We numerically propose a scheme for realizing an all-optical femtosecond soliton diode based on a tailored heterojunction Bragg grating, which is designed by two spatially asymmetric chirped cholesteric liquid crystals. Our simulations demonstrate that with the consideration of optical nonlinearity, not only the femtosecond diode effect with nonreciprocal transmission ratio up to 120 can be achieved, but also the optical pulse evolving into soliton which maintains its shape during propagation through the sample is observed. Further, the influence of pulse width and the carrier wavelength to the femtosecond diode effect is also discussed in detail. Our demonstrations might suggest a new direction for experimentally realizing the femtosecond soliton diode based on the cholesteric liquid crystals.Diode, which allows the nonreciprocal transportation of electric current, is one of the most important electronic devices in the integrated circuit. In optics, the nonreciprocal effect also plays a significant role in the modern information processing as well as in optically integrated devices. However, optical light beam is usually reciprocal and therefore how to transmit optical signal only in one direction and block that in the opposite direction remains a challenging issue.In the past decades, many schemes were proposed to solve this problem. The most significant proposal was based on the optical isolator realized by the Faraday effect in magneto-optical crystals [1]. Since the magneto-optical isolator requires a strong external pump, it hinders the applications in a highly integrated photonic systems. Other schemes were also reported with different principles or materials such as using optoacoustic effect [ [13,14] and parity-time system [15]. We note that although high nonreciprocal transmission ratio could be achieved using these schemes, the shape of the light field after propagating through the devices is usually neglected. Due to diffraction/dispersion as well as the interaction with materials, the light beam might cannot maintain its profile, which would limit the application in optical processing. Recently, linearly-coupled waveguide system in which the unidirectional propagation are expected in the nonlinear regime [16] was reported. Based on the fiber Bragg grating (FBG), a sandwich structure was proposed to realize optical nonreciprocal effect [17]. * Electronic address: yongyaoli@gmail.comWe should mention that with the consideration of optical nonlinearity, these optical waves [16,17] could maintain their profiles during propagation through the nonlinear devices. Indeed, the light wave propagating though these nonlinear systems is in a form of solitons which can preserve its shape during propagation [18][19][20][21][22][23][24][25].In this Letter, we extend the concept of optical diode from picosecond [17] to femtosecond (fs) domain for the first time, which is of particular interest in the ultrafast data processing. However, the realization of fs diode becomes more difficult than that realized in the pic...
We demonstrate the nonreciprocal dynamics of discrete solitons (DSs) induced by a uniform synthetic gauge phase (SGP) in one-dimensional waveguide array. The SGP is embedded into the coupling constant between the waveguides, which provides a directional momentum to the propagating fields and creates a nonreciprocal for the system. When a kicked Gaussian wave packet propagates through the waveguide arrays, diode effects are formed. Dependence between the diode effect and the SGP is studied. We found that the threshold of the reverse breakdown of this optical diode exhibits a perfect linear dependence against the SGP, and an extremely high diode quality can be achieved when the initial phase tilt exactly compensates the initial momentum provided by the SGP. Moreover, the direction of the diode can be switched by the direction of the SGP, which brings additional freedom to control the one-way propagation of the DSs. Our finding may have potential application to realizing new devices in high-speed all-optical communications.
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