We propose the generation of double-ring vortex beams by coaxial superposition of Laguerre-Gaussian modes with
different topological charge numbers and different waist parameters. The formation and distribution characteristics of
double-ring vortex beams are analyzed in theory. A computer-generated holography based on conjugate-symmetric
extension is applied to encode the holograms, with which we reconstruct the double-ring vortex beams by optical
experiments. It is found that each ring of the double-ring vortex beams carries different orbital angular momentum.
Furthermore, when the internal topological charge remains unchanged, the distance between the two rings becomes
bigger with the increase of external topological charge. Excellent agreements between theoretical and experimental
results are observed. The double-ring vortex beams may find their potential application value in the fields of micro
particles manipulation and optical information encoding as different orbital angular momentum is respectively carried by
the internal and external rings.
The characteristics of optical fiber are quite important for improving the performance in various application of the optical fiber including communication and sensor systems. Based on optical Mach-Zehnder interferometer, a new measuring method of optical fiber refractive index profiling using digital holography is proposed in this paper, which simplifies the experimental setup compared to traditional holography. Several kinds of fiber samples such as multimode fiber, polarization-preserving fiber and special fiber are tested and their holograms are recorded by CCD. After filtering of the hologram, the phase distribution of fiber sample can be reconstructed and extracted. At last the experimental results of refractive index profiling of fiber are given.
A new method of synthesizing computer-generated hologram of three-dimensional (3D) objects is proposed from their projection images. A series of projection images of 3D objects are recorded with one-dimensional azimuth scanning. According to the principles of paraboloid of revolution in 3D Fourier space and 3D central slice theorem, spectra information of 3D objects can be gathered from their projection images. Considering quantization error of horizontal and vertical directions, the spectrum information from each projection image is efficiently extracted in double circle and four circles shape, to enhance the utilization of projection spectra. Then spectra information of 3D objects from all projection images is encoded into computer-generated hologram based on Fourier transform using conjugate-symmetric extension. The hologram includes 3D information of objects. Experimental results for numerical reconstruction of the CGH at different distance validate the proposed methods and show its good performance. Electro-holographic reconstruction can be realized by using an electronic addressing reflective liquid-crystal display (LCD) spatial light modulator. The CGH from the computer is loaded onto the LCD. By illuminating a reference light from a laser source to the LCD, the amplitude and phase information included in the CGH will be reconstructed due to the diffraction of the light modulated by the LCD.
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