- Email: [email protected]
Microwave photonic signal processing techniques and radio-over-fiber transmission demonstration
The Journal of China Universities of Posts and Telecommunications September 2009, 16(Suppl.): 6–9 www.buptjournal.cn/xben
Microwave photonic signal processing techniques and radio-over-fiber transmission demonstration XU Kun ( ), LI Jian-qiang, YIN Jie, ZHANG Ye, HUANG Hao, LIN Jin-tong Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing 100876, China
Abstract
Radio-over-fiber (RoF) utilizing microwave photonic signal processing techniques is a powerful solution for the future super-broadband wireless access. In this paper, we review our recent works on photonic processing techniques of microwave signals for RoF applications and experimental demonstration of RoF transmissions. Our works specifically focus on impulse-response ultra-wideband (IR-UWB) pulse generation for UWB-over-fiber systems, photonic vector modulation, novel analog modulation format, multi-service RoF system design and experimental demonstrations. Keywords microwave photonics, radio-over-fiber (RoF), impulse-response ultra-wideband (IR-UWB)
1
Introduction
Microwave photonics, which is known as a cross-disciplinary study combining the two worlds of microwave engineering and optoelectronics, has been under intensive investigations for more than 30 years [1–2]. Photonic processing of microwave signals, which is a crucial branch of the subject of microwave photonics, is referred to as a promising technique of microwave signal processing with the help of photonic technologies. This technique is expected to provide an alternative solution to cope with the situations that implementation of several processing functions are complicated or even impossible just in microwave domain. The unique and beneficial merits of this technique have led to various applications especially for communications industry and military purpose. Regarding the applications in communications, photonic microwave processing techniques are supposed to settle down in RoF systems where there is a strong demand for generation, processing and distribution of microwave signals directly in the optical domain. In an RoF system typically composed of a central station (CS) and several remote base stations (BSs), the radio frequency (RF) signals are distributed over optical fiber, where wavelength-division multiplexing (WDM) is available to make full use of the bandwidth of fiber. Received date: 29-06-2009 Corresponding author: XU Kun, E-mail: [email protected] DOI: 10.1016/S1005-8885(08)60367-2
Furthermore, RoF systems operating at millimeter-wave (mm-wave) band are considered as an enabling approach to provide broadband services for the emerging high-speed wireless access [3–4]. Our previous works focus on photonic processing of microwave signals and its applications in mm-wave band RoF systems. In this paper, we summarize the results of our recent works including IR-UWB pulse generation for UWB-overfiber systems, photonic vector modulation, novel analog modulation format, multi-service RoF system design and experimental demonstrations. The following of this paper is divided into three main parts. Sect. 2 will present the results of several microwave photonic processing techniques for mm-wave RoF application. Experimental demonstration of multi-service fiber and wireless transmission of RF signals will be introduced in Sect. 3. Finally, we summarize this paper.
2 Photonics processing of microwave signals 2.1
Photonic IR-UWB pulse generation
UWB technology is considered as an attractive solution to wireless personal communications due to low cost, immunity to multi-path fading, high data-capacity, and low power consumption, etc. In a typical IR-UWB system, a message symbol is represented by a simple short pulse which is directly radiated to the air for base-band propagation, it
Supplement
XU Kun, et al. / Microwave photonic signal processing techniques and radio-over-fiber…
simplifies the transmitters by avoiding the expensive RF components. It has been reported that Gaussian monocycle pulse is a good alternative in UWB impulse radio systems. Many modulation schemes have been proposed in order to meet different design requirements in different applications, such as pulse position modulation, pulse amplitude modulation, and pulse polarity modulation also called bi-phase modulation. On the other hand, the main limitation on a UWB impulse radio system is the limited propagation distance (typically < 10 m) over which the expected high
7
data-rate can be realized. UWB-over-fiber systems are accordingly emerging to exploit the advantages provided by fiber optics, where there is a strong demand to generate, modulate and distribute UWB signals directly in the optical domain. Recently, many schemes have been proposed to optically generate UWB pulses. Recently, we proposed several photonic-assisted approaches to UWB monocycle pulse generation using a single Mach-Zehnder modulator (MZM) [5], a Sagnac interferometer [6–7], and a nonlinear optical loop mirror (NOLM) [8], as shown in Fig. 1.
