Optocoupler, optical coupler

Thursday, 18 January 2007

Optical couplers, also referred to as optocouplers, are well known devices used to direct light from one light source to a light receiving member. Optical couplers are the heart of an optical communication network. Optical fiber technology is used in a variety of applications such as telecommunication, computer, and medical applications. In the past, optical fiber communication technology and optical fiber communication elements mainly were used on backbone networks. These days they are widely used in metropolitan optical communication networks. An important aspect of optical fiber technology is the coupling of an optical fiber to an optoelectronic device for transmitting information conducted by the optical fiber. Fiber optic systems have a number of features that make them superior to systems that use traditional copper cables. For example, fiber optic systems can have a much larger information-carrying capacity and are not subject to electrical interference. Signals transmitted over long-distance optic fibers need less amplification tham do signals transmitted over copper cables of equal length. Optical fibers have by far the greatest transmission bandwidth of any conventional transmission medium, and therefore optical fibers provide an excellent transmission medium. An optical fiber is a thin filament of drawn or extruded glass or plastic having a central core and a surrounding cladding of lower index material to promote internal reflection. Optical fibers are typically arranged in a bundle and protected by a sheath. Such a bundle of optical fibers is often referred to as an optical cable. The light receiving and emitting ends of the optical fibers are housed in fiber ferrules. The fiber ferrule at the light receiving end of the bundle is coupled to a light emitting device via an optical interface unit. Likewise, the fiber ferrule at the light emitting end of the bundle is coupled to a light detecting device via an optical interface unit. Optical radiation is coupled into the end face of an optical fiber by focusing the light onto the core.

An optical coupler is a passive device for branching or coupling an optical signal. Generally, a coupler is centralized by joining the two fibers together so that the light can pass from the sender unit to the two receivers, or else it can be made by juxtaposing the two "receiver" fibers which will then be aligned and positioned so as to be facing the "sender" fiber. The function of branching or coupling an optical signal in optical communications can be simply performed by various photomechanical connections, similar to branching or coupling in electric communications. However, the optical signal cannot be simply realized because of the characteristics of the optical fiber, so that a special optical coupler is employed as a light branching and coupling device. Optocouplers are used to electrically isolate an input signal from a corresponding output signal. Optocouplers, also referred to as optically coupled isolator devices or optical coupler circuits, provide isolation between different circuit portions which operate at vastly different voltages. The optocoupler offers an advantage of providing electrical isolation between the two circuits, thus reducing interface problems. Optocouplers have been used for electrical isolation in systems such as computers, power supplies, telecommunications, and controllers. For example, optocouplers are used in applications such as telecommunications equipment, programmable controllers, direct current (DC) to DC converters, alternating current (AC) to DC converters and battery chargers. Optocouplers are commonly used in switched-mode power supplies and other analog circuits to provide an analog feedback control signal across the isolation barrier. Optocouplers are also commonly used in circuits as indicators, or as control devices, wherein the light-responsive transistors are energized to control other circuits. Optocouplers usually include a light-emitting diode (LED) and a light-responsive transistor (light sensor) such as a phototransistor or a photodiode. Electrical isolation occurs because information is transmitted using light emitted by the LED and received by the light-responsive transistor. When the current driving the LED is changed, the amount of light that is emits also changes proportionally, and consequently also the electrical resistance of the photoresistor.

Optical couplers are key components in optical networks. Optical couplers, optical switches, and optical power splitters are needed in many optical applications. In fiber optical transmission systems the light beams traveling in two or more fibers must often be combined into a single fiber, a device which accomplishes this is called a combiner or multiplexer. Similarly, in such systems one beam must frequently be split into two or more beams, a device which accomplishes this is called a splitter or divider. The optical fiber coupler, also called optical fiber splitter, is an essential element to implement Fiber-To-The-Home (FTTH). Optical couplers are optical transmission system components used to connect planar arrangements of waveguides. Optical couplers are used for routing signals from one waveguide to another and/or for splitting optical signals into two independent signals at a predetermined power ratio to be transmitted over two different waveguides. Optical couplers are typically utilized to separate or combine an optic signal, such as an optic signal in a fiber optic cable. An optocoupler is generally used for causing outgoing light from an end face of an optical fiber to fall on another optical fiber. It is important for the optocoupler to be able to cause outgoing light from an optical fiber to fall on another optical fiber without loss and generation of optical noises. Optical fiber couplers have a coupling section which connects a plurality of optical fibers and, at the coupling section, separate or combine the light within the optical fibers. Typical optical couplers are comprised of a plurality of fiber optic cables. Where an optic signal is to be combined, the number of inputting signals is greater than the number of outputting signals. Where an optic signal is to be split, the number of cables inputting a signal is less than the number of cables outputting a signal. The optical fiber coupler usually is fabricated through a fused biconical tapered fiber coupling technique. The optical fiber passive device thus made costs less and has excellent optical characteristics.

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