Choosing Fiber Optic Connectors for Your Application

Optical Loss – A Critical Consideration
Whether a fiber optic connector must interface with a simple transmitter or the latest ROADM multiplexer, the connector interface is of critical importance because of its unique loss characteristics. To illustrate this point, consider the difference between connectors for fiber optic cable vs. copper cable.
Power loss for both types of connectors are stated in decibels (dB). That’s about where the similarity ends, because copper connectors and fiber optic connectors have opposite loss characteristics.
Copper connectors produce negligible loss when compared to losses produced by the copper twisted-pair cable to which they are attached. With fiber, the exact opposite is true. In a typical fiber optic system, fiber optic connectors produce far more loss than that produced by the fiber optic cabling. That’s why careful connector selection, particularly in regard to a connector’s loss specifications, is so crucial.
Other considerations that affect connector loss involve how the connector is joined to the field fiber, and how meticulously fiber optic connectors are cleaned and inspected prior to coupling.
Narrowing the Field
There are nearly 100 styles of fiber optic connectors, so choosing the right one for a particular application might seem daunting. However, this connector guide simplifies the selection process by focusing on the most useful and popular connector styles currently available.
In many cases, the types of connectors that you must use are dictated to you, especially if you are upgrading a legacy system. In that case, you may have to use the same type of connectors that are already in place in order to accommodate existing equipment and cabling. Even so, it’s a good idea to know the loss characteristics and other attributes of the connectors that you are working with. For example, a connector’s “insertion loss” specification relates to optical loss that results from differences in concentricity, ferrule endface geometry or other irregularities. Knowing the connector’s insertion loss specification can be useful when testing.
In some cases, such as a new install, connectors may or may not be specified. If connectors are not specified, you will likely be presented with a loss budget for cabling and connectors that you must adhere to. In this case, you have to give some serious thought to selecting the best connectors for the job. You also have to take into account the connector termination method (e.g. fusion splicing, epoxy, or mechanical termination) because this can have a significant impact on optical loss and back reflection characteristics.
Choosing The Right Connector
The following are considerations for choosing fiber optic connectors for your application.
Talk Like a Pirate….ARRG!
ARRG stands for Alignment, Ruggedness, Repeatability and Geometry. When choosing connectors, this memory aid will help you recall desirable connector qualities. The following attributes apply to most connector styles.
Alignment – A quality connector will keep fiber properly aligned with the fiber to which it is mated. Proper alignment is especially critical for single mode fibers which have a very small fiber core through which signals are transmitted. Always buy quality connectors and mating sleeves from recognized manufacturers to ensure that connectors are manufactured to high tolerances and provide optimal alignment.
Ruggedness – Will connectors be installed in high-traffic areas? If so, a good choice are epoxy-style connectors, which have the fiber bonded to the ferrule. This resists optical disconnects caused by tugging, temperature changes and other external forces. As added protection, consider a spring-loaded “non-optical disconnect” connector, such as the SC connector or LC connector, which are specifically designed to prevent optical disconnects. For harsh outdoor environments, “hardened” connectors are available.
Repeatability – Will there be a number of occasions when your connector will be disconnected? If so, consider using a connector that is known for good “repeatability.” The term repeatability refers to the performance of any class of connectors that are known to provide consistent loss performance that varies by a relatively narrow margin. Such connectors are typically keyed, or contain a keyway feature that prevents ferrule endface rotation. Keyed connectors ensure that connectors that are uncoupled from one another maintain the same ferrule endface orientation when they are recoupled, resulting in connector losses that are predictable, consistent and “repeatable”.
