Plastic Optical Fiber for In-Home communication systems

Transcription

1 Plastic Optical Fiber for In-Home communication systems Davide Visani 29 October 2010 Bologna

2 Summary Reason for Fiber in the Home (FITH) FITH scenario Comparison of CAT5 and fiber solutions 1mm PMMA POF overview Discrete Multitone Modulation (DMT) Experimental results Conclusions

3 Reason for FITH Services in the residential area state of the art Services Wired solution

4 FITH scenario Converged In-Home network Satellite dish/ FWA dish optical fibre Important charactetistic Private Network Cost is not shared webcam Mobile network (GSM, UMTS, ) Coax Cable network Twisted Pair network Optical Fibre network RG HDTV mobile optical fibre mp3 download laptop PC VoIP fax PDA print We need a cheap solution

5 FITH scenario Today

6 FITH scenario Tomorrow?

7 Comparison of CAT5 and fiber solutions Most common solution for Local Area network (LAN) It use 4 twisted pair and can achieve Gigabit speed (1000-BASE TX) over 100 m Advantages: widespread solutions (high volume market) simple installation for the user especially inside the same room

8 Comparison of CAT5 and fiber solutions In the near future we need to go to 10 Gbit/s (since the Acces Network is going in this direction), and maybe further above. Electrical solutions can be: Cat6a that nominally can guarantee 10 Gbit/s over 100m (now limited to lower distance) Copper cable No more Cat5! Fiber solutions become to be interesting But what kind of fiber optic system?

9 Comparison of CAT5 and fiber solutions Fiber solutions common advantages: Electromagnetic Immunity Size of media Security (difficult to tap or monitor without detection) Silica fiber solutions 9/125µm Single mode fiber (SMF) Huge bandwidth Very costly connection, termination and electronics 50/125µm Multimode fiber (MMF) Less bandwidth Less costly connection, termination and electronics Silica SMF and MMF are considered for the standardization of 40 and 100 Gbit/s LAN, but requires a new network deployment (green field installation)

10 Comparison of CAT5 and fiber solutions 1mm core Plastic Optical Fiber (POF) Comparison Less bandwidth compared to silica fiber solutions (dependent on the exact fiber type) Very simple connectorization and installation 50/125µm Multimode fiber (MMF) 1mm core PMMA POF are a cheap solution and are suitable for upgrading an existing network (brown field installation) 900/1000 µm Polymethylmetacrylate (PMMA) POF

11 1mm PMMA POF overview PMMA POF has a large core of Poly-methylmetacrylate and a cladding of Fluorinated PMMA PMMA core Fluorinated PMMA cladding The refractive index changes is kept high ( 5-6 %, silica fiber 1 %) to have well guided modes Since the basic material is PMMA, the attenuation will depend mostly on his physical characteristics

12 1mm PMMA POF overview Attenuation curve of Step Index (SI) POF The attenuation is more than 300 times bigger compared to silica fiber PMMA POF suitable only for m links There are three local minima windows in the green, yellow and red regions The red regions is interesting because can use off-the-shelf component like red led and also red VCSEL

13 1mm PMMA POF overview plastic glass plastic 1 mm 10 µm glass POF has 100x larger diameter (1 mm) than standard single-mode glass fiber: Easy coupling Cheap (plastic housing, LED) Less sensitive to bending Robust to mechanical stress Finite bandwidth

14 1mm PMMA POF overview Some commercial solutions for 100 Mbps on POF POF plug POF media converter POF switch for ring/mesh network

15 1mm PMMA POF overview Numerical aperture Maximum acceptance angle n cladding Numerical aperture: θ max For Step index MMF: n core We can also show that the product bandwidth-length for Step index MMF is related to NA

16 1mm PMMA POF overview Bandiwidth of Step Index (SI) POF SI-POF has a very large numerical aperture (NA 0.5), and for this reason it has a very high modal dispersion From the study of the multimode step index fiber we know we can increase the modal bandwidth diminishing the numerical aperture of the fiber However reducing the numerical aperture (that means less propagating modes): the tolerance to transceiver-receiver coupling decrease the bending loss increase We need more interesting solutions

17 1mm PMMA POF overview DSI-POF Double SI-POF MSI-POF Multi SI-POF MC-POF Multi core POF DSI-MC-POF Double MC-POF GI-POF Graded Index POF

18 1mm PMMA POF overview MC-POF (Multi core) MSI-POF (Multi Step Index) GI-POF (Graded Index)

19 1mm PMMA POF overview Bandwidth (MHz) for 100 m GI-POF MC-POF DSI-MC-POF MSI-POF SI-POF DSI-POF MC-POF

20 1mm PMMA POF overview GI-POF loss curve GI-POF with benzilmethacrylate (BzMA) dopant The attenuation increase to respect to SI-POF, but the bandwidth drastically increase too SI-POF

21 1mm PMMA POF overview Transceiver: Availability at 650 nm Availability at 570 nm Availability at 520 nm Modulation Bandwidth Cost LED RC-LED VCSEL LD Yes Yes Yes Yes Yes Yes No No Yes Samples No No It is important to say that the regulation on eye-safeness states that the maximum output power of the transceiver should be below 1 mw (0 dbm)

