Fiber optic attenuators are small passive devices designed to reduce the strength of an optical signal. For those who are unfamiliar, attenuation refers to the rate at which the light or signal loses its strength. Optical attenuators are available in different types, including, fixed, step-wise variable, and continuously variable optical attenuators.
When people learn what fiber optic attenuators means, they typically wonder why anyone would want to introduce attenuation purposely on a fiber optic network. If you are also the one, then keep reading.
Why are fiber optical attenuators useful? Why do you need to accentuate signals?
There are many scenarios in which you need a mechanical variable optical attenuator. For instance, in a multi-wavelength fiber optic system, you need to equalize the strength of optical channel so that every channel has similar power levels. This requires you to reduce the strength of optical signals so that they lower down to match the channels with lower power.
Another example includes the system where received optical power is so much strong that it saturates the receiver. In this case, you will also need an optical attenuator to ensure that the receiver can detect the signal correctly.
Hence, you can say that they are proved to be very useful in conditions when the signal arriving at the receiver is too strong and can overpower the receiving equipment.
But, why does a transmitter send too strong signals? This often occurs due to a mismatch between transmitters and receivers. Sometimes, it happens because the media converters are meant to be used for much longer distance than they are currently being used for.
Apart from preventing the receiver from being overwhelmed by too strong signals, optical attenuators are also widely used for stress testing a network link by reducing the signal strength incrementally until the optical link fails. It helps in determining the signal’s existing safety margin.
What are the different types of fiber optical attenuators?
While fiber optical attenuators are typically used in single-mode circuits because of the use of stronger lasers for distance transmission, you can also find multi-mode attenuators.
Male to female attenuators are the most common type of attenuators. They are also known with other names, such as plug-style or buildout style. These attenuators are designed to mount on one end of a fiber optic cable so that the cable can be plugged into the receiving equipment or panel.
There are also female to female attenuators, also called bulkhead attenuators that are often mounted in patch panels or used to connect two optic cables together.
Apart from these, there are variable optical attenuators that are highly useful for testing applications but are more expensive than other types of attenuators. Thus, before you place any order for fiber optical attenuator, you must check which type of attenuator you need and for which application.
Nowadays, fiber lasers and amplifiers are being used in a wide range of applications. Their popularity is only increasing as they provide high wall-plug efficiency and superior beam quality even at high power levels. Since their usage is increasing in the commercial sector, the utmost focus is given on their reliability and also of other components required in the system. Thus, to enhance the reliability and robustness of all-fiber lasers and amplifiers at high power, you need to manage unwanted light with extreme efficiency. That’s where a cladding power stripper (CPS) comes into the picture.
Once you are able to properly manage the unwanted light, you can significantly improve the quality of the system and the output light beam as well. The unwanted light generates across the chain of components forming a system, and each of these components has a specific task to perform. For instance, tapered fused bundle (TFB) couplers are used for combining signal and pump light. They typically have low transmission loss but require protection against the backward traveling light to ensure that they safely function at high power in a real system. Here, you can use cladding power strippers to ensure their safe functioning.
By now, you might have got an idea of what cladding power strippers do. But what are they exactly?
What is a cladding power stripper?
A cladding power stripper is a mode stripping device designed to remove any light that travels in the cladding and helps ensure that the measurements are based only on the effects of the core and not the cladding.
An ideal cladding power stripper features high stripping efficiency, low signal loss, low beam quality degradation, high extinction ratio, high-temperature stability, high power handling capability, and extreme reliability.
It helps you ensure that optical powers are absorbed in a widespread area and that generated heat can be dissipated safely without affecting or damaging the surrounding components.
What are the uses of a cladding power stripper?
A cladding power stripper is widely used in:
Fiber amplifiers
Fiber laser systems
ASE Stripping
Life science and Imaging
Quantum optics
Telecommunication systems
Biomedical applications
Metrology field
Why do I need to strip light from the cladding of an optical fiber?
The unwanted light in the cladding of the fiber leads to poor beam quality and incorrect measurements. These effects can be more pronounced when you are working with high-power systems. Apart from improving the beam quality, you might also want to prevent the residual light from accompanying the amplified signal or from reaching the signal source. Undesired light in the cladding can also lead to excessive heat which can destroy the coating. Hence, you will need to use cladding power strippers to remove the unwanted light that travels in the cladding.
If you need cladding power strippers in standard or custom specifications or have any queries about cladding power strippers, please feel free to contact us. We offer cladding power strippers in a range of specifications and make sure that we provide you with only quality products.
Fiber Optic fused Couplers are the key elements in fiber-optic networks for the redistribution of optical signals. Fiber coupler devices are used as small components within various optical modules and systems for long-distance signal transmission, signal amplification, monitoring, and conditioning. They are also widely used in passive optical access networks.
