The application of the microstructured metallic grating to light emission extraction

Abstract

Microstructured metallic gratings can be used to enhance the light emission efficiency of LEDs, and the spectral radiation properties of the LEDs vary with the different metallic materials used, leading to variation of the light emission enhancement at the same wavelength for different metallic grating materials. In this paper, the finite difference time domain (FDTD) method has been used to investigate the light emission extraction enhancement of LEDs in which gratings with different metallic materials have been applied. Through analysis of the permittivity of the metals and the quality factors of the surface plasmons (SPs), we concluded that the larger the plasma frequency obtained for the metallic interband transition, then the more suitable the metals are for light emission extraction of photons with relatively short wavelengths. This is because of the abundance of free electrons in the metals with large plasma frequencies. We also found that the wavelength-dependent trends of the extraction enhancement resulting from the scattering mechanism for different metallic materials are similar to each other. For SP-induced enhancement, either the enhancement peak position or the peak value changes significantly with the different metals.

Experiment and Simulation of a Selective Subwavelength Filter with a Low Index Contrast

“…Such gratings have led to the developments of selective optical elements [6,7,8,9,10,11,12] due to the elimination of non-zero order diffraction modes with increased coupling efficiency. Subwavelength gratings have been successfully applied to achieve angular selectivity both in the near infrared [13] and mid-infrared domains [14,15] while metallic sub-wavelength gratings have been used to realize polarizers and phase shifters in a wide range of frequency domains [16,17,18,19,20]. Due to losses in metals, recent interest has been focused on developing dielectric sub-wavelength gratings with high dielectric constant surrounded by vacuum [21] commonly known as high contrast gratings (HCG).…”

“…In fact, the concept of nanoimprinting large scale photonic structures has already been proposed for photon managements in solar cells [26]. The concept of photon management is widely discussed in spontaneous downconversion processes for augmented photosynthesis [27] and enhancing LED efficiency [19,28]. These applications typically require both angular and wavelength selectivity.…”