POLYMER OPTICAL FIBERSBY:-Harshit Agarwal.
TOPICS TO BE DISCUSSEDIntroductionPrinciple Of Optical Fiber CommunicationHistory Of Polymer Optical FiberComparison of Polymer and Glass Optical FiberClassification Of PofsMaterials Used In PofsApplication Of PofsFabrication Of PofsFabrication Of Si- PofsFabrication Of GI- PofsPolymer Optical Fiber Plastic Optical Fiber Passive DevicesFuture Aspects Of PofsPotential Of Pofs
INTRODUCTIONAnoptical fiber(oroptical fiber) is a flexible, transparent fiber made bydrawingglass or plastic to a diameter slightly thicker than that of ahuman hair.Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage infiber-optic communications, where they permit transmission over longer distances and at higherbandwidthsPlastic optical fiber (POF)is anoptical fiberthat is made out ofpolymer. Similar toglass optical fiber, POF transmits light (for illumination or data) through the core of the fiber.
PRINCIPLE OF OPTICAL FIBER COMMUNICATIONPrinciple of operationTotal Internal Reflection
HISTORYFirst introduced in 1960 by Dupont at nearly the same time Glass optical fibers were introduced.Faced problems of very high attenuation of the order of 1000 dB/km.Application in communication almost impossible.Mitsubishi Rayon, Japan improved Duponts technology to reduce attenuation to 300dB/ km but still quite high value.In 1980 Graded Index POFs were introduced.New processing techniques such as swollen Gel Polymerization helped reduced attenuation problem considerably.In mid 1990s the use of POFs for short distance high speed communication were introduced.
COMPARISON B/W POFs & GOFsPOLYMER OPTICAL FIBER
Plastic optical fiber, polymer optical fiber is an optical fiber which is made out of plastic. It comprises of PMMA as the core that facilitates the transmission of light, and fluorinated polymers as the cladding material.Simpler and less expensive components.Greater flexibility and light weight.Bit rate upto 10Gbps.GLASS OPTICAL FIBERS
Glass optical fiber, just as its name shows, is an optical fiber made of glass. Being a delicate type of optical fiber, it cannot be cut, spliced or repaired.
Difficult handling and delicate.Less resistant to flexibility and accidental breakage.Higher information transmission capacity & lower losses.
Used in low speed and short distance applications (upto 100 m).Generally in car networks, home networks, industrial networks etc.
Used in longer distance transmissions at higher speeds.Under ground data transmission systems etc.
TYPES OF POLYMER OPTICAL FIBERS
STEP INDEX POLYMER OPTICAL FIBERS
A step index plastic optical fibre has a simple structure of a concentric core and cladding. Consequently rather simple methods can be used for its fabrication
GRADED INDEX POLYMER OPTICAL FIBERS
GI POFs has drawn considerable interest recently as a high band width data transmission medium for short distance application .
MATERIALS USED IN POFsPMMAPMMA are used as the core, with refractive indices of 1.49.Generally, fiber cladding is made ofsiliconeresin (refractive index ~1.46).Highrefractive indexdifference is maintained between core and cladding.Highnumerical aperture.Have high mechanical flexibility and low cost.Industry-standard step-index fiber has a core diameter of 1mm. Attenuation loss is about1dB/m@650 nm. Bandwidthis~5 MHz-km@650 nm. FLUORINATED POLYMERSFluorine (F) has a greater mass than both H and D, allowing for lower attenuation, theoretically approaching that of silica glass fiber.Fluorinated polymers such a s poly tetra fluoro ethylene or Teflon) typically form the crystalline structures.Random copolymers result in the least amount of crystallization.
APPLICATIONSCurrently the application of POFs can be divided into four major categories:LightingCommunications.Sensors.Automobiles.
LIGHTINGDecorations- lamps and pools.Inspection of mechanical welds in pipes and engines (airlanes, rockets and automobiles).Medical applications- Endiscopes, Bronchoscpoes, Laproscopes
COMMUNICATIONResearch is being conducted to reduce attenuation and increase bandwidth to increase usage in long distance communication.Ideal for short distance network cabing - New standard for LAN cabling. -Material cost fall between copper and glass. -Ease of installation.Gigabit Ethernet- Transport of 1.25Gbit/s Ethernet traffic over 900 m has been demonstrated successfully.
