Wen-Chi Hung

Low-cost and low-electromagnetic-interference packaging of optical transceiver modules

The low-cost and low-electromagnetic-interference (EMI) packaging of optical transceiver modules employing housings of plastic composites are developed and fabricated. Optical transceiver modules fabricated by the plastic composites with transmission rates of 1.25 and 2.5 Gb/s are tested to evaluate the electromagnetic (EM) shielding against emitted radiation from the plastic packaging. The results show that these packaged optical transceiver modules with their high shielding effectiveness (SE) are suitable for use in low-cost and low-EMI Gigabit Ethernet lightwave transmission systems. By comparison of cost, weight, and shielding performance for optical transceiver modules fabricated by the housings of nylon and liquid-crystal polymer with carbon fiber filler composites, woven continuous carbon fiber (WCCF), and nanoscale hollow carbon nanocapulses (HCNCs) epoxy composites, the WCCF composite shows lower cost, lighter weight, and higher EM shielding than the other types of composites. Future studies may develop the low-cost and low-EMI optical transceiver modules using nanoscale HCNCs that have the combination of excellent physical and mechanical properties, light weight, and thinness compared with the conventional fabrication techniques.

Surface plasmon enhanced diffraction in cholesteric liquid crystals

The authors report the observation of an enhanced optical diffraction in cholesteric liquid crystals (CLCs) due to the presence of silver nanoparticles. The silver nanoparticles are deposited on the surface of one of the indium tin oxide electrodes of the CLC cell. With the application of a proper voltage, the liquid crystals assume its cholesteric phase with the helical axis perpendicular to the applied electric field. The CLC grating was probed by a beam of polarized light in the spectral range from 450to750nm. The direction of propagation of the beam is perpendicular to the helical axis of the liquid crystals. The authors report a significant enhancement in the first-order diffraction efficiency at around 543nm. The results of the experimental observation are presented and discussed.

Dynamics of single-layer polymer breath figures

A single-layer of breath figure pattern was explored via the dynamical optical images and the temperature evolution. The pattern was prepared with the solution of carbon disulfide (CS(2)) dissolved 1% weight concentration of polystyrene. The evaporation of CS(2) was considered to be the most important role to the formation of the breath figure pattern. The understanding of the breath figures pattern will promote the technique to fabricating an imprinted template with demanded hexagonal structures.

Sensitive voltage-dependent diffraction of a liquid crystal Fresnel lens

This investigation proposes a Fresnel liquid crystal (LC) lens with high diffraction efficiency and a low driving voltage. A Fresnel zone electrode was fabricated on a glass plate. A Fresnel zone-distributed electric field in the LC cell was induced by a proper driving voltage, yielding a concentric structure of LCs as a Fresnel phase lens. A remarkable diffraction efficiency of ~39%, close to the theoretical limit of 40.5%, was detected when the LC lens was probed using a polarized incident beam with a wavelength of 632.8 nm. The diffraction efficiency of the Fresnel LC lens was demonstrated to depend sensitively on the applied voltage. The most suitable driving voltage of the Fresnel LC lens was as low as 0.9 V. This study may support progress in the electrical modulation of the optical properties of various optical systems.

Surface plasmons induced extra diffraction band of cholesteric liquid crystal grating

Diffraction behavior of cholesteric liquid crystal (CLC) grating with the surface plasmon effect was investigated. One indium tin oxide plate of the CLC grating cell was covered with silver nanoparticles. With the application of a proper voltage, a well formed phase grating was constructed in the CLC cell. The CLC grating was probed by a beam of the polarized-monochromatic light, and the wavelength range was from 450 to 700 nm. It was shown that an extra first-order diffraction band was observed around 505 nm. The physical reason of the extra diffraction band could be the surface plasma effect emerged from silver nanoparticles. The extra diffraction band due to the surface plasmon effect can offer potential applications in nano-optics, such as the optical switch function.

Laser pulse induced gold nanoparticle gratings

We report the results of our experimental investigation of laser induced gold nanoparticle gratings and their optical diffraction properties. A single shot of a pair Nd-YAG laser pulses with the same polarization is directed toward a 6 nm thick gold film on a substrate of polymethyl methacrylate. As a result of the laser illumination, the thin gold film is fragmented into an array of nanoparticles. Through the observation of scanning electron and dark-field optical microscopes, we discovered that the morphology of the gold nanoparticle grating is dependent on the fluence of laser pulse. The spectrum of first order diffraction shows the dependence on the absorbance property due to the presence of the nanoparticles. The ablation of nanothickness thin films via the use of laser pulses may provide a simple and efficient method for the fabrication of nanoscale structures, including two dimensional arrays of nanoparticles.

High electromagnetic shielding of plastic package for 2.5-Gb/s optical transceiver modules

A lightweight, low-cost plastic package for a 2.5-Gb/s optical transceiver module, that also has good electromagnetic shielding properties, has been fabricated using woven continuous carbon fiber (CCF) epoxy composite. The shielding effectiveness (SE) of the CCF epoxy composite has been modeled theoretically and measured from 500 MHz to 3 GHz using the ASTM D4935 and a near-field test method. Two types of weaving patterns were studied: a balanced twill structure (BTS) and a parallel structure. The BTS was able to achieve an SE of about 80 dB under plane wave conditions and about 50 dB under near-field conditions because of the numerous conductive between crossing fibers. The SE of the proposed package is at least 20 dB greater than the previous package which used a liquid crystal polymer composite. In addition to better shielding performance, the proposed package costs less because it uses less carbon fiber. The proposed package for an optical transceiver is suitable for use in a low-cost lightwave transmission system

Diffraction of cholesteric liquid crystal gratings probed by monochromatic light from 450 to 750 nm

We investigated both theoretically and experimentally the diffraction property of cholesteric liquid crystals (CLCs) in the configuration of transmission grating. The CLCs are treated as birefringent index gratings whose diffraction property is strongly dependent on the polarization state of the incident beam. In our experimental studies, the CLC index gratings are constructed by applying an electric voltage to liquid crystal cell. The grating is probed by a monochromatic light in spectral range from 450 to 750 nm and the measured diffraction efficiency approximately agrees with the theoretical predictions. The dependence of polarization and wavelength of polarized monochromatic light may possibly lead to a light switch in optical communication system.

Sensible measurement of localized surface plasmon based on lithographic gratings

The optical diffraction efficiency of lithographic grating was probed in this study. The enhanced first order spectral diffraction efficiency emerged from localized surface-plasmon excitation of gold nanoparticles which are alternatively uniformly and randomly spread in grating strips. The sensible measurement more than traditional method is reported.

Simple parameter determination for twisted nematic liquid-crystal display

A simple and accurate measurement method for determining the cell parameters of a twisted nematic liquid-crystal display (TN-LCD) is proposed. Based on the measurement of the maximum reflectance and the maximum transmittance of a TN-LCD by rotating the polarizer at a particular angle, between the front director of the liquid crystals and the transmission axis of the polarizer, the cell gap and the twist angle can be determined according to the Jones matrix theory, and the twist sense can also be determined easily by applying an external small voltage to slightly change the effective refractive index of the liquid crystal.