Fiber optic connector

Wednesday, 03 January 2007

Fiber optics has become the core of telecommunications and data networking infrastructures. Fiber optic communication systems transmit signals between ends of the fiber optic cable, utilizing a signal encoded with light rather than the signal being encoded with an electric current within an electric conductor. Fiber optic cables are increasingly being used for communicating wide bandwidths of data at high data transmission rates. The applications for fiber optic cables vary widely, from telecommunications, to cable television, to highly advanced aircraft and spacecraft systems. The speed and bandwidth of data transmission over fiber optic cable renders optical fiber communication particularly advantageous for certain applications. Fiber optic cables are used in the telecommunication industry to transmit light signals in high-speed data and communication systems. Fiber optic communication systems provide immunity from electromagnetic interference (EMI), provide virtually unlimited bandwidth, and provide that data can be quickly transferred over long distances. The use of fiber optics typically becomes cost efficient as compared, for instance, to copper cables, when the data rates exceed about 100,000 bits per second (bps). Optical energy may be modulated at much higher frequencies than electrical energy. In addition, and unlike electrical energy, optical energy can be constrained within small fibers. Optical fibers allow multiple secure high bandwidth transmissions to occur within close physical proximity of each other. The long distance telecommunications and military industries have gained much benefit from fiber optics. Because optical fibers transmit voice and other data far more rapidly and efficiently than copper wire, the demand for optical fibers is continuing to increase. For example, optical fibers no longer serve merely as the medium for long distance signal transmission but are increasingly routed directly to the home or, in some instances, directly to a desk or other work location to network computers. The heart of such transmission systems is an optical fiber of silica glass or other suitable material that has been clad with an appropriate material to create a waveguide along which light energy can travel in a controlled manner. A standard fiber optic cable includes a fiber with an inner light transmitting optical core. Optical fibers are extremely small and when they are incorporated into a transmission system it is necessary to effect interconnections between separate lengths of such fibers, or between fiber and active transmitters or receivers. Surrounding the fiber is an outer protective casing. A fiber terminates at a fiber optic connector. A fiber optic system begins with a source such as a laser which generates a light energy signal and injects it into an optical fiber. The signal travels through the system via a series of optical fibers which are connected in end-to-end fashion by connection assemblies. Each connection assembly is made up of a fiber optic connector attached to or terminated to the end of an optical fiber, and an adapter which receives the ends of the connectors and precisely aligns the optical fibers in the connectors in abutting, end-to-end relationship. To use optical fibers effectively for communications, demountable connections are required. A connector allows a demountable connection between fibers or between a fiber and a source or detector. Fiber optic connectors are frequently used to non-permanently connect and disconnect optical elements in a fiber optic transmission system.

