limitations on the Transmission Distance

Transmission distance is the NO.1 factor that designers would take into account when deploying network because the exact transmission distance that fiber optic can support is usually limited by many factors. How to avoid this situation? Is there a method that can help us to achieve long transmission distance? This article today will pay attention to the factors that limit optical transmission distance and provide some practical solutions accordingly.

Optical Cable Type
The maximum transmission distance of fiber optic cable (single-mode or multi-mode fiber) is typical limited by dispersion. Multi-mode transmission is affected by the modal dispersion, while single-mode fiber is limited by chromatic dispersion. The core of the single-mode fiber optic is much smaller than that of multi-mode fiber. That’s why single-mode can transmit over longer distance than multi-mode fiber. Most designers should attach importance to review the specifications and limitations of transceivers and have them work optimally in their devices. Then it is highly recommended that we use multi-mode fiber optic transceivers for shorter distances and single-mode fiber for long distance transceivers. Take QFX-QSFP-40G-SR4 as an example, it is the compatible Juniper 40GBASE-SR4 QSFP+ transceiver that operates over multi-mode fiber. Although our application may call for an long reach, we can only use multi-mode fiber on this module for a distance of 150m. If you use an single-mode fiber on this transceiver, it may cause an error.

Light Source of Fiber Optic Transceiver
Optical signals must be converted into electronic signals over the optical transceiver because most of the devices are electric based. And the conversion between them is largely depend on a LED (light emitting diode) or a laser diode inside the optical transceiver. Fabry Perot (FP) laser, Distributed Feedback (DFB) laser and Vertical-Cavity Surface-Emitting (VCSEL) laser are the common type of light source inside the transceiver module that may have an impact on optical transmission distance. Table 1 present a comparison between these light sources, which would be a factor that designers should take into account when picking an optical transceiver to achieve long transceiver distance.

Splice and Optical Connectors
The signal loss can be caused when passing through fibers or connector, which will largely affect the transmission distance. Fusion splicing is the method of joining two optical fibers end-to-end using heat. Alternatives to fusion splicing include using optical fiber connectors or mechanical splices both of which have in general higher insertion losses, lower reliability and higher return losses than fusion splicing. Network designers nowadays choose to use fusion splicing because the goal of such a way that optical signal passing through the fibers is not attenuated or reflected back by the splice. In other word, fusion splicing will have less effect in the transmission distance that fiber optic cable can support. Here are some tips for fusion splicing that may help you.

1. Clean the fiber
2. Stripping the coating off the two fibers that will be spliced together
3. Cleaning of the stripped fiber
4. Each fiber must be cleaved so that its end-face is perfectly flat and perpendicular to the axis of the fiber
5. Aligning of two end-faces of the fibers. This is normally done by the splicing machine by means of: fixed V-groove, optical core alignment, cladding alignment or local injection and detection of light (LID)
6. The two fibers are fused together
7. Check mechanical strength of the splice (normally done by the splicing machine)
8. The bare fiber area around the splice is protected with a splice protector and use the same batch of high quality bare fiber on a route
9. Choose installers who have adequate training and rich experience in fiber connection

As noted above, the optical transmission distance is affected by a variety of factors, like fiber optic cable type, light source of transceiver, and splices and connectors. Frequency of transmission and bandwidth should also be considered to minimum the limitations on the transmission distance. I hope all the suggestions that I have provided above can help you to achieve long transmission distance. Fiberstore offers a variety of high-quality fiber optic cable and optical transceiver modules (like the popular 40G QSFP) that are fully tested. Meanwhile, components like repeater and optical amplifiers are also useful to support the long distance transmission. If you have any interest in our products, please contact us directly.

Reference:
http://www.cisco.com/c/en/us/products/collateral/interfaces-modules/transceiver-modules/white_paper_c11-463677.pdf

How to Select the Basic Materials of the LAN

Installing or designing network may pose a challenge as there are multiple optical solutions that meet the same specification or requirement. But by understanding the basic optical components and the specific performance requirements, you will be able to generate a cost-efficient bill of materials for your project. Thus before picking any products for your infrastructure, you must read this article.

Fiber Type
There are two basic fiber types: single-mode and multi-mode. Multi-mode fiber is graded by OM (optical multi-mode), the higher the OM grade, the better bandwidth performance you can expect. And it comes in both 50μm and 62.5μm core sizes with 50 μm multi-mode available in both standard (OM2) as well as a laser-optimized version (OM3/OM4). Single-mode are graded by OS (optical single-mode) and can run at OS1 and OS2, as described in TIA-568 C.3. Keep the consistency within your network is critical for long-term performance, therefore you shouldn’t mix new fiber type or performance with your old plant.

In addition, the cost of the components should be considered. The transceiver associated with single-mode fiber are more expensive than those for multi-mode. For example, the price of JG661A (compatible HP 40GBASE-LR4/OTU-3 QSFP+ transceiver) is much higher than JG325B (compatible HP 40GBASE-SR4 QSFP+ transceiver). The decision must be made to balance the performance and the cost. Single-mode system will provide for future expansion, yet multi-mode fiber is only for today and the near future. To sum up, single-mode fiber operate better at long reach while multi-mode fiber is ideal for short reach, choosing single-mode or multi-mode depends on your networks needs.

Termination Method
Deciding on a termination methods is typical affected by many factors. If your biggest concern is time, no epoxy/no polish connectors are probably your best choice. The fiber end faces are factory polished and easily installed with a tool kit. This types of termination method allows you to perform terminations quickly, but the cost is usually higher than that of epoxy and polish connector.

