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Liang Polarization reconfigurable U-slot patch antenna, In: IEEE Trans Antennas Propag 58 (2010), 3383 3388. 2012 Wiley Periodicals, Inc. FULL COLORLESS GIGABIT WAVELENGTH-DIVISION MULTIPLEXED- PASSIVE OPTICAL NETWORK SUPPORTING SIMULTANEOUS TWO DIFFERENT DATA TRANSMISSION Yong-Yuk Won, 1 Hyun-Seung Kim, 2 Yong-Hwan Son, 2 and Sang-Kook Han 2 1 Yonsei Institute of Convergence Technology, Yonsei University, Incheon 406-840, Korea; Corresponding author: bluejerry@yonsei.ac.kr 2 Department of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea Received 8 September 2011 ABSTRACT: A novel wavelength-division multiplexed-passive optical network scheme supporting the transmission of heterogeneous data and broadcast signal is proposed in this article. Both optical carrier suppression and multiplexing of arrayed waveguide grating with 50-GHz channel spacing are used to generate each optical carrier for the transmission of these data. A reflective semiconductor optical amplifier is also used, so that this architecture operates irrespective of wavelength. In case of downlink transmission, error-free transmissions (bit error rate of 10 11 ) of 1.25- and 2.5-Gb/s baseband data are achieved at the same time. Also, 64-quadrature amplitude modulation signal of 60 Mb/s is transmitted showing the error vector magnitude of 4.7% in the presence of the transmission of 2.5-Gb/s baseband data. VC 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1757 1761, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26893 Key words: arrayed waveguide grating; passive optical network; optical carrier suppression; reflective semiconductor optical amplifier; wavelength-division multiplexing 1. INTRODUCTION A wavelength-division multiplexed-passive optical network (WDM-PON) has been an essential technology for several customers in various in-building networks [1 6]. However, a conventional WDM-PON system does not meet the requirements of various multimedia services by subscribers, because its function has been limited to point-to-point data service until now. Network functions need to be more flexible to keep up with the demands for various multimedia services fully; both point-to-point data service and broadcast video/data service have to be provided at the same time. Some efforts have been made to implement the WDM-PON link, which is capable of transmitting heterogeneous data simultaneously [7 14]. The proposed techniques can be divided into two categories. One approach is to use one or more additional optical sources to introduce new multimedia services. The allocation of additional wavelengths will lead to considerable costs and complexity inevitably [7 9]. The other is to transmit two kinds of data simultaneously based on a single optical source using a subcarrier multiplexing (SCM) method [10 14]. At this technique, the channel bandwidth should be shared or limited, and high-frequency microwave components have to be required to generate the mixing processes at both optical network terminal (ONT) and optical network unit (ONU), which gives rise to the increase of their complexities. To solve these problems, the technique of using different modulation formats for two kinds of services was proposed [15, 16]. However, additional optical device such as delay interferometer is required to recover data based on phase modulation format. In this article, a new WDM-PON architecture, which can provide two different point-to-point data services including broadcast video/data service simultaneously, is proposed. It uses both a single-armed Mach-Zehnder modulator (MZM) and arrayed waveguide grating (AWG) with 50-GHz channel spacing to generate optical carriers for the simultaneous transmission of various kinds of data at ONT. Also, 50-GHz-spaced AWG is used as a remote node (RN). A reflective semiconductor optical amplifier (RSOA) is used to modulate and amplify downlink data as well as uplink one. This scheme is demonstrated and verified by measuring both the bit error rate (BER) of the transmissions of up/downlink data (1.25 and 2.5 Gb/s) and error vector magnitude (EVM) of 60-Mb/s 64-quadrature amplitude modulation (QAM) broadcast signal. 