Development in Plastic Optical Fibres and Semiconductor Light Sources - Term Paper Example

Note: Drawing in PowerPoint to follow..please wait. Thanks DEVELOPMENT IN PLASTIC OPTICAL FIBRES AND SEMICONDUCTOR LIGHT SOURCES Plastic optical fibres and light emitting diodes uses and applications Table of Contents Contents Contents 2 1. Introduction Plastic fibres in general are considered the most economical solution for transmitting visible light in short distances thus it is commonly used as optical sensors, illuminators, and so on. Their cores are made of polystyrene and polycarbonate to increase temperature resistance. Lightweight, plastic fibres are flexible and can withstand stress, flex, and vibrations (Grote & Venghaus, 2001, p.40). Dupont demonstrated the first Plastic Optical Fibre in the mid 1960s and it had a step index or SI polymethylmethacrylate or PMMA core (Kaminow, 2008, p.595). Advancement in optical fibre technology led to the development of polymer-based graded index POF that has better attenuation and transmission rate. Solid-state lighting devices were also developed such as Light Emitting Diodes and its variants providing better alternative to conventional lighting. The following section discusses the various aspects of Plastic Optical Fibre and Light Emitting Diode, their capability, application, performance, and limitations. It includes discussion of advantages and disadvantages, and comparison with other similar technology. 2. Type of Plastic Optical Fibres There are three types of Plastic Optical Fibres and their primary difference is the size of the core – PMMA core SI POF, PMMA core GI POF (500/750), and PF Polymer core GI POF (120/500). Plastic fibre-based on step index has limited bandwidth and is based on PMMA material. Step Index Plastic Fibres has a max bandwidth of 12.5 MHz/km and an attenuation of 180 dB/km. A graded index plastic fibres or GI POF has overcome this limitation and capable of 3 Gb/s transmission over 100m and 16 dB/km attenuation at 650 nm (Elliott & Gilmore, 2001, p.52). 2.1 PMMA core SI POF The manufacturing cost of PMMA fibres are almost the same as those with glass or silica but the thermal stability of PMMA is less. Step index fibres are available in sizes of 500, 750, and 1000 micron total diameter and majority of the diameter is the core covered by a thin layer of fluorinated PMMA for the cladding. Such type of plastic fibres has attenuation minima occurring between 570 nm and 650 and they are achievable at wavelength between 35 and 106 dB/km respectively (Elliott & Gilmore, 2001, p.52). 2.2 PMMA core GI POF To improve step index plastic fibres, another type PMMA was introduced and designed to reduce attenuation occurrence at 20 dB/km. However, to further increase the capability of plastic fibres, a graded index or GI plastic fibre was developed to increase transmission rate at 3 Gb/s over 100 m. Graded index plastic fibres can achieve attenuation at 16 dB/km and created using Perflourinated plastic (Elliott & Gilmore 2001, p.53). Asahi Glass Co. In 1997 developed a GI POF that has one-third of attenuation of SI POF. Experimental result shows that GI POF has the potential to deliver data at 100 m data link media in Gbps range thus can be use in various applications such as high-speed multimedia network (Pan, 1998, p.6). It is commercially available as a brand name of Lucina by Asahi Glass and contains no Carbon-Hydrate bond and crystal in its molecular structure thus with better transparency from 650nm to 1300nm wavelength. Moreover, this GI POF has lower material dispersion compared to glass optical fibres thus offering easy and inexpensive connection and operability with existing local area network equipment (IGI, 2002, p.2). 2.3 PF Polymer core GI POF Compared to traditional plastic fibres where the cladding could be made of PMMA, PF Polymer GI POF use polymer material for both the core and the cladding. The attenuation of PF polymer based graded index plastic optical fibre is 10 dB/km in 0.8 – 1.3 micro wavelength range and it has a large advantage in terms of lower material dispersion compared to silica. For this reason, PF polymer based GI POF have higher data transmission rate compared silica based MMF. Moreover, aside from the benefit of having 0.85-micrometer wavelength, bandwidth dependence on wavelength is significantly small thus PF polymer based GI POF can cover more than 10 Gb/s at almost any wavelength (Horie 200, p.157). An advanced form of PF polymer based GI POF is Microstructured Polymer