Optical fiber connectors are an essential part of optical fiber communications systems. Fiber optic connectors are used to provide optical connections between fibers and input/output ports of optical components. Optical fiber connectors may be used to join lengths of optical fiber into longer lengths, or to connect optical fiber to active devices such as radiation sources, detectors, repeaters, or to passive devices such as switches or attenuators. Light bearing information can be transmitted to different terminals via such connectors. Fiber optic connectors are attached at to ends of optical fibers to enable one or more optical fibers to be optically coupled with one or more other optical fibers of another connector or other optical transmission device. An optical fiber connector may include a connector housing with numerous passages and an alignment assembly lying in a front portion of each passage. Each alignment assembly includes an alignment sleeve and may include an outer sleeve that surrounds the alignment sleeve. Usually, one or more optical fibers pass through the ferrule and have ends that are flush with or project slightly beyond the forward end of the ferrule for coupling with the end of one or more other optical fibers in a complementary fiber optic connector or device. The ferrule is a long thin cylinder that is bored through the center at a diameter that is slightly larger than the diameter of the cladding of the fiber optic cable. The end of the fiber optic cable is located at the end of the ferrule. The ferrules retain fibers in a fixed position within a fiber passage. The fiber held by the ferrule is polished to a flat mirror finish. An endface of the fiber is finished to be flush with an endface of the ferrule. A ferrule holder or other housing component of the connector embraces the ferrule and may be fabricated of such material as molded plastic. A spring may be disposed within the housing or ferrule holder such that the ferrule is yieldably biased forwardly for engaging another fiber-mounting ferrule of a mating connecting device. The geometry of the coupling mechanism is generally independent of the ferrule. Ferrules may comprise a precision ferrule capillary providing a fiber retention and alignment function held by a ferrule base. Ferrules are typically made of metal or ceramic, but may also be constructed of plastic. In addition to the ferrule and the connector housing, a fiber optic connector typically includes a crimp body connected to a rear portion of the connector housing and a spring disposed between the crimp body and the rear surface of the ferrule for urging the ferrule forwardly in the internal cavity defined by the connector housing. The housing of the connector typically includes features for locking the connector in engagement with the complementary connector or device. A fiber optic connector also typically includes a crimp band for cooperating with the crimp body to engage one or more strength members of an optical cable to securely attach the fiber optic connector to the fiber optic cable, as well as a connector boot for providing strain relief for the optical fibers. In addition, a fiber optic connector can include one or more optional components, such as a pin keeper, a spring centering element, a lead-in tube, and a divider. Most fiber optic connectors do not use the male-female configuration common to electronic connectors. Instead, a coupling device (the fourth component), such as an alignment sleeve, is used to mate the connectors. Fiber optic connector sleeves are frequently utilized to facilitate the mating of one or more fiber optic connectors. In this regard, a pair of fiber optic connectors can be inserted into the opposed ends of a fiber optic connector sleeve. The fiber optic connector sleeve serves to align the fiber optic connectors to some degree such that the optical fibers upon which the fiber optic connectors are mounted are also appropriately aligned. Generally, a fiber optic connector must provide that the end of one optical fiber becomes axially aligned with the end of another optical fiber. After the connection is made, all of the light from one optical fiber can travel into the other optical fiber. Because optical fibers are extremely small and because it is important that no data be lost at the point at which two optical fibers are joined, it is important that a connector be able to join two optical fibers with a relatively high amount of accuracy and precision.

Fiber optic connectors of a wide variety of designs have been employed to terminate optical fiber cables and to facilitate connection of the cables to other cables or other optical fiber transmission devices. A number of simplex, duplex and multi-fiber connectors including standard ferrules, such as SC, LC, FC, MU, MT and MTP, have been designed. Different connector types have different characteristics, advantages, disadvantages, and performance parameters. A common type of connector includes an angled-physical-contact (APC) ferrule that is designed to make physical contact with another APC ferrule during the process of interconnecting optical fibers (i.e., mating opposing fiber optic connectors). The APC ferrule geometry advantageously diverts back reflections into the cladding of the fiber. The end face of an APC ferrule is disposed at a non-orthogonal angle. APC ferrules may be preferred over physical-contact (PC) ferrules, as well as ultra-physical-contact (UPC) ferrules, because the angled end face of an APC ferrule advantageously reduces undesirable reflections of optical signals at the interface between the mating optical fibers, thereby decreasing losses and correspondingly increasing signal transmission. A typical SC fiber optic connector includes a housing having a front end positioned opposite from a rear end. The front end of the SC connector housing is commonly configured to be inserted within an adapter. The SC connector typically further includes a ferrule that is positioned within the front and rear ends of the housing, and adjacent the front end. The ferrule is axially moveable relative to the housing, and is spring biased toward the front of the connector. The fiber optic cable has an end that is stripped. The stripped end includes a bare fiber that extends into the connector and through the ferrule. Fiber stub connectors were designed to eliminate the need for expensive fusion splicing equipment, splice protection, and lengthy termination steps. The stub connector employs a short fiber stub that is spliced to the field fiber within the connector. Stub connectors typically require a crimp to either activate the splice or retain the field fiber, or both. A fanout connector is typically used with a ribbon-type optical fiber cable. The individual optical fibers of the cable are very closely spaced. A fanout connector includes a fanout means such as a fanout insert for receiving and spreading the individual fibers of the cable transversely thereof so that the fibers are more easily connectorized according to hardware interface requirements. The pigtail type connector wherein a premanufactured connector includes a cylindrical ceramic ferrule having a highly polished front face, a fiber stub adhered within an axial aperture in the ferrule, wherein the fiber stub extends rearwardly beyond, and thereby protrudes from, a rear end of the ferrule. Multifiber cables are being increasingly employed in a wide variety of applications. Multifiber connectors generally include a multifiber ferrule, such as a DC ferrule or an MT ferrule, that define a relatively large opening proximate the rear end of the ferrule for receiving the multifiber ribbon. Typically, the spacing between the bores defined by a multifiber ferrule and the spacing between the optical fibers of a multifiber ribbon are approximately equal. The end portions of the optical fibers of the multifiber ribbon can be inserted into respective bores defined by the ferrule once the multifiber ribbon has been guided into general alignment with the plurality of bores by the opening defined by the rear portion of the ferrule. Multifiber connectors can also include a lead-in tube to guide the multifiber ribbon into the opening defined by the rear portion of the ferrule. Typically, the lead-in tube is a cylindrical tube that serves to guide the multifiber ribbon as a whole and not individual ones of the optical fibers. The 24-fiber, multiple ribbon MT ferrule has been designed with stepped rows of v-grooves inside the ferrule, each groove row functioning to guide and to accommodate a ribbon. The mechanical transfer (MT) connector has a connector housing with a front end and a ferrule movably mounted in the housing. The MT connector, more accurately described as an MT ferrule, is essentially a housing that encapsulates the ends of a plurality of fibers and thus aids in aligning the fibers so that the ends of the fibers can be mechanically joined together to establish a connection between two groups of fibers in a manner analogous to the connection made by an electrical connector. The ferrule is biased by a spring to a forward position. When the ferrule is in the forward position, a front face of the ferrule projects from the housing. A multi-fiber cable extends into the housing. The individual fibers of the cable extend through the ferrule to the front face. The front face of the ferrule, and the ends of the fibers, are polished to form a flat surface. A male MT-type connector has pins in these bores projecting beyond the front face, whereas a female MT connector has the bores empty. Two cables may be connected to one another by engaging male and female MT connectors with one another so that the pins of the male connector enter the pin receiving bores of the female connector.

