Optical passive devices is an important part of the communication device, but also the other optical components indispensable application areas. There are mainly four categories of Optical Passive.

(A) Active Fiber Optic Cable Connector

Fiber optic cable connector is connected to two active optical fiber to form a continuous optical path and can be repeated assembly and disassembly of passive components; also has the fiber optic cable with active devices, fiber optic cable and other passive components, fiber optic cables and systems and instrumentation carry out activities connections. Active connector along with the development of optical communication development, has now formed a complete range, a wide variety of systems products, fiber applications are indispensable, the most widely used component of the foundation.

Their function can be divided into the following sections: Connector plugs, fiber jumpers, converters, inverters, etc. These components may be used alone as the device, a component can be used together. In fact, an active connector is used to refer two connector plug plus a converter.

(B) Optical Attenuator

Optical attenuator is a certain amount of optical power can attenuation device. Optical attenuator can be broadly divided into fixed and variable types. Fixed attenuator and variable attenuator of the main indicators of its attenuation accuracy, precision, and stability or repeatability, as well as applicable wavelength region.

A fixed optical attenuator fixed amount of attenuation of the optical path of the light energy is mainly used for its excellent temperature characteristics. Debugging the system, commonly used in analog optical signals through a fiber attenuation and the corresponding relay station or decrease in the optical power of the room to prevent the optical receiver saturation; also be calibrated for an optical measuring instrument calibration.

For different line interface, you can use different fixed attenuator; if the interface is a pigtail type available pigtail type optical attenuator welded to the optical path between the two sections of fiber; If you are debugging the system connector interface converter or inverter-type fixed attenuator. In practical applications often require attenuation amount of the optical attenuator can be changed with the user needs. Therefore, the variable attenuator wider range of applications. For example, EDFA, CATV optical system design margin of the actual system is not exactly the same, the optical power margin of the system BER assessment, to prevent the receiver is saturated, it must be inserted in the system variable optical attenuator, another , fiber optics (such as a power meter or OTDR) measurement, calibration will also use the variable attenuator. From the perspective of market demand, on the one hand, the optical attenuator development toward miniaturization, serialization, low price direction. On the other hand, due to the common type optical attenuator, optical attenuator is development direction toward high-performance, intelligent optical attenuator, high return loss optical attenuator.

(C) Optical Switch

Optical switch is an optical path control device, the optical path switching plays a role in the optical fiber transmission network and a variety of optical switching systems, computer control can be achieved spectral exchange, to achieve between the terminals, between the center terminal and the distribution of information and exchange intelligence; in the ordinary optical transmission system, an optical path for the active and standby switching can be used in optical fiber, optical devices and optical fiber sensor network test, the optical fiber transmission systems, measuring instruments or the sensing system is stable and reliable easy to use.

CATV optical network in order to ensure uninterrupted operation of cable systems, should be equipped with a backup optical transmitter, an optical transmitter is working when a failure, the use of optical switch can be in a very short time (less than 1ms) to Backup optical transmitter access system to ensure it is working properly.

According to its operating principle, the optical switch can be divided into mechanical and non-mechanical two categories. Mechanical optical switch optical fiber or optical components by moving the optical path changes, currently on the market are generally mechanical optical switch, the advantage of low insertion loss, typically less than 1.5dB; high isolation, typically greater than 45dB, and without polarization wavelength effects. Non-mechanical optical switch is to rely on electro-optic effect, magneto-optical effect, sound and light effects and thermo-optic effect to change the refractive index of the waveguide, the optical path is changed, which is a new technology, the advantages of this type of switch: switch time is short, Small size, easy integration of optical or electro-optical integration; deficiencies are large insertion loss, isolation is low.

(D) WDM Multiplexer and Demultiplexer

Optical wavelength division multiplexing (WDM) technology in an optical fiber multiple wavelengths of light simultaneously transmitted carrier signal, and each optical carrier by FDM or TDM mode, each carrying multiple analog or digital signals. The basic principle is the sending side optical signals of different wavelengths are combined (multiplexed), and is coupled to the same fiber optical cable for transmission, the receiving end turn these combined signals at different wavelengths separated ( demultiplexing), and further processed to recover the original signal into a different terminal. Therefore, this technology called optical wavelength division multiplexing, short wavelength division multiplexing technologies.

Source: FiberStore

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

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/