Developments in Plastic Optical Fibres and Semiconductor Light Sources - Research Paper Example

Developments in Plastic Optical Fibres and Semiconductor Light Sources Plastic Optical Fibre (POF) also known as fibre is an optical fibre which is made out of plastic. Optical fibre is also known as fibre optic. It is the medium and technology associated with the transmission of information as light pulses along a glass or plastic strand or fibre. Optical fibre carries much more information than the conventional copper wire and is generally not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now made of fibre optic. Transmission over fibre optic cables requires devices called repeaters that regenerate signals to extend signal distance. Traditionally, PMMA meaning Poly (methyl methacrylate), sometimes called acrylic glass is used as the core material. It is a clear or transparent plastic used as a shatterproof replacement for glass. Fluorinated polymers are then used as the cladding material. In large-diameter fibres, 96 percent of the cross-section is the core that facilitates the transmission of light. Quartz fibre is widely used for infrastructure. However, Plastic Optical Fibre has been called the "consumer" optical fibre. This is due to the fact that costs of Plastic Optical Fibre, associated optical links, connectors and installation costs are low. Despite the material used for Plastic Optical Fibre being typically PMMA, there are many other types of optical fibre. The individual characteristics of these fibres are applied to a variety of fields. Fibre optics falls into two categories, (Fibre Optics Association, 1999-2008) they are multimode and singlemode. Optical fibres are identified by their core and cladding diameters expressed in microns (one millionth of a meter). 1. Multimode Multimode has a larger core which supports the transmission of multiple modes/rays of light. Multimode is generally used with LED sources at wavelengths of 850 and 1300 nm (see below!) for slower local area networks (LANs) and lasers at 850 (VCSELs) and 1310 nm (Fabry-Perot lasers) for networks running at gigabits per second or more. Multimode can either be Step index multimode or Graded index multimode. Step index multimode was the first fibre design. It has higher attenuation and is too slow for many uses, due to the dispersion caused by the different path lengths of the various modes travelling in the core. Step index fibre is not widely used - only POF and PCS/HCS (plastic or hard clad silica, plastic cladding on a glass core) use a step index design today. Graded index multimode fibre uses variations in the composition of the glass in the core to compensate for the different path lengths of the modes. It offers hundreds of times more bandwidth than step index fibre - up to about 2 gigahertz. Two types are in use, 50/125 and 62.5/125, where the numbers represent the core/cladding diameter in microns. Singlemode fibre has a smaller core, so that the light travels in only one ray/mode. It is used for telephony and CATV with laser sources at 1300 and 1550 nm because it has lower loss and virtually infinite bandwidth. Plastic Optical Fibre (POF) is large in core (about 1mm) fibre, usually step index that is used for short, low speed networks.  PCS/HCS (plastic or hard clad silica, plastic cladding on a glass core) has a smaller glass core (around 200 microns) and a thin plastic cladding. Unlike glass optical fibres mainly used in telecommunication, (Polishuk, 2006, p.15) plastic optical fibres applications are found in many industries, with its two major applications in industrial controls and automotive fields. Plastic fibres (timbercon, 1997-2012) are used in the following fields: 1. Medical field Traditional medical optic fibre applications include light therapy, x-ray imaging, ophthalmic lasers, lab and clinical diagnostics, dental hand pieces, surgical and diagnostic instrumentation, endoscopy, surgical microscopy and a wide range of equipment and instrument illumination. Medical instruments utilize fibre optics for a variety of applications including illumination, image transfer and laser signal delivery. A large portion of fibre used in these applications support site illumination either as an integrated component of an instrument or as an individual light source. 2. Automotives field Used for lighting, communications and sensing requirements. In lighting fibre transmits ‘cold’ light making it a safe alternative to traditional sealed beam or halogen lighting. The light source is easily accessible and offers much more in creative freedom of design. Fibre also allows light source and output location separation creating high performance lighting options with reduced physical space requirements for difficult and restricted access locations. Communication and sensing in automobiles is also important with the continued increase in onboard safety devices and systems for example air bags, traction jcontrol devices and safety systems. 3. Cable Television systems The systems support multiple services like broadcast television, on demand entertainment/video and high speed internet access. 