A fiber optic coupler or optical fused coupler is an optical device that is used to distribute the optical signal from one fiber into two or more fibers and vice versa. A basic optical coupler has N input ports ranging from 1 to 64 and M output ports ranging from 1 to 64 for signal distribution. The number of ports on both sides depends on the optical application and network
Manufacturing of Fused Optical Couplers
The manufacturing process of optical fused couplers is known as the Fused Biconical Taper (FBT) process. A fused coupler has two parallel optical fibers that are fused together to bring their core very close to from a Coupling Region. The length of this region determines the coupling ratio from one fiber optic to the other. A light signal is launched into the input port to carefully monitor the output power from each output port during the manufacturing process. After achieving the desired coupling ratio, the manufacturing process is stopped for the particular fused optical coupler.
Types of Fiber Optic Couplers
Fiber optic couplers can be categorized based on various parameters to achieve desired functionality for a specific optical application in a fiber network.
Optical Couplers Classified by Shape
Y Coupler
It Resembles the English letter Y, and also known as optical tap coupler. A single input signal is distributed into two output signals using a Y coupler with any coupling ratio from 0.1% to 50% for specific applications. The power distributions ratio is precisely controlled for an optical network.
X Coupler (2×2)
It usually resembles the function of an optical signal splitter or combiner. It is used to combines or divides optical power from the input ports to the output ports.
Star Coupler
Star coupler combines several input and output ports for desired signal distribution. The number of input and output ports can be in any combination for optical power distribution using start couplers. However, the coupling rations remain equal among all the output ports.
Tree Coupler
It is also a multiport coupler, buy only at the output side. It is used to optical power from one input fiber to N numbers of output fibers in an optical fiber network. It is also used reversely to combine multiple optical signals to one output fiber.
Optical Couplers Classified by Wavelength
Optical couplers are usually designed for single wavelength, dual-wavelength or wideband transmissions. You can select optical fiber couplers based on bandwidth, regardless of the type of ports used. As the name suggests, single-window couplers incorporate a single wavelength, dual-wavelength couplers work with two wavelengths at the same time, and wideband couplers are designed for a wider range of wavelengths for optical signal transmission.
At DK Photonics, we sell a wide range of optical fused couplers for a variety of applications in different settings. All the products are tested for high stability and reliability in your fiber network. We also help our clients with customized solutions to meet their specific requirements with high-quality optical passive components. Contact us to discuss your custom needs and requirements.
Fiber-optic communication is the ideal choice for the transmission of data beyond gigabits. It is used to transmit all kinds of data in form of light signals over long distances for efficient and fast communication. A fiber-optic system uses lightwave technology to transmit data over fiber cables at low attenuation and maximum transmission security.
To transmit light signals over optical fiber in fiber optic communication and fiber laser systems, there are a lot of components such as a 1064nm bandpass filter, polarization optical isolator, single-mode fused coupler, and many more for accurate and efficient light signal transmission. Here’re some of the most widely used fiber optic components in fiber optic systems:
Single-Mode Fused Coupler: Single-mode fused couplers are used to split a portion of a light signal. They are widely used in transmission equipment and amplifier power control systems for feedback control and performance monitoring. Single-mode fused couplers are available in a wide range of length, polarization-dependent loss value, split ratio, sensitivity, and packaging to meet different types of applications in optical networks.
Band Pass Filter: Bandpass filters are used to block unwanted signals in fiber communication and laser systems. Some of the common characteristics of bandpass filters include high return loss, low insertion loss, high isolation, high-power handling capability, and excellent environmental stability. They are extensively used in fiber lasers, fiber amplifiers, high-speed communication systems, and instrumentation applications. Some examples of bandpass filters are the 1064nm bandpass filter, 1030nm bandpass filter, and 1053nm bandpass filter.
Polarization Insensitive Optical Isolator: It is an optical device that guides light in one direction and reflects back unwanted scattered and reflected light signals at any polarization state. Optical isolators have the characteristics such as high isolation, low insertion loss, and high return loss. They are widely used fiber lasers, EDFAs, transmitters, Raman amplifiers, and fiber optic communication systems to eliminate back reflection and backscattering. They are available in a wide range of wavelength and power handling to meet different requirements.
Polarization Insensitive Optical Circulator: It is a high-performance optical device that is used to route incoming signals to different ports. For example, if you want to route an incoming light signal from port 1 to port 2, optical circulators act as signal routers to route light signals from an input fiber to output fibe.
Faraday Mirror: It is a passive optical device that provides rotation of the input light at an angle of 45 or 90 degrees depending on the polarization state. It is widely used in measurement applications and fiber optic networks to eliminate the polarization sensitivity of the system. Faraday mirrors are extensively used in Brillouin amplifier systems, fiber interferometers, fiber optic antenna remoting systems, and fiber laser systems.
Pump and Signal Combiner: It is an optical device designed for high-power applications with exceptional characteristics. They can combine multiple pump lasers into one fiber to create a high-power laser source for applications in industries like the military, telecommunication, and medical.
These are some of the most common optical components used in fiber-optic networks, amplifiers, transmitters, optic laser systems, and other fiber optic communication systems across industries. At DK Photonics, we sell optical components in a wide range of wavelengths, lose value, power handling capability, and sensitivity to meet custom requirements. You can also contact us with your desired specifications and quote a custom component as per your unique requirement. We can help you with all kinds of custom solutions to meet your fiber optic system requirements.