SENSORSOptical measurement of flow, biofilm growth, toxicity, rotation, humidity, fluoroscence.Humidity measurement- POG with PVA film.-Oil insulated power equipment.Toxicity biosensors. - The fluoroscence produced by biological reaction is collected and transmitted by POF.
The number of electronic devices in a car increases year by year, primarily due to an increase in the entertainment equipment desired for modern passenger cars.
This ubiquitous connection need is a huge problem in networking system designs forautomotive fiberfrom the viewpoint of both physical space and system load. Consequently, POF is specified in the MOST standard to achieve the lowest overall system weight and easiest connectivity
FABRICATION OF POFs
FABRICATION OF STEP INDEX POFs A step Indexed plastic optical fiber has a simple structure of a concentric core aand cladding. Consequently rather simple fabrication techniques can be applied for its fabrication, these techniques are described as under.Continous Extrusion Technique.Preform Method
CONTINOUS EXTRUSION METHOD
The polymer which becomes the core of SI- POF is then fed into a extruder by a gear pump. The extruder is capable of devolatalisation, which removes monomer residue and returns them to the reactor. The core material and the cladding material, which are fed by separate extruders, proceed into a extrusion die where concentric core - cladding structure of an SI- POF is formed.
PREFORM METHOD (SI POFs)Method involves two stages:A cylindrical preform 1-5 cm in diameter and upto 1 m in length is made. The preform is drawn into a fiber by heat drawing process.
FABRICATION OF GI- POFsGI- POF has drawn considerable attention in the recent past as a high bandwidth data transmission medium. The bandwidth of the POF is maximized by optimizing the Distribution of Refractive Index. Thus in manufacturing of GI- POF, the obtainable bandwidth of a GI POF is directly related to the ability to control profile. To date several methods have been proposed to for the manufacture of GI POF. These methods are described in the upcoming sections.Photo copolymrization.Swollen Gel Polymerization.Closed Extrusion Method.Centrifugal Method.
PHOTO COPOLYMERISATION (GI POFs)
A 2.9 mm diameter glass tube was was filled with a monomer mixture methyl methacrylate and vinyl benzoate and an initiator benzoyl per oxide. the glass tube reactor was then positioned vertically in a constant temperature chamber and rotated about its vertical axis It is irradiated by UV. the UV radiation was applied locally by using a shade while the UV lamp transversed from the bottom of the tubular reactor to the top at a constant speed.
SWOLLEN GEL COPOLYMERIZATION (GI POFs)
A two stage process:The monomer mixture is filled in the polymer tube to form gel at a lower temperature to form a gel without significant copolymerization.The temperature is raised to polymerization temperature to polymerize the monomer, hence a rod is formed, which can be drawn into graded index polymer optical fibre.
CLOSED CO EXTRUSION METHOD (GI POFs)
Versatile technology for making GI POFs.The figure shows a schematic diagram of the a N layer internal diffusion and surface evaporation co extrusion process.The tanks labeled 1- N are filled with polymer melts.They are arranged so that when fed to the concentric die the materials are in decreasing order of the refractive index of the polymers. It is thed passed through a hardening zone H and is then receives by rolls.
CENTRIFUGAL METHOD (GI POFs)
The centrifugal method is regarded as a potential method for the preparation of the GI polymer rods because of the ability to form large diameter GI rods. The figure here shows the schematic representation of the preparation of the GI polymeric rods by centrifugal method. Many aspects of this method are still being studied
POLYMER OPTICAL FIBER GRATINGS
Fiber Bragg Grating is characterised by a periodic index change induced by ultraviolet irradiation in the core along the fiber. Light propagating along the fiber grating is periodically and partially reflected in accordance with the pattern of the index change. When theses reflections are in phase, they can produce an enhanced near 100% reflection.
It is a method used in glass optical fiber to imrove transmissions and reduce losses.Introdeuced in POF by doping and base material is significantly photosensitive at uv wavelengths. POF gratings can be fabricated by making use of these photo senstivities.
FABRICATION OF POF GRATINGSABLATION: This involves melting and burning the polymer surface.
CHAIN SCISSION: This involves breaking the polymer chains, thus decreasing the chain density, which in turns reduces the refractive index.CROSS LINKING: This involves inducing free radicals and then giving rise to the combination of polymer chains. This has the effect of increasing the density of chains, thus increasing the refractive index of the polymer.PHOTO POLYMERISATION: The incident light generates free radicals , thus causing the polymerization of unreacted monomer within the polymer. As a result, the polymerization density increases and