Category: Fiber Transceivers

Shielded cables are not all the same

These are the six shielded network cable construction types that you will encounter:

F/UTP

This construction type is more commonly referred to as FTP. FTP only has foil shielding around the bundle of the 4 pairs. The individual pairs are NOT wrapped, this is the most common type of shielded cable and is perfectly acceptable for the majority of applications. This is the construction type used in our Cat5e and Cat6A shielded patch cables.

S/UTP

The difference between this type and the foil type described above is the shielding material. With S/UTP the shielding material is metal braid rather that foil, the individual pairs are not wrapped. Metal braid is far less flexible than foil shielding and therefore this cable type will be more rigid than its foil counterpart.

SF/UTP

This cable type is a combination of the two types above. Both foil and braid are used as the outer shield, individual pairs are not shielded. As you can imagine this shielding type is very effective.

The above two types are designed to deal with interference from outside the cable, but the individual pairs can interfere with each other. This is not usually a consideration in the home and office, but for some commercial, data center and industrial applications it may be desired or even necessary.

S/FTP

This cable type has a single metal braid shield around the four wire pairs, and each one of those pairs is individually wrapped in metal foil. As described above this limits the amount of crosstalk between the pairs. This is the construction type used in our Cat7 shielded patch cables.

F/FTP

The overall shielding material is foil, with each individual pair wrapped in foil. This cable type is commonly used for 10GBaseT applications.

U/FTP

There is no overall shielding material utilized, the individual pairs are foil wrapped only.

In summary

The main point we want you to take from this article is that there are different types of shielded cable, but more importantly the term “STP” is fairly misleading. The natural assumption is that if UTP stands for Unshielded Twisted Pair, then STP stands for Shielded Twisted Pair. But as you have seen in this article there are many types of shielding that have very specific applications.

Most applications only require F/UTP (commonly FTP) this is the type that we sell the most of. Our Cat 7 patch cables are S/FTP, this is for 10GBaseT transmission rates as well as protection from external interference sources.

Today, I am going to discuss what happens at the other end of a fiber link — detectors. Optical detectors, as the name implied, can detect the amount of light received. Our very own eyes are a pair of detectors as they can receive light information with the retina and transmit that light data to our brain. In the visible light spectrum, our eyes are great detectors to inspect fiber break or light leakage. However, most fiber works in the invisible wavelength spectrum where human eyes won’t be able to see. That is the where the optical detectors come in.

Photoelectric effect

It is impossible to explain how optical detectors work without mentioning the photoelectric effect.

This phenomenon was first observed by German scientist Heinrich Hertz who only published his observations. It was Albert Einstein who later studied this effect and quantified the discrete light energy as photons in one of his famous papers that won him a Nobel Prize in 1921. Vacuum photodiodes and photomultipliers take advantage of this technology and can convert the light signal back to electric signals. One critical parameter for characterizing detector is responsivity. It is the ratio of output electric current to the optical input power, with the unit A/W.

In the end, we will compare the responsivity of different detectors and choose wisely based on each application.

Vacuum Photodiode and Photomultiplier

A vacuum photodiode (or phototube) is mainly comprised of a cathode and an anode. When the cathode detects photons, electrons are emitted according to the photoelectric effect, and current will go through the circuit since electrons are attracted to the anode. The following sketch shows how vacuum photodiode works2.

The limitation of a vacuum tube is that it is physically too big and operates in a wavelength range lower than what fiber communication requires. Another issue is that it also involves much voltage to power it. The typical responsivity of a vacuum photodiode is in the magnitude of mA/W.

Photomultiplier, on the other hand, works more efficiently because of its built-in gain mechanism. In addition to the anode and cathode, it also has a series “dynodes” for accelerating the electrons. The following illustration shows the simplified circuitry of a photomultiplier3.

Just like in vacuum tube, electrons are radiated after photons got absorbed by the cathode. However, the emitted electrons are attracted by intermediate dynodes which have very high voltage. What is so good about dynodes is that there can be more than one electron gets emitted when only one electron is attracted to it. This is called secondary emission caused by high kinetic energy electrons possess. Each electron now becomes more than one electron after hitting each dynode, causing a series of multiplying which eventually leads to electric signal amplification.

