Brewster-coupling-based thin film filter design for wide-angle high-efficiency phosphor emission.

In this paper, we propose a bandpass filter design method for laser activated remote phosphor (LARP) usage. This design uses the Brewster angle as the passband instead of a wavelength passband. Two advantages are found with this design. First, the transmittance at the Brewster angle is naturally 100%, which is optimal. Second, the stop band reflectance with a wide angular range is better compared to the dichroic filter in a LED-phosphor model. We design two optical thin film filter samples to enhance the extraction efficiency of YAG:Ce phosphor with the same design criteria, objective function, and optimization algorithm. With 50-layer designing, the optical losses for LARP are 23.7% and for LED-phosphor are 26.0%.

Optical thin-film filter design with Bragg pair constraint and a divide-and-conquer approach for reduction of the Brewster hole.

Bragg pairs are used as fundamental units to realize optimized thin-film structures. This method is efficient in designing for a large number of layers, such as in a bandpass filter or an edge filter with a relatively wide stopband or angular range. It adapts readily to conventional optimization methodology (such as genetic algorithms). In this paper, the method is first illustrated by application to a conventional high-pass coating on glass, using one set of Bragg pair materials. This demonstrated a 10% improvement over an alternative design technique. A second example is demonstrated using two sets of Bragg pair materials, designed with a more complex merit function, to increase the reflectance around the Brewster angle for p-polarized light. This demonstrated a 19% average reflection improvement across the stopband compared to a two-material design.

Designing large, high-efficiency, high-numerical-aperture, transmissive meta-lenses for visible light.

A metasurface lens (meta-lens) bends light using nanostructures on a flat surface. Macroscopic meta-lenses (mm- to cm-scale diameter) have been quite difficult to simulate and optimize, due to the large area, the lack of periodicity, and the billions of adjustable parameters. We describe a method for designing a large-area meta-lens that allows not only prediction of the efficiency and far-field, but also optimization of the shape and position of each individual nanostructure, with a computational cost that is almost independent of the lens size. As examples, we design three large NA = 0.94 meta-lenses: One with 79% predicted efficiency for yellow light, one with dichroic properties, and one broadband lens. All have a minimum feature size of 100nm.

Light extraction from luminescent light sources and application to monolithic ceramic phosphors.

An extension of a theorem for light extraction [Adv. Opt. Technol.2, 291 (2013)] from a higher index luminescent body (LED or phosphor) through an extracting surface into a lower index output medium is derived. The result is valid for both geometric and diffractive surface structures. Using this bound and radiation transport calculations, we show that extraction from LEDs or phosphors requires a combination of cavity effects to enhance radiance behind the extracting surface and scattering or diffraction to couple trapped total-internal-reflection modes to propagating modes. The treatment applies to macroscopic luminescent sources whose thickness exceeds the longitudinal coherence length of the luminescent radiation.