Microstructured void gratings for outcoupling deep-trap guided modes

Abstract

Breaking the total internal reflection far above a critical angle (i.e., outcoupling deep-trap guided modes) can dramatically improve existing light-emitting devices. Here, we report a deep-trap guided modes outcoupler using densely arranged microstructured hollow cavities. Measurements of the leaky mode dispersions of hollow-cavity gratings accurately quantify the wavelength-dependent outcoupling strength above a critical angle, which is progressively improved over the full visible spectrum by increasing the packing density. Comparing hollow- and filled-cavity gratings, which have identical morphologies except for their inner materials (void vs. solid sapphire), reveals the effectiveness of using the hollow-cavity grating to outcouple deep-trap guided modes, which results from its enhanced transmittance at near-horizontal incidence. Scattering analysis shows that the outcoupling characteristics of a cavity array are dictated by the forward scattering characteristics of their individual cavities, suggesting the importance of a rationally designed single cavity. We believe that a hollow-cavity array tailored for different structures and spectra will lead to a technological breakthrough in any type of light-emitting device.

Engineered Unidirectional Scattering in Metal Wire Networks for Ultrahigh Glass-Like Transparency

“…Figure a shows typical scattering distributions of a submicron (diameter, D = 800 nm), hemicylindrical Ag wire for a normally incident plane wave (λ = 530 nm) with transverse electric (TE) or transverse magnetic (TM) polarization obtained using finite-difference time-domain (FDTD) simulation (see Methods). The bare Ag wire diffused the incident light into all directions, thereby exhibiting wide scattering distribution in both forward and backward planes. Such strong scattering in metal wires significantly increases the haziness of the metal-wire embedded dielectric films, ,, limiting the extension of their applications to display devices.…”

“…Metal nanostructures are frequently used to improve the outcoupling efficiency of light-emitting diodes due to their strong scattering characteristics that help extract light confined by total internal reflection (TIR) into an ambient medium. Therefore, measurements of transmittance under TIR conditions offer a legitimate way to evaluate the level of scattering (particularly, forward scattering) in metal nanostructures. , As metal nanostructures scatter incoming light more actively to the forward plane, there is a greater likelihood of extracting TIR confined light. To demonstrate this, we developed a prism-coupled transmittance measurement setup in which a supercontinuum laser was incident on a sample through the prism, as shown in Figure a.…”

“…Therefore, measurements of transmittance under TIR conditions offer a legitimate way to evaluate the level of scattering (particularly, forward scattering) in metal nanostructures. 25,30 As metal nanostructures scatter incoming light more actively to the forward plane, there is a greater likelihood of extracting TIR confined light. To demonstrate this, we developed a prism-coupled transmittance measurement setup in which a supercontinuum laser was incident on a sample through the prism, as shown in Figure 4a.…”

High-index-contrast photonic structures: a versatile platform for photon manipulation

“…An individual HC or an array of HCs can be exploited as a localised optical antenna 4 , a low-loss resonator 5 or a strong-diffraction grating 6 , depending on the scale of the HC relative to the working spectrum. The range of applications can be categorised by function: antireflective films for lenses and solar cells 7 , strong scattering particles for colouration 8 , strong diffraction gratings for light-emitting diodes (LEDs) 9 and high-reflectivity radiative coolers 5 and mirrors for lasers 10 (Fig.…”

“… a HCs with a variety of optical functionalities: (left) antireflection 7 , (middle) scattering/diffraction 6 , 8 and (right) reflection 10 , 11 . b Scattering efficiency spectra of (left) hollow ( n = 1.0) and (right) silica ( n = 1.5) nanoparticle as a function of D of the nanoparticle.…”