(a) USB pulse generation scheme based on MZM
(b) UWB monocycle pulse
(d) Electrical spectra of the UWB monocycle pulse
(c) UWB monocycle pulse with reversed polarity
(e) Electrical spectra of the UWB monocycle pulse with reversed polarity
(f) UWB pulse generation scheme based on Sagnac interferometer Fig. 1 Photonic ultra-wideband (UWB) monocycle pulse generation
8
2.2
The Journal of China Universities of Posts and Telecommunications
Photonic vector modulation of microwave signals
For air transmissions in wireless communications, many advanced modulation formats which carry several data bits in a single symbol, including amplitude shift keying (ASK), phase shift keying (PSK) and quadrature amplitude modulation (QAM), have been investigated over the past ten years for increasing spectral efficiency while reducing symbol rate. Among these efficient formats, QAM is particularly attractive for its relatively low signal-to-noise ratio (SNR) requirement compared with ASK or PSK when having the same bits per symbol. The generation of such multi-level vector signals at microwave (especially mm-wave) band may increase the complexity of the electronic driven circuits. Therefore, multi gigabit-per-second mm-wave band signals are proposed to be generated by all-optical approaches in order to reduce cost and overcome the electronic bottleneck. Based on photonic vector modulation (PVM) techniques, several novel schemes have been proposed to generate square 16-QAM [9] and circular QAM signals [10] at mm-wave band. In these schemes, the modified setup can also be used to generate 16-ASK [9] and differential-phase ASK signals [10]. Compared with the conventional methods, the proposed schemes can greatly simplify the electronic driven circuits by employing PVM techniques, which can be applicable in future high-speed super wideband optical-wireless networks. 2.3
BPSK signal generation under optical SSB modulation
All-optical components for RF signal modulation and transmission is an attractive technique for the emerging RoF systems. Generally, baseband data is electrically modulated onto the RF carrier before the modulated RF signal is applied to an electro-optic intensity/phase modulator. By this way, the maximum data rate is limited by the bandwidth of electrical modulators. This problem can be overcome by employing all-optical RF modulation schemes. A number of techniques have been proposed to achieve all-optical modulation of microwave signals at high bit rates. Optical delay module has always been employed in many subcarrier phase modulation schemes to change the phase of RF signal in the optical domain. However, those techniques suffered from the RF power fading due to the dispersion of fiber. The schemes using optical single sideband (SSB) format can improve the dispersion tolerance. Differing from typical optical SSB modulation, we have
2009
proposed a novel photonic BPSK modulator with optical SSB modulation [11]. The key element is a tunable optical comb filter constructed by an electro-optic phase modulator (EOPM) loop mirror. By applying baseband data to the EOPM within the fiber loop mirror, a shift of the comb filter is achieved for polarity switch. With heterodyning of the optical carrier and the obtained switchable optical SSB at photodiode (PD), microwave binary phase shift keying (BPSK) signals are generated.
