Toward Gigabit Home Network Using Plastic optical Fiber

Summary:  

POF systems provide benefits compared to GOF and copper wire, which include: simpler and less expensive components, operation in the visible range , greater flexibility and resilience to bending, shock and vibration, ease in handling and connecting , use of simple and inexpensive test equipment.

The increasing demand for broadband services raises the need for a high bandwidth link, which should extend from the terminals to the customer’s premises. In-building networks presently are using a wide range of transmission media: coaxial copper cables, twisted copper pair cables, free-space infrared links, wireless local area network (LAN) links, etc. Each of these networks is optimized for a particular set of services; this complicates the introduction of new services and the creation of links between services (such as between video and data services). A single broadband multi-services network could provide an efficient solution to host and connect all existing and upcoming services together.

The target for data rate (DR) delivered in home could be up to 1Gbit/s in case of fiber to the home (FTTH) or up to 120Mbit/s in case of very high bit rate digital subscriber line (VDSL2) technology. The home network must not represent a bottleneck for the expected evolution for services such as the introduction of high definition quality internet protocol television (IPTV), multi-room/multi-vision configuration and high quality video communication via the TV set. The home network can be used, for example, to share multimedia contents not necessarily delivered in real time by access network, this content can be stored in a device inside the house and use it afterwards [11].

At present, twisted pair and coaxial cables are used as the physical medium to deliver telecom services within the customer’s premises. These two transmission mediums 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 [2]. Glass optical fibers (GOF), however, are not suitable for use within the customer premises because of the requirement of precise handling, and thus, the high costs involved. On the other hand, it is important to have very simple and low-cost solutions. Also the enormous capacity of the single-mode GOF is never necessary in this short distance application. The Poly-Methyl-Methacrylate Plastic Optical Fiber (PMMA-POF) is an excellent candidate for implementing such a short distance network.

Certain users find that POF systems provide benefits compared to GOF and copper wire, which include:  simpler and less expensive components, operation in the visible range (the transmission windows are 530nm, 570nm, and 650nm), greater flexibility and resilience to bending, shock and vibration, ease in handling and connecting (standard step-index POF core diameters are 1mm compared with 8–100µm for glass), use of simple and inexpensive test equipment. Finally, POF transceivers require less power than copper transceivers. These advantages make POFvery attractive for use within in-building networks, industrial control and automotive fields as depicted in Figure 1 [3].

Figure 1 Main POF applications

The main disadvantage of the PMMA-POF is its high transmission loss (150dB/km at 650nm and less than 90dB/km at 530nm and 570nm) which limits the use of PMMA plastic fibers for transmitting light to less than 100m. Most cheap commercial POFs have a uniform, or step index of refraction that is the same across the width of the fiber, and step-index fibers (SI-POF) have the lowest bandwidth among multimode fibers [3]. This small bandwidth limits the maximum data rate (DR) which can be transmitted through POF.

To overcome the problem of POF high transmission loss, very sensitive receivers must be used to increase the transmitted length over PMMA POF. The SI-POF limited bandwidth problem can be decreased by using multilevel signaling like Multilevel Pulse Amplitude Modulation (M-PAM), see Figure 2, and Qudrature Amplitude Modulation (M-QAM). Also the DR can be increased more with the limited POF bandwidth by using spectral efficient modulation techniques like Discrete Multi Tone (DMT) [4,5,6,7].

Figure 2 Multilevel pulse amplitude modulation (M-PAM)

Pre-equalization for the light source and post-equalization techniques can be used to equalize for the SI-POF small bandwidth [8,9,10]. Pre-equalizing of light source (peaking) lowers the light source modulation depth; this reduces the actual power per pulse compared to rectangular pulses without peaking. This is at the expense of system power budget. Post equalizer introduces additional noise and a higher optical power is needed to achieve the required sensitivity. It follows that the use of pre- or post-equalization methods are of particular interest in systems that have adequate power reserves. Also, for a fixed equalization if the frequency response changes, as a result of different lengths of the POF or a bend in the fiber, the result will be too much or too little compensation and the bit error rate (BER) will increase.

Today on the market several suppliers offer PMMA POF media converter solutions at 100 Mbit/s. With such performance SI-POF may be used in the home to interconnect all devices usually communicating through Fast Ethernet interfaces; for example the link between the home gateway and the Set Top Boxes (STB). The standard requirements for 100 Mbit/s and 1Gbit/s PMMA SI-POF systems introduced by The European Telecommunications Standards Institute (ETSI) are illustrated in Table 1.

Table 1 ETSI for 100 Mbit/s and 1Gbit/s PMMA POF systems

For multilevel modulation, there is a need for an integrated optical receiver with a good performance. The optical receiver used with multilevel signaling must deliver a linear response over a large input optical power range. This leads to a more sophisticated design of the automatic gain control (AGC) compared to the conventional binary receivers, where a significant part of the large dynamic range is achieved by a simple limiting amplifier [11,12].

