In this paper, an experimental study is conducted to investigate three light uniformers based on liquid guide for their possible usages as color mixing elements. In this study, three types of light uniformers are systematically analyzed, which include a straight light guide, a tapered light guide, and a U-shaped light guide. This study consists of two parts: a computer-aided optical modeling using a commercial ray tracing software package; and an experimental study verifying the results obtained from the computer simulations. Beam uniformity, in terms of illuminance and color, is compared among different light uniformers. The experimentally observed results agree well with the simulated results. Light transmission efficiency is also calculated for each light uniformer based on the simulation results. It is found in this study that the U-shaped light uniformer has high light transmission efficiency and the best color mixing effect among the three investigated light guides and offers a compact, practical, and inexpensive solution for color mixing in many industries.
High precision control is highly desirable when using the selective chemical etching technique to fabricate tapered fibers for many practical applications. So far, various methods have been proposed on this topic. In this paper, we proposed a novel and effective method to make tapered fibers in different shapes and sizes based on automatic control of the immersion depth in chemical etching. We adopted the diluted Hydrofluoric acid as etching solution in our
preliminary experiment, and common selective chemical etching scheme was also implemented in our experiment in which the buffered hydrofluoric acid solution is used. We found out in our study that the etching process can be further controlled by controlling the evaporation of the etching solution. Under near-saturation condition, the ammonium fluoride (NH<sub>4</sub>F) in the etching solution tends to crystallize as the water evaporates. The evaporation of the water and the crystallization of the ammonium fluoride cause the immersion depth of the etched fiber to decrease in certain rate, which leads to different etching time on different parts of the etched fiber. This fact enables the etched fiber to have a very smooth tapered part. By controlling the changing rate of immersion depth and other etching conditions, we can finely control the shape and size of etched fibers.
Highly luminous polymers have been successfully prepared by copolymerization of various arylene vinylene units. Among the copolymers synthesized, poly(phenylene vinylene) (PPV) and its derivatives have been studied most intensively because they show fairly strong fluorescence and have a wide structural variety. In this paper, light-emitting polymers and traditional organic LED technology are briefly reviewed at first. A novel and unique point source based on the organic LED fabricated on an optical fiber is then proposed. As proof of concept, some preliminary experimental results are shown. Two light-emitting materials needed for our experiments are synthesized. It is illustrated that the unique point OLED source is feasible, which can lead to many practical applications, such as biomedical imaging.
Hetero-core fiber structure consists of a sandwiched structure of fibers with different core diameters. Hetero-core fiber structure has found its application in both intensity based and phase change based sensors. In this paper, an analysis of hetero-core fiber structure in photonic crystal fibers (PCF) and waveguides is presented. With the finite-difference time-domain (FDTD) method, the performance of such a structure in a fiber specklegram sensor and the refractive index modulation on PCF section are investigated. It is found that the unique photonic nanostructures can substantially enhance the sensitivity of the specklegram sensor with added dynamic range tunability, which can lead to many practical applications in optical sensors.
Optical windows have been widely used in optical spectrographic processing system. In this paper, various window profiles, such as rectangular, triangular, Hamming, Hanning, and Blackman etc., have been investigated in detail, regarding their effect on the generated spectrograms, such as joint time-frequency resolution ΔtΔw, the sidelobe amplitude attenuation etc.. All of these windows can be synthesized in a photorefractive crystal by angular multiplexing holographic technique, which renders the system more adaptive. Experimental results are provided.
An analysis of volume holographic long period gratings in photonic nanostructured fibers and waveguides is presented. It is found that the unique photonic nanostructure could substantially enhance the tuning capability of the spectral response of the grating, which could result in many practical applications in optical communications and sensors, such as wide tuning range wavelength filters and ultrahigh sensitivity optical sensors.
In this paper, an analysis of long period gratings in photonic nanostructured fibers and waveguides is presented. With the finite-difference time-domain (FDTD) method, a detailed quantitative study on the relationship between the spectral response shift of the gratings and the parameters of the photonic nanostructures is performed. It is found that the unique photonic nanostructures can substantially enhance the tuning capability of the spectral response of the gratings, which can lead to many practical applications in optical sensors and communications, such as optical sensors with ultra high sensitivity and wavelength filters with wide tuning range.