3 3.1
Experimental demonstration of RoF systems Simultaneous RF and baseband fiber transmissions
It is essential and necessary to upgrade or redesign access networks for satisfying the increasing demand of broadband wireless and wired access. Wavelength-division-multiplexing passive optical networks (WDM-PONs) have been widely investigated as a promising solution to the realization of fiber-to-the-home (FTTH), where the huge bandwidth of optical fiber is explored to achieve up to multi-gigahertz wired access. Taking into account the requirements on flexibility and mobility, radio systems operating at microwave frequency play a crucial role in wireless access networks. However, the conventional wireless communication systems are confronted with a series of challenges, such as the high loss of coaxial cable, frequency congestion, and limited capacity. Recently, mm-wave band RoF systems and optical-wireless converged networks emerge to integrate wireless communications with beneficial fiber-optic technology, which makes it feasible to cost-effectively support both wireless and wired services over the same fiber-optic infrastructure. In the most previous works, WDM-PON and RoF systems were studied separately for supporting either wired or wireless services. Many techniques have been proposed to implement low-cost, flexible, and function-centralized fullduplex operations for either WDM-PON or RoF systems. Although the previous demonstrations have testified that RoF systems are capable of sharing the fiber-based infrastructure with WDM- PON, it is still a challenge to simultaneously guarantee broadband dual-service operations for both wireless and wired access in a single WDM channel. On the other hand, polarization multiplexing (PolMUX) can double the capacity in one WDM channel, and has been successfully demonstrated in the optical transmission experiments by transmitting independent signals in two orthogonal
Supplement
XU Kun, et al. / Microwave photonic signal processing techniques and radio-over-fiber…
states of polarization. Therefore, the introduction of PolMUX will be potential and favorable in dual-service fiber-based access networks due to high spectrum-efficiency and convenience to separate different services. Furthermore, the impact of several polarization-dependent interferences becomes insignificant due to the relatively short transmission distance in access networks, such as polarization-mode dispersion (PMD) and polarization dependent loss (PDL), etc. We have proposed and experimentally demonstrated a hybrid fiber-based WDM system by introducing PolMUX to provide broadband wireless and wired services [12]. In such a dual-service access network, the wireless and wired services are separately delivered in two orthogonal states of polarization with well independence in a single WDM channel. Feasibility of PolMUX is experimentally demonstrated with a power penalty at BER=10–9 of about 0.5 dB and 1 dB for 2.5 Gbit/s wired and wireless services, respectively. 3.2
9
many consumer electronics applications for its simplicity and huge bandwidth.
(a) Diagram
Fiber and wireless transmission of multiband RF signal
Besides the convergence of wireless and wired services, there is a strong demand for generation and distribution of multiband RF signals, which can facilitate a rich mix of value added and differentiated services via a shared infrastructure. We have proposed a simple RoF system for providing multiple services by operating at multiple RF bands [13]. Generation and transmission of downstream 1.25 Gbit/s over 34.8 GHz and 622 Mbit/s over 11.2 GHz have been experimentally demonstrated over 25 km SMF. In addition, the wireless transmission of 34.8 GHz mm-wave signal was also experimentally validated over several meters. The system used only one 10 GHz MZM and a comb filter, as well as a 5.8 GHz microwave source to achieve frequency doubling and frequency sextupling, which can make CS and BS very compact and robust. 3.3 RoF transmission demonstration of high definition television (HDTV) signals In our laboratory, we realized a photonic mm-wave transmission experiment, in which 1.3 Gbit/s of uncompressed HDTV data are frequency-up converted at 32 GHz in the optical domain, as shown in Fig. 2. Both the cost and complexity of the video display equipment (e.g. HDTV) can be decreased, as there is no need to use a trans-code to convert a compressed high definition video into another compression format. The 32 GHz mm-wave RoF transmission demonstration of HDTV signals also provides a new chance of multi-gigabit per-second transmission for
(b) Experimental setup Fig. 2 RoF transmission demonstration of HDTV signals on 32 GHz mm-wave
4
Conclusions
We have reviewed our recent works on photonic processing techniques of microwave signals for mm-wave band RoF applications and experimental demonstrations of multi-service fiber and wireless transmissions including HDTV, which indicates RoF utilizing microwave photonic signal processing techniques is a powerful solution for the future superbroadband wireless access. Acknowledgements This work was supported by the Hi-Tech Research and Development Program the China (2007AA01Z264, 2006AA01Z256), the National Natural Science Foundation of China (60702006, 60736002, 60837004), the New Century Excellent Talent Project in Ministry of Education of China (NCET-06-0093), the PCSIRT (IRT0609),
the
MOST
International
Cooperation
Program
(2008DFA11670), the 111 Project (B07005), and the Project Funded by State Key Laboratory of AOCSN.
