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Based on additive manufacturing via photopolymerization, this study combines polymer-dispersed liquid crystal (PDLC) technology with 3D printing technology to produce tunable micro-optical components with switchable diffraction or focusing characteristics. The diffraction grating and Fresnel zone plate are the research targets. Their structures are designed and simulated to achieve expected optical functions. A liquid crystal display (LCD) 3D printer is used to produce structures on transparent conductive substrates. The printed structures are filled with PDLCs and covered with transparent conductive substrates to achieve tunable functions. The proposed configurations are implemented and verified. The experimental results show that the diffraction efficiency of the 0th order increases from 15% to 50% for the diffraction grating and the focusing spot intensity decreases from 74% to 12% after the application of an electric field. These results demonstrate the feasibility of the proposed tunable optical component configurations. [ABSTRACT FROM AUTHOR]

We present a high-sensitivity fiber optic soil moisture sensor based on side-polished multimode fibers and lossy mode resonance (LMR). The multimode fibers (MMFs), after side-polishing to form a D-shaped structure, are coated with a single-layer SnO2 thin film by electron beam evaporation with ion-assisted deposition technology. The LMR effect can be obtained when the refractive index of the thin film is positive and greater than its extinction coefficient and the real part of the external medium permittivity. The D-shaped fiber optic soil moisture sensor was placed in soil, allowing moisture to penetrate into the thin film microstructure, and it observed the resonance wavelength shift in LMR spectra to measure the relative humidity change in soil. Meanwhile, an Arduino electronic soil moisture sensing module was used as the experimental control group, with soil relative humidity ranging from 10%RH to 90%RH. We found that the D-shaped fiber with a residual thickness of 93 μm and SnO2 thin film thickness of 450 nm had a maximum sensitivity of 2.29 nm/%RH, with relative humidity varying from 10%RH to 90%RH. The D-shaped fiber also demonstrates a fast response time and good reproducibility. [ABSTRACT FROM AUTHOR]

The subwavelength structures formed by data tracks in an optical disk are applied to improve the light-trapping effect for thin-film amorphous silicon (a-Si) solar cell applications. An antireflection coating (ARC) consisting of at least two dielectric layers (Si[O.sub.2] and ZnS--Si[O.sub.2]) is designed for the top planar surface of the disk. The a-Si thin-film solar cell layer is deposited below the bottom surface of the disk. Finally, a reflective metal coating is attached to the a-Si layer to fully reflect the incident light and extend the round-trip light path. With the proposed configuration, the reflectance and absorptance can be effectively decreased and enhanced by more than 10% compared with those without ARC and structured surfaces. OCIS codes: 050.6624, 310.1210, 210.4590, 350.6050.

For the purpose of backward compatibility to the CD and DVD specifications, the optical pickup head (OPH) design with multiple laser wavelengths and numerical apertures (NAs) is necessary for the Blu-ray Disc (BD) system. By utilizing the features of an integrated optical unit (IOU) and a holographic optical element (HOE), this study presents a novel three-wavelength BD OPH configuration with compactness in a single optical path. There are two OPH designs with the astigmatic and knife-edge focusing detection methods applied to the IOU configurations in this paper, respectively. The simulation results are satisfactory and show the feasibility of the designs. Index Terms--Blu-ray Disc (BD), holographic optical element (HOE), integrated optical unit (IOU), optical pickup head (OPH), three-wavelength.

This paper presents the design and fabrication of a small-form-factor optical pickup head (OPH) for both red and blue wavelength. A holographic optical element (HOE) is used for beam splitting, aberration correction, and servo-signal generation to reduce the number of components and simplify the assembly procedure. In addition to demonstrating this OPH by using existing discrete components, several key components and processes are developed to use micro-electro-mechanical system (MEMS) technology to facilitate batch fabrication and wafer level assembly of the micro OPU. Index Terms--Assembly, batch fabrication, MEMS, optical pickup head, small form factor.

The optical configuration proposed by Optware Corporation has the features of recording the holographic versatile disk (HVD) and backwardly retrieving CD and DVD. This paper presents a novel design that applies the technology of integrated optical unit to the HVD system. This unit comprises a holographic optical element for splitting light and generating servo signal. A transmissive spatial light modulator (SLM) with central data part and outer-ring reference part is adopted for modulating the laser beams. A new outer-ring polarizer is accompanied with the SLM. Two lasers, one with 532 nm for the HVD and the other with 650 nm for the CD/DVD, are included in the unit. Analysis for the system was performed. Simulation results show the feasibility for implementing an integrated collinear holographic system with miniaturized size. Index Terms--Collinear holography, holographic versatile disk (HVD), holographic optical element (HOE), integrated optical unit, optical pickup head.

This paper discloses the configuration of a dual-mode three-beam grating which adopts the liquid-crystal (LC) modulator technologies and has the function of switching diffraction properties. With the specific design of the top, bottom, and complementary electrodes, the grating has the feature of being modulated by external electric field for generating two diffraction modes. Two modes corresponding to different diffraction directions and angles were verified by experiments. This device could be applied to the fabrication of a monolithic three-beam grating, which is necessary for the tracking detection of a rewritable two-wavelength optical head using a two-wavelength integrated laser diode (TWIN-LD). Index Terms--Diffractive optical element (DOE), liquid crystal (LC), two-wavelength integrated laser diode (TWIN-LD), optical pickup head, three-beam grating.

There are several methods to avoid optical feedback and reduce laser noise in optical recording systems. However, most of them utilize high cost optical components or electronics or increase the pickup head size. Furthermore, it is difficult to fit these components into in a small package like a holographic laser module. In this paper, a simple method for avoiding feedback noise in a holographic pickup head is proposed. A single wave plate is added to the optical system to rotate the polarization of the laser feedback to be orthogonal to the emitting polarization state. Experimental results show that it is feasible and practically reduces laser noise.

It is well known that holographic hybrid pickup beads have a number of advantages in terms of size, modularity, and perhaps cost, but are less efficient than conventional discrete component type pickup heads. We introduce a new design for the HOE which places the 3-beam grating on the same surface with the holographic beamsplitter and utilizes light that would otherwise be wasted to create the satellite beams for 3-beam tracking. Efficiency is gained by avoiding the [approximately]35% loss typically associated with the 3-beam grating and by blazing the holographic beamsplitter.