2. SCHEMATICS Figure 1 shows the proposed colorless WDM-PON architecture, which is capable of providing both point-to-point data service and broadcast video/data service at the same time. A light from a continuous wave optical source (CW) is transformed into two optical sidebands (frequency spacing of 2f 0 ) using a MZM modulated by a RF subcarrier of f 0 at the bias point of V p. The frequency of RF subcarrier is adjusted, so that two optical sidebands fall into each channel bandwidth of dense WDM multiplexer (DWDM MUX) as shown in the inset. After demultiplexing (DWDM MUX/DEMUX 1) via optical circulator 1, each optical sideband is injected into each RSOA and modulated by downlink data 1, downlink data 2, or broadcast data, respectively. These two modulated lights are transmitted through the single-mode fiber (SMF) via optical circulator 2. At the RN, they are demultiplexed by DWDM MUX/DEMUX 2 and then fed to ONU to detect each downlink data and broadcast data with baseband receivers (Rx). A demultiplexed optical sideband with downlink data 1 is injected into RSOA for uplink data modulation based on wavelength reuse. All the uplink channels are multiplexed by DWDM MUX/DEMUX2 and then retransmitted back to the ONT. After demultiplexing (DWDM DEMUX 3), each uplink datum is detected by the technique of baseband detection at an optical receiver (Rx). 3. EXPERIMENTAL SETUP Figure 2 shows the experimental setup for the proposed bidirectional colorless WDM-PON link for two different data DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 7, July 2012 1757
Figure 1 Schematic of full colorless WDM-PON link with heterogeneous data transmissions. [Color figure can be viewed in the online issue, which is transmissions including broadcast video/data service. A light from a tunable light source was converted into two sidebands with a double-sideband suppressed carrier (DSB-SC) modulation using a single-armed MZM modulated by a 30-GHz RF signal at the bias point of Vp (5 V). A polarization controller (PC 1) was used to maximize the coupling efficiency of MZM. A Gaussian athermal AWG with 50-GHz channel spacing and 16 channels was used, which had insertion loss of 2.5-dB, 3-dB passband of 0.24 nm, adjacent crosstalk of 30 db, and nonadjacent crosstalk of 38 db. The first (1547.015 nm) and the second Figure 2 Experimental setup for bidirectional optical transmission of 1.25- and 2.5-Gb/s wired and 64-QAM broadcast data of 60 Mb/s using a proposed architecture. 3dB, 3-dB coupler. Insets: measured optical spectra of each point (A F). [Color figure can be viewed in the online issue, which is 1758 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 7, July 2012 DOI 10.1002/mop
downlink light with 2.5-Gb/s baseband data at RSOA 3. The remodulated light was retransmitted back to the ONT and then detected at 1.25-GHz Rx. An OBPF was utilized instead of optical MUX. The BER and EVM curves of both the downlink (1.25-Gb/s, 2.5-Gb/s, and 60-Mb/s based on 64-QAM broadcast data) and the BER curves of the uplink (1.25-Gb/s) were measured repeatedly to verify the proposed architecture. At the next section, the measured performances about bidirectional optical transmissions of three sorts of data will be presented. The flexibility of RF subcarrier applied to MZM will be shown using the variation of receiver sensitivity at the BER of 10 11 against the center frequency of RF subcarrier. The impact of 2.5-Gb/s downlink data on the performance of 1.25-Gb/s uplink one will also be investigated showing its power penalty after 23-km transmission. Figure 3 Variation of receiver sensitivity of 2.5-Gb/s downlink data against the center frequency of RF signal applied to MZM from 10 to 40 GHz (1547.415 