A Single-Fiber Bi-directional Self-Healing WDM Metro-Ring Network with Bi-directional OADM

We propose and demonstrate a single-fiber bi-directional WDM self-healing ring network with simple bidirectional OADM. By employing our proposed alternate-path switching scheme, the bi-directional traffic can be restored promptly under single fiber failure. Introduction Bi-directional wavelength division multiplexing (WDM) self-healing ring (SHR) network [1-2] is an attractive and cost-effective approach for reliable data delivery. In this paper, we propose and demonstrate a new single-fiber bi-directional WDM SHR network with a simple low-cost bi-directional optical add-drop multiplexer (B-OADM) at each network node. By making use of the spectral periodicity of the N×2 AWG at the hub node, a novel wavelength assignment plan is proposed to enable bi-directional data transmission and a simple alternate-path switching scheme is employed for protection against single fiber failure. Network structure and wavelength assignment Fig. 1 shows our proposed single-fiber bi-directional SHR network with N access nodes (ANs), where N = 4 for example. Each downstream wavelength originated from the hub node is destined for its respective ANs in either clockwise (CW) or counterclockwise (CCW) direction, whichever having the shortest path. In contrast, the upstream wavelengths from each AN traverses towards the hub node in both CW and CCW directions. Fig. 2 illustrates the proposed wavelength assignment plan. For index i=1,...,(N/2), the wavebands A (λi) and B (λN/2+i) are allocated for downstream and upstream channels of the ANs with odd indices (AN2i-1), respectively; while the wavebands C (λN+i) and D (λ3N/2+i) are for downstream and upstream channels of the ANs with even indices (AN2i), respectively. Besides, wavelength λi is separated from  λN+i by one freespectral range (FSR) of the AWG; while the upand down-stream wavelengths assigned to each AN are separated by half of the FSR of the AWG. The proposed B-OADM for the AN is shown in the inset of Fig. 1. It consists of two optical couplers and a Mach-Zehnder interferometer with identical fiber Bragg gratings on its arms (MZI-FBG) [3]. The upstream signal is added through two optical couplers and transmitted to the hub node in both CW and CCW directions. The downstream wavelengths λk originating from either CW or CCW direction is dropped by the MZI-FBG and transmitted to the receiver via an optical coupler, while the rest of other downstream wavelengths will simply bypass the AN. λ1,λ5