22 1mm PMMA POF overview

23 Discrete Multitone Modulation (DMT) The finite bandwidth of POF need to be exploited with proper solutions We have different options: Binary modulation with strong equalization Multi-level Pulse Amplitude Modulation (PAM) Orthogonal Frequency Division Modulation (OFDM)

24 Discrete Multitone Modulation (DMT) On-Off Keying: Simple but requires strong equalization techniques Multi-level modulation: Bandwidth efficient but more sensitive to non-linearities Discrete Multitone Modulation: Completely adaptively to the channel but with an high poweraverage-to-peak ratio

25 Discrete Multitone Modulation (DMT) The finite bandwidth of POF need to be exploited with proper solutions We have different options: Binary modulation with strong equalization Multi-level Pulse Amplitude Modulation (PAM) Orthogonal Frequency Division Modulation (OFDM) In this presentation we consider a baseband version of OFDM: Discrete Multitone Modulation (DMT)

26 Discrete Multitone Modulation (DMT) It s the baseband version of OFDM, used for example in xdsl technology The idea is to divide the fast serial input in many slow parallel flows, each one using a little part of the channel bandwidth DMT transmitter DMT receiver High-speed serial binary input Serial to Parallel QAM Modulation f1 f2 fn Inverse FFT Parallel to Serial DAC Low-speed parallel frequencies (multiplexed) ADC Serial to Parallel Forward FFT Equalizer QAM Demod. Parallel to Serial High-speed serial binary output We can achieve a high spectral efficiency using simple equalization techniques

27 Bit loading in DMT Another good aspect of DMT is that we can choose the constellation in every subcarrier We can use the maximum supported constellation in every subcarrier To obtain automatically this configuration we use a bit loading algoritm that maximize the total bit rate under the condition of finite total power

28 DMT in IM-DD systems DMT is characterized by an high peak to average power ratio (PAR) To reduce the PAR we clipped the signal DMT time signal LED/laser output power P opt 0 0 I

29 DMT in IM-DD systems However the clipping introduce a distortion of the DMT signal, that can be considered as an equivalent noise There are also other two important noise sources: Quantization noise (DAC and ADC conversion) Thermal noise at the receiver We should choice the clipping level of the signal to work in a thermal noise limited system

30 Experimental setup General scheme DMT Tx Off-line processing DMT Rx Arbitrary Waveform Generator DAC TX speed Tektronix AWG7122B Real-time Oscilloscope ADC Rx speed Bias E/O converter PMMA POF O/E converter Transmitter: LED RC-LED VCSEL PMMA POF: SI-POF MC-POF GI-POF Tektronix DPO72004 Offline modulation and de-modulation (DMT format) Receiver: Si-PD APD

31 Experimental setup Case of study DMT Tx Off-line processing DMT Rx Peak to peak voltage: 1 V Arbitrary Waveform Generator DAC TX speed Tektronix AWG7122B Real-time Oscilloscope ADC RX speed Tektronix DPO72004 Bias VCSEL 667nm PMMA GI-POF Si-pin-PD TIA Transmitter: Firecomms VCSEL (RVM665T) Wavelength 667nm BW (specs) ~ 3 GHz PMMA GI-POF: OptiMedia 50-m 1mm core nm BW ~ 1.3 GHz Receiver: 400µm Si-PD with TIA BW (specs) ~ 1.6 GHz

32 Experimental setup Receiver VCSEL PIN PD TIA

33 Experimental setup Power budget and frequency response Optical power of VCSEL: 0 dbm POF loss: 15 db coupling loss (TX and RX): 1-2 db Frequency response Received optical power: -20 dbm We will use a DMT signal in a 2.25 GHz: TX speed = 4.5 Gsample/sec RX speed set at the maximum possible: ~ 1.3 GHz RX speed = 50 Gsample/sec

34 Experimental results Transmitted DMT signal Received DMT signal 4 QAM 32 QAM 16 QAM 8 QAM

35 Experimental results POF length Data Rate BER 10 m 7.6 Gb/s 6.7 E-4 20 m 7.2 Gb/s 6.3 E-4 35 m 6.2 Gb/s 8.8 E-4 50 m 5.3 Gb/s 8.5 E-4 Total Bit Rate achieved: 5.3 Gbit/s with BER < 10-3

36 Experimental results Total Bit Rate achieved: 5.3 Gbit/s with BER < 10-3 Some parametric evaluation: Number of subcarrier Clipping level (crest factor)

37 Experimental results Subcarrier number 256 subcarrier are sufficient to achieve almost maximum bit rate Percentage variation

38 Experimental results Crest factor (Clipping level) We fix the crest factor: In our case the optimum value is around 8 db

39 Experimental results The problem of PMMA GI-POF is that the bending radius is around mm 180 bend At 20 mm we loose 10 % of the bit rate!

40 Conclusions Plastic optical fiber is a suitable solution to be used as an optical in-home backbone (FITH) The way to exploit the finite bandwidth of this medium can be addressed in different ways We considered Discrete Multitone Modulation with a bitloading algorithm to achieve high spectral efficiency on POF link with simple equalization techniques We demonstrate 5.3 Gbit/s over 50m 1mm diameter graded-index POF using red VCSEL and silicon photodetector.