nm) channels of AWG were used to demonstrate the proposed architecture conceptually. A transformed light was demultiplexed by AWG 1 with 50-GHz channel spacing, and then, each light was injected into RSOA 1 and RSOA 2, respectively. PC 2 and PC 3 were used to maximize the optical gain of an input light injected into an RSOA. A polarization controller before RSOA 2 was not used, because it had the characteristics of polarization insensitive device with polarization-dependent loss of below 0.5 db. A RSOA 1 was directly modulated by a 2.5-Gb/s baseband data with a 2 3 1 1 pseudorandom binary sequence (PRBS) and 2 V p p swing depth. A demultiplexed light injected into a RSOA 2 was modulated by a 1.25-Gb/s baseband data or 64-QAM data with 60 Mb/s over 1-GHz RF subcarrier. Optical spectra were measured to visualize clearly how this scheme operates at each point and are shown in insets (A), (B), (C), (D), (E), and (F) of Figure 2. Their resolution bandwidth and video bandwidth were 0.065 nm and 1 khz, respectively. As shown in the inset of (A), a center mode of optical spectrum is reduced incompletely because of the imperfect optical carrier suppression. We can observe that demultiplexed lights were filtered out very well by AWG with 50-GHz channel spacing as shown in the insets of (B), (C), (E), and (F). The right-handed component of the combined lights after multiplexing (AWG 1) became small slightly because of the difference of optical gain between RSOA 1 and RSOA 2. In case of downlink, the propagation loss of this small test bed was about 20 db, including AWG 1(twice path of 6 db), AWG 2 (3 db), two circulators (3 db), 3-dB coupler, and 23-km SMF (5 db). The propagation loss of uplink was about 12.5 db, including AWG 2 (3 db), 23-km SMF (5 db), one circulator (1.5 db), and optical bandpass filter (OBPF) with 3-dB bandwidth of 0.25 nm (3 db). Each input optical powers injected into RSOA 1 and RSOA 2 was all 3.5 dbm. At this input optical power, optical gains of RSOA 1 and RSOA 2 were 2 db and 3 db, respectively, considerably lower than the small signal gain of 20 db at an input optical power of 20 dbm and had a polarization-dependent gain of 2 db at this input optical power. This tells us that an RSOA was operated under a gain-saturation region. After demultiplexing via 23-km SMF, 2.5-Gb/s baseband, 1.25-Gb/s baseband, and 64-QAM data of 60 Mb/s mixed with 1-GHz RF subcarrier were detected at 3.5-GHz band pin photo-detector (3.5-GHz Rx). A 1.25-Gb/s uplink data was remodulated by reusing the 4. RESULTS AND DISCUSSION This section consists of three subsections as follows. In Section 4.1, simultaneous downlink transmissions of 1.25- and 2.5-Gb/s baseband data, which can support point-to-point different data services, are investigated by presenting each BER result. Simultaneous transmission of 2.5-Gb/s baseband and 64-QAM with 60-Mb/s broadcast data is also evaluated based on EVM result and BER one in Section 4.2. Last, the variation of BER curve of 1.25-Gb/s uplink data depending on the downlink data transmission is shown and analyzed in Section 4.3. 4.1. Simultaneous Downlink Transmissions of 1.25-Gb/s and 2.5-Gb/s Baseband Data The variation of the receiver sensitivity of 2.5-Gb/s downlink data against the frequency of RF signal applied to MZM is presented in Figure 3. The center frequency of RF signal was changed from 10 to 40 GHz, because the 3-dB passband of a used AWG was 0.24 nm (30 GHz). The first channel (1547.015 nm) of AWG was directly modulated by 2.5-Gb/s downlink data. This result was measured repeatedly at the BER of 10 11. As shown in Figure 3, we could observe that received optical power was the lowest at the RF frequency of 25 GHz corresponding to the peak wavelength of the first channel. An overall change of receiver sensitivity was similar to the Gaussian profile of AWG. This result tells us that the frequency of RF signal, which is used to generate a DSB-SC optical carrier, can be flexible into the