The gain at each dynode is about 5, so if there are 3 dynodes in the tube, the total increase will 125 (5x5x5). In reality, there are typically 5 to 10 dynodes in each photomultiplier, so the actual gain is in the magnitude of millions. Photomultiplier tubes are high-speed but also consume hundreds of voltage to power each dynode. It is heavy and big, almost the size of a hand grenade4. Unfortunately, photomultipliers are not suitable for the fiber optic communications.

Learning to operate an OTDR properly is a critical skill for field technicians managing and servicing fiber optic networks.  The OTDR is used frequently to determine length and loss characteristics, including testing optical fibers for faults and related issues that can negatively affect network performance.

There are a number of excellent OTDR devices available in the market, from small portable units designed for field use, to sophisticated laboratory-grade devices that can provide a wide range of features intended for advanced users.  Regardless of the type of OTDR itself, the one complimentary training item that is always required is a length of test fiber.  (Note:  An OTDR launch fiber may also be required for overcoming the “dead zone” of a fiber-under-test, which is discussed here).  More importantly, the length of fiber should include issues or “events” to be identified by the device, simulating real-world factors in the classroom.

While most training facilities use unsecured fiber spools on the desktop, this is generally not a best practice, as the delicate fiber is frequently at risk of damage during handling.  Since the fiber will be used by many students over time, it is a benefit to both the instructors and the students to utilize a more professional setup designed to protect the fiber and provide consistent results.

By utilizing a Fiber Lab solution from fiber-mart.com, a number of benefits can be realized that are not available when using a traditional, unsecured fiber spool.  For convenience, we have outlined a number of key benefits below.

Key Benefits of Using a Fiber Lab for OTDR Training:

Easy-to-handle, professionally-designed enclosures protect fiber from accidental damage while providing consistent results

Any types or custom lengths are available, enabling a wide array of real-world scenarios, especially when combining multiple spools

The fiber can include in-line events representing field splices, connectors and patch panels, or other factors that affect performance.

A Fiber Lab offers both a training facility and it’s students the opportunity to bring the field network right into the classroom for practical, hands-on experience.  For the instructors, it is a great value to have a useful tool that can be used for teaching demonstrations and tests, while ensuring that students have learned the OTDR skills necessary to be successful in the field.

An Optical Time Domain Reflectometer (OTDR) is an optical measurement instrument designed to detect faults, splices and bends in optical fiber cables.  It functions by launching pulses of light into the optical fiber and measuring the back reflections created by the faults, splices, and bends.  It can identify the exact location of the fault by measuring the round trip time from the launch to the detection of the reflected returning pulse.  The time is determined by the speed of light in the glass core of the optical fiber.

With so many factors affecting the launch and detection process, problems such as unreliable traces of measurements are likely to be seen especially when only a little amount of light comes back to the OTDR for analysis.  This occurs when trying to look at a very long length optical fiber.  If you are trying to look at a very long optical fiber, it is necessary to launch a lot of power to see the end.  When a lot of optical power is launched, the pulse width of the launched optical signal is increased.  The large pulse width decreases the resolution of the measurement and can be as much as several hundred meters.  Faults near to the launch end are then masked because of the hundreds of meters between the launch pulse and the receiver being able to see the reflected pulse.  If there is a fault near the launch point, it can also create large reflections that saturate and overload the receiver.  This length of fiber is sometimes called the Dead Zone because the faults are masked in the length close to the OTDR.  The receiver requires an amount of time to recover from saturation.  Depending on the OTDR design, wavelength, and magnitude, the OTDR may take up to 500 meters or more to fully recover.

Most OTDR manuals suggest the use of launch fibers to resolve these issues.  Launch fibers place the necessary length of fiber between the OTDR and the actual fiber being measured providing time for the receiver to settle and also for the pulse width dependent resolution to be overcome.  When launch fibers are used, faults close to the end of the fiber being measured can be seen by the OTDR.  They do not interfere with the actual fiber being measured and thus are very secure and proven as a technique for identifying faults in the total length of fiber from the first interface to the last.

An OTDR launch fiber, often available on a small spool or within a “launch box”, is used to create the proper conditions for testing another similar optical fiber for faults.  This method avoids undesirable variations in loss and distance measurements.  A launch fiber will help to overcome the blind spot or Dead Zone of an OTDR brought about by high launch power or faults near the launch end of the fiber.  In summary, an OTDR launch fiber provides both the time and distance required for the OTDR to effectively look at and measure the characteristics of the entire length of fiber being tested, especially the length closest to the OTDR.

