Currently most light emitting diode (LED) components are made with individual chip packaging technology. The main manufacturing processes follow conventional chip-based IC packaging. In the past several years, there has been an uprising trend in the IC industry to migrate from chip-based packaging to wafer level packaging (WLP). Therefore, there is a need for LEDs to catch up. This paper introduces advanced LED WLP technologies. The contents cover key enabling processes such as preparation of silicon sub-mount wafer, implementation of interconnection, deposition of phosphor, wafer level encapsulation, and their integration. The emphasis is placed on how to achieve high throughput, low cost manufacturing through WLP.
This work demonstrates high-performance and current crowding-free InGaN/GaN light-emitting diodes (LEDs) using an electrically-reverse-connected Schottky diode (SD) and an Mg-delta (
High power light-emitting diodes (LEDs) lighting has drawn a great interest in the field of street light system in recent years. Key parameters for successful launching of LED street light in the commercial market are price and light efficiency, respectively, and they are greatly influenced by the materials and design factors used in high power LED package. This article presents a new design and materials processing technology to realize the solution of LED packaging with advantageous in price and performance. Cost effective materials and processing technology can be realized via thick film glass-ceramic insulating layer and silver conductor. Highly effective thermal design using direct heat dissipation to heat sink in LED package is demonstrated.
Optical constants, including scattering coefficient, absorption coefficient, asymmetry parameter and reduced scattering coefficient, of cerium-doped yttrium aluminium garnets (YAG:Ce) phosphor blended with SiO2 particle for white light-emitting diode (LED) packages were calculated based on Mie theory in this study. Calculation processes were presented in detail. Variations of the optical constants with the changes of phosphor weight fraction, dopant weight fraction, phosphor particle radius and SiO2 particle radius, were shown and analyzed separately. It was found that the asymmetry parameter is the intrinsic characteristic of the particles, and the increase of the phosphor weight fraction (or concentration) will lead to the increase of the optical constants. It was also discovered that the increase of the dopant weight fraction will enhance the scattering coefficient, but result in the decreases of the reduced scattering coefficient and the absorption coefficient.
Phosphor-converted light-emitting diodes (pc-LEDs), which employ blue LEDs with yellow phosphors to generate white light illumination, is a widely used solid-state lighting source. In order to conduct a phosphor layer coating with high quality on LED chip, a self-adaptive coating technology is introduced in this paper. A slurry coating technique combined with self-exposure method is applied and developed to demonstrate the benefits of self-adaptive coating layer. For self-exposure, the slurry coating is exposed to the blue emission of LED itself other than to ultraviolet (UV) light outside to make photoresist crosslinking. Results of measurement indicate that white LEDs with self-adaptive coating have shown self-adaptability to the angular distribution of intensity of blue light and performed higher spatial color uniformity than those with conventional coating and other conformal coating.
Effects of tilt angles of reflective cup structure and phosphor surface geometries on light extraction efficiency and angular color uniformity (ACU) of phosphor converted light emitting diodes (pcLED) are investigated by Monte Carlo ray-tracing simulations. It is found that tilt angles of reflective cup and phosphor surface geometries affect the light extraction efficiency and the ACU distinctly. When the tilt angle varied from 60° to 15°, the light extraction efficiency of LED can achieve the improvements of 13.87%, 18.25% and 14.79% respectively, when the phosphor surface geometry is concave, flat and convex, respectively. It is also found the variety law of phosphor concentrations with the change of tilt angles and phosphor surface geometries to maintain a fixed correlated color temperature (CCT).
The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells (QWs) to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. In this review, we will cover both fundamental aspects and technological approaches of QD VECSEL devices. Lastly, the presented review here has provided deep insight into useful guideline for the development of QD VECSEL technology, future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).
Scanning near-field optical microscopy (SNOM) is an ideal experimental measuring system in nano-optical measurements and characterizations. Besides microscopy with resolution beyond the diffraction limit, spectroscope with nanometer resolution and other instruments with novel performances have been indispensable for researches in nano-optics and nanophotonics. This paper reviews the developing history of near-field optical (NFO) measuring method and foresees its prospects in future. The development of NFO measurements has gone through four stages, including optical imaging with super resolution, near-field spectroscopy, measurements of nano-optical parameters, and detections of near-field interactions. For every stage, research objectives, technological properties and application fields are discussed.
Constant fraction discriminator (CFD) is one of theoretic method which can locate timing point at same fraction of echo pulse in pulsed time-of-flight (TOF) laser rangefinding. In this paper, the theory of CFD method was analyzed in reality condition. The design, simulation and printed-circuit-board (PCB) performance of CFD circuit were shown. Finally, an over amplified method was introduced, by which the influence of direct-current (DC) bias error could be reduced. The experimental results showed that timing discriminator could set the timing point to a certain point on echo pulse, which did not depend on the amplitude of echo pulse.
