Ken-Yuh Hsu

Confocal displacement sensor with varifocal lens

A confocal displacement sensor with a varifocal lens and a multi-wavelength rainbow laser was established in this study. The surface curvature of varifocal lens was varied by different current driving so that the focal length can be easily changed. Thus, we can quickly measure the distance between the sensor head and targets by detecting the reflective power according to the principle of confocal laser. This rainbow laser can operate at four different wavelengths. The laser beams with different colors can be used to measure the dispersion of varifocal lens. The range of measuring displacement with 20X objective lens in this displacement sensor is from 4.9mm to 5.9mm. The FWHM resolution of displacement is about 70μm. The step-height aluminate plate was measured by this system and the error of measuring distance is less than 35μm (0.75%).

Exploiting the image of the surface reflectivity to measure refractive index profiling for various optical fibers

A direct image method of surface reflectivities on a cleaved fiber end with a filtered halogen lamp and a TE-cooled CCD with high dynamic range is proposed to measure the multi-wavelength refractive index profiling (RIP). A polished black glass is used to be a reference standard for measuring the absolute reflectivity of the fiber end. With the developed calibration procedures, both the spatially dependent sensitivity and spectral responsivity of the CCD pixels can be eliminated to achieve the high spatial accuracy. Tested fiber is connected with a fiber terminator to prevent errors from the backside return light. With the present method, the RIP can be precisely measured for not only multi-mode fibers but also single-mode fibers.

Liquid crystal cell with graphene electrodes

We demonstrate a graphene-based nematic liquid crystal cells fabricated by photo alignment technique. The modulation characteristics have been measured revealing that photo alignment method shows great potential for protecting the graphene layer on glass substrate during LC device fabrication.

Developing a microspectrophotometer to measure the dependence of broadband refractive indices on Ge-doped concentrations in GRIN rods.

A confocal microspectrophotometer is utilized to scan the surface reflectivities of a polished gradient-index (GRIN) rod in the range of 400 to 900 nm. The pure fused silica is used to be a reference standard for deducing the absolute reflectivities of the Ge-doped core. Then, multi-wavelength refractive index profiles of the Ge-doped core can be further determined based on the Fresnel equation. Moreover, this work shows a connection between the material dispersion of the GRIN rod and the Ge-doped concentrations measured by an energy dispersive spectrometer. Finally, the dependence of the refractive index of the Ge-doped core on the doping concentrations at a certain wavelength can be easily expressed as a linear form.

Broadband microspectrophotometer with tablet PC control

This study investigated the design, fabrication, and performance characterizations of a broadband microspectrophotometer with tablet PC wireless control. The microspectrophotometer system performed rapid measurements, was highly accurate, and was easy to operate. The calibrations for two measurement modes for transmittance and reflectance spectra were performed with bulk and multilayer thin-film samples. Objective lenses with various magnifications were introduced to verify the possibility of microscopic spectra measurements in the system. A polarization identification capability was also included in the system.

Compact motorized circular wheel of polarization optics for ultra-broadband polarization state generation

This study proposes an innovative optical mechanism with a miniature motorized circular wheel for polarization optics for an ultra-broadband polarization state generator. The proposed apparatus can be suitable for a polarimetric microspectrophotometer for measurements of micro optics and metamaterials with circular dichroism and linear dichroism. Different types of micro optics have their own wavelength dependence, meaning different curves in the broadband range of light. This study presents an ultra-broadband platform for measuring and identifying micro optics such as chiral metamaterials, plasmonics, micro polarizers, and patterned retarders. The key component of a polarimetric microspectrophotometer is a polarization state generator (PSG). A simple PSG consists of a polarizer and a waveplate. An arbitrary polarization state can be created by rotating either the polarizer or the waveplate. Sheet polarizers and achromatic waveplates have a limited bandwidth range. For the ultra-broadband measurement range of 400 nm to 1700 nm, the PSG needs at least three sheet polarizers and three achromatic waveplates: 400 nm-700 nm, 700 nm-1000 nm, and 1000 nm-1700 nm. This optical mechanism, which consists of only one control motor and two high precision unidirectional bearings, includes several polarizers and waveplates arranged in a matrix on a circular wheel. This apparatus can shift one of the polarizers and waveplates to a predetermined position and rotate all the polarizers to change the polarization status. An ultra-broadband polarimetric microspectrophotometer with a compact motorized wheel is an advanced polarization optical instrument for research on chiral metamaterials, plasmonics, micro polarization optics, green optics, and bio optics.

The influence of Rh doping on the light-induced properties of Bi 4 Ge 3 O 12 single crystals

The influence of different doping concentrations of rhodium on the light-induced and holographic properties of BGO crystal is investigated. It is found that Rh addition generates sufficient density of traps for photoinduced charge carriers such that holographic gratings are successfully recorded in the blue–green spectral range. The measured steady state diffraction efficiency at 514 nm is 0.14%, which corresponds to a refractive index modulation of Δn~1.5 × 10−6 for higher Rh concentration. A photochromic effect and nonlinear dependence of photoconductivity on light intensity are observed indicating deep level and shallow level contributions to the charge transport mechanism of Rh-doped BGO.

In-line polarization holographic memory system using PQ doped PMMA photopolymer(Conference Presentation)

Polarization hologram provides some unique features over classical phase or amplitude hologram. One of the most important features is that the photo-induced anisotropy in those materials leads to the polarization-dependent diffraction from the hologram. This property is useful for many applications, such as optical interconnection, holographic data storage and bio-imaging …etc. Recently, the 9, 10-phenanthrenequinone -doped poly(methyl methacrylate) (PQ/PMMA) photopolymer with cm thickness has attracted intense research interesting for the volume holographic applications because the experiments demonstrated that PQ/PMMA photopolymers possess not only high optical quality but also negligible shrinkage effect under light exposure [3-5]. Additionally, in terms of chemical formula, the PQ/PMMA consists of planar structures PQ molecules dispersed in amorphous PMMA polymer so that it is possible to be oriented if irradiated with polarized light, resulting in a photoinduced birefringence. This phenomenon makes it capable for permanent polarization holographic recording via photochemical reaction. Thus, combining these two properties may make PQ/PMMA photopolymer attractive for volume polarization holographic applications. In this paper, we particularly characterize polarization holographic recording in our materials for high-density data storage. Then, we will demonstrate a in-line polarization holographic memory system using PQ/PMMA photopolymer.

Optimization of holographic data storage system based on Seidel aberrations reduction

In this research, we investigate the influence of Seidel aberrations on the point spread function and the probability density function of holographic data storage systems, and thus the storage capacity and bit error rate of storage system can be obtained. The aberrations tolerances of storage systems with different numerical aperture are obtained. Optimization on BER and SC of holographic data storage systems by reducing Seidel aberrations will be demonstrated numerically.

Tunable Single-Pair Hollow-Beam-Converter Dark-Field Microscopy

A tunable single-pair hollow-beam-converter (TSHBC) dark-field microscopy is proposed and fabricated. The TSHBC is composed of one pair of parallel reflective mirrors of complementary cone shape. By simply adjusting the longitudinal separation between the two mirrors of TSHBC, a dark-field image with more high contrast and high energy efficiency can be obtained for a given objective lens. Furthermore, the selection criteria of the condenser lens and objective lens are provided for the structure of an optimal dark-field microscopy with TSHBC.