A passive optical network is a point-to-multipoint network architecture to serve multiple premises. It allows communication service providers to serve several customers using a single connection. There is no need for any active components for electrical-to-optical or optical-to-electrical conversion during the operations. Some of the most common optical passive components include optical couplers, optical splitters, optical filters, optical connectors, optical attenuators, optical circulators, optical isolators, optical switches, and optical add/drop multiplexers. These components have become a promising solution for modern-day telecommunication needs.
Top 5 most widely used Optical Passive Components
Optical Coupler/Splitter
Optical fiber couplers/splitters are the most popular optical passive components for wavelength multi-demultiplexing of optical signals. An optical coupler is used to combine the signal from different fibers while an optical splitter is used to separate light signals in different fibers. In general, there is no significant difference between a coupler and splitter as an optical device. The functional difference is associated with the end you use as the input or the output as per your connection needs.
Optical Filter
An optical filter is also a wavelength multi/demultiplexing device but with a dielectric thin film that allows you to add or drop any specific wavelength during a fiber communication. The dielectric thin film is a multilayered film with different refractive indexes deposited on different layers to enable specific wavelengths to reflect or transmit at the layer interfaces. It is basically used to filter out a specific wavelength in the midst of fiber as per specific settings.
Optical fiber communication has brought us a fast and efficient mode of data transmission. There are various kinds of optical components and technologies used to achieve maximum reliability, functionality, and economical efficiency of an optical network. Optical passive components play a significant role in today’s data networks and FTTH applications to establish effective fiber communication.
Optical Connector
Optical connectors or fiber optic connectors are used to create a temporary joint connection between two optical fibers, cables, or devices. There are different types of optical connectors have been developed by manufacturers of optical passive components to meet different communication needs. The most common optical connectors include ST, LC, FC, SC, and MTRJ style connectors.
Optical Attenuator
Optical attenuators are fiber optic devices used to reduce the power of transmitted light in a controlled manner. It is used to:
Preserve receivers from saturation state
Balance wavelength power
Equalize node power
There are four types of optical attenuators available in the market for power balancing in fiber communication – plug-style attenuators, in-line attenuators, variable attenuators, and fixed attenuators.
Optical Switch
Optical switches are the fiber optic devices used to control physical connection between input and output ports. They are mainly used in:
Automatic measurement
Optical fiber network remote monitoring
Transplanting multiplexing
Optical path monitoring system
Optical fiber sensing system
Optical device testing
DK Photonics is a world-class manufacturer of high-quality optical passive components for fiber laser and Optical Fibers applications. We offer a low-cost and high-quality option for all the components for the full-range solution of any passive optical network project.
Pump Combiner is a passive component, widely used in different applications such as fiber laser, fiber amplifier, high power EDFA, biomedical systems, sensor systems, and more. They are made using the Fused Biconical Taper (FBT) technique. According to their design principle, several pump fibers are arranged around a signal fiber and the whole bundle that is typically surrounded by a glass tube is tapered down in a way that its dimensions align perfectly with that of the active fiber.
Pump combiners are available in three different constructions, namely:
Multimode NX1
(N+1)x1 Pump and Single-mode Signal Combiners
(N+1)x1 Pump and PM Signal Combiners
Multimode Pump Combiners
Multimode Pump Combiners are usually the ones that couple 7 or 19 multimode sources directly into cladding-pumped fiber. They combine the optical power from different optical fibers to create a high power output.
Multimode combiners facilitate highly efficient power transfer to cater to the needs of high-power applications like direct diode material processing and pump cascading while ensuring maximum brightness conservation.
The main applications of multimode pump combiners are fiber lasers, fiber laser combination, industrial, and research. They are available in different configurations of N x 1, such as 2×1, 3×1, 4×1, 7×1, 19×1, 37×1, and so on.
(N+1)x1 Pump and Single-mode Signal Combiners
These types of combiners are designed to couple 6 or 18 multimode sources and 1 SM signal source either to provide a combined power output or to use with a cladding-pumped fiber.
In other words, single-mode combiners are those pump combiners where the signal input is transferred via a single-mode fiber and not the pump inputs. Pump inputs are typically used in multimode pump combiners.
The signal-fiber design is often used in the military and medical industries. It can also be used to design an amplifier for use in telecommunications.
(N+1)x1 Pump and PM Signal Combiners
These combiners are built to couple 6 multimode sources and 1 polarization-maintaining (PM) source to produce combined power output or be used with a PM cladding-pumped fiber. Polarization-maintaining combiners are said to possess polarization-maintaining properties for the signal only.
Just like other pump combiners, they are also used to design amplifiers that require signal polarization outputs for use in industrial, military, medical and telecommunications applications.
Key Properties to Look for in Quality Pump Combiners
The diameters of fibers should be the same to ensure high-quality fusion splicing with the proper matching of core positions.
The pump fibers must have high compatibility with fibers of pump laser diodes. The core diameter and numerical aperture must be at least as high as those of pump diodes’ pigtails. While larger values of pump input fibers don’t affect power coupling efficiency, it might mean that the pump brightness won’t be utilized fully.
