Gamatham, Romeo

Gibbon, Timothy Braidwood

Guerrero Gonzalez, Neil

Tafur Monroy, Idelfonso

Yu, Xianbin

We demonstrate 3.125 Gb/s photonic impulse radio UWB generation using an uncooled distributed feedback laser. After 50km fiber transmission the signal is recovered without errors using a digital signal processing receiver

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Downloaded from orbit.dtu.dk on: Dec 19, 20173.125 Gb/s impulse radio UWB over fiber transmissionGibbon, Timothy Braidwood; Yu, Xianbin; Gamatham, Romeo; Guerrero Gonzalez, Neil; Tafur Monroy,IdelfonsoPublished in:Conference proceedings of the European Conference on Optical CommunicationPublication date:2009Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Gibbon, T. B., Yu, X., Gamatham, R., Guerrero Gonzalez, N., & Tafur Monroy, I. (2009). 3.125 Gb/s impulseradio UWB over fiber transmission. In Conference proceedings of the European Conference on OpticalCommunication (pp. 1-2). IEEE.3.125 Gb/s Impulse Radio UWB over Fiber Transmission T.B. Gibbon1, Xianbin Yu1, R. Gamatham1,2, N. Guerrero Gonzalez1 and I. Tafur Monroy11) DTU Fotonik-Department of Photonics Engineering, Technical University of Denmark DK-2800, Kgs. Lyngby, Denmark. tbgi@fotonik.dtu.dk2) Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa. Abstract We demonstrate 3.125 Gb/s photonic impulse radio UWB generation using an uncooled distributed feedback laser. After 50km fiber transmission the signal is recovered without errors using a digital signal processing receiver.Introduction Current requirement from short-range wireless communication systems include low power consumption, radiating low power levels into the environment, and capability of supporting bandwidth intensive applications such as high definition TV. Impulse ultra-wideband (UWB) radio is a promising technology for meeting these requirements. At radiation below -41.3 dBm/MHz wireless UWB signals can however at best only propagate several meters. Photonic UWB is thus invaluable for distributing UWB signals through fiber transmission in converged optical wireless access networks. The challenge to date has been high speed photonic impulse radio UWB (IR-UWB) generation. Previous demonstrations include 500 Mb/s with pulse shaping1, 625 Mb/s with frequency up-conversion2 , 781.25 Mb/s 3 , and 1.025 Gb/s 4 and 1.625 Gb/s 5featuring wireless transmission.  In this paper we demonstrate 3.125 Gb/s photonic impulse radio (IR) UWB signal generation based on incoherent optical field summation resulting from cross gain modulation (XGM) of an uncooled distributed feedback (DFB) laser injected with a 12.5 Gb/s modulated external cavity laser (ECL). The UWB signal is transmitted over 50 km of fiber and subsequently recovered without errors using a digital signal processing (DSP) receiver. Experimental setup Fig. 1(a) shows the experimental setup. A 1552.8 nm ECL intensity modulated at 12.5 Gb/s is injected into an uncooled DFB laser with a central wavelength of 1551.5 nm. A polarization controller (PC) placed before the circulator is used to adjust the state of polarization of the modulated ECL to ensure the XGM introduced within the DFB laser is maximized. The IR-UWB signal exiting the UWB generator after the circulator is launched into 25 km of single mode fiber (SMF) followed by 25 km of matching inverse dispersion fiber (IDF). The IR-UWB pulse is subsequently detected by a photodiode (PD). The electrical spectrum is measured and compared to the US Federal Communications Commission (FCC) requirement at the photodiode. The bit error rate (BER) is also determined using an Agilent 40 GSa/s Digital Storage Oscilloscope and custom offline DSP algorithm. In addition to the high bit rate that is achieved, our scheme avoids the use of complex mode-locked lasers, custom fiber Bragg gratings, spectral shaping components, and nonlinear elements as in many previously reported optical IR-UWB generation techniques. 0=0(&/˨(&/ QP*EV15=˨')% QPNP ,') NP 60)')%3& 3&$WW3'(a)(b)1549 1550 1551 1552 1553 15540.00.20.40.60.81.01.21.4  DFB laser(1551.5 nm)  Free running DFB laserFig. 1: (a) Experimental setup. (b) Optical spectra measured at the output of the UWB Generator.  DFB laser with injected ECL      ECL(1552.8 nm) Normalized Power (dBm)Wavelength (nm)Photonic UWB signal generation Fig. 1(b) shows the optical spectra measured directly after the circulator. The ECL wavelength is chosen to correspond with a first-order DFB laser sidemode, thus ensuring strong XGM transfer to the 1551.5 nm DFB laser wavelength. Fig. 2 illustrates the generation principle for a 101101 UWB bit sequences. The ECL modulated at 12.5 Gb/s with the sequence 1000 0000 1000 1000 0000 1000 produces the XGM output of the DFB laser as shown in Fig. 2 (a). Noticeable are the overshoot and relaxation oscillations of the DFB laser6. UWB bits are subsequently created from the incoherent sum of the ECL and DFB signals7 as shown in Fig. 2 (b). The 12.5 Gb/s modulation sequences 1000 and 0000 of the ECL correspond to 1 and 0 UWB ECOC 2009, 20-24 September, 2009, Vienna, Austria Paper P6.01978-3-8007-3173-2  © VDE VERLAG GMBHAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on November 4, 2009 at 07:17 from IEEE Xplore.  