Geometry – The shape of the connector ferrule endface has a major affect on interface loss. For example, UPC connectors have ferrules that have a domed endface surface to insure contact at the core of two mated fibers, which helps to reduce insertion loss. Other connectors have an angled ferrule endface (APC connectors) which helps to minimize back reflection by directing endface reflections away from the core of the fiber. Knowing how ferrule endface geometry affects loss is important when selecting connectors, especially if you plan to polish your own connectors. Polishing procedures vary for different endface geometries.
Now that you know the general qualities you are looking for, it’s time to choose a specific connector for your application. The following approach uses a simple 3-step process of elimination.
Step 1. Weed Out Connectors that Can’t Meet the Loss Budget – Loss budgets will usually have connectors and cabling losses broken out separately from the rest of the network. Except for very long fiber links, losses for fiber optic cabling are usually negligible, so you’ll want to focus most of your attention on choosing the right connectors. Begin by narrowing down your possible connector choices to those that can stay within the loss budget of your application. For each connector being considered, simply multiply the number of connectors required by the dB loss specified for that type of connector. Now add fiber-optic cable loss to that number. If you are still within loss budget, great. You can proceed to Step 2.***
***It is possible to be within the loss budget but still have connections that produce unacceptable levels of back reflection. An Optical Return Loss (ORL) Test Set can be used to measure the level of back reflection. Also, an OTDR is useful for identifying the location of high-ORL events such as defective splices and connectors so that corrective action can be taken.
Step 2. Consider Installation Time, Material Costs, and Skills Required – After narrowing your list down in Step 1, it’s time to consider the costs associated with each type of connector, including installation skills required. Will you have to put your best installers on the job?
Step 3. Your Own Preferences – After completing Steps 1 and 2, let’s say that you have narrowed your connector list down to two possibilities. Now you can use your own personal preference to make the final decision. Simply choose the connector with which you are most comfortable and proficient. This will increase your speed and productivity on the jobsite and help to ensure quality terminations.
Tip: When trying new connectors and termination procedures for the first time, do enough of them in the shop to become proficient. Experimenting in the field is never a good idea.
Most Popular Connector Styles
Name: SC Connector
• Mode: Singlemode and Multimode
• Applications: Wide variety of singlemode applications especially datacom and telecom including premises installation. Often found in older corporate networks. It was designed to replace the ST connector.
• Ferrule size: 2.5mm
• Ferrule construction (typical): Pre-radiused zirconia
• Connector body: Composite. Similar in appearance to LC connector, except the SC is larger. Color coded according to fiber type; blue or green for singlemode, beige or black for multimode.
• Styles available: Simplex and duplex
• Latching mechanism: Push-pull, snap-in design
• Optical loss:
    Insertion loss: SM 0.10 – 0.30 dB; MM 0.10 – 0.40 dB
    Repeatability: 0.20 dB
• Meaning of name: Subscriber Connector, Square Connector or Standard Connector
Advantages: An excellent performer. Non-optical disconnect design (an advantage over the ST connector which the SC is replacing). Minimum back reflection when ultra-polished. Push-pull design helps prevent endface damage during connection. Square shape allows connectors to be packed closely together. Can fit into smaller spaces where the ST or FC cannot. The SC’s push-pull design allows quick patching of cables into rack or wall mounts.
• Disadvantages: Smaller LC connectors are replacing SC connectors in high density applications where space is at a premium.

