368 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 21, NO. 6, MARCH 15, 2009 Separated Unicast/Multicast Splitter-and-Delivery Switch and Its Use in Multicasting-Capable Optical Cross-Connect Hong Du, Weisheng Hu, Member, IEEE, Hao He, Chunlei Zhang, Yi Dong, Weiqiang Sun, Member, IEEE, Wei Guo, Member, IEEE, Yaohui Jin, Member, IEEE, and Shilin Xiao Abstract—We propose a novel separated unicast/multicast splitter-and-delivery (SUM-SaD) switch for mixed unicast and multicast traffic. Only multicast connections undergo extra split- ting loss but are compensated by incorporated optical amplifiers. A typical multicasting-capable optical cross-connect is constructed by using the proposed SUM-SaDs. Theoretically, we prove that it is strictly nonblocking for both unicast and multicast connections if , where and are the dimension of SUM-SaD and the number of SaD input ports, respectively. Therefore, means the maximum accommodated trees in the SUM-SaD. To save cost, can be less than , and the throughput performance is investigated by simulation. The results show that the throughput is improved when increases. In the experiment, we construct a 4 4 SUM-SaD prototype and measure the bit-error rate (BER) of unicast connection, multicast connection with or without optical amplifier. There is no clear BER difference between them for the small dimensional SUM-SaD switch. Index Terms—Multicasting capable, optical cross-connect, splitter-and-delivery (SaD), wavelength-division multiplexing (WDM). I. INTRODUCTION W ITH the proliferation of Internet, triple-play, and mobile communication services, there is a growing demand for bandwidth-intensive multicast applications such as high-definition television, video-conferencing, interactive distance learning, distributed games, etc. This is encouraged by the promise of terabit fiber bandwidth with wavelength-division multiplexing (WDM), optical cross-connect (OXC), and re- configurable optical add and drop multiplexing (ROADM) technologies [1]. In order to support multicast in the OXC nodes at the WDM layer [2], the concept of the light-tree was introduced, which Manuscript received November 12, 2008; revised December 15, 2008. First published January 27, 2009; current version published March 11, 2009. This work was supported in part by the NSFC under Grant 60632010 and Grant 60825103, by the 863 Program, SRFDP, and by Shanghai Public R&D Plat- form (07dz22010). H. Du, W. Hu, H. He, Y. Dong, W. Sun, W. Guo, Y. Jin, and S. Xiao are with the State Key Laboratory of Advanced Optical Communications Systems and Networks, Shanghai Jiao Tong University, Shanghai 200240, China (e-mail: sunnyduhong@gmail.com; wshu@sjtu.edu.cn; hehao@sjtu.edu.cn; yidong@sjtu.edu.cn; sunwq@sjtu.edu.cn; wguo@sjtu.edu.cn; jinyh@sjtu. edu.cn; slxiao@sjtu.edu.cn). C. Zhang is with Lanzhou Jiao Tong University, Lanzhou 730070, China (e-mail: Zhang_chl@mail.lzjtu.cn). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2008.2011996 is an extension of a light-path in the unicast optical network [3]. The primary benefit of light-trees is that only one source (transmitter) is required for transmission and multiple members can share intermediate tree channels. A node with splitting can forward an incoming signal through multiple output channels and, therefore, is multicast-capable (MC). Several MC nodal architectures have been proposed [4]–[6]. The splitter is a fundamental component for optical signal copy but not reconfigurable [2]. So, the splitter-and-delivery (SaD) switch [4] is designed such that each input signal is initially split into multiple members. The SaD switch provides a nonblocking service but does not distinguish unicast and multicast traffic types. The unicast traffic undergoes unnec- essary power loss and this structure would need more optical amplifiers. To improve the power efficiency, a multicast-only splitter-and-delivery (MO-SaD) was proposed in [5]. Only one output port of each space switch matrix is connected to a split-switch bank or tap-and-continue coupler that is used to split the incoming signal. Hence, splitting is only applied to multicast connections. However, due to splitter sharing concept, there is no provision for two or more trees, where blocking arises [6]. In this work, we combine the SaD and the three-plane switch to form a novel power-efficient and nonblocking separated uni- cast/multicast SaD switch, which is termed as separated unicast/ multicast splitter-and-delivery (SUM-SaD). Any unicast con- nection is switched by the three-plane switch, and only multi- cast connection is delivered by the SaD undergoing extra loss. The splitting loss of multicast signals is compensated by the in- corporated optical amplifiers. The proposed structure is strictly nonblocking for unicast and multicast connections. Both theo- retical analysis and simulation prove that SUM-SaD has the ad- vantages of SaD and MO-SaD. II. PROPOSED SUM-SaD AND MULTICASTING-CAPABLE OPTICAL CROSS-CONNECT (MC-OXC) ARCHITECTURE Fig. 1 shows the structure of the proposed SUM-SaD switch at the dimension . It consists of one three-plane switch at the dimension [e.g., microelectromechanical sys- tems (MEMS)], one SaD switch at the dimension , and optical amplifiers [e.g., erbium-doped fiber amplifiers (EDFAs)] to compensate the splitting loss produced by the SaD switch [8]. The unicast signals are completely switched by the three-plane switch. It is clear that unicast cross-connections are strictly nonblocking and do not undergo extra splitting loss. The multicast signals are first, switched by the three-plane switch to the output ports beyond the th, second, delivered 1041-1135/$25.00 © 2009 IEEE