W.H. Cheng

Novel broadband glass phosphors for high CRI WLEDs

New broadband glass phosphors with excellent thermal stability were proposed and experimentally demonstrated for white light-emitting-diodes (WLEDs). The novel glass phosphors were realized through dispersing multiple phosphors into SiO₂ based glass (SiO₂-Na₂O-Al₂O₃-CaO) at 680°C. Y₃Al₅O₁₂:Ce³⁺ (YAG), Lu₃Al₅O₁₂:Ce³⁺ (LuAG), and CaAlSiN₃: Eu²⁺ (nitride) phosphor crystals were chosen respectively as the yellow, green, and red emitters of the glass phosphors. The effect of sintering temperature on inter-diffusion reduction between phosphor crystals and amorphous SiO₂ in nitride-doped glass phosphors was studied and evidenced by the aid of high-resolution transmission electron microscopy (HRTEM). Broadband glass phosphors with high quantum-yield of 55.6% were thus successfully realized through the implementation of low sintering temperature. Proof-of-concept devices utilizing the novel broadband phosphors were developed to generate high-quality cool-white light with trisstimulus coordinates (x, y) = (0.358, 0.288), color-rending index (CRI) = 85, and correlated color temperature (CCT) = 3923K. The novel broadband glass phosphors with excellent thermal stability are essentially beneficial to the applications for next-generation solid-state indoor lighting, especially in the area where high power and absolute reliability are required.

High-performance glass phosphor for white-light-emitting diodes via reduction of Si-Ce 3+ :YAG inter-diffusion

A novel Ce3+:YAG doped sodium glass (CeYDG) with low-melting temperature of 693°C and high internal quantum yield of 68% for white-light-emitting diodes (WLEDs) is demonstrated. The glass phosphor possesses glass transition temperatures of 578°C which exhibits a better thermal stability to overcome the thermal limitation of conventional Ce3+:YAG doped silicone due to low thermal stability of around 150°C. To the best of authors’ knowledge, this is the highest quantum yield yet reported for thermally stable glass phosphors. The high quantum yield is achieved by lowering the sintering temperature of 700°C for glass phosphor, which substantially reduces Si-Ce3+:YAG inter-diffusion, evidenced by high-resolution transmission electron microscopy (HRTEM). This new CeYDG with high-quantum yield is essentially beneficial to the applications for next-generation solid-state lighting in the area where high power and absolute reliability are required and where silicone simply could not stand the heat or other deteriorating factors due to its low thermal stability.

Chromaticity tailorable glass-based phosphor-converted white light-emitting diodes with high color rendering index

In this paper, Lu3Al5O12:Ce3+ and CaAlSiN3: Eu2+ co-doped glass are presented as color conversion materials for white light-emitting diodes (WLEDs). Through adjusting the thickness of the glass phosphors, the chromaticity and CCT of the WLEDs follows the Planckian locus well. The WLEDs show CCT ranging from ~4000K to ~7000K with high CRI ranging from 83 to 90 due to the wide emission spectrum from the proposed glass phosphors. The glass phosphors provide an effective way to achieve chromaticity-tailorable WLEDs with high color quality for indoor lighting applications.

Spectral characteristics for a fiber grating external cavity laser

A numerical investigation has been carried out on the influence of the antireflection (AR) coating of laser, the coupling efficiency of laser and fiber (η), and the reflectivity of fiber grating (Rg) on the side-mode suppression ratio (SMSR) of the fiber grating external cavity laser (FGECL). The FGECL was fabricated by the assembly of the multimode Fabry–Perot (FP) laser chip and fiber grating. The results showed that the FGECL with a lower AR coating, higher η and Rg exhibited a better SMSR. A comparison of the SMSR dependence on the η and Rg showed that SMSR increased more rapidly with increasing η than SMSR for Rg. These spectral characteristic studies of the SMSR dependence on the device parameters of the AR coating, η, and Rg may provide useful device designs for the practical fabrication of a FGECL for use in dense wavelength division multiplexing (DWDM) applications.