How to clean a fiber optic connector?

Do you know how important is to maintain a fiber connector clean? In fact, having a clean eviroment for the connector is one of the most important procedures in the conservation of a fiber optic system. This is necessary to keep quality connections.
If any particle of dust, lint, oil or any other dirt get on the end of the connector, this will interrupt the correct function of the signal that is being sent over the fiber.
An improper maintenance of the cables can also cause other problems such as scratching the glass surface, instability in the laser system, and a misalignment between the fiber cores.
So, the questions is: What to do to clean my fiber optic? Simple:
Before beginning all the process, make sure the cable is disconnected from both ends and turn off any laser sources. Don’t forget to wear safety glasses and check the connectors before you clean them.
Step 1: Inspect the fiber optic connector, component, or bulkhead with a fiberscope.
Step 2: If the connector is dirty, clean it with a dry cleaning technique. This procedure consists of using a reel-based cassette cleaner with medium pressure, wipe the connector end face against a dry cleaning cloth in one direction. This step must be done in both parts of the fibre optic and can be repeated at least two times.
Step 3: If the connector is still dirty, clean it with a wet cleaning technique followed immediately with a dry cleaning in order to ensure no residue is left on the end face. You can use a special solution for fibre optic or 91% Isopropyl Alcohol. Wipe the end face against the wet area and then onto a dry area to clean potential residue from the end face.
Wet cleaning is more aggressive than dry cleaning, and will remove airborne contamination as well as light oil residue and films.
Similar to the dry cleaning method, this one, can be done twice if you consider that the fiber optic isn’t clear yet.
IMPORTANT: The end face of the connector should never be touched during the cleaning process and also the clean area of a tissue should not be touched or reused.
The fiber end should be inspected with a fiberscope of at least 200x magnification, and if it is contaminated, it should be cleaned with one of the methods explained before.
DO’s and DON’Ts when it comes to cleaning a Fiber Optic:
 DO’s:
Turn off any laser sources before you inspect fiber connectors, optical components, or bulkheads.
Make sure that the cable is disconnected at both ends and the card or pluggable receiver is removed from the chassis.
Wear the appropriate safety glasses when required in your area. Be sure that any laser safety glasses meet federal and state regulations and are matched to the lasers used within your environment.
Inspect the connectors or adapters before you clean.
Use the connector housing to plug or unplug a fiber.
Keep a protective cap on unplugged fiber connectors.
Store unused protective caps in a resealable container in order to prevent the possibility of the transfer of dust to the fiber. Locate the containers near the connectors for easy access
Discard used tissues and swabs properly.
 DON’TS:
Use alcohol or wet cleaning without a way to ensure that it does not leave residue on the end face. It can cause damage to the equipment.
Look into a fiber while the system lasers are on.
Clean bulkheads or receptacle devices without a way to inspect them.
Touch products without being properly grounded.
Use unfiltered handheld magnifiers or focusing optics to inspect fiber connectors.
Connect a fiber to a fiberscope while the system lasers are on
Twist or pull forcefully on the fiber cable.
Reuse any tissue, swab, or cleaning cassette reel.
Touch clean area of a tissue, swab, or cleaning fabric.
Touch any portion of a tissue or swab where alcohol was applied.
Touch the dispensing tip of an alcohol bottle.
Use alcohol around an open flame or spark; alcohol is very flammable.

How do Optical Attenuators work?

The power reduction is done by such means as absorption, reflection, diffusion, scattering, reflection, diffraction, and dispersion, etc.
Optical attenuators usually work by absorbing the light, like sunglasses absorb extra light energy.
They typically have a working wavelength range in which they absorb all light energy equally.
They should not reflect the light or scatter the light in an air gap since that could cause unwanted back reflection in the fiber system. Another type of attenuator utilizes a length of the high-loss optical fiber, that operates upon its input optical signal power level in such a way that its output signal power level is less than the input level.
Optical Attenuator Performance:
Amount of attenuation and insertion loss: insertion loss and the attenuation amount of the optical attenuator is an important indicator of the amount of attenuation of the optical attenuator indicator to actually insertion loss, and attenuation amount of the variable attenuator addition, there are separate indicators insertion loss, high quality can be variable attenuator insertion loss 1.0dB or less, in general, common variable attenuator of the index is less than 2.5dB can be used. When the actual selection adjustable attenuator insertion loss as low as possible.
Optical attenuator accuracy: attenuation accuracy is an important indicator of the optical attenuator.
Typically mechanical type variable optical attenuator for attenuation accuracy of ± 0.1 times that amount. Its size depends on the degree of processing of precision mechanical components. High attenuation accuracy fixed optical attenuator. Typically the higher the attenuation accuracy, the higher the price.
Return loss: an important indicator of the impact of system performance in optical device parameters return loss.
The retroreflective optical network system effects are well known. Optical attenuator Return loss is the light energy incident on the optical attenuator and the attenuator light energy incident along the road reflecting ratio.
For now, you can understand how fiber optics attenuators work, and you also are aware of the importance of them for your fiber infrastructure. That’s why Beyondtech has them available at our several distribution locations for 24 hours shipping and they were carefully tested each one of them for your reliability and for a complete solution-oriented approach.

Fiber Optics Attenuators – The Ultime Guide on How they work?

