This paper presents a new design method of infrared search and track systems, that is, optical-digital joint optimization design method for IR detection of unresolved target. It is different from the traditional design concept of optics-detector-preprocessor sequential and independent optimization. The merit function suitable for infrared unresolved target detection is constructed for the whole infrared search and track system, and the design parameters of optical lens, infrared detector and digital preprocessor are taken as optimization variables, and then the global optimization is carried out through effective algorithm to find the overall optimization results. The proposed method belongs to an advanced form of computational optical imaging, which relaxes the local design constraints, and has a greater degree of design freedom. The research results show that it is significantly better than the traditional method.
We report the results of our recent experimental investigation of the modulation frequency detuning effect on the output pulse dynamics in a pulse modulated actively mode-locked ytterbium doped fiber laser. The experimental study shows the existence of five different mode-locking states that mainly depend on the modulation frequency detuning, which are: (a) amplitude-even harmonic/fundamental mode-locking, (b) Q-switched harmonic/fundamental mode-locking, (c) sinusoidal wave modulation mode, (d) pulses bundle state, and (e) noise-like state. A detailed experimental characterization of the output pulses dynamics in each operating mode is presented.