passband of AWG. Figure 4 shows BER curves of 1.25- and 2.5-Gb/s downlink data after 23-km simultaneous optical transmission. Figure 4(a) is in case of 1.25-Gb/s baseband, whereas Figure (b) is in case of 2.5-Gb/s baseband. Insets show the RF spectrum and eye pattern at the lowest BER value. Power penalty below 0.5 db was observed after 23-km transmission, because there is little chromatic dispersion effect up to 2.5-Gb/s data rate. No impact of the transmission of 1.25-Gb/s baseband data at the second channel on the receiver sensitivity of 2.5-Gb/s baseband data, vice versa, was also checked, because a light from the first channel is suppressed fully at the second channel depending on the values of its adjacent crosstalk and nonadjacent one. This result tells us that there will be no problem due to the optical transmission in the case of the proposed architecture as a multifunctional WDM-PON system. 4.2. Downlink Transmission of 64-QAM Broadcasting Signal of 60-Mb/s in the Presence of 2.5-Gb/s Baseband Data To analyze the influence of 2.5-Gb/s baseband data on the transmission of 64-QAM broadcasting signal of 60 Mb/s, its EVM was measured repeatedly as the frequency of RF subcarrier DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 7, July 2012 1759
Figure 4 Measured BER curves after simultaneous heterogeneous baseband transmission. (a) 1.25-Gb/s and (b) 2.5-Gb/s. Insets: Eye pattern at the lowest BER value and RF spectrum. [Color figure can be viewed in the online issue, which is Figure 5 Variation of EVM against RF subcarrier frequency required for SCM transmission of 64-QAM broadcasting signal in the presence of 2.5-Gb/s baseband data Figure 6 (a) Measured EVM and SNR against received optical power. (b) Constellation, eye pattern, RF spectrum, and EVM of the demodulated downlink 64-QAM data at the received optical power with the highest SNR. [Color figure can be viewed in the online issue, which is required for SCM transmission of 64-QAM data changes from 50 MHz to 2.5 GHz depending on the transmission of 2.5-Gb/s baseband data as shown in Figure 5. A square line is in case of simultaneously transmitting a 2.5-Gb/s baseband data, whereas a circle line is in case of transmitting 64-QAM signal except for a 2.5-Gb/s baseband data. As we can see, there is no power penalty of 64-QAM signal due to the simultaneous transmission of two different data (64-QAM signal and 2.5-Gb/s baseband data). Also, its EVM went up to 7% as the frequency of RF subcarrier increased from 50 MHz to 2.5 GHz. This is because the modulation efficiency of 64-QAM signal decreases gradually depending on the frequency response of RSOA. Figure 6(a) shows the EVM and signal-to-noise ratio (SNR) curves of 64-QAM (60 Mb/s) broadcast data over 1-GHz RF subcarrier. Figure 6(b) shows the constellation, eye pattern, RF spectrum, and EVM of 64-QAM data of 60 Mb/s. The lowest EVM after 23-km transmission was 4.7%, which corresponded to SNR of 22.8 db. The lowest EVM, which can be achieved by vector signal generator (VSG) and vector signal analyzer (VSA) used in the experimental setup, was 4% without device under test. This limitation is because there are various losses of RF devices (Mixer, RF amplifiers, etc.) utilized in the VSG and VSA to generate and recover a 64-QAM data. The power penalty of 2 db was observed after 23-km transmission at the received optical power with the lowest EVM (4.7%). This is attributed to the remained amplified 1760 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 7, July 2012 DOI 10.1002/mop