The intensity profile of the fundamental signal fiber mode should match the fundamental mode of the active fiber core. It will help you couple signal light into the fundamental mode efficiently.
The pump light should suffer minimum losses when propagating through the combiner. It will help ensure a coupling efficiency higher than 90 percent and minimized thermal damage.
In a pump or signal combiner, there should be only a minimal loss of brightness.
The combiner should withstand the intended optical power levels.
Whenever you buy pump combiners, keep all these factors in mind to ensure that you make the right choice. Besides, you also have the freedom to order customized pump combiners. So, if you don’t find the pump combiner you are looking for, don’t hesitate to get in touch with the manufacturer and discuss your requirements.
Modal Effects on Multimode Fiber Loss Measurements
In order to test multimode fiber optic cables accurately and reproducibly, it is necessary to understand modal distribution, mode control and attenuation correction factors. Modal distribution in multimode fiber is very important to measurement reproducibility and accuracy.
What is “Modal Distribution” ?
In multimode fibers, some light rays travel straight down the axis of the fiber while all the others wiggle or bounce back and forth inside the core. In step index fiber, the off axis rays, called “higher order modes” bounce back and forth from core/cladding boundaries as they are transmitted down the fiber. Since these high order modes travel a longer distance than the axial ray, they are responsible for the dispersion that limits the fiber’s bandwidth.
In graded index fiber, the reduction of the index of refraction of the core as one approaches the cladding causes the higher order modes to follow a curved path that is longer than the axial ray (the “zero order mode”), but by virtue of the lower index of refraction away from the axis, light speeds up as it approaches the cladding and it takes approximately the same time to travel through the fiber. Thus the “dispersion” or variations in transit time for various modes, is minimized and bandwidth of the fiber is maximized.
However, the fact that the higher order modes travel farther in the glass core means that they have a greater likelihood of being scattered or absorbed, the two primary causes of attenuation in optical fibers. Therefore, the higher order modes will have greater attenuation than lower order modes, and a long length of fiber that was fully filled (all modes had the same power level launched into them) will have a lower amount of power in the higher order modes than will a short length of the same fiber.
This change in “modal distribution” between long and short fibers can be described as a “transient loss”, and can make big differences in the measurements one makes with the fiber. It not only changes the modal distribution, it changes the effective core diameter and numerical aperture also.
The term “equilibrium modal distribution” (EMD) is used to describe the modal distribution in a long fiber which has lost the higher order modes. A “long” fiber is one in EMD, while a “short” fiber has all its initially launched higher order modes.
What Does Fiber Modal Distribution Look Like ?
Relative Modal Distribution of Multimode Fibers Modal distribution in a multimode fiber depends on your source, fiber, and the intermediate “components” such as connectors, couplers and switches, all of which affect the modal distribution of fibers they connect. Typical modal distributions for various fiber optic components are shown here.
In the laboratory, a lensed optical system can be used to fully fill the fiber modes and a “mode filter”, usually a mandrel wrap which stresses the fiber and increases loss for the higher order modes, used to simulate EMD conditions. A “mode scrambler”, made by fusion splicing a step index fiber in the graded index fiber near the source can also be used to fill all modes equally. If one has a proper optical system, one can control the launch conditions to very specific levels as desired for the measurements being performed.
A fully filled fiber means that all modes carry equal power, as shown by the line across the top of the graph. A long length of fiber loses light in the higher order modes faster, leading to the gently sloping “EMD” curve. Mode filtering strips off the higher order modes, but provides only a crude approximation of EMD. The microlensed LED , often thought to overfill the modes, actually couples most of its power in lower order modes. The E-LED (edge-emitting LED) couples even more strongly in the lower order modes. Connectors are mode mixers, since misalignment losses cause some power in lower order modes to be coupled up to higher order modes.
Measuring Modal Fill In MM Fibers Modal fill can be measured by either a nearfield scan or a far field scan. The technique is similar to measuring numerical aperture (NA) by looking at the light exiting the fiber. If light fills more modes the scan (intensity vs. position across the fiber end, either near or far field) will be wider, as shown by the red and green modes and profiles below. The presentation of the data is where changes have occured over the years. Mode power distribution has been used for years but has been replaced by encircled flux for standards. CPR has also been used as a simple metric but has serious problems and is becoming obsolete.
Mode Power Distribution Mode power distribution (MPD) has been used for a long time as a metric for modal distribution. It is a result of a far field scan of the output of a fiber with some mathematical manipulation to show the power in the modes, all normalized, as shown in the graph below. The dark lines are the limits set for test sources. Needless to say, it’s not a very easy function to visualize, leading to searches for other ways to measure and define modal distribution.
Coupled Power Ratio Coupled power ratio is an easier metric to understand, as it is simply the difference in dB of the power coupled from a fiber under test to both a similar MM fiber and a SM fiber. The rationale is the measurement is the difference between the total power in the fiber and the power in the central modes, so a fully filled fiber will have a greater dB difference in CPR. What often gets ignored when measuring CPR is at 850 nm, the SM fiber must be a 850 SM fiber with a core diameter of ~5 µm which is not a common fiber – not a regular 1300 nm SM fiber.