Fibre, which was designed to improve transmission speed and distance covered, by traditional polymer based plastic optical fibres. The idea behind MPOF is to use gaps of air arranged symmetrically around the core centre as light-guiding structure so it can achieve low attenuation of 0.01 dB/km with single-mode operation over a wide range of wavelengths. MPOF also has low material dispersion and low polarization mode dispersion and can support high power transmission. In data communication, MPOF retains the advantage of having large core and flexibility plastic optical fibres (IGI, 2008, p.34). Plastic Optical Fibres are typically use for data communication and sensing There are two main types of Plastic Optical Fibres and these include fluorescent fibres that are sensitive to visible radiation containing dopants that increases its wavelength emission. Another is scintillating fibres that are sensitive to ultraviolet radiation and excited by alpha, beta, and gamma emission (Grattan & Meggit, 2000, p.34). 2.4 Fluorescent and scintillating Plastic Optical Fibres for Sensing Plastic Optical Fibres belonging to this category are typically doped with organic dyes that are commonly used in printing. These Plastic Optical Fibres are commonly use for decoration but clad and coated fibres with fluorescent core are sensitive and have the ability to capture light thus used in sensing and measurement. For instance, fluorescent plastic optical fibres can measure ambient lighting, monitor faults in electrical circuits and switches, and can detect level or elevation. More importantly, they can be used to detect intruders, measure humidity, gaseous pollutants in the air (Grattan & Meggitt, p.35). On the other hand, scintillating plastic optical fibres is somewhat the same as fluorescent POF but the dopant used has limited absorption at a shorter wavelength and responds to ionizing radiation. For these reasons, they are commonly used as track detectors, high-resolution spatial detectors and for particle and energy measurement (ibid 35). 3. Applications of Plastic Optical Fibres 3.1 Digital home appliances interfaces NEC Corp and Keio University made Plastic Optical Fibre a high-speed data medium when they succeeded transmitting 2.5 Gbps in one experiment involving a 100-metre plastic fibre and edge emitting red laser diode or LD with a 647 nm wavelength. This experiment paved the way for advanced POF to find their way to high-speed data transmission such as MPEG2 video signals, red LDs, and optical detectors in home appliance such as remote and so on. Since traditional plastic optical fibres are generally SI and normally has narrow bandwidth of 5 MHz/km, they are commonly use in audio and video equipment (Information Gatekeepers, 1994, p.5). Although the use of plastic optical fibre is commonly found in automotive electronics such as digital signal processor for engine and transmission control, power windows, and others, plastic optical fibre particularly polymer based are being used in microwave oven, refrigerator, and others (Gupta 2005, p.6). 3.2 Home networks Plastic Optical Fibre capable of high-speed data transmission particularly those with 100Mbps and 1 Gbps specifications are often use to support Fast and Gigabit Ethernet-based networks. For instance, Firecomm’s Fast Ethernet transceivers and OptoLock are compliant with POF- based CPE and networking solutions thus they are able to make cutting and termination of POF on site. These include home network solutions with POF installed on ducts rather than traditional unshielded twisted pair cables (Information Gatekeepers, 2009, p.8). Specifically, plastic optical fibre made of polymer materials has much lower elastic moduli than silica thus, it can maintain its mechanical properties even with very large cores. Moreover, amorphous perflourinated polymers reduced absorption loss significantly thus ideal for data transfer (Franzen, 1999, p.135). The need to share information and resources between workstations demand a reliable media for Local Area Network but glass fibres are expensive while twister pair can only accommodate short distance applications. Consequently, as computer applications become increasing graphics intensive, POF is widely considered for its cost and its suitability for high bandwidth applications (Information Gatekeepers 1993, p.60). 