Bidirectional WDM self-healing ring network based on wavelength-interleaved bidirectional add/drop amplifier modules

We demonstrate a cost-effective bidirectional WDM self-healing ring network using wavelengthinterleaved bidirectional add/drop amplifier modules. The measured restoration time was less than 10 ms. Recently, bidirectional WDM self-healing ring (SHR) networks based on bidirectional transmission have been proposed [1]-[3]. In these networks, each node should be implemented by using a bidirectional WDM add/drop multiplexer (B-ADM). However, in a bidirectional network, the relative intensity noise (RIN) due to Rayleigh backscattering and optical reflection could degrade the system performance and limit the network scalability significantly. In this paper, we demonstrate a bidirectional WDM SHR network by using the recently proposed wavelength-interleaved bidirectional add/drop amplifier (BADA) module [4]. This simple module can be implemented cost-effectively by using only one N x N multiplexer. In addition, the RIN can be suppressed efficiently by interleaved allocation of wavelengths. The schematic diagram of the node in the network is shown in Fig. 1(a). It consists of a BADA module (BADM and two bidirectional EDFA’s for the working ring), two optical switches, and an additional bidirectional EDFA for the protection ring. Fig. 1(b) shows the schematic diagram of the B-ADM which is implemented by using only one N x N arrayed waveguide grating (AWG) multiplexer and two circulators. The upstream and downstream WDM channels were interlaid (channel 1, 3, 5, and 7 for upstream and channel 2, 4, 6, and 8 for downstream) with 200-GHz channel spacing. We can accommodate up to 7 channels in each direction with 100GHz channel spacing. The relative intensity noise (RIN), caused by Rayleigh backscattering and/or optical reflections, may degrade the receiver sensitivity in a bidirectional transmission system. In our BADA module, there are three RIN paths induced by Rayleigh backscattering and optical reflection. These RIN’s were suppressed by interleaved wavelength allocation [4]. Thus we do not need extra optical band pass filters to suppress the RIN. Two electro-mechanical switches are used for the automatic restoration of the transmission failure by monitoring the signal in the working ring. In case of fiber-cut, the optical switches (adjacent to the fiber-cut) transfer the signals from the working ring to the protection ring. The additional bidirectional EDFA located at the protection ring compensates the fiber and component losses.