4. Network equipment Fibre optics is used as internal components or interconnects associated with finished products for example switches, routers and directors. These applications use fibre cabling and interconnects designed around industry standards. However, some equipments and/or applications require fibre cabling products to be customized to ensure optimal performance or to meet space or physical constraint limitations. 5. Electronics Typically used in professional audio/video, alarm/security and OEM component connections, fibre optics provide high bandwidth, Electro Magnetic Interference (EMI) and Radio Frequency Interference (RFI) immunity, and compact packaging enabling product designers and manufacturers to offer small, lighter and higher performance finished products. 6. Harsh environments Products are designed and manufactured specifically for use in adverse conditions and harsh environments. Harsh environment conditions include conditions in which these products are exposed to extreme high/low temperatures, shock, vibration, radiation, corrosive conditions, high electromagnetic interference (EMI), high radio frequency interference (RFI) and pressure extremes. 7. Education Educational institutions are finding many ways to apply fibre optic technology. From research and classroom applications to setting up networks to connect students, administrators, professors and researchers the technology is gaining popularity amongst universities and colleges. Bit rates describes the rates at which bits are transferred from one location to another, it measures how much data is transmitted in a given amount of time. Bit rate is commonly measured in bits per second (bps), kilobits per second (Kbps), or megabits per second (Mbps). Until early 1990s, plastic optical fibres had low bandwidth and there were very few reports regarding high bit rate transmission by plastic optical fibre. Reasons were that, there were no good laser diode and photo detector for POF. In 1994, NEC succeeded in a 2.5 Gb/sec data transmission experiment with plastic optical fibre. Consequently, much more interest has been focused on plastic fibre data link. Since then, progresses in development of low attenuation PF-polymer-based graded-index plastic optical fibre have vastly improved the bit rate-distance product. And then in 1999, Bell Lab and Lucent made a shocking demonstration of 11 Gb/sec data transmission over 100 meters of PF-polymer-based graded-index POF at 1300nm wavelength. This has stimulated even more interest in the development of high bandwidth POF. Numerical aperture is the measurement of the acceptance angle of an optical fibre, which is the maximum angle at which the core of the fibre will take in light that will be contained within the core. Attenuation is the reduction of signal strength during transmission. It also means loss of optical power. Step index plastic fibre available today, or SIPOF, today has a best bandwidth of 12.5 MHz.km and an attenuation of 180 dB/km. Graded index plastic optical fibre, or GI-POF, offers the potential of 3 Gb/s transmission over 100 m and 16 dB/km attenuation at 650 nm. Dispersion is the spreading out of a light pulse in time as it propagates down the fibre (Fibre Optics For Sale Co., 2012). Dispersion in optical fibre includes model dispersion, material dispersion and waveguide dispersion. 1. Model Dispersion in Multimode Fibres Multimode fibres can guide many different light modes since they have much larger core size. This is shown as the 1st illustration in the picture above. Each mode enters the fibre at a different angle and thus travels at different paths in the fibre. Since each mode ray travels a different distance as it propagates, the ray arrives at different times at the fibre output. So the light pulse spreads out in time which can cause signal overlapping so seriously that you cannot distinguish them anymore. Model dispersion is not a problem in single mode fibres since there is only one mode that can travel in the fibre. 2. Material Dispersion Material dispersion is the result of the finite line width of the light source and the dependence of refractive index of the material on wavelength.  It is shown as the 2nd illustration in the first picture. Material dispersion is a type of chromatic dispersion. Chromatic dispersion is the pulse spreading that arises because the velocity of light through a fibre depends on its wavelength. 3. Waveguide Dispersion Waveguide dispersion is only important in single mode fibres. It is caused by the fact that some light travels in the fibre cladding compared to most light travels in the fibre core. It is shown as the 3rd illustration in the first picture. Since fibre cladding has lower refractive index than fibre core, light ray that travels in the cladding travels faster than that in the core. Waveguide dispersion is also a type of chromatic dispersion.  It is a function of fibre core size, V-number, wavelength and light source line width. Research on use of plastic fibre optic by certain users (Polishuk, 2006, p.2) shows the following advantages and disadvantages compared to glass fibre or copper wires: Advantages 1. Simpler and less expensive components. 2. Lighter weight. 3. Operation in the visible. 4. Greater flexibility and resiliency to bending, shock and vibration. 5. Immunity to electromagnetic interference. 6. Ease in handling and connecting. POF diameters are 1mm compared with 8-100mm for glass. 