To p. 14
14
4
The Journal of China Universities of Posts and Telecommunications
Conclusions
In the future, the RoF downlink should have higher communication capacity. Hence, millimeter wave generation will be a hot research topic. In this article, we propose a configuration for millimeter wave generation. And then, we demonstrate this scheme can be adopted as a RoF system, and it is achieved easily. Especially, the DC bias of MZM is 0.97–1.04 V, if the carrier suppression ratio is defined its value is not lower than 10 dB. The generated millimeter wave optical signal was transmitted over 20 km SMF, and the received power penalty is only 0.28 dB.
3.
4.
5.
6.
Acknowledgements 7.
This work was supported by the National Natural Science Foundation of China (600837004, 60777010), the Hi-Tech Research and
8.
Development Program of China (2009AA01Z253, 2007AA01Z260) and Shuguang Fund.
References 1. Ogawa H, Polifko D, Banba S. Millimeter-wave fiber optics systems for personal radio communication. IEEE Transactions on Microwave Theory and Techniques, 1992, 40(12): 2285–2293 2. Yu Jian-jun, Jia Zhen-sheng, Chang Gee Kung. A novel optical frontend for ultra-high capacity of 322.5Gbit/s data delivery in radio-over-fiber
9.
2009
systems. Proceedings of 31st European Conference on Optical Communication (ECOC’05): Vol 1, Sep 25–29, 2005, Glasgow, UK. Piscataway, NJ, USA: IEEE, 2005: 55–56 Frankel M Y , Esman R D. Optical single-sideband suppressed-carrier modulator for wide-band signal processing. Journal of Lightwave Technology, 1998, 16(5): 859–863 Jianxin Ma, J. Yu, Chongxiu Yu, Xiangjun Xin, Junying Zeng, and L. Chen. Fiber Dispersion Influence on Transmission of the Optical Millimeter-Waves Generated Using LN-MZM Intensity Modulation. Journal of Lightwave Technology, 2007, 25(11): 3244– 3256 David Wake, Claudio R. Lima, and Phillip A. Davies. Optical Generation of Millimeter- Wave Signals for Fiber-Radio Systems Using a Dual-Mode DFB Semiconductor Laser. IEEE Transactions on Microwave Theory and Techniques, 1995, 43(9): 2270–2276 Radoslaw Piesiewicz, Christian Jansen, Daniel Mittleman, Thomas Kleine-Ostmann, Martin Koch, and Thomas Kürner. Scattering Analysis for the Modeling of THz Communication Systems. IEEE Transactions on Antennas and Propagation, 2007, 55(11): 3002–3009 Schmuck H. Comparison of optical millimetre-wave system concepts with regard to chromatic dispersion. Electronics Letters, 1995, 37(21): 1848–1849 Christina Lim, Manik Attygalle, Ampalavanapillai Nirmalathas, Dalma Novak and Rod Waterhouse,. Analysis of Optical Carrier-to-Sideband Ratio for Improving Transmission Performance in Fiber-Radio Links. 2006.IEEE Transactions on Microwave Theory and Techniques, 2006 54(5): 2181–2187 Lin Chun Ting, Chen Jason (Jyehong), Dai Sheng Peng, et al. Impact of nonlinear transfer function and imperfect splitting ratio of MZM on optical up-conversion employing double sideband with carrier suppression modulation. Journal of Lightwave Technology, 2008, 26(15): 2449–2459
From p. 9 References 1. Seeds A J, Williams K J. Microwave photonics. Journal of Lightwave Technology, 2006, 24(12): 4628–4641 2. Capmany J, Novak D. Microwave photonics combines two worlds. Nature Photonics, 2007, 1(6): 319–330 3. Smith G H, Novak D, Lim C. A millimeter-wave full-duplex fiber-radio star-tree architecture incorporating WDM and SCM. IEEE Photonics Technology Letters, 1998, 10(11): 1650–1652 4. Jia Z, Yu J, Chang G K. A full-duplex radio-over-fiber system based on optical carrier suppression and reuse. IEEE Photonics Technology Letters, 2006, 18(16): 1726–1728 5. Li J, Fu S, Xu K, et al. Photonic ultra-wideband monocycle pulse generation using a single electro-optic modulator. Optics Letters, 2008, 33(3): 288–290 6. Li J, Xu K, Fu S, et al. Photonic polarity-switchable ultra-wideband pulse generation using a tunable sagnac interferometer comb filter. IEEE Photonics Technology Letters, 2008, 20(15): 1320–1322 7. Li J, Xu K, Fu S,et al. Ultra-wideband pulse generation with flexible pulse shape and polarity control using a Sagnac-interferometer-based intensity