Polarization maintaining fused coupler is covering a wide range of optical devices that may have been used or not, includes optical splitters, optical combiners, and couplers. The couplers are operating in different applications that require other than specific connections. The fused coupler is used to split optical signals between two fibers into one and they are constructed by fusing & tapering the fibers together. This method is used for creating a simple and rugged method of splitting. Polarization maintaining fused coupler is built using unique fusing technique and polarization maintains fiber.

What is the main use of PM fused couplers?

The PM fused coupler is the type of component that is allowing the redistribution of optical signals. The device is able to distribute the other optical signals from one fiber among two or more fibers. The coupler is having the ability to combine the optical signals from two or more fibers into a single fiber.  The input signal is not directly transmitted from one fiber to another, but divided among the output ports.

The operating wavelength of fused PM Splitter is up to ±20 nm for 1550 nm region devices. If you are looking for a fused coupler for operations within the standard bandwidth or splitter, it is best to order a standard center wavelength. There are companies manufacturing the polarization maintaining fused coupler. The manufactures uses unique fusing techniques and PM fiber to build couplers. They have the features of excess loss, small size and high polarization extinction ratio.

The PM fused coupler is split into high power linearly polarized light into multiple paths without perturbing the line. It is also used as the power tap to monitor signal power in a PM fiber system without disturbing the linear SOP of light propagating in the PM fiber.

Listed below are the features of PM fused coupler –

Available for slow or fast axis operation

Compact in-line package

High extinction ratio

Low insertion loss

High stability and reliability

The fused coupler is used in applications like fiber optic instruments, fiber amplifiers, fiber sensors, coherent detecting, and research. Optical couplers are important devices in optical communication and there are various types of optical couplers with different transmission characteristics. Fused PM splitters have a wide variety of options with the standard configuration of 1×2, 2×2, 1×3 (monolithic) and 1×4 (compact cascaded). The couplers are configured and built in-line with the industry requirement.

The optical couplers are fused fiber branching devices that split the portion of light allowing optical monitoring. The devices are used extensively in amplifier power control and in transmission equipment for monitoring the performance. The polarization dependent loss coupler is offering low levels of sensitivity to polarization and enables effective management of optical networks. The couplers are available in a wide range of split ratios, lengths and packaging. The Polarization maintaining fused coupler can be bought online for its best usage.

A fused coupler is consisting of two, parallel fibers that can be stretched, twisted, and fused together. The length of the coupling region determines the coupling from one fiber to the other. The Polarization maintaining fused coupler is used to add additional functionality to the network such as network status monitoring. It is the most cost-effective way to minimize the loss and maximize the wavelength isolation. Polarization maintaining fiber coupler is capable of combining two or more inputs into a single output and also divides a single input into two or more outputs.

fiber-mart.com is the most unique fusing technique that builds the 980/1030/1064nm polarization maintaining fused coupler (PMC). The ratio can be selected according to the requirement and the businesses can benefit a lot buying the fused coupler online.  It features low excess loss, small size and high polarization extinction ratio. The polarization maintaining fused coupler is widely used for optical sensors and amplifiers. A unique fusing technique is used for building the polarization maintaining fused coupler.

How does a fused fiber coupler work?

A fused coupler is consisting of two, parallel optical fibers which are close to each other due to twisting, fusing, and stretching. The length of coupling region determines the coupling ratio from one fiber to the other. Light is launched into the coupling ratio during the manufacturing process and the output power from each output port is carefully monitored. After the achievement of the desired coupling ratio, the fully automated process stops. The process is known as Fused Biconical Taper (FBT) process.

These are the features of Polarization maintaining fused coupler

It incorporates Low Insertion Loss

It has high extinction ratio

Available in compact In-Line Package

It enables high stability and reliability

It maintains good uniformity with high directivity

Wide variety of wavelengths 780 nm-2005 nm

It is used for fiber optic instruments and fiber sensors

It is also used in research works and enables coherent detection

Polarization maintaining fiber coupler is capable of combining two or more inputs into a single output and also divides a single input into two or more outputs. Make sure that you have the fused coupler for your business or job at the best price and specifications. The coupler are developed using fusing technique and polarization maintaining fiber.