CPR was divided into classes. The rated category values in dB for both 850nm and 1300nm into a 62.5/125 multimode fiber, are as follows:
850nm: Category 1 (overfilled) 25-29 dB Category 2 21-24.9 dB Category 3 14-20.9 dB Category 4 7-13.9 dB (similar to typical VCSELs) Category 5 (very under filled) 0-6.9 dB
1300nm : Category 1 (overfilled) 21-25 dB Category 2 17-20.9 dB Category 3 12-16.9 dB Category 4 7-11.9 dB Category 5 (very under filled) 0-6.9 dB
In use a overfilled (Category 1) source with a mandrel wrap was specified for testing (see below). CPR was used for almost 20 years until it was realized that it was subject to large errors in fibers which had central dips in the index profile, a common fault in poorly made fibers. It was determined that a better metric would be a profile created by an integral of the light included inside a given radius of the fiber, leading to the defining of encircled flux.
Encircled Flux Recently, a more precise method of defining mode fill has been adopted. Encircled flux (EF), defines the integral of power output of the fiber over the radius of the fiber. When you look look at the graph below, consider that the vertical axis is the total amount of optical power from the source coupled into a fiber core inside the radius shown in the horizontal axis. EF was defined during the development of 10 GB Ethernet as a way to define the light output from an ideal VCSEL source which concentrates more of its power in the center of the fiber than a LED. The EF definition was used for bandwidth simulation only at that point. Of course a real VCSEL may be (is likely to be) different, but this model allowed calculating the bandwidth of this ideal VCSEL in various types of fibers of various lengths to determine their capability of supporting 10 GBE. It was later decided that EF would be a better way to define mode fill for loss testing.
This method of measuring mode fill should be more precise than other methods like CPR. EF should be easier to measure using imaging devices that can be calibrated.
EF is a more sensitive way of defining power and it can be measured using imaging techniques. The vertical (Y) scale shows the total power from the core of the fiber up to a point on the radius (in microns), so when one gets to 25 microns, one measures all the power. The shape of the curve is chosen to emulate an idealized source that is between underfill and overfill conditions.
EF has become part of several new MM testing standards. It is intended to create a more reproducible modal condition for testing that is similar to the CPR/mandrel wrap method described below. However, data shows a close correlation between EF and the results of a mandrel wrap conditioner.
Real World Sources
In an actual operating communications system, such controlled conditions obviously do not exist.
It has been accepted as “common knowledge” that microlens LEDs (as used with most multimode datacom systems) overfill fibers, and when we use them as test sources, we are testing with an overfilled launch. That is not necessarily so. Tests on microlens LEDs indicate that they may underfill compared to EMD. And edge-emitter LEDs (E-LED), typical of the high speed emitters at 1300 nm, concentrate their power even more into the lower order modes. VCSELs also underfill fibers. Production variations of all LEDs, VCSELs and lasers mean that actual mode fills can vary widely, especially since some devices emit off axis and are carried in skew modes, creating an uneven mode fill.
Other results show that connectors mix some power back into the higher order modes due to angular misalignment and switches strip out higher modes . In a simulated FDDI system using 8 fiber optic switches and 20 pairs of connectors, with fiber lengths of 10 to 50 meters between them, the majority of system power was concentrated in the lower order modes.
What conclusions can we draw ? The most significant conclusions is that it may not be prudent to design datacom and LAN systems on the worst-case loss specifications for connectors and switches. In actual operation, the simulated system exhibited almost 15 dB less loss than predicted from worst case component specifications (obtained with fully filled launch conditions). In most of today’s high speed systems, LEDs are too slow to be used as transmitters, so a special type of low cost 850 nm laser called a VCSEL (vertical cavity surface-emitting laser) is used as a transmitter. VCSELs couple light tightly into the core of a multimode fiber, similar ot a eLED in the diagram above.
And, when testing cables designed for low speed LED transmitter type systems, using a LED source similar to the one used in the system and short launch cables may provide as accurate a measurement as is possible under more controlled circumstances, since the LED approximates the system source. For newer sytems using VCSEL sources, one should use at least a LED with a mandrel wrap (see below) or a commercially-available mode modifier. Bandwidth also can vary widely with mode fill. Modal bandwidth in MM fibers is highly sensitive to the higher order modes which have the highest dispersion and are harder to control. Most fibers are tested for bandwidth with an overfill condition, but laser-optimized fibers are more appropriately tested with a EF fill which was designed to approximate a VCSEL.
The Effect on Measurements
If you measure the attenuation of a long fiber in EMD (or any fiber with EMD simulated launch conditions) and compare it to a normal fiber with “overfill launch conditions ” (that is the source fills all the modes equally), you will find the difference is about 1 dB/km, and this figure is the “transient loss”. Thus, the EMD fiber measurement gives an attenuation that is 1 dB/km less than the overfill conditions.
Fiber manufacturers use the EMD type of measurement for fiber because it is more reproducible and is representative of the losses to be expected in long lengths of fiber. But with connectors, the EMD measurement can give overly optimistic results, since it effectively represents a situation where one launches from a smaller diameter fiber of lower NA than the receive fiber, an ideal situation for low connector loss.