modulator. Optics Express, 2007, 15(26): 18156–18161 8. Huang H, Xu K, Li J, et al. All optical UWB pulse generation and distribution based on XPM in NOLM. Journal of Lightwave Technology, 2008, 26(15): 2635–2640 9. Zhang Y, Xu K, Zhu R, et al. Photonic generation of M-QAM/M-ASK signals at microwave/millimeter wave band using dual-drive mach-zehnder modulators with unequal amplitudes. Journal of Lightwave Technology, 2008, 26(15): 2604–2610 10. Zhang Y, Xu K, Zhu R, et al. Photonic DPASK/QAM signal generation at microwave/millimeter-wave band based on electro-optic phase modulator. Optics Letters, 2008, 33(19): 2332–2334 11. Sun X, Xu K, Fu S, et al. All-optical WDM subcarrier modulator for binary phase shift keying (BPSK) with optical SSB format using a phase modulator loop mirror filter, OFC2009, JWA56, San Diego, CA, USA, Mar. 2009 12. Li J, Xu K, Wen Y, et al. Experimental demonstration of polarization multiplexing for simultaneously providing broadband wireless and wired access. Optics Communications, 2008, 281(10):2806–281 13. Huang H, Xu K, Li J, et al. Simultaneous generation of millimeter wave and microwave using a single MZM. Electronics Letters (in Press)
Microwave photonic signal processing techniques and radio-over-fiber transmission demonstration XU Kun ( ), LI Jian-qiang, YIN Jie, ZHANG Ye, HUANG Hao, LIN Jin-tong Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing 100876, China
Abstract
Radio-over-fiber (RoF) utilizing microwave photonic signal processing techniques is a powerful solution for the future super-broadband wireless access. In this paper, we review our recent works on photonic processing techniques of microwave signals for RoF applications and experimental demonstration of RoF transmissions. Our works specifically focus on impulse-response ultra-wideband (IR-UWB) pulse generation for UWB-over-fiber systems, photonic vector modulation, novel analog modulation format, multi-service RoF system design and experimental demonstrations. Keywords microwave photonics, radio-over-fiber (RoF), impulse-response ultra-wideband (IR-UWB)
1
Introduction
Microwave photonics, which is known as a cross-disciplinary study combining the two worlds of microwave engineering and optoelectronics, has been under intensive investigations for more than 30 years [1–2]. Photonic processing of microwave signals, which is a crucial branch of the subject of microwave photonics, is referred to as a promising technique of microwave signal processing with the help of photonic technologies. This technique is expected to provide an alternative solution to cope with the situations that implementation of several processing functions are complicated or even impossible just in microwave domain. The unique and beneficial merits of this technique have led to various applications especially for communications industry and military purpose. Regarding the applications in communications, photonic microwave processing techniques are supposed to settle down in RoF systems where there is a strong demand for generation, processing and distribution of microwave signals directly in the optical domain. In an RoF system typically composed of a central station (CS) and several remote base stations (BSs), the radio frequency (RF) signals are distributed over optical fiber, where wavelength-division multiplexing (WDM) is available to make full use of the bandwidth of fiber. Received date: 29-06-2009 Corresponding author: XU Kun, E-mail: [email protected] DOI: 10.1016/S1005-8885(08)60367-2
Furthermore, RoF systems operating at millimeter-wave (mm-wave) band are considered as an enabling approach to provide broadband services for the emerging high-speed wireless access [3–4]. Our previous works focus on photonic processing of microwave signals and its applications in mm-wave band RoF systems. In this paper, we summarize the results of our recent works including IR-UWB pulse generation for UWB-overfiber systems, photonic vector modulation, novel analog modulation format, multi-service RoF system design and experimental demonstrations. The following of this paper is divided into three main parts. Sect. 2 will present the results of several microwave photonic processing techniques for mm-wave RoF application. Experimental demonstration of multi-service fiber and wireless transmission of RF signals will be introduced in Sect. 3. Finally, we summarize this paper.
