Volume-7, Issue-6, November-December 2017 International Journal of Engineering and Management Research Page Number: 115-120 Multimode Graded-Index Polymer Optical Fiber for High-Capacity Long Haul Multiplexed Transmission Chandan Kumar Roy 1, S. Kishor Krishna Kumar 2 1,2 Assistant Professor, Department of ECE, Mlla Reddy College of Engineering, Maisammagudda, TS, INDIA ABSTRACT Data traffic is growing exponentially due to the emergence of various network services. Although the transmission capacity of optical fibers has dramatically increased thanks to advanced communication technologies such as Copper based technologies but Copper based technologies suffer strong susceptibility to electromagnetic interferences and have limited capacity for digital transmission as well as the presence of crosstalk. Compared to these copper based technologies, optical fiber has smaller volume; it is less bulky and has a smaller weight. In comparison with data transmission capability, optical fiber offers higher bandwidth at longer transmission distances. The main objective of Polymer Optical Fiber(POF) to integrate voice, video, and data streams over all-optical systems as communication signals make their way from LANs down to the end user by Fiber-To-The-x (FTTx), offices, and in-homes. This paper reviews the major achievements of our polymer optical Fiber based MMF research and development. Keywords-- Graded index polymer optical Fiber, wavelength division multiplexing, Multimode optical Fiber, LAN. I. INTRODUCTION At present, twisted pair and coaxial cables are commonly used as the physical medium to deliver telecom services within the customer s premises. However, these two transmission medium suffer from serious shortcomings when they are considered to serve the increasing demand for broad-band services. For instance, twisted pair has a limited bandwidth and it is susceptible to electromagnetic interference (EMI). Coaxial cable offers a large bandwidth, but it poses practical problems due to its thickness and the effort required to make a reliable connection. Moreover, the coaxial cable is not immune to EMI. Optical fiber is extensively used for long-distance data transmission and it represents an alternative for transmission at the customer premises as well. Optical fiber connections offer complete immunity to EMI. Optical silica-glass fibers, however, are not suitable for use within the customer premises because of the requirement of precise handling, and thus, the high costs involved. Polymer optical fibers are very attractive for use within the customer premises with their easy handling and low cost. This is mainly due to their relatively thick core. In fact, several polymer fiber-based systems are commercially available. However, these systems are based on the use of the multimode step index polymer optical fiber (SI- POF), whose bandwidth distance product is limited to a few MHz km. The way toward broad-band POF systems is opened by the use of graded-index polymer optical fiber (GI-POF). The high bandwidth of the GI-POF (typically 2 GHz km) compared to SI-POF, is attributable to the graded-index profile in the core. The transmission media used at present are not suited for provisioning highbandwidth services at low cost. For instance, today's wiring in LANs is based mainly on copper cables (twisted pair or coaxial) and silica (glass) fiber basically of two kinds: single mode optical fiber (SMF) and multimode optical fiber (MMF). Copper based technologies suffer strong susceptibility to electromagnetic interferences and have limited capacity for digital transmission as well as the presence of crosstalk. Compared to these copper based technologies, optical fiber has smaller volume, it is less bulky and has a smaller weight. In comparison with data transmission capability, optical fiber offers higher bandwidth at longer transmission distances. However, the use of MMFs is at a cost of a bandwidth penalty with regards to their SMF counterparts, mainly due to the introduction of modal dispersion. This is the reason MMF is commonly applied to short-reach and medium-reach applications due to its low intrinsic attenuation despite its limited bandwidth. In particular, in the access network, the use of MMF may yield a considerable reduction of installation costs although the bandwidth-times length product of SMF is significantly higher than that of MMF. As in the access network, the fiber link lengths are less than 10km, 115 Copyright 2017. Vandana Publications. All Rights Reserved.