3.3 Car Networks Plastic optical fibre is commonly used in car entertainment and navigation systems and some manufacturers are now using it to control steering, braking, and manage engine. Since plastic optical fibres have high thermal resistance, it is much favoured for copper wires (Helps, 2001, p.138). Since the 1990s plastic optical fibres is being used for multiplexed networking application such as engine monitoring and control, traction control, ABS brake systems, and transmission systems. In Japan, car manufacturers are taking advantage of POF’s LED-based systems and LAN application in their automobiles. For instance, LIGHTWAVE is a mini-map network connecting a maximum of 24 workstations, numeric control machines and automation computers by plastic fibre (IGIC, 1994, p.217). According to Cirillo et al. (1992), transmission distances in automobiles are relatively short thus, plastic optical fibres can do much more. More importantly, the plastic nature of POF allows for quick and easy installation and it is not as fragile compared to glass. Before, plastic optical fibre is used for illumination such as backlighting but significant development in POF made it a choice for high-speed vehicle data communication as it can eliminate electromagnetic concern at high data rates applications. For instance, CD players and Digital Audio Tape players in cars demand point-to-point high-speed transfer of digital audio data. Similarly, video displays for driver information such as navigation requires data rates higher than 7 Mbd for a single video channel to 50 Mbd for some applications (p.20). 4. Bit Rates, Attenuation, Numerical Apertures, and Dispersion Attenuation and dispersion of plastic step index optical are considered the major limiting factors in achieving longer transmission distance and bitrates (Bates et al, 1993, p.47). According to Pan (2007), transmission and dispersion properties of traditional plastic optical fibres is low compared to silica fibre as it is only on the order of 100dB/km compared to < 1 dB/km of silica. It is therefore limited to short-haul data communication networks where speed of transmission and attenuation are not major issues (p.327). Since step index in its design limits the bandwidth available for plastic fibre, it can only attain 12.5MHz/km and an attenuation of 180 dB/km compared to 500MHZ bandwidth and 1 dB/km of glass optical fibre. Consequently, some plastic optical fibre use graded index to overcome bandwidth limitations as such approach has the potential to increase transmission up to 3 Gb/s over 100 metre at 16 dB/km attenuation at 650 nm. This type of plastic optical fibre is made of Perflourinated plastic or PF with low attenuation at 1 db/km at 1300 nm with a fibre of about 750-micron diameter and a 400-micron core (Elliott & Gilmore, 2001, p.53). According to Pan (1995), fluorinated polymer-based graded index POF can transmit higher bit rates than PMMM-based GI POF and has lower material dispersion and attenuation (p.2). Experiments conducted in 1994 at Keio University shows that GI POF could do gigabit data transmission using a laser diode. For instance, a PMMA based GI POF at 650 nm wavelength achieved a maximum bit rate of 3-5 Gbps which is governed by the numerical dispersion of the PMMA or 0.305 ns/nm/km. For a fluorinated polymer GI POF, the bit rate achieved is around 10 Gbps for 100-metre length because of small material dispersion of 0.136 ns/nm.km. It has an attenuation of less than 50 dB/km at 1300 nm. By calculation, the overall result suggest that at 780 nm, both polymer-based GI-POF and PPMA-based GI POF can achieved maximum bit rates of 25.7 Gbps and 13.6 Gbps respectively (IGI, 1996, p.38). 5. Advantages and Disadvantages of Plastic Optical Fibres 5.1 Plastic Optical Fibres and Glass Fibres, UTP, STP, Coax Cables Glass optical fibre has silica core and was designed for high bandwidth and long distance applications. It is significantly smaller compared to plastic optical fibres and offer low attenuation at 0.5 dB/km and low NA suitable for large bandwidth up to 500MHz. However, constructing a glass fibre network is expensive particularly those associated with hardware and cable installation cost. Moreover, glass fibre termination is time consuming and labour intensive (Information Gatekeepers, 1993, p.64). Generally, the advantage of Plastic Optical Fibres as compared to glass fibres include simplicity and inexpensiveness, lightweight, flexibility, resistance to EMI or Electromagnetic interference, easy to work with and connect since POF are 1 mm in diameter compare to glass with 8-100mm. Moreover, it does not need complicated and expensive test equipment and provide greater safety