Bidirectional Passive Optical Network for the Transmission of WDM Channels with Digital Broadcast Video Signals E. S. Son, K. H. Han, J. K. Kim, and Y. C. Chung Korea Advanced Institute of Science and Technology Department of Electrical Engineering 373-1 Kusong-dong, Yusong-gu, Taejon 305-701, Korea (Phone) +82-42-869-3456, (FAX) +82-42-869-3410, (E-mail) ychung@ee.kaist.ac.kr Abstract: We demonstrate an easily upgradable bidirectional passive optical network for the transmission of WDM channels and digital broadcast video signals. The proposed network could transmit fifteen 2.5-Gbps downstream channels, fifteen 155-Mbps upstream channels, and one broadcast channel consisting of more than 70 digital video signals.  2001 Optical Society of America OCIS codes: (060.2330) Fiber optics communications I. Introduction Wavelength-division-multiplexed passive optical networks (WDM PON’s) offer many advantages including large capacity, easy management, network security, and upgradability [1]. In these networks, the waveguide-grating- routers (WGR’s) are often used for virtual point-to-point connectivity. However, the wavelength-routed WDM PON is not suitable for the delivery of broadcast services due to the wavelength-dependent routing property of WGR. There have been some efforts to solve this problem by using WDM overlay on TDM PON or broadband LED source for broadcast signal [2,3]. However, the first technique requires a large number of WDM filters and couplers [2]. The second technique used a pair of fibers and frequency up/down-conversion of a video signal due to the limited modulation characteristics of LED [3]. In this paper, we propose and demonstrate a new bidirectional PON for the transmission of digital broadcast video signals as well as WDM channels. The proposed network utilizes a laser operating at 1530 nm for the broadcast service (more than 70 digital video channels), WDM lasers operating at the 1550-nm band for the downstream data (up to 2.5 Gbps), and LED’s operating at the 1300-nm band for upstream data (155 Mbps). Thus, this network could support bidirectional transmission using single strand of fiber and does not require the frequency up/down-conversion of a video signal. In addition, we also demonstrated that the capacity of this network could be upgraded easily by inserting an additional WDM filter and a receiver at the ONU for the digital video signals. II. Experiment Fig. 1 shows the experimental setup to demonstrate the proposed bidirectional WDM PON. For downstream baseband transmission, we used fifteen lasers (in the range of 1548.8 ~ 1560.9 nm) directly modulated at 155 Mbps, 622 Mbps, or 2.5 Gbps at the central office (CO). The output power of each laser was set to be 0 dBm. These WDM channels were first passed through the 1.3/1.5-µm couplers, which were used for the separation of upstream and downstream channels, and then were multiplexed by using a 16×1 WGR. We used a directly modulated laser operating at 1533.5 nm for the broadcast digital video signal. This signal consisted of a digital video signal of Korea Satellite 2 (KS2) (in the range of 0.98 ~ 1.05 GHz) and electrical noise (in the range of 1.13 ~ 1.53 GHz). This was to simulate more than 70 digital video channels. The rms (root-mean-square) optical modulation index (OMI) per channel was set to be 2.6 %. The video signal was amplified by an EDFA (output power: 17 dBm) and multiplexed with the fifteen downstream baseband channels at the WGR. These multiplexed channels were transmitted to the remote node (RN) through 10 km of single mode fiber (SMF). At the RN, the downstream channels were separated into baseband data and video signal using the 1.3/1.5- and 1.53/1.55-µm WDM couplers. The video signal was split by using a 1×16 splitter and sent to the fifteen input ports of the 16×16 WGR. These signals were directed to the fifteen optical network units (ONU’s) via 3 km of SMF. The baseband signals were demultiplexed by using WGR and sent to each corresponding ONU. Both the video and baseband signals were detected by using a PIN-FET receiver (bandwidth: 1.7 GHz) via a 1.3/1.5-µm WDM coupler. Thus, we used only one receiver to detect both the video and baseband signals when the data rate of the downstream baseband signal was either 155 Mbps or 622 Mbps. The output signal of the receiver was split, and sent to an error detector and a TV for the BER and video quality measurements, respectively. However, when the downstream data rate was 2.5 Gbps, we separated the baseband and video signal using a 1.3/1.5-µm WDM coupler and sent to two independent receivers. This was necessary to