The Fiber Optic Center (FOC), an international distributor of fiber optic components, equipment and supplies, has introduced a “High Refractive Index Coating”, AngstromLink AL-2264.
The performance of many solid-state devices including emissive displays, optical sensors, integrated optical circuits and LEDs can be improved by applying a transparent high refractive index coating.
According to FOC, the product, AL-2264, is an optical polymer dissolved in an evaporative solvent, can be applied by simple methods, i.e. dip, spin coating, drawdown, printing, etc. Upon drying it creates a hard, durable, polymer coating with a refractive index of 1.64. This polymer contains no metals, and the product contains no nanoparticles. The standard concentration leaves behind an approximately 20 μm layer coating thickness (using a single dip coating process). Coating thickness is easily reduced by diluting the standard concentration with the compatible solvent. The solvent is easily removed by baking at 100°C for 15 minutes.
Optically clear, high refractive index coatings can be used to improve the performance of light gathering/dispersing devices. Many solid state optical devices, i.e. imaging/optical sensors, emissive displays, LEDs, are made of light emitting semiconductors with significantly higher refractive indices (>2) than air (1.0). Light is partially reflected when it encounters a sudden difference of refractive index. Light transmission at such boundaries is improved with a layer of an intermediate refractive index material, thus improving the optical efficiency of the device – effectively raising the numerical aperture (NA) of the optical system.
For semiconductors and air, that desirable refractive index is in the >1.6 range. Additionally, in this case, the ‘air’ side of the coating directly contacts the environment and must be protective: hardness and durability are required; chemical resistance is a plus.