X. L. Yang’s research while affiliated with Shandong University and other places

Metasurface is emerging as an important platform to design various functional devices due to the superior capability in controlling amplitude, phase and polarization of light through its ultrathin engineering interface. A polarized-selective hologram of all-dielectric metasurface is proposed to reconstruct multiplexed holographic images on different linear polarization status. Unlike early metasurfaces composed of plasmonic resonators with great ohmic loss at visible spectrum, the designed metasurface made of silicon nanoblocks supports a broader spectral response over the bandwidth from 600 to 760 nm with high diffraction efficiency and low crosstalk between different polarization states. Both simulation and experiment have demonstrated the feasibility and adjustability of the polarization-multiplexed metasurface hologram. We believe it will have significant technological potential in the design of optical functional devices.

The precise location of the Dirac-like point of a finite photonic crystal array with a triangular lattice can be identified easily from the transmittance spectrum of any output interface with the characteristic of a sharp cusp embedded in the extremum spectrum near the Dirac-like point. The transmission properties of the finite triangular lattice photonic crystal arrays with square and hexagonal shapes have been investigated systematically to demonstrate that the transmittance at the Dirac-like point has a close relation with the output interface feature of the photonic crystal array and the output interfaces with the same feature will bring about the uniform transmission characteristics in different directions. These results provide us with a more accurate and convenient method to identify the Dirac-like point of a photonic crystal with different lattice structures, array sizes and shapes, and give guidelines for its use in experiments.

By combining the iterative phase retrieval algorithm in the Fresnel domain with the shift rotation permutation operations of row vectors and column vectors, a new kind of asymmetric multiple-image authentication based on complex amplitude information multiplexing and RSA algorithm is proposed, where multiple complex amplitude information in the input plane is retrieved and generated by the phase retrieval algorithm in the Fresnel domain. In original binary amplitude mask, the row vector and column vectors random numbers are randomly generated in advance, such that each sampling mask for each authenticator is obtained by the shift rotation permutation operations of corresponding row vector and column vectors random numbers for original binary amplitude mask. Thus, one synthesized complex amplitude is generated by the operations of sampling, overlap and multiplexing, and then sent to the certification center for authentication use. At the same time, the row vector and column vectors random numbers are encoded to ciphers by the public keys of RSA algorithm, and then delivered to the corresponding authenticators. During the authentication process, the row vector and column vectors random numbers are first decoded by the private keys possessed by the authenticator; second, the authenticator's sampling mask is reconstructed by the shift rotation permutation operations of the above decoded random numbers for original binary amplitude mask. Finally, the authenticator with other additional authentication keys is prompted to place the synthesized complex amplitude information and its sampling mask at the corresponding positions, when the system is illuminated by a plane wave with the correct wavelength. A recovered image is then recorded in the output plane, by calculating and displaying the nonlinear correlation coefficient between the recovered image and the certification image, if there exists a remarkable peak in its nonlinear correlation coefficient distributions, indicating that the authentication is successful. On the contrary, if there is no remarkable peak but uniformly distributed white noise in the map, the authentication process is a failure attempt. Any intruder with randomly generated forged authentication keys will end up with a failure which enhances the security of the system to some extent.

This study proposes a novel beam splitter system based on graded photonic crystals, wherein the GPCs are part of a circular PC. A self-collimating PC structure with a square lattice is added to improve transmissivity. The total transmissivity is increased by extending the defect of the self-collimating PC. This study presents a beam splitter system with low energy loss and the best total transmissivity of almost 90%. Furthermore, the relationship between the beam-splitting ratio and the light position is discovered, and the beam-splitting ratio may be changed discretionarily and expediently. Numerical results are obtained using finite-difference time domain and plane wave methods. The proposed structure has significant application potential in optical integration.

In this paper, a new structure used to realize optical coupling is proposed. This structure is made up of half of a two-dimensional circular photonic crystal and a photonic crystal waveguide. It is shown that the peak value of the transmissivity shifts by choosing appropriate parameters of SCPC. This structure has great potential in optical integration and other areas.

A method to measure thickness variation and optical inhomogeneity simultaneously with a dual-wavelength phase-shifting photorefractive holographic interferometer is proposed. This method has no special requirements on the sample surfaces, and additional operations such as coating refractive index matching liquid on surfaces is not needed. With the help of photorefractive holographic interferometry, the wavefront distortion caused by the interferometer system is compensated automatically. Compared with other methods, this method is simpler and more accurate. Computer simulation and optical experiment have verified its feasibility and reliability.

Combining the techniques of double random phase encoding and phase-shifting interferometry, an information hiding system is proposed, in which the information to be hidden can be encrypted into multiple interferograms. By choosing the appropriate weighting factor, the interferograms can be embedded in the host image. The secrete information can be successfully extracted and decrypted by special phase-shifting reconstruction formula and inverse Fresnel diffraction transform. A software of information hiding system is designed by mixed programming between Visual C++ and Matlab based in the Matcom software environments. By testing the software interface, the designed software can successfully realize the main functions, such as image reading and displaying, input of basis geometrical parameters, information encrypting and embedding, information extracting, decrypting, robustness testing, etc..

We present a dual-negative refraction effect based on the overlapping bands in a two-dimensional triangular photonic crystal formed by holographic lithography. Under certain conditions, one incident plane wave launched into this photonic crystal can be dispersed into two negative refracted waves at the same frequency and the same perpendicular polarization state with different phase velocities and group velocities. We find that this dual-negative refraction behavior can be easily manipulated by adjusting the incident angle, the frequency of incident wave and the filling ratio of the PhC. This special effect can be applied to realize wave-front division and optical interference in optical holography. Based on this effect, a double focusing imaging phenomenon has been achieved by the PhC slab. These unique features may show great impacts on both fundamental physics and optical device applications.

Light Emitting Diode (LED) has been developing rapidly in recent years because of its various characteristics, such as small size, long life, high brightness, low calorific power and so on. But the poor efficiency of light extraction is the major factor which constrains the development of LED. The two-dimensional (2D) photonic crystals (PhCs) are very suitable for improving the efficiency of light extraction. The PhCs whose size is centimeter level can be fabricated by holographic lithography. It is low cost and easier for the industrialization of production. To research the condition of making 2D PhCs for improving the efficiency of light extraction, we use 532nm laser as the light source and SU-8 negative photoresist as the mask. The 2D PhCs whose duty cycle is 1:1 are created by double-beam double exposure method. It is verified that the PhCs can be used to improve the efficiency of light extraction.

We have investigated for the first time the anomalous refractive effects of a photonic crystal (PhC) formed by holographic lithography (HL) with triangular rods arranged in a honeycomb lattice in air. Possibilities of left-handed negative refraction and superlens are discussed for the case of TM2 band with the index contrast n = 3.4:1. In contrast to the conventional honeycomb PhC made of regular rods in air, the HL PhCs show left-handed negative refraction over a wider and higher frequency range with high transmissivity (>90%), and the effective indices quite close to −1 for a wide range of incident angles with a larger all-angle left-handed negative refraction (AALNR) frequency range (Δω/ω ≈14.8%). Calculations and FDTD simulations demonstrate the high-performance negative refraction properties can happen in the holographic structures for a wide filling ratio and can be modulated by changing the filling ratio easily.