1+1 protection is usually used to implement fast failure recovery and provide high reliability to data connections. A typical scheme of 1+1 protection employs a primary working lightpath and a dedicated diversely-routed backup ligthpath to carry the same data, in which the same wavelengths are always used for the two lightpath, thus putting edge-disjoint restrictions on the wavelength routing. Because current standard requires <50-ms protection-switching time, a mechanical switches with several millisecond switching time can be used before the receiver for channel switching. However, with the transmission speed of single wavelength channel increasing to tens of Gb/s, a faster switching time is highly desired to reduce the amount of data loss. In this paper, we propose an out-of-band 1+1 protection scheme, which employs two different wavelengths for primary working lightpath and protection backup path, respectively. At the destination node, a fast tunable heterodyne-detection receiver is used to select the desired wavelength lightpath. The proposed fast tunable receiver significantly reduces the protection switching time between the two paths. To investigate the performance of the proposed protection scheme, a fast channel selection experiment is performed. Two optical wavelength channels were modulated simultaneously by a
Mach-Zehnder (MZ) external modulator with data rate 1.25Gb/s. The tunable heterodyne receiver switches between the working lightpath and protection lightpath to demonstrate the capability of 1+1 protection. A <0.8-ns switching time is obtained which demonstrates the potential of hitless protection switching, if the switching occurs at the transition of two neighboring '1's.