Fiber optic connectors can be mounted on end portions of a pair of fiber optic cables, each of which include a number of optical fibers. The optical fibers of the fiber optical cables can transmit data or control signals between various remote devices, such as sensors or actuators, and a central control computer, such as a flight controller of an aircraft. Optical fiber connectors can be used to tap the optical signals from the optical fiber along intermediate points thereof. The optical fiber connector can also be used to terminate the optical fiber. In either arrangement, the optical signals are carried by the optical fiber connector from the optical fiber into an optical device such as a light detecting diode or photo transistor which would then generate an electrical signal based on the tapped optical signal. The most common design for fiber optic connectors uses precision ferrules to hold the optical fiber. The ferrule on one side of a connection is held in a bushing/adapter (female side), which is secured inside an assembly or on a bulkhead. The other side is pushed into the bushing/adapter to make the optical connection. In order to efficiently transmit signals between optical fibers, the fiber optic connectors must precisely align the individual optical fibers such that the optical signals transmitted therethrough are efficiently coupled from fiber to fiber. In order to effectively couple optical signals from fiber to fiber, a fiber optic connector must maintain the precise alignment of the individual optical fibers in a predetermined manner such that the optical fibers will remain aligned as the fiber optic connector is mated with another fiber optic connector or with other types of optical device. A fiber optic connector requires mutual alignment of respective fiber cores in a repeatable separable interconnect. The connector must also maintain performance characteristics over multiple matings and unmatings under various environmental conditions. A fiber optic connector must be capable of joining optical fibers with a minimum of insertion loss, and must provide mechanical stability and protection to the junction between the optical fibers in the working environment. The achievement of low insertion loss in coupling two fibers together is a function of the alignment of the optical fiber ends, the width of the gap between the ends, and the optical surface condition of the fiber ends. The termination of an optical fiber may be indirect, i.e., the fiber may be connected to some other (passive) optical device, such as a beam splitter or polarizer, before the light beam is directed to the active optical device. During termination of a fiber optic connector, epoxy may be injected into a fiber passage internal to the ferrule. The process of injecting the epoxy subjects the ferrule capillary to an axial force relative to the ferrule base. It is desirable that the ferrule capillary resist axial movement in response to this "push out" force. Before a fiber optic cable can be joined to the end of a like cable to create a continuous fiber optic cable assembly, it is necessary to polish the ends of the tiny optical fibers at a mating face of the ferrule. It is often necessary to polish these optic ends to a precise length which they project from the mating face of the ferrule. Fiber optic connectors need to be cleaned every time they are mated and unmated. They also need to be mated or covered immediately after cleaning.

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