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This slide opens the presentation with an explanation of why fiber is preferred over copper wire. The main advantage is that fiber has low loss and low spreading properties. This means much more data per second of transmission can be compressed and sent much farther downstream than with copper wire.

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Light travels in waves with each color having it own particular wave length. The chart above shows the wavelengths in nanometers for each particular color. The human eye is structured to “see” colors from about 400 nm to about 800nm. Below this visible spectrum is the ultraviolet region and above the visible spectrum is the infrared. Most fiber transmission systems are designed for the infrared region to take advantage of glass fiber properties (loss and spreading) in this region of the spectrum.

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This slide explains the bending properties of light which is very dependent on the index of refraction for the material. This is a very important property for fiber optic transmission. If light did not bend as it entered different materials, light in fiber optics would simply escape out the side and not travel downstream.

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This slide shows that when light travels at a very sharp angle toward a material with a different index of refraction, all the light gets reflected back or Total Internal Reflection (TIR). The angle where this occurs is called the “critical angle”. The angle varies with the materials involved and their respective indices of refraction.

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This slide further explains TIR.

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This slide explains that using just two kinds of glass (each with their own index of refraction) is enough to create TIR.

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Regardless of whether light is emitted from an LED or Laser, light is comprised of several sections or modes. These modes take a different path inside optical fiber. Some paths are shorter or longer than others. The main mode is called the “zero order mode”. Since multimode fiber will capture many modes of light, all of the modes will arrive at the other end at different times. This causes the signal to spread (dispersion) enough so that it will have to be repeated after some distance (roughly 500 meters). Single mode is a unique fiber design where only the main mode is captured by the fiber. Since there is very little modal dispersion, single mode signals can travel many many kilometers before requiring repeating.

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This slide shows the typical fiber designs in today’s markets. The last fiber design (100/140) is seldom used.

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This slide explains the two types of loss inherent in fiber optics. Glass fibers are never perfectly constructed and are never without some impurities. This means that the signal will degrade in strength as it travels down the fiber. Fiber loss can also come from bending the fiber as bending the fiber will defeat the critical angle needed for TIR.

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The graph on the left shows the loss properties of standard single mode fiber versus the wavelength. Notice that two low loss areas of the infrared transmission spectrum are apparent. One at 1310nm and one at 1550nm. Single mode systems are designed at these wavelengths to take advantage of this low loss region. In between these two areas of low loss transmission is a high loss area known as the “water peak”. Fiber optics has water ions (OH-) which greatly absorb light at the 1400nm wavelength. Newer “zero water peak” fibers eliminate this high loss and are perfect for fiber optic systems with multiple transmissions going through them – each at a slightly different color. These kinds of systems are call WDM or Wavelength Division Multiplexed systems.

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This slide shows that bandwidth is the key parameter for fiber optic systems. The more bandwidth you can pack into a fiber, the more revenue for the communications provider. Bandwidth is limited by two important parameters of fiber optics – Intermodal Dispersion and Intramodal Dispersion (also called Chromatic Dispersion). You can see that at different wavelengths, the index of refraction varies. Light at differing wavelengths travel at different speeds causing signal spreading (or dispersion). Both parameters seek to spread the signal as it travels down the fiber. If the signal spreads too much, then the signal is distorted enough where the light detector on the other end cannot differentiate if there was a pulse or not. This creates bit errors and causes the system to re-transmit which slows it down (causing less effective bandwidth). Notice the bandwidth difference between single mode and multimode systems.

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This slide shows the difference between LED based transmission systems and those based on Lasers. LED based systems overfilled the fiber with many modes of light while Laser systems typically will launch only a single mode of light. Multimode based systems are less expensive and work great for short distances. Single mode systems are typically for long distance transmission.

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This slide shows the evolution of multimode system designs. Early multimode systems were LED based since LEDs were cheap to make and Lasers were expensive. Multimode systems today are now using Lasers (to increase bandwidth) but the Lasers they are using are cheaper ones called VCSEL or Vertical-Cavity Surface-Emitting Laser. Notice that by using Lasers and better designed 62.5micron fibers, that bandwidth (and distance) is greatly increased over the original multimode fiber designs of OM1 and OM2.

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The latest feature demanded by installers of fiber transmission system is “bend insensitive” fibers. These fibers have special designs that limit the amount of light that escapes the fiber when the fiber is bent. Almost all fiber being manufactured today is “bend insensitive”.

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This slide shows the cross section of a typical fiber optic cable (with one fiber). The fiber itself is actually comprised of three sections. The inner section is called the core area and is made of very pure glass. The area around the core area is also made of glass but is called the cladding. The cladding is made from quartz and has a different index of refraction than the core region. A clear plastic acrylate coating is then extruded onto the glass in order to protect it from moisture and abrasions. The plastic coated fiber is then surrounded by a thicker plastic coating that is called the buffer. It can either be tightly extruded onto the plastic coated fiber or be surrounded by a loose tube of the same size (900 microns). Finally, strength members (Kevlar) and an outer jacket are applied.

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This slide shows some commonly available patch cords (also called jumpers). The majority of patchcords are either single fiber or duplex fiber designs. The are many variations of patchcords (length, cordage, connector type, fiber type, boot type) available depending on the application and customer preferences.

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Also available are connectorized cable assemblies which come with multiple fibers in them ranging in fiber counts from 2 to 144 fibers. A common term used when ordering connectorized cable assemblies is the breakout length. The breakout length on each end of the cable is typically described as the length between where the outer jacket ends and the end of the connectors. It is in this area where customer must decide what kind of outer protection each individual fiber will receive (after the outer jacket has been removed). For micro-distribution cable, each fiber needs to be up jacketed to at least a 900um tube in order for the fiber to be connectorized.