The difference in connector loss caused by modal launch conditions can be dramatic. Using the same pair of non-PC (physical contact) connectors, it is possible to measure 0.6 to 0.9 dB with a fully filled launch and 0.3 to 0.4 dB with a EMD simulated launch. PC connectors (ST, SC or LC) will have smaller but measurable differences.
Here is a drawing showing testing with a fully filled fiber and one where the higher order modes have been stripped off to simulate the fiber with a typical VCSEL source.
In class, the instructors had each made at least one good connector in our termination lab (we were using the most basic technique, heat-cured epoxy and polishing) so we decided to test their connectors with and without a mandrel wrap mode conditioner (described below) to see if it made a difference.
After adding the mandrel wrap to the launch cable, we tested the LED test source using a HOML (higher order mode loss) test as described in the page on EF. With the mandrel wrap, the power was reduced by ~0.6dB, so we left the mandrel on for our testing.
Adding the mandrel wrap certainly did make a difference. Connectors tested single-ended without the mandrel wrap at ~0.6dB loss were measured at ~0.2dB with the mandrel wrap. That’s how much difference modal conditioning can make on a single connector.
Which is a valid number to use for a connector pair’s loss ? That depends on the application. If you are connecting two fibers near a LED source, the higher value may be more representative, since the launch cable is so short. But if you are connecting to a cable one km away, the lower value may be more valid.
Mode Conditioners
In the early days (early-mid 1980s) when even long distance links were 50/125 multimode fiber, the goal was to create modal conditions similar to what one would see in long distance links after equilibrium was established, usually several km from the source. EMD (equilibrium modal distribution) was obtained using a combination of mode scramblers and filters created using stressed fibers and/or a combination of step index and graded index fibers. Other methods were developed for testing premises cabling with LED test sources also, including custom-made step index fibers and using a mandrel wrap mode filter with sources characterized using a simple method called “coupled power ratio” (CPR) that compares the power of a LED source with multimode and special singlemode (850 nm, 5 micron core) fibers. Another method is it use a gap loss attenuator calibration, with gap loss being one easy way to control mode filtering. Some of these methods have been patented around the world, but it’s highly doubtful than any of these patents are enforceable due to prior art dating back 30 years.
Practice The easiest way to make such a device is to create a simple mode scrambler with a multimode fiber under stress or laid in a tight serpentine followed by a gap loss. The gap can be made with a mechanical splice like a 3M Fiberlok or two connectors with a small washer inside the mating adapter between the two connectors. In theory, one could use a prepolished/splice connector where the gap is added to the internal mechanical splice for the simplest implementation.
There are three basic “gadgets” to condition the modal distribution in multimode fibers :
mode strippers which remove unwanted cladding mode light,
mode scramblers which mix modes to equalize power in all the modes, and
mode filters which remove the higher order modes to simulate EMD or steady state conditions.
These devices are used to condition modal fill in multimode fiber to reduce measurement uncertainty in testing loss or bandwidth. For more information on loss testing, see Accuracy.
Cladding Mode Strippers
Cladding mode strippers are used to remove any light being propagated in the cladding to insure that measurements include only the effects of the core. Most American fibers are “self-stripping”; the buffer is chosen to have an index of refraction that will promote the leakage of light from the cladding to the buffer. If you are using at least 1 meter of fiber, cladding modes will probably not be a factor in measurements. One can easily tell if cladding modes are a factor. Start with 10 meters of fiber coupled to a source and measure the power transmitted through it. Cut back to 5 meters and then 4, 3, 2, and 1 meter, measuring the power at every cutback. The loss in the fiber core is very small in 10 meters, about 0.03 – 0.06 dB. But if the power measured increases rapidly, the additional light measured is cladding light, which has a very high attenuation, and a cladding mode stripper is recommended for accurate measurements if short lengths of fiber must be used.
To make a cladding mode stripper, strip off the fiber’s buffer for 2 to 3 inches (50 to 75 mm) and immerse the fiber in a substance of equal or higher index of refraction than the cladding. This can be done by immersing the fiber in alcohol or mineral oil in a beaker, or by threading the fiber through a common soda straw and filling the straw with index matching epoxy or an optical gel (Note: stripping the buffer away from the end of a fiber is easily done, using a chemical stripper. If the fiber cannot be chemically stripped, like those with Teflon buffers, check with the fiber manufacturer for instructions.) A caution. Do not stress the fiber after the mode stripper, as this will reintroduce cladding modes, negating the effects of the mode stripper. Mode stripping should be done last if mode scrambling and filtering are also done on a fiber under test.
Mode Scramblers
Mode scrambling is an attempt to equalize the power in all modes, simulating a fully filled launch. This should not be confused with a mode filter which simulates the modal distribution of a fiber in equilibrium modal distribution (EMD). Both may be used together sometimes however, to properly simulate test conditions. Mode scramblers are easily made by fusion (or mechanical) splicing a short piece of step index fiber in between two pieces of graded index fiber being tested. Simply attaching a step index fiber to a source as a launch cable before a reference launch cable will also work.