An optical attenuator is a passive device used to reduce the power level of an optical signal, either in free space or in an optical fiber. There are various types of them from the fixed ones, step-wise variable, and continuously variable.
Attenuators are usually used when the signal arriving at the receiver is too strong and hence may overpower the receiving elements. This may occur because of a mismatch between the transmitters/receivers, or because the media converters are designed for a much longer distance than for which they are being used.
Sometimes attenuators are also used for stress testing a network link by incrementally reducing the signal strength until the optical link fails, determining the signal’s existing safety margin.
Although fiber optic attenuators are normally used in SM (Single Mode) circuits, because this is where the stronger lasers are used for distance transmission, there are also multi mode attenuators available.
The most common version of attenuators are male to female units, often called plug-style or buildout style. These plug-style attenuators simply mount on one end of a fiber optic cable, allowing that cable to be plugged into the receiving equipment or panel.
There are also female to female (bulkhead) attenuators, often used to mount in patch panels or for connecting two fiber optic cables together. More expensive, but useful for testing, are variable attenuators which are adjustable between 1dB and 30dB.
Bear in mind that the dB ratings are a measure of signal strength and can sometimes be confusing. The chart below will give you an idea of the percent of attenuation of your signal for specific dB values.
Fiber optic attenuators are usually used in two scenarios.
The first case is in power level testing. Optical attenuators are used to temporarily add a calibrated amount of signal loss in order to test the power level margins in a fiber optic communication system. In the second case, optical attenuators are permanently installed in a fiber optic communication link to properly match transmitter and receiver optical signal levels.
How many types of Optical Attenuators (OA) can you find?
There are four different types of OA and they can take a number of different forms and are typically classified as fixed or variable attenuators. What’s more, they can be classified as LC, SC, ST, FC, MU, E2000 etc. according to the different types of connectors.
1. Fixed Attenuators: Fixed optical attenuators used in fiber optic systems may use a variety of principles for their functioning. Preferred attenuators use either doped fibers, or misaligned splices, or total power since both of these are reliable and inexpensive.
Inline style attenuators are incorporated into patch cables. The alternative build out style attenuator is a small male-female adapter that can be added onto other cables.
Non-preferred attenuators often use gap loss or reflective principles. Such devices can be sensitive to modal distribution, wavelength, contamination, vibration, temperature, damage due to power bursts, may cause back reflections, may cause signal dispersion etc.
2. Loopback Attenuators: Loopback fiber optic attenuator is designed for testing, engineering and the burn-in stage of boards or other equipment. Available in SC/UPC, SC/APC, LC/UPC, LC/APC, MTRJ, MPO for single mode application.
3. Built-in Variable Attenuators: Built-in variable optical attenuators may be either manually or electrically controlled. A manual device is useful for one-time set up of a system, and is a near-equivalent to a fixed attenuator, and may be referred to as an “adjustable attenuator”. In contrast, an electrically controlled attenuator can provide adaptive power optimization.
Attributes of merit for electrically controlled devices, include speed of response and avoiding degradation of the transmitted signal. Dynamic range is usually quite restricted, and power feedback may mean that long-term stability is a relatively minor issue.
The speed of response is a particularly major issue in dynamically reconfigurable systems, where a delay of one millionth of a second can result in the loss of large amounts of transmitted data.
Typical technologies employed for high-speed response include liquid crystal variable attenuator (LCVA), or lithium niobate devices.
There is a class of built-in attenuators that is technically indistinguishable from test attenuators, except they are packaged for rack mounting, and have no test display.
4. Variable Optical Test Attenuators: this type generally uses a variable neutral density filter. Despite the relatively high cost, this arrangement has the advantages of being stable, wavelength insensitive, mode insensitive, and offering a large dynamic range.
Other schemes such as LCD, variable air gap etc. have been tried over the years, but with limited success.
They may be either manually or motor control. Motor control gives regular users a distinct productivity advantage since commonly used test sequences can be run automatically.

The best way to Install CWDM MUX/DEMUX System?

