We experimentally investigate the multifold intensity enhancement and spectral narrowing of photoluminescence (PL) from amorphous silicon quantum dots (a-Si QDs) embedded in a silicon-rich SiOx film of the Ag/SiOx:a-Si QDs/Au plasmonic nanocavity, through the resonance coupling between the localized surface plasmon (LSP) mode and the Fabry-Pérot (FP) cavity mode, by tuning a one-dimensional (1-D) Ag grating on the top. The LSP resonance can be precisely tuned by adjusting the Ag line widths of the 1-D Ag grating. It is found that the LSP mode strongly couples with the FP cavity mode, resulting in a narrower emission line width and a larger PL enhancement. An optimized Ag grating structure is found to exhibit a narrow emission line width of 15 nm and 2.77-fold enhancement in the PL peak intensity, as compared to an SiOx:a-Si QDs/Au structure without 1-D Ag grating, due to the strong resonance coupling between the two modes.
An electrically controllable fiber Bragg grating (FBG) for working in the communication band is demonstrated by utilizing holographic polymer-dispersed liquid crystal (HPDLCs). PDLC is infiltrated in hollow-core fibers which are about 2μm and 5μm by means of capillarity. For the purpose of periodically separating polymer and liquid crystal to form an FBG, a two-beam interference system based on an argon laser (wavelength: 364nm) is used. To reduce coupling loss, we directly connect single-mode fibers (SMFs) to input and output ports. A maximum transmission loss dip of approximately 5-dB band rejection is obtained. After the cladding diameter is etched by buffered oxide etchant (BOE) solution to 12μm and a 150V external voltage is applied, a dip shift by ~ 15nm is measured
We present preliminary experimental results obtained for a Vertically-Aligned Polymer Stabilized Liquid Crystal (VA-PSLC) with a curing voltage. The curing voltage was found to help reduce the otherwise strong scattering effect of the VA-PSLC. This liquid crystal was placed inside a Fabry-Perot cavity to achieve a wavelength tunable filter. Wavelength tuning range was found to decrease as curing voltage increased, which is consistent with what we expected since molecules were already tilted at a large angle when the curing voltage was high. Shortening of response time was found since the polymer effect helped improve the response speed. The filters can have potential applications in wavelength tuning applications (e.g. WDM) in telecommunication systems where high speed is desirable.
Head-up display (HUD) commonly uses liquid crystal to generate images. However, the intensity of the light decreases a lot because of passing through the polarizers. Therefore, polarizer-free display is a way to enhance the light efficiency. We demonstrate the feasibility of using Polymer Dispersed Liquid Crystal (PDLC), which consists of polymer and liquid crystal, as an optical switch to fabricate a simple see-through projected display device. Due to the unique E-O characteristics of PDLC, it can be a role to define the projected image shape. In our device, we use the ultra-bright collimated LED as a backlight source so that the projected image can also be seen clearly in broad daylight. Besides, PDLC do not need to utilize polarizers. It is achieved to obtain very high light efficiency (~70%). In this paper, we show some results of projected images with various colors (RGB) that can be applied to see-through projected display. From our experiment result, the see-through projected display device by PDLC can achieve high contrast ratio (~1000:1) and response time is about 15~20 ms. The driving voltage is around 20~25 V. Further improvement can be achieved by optimizing the LC material/monomer concentration or others parameters.
We demonstrate the feasibility of using a Vertically-Aligned Polymer-Stabilized Liquid Crystal (VA-PSLC) film, which is also known as LC gel, as a transparent image generator to form a see-through display system. This is achieved, in its simplest form, by projecting a collimated LED light source onto a transparent glass screen, with the image generated by the scattered light from the VA-PSLC. By moving the observer’s head slightly away from the incident light specular reflection direction, a clear image can be observed on the transparent glass screen together with the background objects that are behind the screen. From our experimental results, this see-through display system using VA-PSLC transparent image generator can achieve a fast response time (with rise time of ~10 ms and fall time of ~5ms) and an acceptable contrast ratio (< ~100:1). The driving voltage is about 15~20V. Further improvements can be achieved by further optimizing the LC material/monomer parameters, device fabrication process/conditions and the optical system setup. In this system, polarizers are not required so that very high light efficiency can be obtained.
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