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Shown are the more popular connector types. The “/PC” or “/UPC” designation means the connector is polished for “physical contact”. A connector polished for “physical contact” is polished with a radius so that the fiber in the center of the connector is the main contact area of the connector’s end face. This polishing technique guarantees good fiber contact during interconnection allowing for low loss connector performance.

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Single mode connectors designated as “/APC” are polished at an angle in order to greatly reduce reflections (or return loss) from the end face of a connector. Reflections from connector end faces travel back into the single mode laser source and cause transmission problems. Video transmission systems (CATV) and very high speed digital systems are very sensitive to reflections.

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This slide shows the main parts of a fiber optic connector: Ferrule – typically ceramic with a 1.25mm or 2.5mm outside diameter. The hole size is always around 125 to 127 microns in order to fit a fiber that is 125 microns in diameter. Body – typically a metal backbone (barrel) that holds the ferrule and an outer plastic housing that holds the barrel/ferrule assembly. Crimp Ring – used to crimp the cable’s strength members (Kevlar) to the back of the connector providing strain relief. Boot – use to limit the bending of the fiber around the area where it enters the connector (not shown).

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Cut-out side view of a fiber inside a connector. Connectors need to have at least a 900 micron covering in order to be used by most connector designs. In order for the fiber to enter the ferrule, it must be stripped down to bare glass (125 microns). This means removing the 900 micron buffer and the 250 micron plastic acrylate coating.

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This slide shows the various steps in attaching a connector to the end of a fiber optic cable. These process steps are roughly the same regardless of connector type.

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Good end face geometry as shown above is essential for good loss performance (insertion and return loss). Good polishing equipment, polishing paper, and polishing techniques are required in order to achieve these parameters. The schematic shown on the right shows how the fiber is purposely lower in height (undercut) than the surrounding ceramic. The purpose here is so the ceramic will compress slightly during mating and allow the fiber to gently touch the fiber on the other side without absorbing all of the stress of the connection. Too much compression on the fiber may cause high return losses and may eventually damage the end face of the fiber causing transmission outages.

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Fiber optic connector end faces must be free of surface debris and blemishes in order to achieve good loss performance. Above are examples of good and bad end faces.

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The slide above describes Insertion and Return Loss – two very important parameters in connector performance. Insertion loss is best describe as to how much power leaves one connector and is capture by the other connector when mated. Return loss is the amount of light reflected back from the connector. Notice that “angled connectors” reflect light back at an angle and thus have very low return loss issues. Typical single mode return loss performance is stated as < -55dB. This means that if 1 million photons are launch downstream, there can only be about 4 photons allowed to be reflected back by the connector at the end.

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The slide above shows some of the various materials used to jacket fiber optic cable. Different materials are used depending on the specific application of the cable. Polyethylene or PE is typically used on outside plant cable due to its toughness and wide operating range. PolyVinyl Chloride or PVC is typically used for indoor cables that will be installed between floors of a building. PolyVinyl Diflouride or PVDF is used to produce Plenum rated indoor cables for use inside plenum spaces (inside a drop ceiling or under a raised floor). Low Smoke Zero Halogen is sometimes specified for indoor use to maximize on a cable’s non-flammability and non-toxicity during a fire event.

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This slide attempts to distinguish the difference between Riser rated cables and Plenum rated cables.

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Breakout cables are different from distribution cables in that the fibers have a thick outside jacket of 1.6, 2.0, or 3.0mm. This is a more robust design as each fiber has Kevlar wrapped around it providing more strength. Cables of this design are typically larger in size due to the extra protection provided to each fiber.

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Examples of distribution cable. Some have units of 12 fibers, each fiber having a 900 micron buffer (see left picture) and some do not have units like the picture on the right. Some cables are rated only for indoor (riser or plenum). Riser rated can be used anywhere inside an office except inside ductwork, drop ceiling, or sub floor (like raised floors inside computer rooms). Plenum rated cables have fire retardants in them which allow these cables to be used where riser rate cables cannot. Plenum rated cables are generally more expensive then riser rated. Another cable design can be used inside and outside (indoor/outdoor cable). This eliminates the need for a transition point where the outdoor cable meets the indoor cable at the entrance to the office.

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Examples of micro-distribution cable. Most designs have units of 12 fibers with each fiber only having its 250micron coating as protection. The fibers in these kinds of cables will need to be up jacketed to 900um in order to be connectorized. Some cables are rated only for indoor (riser or plenum). Riser rated can be used anywhere inside an office except inside ductwork, drop ceiling, or sub floor (like raised floors inside computer rooms). Plenum rated cables have fire retardants in them which allow these cables to be used where riser rated cables cannot. Plenum rated cables are generally more expensive then riser rated.

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This cable design can be used inside and outside (indoor/outdoor cable). This eliminates the need for a transition point where the outdoor cable meets the indoor cable at the entrance to the office.

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This slide shows an example of a loose tube cable. Most designs have units of 12 fibers with each fiber only having its 250micron coating as protection. The fibers in these kinds of cables will need to be up jacketed to 900um in order to be connectorized. This cable design is typically used in the outside plant.

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This slide shows an example of an Indoor Inter-Locking Armored cable. Some have units of 12 fibers, each fiber having a 900 micron buffer (tight buffer) and some do not have units like the cable pictured above.

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This slide shows some very good Internet links if one is interested in knowing more about fiber optics.

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