2 Photonics processing of microwave signals 2.1
Photonic IR-UWB pulse generation
UWB technology is considered as an attractive solution to wireless personal communications due to low cost, immunity to multi-path fading, high data-capacity, and low power consumption, etc. In a typical IR-UWB system, a message symbol is represented by a simple short pulse which is directly radiated to the air for base-band propagation, it
Supplement
XU Kun, et al. / Microwave photonic signal processing techniques and radio-over-fiber…
simplifies the transmitters by avoiding the expensive RF components. It has been reported that Gaussian monocycle pulse is a good alternative in UWB impulse radio systems. Many modulation schemes have been proposed in order to meet different design requirements in different applications, such as pulse position modulation, pulse amplitude modulation, and pulse polarity modulation also called bi-phase modulation. On the other hand, the main limitation on a UWB impulse radio system is the limited propagation distance (typically < 10 m) over which the expected high
7
data-rate can be realized. UWB-over-fiber systems are accordingly emerging to exploit the advantages provided by fiber optics, where there is a strong demand to generate, modulate and distribute UWB signals directly in the optical domain. Recently, many schemes have been proposed to optically generate UWB pulses. Recently, we proposed several photonic-assisted approaches to UWB monocycle pulse generation using a single Mach-Zehnder modulator (MZM) [5], a Sagnac interferometer [6–7], and a nonlinear optical loop mirror (NOLM) [8], as shown in Fig. 1.
(a) USB pulse generation scheme based on MZM
(b) UWB monocycle pulse
(d) Electrical spectra of the UWB monocycle pulse
(c) UWB monocycle pulse with reversed polarity
(e) Electrical spectra of the UWB monocycle pulse with reversed polarity
(f) UWB pulse generation scheme based on Sagnac interferometer Fig. 1 Photonic ultra-wideband (UWB) monocycle pulse generation
8
2.2
The Journal of China Universities of Posts and Telecommunications
Photonic vector modulation of microwave signals
For air transmissions in wireless communications, many advanced modulation formats which carry several data bits in a single symbol, including amplitude shift keying (ASK), phase shift keying (PSK) and quadrature amplitude modulation (QAM), have been investigated over the past ten years for increasing spectral efficiency while reducing symbol rate. Among these efficient formats, QAM is particularly attractive for its relatively low signal-to-noise ratio (SNR) requirement compared with ASK or PSK when having the same bits per symbol. The generation of such multi-level vector signals at microwave (especially mm-wave) band may increase the complexity of the electronic driven circuits. Therefore, multi gigabit-per-second mm-wave band signals are proposed to be generated by all-optical approaches in order to reduce cost and overcome the electronic bottleneck. Based on photonic vector modulation (PVM) techniques, several novel schemes have been proposed to generate square 16-QAM [9] and circular QAM signals [10] at mm-wave band. In these schemes, the modified setup can also be used to generate 16-ASK [9] and differential-phase ASK signals [10]. Compared with the conventional methods, the proposed schemes can greatly simplify the electronic driven circuits by employing PVM techniques, which can be applicable in future high-speed super wideband optical-wireless networks. 2.3
BPSK signal generation under optical SSB modulation