One can also use methods that produce small perturbations on the fiber, such as running the fiber through a tube of lead shot or a fixture that holds the fiber in a serpentine and puts several tight bends in the fiber. But these scramblers are difficult to fabricate and calibrate accurately. In the laboratory, they are usually unnecessary, since accurate launch optics are used to produce fully filled launch conditions.
Mode Filters – The “Mandrel Wrap”
Mode filters are used to selectively remove higher order modes to attempt to simulate EMD or Encircled Flux conditions with fully an LED source. Higher order modes are easily removed by stressing the fiber in a controlled manner, since the higher order modes are more susceptible to bending losses.
The most popular mode filter is the “mandrel wrap”, where the fiber is snugly wrapped around a mandrel several times. The size of the mandrel and the number of turns will determine the effect on the higher order modes. Other mode filters can be made where the fiber is subjected to a series of gentle S bends, either in a form or by wrapping around pins in a plate or by actually using a long length of fiber attached to an overfilling source.
Below is the mandrel wrap specification from TIA 568, which is to be used with what is basically an overfilled (Category 1 CPR) LED source.
TIA-568 Specified Mandrel Size (Wrap launch reference cable five turns over the specified size mandrel)
Fiber Type
3mm Jacketed Cable
2.0 or 2.4mm Jacketed Cable
1.6mm Jacketed Cable
900 micron Buffered Fiber
50/125
22 mm
23 mm
24 mm
25 mm
62.5/125
17 mm
18 mm
19 mm
20 mm
NOTE – The mandrel diameters are based on nominal values of 20 mm (0.79 in) and 25 mm (0.98 in)) reduced by the cable diameter and rounded up.
The target weights for 50 μm optical fibre at 850 nm have been studied most extensively. The results were very close to the upper limit of the 10 Gb/s Ethernet limit for transmitters, which means that using it would be conservative; i.e. if the cabling ‘passed’ when tested using this metric then it would be certain to support 10Gb/s Ethernet. The results were very close to an OFL followed by an 18 mm to 20 mm mandrel with five turns. This is close to what had been defined in some standards as the requirement for testing in premises cabling. Thus using the traditional mandrel wrap will closely follow EF guidelines.
Checking Mandrel Wrap with HOML – Higher Order Mode Loss
HOML is simple to use. Connect the launch reference cable to a source and measure the output of the reference cable with a power meter. Wrap the launch reference cable around the specified mandrel and measure the output again. If the measured power is reduced by 0.2 to 0.6 dB, the source is essentially EF compliant and ready to use, without the mandrel. Remove the mandrel and make your tests. If the HOML is >0.6dB, leave the mandrel on the reference launch cable and make measurements. If the HOML is <0.2dB, the source has too low a mode fill and should not be used.
Following this method using conventional fibers will result in a mode fill similar to EF, the new requirement for MM testing standards.
When Do You Use Them ?
Obviously, if you are working in the laboratory measuring fiber attenuation using a lamp source and monochrometer, you probably need a combination of all of the above. If you are using a LED or laser source, you might not need any of them, since they greatly underfill the higher order modes. LEDs and lasers also are the same mode fill as actual system sources, providing a proper simulation of actual operating conditions without mode modifiers of any kind.
Bend-Insensitive Fibers Bend-insensitive fibers (both MM and SM) have become popular for use as patchcords and running cables inside buildings where tight bends may be needed. BI fiber uses changes in the index profile to reflect leaky modes back into the fibers. BI MM fibers may have more higher order modes and thus more mode fill. They also do not respond to mandrel wrap mode filtering in the same way, generally requiring much tighter bends to achieve the same effect. When using BI MM fibers for launch cables that need modal conditioning, contact the fiber manufacturer for their recommendations, but most fiber manufacturers recommend not using BI fiber as reference launch cables.
Testing SM Fiber
Testing single mode fiber is easy compared to multimode fiber. Singlemode fiber, as the name says, only supports one mode of transmission for wavelengths greater than the cutoff wavelength of the fiber. Thus most problems associated with mode power distribution are no longer a factor. However, it takes a short distance for singlemode fiber to really be singlemode, since several modes may be supported for a short distance after connectors, splices or sources. Singlemode fibers shorter than 10 m may have several modes. To insure short cables have only one mode of propagation, one can use a simple mode filter made from a 4-6 inch loop of the cable.
An
abbreviated form of Coarse Wavelength Division Multiplexing, CWDM technology is
a great way of creating a flexible “pay-as-you-grow” type of high capacity
optical network. This technology is widely used in dual fiber applications.
Once you get CWDM
Mux/Demux module installed in your network, you can benefit from the added
capacity without ever having to interrupt or break the existing traffic.
The Mux/Demux Module
A
Mux/Demux module is made of a multiplexing unit that has the capacity of
combining all eight wavelengths into a single mode fiber strand and a
demultiplexing unit that has the capacity of splitting the incoming light into
eight different data channels. This device gives up to 16-channel and even
18-channel multiplexing on a single fiber. A standard CWDM Mux/Demux bundle
sort consists of ABS box bundle, LGX package, and 19” 1U rackmount.
