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Fiber Link Power Budget: How to Make It Right?

Fiber Link Power Budget: How to Make It Right?

In optical communication system, fiber patch cables and optical transceivers are necessities to complete the pathway for optical signal, enabling data to transmit between devices. To ensure that the fiber system has sufficient power for correct operation, it is vitally important to calculate the span’s power budget. A solid fiber link performance assures the networks run smoother and faster, with less downtime. This article addresses the essential elements associated with link power budget, and illustrates how to calculate power budget effectively.

Power Budget Definition

Power budget refers to the amount of loss a data link can tolerate while maintaining proper operation. In other words, it defines the amount of optical power available for successful transmitting signal over a distance of optical fiber. Power budget is the difference between the minimum (worst case) transmitter output power and the maximum (worst case) receiver input required. The calculations should always assume the worst-case values, in order to ensure the availability of adequate power for the link, which means the actual value will always be higher than this. Optical power budget is measured by dB, which can be calculated by subtracting the minimum receiver sensitivity from the minimum transmit power:

PB (dB) = PTX (dBm) – PRX (dBm)

fiber link power budget

Why Does Power Budget Matter?

The purpose of power budgeting is to ensure that the optical power from transmission side to receiver is adequate under all circumstances. As data centers migrate to 40G, 100G and possible 400G in the near future, link performance becomes increasingly essential. Link failures would stir up a sequence of problems like system downtime, which equates to accelerated costs, frustrated users, deteriorated performance and increased total cost. While with appropriate power budgeting, a high-performance link can be achieved for better network reliability, more flexible cabling and simplified regular maintenance, which is beneficial in the long run.

Critical Elements Involved In Calculating Power Budget

When performing power budget calculation, there are a long list of elements to account for. The basic items that determine general transmission system performance are listed here.

link power budget vs. distance

Fiber loss: fiber loss impacts greatly on overall system performance, which is expressed by dB per kilometer. The total fiber loss is calculated based on the distance × the loss factor (provided by manufacturer).

Connector loss: the loss of a mated pair of connectors. Multimode connectors will have losses of 0.2-0.5 dB typically. Single-mode connectors, which are factory made and fusion spliced on will have losses of 0.1-0.2 dB. Field terminated single-mode connectors may have losses as high as 0.5-1.0 dB.

Number and type of splices: Mechanical splice loss is generally in a range of 0.7 to 1.5 dB per connector. Fusion splice loss is between 0.1 and 0.5 dB per splice. Because of their limited loss factor, fusion splices are preferred.

Power margin: power budget margin generally includes aging of the fiber, aging of the transmitter and receiver components, additional devices, incidental twisting and bending of the fiber, additional splices, etc. The margin is needed to compensate for link degradation, which is within the range of 3 to 10 dB.

How to Properly Calculate Power Budget?

Here we use the following example to demonstrate how to calculate power budget of an optical link: Example: the system contains the transmitter and receiver, the optical link contains optical amplifier, 4 optical connectors and 5 splices. The following table presents attenuation or gain of each components.

Tx power:   3dBm

Connector loss: 0.15dB

Splice loss: 0.15dB

Amplifier gain: 10dB

Fiber optic loss: 0.2 dB/km

fiber link power budget calculation

The total attenuation of this link PL is the sum of:

Fiber optic loss: (30 km + 50 km) ×0.2dB/km = 16 dB

Attenuation of connectors: 4×0.15 dB = 0.60 dB

Attenuation of splices: 5×0.15 dB = 0.75 dB

So PL = 16 Db + 0.60 Db + 0.75 Db = 17.35 dB

The total gain of the link is generated by optical amplifier, which is 10 dB in this case. So PG = 10 dB

Considering link degradation, power margin should be calculated as well. A good safety margin  PM = 6 dB

To select the receiver’s sensitivity at the end of the optical path, it is sufficient to rearrange and solve the equation. So:

Ptx – Prx < PL – PG + PM

Prx > Ptx – PL + PG – PM

Prx > 3 dBm – 17.35 dB +10 dB – 6 dB

Prx > -10.35 dB

The receiver should provide sensitivity better than -10.35 dBm.

Conclusion

With data centers migrating to 40G, 100G, 200G and even 400G, fiber link performance becomes more important than ever before. Understanding link power budget will help you optimize your fiber link design as well. In addition, high-performance cables, quality transceivers and high-performance installation practices also assist to ensure better link performance.

Difference Between Tight-Buffered Breakout and Distribution Cables

Difference Between Tight-Buffered Breakout and Distribution Cables

Tight-buffered cables are optimal for indoor applications. With the design of armored layer, they are also used for indoor/outdoor applications. They are mostly applied in breakout cables and distribution cables. Today, I’d like to talk the difference between these two types of tight-buffered cables, mainly in two aspects.

