| Great progress has been made in the research and application of gallium nitride(GaN)based light-emitting devices(such as LED and LD).In the future application of new display technologies(such as AR/VR display and wearable display),higher requirements have been put forward for imaging systems composed of light-emitting devices and optical components.For example,the size of light-emitting chips is required to be smaller,the optical integration system is thinner,and it can be integrated with flexible multifunctional substrates,etc.Conventional optical components are usually above millimeter level,which greatly limits their application in micro/wearable optical display integration systems.Therefore,it is particularly important to develop new optical elements and imaging systems that can be easily integrated with GaN light-emitting devices.Using micro-nano structures to control light field provides a new solution to the above problems.In recent years,some progress has been made in the development of nanostructures based on GaN materials.Due to the advantages of no bond and reduced coupling efficiency when integrated with GaN optoelectronic devices,and the manufacturing process can be expanded on the basis of traditional semiconductor processes.Therefore,it has great application prospect and research value in the fields of highly integrated optoelectronic devices and new optical display technology.In this paper,the specific modulation of the light field,such as polarization conversion,focusing,imaging and collimation,is realized based on the GaN nanostructures and arrays,and is integrated with GaN based photonic devices(such as LD,LED,etc.)to form an active photonic device with specific optical output characteristics.The aim is to break through the limitation of "single" traditional bulk optical elements and realize the efficient optical characteristics(such as polarization conversion,focusing,imaging and collimation,etc.)that can only be obtained by the traditional optical system consisting of optical elements and light-emitting devices.The specific research content and innovation results are as follows:(1)A highly efficient circular polarization laser source based on GaN-based green laser was innovatively proposed.The function of converting linearly polarized emission into circularly polarized emission is realized by integrating the GaN nanomgrating supersurface with the laser.The experimental results show that the efficiency of the integrated device is up to 80%and the degree of polarization of circularly polarized light is about 0.99.(2)Innovative combination of GaN Nano-Grating metsurface and GaN metalens to achieve micron level efficient focusing function of gallium nitride green laser.First,the GaN Nano-Grating metsurface fuctions as a quarter-wave plate to output circularly polarized light from GaN LD,and then the circularly polarized light is focused efficiently by the GaN metalens.Finally,it realizes the optical control on a single element,which can only be achieved by integrating two or more optical elements.The experimental results show that the designed integrated device has a focal length of 1490 nm and a focusing efficiency of 72%.(3)Aiming at the three primary colors of LED,the polarimetric insensitive GaN metalens and its array were designed respectively.We proposed to reduce the difficulty of fabrication by increasing the dimension of GaN nanostructure adjustment parameters,so as to realize the efficient focusing and imaging of any polarization state light in a wide band.The focusing test results show that the focusing efficiency of blue light is 57%.The focusing efficiency of green light is 62.3%.The red focusing efficiency is 75%.The diffraction limit resolution can reach 1.29 μm.Finally,based on the concept of synthetic aperture optical lens,we designed and fabricated a fan-shaped synthetic aperture GaN metalens composed of GaN nanoblock array in visible light,with an effective aperture of 0.72 mm.The experimental results show that the diffraction limit resolution of the fan-shaped GaN metalens is 5.47 μm under arbitrary polarization state incident of red light 632.8 nm,which is close to that of the full-aperture GaN metalens.It is worth noting that the effective aperture of the superlens is only 1/3 of the processing area of the same aperture(duty cycle is 0.313),which can effectively shorten the processing time and reduce the manufacturing cost.(4)For LED which emits polarized light by itself,an all-dielectric nanostructure was innovatively designed,mainly consisting of one-dimensional photonic crystals composed of periodically stacked Al2O3/SiO2 films and TiO2 nanogratings integrated on the surface.Al2O3 and SiO2 are interlaced deposited on the surface of P-GaN.The results show that 77%of the spectral radiation energy of polarized blue LED can be concentrated within±5.5° by the designed all-dielectric nanostructure.The far-field radiation angle of polarized LED light can be controlled within ± 6°,meanwhile,the light output efficiency was 77%.The peak intensity of far-field radiation is 6.6 times higher than that of unstructured LED.Aiming at the LED which emits polarized light by micro-nano structure,a nano-grating structure with the function of wave plate is innovatively designed and integrated on the back of LED,which can further convert the unutilized TE polarization component reflected by the micro-nano structure into TM polarization component and radiate it out.The results show that,the polarized light extraction efficiency of the LED device with integrated GaN metasurface on both side is increased more than 50%on average compared with the LED with no structure on the bottom.And the average ER measured by the integrated device is greater than 20 dB,in a wide angle range of±60°... |
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