Thermal-Stability Comparison of Glass- and Silicone-Based High-Power Phosphor-Converted White-Light-Emitting Diodes Under Thermal Aging

The lumen degradation, chromaticity shift, transmittance loss, and mean-time-to-failure (MTTF) evaluation in glass- and silicone-based high-power phosphor-converted white-light-emitting diodes (LEDs) (PC-WLEDs) under accelerated thermal aging at 150 °C, 200 °C, and 250 °C are presented and compared. The silicone-based PC-WLEDs exhibited less thermal stability than the glass-based PC-WLEDs by 1.86, 2.79, and 4.76 times higher lumen losses, 3.05, 3.26, and 6.84 times larger chromaticity shifts, and 1.82, 2.62, and 6.67 times greater transmittance losses at 150 °C, 200 °C, and 250 °C, respectively. The results also showed that the glass-based PC-WLEDs exhibited higher MTTF than the silicone-based PC-WLEDs by 20 times at room temperature. The peaks of the emission and excitation spectra for both silicone and glass phosphors were not significantly changed after thermal aging, evidenced by fluorescence spectrophotometer analyses. This indicated that the fluorescent ability of Ce:YAG-doped phosphor materials did not change after thermal aging and the transmittance loss was corresponding to the lumen loss and chromaticity shift. The results of the lumen loss, chromaticity shift, transmittance loss, and MTTF investigations clearly demonstrated that the thermal-stability performance of the glass-based PC-WLEDs was better than that of the silicone-based PC-WLEDs. The advantage of employing doped glass encapsulation in high-power PC-WLEDs could be explained: The material property of glass transition temperature of 750 °C was higher than that of silicone transition temperature of 150 °C. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to many applications where the LED modules with high power and high reliability are demanded for use in next-generation solid-state lighting.

Optical Model for Novel Glass-Based Phosphor-Converted White Light-Emitting Diodes

We proposed an optical model for phosphor-converted white LEDs (pc-WLEDs) that utilized Ce:YAG doped glasses as novel phosphor-converted materials. In this model, precise simulation of the chromatic performance of the glass-based pc-WLEDs was conducted. Between optical simulation and experimental measurement, the color difference

Multilayer dielectric materials of SiOx/Ta2O5/SiO2 for temperature-stable diode lasers

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Post-weld-shift in semiconductor laser packaging

was 1.2%. Meanwhile, the difference of correlated color temperature limited from 1 wt% to 5 wt% phosphor concentration between the simulation and measurement was 184 K. Such a model for glass phosphors will be helpful to design high-power glass-based pc-WLEDs.

High thermal stability of high-power phosphor based white-light-emitting diodes employing Ce:YAG-doped glass

Abstract A novel athermal waveguide for temperature-stable diode lasers was investigated. The waveguide consisted of SiO X , Ta 2 O 5 and SiO 2 dielectric layers deposited on a Si substrate. A theoretical calculation shows that the optical path (defined by the product of the effective index of the waveguide and the waveguide length) of the waveguide can be independent of temperature if the thicknesses of Ta 2 O 5 and SiO X layers are properly chosen. The Ta 2 O 5 and SiO X layers were deposited using the magnetron sputtering technique. The indices of SiO x and Ta 2 O 5 films are 1.5 and 2.12, respectively. The SiO 2 layer was fabricated by flame hydrolysis deposition with a thickness of 4 μm. Good surface morphology and thickness uniformity of the SiO 2 layer were obtained. The index-temperature drift of SiO 2 was measured to be 3 × 10 −5 / °C which is about 10 times less than that of a III–V semiconductor. A comparison of the temperature dependence of the SiO X /Ta 2 O 5 /SiO 2 waveguide and Ta 2 O 5 /TiO 2 /SiO 2 waveguide is also presented.

A simple passive-alignment packaging technique for laser diode modules

Post-weld-shift (PWS) in laser welding technique for a package (DIP) with fiber pigtail to laser connection has been studied experimentally and numerically modelled. Experimental results show that the PWS of optical component welded by a dual-beam laser welding system shifts more to the counterclockwise as the energy difference of the laser beam increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam energy delivery. A finite-element method (FEM) has been carried out to analyse the effect of laser beam energy variation on PWS in laser packaging. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM provides one of the effective methods for predicting the PWS in laser welding technique for optoelectronic packaging.Post-weld-shift (PWS) in laser welding technique for a package (DIP) with fiber pigtail to laser connection has been studied experimentally and numerically modelled. Experimental results show that the PWS of optical component welded by a dual-beam laser welding system shifts more to the counterclockwise as the energy difference of the laser beam increases. This indicates that the PWS in laser packaging can be minimized by properly controlling the laser beam energy delivery. A finite-element method (FEM) has been carried out to analyse the effect of laser beam energy variation on PWS in laser packaging. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM provides one of the effective methods for predicting the PWS in laser welding technique for optoelectronic packaging.