Difference in Cable Structure

Tigh-buffer breakout cables and distribution cables both consist of 900μm tight-buffered fibers. But they differ from each other in the cable structure.

Tight-Buffered Breakout Cables
The tight-buffered breakout cables consist of several individually jacketed tight-buffered fibers (basically simplex cordage) bundled together, as shown in picture below. A tight-buffered breakout cable has individual “subcables” within a primary outer cable sheath. Flame ratings of tight-buffered breakout cables are available in Plenum, Riser, and General (LSZH).

Cable structure: tight-buffered breakout cable
Cable Structure: Tight-Buffered Breakout Cable

Tight-Buffered Distribution cable
Tight-buffered distribution cable can be divided into two types—non-untized distribution cable and unitized distribution cable. The former contains several non-unitized tight-buffered fibers bundled under the same jacket. It is easy to identify the non-unitized cable and breakout cable through their cable structure. The unitized distribution cable consists of jacketed groups of tight buffered fiber, namely “subunits” consolidated in a single cable. It is similar with the breakout cable. But the “subunits” of unitized distribution cable is parts of the distribution cable while “subcables” of breakout cable is an individual fiber cable. Tight-buffered distribution cables are usually plenum or riser rated but can also be constructed as an indoor/outdoor or low-smoke (LSZH) cable. The following picture shows us the structures of non-unitized distribution cable and unitized distribution cable.

cable structure: non-unitized distribution cable
Cable Structure: Tight-Buffered Non-unitized Distribution Cable

cable structure: unitized distribution cable
Cable Structure: Tight-Buffered Unitized Distribution Cable

Difference in Cable System Layouts

Because of the difference in cable structure, the cable system layouts with tight-buffered breakout cable and distribution cable are also different. Tight-buffered breakout cable is the cable of choice for direct connectivity. Because each fiber has its own aramid strength member for connector tie-off so that the subcables can be directly connected to equipment without fear of fiber damage or connector/fiber end-face damage in most situations. See the picture below:

cable-layout: breakout cable

Tight-buffered distribution cables provide easy routing, and their 900µm tight-buffered fiber supports fast and robust field-terminations. As the following picture shown, the terminated fibers is placed in a patch panel, and jumper cables are used to interconnect panel and equipment.

cable-layout: distribution cable

Conclusion

Tight buffered cables provide improved reliability and quick termination for today’s cable installation systems. Tight-buffered breakout cables and distribution cables are two main types of the tight-buffered cables. This post presented their difference in cable structure and cable system layouts which help users more understand their features. Users can choose the right one according to their requirements of practical applications.


Good News for Buyer: A new inventory of tight-buffered distribution cables including non-unitized distribution cable and armored distribution cables is soon coming in FS.COM‘s USA Local warehouse (located in Seattle, USA) and accepting for reservation now. Once the inventory arrived, you can enjoy same-day shipping from United States and get your order as soon as possible. For more information, please contact sales@fs.com or live chat.

Is Bend Radius Really a Concern?

Is Bend Radius Really a Concern?

A: Do I really need to be concerned about bend radius?
B: Yes, bend radius is a real issue.

The question “A” asked is a common question in fiber optic cable installation. And thanks “B” to show us the right answer. To almost every FOC (fiber optic cable) installer or technician, one of the most important considerations when installing fiber optic cable is maintaining the minimum bend radius. Why? Just keep reading, you may find out the reason.

Understanding Bend Radius

bend-cablesAs we know, most of the fiber optic cable is made of glass. It is very amazing that the bundle of fiber can transmit a huge amount of signals and data. But, do you know that the cable can be pretty delicate because of the material itself? Thus, we need to set a standard (e.g. EIA/TIA 568) to define the minimum bend radius in order to keep cables in good working order.

The “bend radius” of a fiber optic cable is the term for how sharply a cable can safely bend at any given point. All cabling has a bend radius, and the bend radius may be different according to different types or different make of cables.

Minimum Bend Radius

The minimum bend radius for fiber optic cable should be specified both for long-term installation, and for when the cable is subject to tensile load. A typical value for a cable under no load (or “unloaded”) conditions is 10 times the cable’s outside diameter. When a cable is under tensile load (or “loaded”), the minimum bend radius is usually 15 times the cable’s outside diameter. For instance, for most of the premises cables, they require a bend radius of 10 times the cable outside diameter unloaded and 15 times the outside diameter when under the maximum rated pulling tension for that cable.

bend-radius

Bending a Fiber Optic Cable

Bending a fiber optic cable excessively may cause the optical signal to refract and escape through the cladding. It could also cause permanent damage by creating micro cracks on the delicate glass fibers. And when overbending interferes with light transmission, the resulting increased attenuation compromises the integrity of your valuable data. So, always remember that do not bend the fiber beyond it’s specified bend radius.

