Light emitting diode (LED) has been recognized as an applicable light source for indoor and outdoor lighting, city
beautifying, landscape facilities, and municipal engineering etc. Conventional LED has superior characteristics such as
long life time, low power consumption, high contrast, and wide viewing angle. Recently, LED with high color-rendering
index and special spectral characteristics has received more and more attention. This paper is intended to report a solar
spectrum simulated by multichip LED light source. The typical solar spectrum of 5500k released by CIE was simulated
as a reference. Four types of LEDs with different spectral power distributions would be used in the LED light source,
which included a 430nm LED, a 480nm LED, a 500nm LED and a white LED. In order to obtain better simulation
results, the white LED was achieved by a 450nm LED chip with the mixture of phosphor. The phosphor combination
was prepared by mixing green phosphor, yellow phosphor and red phosphor in a certain proportion. The multichip LED
light source could provide a high fidelity spectral match with the typical solar spectrum of 5500k by adjusting injection
current to each device. The luminous flux, CIE chromaticity coordinate x, y, CCT, and Ra were 104.7 lm, 0.3337, 0.3681,
5460K, and 88.6, respectively. Because of high color-rendering index and highly match to the solar spectrum, the
multichip LED light source is a competitive candidate for applications where special spectral is required, such as
colorimetric measurements, visual inspection, gemstone identification and agriculture.
With the development in material growth, device fabrication and packaging of LEDs, emission spectral of LED is able to cover the visible spectrum. In addition to the well-known lighting applications of LED, display is also one of the important applications of LED. In contrast with LCD, LEDs display has better contrast ratio, higher response rate, etc., which makes LEDs along with other self-illumination technologies an ideal candidate in making display panel. With the popularization of HD and Ultra HD standard, display panel with better image quality is needed. The number of pixels of the panel needs to be increased and the size of each pixel needs to be minimized. In this paper, we prepared a LED full-color display panel based on a 32×32 LED matrix with typical pixel size of 0.5mm. LED full-color display array with small pixel was obtained by mounting red LEDs, green LEDs and blue LEDs directly onto an isolating substrate such as sapphire . In addition, the substrate has metalized pads and connection before the matrix was connected to control unit. The control line and the column data line are prepared on the substrate, and there is an effective electrical insulation layers between them. The isolation layers consists of a SiO2 layer of 1000nm and polyimide layer of 3000nm. Polyimide as an important electrical insulating layer, we study some properties of it, such as :PI amination rate as a function of the curing temperature, PI resistivity as a function of the curing temperature and the punction electric field intensity of PI as a function of the film thickness of PI.
Spectral power distribution together with color consistency and constancy of natural light is studied and simulated before the white-light LED systems are fabricated to reproduce the natural light. The model with 3, 4, 6 and more primary LEDs based on the real measured spectrum and theoretical spectrum are analyzed. The spectral power sensitivity relation between the LEDs with different wavelength and color characteristic is analyzed. This research simplifies the approach of visible spectrum reconstruction which is an efficient way to use in the design and realization of LED-based luminaire.
In this paper, an array of blue LEDs with high optical power was presented and discussed. Optical of the novel design
was completed with the help of running simulation in TracePro to predict the performance of the module. 36 Cree XP-E
blue LEDs with a square reflector were used in the novel design. Optical simulation obtained from TracePro showed that
the total optical power of the LED array could reach 16.83W. To verify the simulation results, Aluminum PCB, Copper
PCB and Aluminum square reflector have been made respectively. Firstly, 36 Cree XP-E blue LEDs with small-pitch
were fixed on each PCB, then; an Aluminum square reflector was assembled on each PCB. This optical module was
installed on a radiator and tested. The optical output power of sample 1 used Aluminum PCB and Aluminum reflector
and sample 2 used Copper PCB and Aluminum reflector was 8.126W and 9.445W at 2A, respectively. It could be
observed that the optical output power of sample 2 was higher than that of sample 1. It could be attributed to the better
thermal dispersion performance of Copper. In order to improve the light reflectivity and reduce the loss of light, ultrathin
silver was coated on the Aluminum reflector by electron beam evaporation. The optical output power of sample 3 used
Copper PCB and silver-plated Aluminum reflector was 12.541W at 2A. A uniform square spot with high optical power
Thanks to the development in epitaxial growth, chip fabrication and packaging of LEDs, emission spectral of the device
is capable of covering the visible spectrum. Therefore, Light-emitting diode (LED) is currently undergoing a growing
interest in many applications, such as lighting. Besides lighting, LEDs offer a wide range of potential applications
including display. In contrast with LCD, LEDs display has better contrast ratio, higher response rate etc which makes
LEDs along with other self-illumination technologies an ideal candidate in making display panel. Due to the
popularization of HD and Ultra HD standard, display panel with better image quality is needed which means the number
of pixels of the panel needs to be increased while the size of each pixel needs to be minimized. In this paper, we describe
the design and fabrication of a colour tuneable and addressable LED micro display based on a 16×16 and 32×32 LED
matrixes with typical pixel size of 0.7 and 0.5mm respectively.
