We put forward a technique to manipulate the size of orbital angular momentum (OAM) beams based on space diffraction compensation. Paraxial Fresnel diffraction which carries a negative spatial quadratic phase distribution can be regarded as a negative diffractive effect. To compensate the negative diffraction, we employ a 4f Fourier lens system containing a phase mask to generate an inverse quadratic phase. The size of OAM beams can be easily controlled by designing the phase mask profile without changing the OAM. The applications of space diffraction compensation in OAM demultiplexing, ring fiber coupling for OAM beams and optical manipulation of micro particles are also discussed.
Recent progress in silicon nanophotonics has dramatically advanced the possible realization of large-scale on-chip optical interconnects integration. Adopting photons as information carriers can break the performance bottleneck of electronic integrated circuit such as serious thermal losses and poor process rates. However, in integrated photonics circuits, few reported work can impose an upper limit of optical power therefore prevent the optical device from harm caused by high power. In this study, we experimentally demonstrate a feasible integrated scheme based on a single all-passive micro-ring resonator to realize the optical power limitation which has a similar function of current limiting circuit in electronics. Besides, we analyze the performance of optical power limiter at various signal bit rates. The results show that the proposed device can limit the signal power effectively at a bit rate up to 20?Gbit/s without deteriorating the signal. Meanwhile, this ultra-compact silicon device can be completely compatible with the electronic technology (typically complementary metal-oxide semiconductor technology), which may pave the way of very large scale integrated photonic circuits for all-optical information processors and artificial intelligence systems.
We put forward a double-slit interference device based on two metal subwavelength slit arrays to measure the orbital angular momentum (OAM) and the polarization of beams simultaneously. The subwavelength slit serves as a localized spatial polarizer, and each slit array can be regarded as a wide diffraction-slit. When an OAM beam is normally incident upon the two slit arrays, the interference fringes twist, and the displacement depends on the topological charge of OAM beams. We present a detailed theoretical analysis of this measurement model. This model does not need additional reference light and is a linear model.
We experimentally demonstrate a temporal imaging system based on a time pinhole. In accordance with the spatial pinhole-imaging counterpart, it consists of two sections of dispersion fibers connected by a temporal shutter, which is experimentally realized by a logic AND-gate with a short pulse. Both theoretical analysis and experimental results show that the output waveform is the scaled and broadened profile of the input waveform. Specifically, the output waveform is reversed if the signs of the dispersion on both sides of the time-gate are identical, otherwise it is non-reversed if the signs of the dispersion are opposite. Furthermore, we adjust the duration of the temporal shutter by changing the spectral width of the pulse, and investigate the effect of the shutter time on the performance of the output waveform.
Microgravity and radiation, common in space, are the main factors influencing astronauts health in space flight, but their combined effects on immune cells are extremely limited. Therefore, the effect of simulated microgravity on heavy ion radiation-induced apoptosis, and reactive oxygen species (ROS)-sensitive apoptosis signaling were investigated in human B lymphoblast HMy2.CIR cells.
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