Optical design of dental light using a remote phosphor light-emitting diode package for improving illumination uniformity.

The projection-type dental lighting based on the remote phosphor light-emitting diode (LED) package is designed to enhance uniformity of illuminance and correlated color temperature (CCT) on a target plane and to remove glare in the eyes of the patient. This dental lighting enables dentists to illuminate effectively the patient's mouth by increasing the inner area (50 mm×25 mm) described in ISO 9680. The optical module comprised of the LED package and optical lens is modeled to satisfy the inner area wider than 100 mm×50 mm and illuminance over 5,000 lx per the designed optical module. The fabricated prototype dental lighting contains four optical modules, and the maximum illuminance is 22,786 lx. The measured inner area is 105 mm×74 mm, and the ratio of inner area to outer area is about 76%. Also, the CCT variation is below 450 K in total illuminance pattern.

Improvement of phosphor modeling based on the absorption of Stokes shifted light by a phosphor.

We have found that the emission spectrum of phosphors measured in the powder state differs from that measured for a single phosphor. When the emission spectrum of the powder state is adopted in an optical simulation, the simulated optical properties e.g., the correlated color temperature, color rendering index, and chromaticity coordinates, show a remarkable discrepancy from those of the fabricated LED package. However, the discrepancy is significantly improved when the emission spectrum from a low concentration of phosphor in a silicone binder is employed. We suggest that the discrepancy originates from the absorption of Stokes shifted light by a phosphor.

Thermo-optic coefficient measurement of liquids based on simultaneous temperature and refractive index sensing capability of a two-mode fiber interferometric probe.

A fiber-optic interferometric probe based on a two-mode fiber (TMF) is proposed and demonstrated for measuring the thermo-optic coefficients (TOCs) of liquid samples. The proposed probe can be simply fabricated by fusion-splicing a short piece of TMF to a lead single mode fiber (SMF) with small lateral offset, which makes interference between LP(01) and LP(02) modes. The sensing responses of the probe to temperature and surrounding refractive index (SRI) have been experimentally investigated to show the capability of simultaneous measurements; the phase change of the reflection spectrum was related to temperature variation and the intensity change was to SRI variation. The data analysis is made not only in the spectral domain but in the Fourier domain also to effectively quantify the measurements. The TOCs of several liquid samples including water, ethanol, and acetone have been obtained with the proposed method.

A wide dynamics and fast scan interrogating method for a fiber Bragg grating sensor network implemented using code division multiple access.

We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS) pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 µÎµ and a low crosstalk of 950:1.

OSNR monitoring technique based on cascaded long-period fiber grating with optically tunable phase shifter.

An optical signal-to-noise ratio (OSNR) monitoring technique using a cascaded long-period fiber grating with a tunable phase shifter is proposed for non return-to-zero on-off-keying (NRZ-OOK) and differential phase shift keying (DPSK) signals. This method is based on two key points: first, the cascaded long period fiber grating (CLPG) acts as an optical delay interferometer (ODI) by Mach-Zehnder configuration consisting of the core and cladding modes inside the CLPG. Secondly, an optically tunable phase shifter using an Yb(3+) doped optical fiber (YDF) is inserted between the CLPG. The phase of the modulated signal propagating along the core mode of YDF is controlled by adjusting pumping power of 976-nm laser diode (LD). By combining the CLPG with the optically tunable phase shifter, the OSNR monitoring could be successfully executed.

Organic-inorganic hybrid perovskite quantum dots with high PLQY and enhanced carrier mobility through crystallinity control by solvent engineering and solid-state ligand exchange.

The photoluminescence quantum yield (PLQY) and charge carrier mobility of organic-inorganic perovskite QDs were enhanced by the optimization of crystallinity and surface passivation as well as solid-state ligand exchange. The crystallinity of perovskite QDs was determined by the Effective solvent field (Esol) of various solvents for precipitation. The solvent with high Esol could more quickly countervail the localized field generated by the polar solvent, and it causes fast crystallization of the dissolved precursor, which results in poor crystallinity. The post-ligand adding process (PLAP) and post-ligand exchange process (PLEP) increase the PLQY of perovskite QDs by reducing non-radiative recombination and the density of surface defect states through surface passivation. Particularly, the post ligand exchange process (PLEP) in the solid-state improved the charge carrier mobility of perovskite QDs in addition to the PLQY enhancement. The ligand exchange with short alkyl chain length ligands could improve the packing density of perovskite QDs in films by reducing the inter-particle distance between perovskite QDs. The maximum hole mobility of 6.2 × 10-3 cm2 V-1 s-1, one order higher than that of pristine QDs without the PLEP, is obtained at perovskite QDs with hexyl ligands. By using PLEP treatment, compared to the pristine device, a 2.5 times higher current efficiency in perovskite QD-LEDs was achieved due to the improved charge carrier mobility and PLQY.