Optical Attenuator Types and Applications

Optical attenuator is a very important fiber optic passive components. It’s an indispensable device for fiber CATV. So far the market has formed four series that are fixed-step, variable, continuously variable and intelligent optical attenuator.

Types of Optical Attenuators

A. Displacement Optical Attenuator

As we all know, when the two sections of optical fiber connection, must meet a really high accuracy, in order to make the optical signal a smaller loss transmission previously. Conversely, when the fiber to help make the appropriate alterations in the precision, you can control the amount of attenuation. Displacement-type optical attenuator is based on this principle, the intention of the fiber within the butt, the appearance of certain dislocation. The sunshine energy loss, in order to achieve the purpose of a controlled amount of attenuation, the displacement-type optical attenuator is divided into two types: the lateral displacement type optical attenuator, the axial displacement of the optical attenuator. The lateral displacement from the optical attenuator is a classical method, due to the magnitude from the lateral displacement parameters in the micron level, so generally do not have to produce a variable attenuator is used only for producing fixed attenuator, and the use of welding or stick connection, there is still a sizable market, the benefit of high return loss, generally more than 60 dB. Axial displacement type optical attenuator by mechanical means as long as the process design of two optical fibers a certain distance with the objective, is possible attenuation. This principle is mainly employed for producing fixed optical attenuator and some small variable optical attenuator.

B. Thin-film Optical Attenuator

This attenuator is created while using principle of sunshine in the reflected light concentration of the top of metal thin film film thickness. When the thickness from the metal thin film deposited around the glass substrate is bound, made of a set optical attenuator. Different attenuation can be obtained if inside a different thickness of a disk-shaped metallic thin wax glass substrate, metallic thin film, so that inserted within the optical road to different thicknesses so that you can alter the intensity of the reflected light within the optical fiber inserted obliquely deposited Cover made of the variable attenuator.

C. Attenuation-sheet Optical Attenuator

Attenuation the chip type optical attenuator directly fixed attenuator through an absorption characteristic in the end surface of the optical fiber or even the optical path to attain the reason for the attenuation from the optical signal, this process can not simply be used to produce a fixed optical attenuator can also be used to produce the variable optical attenuator.

Applications of Optical attenuators

A set optical attenuator fixed amount of attenuation of the optical road to the sunshine energy is principally used for its excellent temperature characteristics. Within the commissioning from the system, widely used in analog optical signal through the corresponding period of optical fiber attenuation or reduce the margin from the optical power the relay station may also be used to prevent saturation from the optical receiver; optical test instrument calibration scaling. For different line interface, you can use different fixed attenuator; if the interface is really a pigtail type available pigtail type optical attenuator welded towards the optical path between the two sections of fiber; If you are debugging the machine connector interface converter or inverter-type fixed attenuator.

In practical applications often require attenuation quantity of the optical attenuator could be changed using the user needs. Therefore, a wider range of applying the variable attenuator. For instance, EDFA, CATV optical system design margin of the particular product is not quite the same, the optical power margin of the system BER assessment, to prevent the receiver is saturated, it should be inserted within the system variable optical attenuator, another , fiber optics (such as a power meter or OTDR) measurement, calibration will also make use of the variable attenuator. From the perspective of market demand, on the one hand, the optical attenuator development toward miniaturization, serialization, low price direction. However, due to the common type optical attenuator, optical attenuator is development direction toward high-performance, intelligent optical attenuator, high return loss optical attenuator.

Source: FiberStore

What you need to know before you purchase Fiber Optic Attenuators

So why do We Need a Fiber Optic Attenuator?

Bigger is much better, right? Or so many people believe. Beginners in fiber optic technology are often confused with why optic attenuators should reduce light intensity. Aren’t we using amplifiers to improve the signal electricity? The fact is that too much light can overload a fiber optic receiver. Optical fiber attenuators are needed when a transmitter delivers too much light, such as when a transmitter is very close to the receiver.

So how exactly does a Fiber Attenuator Work?