by http://www.fiber-mart.com

Coarse wavelength division multiplexing (CWDM) technology is developed to expand the capacity of a fiber optic network without requiring additional fiber. In a CWDM system, CWDM Mux/Demux (multiplexer/demultiplexer) is the most important component. Usually, a CWDM Mux/Demux is used to increase the current fiber cable capacity by transmitting multiple wavelengths, typically up to 18 separate signals over one fiber. This article may mainly describe how to install your CWDM Mux/Demux system. Unless you are an experienced user, we recommend that you follow the detailed installation steps described in the rest of this article.
CWDM MUX/DEMUX Module Overview
CWDM Mux/Demux module is a passive device, very reliable and simple to use. These devices are available with a variety of wavelength combinations, usually from 1270nm to 1610nm (20nm spacing). Based on different applications, a CWDM Mux/Demux module can be designed into different channels. A typical 4 channel Mux/Demux module will be used to multiplex four different wavelengths onto one fiber. This allows you to simultaneously transmit four different data over the same fiber. If you are using a CWDM multiplexer at the beginning of your network, you will must to use a CWDM demultiplexer at the opposite end to separate or demultiplex the wavelengths to allow them to be directed to the correct receivers. Usually, a CWDM Mux/Demux is a module that can be used as a multiplexer or demultiplexer at either end of the fiber cable span. However, it must still be used in pairs.
CWDM MUX/DEMUX System Installation Components
A basic CWDM Mux/Demux system comprises a Local unit, the CWDM Mux/Demux module and a Remote unit. Usually a Local or Remote unit refers to two different switches. In general, to install a CWDM Mux/Demux module, a chassis should be installed first to hold the module. Besides, to connect a CWDM Mux/Demux module to a switch, we should install CWDM SFP transceivers in the switch first. Then using the singlemode patch cables to connect the transceivers to the CWDM Mux/Demux module. Therefore, when we want to build a CWDM Mux/Demux system, the components we need usually include rack-mount chassis, CWDM Mux/Demux module, CWDM SFP transceiver and singlemode patch cables (shown in the table below).
CWDM MUX/DEMUX System Installation Steps
To install a CWDM Mux/Demux system, there are four basic steps:
Install the Rack-Mount Chassis
The CWDM rack-mount chassis can be mounted in a standard 19-inch cabinet or rack. When to attach the chassis to a standard 19-inch rack, ensure that you install the rack-mount chassis in the same rack or an adjacent rack to your system so that you can connect all the cables between your CWDM Mux/Demux modules and the CWDM SFP transceivers in your system.
Install the CWDM Mux/Demux Modules
To insert a module, you should align the module with the chassis shelf (shown in the figure below) first and then gently push the module into the shelf cavity. Finally, tighten the captive screws.
Connect the CWDM Mux/Demux to Switch
After inserting the CWDM SFP transceiver into the switch, then we should use the singlemode patch cable to connect the transceiver to the CWDM Mux/Demux.
Please mind that CWDM Mux/Demux pairs must carry transceivers with the same wavelength.
Because each transceiver will work only at the appropriate port and the data will always flow between devices with the same wavelengths. CWDM SFP transceivers with different wavelength may have different color code. Use the CWDM SFP transceiver color codes shown in picture below to help you connect the CWDM Mux/Demux to your system.
Connect the CWDM MUX/DEMUX Pairs
Once you use a CWDM multiplexer on one end of your networks, you must use a demultiplexer on the other end of the networks. Therefore, the last step to complete CWDM Mux/Demux system is to connect the Mux/Demux pairs (or multiplexer and demultiplexer). For duplex Mux/Demux, a pair of singlemode patch cables must be used. For simplex Mux/Demux, only one singlemode patch cable is enough. After all done, your CWDM Mux/Demux system is then installed successfully.
Conclusion
In summary, Mux/Demux system is a cost-effective solution which is easy to install. CWDM Mux/Demux, CWDM multiplexer only, and CWDM demultiplexer only are a flexible, low-cost solution that enables the expansion of existing fiber capacity and let operators make full of use of available fiber bandwidth in local loop and enterprise architectures. fiber-mart.com CWDM Mux/Demux is a universal device capable of multiplex multiple CWDM (1270~1610nm) up to 18 channels or optical signals into a fiber pair or single fiber. Together with our CWDM transceivers or the wavelength converters, the bandwidth of the fiber can be utilized in a cost-effective way.