All-optical components for RF signal modulation and transmission is an attractive technique for the emerging RoF systems. Generally, baseband data is electrically modulated onto the RF carrier before the modulated RF signal is applied to an electro-optic intensity/phase modulator. By this way, the maximum data rate is limited by the bandwidth of electrical modulators. This problem can be overcome by employing all-optical RF modulation schemes. A number of techniques have been proposed to achieve all-optical modulation of microwave signals at high bit rates. Optical delay module has always been employed in many subcarrier phase modulation schemes to change the phase of RF signal in the optical domain. However, those techniques suffered from the RF power fading due to the dispersion of fiber. The schemes using optical single sideband (SSB) format can improve the dispersion tolerance. Differing from typical optical SSB modulation, we have
2009
proposed a novel photonic BPSK modulator with optical SSB modulation [11]. The key element is a tunable optical comb filter constructed by an electro-optic phase modulator (EOPM) loop mirror. By applying baseband data to the EOPM within the fiber loop mirror, a shift of the comb filter is achieved for polarity switch. With heterodyning of the optical carrier and the obtained switchable optical SSB at photodiode (PD), microwave binary phase shift keying (BPSK) signals are generated.
3 3.1
Experimental demonstration of RoF systems Simultaneous RF and baseband fiber transmissions
It is essential and necessary to upgrade or redesign access networks for satisfying the increasing demand of broadband wireless and wired access. Wavelength-division-multiplexing passive optical networks (WDM-PONs) have been widely investigated as a promising solution to the realization of fiber-to-the-home (FTTH), where the huge bandwidth of optical fiber is explored to achieve up to multi-gigahertz wired access. Taking into account the requirements on flexibility and mobility, radio systems operating at microwave frequency play a crucial role in wireless access networks. However, the conventional wireless communication systems are confronted with a series of challenges, such as the high loss of coaxial cable, frequency congestion, and limited capacity. Recently, mm-wave band RoF systems and optical-wireless converged networks emerge to integrate wireless communications with beneficial fiber-optic technology, which makes it feasible to cost-effectively support both wireless and wired services over the same fiber-optic infrastructure. In the most previous works, WDM-PON and RoF systems were studied separately for supporting either wired or wireless services. Many techniques have been proposed to implement low-cost, flexible, and function-centralized fullduplex operations for either WDM-PON or RoF systems. Although the previous demonstrations have testified that RoF systems are capable of sharing the fiber-based infrastructure with WDM- PON, it is still a challenge to simultaneously guarantee broadband dual-service operations for both wireless and wired access in a single WDM channel. On the other hand, polarization multiplexing (PolMUX) can double the capacity in one WDM channel, and has been successfully demonstrated in the optical transmission experiments by transmitting independent signals in two orthogonal
Supplement
XU Kun, et al. / Microwave photonic signal processing techniques and radio-over-fiber…
states of polarization. Therefore, the introduction of PolMUX will be potential and favorable in dual-service fiber-based access networks due to high spectrum-efficiency and convenience to separate different services. Furthermore, the impact of several polarization-dependent interferences becomes insignificant due to the relatively short transmission distance in access networks, such as polarization-mode dispersion (PMD) and polarization dependent loss (PDL), etc. We have proposed and experimentally demonstrated a hybrid fiber-based WDM system by introducing PolMUX to provide broadband wireless and wired services [12]. In such a dual-service access network, the wireless and wired services are separately delivered in two orthogonal states of polarization with well independence in a single WDM channel. Feasibility of PolMUX is experimentally demonstrated with a power penalty at BER=10–9 of about 0.5 dB and 1 dB for 2.5 Gbit/s wired and wireless services, respectively. 3.2
9
many consumer electronics applications for its simplicity and huge bandwidth.
