Dense Wavelength Division Multiplexing Radio-on-Fiber Systems

Transcription

1 nternational Topical Meeting on Microwave Photonics September, 2003 Dense Wavelength Division Multiplexing Radio-on-Fiber Systems Ken-ichi Kitayama Osaka University, Yamadaoka, Suita, Osaka Japan Phone: +X , Fax: , kitavamaii3comm.ene.osaka-u.ac.ie Abstract Dense wavelength division multiplexing (DWDM) millimeter-wave radio-on-fiber (ROF) systems are presented, in which we will focus on its multiplexing and demultiplexing techniques and photonic frequency conversions. The 25GHz-spacing, 60GHz-band DWDM ROF is experimentally demonstrated. 1. ntroduction n millimeter-wave-band ROF systems, a cenual station (CS) will be connected with a huge number of base stations (BSs) to cover service area as wide as possible. An adoption of dense wavelength division multiplexing (DWDM) techniques to the ROF systems will enhance the multiple access capability by maintaining the compatibility with FTTH access network infrastructure. There have been several reports on such DWDM ROF systems [1]-[3]. To increase the optical spectral efficiency, an optical frequency interleaving technique has been proposed [4],[5]. We have proposed a different type of optical frequency interleaving DWDM ROF systems with an arrayed waveguide grating (AWG) [6], [7]. We have also proposed the photonic downconversion (PDC) technique with optical frequency shift, which could effectively incorporated into DWDM ROF systems [a]. n this paper, DWDM millimeter-wave ROF systems are presented, in which we will focus an its multiplexing and demultiplexing techniques and photonic frequency conversions. The 25GHz-spacing, 60GHz-band DWDM ROF is experimentally demonstrated. 11. DWDM ROF System Architectures A. System Architecture : Without Photonic Downconversion Figure 1 shows the architecrure of DWDM ROF system without PDC with the CS in a star topology. The uplink ROF signals from each BS are multiplexed at the wavelenglh Fig.1 DWDM ROF systemarchitecture 1 without PDC 129

2 ~ -DEMUX ~ wavelength September, 2003 nternational Topical Meeting on Microwave Photonics 1 multiplexer (-MUX) and transmitted over a! single optical fiber link to the CS. A. (n =, 2,..., N) is assumed to be individually allocated to BS. The DWDM ' ROF signal received at the CS is demultiplexed! by the demultiplexer (-DEMUX), put into an individual O/E, and demodulated with an RF-band processor. n Fig. 2 the schematic diagram of 1 -DEMUX is shown [6]. As shown in Fig. 2(a), consists of a high-finess i Fably-Perot etalon (FP), an optical circulator (OC), and a 2 x N AWG For the DWDM ROF signal AD of Fig. 2(b), the FP separates the i carriers Bo from their sidebands CO in Fig. 2(b). The AWG is designed to guide the input signals Do with the frequency interval off, and the RF carrier freqeuency of fw to the same output port. Figure 3 shows the -MUX scheme [7]. The 1-MUX consists of a high-finess FP, an OC, and an N x 2 AWG, where the difference is only the direction of the OC. The AWG is designed to filter the carrier BM and one of the sidebands CM of each input channel and guide them to the distinct output ports. The filtered carriers BM and sidebands CM are combined with the OC and the FP. From the spectra of the input ROF signal and the multiplexed output shown in AM and DM offig. 3(b), this scheme performs the frequency interleaving as well as the SSB filtering for the entire DWDM ROF channels. C, nnnnnnr.nn, DM /-G --YK f f (b) Fig. 2 -DEMUX [5]: (a) configuration and (b) optical spectra. (b) Fig. 3 -MUX [6]: (a) configuration and (b) optical spectra. 130

3 nternational Topical Meeting on Microwave Photonics September, 2003 B. System Architecture 11 : With Photonic Downconversion [B] n Fig. 4, the architecture of a DWDM ROF system with the PDC is shown. The PDC is defined as a frequency-conversion from the RF regime to F. The PDC is introduced in CS. The received DWDM signal is optically pre-processed and then demultiplexed by -VEMUX. Each demultiplexed signal is Fig. 4 DWDM ROF system architecture 11 with PDC. photonic-downconverted via O/E converter and demodulated with the F-band processor. Figure 5 shows the optical spectrum allocation of the VWDM ROF channels with the PDC. n Fig. 5(a), C. and U. represent the camier and the upper sideband (USB) of n-th channel from BS,, respectively. fen, fcm+j,, and frp represent the optical carrier frequency of n-th and (n+l)-th channels, and the RF carrier frequency, respectively. Far simplicity, it is assumed that the optical frequencies arc equally spaced with the interval of f' [= fccn+i1-gm]. n the PDC. at first a lump of the DWDM ROF signals is equally power-split and frequency-shifted by -f~d2 and f~d2. n the frequency-shifted DWDM signals shown in Fig. Xb), Cd., Gun, Udn. and U,, are the down-shifted carrier, the up-shifted camer, the a c., _i: n / C"..,, L s.. Fig. 5 Optical spectrum design [7]: (a) pre-processor input, (b) pre-processor output, and (c) extracted channels 131