Bend Insensitive Fiber

Bend insensitive fiber cables are designed for improved bend performance in reduced-radius applications, such as residential or office environments which have less bend sensitivity. Optical fiber manufacturers used a refractive index “trench” in bend insensitive fiber, which means a ring of lower refractive index material, to basically reflect the lost light back into the core of the fiber. Compared with the conventional fibers, the bend insensitive fiber employs a moderately higher numerical aperture (NA) and offers improved bend performance for applications in the 1310nm and 1550nm range.

Bend-Insensitive Fiber

Summary

Bend radius is always a real issue that we should really need to be concerned about when installing fiber optic cables. Make sure to know the minimum band radius of your installed cables, and do not bend it beyond the specified bend radius. Additionally, if the application needed, you can try to use the bend insensitive fiber.

Optical Fiber Transmission Applications Are Promising In Security Monitoring

Optical Fiber Transmission Applications Are Promising In Security Monitoring

As a variety of image status and data monitoring have more and more requirements, the transmission distance of video signal can not meet the demand anymore. Therefore, the gradual development of optical integrated video and control signals (WDM or DWDM technology) can transmit longer distance. In addition to the combination of images and control, the architecture of optical fiber monitoring transmission can be the spindle of the entire optical fiber transmission building. With a different way of provisioning, it will have different uses and functions.

Fiber optic communications’ application have a wide scope which can be broadly divided into Telecom, Datacom, CCTV, CATV optical fiber transmission network and FITL. In addition to the five above, fiber optic communications applications are also visible in national defense and military.

In the CCTV field, fiber optic communication is more of a backbone as part of the monitoring framework. It may combine a simple video and control signals into optical signals. There are also some converted digital video signals into light TCP/IP signals over TCP/IP network for the way of transmission and restore.

With the development of optical fiber communication technology, there are more and more ways of image transmission, the optical transceiver’s video signal transmission has a greater advantage than others, such as twisted pair, coaxial cable. As is well-known, optical fiber transmission mainly relys on optical transceiver converting the electrical signals into optical signals at one end of the optical fiber cable, and converting the optical signal back to an electrical signal corresponding at the other end. Optical transceiver provides a flexible transmission and networking to optical monitoring system, with its good signal quality and high stability.

In recent years, due to the rapid development of optical communication technology, which makes the cost of optical fiber transmission monitoring system greatly reduced, optical fiber and optical transceiver is becoming increasingly popular in monitoring system. Optical fiber has been widely used in homes and offices fiber access network, the field of intelligent home, office automation, industrial networking, automotive and military airborne communications network. For the high-definition video streaming that requires more transmission bandwidth and transmission distance, achiving high-definition monitoring is no longer a dream in the fiber optic era.

POF Production Has Made Great Breakthrough But Problems Exist In The Marketing

POF Production Has Made Great Breakthrough But Problems Exist In The Marketing

In the construction of modern communication networks, fiber optic cables have been at a dominant position in recent years, such as the FTTH cable. These cables commonly use quartz fiber as the raw material.

Currently, the plastic optical fiber (POF) is increasingly being perceived by people, and the bulk manufacture of this product has made great breakthrough. However, because the market is still at a low level of awareness, business promotion is still too difficult.

So far, the cables that used in fiber optic communication are basically using quartz fiber by adding an appropriate amount of dopant composition to high purity silicon dioxide. In recent years, the plastic optical fiber is also developed gradually. It is an optical fiber made of a light-transmissive polymer. By using a mature and simple drawing technology of the polymer, the POF has a relatively low cost, and is relatively soft, strong, with large diameter (approximately 1mm) and low splice loss.

Plastic fiber optic cable is a light guide medium for transmitting optical signals. It consists of a single or multi-core plastic optical fiber coated by outer PE, PVC and other plastic sheath. POF cables are used in high-speed data transmission, broadband access, FTTH, FTTD, intelligent home and office networking, automotive multimedia, industrial control, factory automation, automotive and aircraft as well as military applications. They are also used in a variety of short-distance data communications including audio jumpers, sensors, ground and short circuit protection, and other plastic indication fiber optic networks, local area networks, home and office optical network, enterprise optical network, digital surveillance, IPTV broadband connection, plastic optical fiber sensors.

The technology of POF’s mass production has made great breakthrough, the plastic optical fiber industry has broad prospects in marketing. Currently, telecommunications companies in Europe and North America and the European POF Union have been testing plastic optical fiber. They believe that this medium has advantages including easy to install, low-cost, flexible, no damage to the naked eye, etc.. They want to slather POF cable into the home and business. In China, the high-tech industry plastic optical fiber has both challenges and opportunities. For its location, losses, costs and chain support, there are still doubts in the industry, and its market awareness is not high enough.

The low market awareness causes that, though plastic optical fiber technology has made great breakthrough, there are problems existing in the promotion of commercial applications.

Source: FiberStore Blog