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Photonics Crystal LEDs - an introduction

Light Emitting Diodes (LEDs) have long been known for their compact bright light, robustness, environmental friendliness and long lifetime. The market and applications for LEDs has been growing significantly in the last couple of decades where many barriers in efficiency and packaging have been broken. Applications in high-brightness LEDs currently cover a diverse range from mobile phones and automotives to display backlighting and traffic signalling.

Dramatic growth in the sales of LEDs is expected once the overall light efficiency of the LED approaches that of fluorescent lighting and the vast general illumination market is penetrated.
The cost of LEDs is currently prohibitive for many applications mainly due to the packaging costs associated with the modification of the light emission profile to suit the application as well as heat management.

Photonic Crystals and LEDs

One method of increasing the light extraction efficiency from a surface emitting LED is by the use of periodic patterning of the diode surface . Early Photonic Crystal patterned LED structures of this type have been shown to increase the light extraction efficiency by several times [Erchak, A. A. et al. “Enhanced coupling to vertical radiation using a 2D Photonic Crystal in a semiconductor LED”, Appl. Phys. Lett. 78, no. 5, 2001, Pg 563].

Photonic Quasicrystals and LEDs

 

 SEM micrograph of a high order symmetry Pinwheel Photonic Quasicrystal structure defined using a selection of tiling rules highlighting the complex non-periodic orientation of the pattern.

As well as increased light extraction efficiency extra benefits such as tailored LED light emission profiles can be achieved by the use of Photonic Quasicrystal LED patterned structures. Quasicrystal patterns are precisely defined at a small scale, but appear to lack order when examined on a larger scale.  Precise tiling rules are employed to arrange the patterns across the surface allowing the high symmetry nature of the quasicrystals to form bespoke far-field emission profiles.

Mesophotonics now offers LED manufacturers a comprehensive design service for complex photonic crystal structures for enhancing LED emission.  Based on over 10 year experience in the design of photonic crystal structures especially those based on quasicrystals, Mesophotonics is also able to offer licenses to its extensive IP portfolio in this area.

Further information regarding the incorporation of photonic quasicrystals into LEDs can be found here