The use of fiber optic systems is expanding at a amazing rate. Only in the past Ten years, fiber optic communications systems have replaced just about all coaxial and twisted pair cables particularly in network backbones. This is also true in almost any long distance communication links.

This can be explained simply. Optical fiber cable is easier to set up, lighter than traditional copper cable, and much smaller than its electronic counterpart. The most crucial factor is it has much more bandwidth. Because fiber optic cables are lighter, they are simpler to survive existing ducts and cable raceways. There are other big benefits of fiber optic cables including their immunity to electromagnetic interference, longer repeater distances, lower power requirements, and better flexibility.

All the above pros make fiber optic cables very attractive and most important of all, very economical. The unstoppable trend for fiber optic applications would be the change from the long haul (long distance) to our desk, our house, and our office. The terms include FTTC ( fiber towards the curb), FTTD (fiber towards the desk), FTTH (fiber towards the home) and FTTB( fiber to the building). Fiber optic cables enable our imagine integrating all our phone, Internet and TV services. Fiber’s wide bandwidth makes this possible. It offers more than enough ability to meet all our voice, data and video requirements.

The transformation from copper to fiber is greatly accelerated through the invention of optical fiber amplifier. Optical fiber amplifiers enable optical signal transmission over very long distances without the expensive procedure for conversion to electronic signals, electronic amplification and the conversion to optical signal again as in traditional regenerators.

Today most of the network traffic switching continue to be done by electronic switches such as those from Cisco. But tremendous interest and effort of utilizing all-optical devices for those network switching are accumulating in the industry. The most important sign of all-optical switching lies in its almost unlimited transmission capacity. However, it is still within the prototype stage for controlling light with light, so optical swith circuits continue to be controlled by electronic circuits now. The switching matrix may be optical circuits but the control are still done by electronic circuits.

Optical fiber is nearly the perfect medium for signal transmission available today and in the foreseeable future. The excellent sign of optical fiber is its immunity to electromagnetic interference. Optical circuits can be crossed inside a common space without cross interference among them. But you will find problems which are impeding the rate of all-optical system development. The most obvious and basic reason may be the compatibility requirements with legacy fiber optic systems.

Another huge advantage of optical fiber is based on the opportunity to multiplex its capacity via WDM (wavelength division multiplexer). WDM modulates each of several data streams right into a different part of the light spectrum. WDM is the optical equivalent of FDM (frequency division multiplexer). The use of WDM can increase the capacity of merely one channel fiber optic communication system by countless times.

In additional to optical communication systems, fiber optic technology is also widely used in medicine, illumination, sensing, endoscopy, industry control and more.

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

An optical switch developed at the Joint Quantum Institute (JQI) spurs the mark integration of photonics and electronics.

What, isn’t electronics adequate? Well, nothing travels faster than light, as well as in your time and effort to hurry in the processing andtransmission of knowledge, the combined use of photons along with electrons is desirable for developing a workable opto-electronic protocol. The JQI switch can steer a beam of light from one direction toanother in only 120 picoseconds, requiring hardly any power, no more than 90 atto joules. At the wavelength used, in the near infrared,this amounts to about 140 photons. This is actually the setup of a waveguide made from a photonic crystal, a great device put into the fiber optic transmission area.

A quantum dot is placed inside a tiny zone free from holes. Light is distributed into and from the waveguide via endcaps. If properly timed, a pump laser pulse allows probe pulse to exit the side. When the probe and pump beams are not aligned, the probe beam will exit the farend of the waveguide. The center piece of most electronic gear is the transistor, a solid-state component where a gate signal is used to a nearby tiny conducting pathway, thus switching on and off the passage of the information signal.

The analogous process in photonics would be a solid-state component which provides a gate, enabling or disabling the passage of light through a nearby waveguide, or as a router,for switching beams in different directions. Within the JQI experiment, prepared and conducted in the University of Maryland and at the National Institute for Standards and Technology (NIST) by Edo Waks and his colleagues, an all-optical switch has been created utilizing a quantum dot placed in the resonant cavity. The dot, consisting of a nm-sized sandwich of the elements indium and arsenic, is so tiny that electrons moving inside can emit light at only discrete wavelengths, as though the dot were an atom. The quantum dot sits inside a photonic crystal, a material that has been tired of many tiny holes.

The holes preclude the passage of sunshine with the crystal except for a narrow wavelength range. Actually, the dot sits in the small hole-free arcade which acts just like a resonant cavity. When light travels on the nearby waveguide a lot of it gets into the cavity, where it interacts using the quantum dot. And it is this interaction which could transform the waveguide’s transmission properties. Although 140 photons are needed in the waveguide to create switching action,only about 6 photons actually are required to bring about modulationof the quantum dot, thus throwing the switch.

Previous optical switches happen to be able to work only by utilizing bulky nonlinear-crystals and high input power. The JQI switch, by comparison, achieves high-nonlinear interactions using a single quantum dot and very low power input. Switching required only 90 atto joules of power, some five times less than the very best previous reported device made at labs in Japan, which itself used 100 times less power than other all-optical switches. Japan switch, however, has the advantage of operating at room temperature, as the JQI switch needs a temperature close to 40 K.

Continuing our analogy with electronics: light traveling on the waveguide by means of an information-carrying beam could be switched from one direction to another using the presence of asecond pulse, a control beam. To steer the probe beam the side from the device, the slightly detuned pump beam needs toarrive simultaneously with the probe beam, that is on resonance with the dot. The dot lies just off the middle tabs on the waveguide, inside the cavity. The temperature from the quantum dot is tuned to become resonant using the cavity, leading to strong coupling. If the pump beam doesn’t reach the same time as the probe, the probe beam will exit in another direction.

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