Attenuators usually works by absorbing the sunshine, such as a neutral density thin film filter. Or by scattering the sunshine such as an air gap. They should not reflect the light since that could cause unwanted back reflection within the fiber system. Another type of attenuator utilizes a length of high-loss optical fiber, that operates upon its input optical signal power level in such a way that it is output signal power level is less than the input level. The power reduction are done by such means as absorption, reflection, diffusion, scattering, deflection, diffraction, and dispersion, etc.

What’s the Most Important Feature Should a Fiber Attenuator Have?

The most crucial spec of an attenuator is its attenuation versus wavelength curve. Attenuators should have the same impact on all wavelengths used in the fiber system or at least as flat as possible. For instance, a 3dB attenuator at 1500nm should also lessen the concentration of light at 1550nm by 3dB or as close as possible, this is also true inside a WDM (Wavelength Division Multiplexing) system.

Different Types of Attenuators

There are two functional kinds of fiber attenuators: plug style (including bulkhead) and in-line. A plug style attenuator is utilized like a male-female connector where attenuation occurs inside the device, that’s, on the light path from one ferrule to another. Included in this are FC fiber optic attenuator, LC attenuator, SC attenuator, ST attenuator and much more. An in-line attenuator is connected to a transmission fiber by splicing its two pigtails.

The key of operation of attenuators are markedly different simply because they use various phenomena to lower the power of the propagating light. The easiest means would be to bend a fiber. Coil an area cable several times around a pencil while measuring the attenuation with a power meter, then tape this coil. Then you definitely got a primitive but working attenuator.

Most attenuators have fixed values which are specified by decibels (dB). They’re called fiber optic fixed attenuator. For instance, a -3dB attenuator should reduce intensity of the output by 3dB. Manufacturers use various light-absorbing material to attain well-controlled and stable attenuation. For instance, a fiber doped with a transition metal that absorbs light in a predictable way and disperses absorbed energy as a heat.

Variable optical attenuator is also available, but it is usually a precision instrument utilized in making measurements. From FiberStore, you can get the best Variable Attenuators Instrument.

Source: http://www.fiberstore.com/

Several Variable Optical Attenuator Introduction

Variable optical attenuator (VOA) has a wide range of applications in optical communication, and its main function is to reduce or control the optical signal.

The basic characteristics of fiber optic network should be Variable, especially with the application of DWDM transmission systems and EDFA in optical communication, it must be carried out in a plurality of optical signal on the transmission channel gain flattening or equalization, channel power in the optical receiver. The side to be dynamic saturation control, optical networks also need to control for other signals, making the VOA become indispensable key components. In addition, VOA also can be combined with other optical communication components and this pushed itself to the characteristics of the high-level module.

In recent years, there appeared many technologies on manufacture of variable optical attenuator, including mechanical VOA, magneto-optical VOA, LCD VOA, MEMS VOA, thermo-optic VOA and acousto-optic VOA.

Mechanical VOA
The principle is to use a stepper motor drag neutral gradient filter, its output optical power at a predetermined attenuation rule change when the different positions of the light beam passes through the filter, so as to achieve the purpose of adjusting the amount of attenuation. There is also a mechanical polarized optical attenuator. Its basic principle is that the light beam emitted from the ingress port reflected by the reflection sheet to the port, the the reflector coupling efficiency between the two ports by the inclination angle of the reflection sheet to the control, enabling adjustment of the light attenuation. The inclination of the reflection sheet from a variety of different mechanisms to control. Mechanical type optical attenuator is more traditional solutions, so far, the VOA application in the system most used mechanical method to achieve attenuation. The type of optical attenuator with mature technology, optical properties, low insertion loss, polarization dependent loss, without temperature control, etc.; disadvantage is that the larger, more complex structure components, the response rate is not high, it is difficult to automate the production is not conducive to integration.