ACKNOWLEDGMENTS This research was supported by the MKE (The Ministry of Knowledge Economy), Korea, under the IT Consilience Creative Program support program supervised by the NIPA (National IT Industry Promotion Agency; NIPA-2010-C1515-1001-0001) and Yonsei University Institute of TMS Information Technology, a Brain Korea 21 program, Korea. Figure 7 Measured BER curves of 1.25-Gb/s uplink data in the presence of downlink transmission. [Color figure can be viewed in the online issue, which is spontaneous emission noises from RSOA 2 and erbium-doped fiber amplifier (EDFA). 4.3. Uplink Transmission of 1.25-Gb/s Baseband Data Figure 7 shows measured BER curves of a 1.25-Gb/s uplink data. They were measured repeatedly in the presence of a 2.5-Gb/s downlink transmission to check the impact of downlink data on the performance of an uplink data owing to the wavelength reuse. The two insets of Figure 7 show each eye pattern depending on the existence of downlink data. It was observed that the power penalty of an uplink transmission due to the wavelength reuse after 23-km transmission was 2 db (between filled square and filled triangle). Additionally, there is a 2-dB power penalty in an uplink transmission after 23-km transmission (between filled square and open square). This is attributed to the Rayleigh backscattering noise caused by the interference between a remodulated uplink light and an amplified Rayleigh backscattered signal from the RSOA of ONU. 5. CONCLUSIONS A new WDM-PON architecture supporting heterogeneous data transmission including broadcast video/data service was proposed. Both optical carrier suppression and multiplexing technique using AWG with 50-GHz channel spacing were used to generate optical carriers for heterogeneous data transmission (1.25- and 2.5-Gb/s baseband data, 64-QAM 60-Mb/s broadcast signal). An RSOA was used at ONT and ONU, so that the proposed scheme is operated colorlessly. Error-free transmissions (BER of 10 11 and EVM of 4.7%) of baseband data and broadcast signal were accomplished after 23- km transmission. We observed that there was 2-dB power penalty of uplink transmission due to the wavelength reuse. Also, the power penalty of 2 db was checked because of Rayleigh backscattering noise. These experimental results confirm that the proposed architecture can be a good model for near future broadband converged access networks based on a WDM-PON. REFERENCES 1. N.J. Frigo, P.P. Iannone, P.D. Magill, T.E. Darcie, M.M. Downs, B.N. Desai, U. Koren, T.L. Koch, C. Dragone, H.M. Presby, and G.E. Bodeep, IEEE Photonics Technol Lett 6 (1994), 1365 1367. 2. L.Y. Chan, C.K. Chan, D.T.K. Tong, F. Tong, and L.K. Chen, IET Electron Lett 38 (2002), 43 45. 3. W. Hung, C.K. Chan, L.K. Chen, and F. Tong, IEEE Photonics Technol Lett 15 (2003), 1476 1478. 4. P. Healey, P. Townsend, C. Ford, L. Johnston, P. Townley, I. Lealman, L. Rivers, S. Perrin, and R. 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Han, J Opt Soc Korea 12 (2008), 359 363. 14. M.-K. Hong, Y.-Y. Won, H.-S. Kim, and S.-K. Han, In: Proceeding of the 35th European conference on optical communication (ECOC 2009), Vienna, Austria. 15. W.I. Way and C. Castelli, IET Electron Lett 24 (1988), 611 613. 16. N. Deng, C.K. Chan, L.K. Chen, and C. Lin, IEEE Photonics Technol Lett 20 (2008), 114 116. VC 2012 Wiley Periodicals, Inc. A MEANDERED INVERTED-F CAPSULE ANTENNA FOR AN INGESTIBLE MEDICAL COMMUNICATION SYSTEM Wonbum Seo, 1 Uisheon Kim, 2 Soonyong Lee, 1 Kyeol Kwon, 1 and Jaehoon Choi 1 1 Department of Electrical and Computer Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791, Republic of Korea; Corresponding author: choijh@hanyang.ac.kr 2 E.M.W. Corporation, 459-24 Gasan-Dong, Gumcheon-Gu, Seoul 153-803, Republic of Korea Received 13 September 2011 ABSTRACT: In this article, a capsule antenna used in an ingestible medical device is proposed. To achieve miniaturization and a wide bandwidth, an inverted-f antenna with a meandered strip line was used. The antenna performance in a human voxel model is analyzed through simulation, and the performance of the fabricated antenna is verified by comparing the measured data with that of the simulation, when the antenna is placed in a human-equivalent liquid phantom. To investigate the performance of the proposed antenna in an indoor environment, a DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 7, July 2012 1761