Counted
under the category of WDM, the main goal of using such a device is to add the
extra capacity to network and to meet a wide range of necessities and system
arrangements. There are various board applications that require channel CWDM
including Gigabit and 10G Ethernet, Fiber Channel, ATM, ESCON, SDH/SONET and
CATV.
Since CWDM items are usually epoxy-free on the optical side, this provides better working conditions. Besides, in CWDM Mux/Demux, there is a high level of channel segregation which prompts better outcomes.
CWDM Mux/Demux Uses
WDM and Access Systems:
Since these channel sorts are a part of WDM class, their best application is in
the WDM and access systems.
Line Checking: Such
devices also find their application as a line observer/checker. Line checking
helps in ensuring that there is no crash in the similar line of another range
or frequency.
Cellular Applications: The
arrangements of CWDM channels have their use and application in the Cellular
area as an unparalleled panacea for various problems.
Telecommunications: The
broadcast communication area has a wide usage of CWDM arrangements at an
incredible rate. CWDM technology is a perfect solution for straightforward
transmission of signals.
Apart
from these applications and elements, the CWDM technology is also used to
uncover the deficiency of fiber and straightforward transmission of exchange
while reducing the charges of system building. This is the reason why Channel
CWDM Mux/Demux modules have a significant place in the realm of fiber optics,
flag transmission, multiplexing and so on.
Do
you also needaCWDM
Mux/Demux module for your application? Contact the leading manufacturer
in the market known for designing high quality optical passive components and
devices.
CWDM MUX and Demux are compact, hot plugging transceivers, which is used in both telecommunication and data communication fields. It is versatile enough that it can be used in both the fields and takes their work pressure on its shoulder. It has the form factor designs and the electrical interface pointed by the multi-source agreement (MSA) under the small factory committee.
Its mechanism
Basically MUX and Demux are called as multiplexers or demultiplexers which are used by combining or separately for different wavelength. They are usually the passive or optical components for Bi or unidirectional operation. Its features are low insertion loss and high channel isolation, compact design for maximum use or optimum system integration; it is high in return loss, high thermal, stable in mechanical and environmental requirements and last but not the least the customer specification. In simple language it is simply understandable that it comes in small and mini size, it has a wide pass band and Epoxy free.
Applications
It is used in transmission system, link monitoring, Add- drop- multiplexing, metropolitan network, CATV system, etc. Its application area is vast as the whole communication and data transmission depends on it. Other than that it is supplied in several housing sizes with tube pigtails and reinforced wire pigtails. It is available in all connector standard types. Ideally, it is applied on line monitoring, WDM network telecommunication cellular application, fiber optical amplifier and access network.
Future aspects
Both the communication and data transmission industries cannot be imagined even working without this product because it is like a fuel injector without which a machine will not work. After having a conversation with the technical experts it can be said that there is no replacement found now for this product. Its future is secured and even it also secures the future of the data and communication industry. The experiments for making the procedure easy is on the way soon our world will have new technology, but the level of success it have, is not easily achievable.
I hope you get the importance, features, designs and applications of the compactCWDM MUX and Demux. It is a whole and a sole pillar for smooth working and easy transmission of the data. It helps in solving the problem of the communication industry and it also tries to keep the problems away. This blog’s object is to educate people about the working style of the industries that are the base of today’s world.
Creativity is not a thing which has certain graphs or moves to develop, it can be considered as anything which is new and innovative, that’s why our technology has also certain thing which gives the right to be creative in any sense, because sometimes weird things make the best innovative stuff. In the support of the above context, here is a technological support to the wire system which gives the space to be creative and make innovative things and that is the polarization maintaining fiber coupler.
The PM coupler is basically used for optical signal polarization which can split the energy or combines the same for several other uses. There is an example of usage of PM coupler and that is the LED wired light which needs such transformation in separating the lights making it brighter than other.
Key Features of PM coupler
Low excess loss
Separation of power
Isolation
Insulation
High power handling
780, 820, 980, 1064, C, L , S bands available
Slow axis operation as standard
Fast axis operation also available
Applications of the PM coupler
It provide help to the power monitoring of PM sources
It also applies on the Coherent communications
Fiber gyroscopes is another applicant of its use
It supports High power fiber lasers
Fiber amplifiers depend on its basic use.
Scope of the PM coupler
The polarization maintaining fiber coupler has a very bright future as it is giving the right kind of space to the innovators by isolating and insulating the power in order to give the innovative place to the thinkers. It is taking all things on the hike that even in future the inventions related lights and other wired things can take place easily. It is based on their simple mechanism where the power isolation and compilation occurs. It helps in making things simple by being a bond of two wires in order to make a unit which can be turn in any direction. According to experts there is no replacement found because it is cheap and useful which is not possible with any other new thing but inventors are taking their attempts in order to make something like that which can help in other procedures too.
I hope the readers will get the importance of polarization maintaining Fiber coupler 115 71 which gives the innovative approach to the engineers in order to create something new and exciting which will take peoples mind. This must be giving the revolutionary change to the world of technology one day.