however, the bandwidth of presently commercially available silica MMFs is quite sufficient. On the other hand, compared to multimode silica optical fiber, polymer optical fiber (POF) offers several advantages over conventional multimode optical fiber over short distances (ranging from 100m to 1000m) such as the even potential lower cost associated with its easiness of II. FUNDAMENTALS OF MULTIPLE OPTICAL FIBER 2.1. Step- index multimode POF Conventional commercial POFs are dominantly step- index multimode (SI-MM) fibers from extrusion. These commercial POFs typically have 1mm outer diameter with a core diameter of 980nm. There are activities to develop novel POFs smaller size and lower numerical aperture with higher bandwidth. installation, splicing and connecting. This is due to the fact that POF is more flexible and ductile, making it easier to handle. Consequently, POF termination can be realized faster and cheaper than in the case of silica MMF. This POF technology could be used for data transmission in many applications areas ranging like inhome, fiber to the building, wireless LAN. transmission of a digital signal across large distances. The attenuation coefficient usually uses units of db/km through the medium due to the relatively high quality of transparency of modern optical transmission media. Attenuation in optical fiber is caused primarily by both scattering and absorption. Polymer Optical Fiber (POF) are based on non-fluorinated polymers such as PolyMethylMethAcrylate (PMMA), widely used as core material for graded-index fiber in addition with the utilization of several kinds of dopants. Although firstly developed PMMA-GIPOFs were demonstrated to obtain very high transmission bandwidth compared to that of Step-Index (SI) counterparts, the use of PMMA is not attractive due to its strong absorption driving a serious problem in the PMMA-based POFs at the near-ir (nearinfrared) to IR regions.. As a result, PMMA-based POFs could only be used at a few wavelengths in the visible portion of the spectrum, typically 530nm and 650nm, with typical attenuations around 150dB/km at 650nm. Now-a-days almost all gigabit optical sources operate in the near-infrared (typically 850nm or 1300nm). Fig. 1. Attenuation of graded index POF. Table1. Specification of a SI-MM POF (ESKA CK40) 2.2 Graded- index multimode POF Graded-index multimode (GI-MM) POFs with both low loss and high bandwidth have been developed with well-tailored index profiles. Since early 1990s, intensive research has been carried out to produce a graded-index POF which would have significantly larger band width length product. III. POF AS TRANSMISSION MEDIUM 3.1 Attenuation Attenuation in fiber optics, also known as transmission loss, is the reduction in the intensity of the light beam with respect to distance traveled through a transmission medium, and being an important factor limiting the 3.2 Dispersion For multimode fibers, modal dispersion and chromatic dispersion are the relevant processes to be considered. Chromatic dispersion is introduced by the effect that the speed of propagation of light of different wave lengths different resulting in a wavelength dependence of the modal group velocity. The end result is that different spectral components arrive at slightly different times, leading to a wavelength-dependent pulse spreading, i.e. dispersion. In PF-based POFs the chromatic dispersion is much smaller than in silica MMF for wavelengths up to 1100nm. For wavelengths above 1100nm, the dispersion of the PF-based GIPOF retains and the dispersion of silica MMF increases. On the other hand, modal dispersion is caused by the fact that the different modes (light paths) within the fiber carry components of the signals at different velocities, which ultimate results in pulse overlap and a garbled communications signal. 116 Copyright 2017. Vandana Publications. All Rights Reserved.
distance is doubled to reach 200 m. Key elements used in the experiment are a silicon avalanche photo-diode (APD) receiver with a record sensitivity of 29 dbm at 2.5 Gb/s. Figure2.Dispersionmechanismsinopticalfibers. 3.3 Bandwidth of POF The advantage in bandwidth of the low material dispersion of PF polymer-based GI-POF has been theoretically and experimentally clarified. It has been shown that the low attenuation and low material dispersion of the PF polymer enables 1- and 10-Gb/s transmission at 850- and 1300-nm wavelengths, respectively, as the PF polymer-based GI-POF has a very low material dispersion (0.0055 ns/nm km at 850 nm), as compared with the conventional PMMA-based POF, and compared with the multimode silica fiber (0.0084 ns/nm km at 850 nm). IV. TRANSMISSION EXPERIMENT In this section, we present a review of transmission experiments using POF as the transmission medium. Their experimental setup and enabling technologies are described in detail. Several experiments have been performed to investigate the validity of theoretical models developed to predict the bandwidth of the fiber. The experiments have also shown the feasibility of POF links for high-capacity transmission. Fig. 4. 2.5-Gb/s transmission over 200 m of PMMA GI-POF. Maximum coupling efficiency. The eye diagram of back-to-back measurement and after 200-m of GI-POF are nearly identical, indicating a sufficient bandwidth (see Fig. 4). The BER curve against received average power at the input of the APD receiver in the back-to-back and after 200 m GI-POF transmission has been measured (see Fig. 5). The back-to-back measurement has been carried out with a short piece of GI-POF of a few meters between transmitter and receiver. The received power has been changed by altering the distance between laser and GI-POF. The sensitivity of the receiver was 29 dbm at 2.5 Gb/s for a BER of 10. The laser output power was 6.8 dbm, so the available power budget was 35.8 db. The attenuation of the 2 100 m GI-POF was 32.8 db. The power penalty due to modal dispersion of the fiber was 2 db (see Fig. 6). The total coupling losses where 0.6 db, so a power budget of 35.4 db was needed. Moreover, the optical output spectrum of the modulated laser at an average output power of 6.8 dbm has been measured (see Fig. 6). The width of the spec-trum, 3 db below the maximum value is 0.4 nm, which limits pulse broadening due to dispersion of the fiber. Fig3. Bandwidth of graded index POF. 4.1 2.5-Gb/s Transmission Over 200 m of PMMA GIPOF A 2.5-Gb/s system experiment over 100 m, using a PMMA GI-POF, a visible light laser at 650-nm wavelength and a sil-icon PIN photodiode has been reported earlier. In our experi-ment, the transmission Fig.5 BER measurement results. 117 Copyright 2017. Vandana Publications. All Rights Reserved.