as it does not require a laser light source (Polishuk 2004, p.1). Traditionally, Plastic Optical Fibres are subject to high transmission losses. According to Vacca (2007), Plastic Optical Fibres transmission rates are lower than glass, which has an average of 100 Mb/s (p.97). However, technological development in plastic fibres made it a viable transmission media as its attenuation is now below 0.2 dB/m while its cost is less than glass fibre. Today, plastic optical fibres provide the same advantages glass fibre offers but at a lower cost. It is commonly use for structured wiring system with a cost similar to UTP installation. Plastic optical fibres offer easy termination and with snap-lock design, a network node can be terminated under a minute. One noticeable advantage of plastic optical fibre in terms of data transmission is dielectric waveguide. This is because unlike UTP, STP, and coax, glass fibre optic does not radiate and not vulnerable to electromagnetic interference. Similar to glass fibre, POF is capable of constant attenuation and can withstand electrical signal intrusions. Moreover, because of its large diameter, it has greater tolerance control in connector design compared to glass as it minimizes the effects of misalignments (Information Gatekeepers 1993, p.65). 6. Solid State Lighting - SSL 6.1 Range of uses of light emitting diodes or LED in optical communication and specialised lighting Solid-state diodes can be made to emit light in red, green, and blue. Conventional light emitting diodes has simple p-n junction in which small amount of light is emitted. There are two types of LED namely Burrus or DH-SLED and the stripe geometry edge emitting LED or ELED. The first type has three layers consisting of n-GaAs serving as substrate, p-GaAs working for as an active region, and SiO2 as an insulating layer. This type of light emitting diodes is efficient in terms of cooling and they can produce light even a higher temperature. However, their output power is becoming less as the temperature rises to 90-100 degrees centigrade (Gupta, 2005, p.3). The Edge Emitting LED or ELED on the other hand are diode based on double hetero-structure LED, which means it, can consist of five layers of Gps III-V semiconductor materials. Compared to Burrus LED, this diode type has several advantages. For instance, since the active region of ELED is very thin, self-absorption of photon is significantly decreased. Its optical power is guided by internal reflection at the heterojunction and is similar in geometry to stripe edge type laser diode (Gupta, 2005, p.4). Light emitting diode or LED is generally known to convert current into light (Garg et al, 2008 p.154). It is the most basic solid-state optical device and light emission occurs whenever electrons and holes recombine in a single step. Light emitting diode is designed to glow or emit light when forward bias occurs. In reverse, LED will act like any common diode that is not capable of emitting light or allow current flow. Although LED can be manufactured to emit any colour, the most common colour is red thus, it is commonly used as an indicator device. However, recent developments on optical electronics have led the creation of high-intensity LED with light intensity near the levels of incandescent bulbs (Slone, 2000, p.211). 6.2 Light Source for Optical Fibre Communication There are two light sources in optical fibre communication and these include light emitting diodes and laser diodes that are all semiconductor devices. Light emitting diodes or LED emits photons in the visible region when the absorption energy is released. High power LEDs are used in optical fibre communication but they are limited to short distance applications such as LAN and short terrestrial communication low bandwidth networks (Gupta, 2005 p.28). Lensed LEDs are commonly used in communication applications such as free-space optical communication in the remote control of consumer appliances – stereo, television, CD player, and so on. Some other communication application includes automobile remote control for door locks and wireless computer peripheral devices such as mouse, keyboard, and others. However, the use of LED for free-space optical communication is limited by line-of-sight and therefore ineffective walls and other barriers. Since the wavelength requirement of free-space optical communication must be near infrared, light emitting diodes are suitable and efficient particularly as visible light source (Shubert, 2006, p.379). 