To receive the multilevel optical signal we need a high linearity optical receiver with multilevel signal, the use of the conventional optical receivers (with limiting amplifier) will not be useful. The use of conventional optical receivers with limiting amplifiers will result in a distorted output signal with unequal voltage levels. This makes the signal decoding very hard or even impossible. In the design of the multilevel signaling optical receiver a linear optical receiver (no limiting amplifiers) will be considered to have equally spaced output signal voltage levels. Also a linear AGC is needed to have a constant output voltage over wide input optical power. This equally spaced output signal voltage levels will ease the decision levels selection for signal decoding from multilevel signal to the original binary signal.

For many applications it is desirable to integrate the photodiode (PD) with a transimpedance amplifier (TIA) into the same chip. Placing the TIA adjacent to the PD improves the performance by reducing lead capacitance and sensitivity to interference, thereby giving higher speed and lower noise. A further advantage of the integration of PD with TIA is the reduction in the external circuitry required. Hence overall cost and PCB board size can be reduced.

Figure 3 shows the general block diagram of the media converter. Both laser diode and fully integrated optical receiver were mounted in a plastic optical clamp. The laser diode is driven with a commercial IC. The integrated optical receiver (A3PICs) consists of an integrated transimpedance amplifier with an integrated 400μm diameter photodiode, limiting amplifier and line driver on a single chip.   The use of high performance fully integrated optical receiver enables the media converter to reach data rate of 1Gbit/s over 50m SI- POF.

 

”][1]“ETSI TS 105 175-1 V1.1.1(2010-01),” http://www.etsi.org/WebSite/homepage.aspx, January 2010.

[2]I. Mollers, , D. Jager, R. Gaudino, A. Nocivelli, H. Kragl, O. Ziemann, N. Weber, T. Koonen, C. Lezzi, A. Bluschke, and S. Randel, “Plastic Optical Fiber Technology for Reliable Home Networking: Overview and Results of the EU Project POF-ALL,” IEEE Communications Magazine, vol. 47 no. 8, pp. 58–68, 2009.

[3]P. Polishuk, “Plastic Optical Fibers Branch Out,” IEEE Communications Magazine, vol. Volume: 44, Issue: 9, pp. 140–148, September 2006.

[4]R. Gaudino, E. Capello, G. Perrone, G. Perrone, M. Chiaberge, P. Francia, and G. Botto, “Advanced Modulation Format for High Speed Transmission over Standard SI-POF Using DSP/FPGA Platforms,” POF Conference 2004, Nuerberg, pp. 98–105, September 2004.

[5]F. Breyer, S. Lee, S. Randel, and N. Hanik, “PAM-4 Signalling for Gigabit Transmission over Standard Step-Index Plastic Optical Fibre Using Light Emitting Diodes,” 34th European Conference and Exhibition on Optical Communication (ECOC 2008), Brussels, Belgium, vol. 3, pp. 81–82, September 2008.

[6]S. C. J. Lee, F. Breyer, D. Cardenas, S. Randel, and A. M. J. Koonen, “Real-Time Gigabit DMT Transmission over Plastic Optical Fibre,” Electronics Letters, vol. 45 ,no. 25, pp. 1342–1343, 2009.

[7]S. C. J. Lee, F. Breyer, S. Randel, R.Gaudino, G. Bosco, A. Bluschke, M. Matthews, P. Rietzsch, H. P. A. van den Boom, and A. M. J. Koonen, “Discrete Multitone Modulation for Maximizing Transmission Rate in Step-Index Plastic Optical Fibers,” Journal of Lightwave Technology, vol. 27, no. 11, pp. 1503–1513, June 2009.

[8]O. Ziemann, L. Giehmann, P. E. Zamzow, H. Steinberg, and D. Tu, “Potential of PMMA Based SI-POF for Gbps Transmission in Automotive Applications,” the 9th International POF Conference, Cambridge, pp. 44–48, October 2000.

[9]F. Breyer, N. Hanik, S. Randel, and B. Spinnler, “Investigations on Electronic Equalization for Step-Index Polymer Optical Fiber Systems,” Proceedings Symposium IEEE/LEOS Benelux Chapter, Eindhoven, pp. 149–152, November/December 2006.

[10]F. Breyer, S. Lee, S. Randel, and N. Hanik, “500-Mbit/s Transmission over 50 m Standard 1-mm Step-Index Polymer Optical Fiber using PAM4-Modulation and Simple Equalization Schemes,” Proc. ePhoton One Summer School , Brest, France, July 2007.

[11]M. Atef, R. Swoboda, H. Zimmermann, An Integrated Optical Receiver for 2.5Gbit/s Using 4-PAM Signaling, The 22nd International Conference on Microelectronic (ICM2010), Cairo, Egypt, 2010.

[12]M.Atef, R.Swoboda, H.Zimmermann, Optical receiver front-end for multilevel signalling, Electronics Letters Journal, January 2009.

[13] Olef Zieman, POF-Plus Handbook, Handbook of the European POF-PLUS Project 2008 – 2011, 2011.

 

Dr.Mohamed Atef  

Assistant Prof. Assiut University, Egypt    

moh_atef@aun.edu.eg

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