In this paper, we demonstrate a novel concept of collision avoidance based on single photon detectors along with time correlated single photon counting techniques, which uses chaotic pulse position modulation for anti-crosstalk considerations. In order to distract the signal from estimated background noise, parameters including pulse rate, discrimination threshold and number of accumulated pulses have been thoroughly analyzed based on the detection requirements, resulting in specified receiver operating characteristics curves. Both simulation and indoor experiments were performed to verify the excellent anti-crosstalk capability of the presented collision avoidance LIDAR despite of ultra-low transmitting power.
In this paper, we present an analysis of transverse mode competition mechanism in multicore fiber lasers based on the transversally-resolved steady rate equations with consideration of transverse gain distribution and mode propagation loss. Based on the model, the output beam properties of 7-core and 19-core fiber lasers are simulated numerically when applying a plane reflection mirror and Talbot cavity as the feedback boundary conditions, respectively. We propose a new parameter of brightness factor to find out the best Talbot distance. We also give analysis on the influence of the fiber core separation distance and core diameter to the output laser beam quality. The study shows that the Talbot cavity can realize the mode selection of multicore fiber lasers and make the in-phase supermode dominate in the output beam, thus enhancing the quality of the output beam. The shorter the core separation distance and the core diameter are, the better the output beam quality would be. The best optimized core separation distance within acceptable beam quality restriction and the processing technic limit is obtained. This work has great prospective in the design and application of multicore fibers.