(a) Diagram
Fiber and wireless transmission of multiband RF signal
Besides the convergence of wireless and wired services, there is a strong demand for generation and distribution of multiband RF signals, which can facilitate a rich mix of value added and differentiated services via a shared infrastructure. We have proposed a simple RoF system for providing multiple services by operating at multiple RF bands [13]. Generation and transmission of downstream 1.25 Gbit/s over 34.8 GHz and 622 Mbit/s over 11.2 GHz have been experimentally demonstrated over 25 km SMF. In addition, the wireless transmission of 34.8 GHz mm-wave signal was also experimentally validated over several meters. The system used only one 10 GHz MZM and a comb filter, as well as a 5.8 GHz microwave source to achieve frequency doubling and frequency sextupling, which can make CS and BS very compact and robust. 3.3 RoF transmission demonstration of high definition television (HDTV) signals In our laboratory, we realized a photonic mm-wave transmission experiment, in which 1.3 Gbit/s of uncompressed HDTV data are frequency-up converted at 32 GHz in the optical domain, as shown in Fig. 2. Both the cost and complexity of the video display equipment (e.g. HDTV) can be decreased, as there is no need to use a trans-code to convert a compressed high definition video into another compression format. The 32 GHz mm-wave RoF transmission demonstration of HDTV signals also provides a new chance of multi-gigabit per-second transmission for
(b) Experimental setup Fig. 2 RoF transmission demonstration of HDTV signals on 32 GHz mm-wave
4
Conclusions
We have reviewed our recent works on photonic processing techniques of microwave signals for mm-wave band RoF applications and experimental demonstrations of multi-service fiber and wireless transmissions including HDTV, which indicates RoF utilizing microwave photonic signal processing techniques is a powerful solution for the future superbroadband wireless access. Acknowledgements This work was supported by the Hi-Tech Research and Development Program the China (2007AA01Z264, 2006AA01Z256), the National Natural Science Foundation of China (60702006, 60736002, 60837004), the New Century Excellent Talent Project in Ministry of Education of China (NCET-06-0093), the PCSIRT (IRT0609),
the
MOST
International
Cooperation
Program
(2008DFA11670), the 111 Project (B07005), and the Project Funded by State Key Laboratory of AOCSN.
To p. 14
14
4
The Journal of China Universities of Posts and Telecommunications
Conclusions
In the future, the RoF downlink should have higher communication capacity. Hence, millimeter wave generation will be a hot research topic. In this article, we propose a configuration for millimeter wave generation. And then, we demonstrate this scheme can be adopted as a RoF system, and it is achieved easily. Especially, the DC bias of MZM is 0.97–1.04 V, if the carrier suppression ratio is defined its value is not lower than 10 dB. The generated millimeter wave optical signal was transmitted over 20 km SMF, and the received power penalty is only 0.28 dB.
3.
4.
5.
6.
Acknowledgements 7.
This work was supported by the National Natural Science Foundation of China (600837004, 60777010), the Hi-Tech Research and
8.
Development Program of China (2009AA01Z253, 2007AA01Z260) and Shuguang Fund.
References 1. Ogawa H, Polifko D, Banba S. Millimeter-wave fiber optics systems for personal radio communication. IEEE Transactions on Microwave Theory and Techniques, 1992, 40(12): 2285–2293 2. Yu Jian-jun, Jia Zhen-sheng, Chang Gee Kung. A novel optical frontend for ultra-high capacity of 322.5Gbit/s data delivery in radio-over-fiber
9.
2009
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