Magneto-optical VOA
Magneto-optical VOA is the use of some of the substances in the magnetic field is shown by the changes in optical properties, such as magnetic rotation effect (Faraday effect) can also be achieved attenuation of the light energy, so as to achieve the purpose of adjusting the optical signal. The magneto-optical effect of the material and in combination with other techniques, you can create a high performance, small size, high response and the structure is relatively simple optical attenuator. This is LLL device using discrete technology to produce the optical attenuator to be a further development of the field.

LCD VOA
Utilizing a liquid crystal refractive index anisotropy in the liquid crystal VOA shows birefringence. When an external electric field is applied, the orientation of the liquid crystal molecules are rearranged, will result in the change in its transmission characteristics. The type of attenuation can be achieved by light intensity change of the type of voltage control is applied to the two electrodes in the liquid crystal. The liquid crystal optical attenuator VOA can achieve the miniaturization and high response. But at the same time the liquid crystal material into a larger loss, the production process is relatively more complex, in particular, is influenced by environmental factors, its advantage is a low cost, there are commercial batch.

MEMS VOA
MEMS is the technology of the new applications in this area, After several years of development, the MEMS chip production process has become more mature, a strong impetus to the application of the MEMS optical attenuator. Optical network applications, MEMS technology-based products also have the obvious advantage on price and performance. MEMS VOA has been very mature, and mass production and large-scale application. Because of yield problems, in terms of price also facing challenges In addition, micro-electro-mechanical components, reliability is sometimes less than ideal. The early MEMS VOA using laser welding, into a larger device, and the production efficiency is low, and high assembly costs. Currently, the market also introduced a MEMS VOA plastic technology, a good solution to this problem.

Thermo-optic VOA
Thermo-optic VOA mainly using some of the material changes in the optical properties of temperature field characteristics, such as temperature changes caused by the thermo-optical refractive index change. According to the structure of the different, can be divided into two categories, leak-and open-light type VOA. Thermo-optic VOA due to heating, cooling device is relatively complex, a function of the mathematical relationship between the temperature field photoconductive medium refractive index is complex and difficult to accurately quantify and control, especially the longer response time hindered its application in modern optical communication .

Acousto-optic VOA
The basic principle is to use the cyclical strain, resulting in a periodic variation of the refractive index, equal to create a phase grating for the acousto-optical crystal in the generated under the action of ultrasonic waves, and so can be modulated using the raster beam. Some companies have already claimed to have developed the acousto-optical crystal variable attenuator (called the AVOA). It is understood that the acquisition of the acousto-optic crystal material is no problem, but at this stage of the total cost is high, about 4-5.

Conclusion:

Variable optical attenuator is one of important optical devices in the optical communication system. Over the years, it has been stuck at a mechanical level. Because its size is not conducive to integration, it is generally only suitable for single-channel attenuation. With the development of DWDM system, as well as market the flexibility to upgrade reconfigurable optical add-drop multiplexer (ROADM) potentially huge demand, there need more channels and small size variable optical attenuator array, in particular the integrated VOA product. Traditional mechanical methods can not solve these problems. With the development of fiber optic network, VOAs development trends are: low cost, highly integrated, fast response time as well as integration of hybrid with other optical communication devices.

Source: http://www.fiberstore.com/

Optical attenuator Wikipedia

An optical attenuator is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. The basic types of optical attenuators are fixed, step-wise variable, and continuously variable.

Applications

Fiber optic attenuator is used in applications where the optical signal is too strong and needs to be reduced. Optical attenuators are commonly used in fiber optic communications, either to test power level margins by temporarily adding a calibrated amount of signal loss, or installed permanently to properly match transmitter and receiver levels.

For example, in a multi-wavelength fiber optic system, you need to equalize the optical channel strength so that all the channels have similar power levels. This means to reduce stronger channels’ powers to match lower power channels. Another example is when the received optical power is so strong that it saturates the receiver, you need an optical attenuator to reduce the power so the receiver can detect the signal correctly.

Fiber optic attenuators are usually used in two scenarios. The first case is in fiber optic 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.

Optical attenuators are typically classified as fixed or variable optical attenuator.

Fixed optical attenuators used in fiber optic systems may use a variety of principles for their functioning. Preferred attenuators use either doped fibers, or mis-aligned splices, 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 on to other cables.