7. Use of simple and inexpensive test equipment. 8. Greater safety than glass fibres or fibre slivers that require a laser light source. 9. Transceivers require less power than copper transceivers. Disadvantages 1. High loss during transmission. 2. A small number of providers of total systems. 3. A lack of standards. 4. A lack of awareness among users of how to install and design with plastic optical fibres. 5. Limited production, which has kept customers form realizing the full potential of plastic optical fibres. 6. Small number of systems and suppliers. 7. Applications research. 8. Certification program from Plastic Optical fibre installers 9. High temperature fibres (125 degrees celcius). Lopez-Higuera (2002, p.67) points out that, not only are Plastic Optical Fibres inexpensive, they also have great mechanical resistance and flexibility allowing them to be handled without any special care. Solid-state Lighting (SSL) refers to lighting applications that use light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or light-emitting polymers. Unlike incandescent or fluorescent lamps, (Lighting research centre, 1995-2011) which create light with filaments and gases encased in a glass bulb, solid-state lighting consists of semiconductors that convert electricity into light. LEDs have been around for nearly 50 years, but until a decade ago were used only in electronic devices as indicator lamps. Solid-state lighting is increasingly used in a variety of lighting applications because it offers many benefits, including: 1. Long life LEDs can provide 50,000 hours or more of life, which can reduce maintenance costs. In comparison, an incandescent light bulb lasts approximately 1,000 hours. 2. Energy savings  The best commercial white LED lighting systems provide three times the luminous efficacy (lumens per watt) of incandescent lighting. Colored LEDs are especially advantageous for colored lighting applications because filters are not needed. 3. Better quality light output LEDs have minimum ultraviolet and infrared radiation. 4. Intrinsically safe  LED systems are low voltage and generally cool to the touch. 5. Smaller, flexible light fixtures  The small size of LEDs makes them useful for lighting tight spaces and for creating unique applications. 6. Durable LEDs have no filament to break and can withstand vibrations. Light Emitting Diodes are either surface-emitting (Encyclopaedia of laser physics and technology, 2011) or edge-emitting. Surface-emitting LEDs (SLEDs) have a thin active layer parallel to the surface from which the light extracted. Edge-emitting LEDs have a structure similar to that of edge-emitting semiconductor lasers, they allow more efficient fibre coupling than surface-emitting LEDs. Applied in optical fibre communications, they allow higher data rates. As LEDs can be quickly modulated, they are suitable for optical fibre communications over short distances. While the poor directionality of their emission requires the use of multimode fibres and thus restricts the transmission distances, the cost is significantly lower than for a system with single-mode fibres and laser diode transmitters. Moderately fast power modulation is also useful, e.g., for application in light barriers, as the modulated LED light is easily distinguished from the ambient light, and for remote controls. Research (Arstechnica, 2008) at the Korea Institute of Science and Technology has led to the development of a new type of plastic optical fibre that could potentially be used to provide low-cost fibre connectivity from the consumer to the provider. Plastic optical fibre isnt as fast as traditional glass, but its 2.5GB/s transfer speed still represents a meteoric leap beyond copper. Currently, the majority of optical fibre is prone to breakage, cannot bend, and can be difficult to connect. The new plastic fibre can be easily bent and connected to additional lines, making it useful in hard-to-reach homes or apartments. Various Japanese companies are also working on their own standards. Verizon and AT&T could also potentially benefit from cheaper optical fibre. Appendix This paper discusses Plastic Optical Fibres with an emphasis on their types, applications, bitrates, attenuation, dispersion and benefits and drawbacks compared to glass fibre or copper wire. Solid-state lighting which uses light emitting diodes for illumination is applied in optical communication and specialized lighting in relation to optical fibres. In this section, types of Light Emitting Diodes, benefits and application in optical fibre communication is covered. As a conclusion, the future of Plastic Optical Fibres is discussed. Fig.1 An outline of Plastic Optical Fibre. Fig. 2 Diameter sizes of the different types of Plastic Optical Fibres. Fig. 3 Size of Plastic Optic Fibre compared to size of Glass fibre Fig. 4 Packaged PMMA Plastic Optical Fibre. Fig. 5 Packaged Plastic Optical Fibre used in optic communication. Reference List Lopez-Higuera, J.M., 2002. Handbook of optical fibre sensing technology. West Sussex. John Wiley & Sons Ltd. Polishuk, P., 2006. Plastic Optical Fires Branch Out. [ebook]. Available at: < http://www.pofto.com/downloads/ieee/pof.branches.v6.pdf> [Accesed 24 February 2012]. Fibre optics for sale, 2012. Plastic optical fibre. 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