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An electrically tunable two-dimensional (2D) holographic polymer-dispersed liquid crystal (H-PDLC) grating with variable period was fabricated by inserting a cylindrical lens in a conventional holographic interference beam. The interference between the plane wave and cylindrical wave resulting in varying intersection angles on the sample, combined with dual exposure along directions perpendicular to each other, generates a 2D H-PDLC grating with varied period. We have identified periods varying from 3.109 to 5.158 µm across a 16 mm width, with supporting theoretical equations for the period. The period exhibits a symmetrical square lattice in a diagonal direction, with an asymmetrical rectangular lattice in off-diagonal locations. With the first exposure at 2 s and the second exposure at 60 s, the phase separation between the prepolymer and liquid crystal was most evident. The diffraction properties and optic-electric characteristics were also studied. The diffraction efficiency of first-order light was observed to be 13.5% without external voltage, and the transmission efficiency of non-diffracted light was 78% with an applied voltage of 100 V. The proposed method provides the capability of generating period variation to the conventional holographic interference path, with potential application in diffractive optics such as tunable multi-wavelength organic lasing from a dye-doped 2D H-PDLC grating. [ABSTRACT FROM AUTHOR]

Abstract: A new type grating, tilted holographic planar structured dichromated gelatin (DCG) grating with large refractive index modulation, is presented in this paper. The grating is inscribed by superposing two coherent laser beams from the front and the thin side surfaces, respectively. The relationship between the tilted angle and the three types of coupling modes is analyzed when coupling with fiber. Besides, the couple mode theory and experimental investigation are applied on major characteristics analysis of the radiation mode DCG grating of tilted angle 45°. Due to the tilted planar structured grating has large refractive index modulation, it not only offers convenience for connecting (or integrating) with other fiber or waveguide-based devices, but also provide some special characteristics such as low wavelength selectivity (which is required for some applications such as multiple spectrum biomedical imaging). Therefore, this unique grating device has a wide application in optical fields such as for the waveguide-based, parallel, multiple spectrum imaging system. [Copyright &y& Elsevier]

Abstract: Vectorial properties of light have significant effects on the focusing properties, especially for the case of tightly focusing, where the requirements on the ratio of the longitudinal field to the traverse fields (RLT) are different for various applications, such as particle acceleration, micronano-fabrication, fluorescent imaging, determination of three dimensional orientation of individual molecules and so on. Here, utilizing inhomogeneous polarization modulation (IPM) method, we demonstrate how to adjust the numbers of focal spots, the RLT, and the depth of focus (DOF) in terms of requirements and create successfully single or multiple focal spots with dominant transverse or longitudinal fields and small size. In terms of this method, not only the asymmetry of the focal spot for linearly polarized illumination with IPM can be obviously decreased, but also its size is the same as that of the short axis of the elliptical focusing spot for the case without IPM. Moreover, it can not only produce the focal spot with dominant transverse field, low sidelobe, and size slightly smaller than that of the radial polarization, but also can realize the identical resolutions in the transverse direction. In addition, for a focal spot with dominant transverse or longitudinal field, both the subdiffraction sizes (0.4λ or 0.5λ) and the DOF of 6.92λ are also achieved. [Copyright &y& Elsevier]

Abstract: The dynamic gain equalizer consisting of gratings made of holographic polymer dispersed liquid crystal is explored and the structure and principle presented. The properties of the holographic polymer dispersed liquid crystal grating are analyzed in light of the rigorous coupled-wave theory. Experimental study is also conducted in which a beam of infrared laser was incident to the grating sample and an alternating current electric field applied. The electro-optical properties of the grating and the influence of the applied field were observed. The results of the experiment agree with that of the theory quite well. The design method of the dynamic gain equalizer with the help of numerical simulation is presented too. The study shows that holographic polymer dispersed liquid crystal gratings have great potential to play a role in fiber optics communication. [Copyright &y& Elsevier]

In this paper, a method has been proposed for high efficiency unidirectional optical transmission diode at 1550 nm. We use a new composite structure, holographic polymer dispersed liquid crystal (H-PDLC) grating-photonic crystal (PC), to realize it. There exists the directional band gap for the PC structure in 1550 nm. Therefore, it is possible to use the H-PDLC Bragg grating to shift the incident angle to a particular value to satisfy the condition so that the PC energy band can be moved from the pseudo-band gap to the passband to achieve the purpose of unidirectional transmission optical diode with high-efficiency. So that when the 1550 nm beam diffracted from the H-PDLC grating to incident the PC structure, it will transmit the composite structure almost totally, but it will be completely none reflected from PC surface. The simulation results show that the forward transmittance is 94.1% and the backward transmittance is near 0. At the same time, H-PDLC grating provide a method to adjust the transmittance of the composite structure diode with its electrically-controlled characteristics. This composite structure design provides another efficient method for the realization of all-optical diodes in the field of optical communication. • This paper proposes a H-PDLC Bragg grating-photonic crystal composite structure. • This structure achieves one-way transmission within a certain band range at 1550 nm. • This structure is simple and has high transmittance while high contrast. • H-PDLC grating can adjust the transmittance of this composite structure. [ABSTRACT FROM AUTHOR]