Variable optical attenuators generally use a variable neutral density filter. Despite 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.

For precise testing purposes, engineers have also designed instrument type variable optical attenuators. They have high attenuation ranges, such as from 0.5 dB to 70dB. They also have very fine resolution, such as 0.01dB. This is critical for accurate testing.

Variable optical attenuator instrument calibration is a major issue. The user typically would like an absolute port to port calibration. Also, calibration should usually be at a number of wavelengths and power levels, since the device is not always linear. However a number of instruments do not in fact offer these basic features, presumably in an attempt to reduce cost. The most accurate variable attenuator instruments have thousands of calibration points, resulting in excellent overall accuracy in use.

Techniques for transmitting signals via optical fiber

There are two techniques of division multiplexing wavelength which means transmitting signals via optical fiber. They are DWDM and CWDM.

DWDM--Dense Wavelength Division Multiplexing means division multiplexing in dense wave longitude. DWDM transmission technique through optical fiber using the C band (1550 nm). That is a multiplexing method very similar to the frequency division multiplexing is used in electromagnetic transmission means. Several carrier signals (optical) are transmitted by a single optical fiber using different wavelengths of laser beam each. Each optical carrier is an optical channel that can be treated independently of other channels that share the medium (fiber optic) and contain different types of traffic. In this way can multiply the effective bandwidth of the optical fiber, so as to provide bidirectional communications. This is a very attractive transmission technique for telecom operators by allowing them to increase capacity without additional wiring or trenching. To transmit using DWDM is needed from complementary devices: a transmitter side muxer y demuxer at a receiver side it. Unlike him CWDM, DWDM is in numbers mayor Get optical channels reducing the chromatic dispersion of each channel through it using a laser Mayor Quality, baja fiber dispersion through him the use of DCM modules Dispersion Compensation Modules. In this MANERO you can combine more channels reducing space between he ello. Currently it pueden get 40, 80 to 160 optical channels separated 100 GHz, 50 GHz to 25 GHz respectively.

CWDM--Coarse Wavelength Division Multiplexing originally was fairly generic, and meant a number of different things. In general, these things shared the fact that the choice of channel spacings and frequency stability was such that erbium doped fiber amplifiers (EDFAs) could not be utilized. Prior to the relatively recent ITU standardization of the term, one common meaning for coarse WDM meant two (or possibly more) signals multiplexed onto a single fiber, where one signal was in the 1550 nm band, and the other in the 1310 nm band. CWDM Multiplexer Modules are available in 4, 8 and 16 channel configurations. These modules passively multiplex the optical signal outputs from 4 or more electronic devices, send them over a single optical fiber and then de-multiplex the signals into separate, distinct signals for input into electronic devices at the other end of the fiber optic link. The Coarse Wavelength Division Multiplexing-CWDM Mux/demux are a flexible plug-and-play network solution, which allows service providers and enterprise companies to cost effectively implement point to point or ring based WDM optical networks. CWDM Mux/demux is modular, scalable and is perfectly suited to transport PDH, SDH / SONET, ETHERNET services over WWDM, CWDM and DWDM in optical metro edge and access networks.

For a new year gift, here is some imformation of a fiber optic machine for you. It may be a necessity in you work--a variable optical attenuator. Optical variable attenuator is a double window (1310/1550nm) of passive components. The variable optical attenuator could continually and variably attenuate the light intensity in the optical fiber transmission. Variable fiber optic attenuator could help simulate distance or actual attenuation in the fiber optic testing work by inserting a calibrated attenuation into the link. By using the variable fiber optic attenuator, technicians could verify the power margin received by testing the fiber optic link power budget. Variable fiber attenuator can help user vary the light power injected from a light source into the optical fiber. Important parameter of variable fiber attenuator include its insertion loss, reflection loss and attenuation range. We supply ST, FC, SC, LC variable fiber optic attenuators with APC, UPC type. Attenuation range available is from 1dB to 30dB.