Fig. 6.Measured optical spectrum of the modulated laser. 4.2 WDM Experiments Per-fluorinated polymer based graded index polymer optical fiber(gi_pof) has a low loss wavelength region from 500 to 1300nm, so many WDM transmission can be applied over a broad wavelength range, which can be separated easily with low-cost devices. As a start of this development, a demultiplexer for splitting up the wavelengths 645, 840, and 1310 nm has been realized with planar interference filters. In Fig.7, the principle of operation of the demultiplexer is shown.first, the light from the input GI- POF is transformed into a parallel beam by means of lens 1. Interference filter 1 First, the light from the input GI-POF is transformed into a parallel beam by means of lens 1. Interference filter 1 deflects the light in the 645-nm wavelength region. The other wave diode of the 645-nm receiver. The light in the 840- and 1310-nm wavelength regions, which passed through filter 1, is split up by filter 3 Light in the 840-nm wavelength region is deflected by filter 3, filtered by filter 4, and focused on the detector of the 840-nm receiver by lens 3. The remaining 1310-nm light is focused on the 1310-nm detector by lens 4. The measured insertion losses for all three wavelengths from GI-POF input to photo detectors are smaller than 1.6 db. Measured crosstalk levels are smaller than 30 db. The demultiplexer has been used for a three channels operating at 2.5 Gb/s over 200-m GI-POF WDM experiment with a record bit rate times distance product. A block diagram of the setup is shown in fig 8. For this experiment the transmitter and receiver described in section4.1 and 4.2 have been used. This experiment carried out using the wavelength 840nm and 1310nm and a GI-POF fiber with a length of 328m of one piece. Because this fiber sample has been an attenuation of more than 100dB/m at 640nm, this wave length could not be used. A block diagram is shown in fig 9. system spans of 300 m at 645-nm wavelength, and 550 m at 840- and 1310-nm wave-lengths have been reached. Using WDM transmission, system capacities have been further enhanced. For instance, we have reported a threechannel 2.5-Gb/s GI-POF WDM transmission over 200-m experiment and a two-channel 2.5 Gb/s over 328-m experiment with record bit-rate distance products. These experiments show the feasibility of high-capacity transmission over POF. It also has been shown that 2.5- Gb/s transmission over 4 km of large-core (148 and 185 m) graded index silica fiber can easily be realized. Maximum transmission distances of the large-core graded index silica fibers are much larger com-pared with the graded index polymer fibers. There is a large difference in attenuation between silica and polymer fibers. The diameter of silica fibers is limited because of the inherent inflexibility of glass materials. Because of the difference in mechanical properties of silica and polymer the handling techniques are different. Fig. 7. Principle of operation of the 645-, 840-, 1310- nm DE-multiplexer. Fig.8. Block diagram of the 3 2 2.5-Gb/s WDM experiment over 200-m GI-POF. V. CONCLUSION The transmission distances of PF GI-POF-based systems are increasing very fast. At bit rates of 2.5 Gb/s, Fig.9. Block diagram of the 2 2 2.5-Gb/s WDM experiment over 328-m GI-POF. 118 Copyright 2017. Vandana Publications. All Rights Reserved.
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