4 * 20 j aj 7/ s /.,=596G 12 - /= = 21.0 Gill s-6- in a mm-wave-band ROF signal are differentially shifted closer to each other. Next, each pair ofthe closely aligned components, S., which consists of C,. and Ud., is filtered out by systems Experimental Results [8] ibl ls5l.o llsl S52.S l553.0 Warclcnelh [nml The measured optical spectra for the DWDM ROF system with PDC are shown in Fig. 6. Figure 6(a) shows the received 25-GHz-spaced DWDM ROF signal. The calsier linewidths at and nm were 300 khz. From Fig. 6(b), each optical component is successfully lower- and upper-shifted. Figs. 6(c) and (d) show the AWG output for Chs. 1 and 2. Two pairs of optical id)! Fig. 6 Measured optical spectra of (a) i pre-processor input, (b) pre-processor output,, (c) selected Ch., and (d) selected Ch. 2. components (at around and tun) are filtered out with a suppression ratio of less than -40 and -25 db for Ch. 1 and 2, respectively. As shown in Fig. 7, the photodetected signals without data are observed in the microwave frequency band. The SpeClNm linewidth is very narrow. This shows that the original mm-wave-band RF signals re properly downconverted to the desired microwave-band F signals through the optical link. As a result! 132

5 nternational ToDical Meeting on Microwave Photonics September, 2003 of bit enor rate (BER) measurement, the BE& of for bath channels are btained without any floor. The experimental results of the MUXDEMUX techniques will be presented on site. V. Conclusion We have presentcd the multiplexing and demultiplexing techniques and photonic frequency conversions for DWDM ROF systems. Theses DWDM techniques would be crucial enablers to accommodate a large number of customers for the future ROF access networks. Acknowledgments The author would like to thank Dr. T. Kuri of Communications Research Laboratory, Tokyo, Dr. H. Toda and Mr. T. Yamashita of Osaka University, Osaka for their collaborations. This research was supported by "Support system for R&D activities in info-communications area" conducted by Telecommunications Advancement Organization of Japan (TAO). Fig. 7 Measured electrical signals without data of (a) Ch. and (b) Ch. 2. References [] K. Kitayama, "Highly spectrum efficient OFDMPDM wireless networks by using optical SSB modulation," EEEVSA J. Llghrwave Techno/.. ~01.16, no.6, pp , June K. Kitayama, T. Kuri, K. Onohara. T. Kamisaka, and K. Murashima, "Dispersion effects of FBG and optical SSB filtering in DWDM millimeter-wave fiber-radio systems," EEE/VSA f. Lightwove Technol., vo1.20,no.8,pp ,2002. [2] K. Kojucharow, M. Sauer, H. Kaluzni, D. Sommer, and C. Schaffer, "Experimental investigation of WDM channel spacing in simultaneous upconversion millimeter-wave fiber transmission system at 60 GHz-band," in MS2000 Tech. Dig, v01.2, WE4C-7, 2000, pp [3] A. Nsrasimha, X. 1. Mag, M. C. Wu, and E. Yablonovitch, "Tandem single sideband modulation scheme for doubling spectral efficiency of analogue fibre links," Electmn. Lett., vo1.36, , p , June [4] C. G Schsffer, M. Sauer, K. Kojucharow, and H. Kalurni, "ncreasing the channel number in WDM mm-wave systems by spectral overlap," internarional Topical Meering on Microwave Photonics (MWP2000), WE2.4, p.164, Oxford (2000). 151 C. Lim, A. Nirmalathas, D. Novak, R. S. Tucker, and R. B. Waterhouse, "Technique for increasing optical spectral efficiency in 133

6 ~ ~ September, 2003 nternational Topical Meeting on Microwave Photonics 1 millimetre-wave WDM fibre-radio,! Eleclron. Leu., vo1.37, no.16, pp , Aug [6] H. Toda, T. Yamashita, K. Kitayama, and T. Kuri, A DWDM millimeter-wave fiber-radio system by optical frequency interleaving for high spectral efficiency, in MWP2OOf Tech. Dig., Long Beach, CA,, USA,Tu-3.3,2002,pp H. Tab, T. Yamashita, T. Kuri, and K. ; Kitayama, 25-GHz channel spacing i DWDM multiplexing using an arrayed! waveguide grating for 60-GHz band 1 radio-on-fiber systems, submitted to 1 MWP2003. [8] T. Kuri, H. Toda, and K. Kitayama, Dispersion-effect-free dense WDM millimeter-wave-band radio-an-fiber signal transmission with photonic! downconversion, in Pmc APMC2003, WE1C-04,2002,pp