If your biggest concern is cost. epoxy and polish connectors might be a good fit because of their low initial price. This type of termination need considerable time to learn how to properly hand-polish connectors that meet specification, and it requires a large workspace to lay out the polishing papers, polishing pucks, epoxy, etc. If your work environment or network condition is not allowed, it is advisable not to select this method.

Fusion Splicer or Optical Connector
Keep in mind that whether to choose fusion splicing or a connector for your network will always need an experienced installer under adequate training. Fusion splicer, as we all know, is very expensive. If your company do not own one, it can be a large investment to make and you need to order the correct splice tray for your hardware and heart-shrinks to keep your splices intact. But if you already have a fusion splicer, fusion-spliced pigtails might be the right choice for you that can provide high quality results and easy to use in areas. The following picture shows a Fujikura FSM-80S Core Alignment Fusion Splicer.

Specifications, density, electronics interfaces and existing plant often drive connector choices. LC connector is favored for its maximum density and room-saving. It is also available in duplex from, which allows you to manage polarity by simply reversing the connector via a duplex clip. SC connectors feature an easy push/pull locking mechanism and are available in simplex and duplex forms. ST compatible connectors have a spring-loaded bayonet locking system that helps them stay in place but are only available in simplex versions.

Hardware
To determine the type of hardware you need, take into consideration the space that will be utilized for the network. If you are installing inside of a closet or other cramped quarters and need low density, wall mountable hardware is the best selection as it does not take up a lot of room. If racks are already in place, or if there is enough room to install them, rack-mount hardware is the best selection because it is sturdy and easy to access.

Additional Information
Designing a network may be a big project as you should take a lot of things into consideration. To make sure the high performance of you network, please think about all the aspects that I have written in this text. What’s more, there are three basic categories for cable: indoor, outdoor and indoor/outdoor. The types of cables you have to choose for your infrastructure depend on where the cables will be run. Fiberstore supplies a whole variety of optical equipment including fiber optical cables, optical transceivers, fusion splicer and optical connectors. Come to us to help your data transmission initiatives for future proof.

Basic Information About Fiber Optic Transceiver

Optical fiber transceivers are also called fiber optic transmitter and receiver, which are used to send and receive optical information in a variety of different applications. The role of the optical module is photoelectric conversion. These optical modules are scalable and flexible in their use, and this is why they are preferred by designers. Here is what you need to know about the basics of fiber optic transceivers.

Fiber Optic Transmitters and Receivers
Fiber optic transmission system consists of a transmitter on one end of a fiber and a receiver on the other end. The transmitter end takes in and converts the electrical signal into light, after the optical fiber transmission in the fiber cable plant, the receiver end again converts the light signal into electrical signal. Both the receiver and the transmitter ends have their own circuitry and can handle transmissions in both directions. Fiber optic cables can both send and receive information. The cables can be made of different fibers, and the information can be transmitted at different times. The following picture shows a fiber optic datalink.

Sources of Fiber Optic Transceiver
There are four types of fiber transmitters used to convert electrical signals into optical signals. These sources of fiber optic transmitters include: distributed feedback (DFB) lasers, fabry-perot (FP) lasers, LEDs, and vertical cavity surface-emitting lasers (VCSELs). They are all semiconductor chips. Take QSFP-40G-UNIV as an example, it is Arista QSFP-40G-UNIV compatible 40G QSFP+ transceiver. It uses DFB lasers as sources for fiber optic transmitters, which are used in long distance and DWDM systems. DFB lasers have the narrowest spectral width which minimizes chromatic dispersion on the longest links.

The choice of the devices is determined mainly by speed and fiber compatibility issues. As many premises systems using multi-mode fiber have exceeded bit rates of 1 Gb/s, lasers (mostly VCSELs) have replaced LEDs. Fiber optic transceivers are reliable, but they may malfunction or become out-dated. If an upgrade is necessary, there are hot-swappable fiber optic transceivers. These devices make it easy to replace or repair without powering down the device.

How Fiber Optic Transceiver Works?
Information is sent in the form of pulses of the light in the fiber optics. The light pulses have to be converted into electrical ones in order to be utilized by an electronic device. Thanks to the conversion by fiber optic transceivers: In its fiber optic data links, the transmitter converts an electrical signal into an optical signal, which is coupled with a connector and transmitted through a fiber optic cable. The light from the end of the cable is coupled to a receiver, where a detector converts the light back into an electrical signal. Either a light emitting diode (LED) or a laser diode is used as the light source.

Packaging
Optical fiber transceivers are usually packaged in industry standard packages like SFP, SFP+, XFP, X2, Xenpak, GBIC. According to the fiber type it connects to, there are MM (multi-mode), SM (Single-mode), as well as WDM fiber (CWDM, DWDM modules). The SFP modules support up to 4.25 Gbps with a connector on the optical end and a standard electrical interface on the other end. The QSFP are for 40 Gigabit networks using a LC duplex connection. Take compatible Brocade 40G-QSFP-LR4 as an example, it supports link lengths of 10km on single-mode fiber cable at a wavelength of 1310nm.

Summary
Keep in mind that fiber optic transceiver has two ends. One has an optical cable plug and another for connecting an electrical device. Each aspect of the transceivers is necessary to properly deliver a signal to its destination. Be aware of all aspects of fiber optic transceivers to purchase what you need for your application. Fiberstore supplies a wide variety of 40GBASE QSFP+ transceiver modules for you to choose from. More detailed, please contact us directly.