Restrictions apply. bits respectively, at an effective UWB bit rate of 3.125 Gb/s. The UWB pulse shape can be altered by slightly tuning the ECL wavelength about the first-order DFB wavelength. This alters the relative delay between the ECL and DFB laser signals caused by chromatic dispersion.  Fig. 2: (a) The ECL and DFB laser signals measured individually using a 0.4 nm FWHM filter at the output of the UWB generator. (b) The IR-UWB signal resulting from the incoherent summation of the ECL and DFB signals.  Photonic UWB signal transmission The photonic back-to-back IR-UWB pulse shape shown in Fig. 3(a) was selected for the fiber transmission demonstration to obtain a high fractional bandwidth and good agreement to the FCC mask, as shown in Fig. 3(b). The -10 dB fractional bandwidth about the central frequency of 7.6 GHz is around 145%. For the transmission demonstration IDF was chosen as an option to compensate the SMF dispersion. IDF has the added benefit compared to dispersion compensating fiber of being used as transmission fibre, thus extending network reach. Inter- and intra-channel dispersion issues of the two wavelengths used in our IR-UWB have yet to be thoughtfully investigated.   Comparison between Fig. 3(a) and (c) shows that transmission does not alter the pulse shape. After fibre transmission the electrical spectrum was found to be practically identical to the back-to-back electrical spectrum and still comply with the FCC requirements. Fig. 3(d) shows the BER results for back-to-back and 50 km fiber transmission of the photonic IR-UWB signal. For each BER measurement point, 6.84105 UWB bits following a 27-1 PRBS pattern are transmitted and recorded using a 40 GSa/s Digital Storage Oscilloscope. The BER is subsequently computed using a DSP algorithm in a bit-for-bit comparison between the transmitted and received bits. The DSP algorithm distinguished between “1” and “0” UWB bits by comparing the average power within the central window of each bit slot to an optimally determined decision threshold. Transmission over the 50 km link is seen to introduce a 1 dB penalty. Transmission without error in 6.84105 UWB bits occurs at receiver sensitivities of -13.4 dBm and -12.4 dBm for back-to-back and fiber transmission respectively.  0.0 0.5 1.0 1.5 2.00.00.10.20.3Time (ns)XGM Output from DFB Laser0.00.10.20.31 0 010010 00Intensity (mW)12.5 Gb/s Modulated ECL Output0 00 1 00 0 00 0 00 000.0 0.3 0.6 0.9 1.2 1.5 1.80.00.20.40.60.81.03.125 Gb/s UWB Signal Experimental measured after UWB generator Computed sum of ECL and DFB outputs Normalized IntensityTime (ns)1 0 1 1 0 1Fig. 3: (a)-(c) The 3.125 Gb/s IR-UWB pulse in the time and electrical domains, before and after transmission over the 50 km fiber link. The spikes with 3.125 GHz spacing in (b) originate from of the PRBS pattern repetition rate. (d) BER results for back-to-back and fiber transmission of the photonic IR-UWB signal.  Conclusions We demonstrate 3.125 Gb/s photonic IR-UWB signal generation based on incoherent optical field summation for an uncooled DFB laser injected by a modulated ECL. The penalty was found to be 1 dB for transmission of the IR-UWB signal over 50 km of fiber. This first ever to our knowledge demonstration of photonic IR-UWB signal generation beyond 3 Gb/s paves the way for high speed converged optical wireless access networks supporting short-range wireless.  References 1. M. Abtahi et al., JLT 26(15), 2795 (2008). 2.. Q. Chang et al., PTL 20(19), 1651 (2008). 3. T.B. Gibbon et al., Proc. OFC’09, OTuB8 (2009).4. M. Hanawa et al., Proc. OFC’09, OTuJ3 (2009).5. H. Shams et al., Proc. OFC’09, OWR2 (2009). 6. V. Torres-Company et al., PTL 20(15), 1299 (2008). 7. X. Yu et al., Proc. OFC’09, JWA60 (2009). (a)(b)-19 -18 -17 -16 -15 -14 -13 -127654321400 Errors in 684 000 bits40 Errors in 684 000 bits4 Error in 684 000 bitsNo errors detectedBack-to-Back  50 km Fiber Transmission-log(BER)Power at Detector (dBm)0.0 0.3 0.6 0.9 1.2 1.5 1.80.00.20.40.60.801.After 50km fiber transmissionNormalised IntensityTime (ns)1 0 1 1 0 10.0 0.3 0.6 0.9 1.2 1.5 1.800.20.40.60.800.1.Back-to-BackNormalized IntensityTime (ns)0 1 2 3 4 5 6 7 8 9 10 11 12-60-50-40-30-20-100101 0 1 1 0 1Back-to-BackFCC Indoor MaskNormalized Spectrum (dB)Frequency (GHz)(b)(a)(d)(c)ECOC 2009, 20-24 September, 2009, Vienna, Austria Paper P6.01978-3-8007-3173-2  © VDE VERLAG GMBHAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on November 4, 2009 at 07:17 from IEEE Xplore.  Restrictions apply. 

3.125 Gb/s impulse radio UWB over fiber transmission

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3.125 Gb/s impulse radio UWB over fiber transmission

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