Design of superperiodic photonic-crystal light-emitting plates with highly directive luminance characteristics

Double-Grating Displacement Structure for Improving the Light Extraction Efficiency of LEDs

“…These improvements primarily include changing the geometric shape of the chips, reducing the duration of total internal reflection in the chips, and decreasing light energy losses. The methods generally applied in realizing such enhancements are using the inverted pyramid structure [ 8 , 9 ], performing surface roughening [ 10 ], constructing a mirror with Bragg grating reflection [ 11 ], and creating a two-dimensional photonic crystal structure on the surface of GaN [ 12 – 15 ]. Using the characteristic of surface plasmons (SPs) to enhance the light extraction efficiency of LEDs has recently become a research focus [ 16 ].…”

Thermodynamics of Light Extraction from Luminescent Materials

“…While great progress has been made in solving the light extraction problem for SSL using various approaches both commercially and in the literature, a general theoretical understanding still seems lacking. In particular, several authors [5][6][7] have pointed out, in various degrees of generality, that surface structures (including nano-optic structures) have strong limits for transmission of radiation. These limits depend on the ratio of the refractive indexes of the output medium n 1 < n 2 , the refractive index of the input medium and, more generally, on the ratios of the combined angular-area phase spaces, or étendues.…”

“…6, the results are derived using simple thermodynamic arguments that are independent of whether a particular surface is effectively in the geometric optic regime or relies on wave-optic effects, and therefore apply to the variety of photonic and geometric optic structures that have appeared in the literature. [8][9][10][11][12][13] This includes 2D nanostructures, for example, to restrict the angular emission cone by selective reflection and transmission from ceramic phosphor converters. [14][15][16] Thermodynamics approaches to optical limits [17][18][19][20][21][22] are useful because they are closely tied to phase-space concepts which ultimately place strict limits on propagation of electromagnetic (EM) radiation in various media.…”

Design and simulation of superperiodic photonic-crystal light emitting diodes with highly directive luminance characteristics

“…1. This design is referred to as a 'super-periodic photonic crystal (super-PhC) with monocell defects' based on the principle of far-field diffraction from the double-periodic structure whose radiation mode, rather than the resonance mode, was tailored to give the desired luminance pattern [6].The design specifically aims at two simultaneous effects: 1) enhancing the light-extraction efficiency, and 2) tailoring the divergence angle of the radiated beam. The first effect has been investigated previously based on numerical simulations [7] and experimental demonstrations by employing some geometrical features of the PhC theory.…”

“…1. This design is referred to as a 'super-periodic photonic crystal (super-PhC) with monocell defects' based on the principle of far-field diffraction from the double-periodic structure whose radiation mode, rather than the resonance mode, was tailored to give the desired luminance pattern [6].…”