Different types of dielectric optical coatings for GaN based high bright LEDs were designed and discussed. The optical
coatings included the anti-reflection (AR) coating, high-reflection (HR) coating, and omni-directional high reflection
coating. Main materials for the optical coatings were dielectric materials such as SiO2, Ta2O5 and Al2O3, which were
different from the metallic reflector such as Ag usually used now. For the application of anti-reflection coating in GaN
LEDs, it was introduced into the design of transparent electrodes with transparent materials such as ITO to form
combined transparent electrodes. With the design of P, N transparent electrodes using the AR coating and ITO for GaN
LEDs, the extraction efficiency was improved by about 15% experimentally. For the dielectric high-reflection coating, it
has higher reflectivity and lower absorption than the metal reflector, and it was supposed to improve the extraction
efficiency obviously. While the dielectric omni-directional reflection coating using dielectric materials was also designed
and discussed in this article, since which was anticipated to improve the extraction efficiency furthermore. Using SiO2
and Ta2O5, the average reflectivity of a design of all dielectric omni-directional high reflection coating on the sapphire
surface was over 94%.
We investigate the relation between the thickness of sapphire substrates and the extraction efficiency of LED. The
increasing about 5% was observed in the simulations and experiments when the sapphire thickness changed from 100μm
to 200μm. But the output power increasing is inconspicuous when the thickness is more than 200μm. The structure on
bottom face of sapphire substrates can enhance the extraction efficiency of GaN-based LED, too. The difference of
output power between the flip-chip LED with smooth bottom surface and the LED with roughness bottom surface is
about 50%, where only a common sapphire grinding process is used. But for those LEDs grown on patterned sapphire
substrate the difference is only about 10%. Another kind of periodic pattern on the bottom of sapphire is fabricated by the
dry etch method, and the output of the back-etched LEDs is improved about 50% than a common case.
In this paper we studied the influence of N electrode on the extraction efficiency of high power light-emitting diodes
(LEDs). Simulation and experimental results show that comparing with traditional metal N electrodes the extraction
efficiency of LEDs with transparent N electrode is increased by 15%, and it is easier in process than the other techniques.
So we proposed a new kind of strip LEDs with transparent electrodes on both P-GaN and N-GaN. The design of
transparent electrodes was trade-off between transmittance and resistance. At the same time, the strip structure has some
advantages over the traditional square LEDs, which can increase the extraction efficiency and reduce the thermal
resistance. Antireflective and high reflective optical coatings were also used in this design. The fabrication of LEDs with
transparent electrodes on both P-GaN and N-GaN has been demonstrated. The output power of blue LEDs is 240mW at
350mA, forward voltage is below 3.5V. The luminous flux of white LEDs reached 65lm at 350mA.
The structure of micro-LEDs was optimized designed. Optical, electrical and thermal characteristics of micro-LEDs were
improved. The optimized design make micro-LEDs suitable for high-power device. The light extraction efficiency of
micro-LEDs was analyzed by the means of ray tracing. The results shows that increasing the inclination angle of sidewall
and height of mesa, and reducing the absorption of p and n electrode can enhance the light extraction efficiency of
micro-LEDs. Furthermore, the total light output power can be boosted by increasing the density of micro-structures on
the device. The high-power flip-chip micro-LEDs were fabricated, which has higher quantum efficiency than
conventional BALED's. When the number of microstructure in micro-LEDs was increased by 57%, the light output
power was enhanced 24%. Light output power is 82.88mW at the current of 350mA and saturation current is up to
800mA, all of these are better than BALED which was fabricated in the same epitaxial wafer. The I-V characteristics of
micro-LEDs are almost identical to BALED.
Width varied quantum wells show a more flat and wide gain spectrum (about 115nm) than that of identical miltiple quantum well. A new fabricating method was demonstrated in this paper to realize two different Bragg grating in an identical chip using traditional holographic exposure. A wavelength selectable DFB laser based on this material grown by MOVPE was presented. Two stable distinct single longitudinal mode of 1510nm and 1530nm with SMSR of 45 dB were realized.
Optoelectronic packaging has become a most important factor that influences the final performance and cost of the module. In this paper, low microwave loss coplanar waveguide(CPW) on high resistivity silicon(HRS) and precise V groove in silicon substrate were successfully fabricated. The microwave attenuation of the CPW made on HRS with the simple process is lower than 2 dB/cm in the frequency range of 0~26GHz, and V groove has the accuracy in micro level and smooth surface.These two techniques built a good foundation for high frequency packaging and passive coupling of the optoelectronic devices. Based on these two techniques, a simple high resistivity silicon substrate that integrated V groove and CPW for flip-chip packaging of lasers was completed. It set a good example for more complicate optoelectronic packaging.