How Multiplexing Techniques Deliver Higher Speeds on Fiber Optic Cabling

by http://www.fiber-mart.com

The Different Multiplexing Techniques:
Different multiplexing techniques are enabling the evolution of network speeds on fiber optic cabling.
Time Division Multiplexing is simply a way of transmitting more data by using smaller and smaller increments of time, and multiplexing lower data rate signals into a higher speed composite signal.
Space Division Multiplexing, more commonly known as parallel optics or parallel fibers, is a way of adding one or more lanes simply by adding one or more optical fibers into the composite link.
Wavelength Division Multiplexing is signaling simultaneously across multiple lanes segregated by different wavelengths (colors) of light that are multiplexed into and out of a single fiber.
Multiplexing Techniques Which Enable The Evolution of Network Speeds
There are a range of different Multiplexing Techniques which enable the evolution of network speeds through fiber optic cabling. Let’s take a look at each one of these techniques in a little bit more detail below;
TECHNIQUE 1: TIME DIVISION MULTIPLEXING
With Time Division Multiplexing, lower speed electrical signals are interleaved in time and transmitted out on a faster composite lane.
So the higher resultant data rate would be multiple times the individual rates going in.
There are examples used today where Ethernet rates are achieved using such parallel electrical signals, combined in a multiplexer and serialized over fiber. For instance, 10Gbps Ethernet has four lane options where each of the lanes is at a quarter rate of 2.5Gbps.
Today’s top speed per lane is 25Gbps for Ethernet, and looking to the future, 50Gbps lane rates are being developed.
With the higher rates, more complex multi-level code schemes are used to get more bits through with each symbol. This is an indication that maximum speed limits are being reached and so alternative techniques are used to increase the composite lane speed.
TECHNIQUE 2: SPACE DIVISION MULTIPLEXING
One of the other techniques is to add more lanes to the composite channel, known as Space Division Multiplexing. A lane in this scenario is physically another fiber strand. It’s an alternative to TDM lanes described above, where signals merged each in time on the same fiber.
There are a number of examples of this technique being used in the industry. 40G SR4 for example delivers 40Gbps over multi-mode fiber using four lanes or fibers. That’s four lanes in one direction and four lanes in the other direction.  That’s also what the four on the end of ‘SR4’ means, four lanes of 10Gbps each.
The standard for the 100Gbps solution uses 10 lanes of 10Gbps called SR10.  There is also a second generation of 100G that has increased the lane rate to 25Gbps and that delivers 100G using four lanes, so mixing the improvements in TDM and parallel optic techniques to achieve the goal of higher speeds.
Taking this further from four lanes in each direction up to 16 or 24 lanes, speeds of 200Gbps, 400Gbps and beyond are made possible. However there are pragmatic limits. Clearly a four lane solution is more practical than a 24 lane solution if you can get away with it.
TECHNIQUE 3: WAVE DIVISION MULTIPLEXING
Going above 16 or 24 lanes is a diminishing return because it drives more cost into the cabling system. That’s where the third multiplexing technique, wave division multiplexing comes in.
As the name implies, the wavelength band available for transmission is divided into segments each of which can be used as a channel for communication. It is possible to squeeze many channels into a small spectrum. The common versions used for long haul, singlemode systems are called Dense Wave Division Multiplexing DWDM or Coarse Wave Division Multiplexing CWDM. In multimode systems, Short Wavelength Division Multiplexing techniques are appearing.
With short wavelength division multiplexing, wavelengths are used in the lower cost short wavelength range around 850nm to add lanes within a single strand of optical fiber.
An example of this on the market today is Cisco’s 40G BD, or Bi-Di. Bi-Di stands for bidirectional and the signals are transmitting in both directions in each optical fiber strand, using two different wavelengths to discriminate between the reflections that might happen.
This technique uses 20Gbps per wavelength in each of two fibers and that way they can get 40Gbps through the 2 core fiber channel using a duplex LC connector.

Picking the right fiber connector – PC, UPC or APC

I wrote a blog post some days ago on the different types of connectors available, which sparked a great deal of feedback and discussion, demonstrating how important the whole topic is to both fiber installers and network planners alike. Thanks again to everyone around the world that contributed, both directly on the PPC’s blog and through various social groups.

I wrote a blog post some days ago on the different types of connectors available, which sparked a great deal of feedback and discussion, demonstrating how important the whole topic is to both fiber installers and network planners alike. Thanks again to everyone around the world that contributed, both directly on the PPC’s blog and through various social groups.

To recap, I covered SC, LC, FC, ST and MTP/MPO connectors, and looking through the comments I thought it would be beneficial to focus on one area that the original post deliberately didn’t cover – the differences between Angled Physical Contact (APC) and Ultra Physical Contact (UPC) connectors. Beside one having a green body and the other being colored blue, the different ways they both treat light is crucial in planning a network, as several readers pointed out.

To help us understand all this jargon, let’s look back at why the original Flat Fiber Connector evolved into the Physical Contact (PC) connector and then onto UPC and APC.