Three novel designs of adaptively modulated optical orthogonal frequency division multiplexing modems using subcarrier modulation (AMOOFDM-SCM) are proposed, for the first time, each of which requires a single inverse fast Fourier transform/fast Fourier transform (IFFT/FFT) operation. These designs not only significantly simplify the AMOOFDM-SCM modem configurations, but also offer extra unique network features such as input/output reconfigurability. Investigations show that these three modems are capable of supporting more than 60 Gb/s AMOOFDM-SCM signal transmission over 20, 40 and 60 km single mode fibre (SMF)-based intensity modulation and direct detection (IMDD) transmission links without optical amplification and chromatic dispersion compensation.
A 3-input all-optical priority encoder is designed. Proof-of-concept experiment is performed at 40-Gbit/s based on a cross-gain modulation (XGM) in two parallel semiconductor optical amplifiers (SOAs). Output logic signals with over 10-dB extinction ratios (ERs) and clear open eye diagrams are obtained. No additional input light beam is used. The proposed scheme may be a promising candidate for future ultrafast all-optical digital signal processing circuits and computing systems.
A simple scheme to generate optical quadrature amplitude modulation (QAM) signals is proposed based on different types of delay interferometers (DIs). The simulated results show that 16QAM, 64QAM and 256 QAM optical signals can be generated by 2×2, 3×3 and 4×4 DI, respectively, and the outputs of the proposed scheme are similar to those of the conventional schemes. The operation principle is discussed and the transmission properties of the square 16QAM as well as 64QAM signals are analyzed and compared with common approach.
A novel design of optical sampling system has been developed by using sum-frequency generation (SFG) in a periodically-poled lithium niobate (PPLN) waveguide and using passive mode-locked fiber laser pulses as optical sampling pulses. The system achieved high temporal resolution and high sensitivity using a 30 mm length PPLN with quasi phase match period of 19.3 μm and 151 fs sampling pulses which were generated by passive mode-lock fiber laser based on nonlinear polarization rotation (NPR). Clear eye-diagram of 10 Gbit/s non-return-to-zeros (NRZ) pseudorandom binary sequence (PRBS) optical signal were successfully reconstructed by this system.
Biodiesel is the product of catalysed transesterification reaction, in which fatty acid is transformed to fatty acid methyl ester (FAME), named biodiesel. The frequency-dependent absorption and refractive characters of biodiesels and its base stocks have been researched in the spectral range of 0.2-1.5 THz by terahertz time-domain spectroscopy (THz-TDS). The biodiesels showed higher absorption value than those of its base stocks because of the concomitant, and the increasing of absorption coefficients of three biodiesels differed with the different transesterification technology. The results suggested that THz-TDS can be a promising method to the quality control and ester transfer efficiency analysis of biodiesel.
In this paper, the principle of subaperture stitching interferometry was introduced. A testing stage with five degrees of freedom for stitching interferometry was built. A model based on least-squares method and error averaging method for data processing was established, which could reduce error accumulation and improve the precision. A 100 mm plane mirror was measured with a 50 mm aperture interferometer by means of stitching interferometry. Compared with the results by a 100 mm interferometer, peak to valley (PV) and root mean square (RMS) of the phase distribution residual are
Titanium dioxide-double-walled carbon nanotubes (TiO2-DWCNTs) with DWCNTs/TiO2 of 20 wt.% is prepared by a conventional sol-gel method. Doping the TiO2-DWCNTs in TiO2 photoanode, a flexible dye-sensitized solar cell (DSSC) is fabricated. The sample is characterized by scanning electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) absorption, ultraviolet-visible spectroscopy (UV-vis) absorption spectra,electrochemical impedance spectroscopy (EIS) technique and photovoltaic measurement. It is found that adding a certain amount of TiO2-DWCNTs can efficiently decrease the resistance of charge transport, improve dye adsorption. Under an optimal condition, a flexible DSSC contained with 0.50 wt.% TiO2-DWCNTs achieves a light-to-electric energy conversion efficiency of 3.89% under a simulate solar light irradiation of 100 mW·cm-2.
This paper proposes a novel continuous variable coherent optical communication mode. In this mode, two quadrature Stokes parameters are regarded as observed physical quantity, and single linearly polarized component is used as carrier wave. At the sending end, electro-optical amplitude modulator (EOM) of 45° azimuth is used to indirectly complete the linear modulation of