6.3 Advantages and disadvantages of light emitting diodes Compared to laser diodes, LED is very simple device but its advantage includes simplicity as p-n junction work without any resonator mirrors and complex striped structure. Just like plastic optical fibres, light emitting diodes are known for their inexpensiveness and compatibility with multimode fibres. Light emitting diodes are reliable in performance, as it does not degrade suddenly, free from modal noise, and easy to work with. It is also dependable in terms of temperature, as variation in temperature does not affect its operation. It requires no cooling and uses simple circuits and therefore easy and inexpensive to maintain. More importantly, light emitting diodes are suitable for optical communication such as LAN and WAN with multimode fibre (Gupta, 2005, p.1). However, light emitting diodes generally has low output power thus it can only produce microwatts of power when use with optical fibres. Its low bandwidth is another disadvantage thus it is only effective for data transfer in LAN and other distributed process control system (Gupta, 2005, p.1). Traditional LED are operating within the range of no more than 30-60 milli watts of electrical power but in 2002, 5 watt LEDS were made available with efficiencies of 18-22 lumens per watt. In the following year, Cree Inc. introduced a new type of blue LED that has an efficiency of 35% at 20mA. This type of LED is capable of producing 65 lumens per watt and considered the brightest until a white LED was introduced in 2006 with efficiency of 131 lumens per watt at 20mA. However, white LED is more vulnerable to degradation as it often use one or more phosphorous that produce more heat and changes in the output light colour. As high-power LED, it can suffer from current crowding or non-homogenous distribution of current density over the junction. Consequently, localized hot spots may be created and lead to thermal runaway or loss of thermal conductivity (Sairam, 2007, p.72). In summary, LED advantages include the ability to emit light of different colour without colour filters, which is more efficient and cost effective. LED does not require external reflectors like conventional incandescent or fluorescent light sources to focus its light as it can be designed to focus in a certain direction. They are often built in solid case, therefore protected, and extremely durable. Compared to other conventional light sources, LED has longer life span, which is about twice of fluorescent bulbs and twenty times of incandescent lamps. More importantly, it produces less heat, light up very quickly, and does not fail abruptly (Sairam, 2007, p.75). 7. Concluding comments and future of Plastic Optical Fibres/SSL Both Plastic Optical Fibres and Solid State Lighting such as Light Emitting Diode are promising technology. In particular, POF and LED are both useful in optical communication and specialized lighting. With the development of polymer-based graded index plastic optical fibres and organic light emitting diodes or OLEDs, these technology can be more flexible and lightweight, and can be used for other applications such wall decorations, inexpensive commercial displays, light sources, luminous cloth, and so on. For instance, advanced light emitting diodes such as RCLED or resonant-cavity light emitting diodes has higher spectral purity compared with traditional LEDs and its characteristics are desirable for local area network and medium bit rate optical communication systems as it has higher emission intensity that can increase transmission rate over optical fibre (Shubert, 2006, p.256). Similarly, plastic optical fibres or POF may find application in not only aircraft such as the network system in Boeing 777 but mass production systems, interactive high bit rate pulse transmission delivery moving fine pictures, medical diagnostic, sensors, and global networking system, and others. 8. Reflections This report provide this author the opportunity to research and understand the various aspects of plastic optical fibre and solid states lighting devices such as LED or light emitting diodes. It has enhanced personal understanding of application and performance limitations of POF and LED, provides several ideas on how such technologies can be improved, and applies in different situations and needs. More importantly, the report strengthens this author’s appreciation of the need for such system and its relevance to engineering practices. 9. 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