The primary issue with Flat Fiber connectors is that when two of them are mated it naturally leaves a small air gap between the two ferrules; this is partly because the relatively large end-face of the connector allows for numerous slight but significant imperfections to gather on the surface. This is not much use for single mode fiber cables with a core size of just 8-9 µm, hence the necessary evolution to Physical Contact (PC) Connectors.

The PC is similar to the Flat Fiber connector but is polished with a slight spherical (cone) design to reduce the overall size of the end-face. This helps to decrease the air gap issue faced by regular Flat Fiber connectors, resulting in lower Optical Return Loss (ORL), with less light being sent back towards the power source.

Building on the convex end-face attributes of the PC, but utilizing an extended polishing method creates an even finer fiber surface finish: bringing us the Ultra Physical Contact (UPC) connector. This results in a lower back reflection (ORL) than a standard PC connector, allowing more reliable signals in digital TV, telephony and data systems, where UPC today dominates the market. Most engineers and installers believe that any poor performance attributed to UPC connectors is not caused by the design, but rather poor cleaving and polishing techniques. UPC connectors do have a low insertion loss, but the back reflection (ORL) will depend on the quality of the fiber surface and, following repeat matings/unmatings, it will begin to deteriorate.

So what the industry needed was a connector with low back reflection, that could sustain repeated matings/unmatings without ORL degradation. Step forward the Angled Physical Contact (APC) connector.

Although PC and UPC connectors have a wide range of applications, some instances require return losses in the region of one-in-a-million (60dB). Only APC connectors can consistently achieve such performance. This is because adding a small 8° angle to the end-face allows for even tighter connections and smaller end-face radii. Combined with that, any light that is redirected back towards the source is actually reflected out into the fiber cladding, again by virtue of the 8° angled end-face.

It is true that this slight angle on each connector brings with it rotation issues that Flat, PC and UPC connectors simply don’t have. It is also the case that the three aforementioned connectors are all inter-mateable, whereas the APC isn’t. So, why then is the APC connector so important in fiber optics?

 

The uses of APC connectors

The best feedback examples from my previous blog came from people experienced with Fttxand Radio Frequency (RF) applications. The advance in analogue fiber optic technology has driven demand for it to replace more traditional coaxial cable (copper). Unlike digital signals (which are either ON or OFF), the analogue equipment used in applications such as DAS, FTTH and CCTV is highly sensitive to changes in signal, and therefore requires minimal back reflection (ORL).

 

APC ferrules offer return losses of -65dB. In comparison a UPC ferrule is typically not more than -55dB. This may not sound like a major difference, but you have to remember that the decibel scale is not linear. To put that into context a -20dB loss equates to 1% of the light being reflected back, -50dB leads to nominal reflectance of 0.001%, and -60dB (typical of an APC ferrule) equates to just 0.0001% being reflected back. This means that whilst a UPC polished connector will be okay for a variety of optical fiber applications, only an APC will cope with the demands of complex and multi-play services.

 

The choice is even more important where connector ports in the distribution network might be left unused, as is often the case in FTTx PON network architectures. Here, optical splitters are used to connect multiple subscriber Optical Network Units (ONUs) or Optical Network Terminals (ONTs). This is not a problem with unmated APC connections where the signal is reflected into the fiber cladding, resulting in typical reflectance loss of -65dB or less. The signal from an unmated UPC connector however, will be sent straight back towards the light source, resulting in disastrously high loss (more than 14dB), massively impeding the splitter module performance.

Picking the right physical contact connector

Looking at current technology, it’s clear that all of the connector end-face options mentioned in this blog post have a place in the market. Indeed, if we take a sidestep across to Plastic Optical Fiber (POF) applications, this can be terminated with a sharp craft knife and performance is still deemed good enough for use in the high-end automotive industry. When your specification also needs to consider cost and simplicity, not just optical performance, it’s hard to claim that one connector beats the others. Therefore whether you choose UPC or APC will depend on your particular need. With those applications that call for high precision optical fiber signaling, APC should be the first consideration, but less sensitive digital systems will perform equally well using UPC. Fiber-Mart can supply many kinds fiber connectors. If you have any questions or requirement of fiber connectors,welcome to contact us: product@fiber-mart.com.