The operation of an unconventional, power-symmetric nonlinear optical loop mirror (NOLM) is investigated. Its principle is based on the creation of a polarization asymmetry between the counterpropagating beams, through the use of a quarter-wave plate and highly twisted fiber in the loop. Using a very intuitive approach, we propose a simple although comprehensive description of the NOLM operation. By adjusting the angle of the quarter-wave plate, the interferometer can be tuned continuously from non-power-dependent operation to nonlinear switching, in a very convenient way. Experimental results confirm theoretical predictions. The properties of the proposed NOLM design make it very attractive for various applications, like pedestal suppression and amplitude regularization of optical pulse trains.
We present experimental measurements and a corresponding theoretical analysis of a novel NOLM device made using a symmetrical (50/50) coupler, highly twisted fiber, and a quarter-wave (QW) retarder plate in the loop. The physical mechanism for the nonlinear properties is the polarization rotation of the counter-propagating optical fields. We also experimentally demonstrate that the nonlinear polarization rotation analysis is correct by controlling the transmission behavior as the QW retarder plate is rotated. We propose a simple description of the NOLM behavior, showing that nonlinear switching is obtained through the polarization asymmetry generated by the QW retarder plate. The proposed NOLM design is very attractive for applications like pedestal suppression and amplitude regularization of optical signals, since it operates stably without day-to-day drifting. We experimentally demonstrate the efficiency of the NOLM for high-order amplitude regularization of an optical pulse train subject to amplitude modulation, as an overall suppression of about 20 dB of the modulation was obtained over all frequencies. An environmentally stable NOLM will enable a wide range of applications, such as, optical switching and demultiplexing, all-optical active and passive mode-locking, and pedestal suppression.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.