Light quality and controllability are crucial factors in plant illumination, posing challenges such as formulating precise light environment and achieving accurate micro-zone lighting. To address these issues, we proposed a resonant cavity light-emitting diode (RCLED) device that incorporates a resonant cavity reflector (RCR) and a metasurface, offering advantages such as high purity and highly directional emission. The RCR, composed of various pairs of distributed Bragg reflectors, was investigated to narrow the full-width at half-maximum (FWHM) of the emitting spectrum, thereby improving the purity. A traditional beam-splitting metasurface was designed to achieve directional emission of the linearly polarized light beam. However, traditional devices with fixed directional emission limit their adaptability. We leverage the Moiré effect to design a two-cascaded metasurfaces system. This device enables tunable deflection angle of the output beam, providing greater flexibility and control. Compared to tradition RCLEDs, our angle-tunable RCR-RCLED with two cascaded metasurfaces boasts a one-third FWHM. Compared to RCR-RCLED integrated with a tradition metasurface, our device has a tunable deflection angle.
Three types of reflectors, including the distributed Bragg reflectors (DBRs), the first hybrid reflectors composed of DBR and Al mirror (DBR-Al), and the second hybrid reflectors composed of DBR, an additional low-refractive-index layer, and Al mirror (DBR-L-Al), were investigated by use of thin-film theory at the central wavelength of 300 nm for flip-chip ultra-violet light-emitting diodes (UV-LEDs). The number of DBR pairs and various high-refractive-index materials were studied. It is shown that the lossless materials with high refractive-index contrast should be selected for DBRs, and the DBR-Al hybrid reflectors provides higher reflectance comparing to DBRs. However, the Al mirror causes a sharp drop near the central wavelength and a blue shift of the peak position. These drawbacks can be suppressed by additional low-refractive-index layer attached on the Al mirror. In addition, the DBR-L-Al reflector leads to higher reflectivity and larger FWHM as compared to DBR-Al reflectors. By use of Monte Carlo ray tracing method, the light-extraction efficiency (LEE) for flip-chip UV-LEDs with (SiO2/ZrO2) 3 -SiO2-Al hybrid reflector or perfect mirror were simulated. The calculated LEE for the (SiO2/ZrO2) 3 -SiO2-Al hybrid reflector is 97 % of that for the perfect mirror. Moreover, the sharp drop in the angular reflectance spectrum of the (SiO2/ZrO2)3 -SiO2-Al hybrid reflector induces a slightly reduction of light intensity as compared to the perfect mirror.
In view of limitation for LED optical design method as ideal point source, a new uniform illumination optical design
method of freeform lens for a high-power LED is present in the paper.By establishing an energy corresponding
relationship between the extended LED source and the point illumination of the receiving surface, a freeform lens optical
model achieving uniform illumination in target plane is obtained.The optical simulation results of uniform light intensity
curve of the model are compared with the one designed by an approximate point source method. The results show that
the new method can effectively overcome the shortages from the point source design.It is more accurately to control the
correspondence relationship of light energy and the outgoing direction of light.The illumination uniformity of the
freeform lens is greater than 75% and also meets the design requirements.
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