The focusing characteristics of Fresnel zone plate (FZP) on vortex beams at 1550 nm are investigated. Employing the Fresnel diffraction integral, the diffraction characteristics on different circular structures are calculated. Many calculations and measurements of the transmission light field-phase distribution demonstrate that the focusing characteristics of the vortex beam through FZP are similar to Gaussian beam. The effect of radius-dependent phase delay on the focus position is verified. At the same time, it is proved that the topological charge has nothing to do with the major focal position and the FZP will not change the topological charge of the incident vortex beam.
An optical code division multiple access (OCDMA) secure communications system scheme with rapid reconfigurable polarization shift key (Pol-SK) bipolar user code is proposed and demonstrated. Compared to fix code OCDMA, by constantly changing the user code, the performance of anti-eavesdropping is greatly improved. The Pol-SK OCDMA experiment with a 10 Gchip/s user code and a 1.25 Gb/s user data of payload has been realized, which means this scheme has better tolerance and could be easily realized.
A prototype of the temperature sensor based on the nano-wire Silicon-on-Insulator (SOI) waveguides, with air cladding
or SiO2 cladding, is proposed with the principle of two mode interference (TMI) in the two mode nano-wire SOI
waveguides. The beatlength, between the two modes with same polarization in the two-mode regime, are shown with the
dependence on the waveguide parameters. The effects of the birefringence on the temperature sensor are discussed.
It is proposed to use bare fiber bundle as probes of photonic Doppler velocimetry (PDV) system to improve the spatial
resolution of measurement. Two-point velocity measurement with spatial resolution of 375μm is experimentally realized.
Because of smaller probe spacing, the measuring results obtained from a probe would be influenced by the reflected light
from another probe. Theoretical and experimental results show that the measuring results are not affected by the stray
light when the target surface has the same velocity, and the measuring errors are related not only with the velocity
difference of two points but also with the intensities and the initial phases of the sensing and stray light when the target
surface has different velocity.
Based on analysis of basic photonic Doppler velocimetry (PDV), a formula to measure velocity variation in a single
cycle is put forward. PDV has been improved in three aspects, namely, the laser, the detector and the data processing. A
measurement system for velocity of the initial stage of a shock motion has been demonstrated. Instantaneous velocity
measurements have been performed. The experimental results have a good agreement with the values obtained from the
accelerometer. Compared with the traditional fringe method, the proposed method in this paper can identify
instantaneous velocity variation. So it is particularly suitable for measuring the velocity in the transient acceleration
process of shock waves and detonation waves.
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