Geometrical optics in thin film light guides

Area of Science:

• Optics
• Materials Science
• Photonics

Background:

• Thin films with high refractive index on lower index substrates act as two-dimensional transmission media for light.
• Geometrical optics can describe light propagation using an effective refractive index (N) dependent on film thickness.

Purpose of the Study:

• To investigate the optical phenomena of refraction and total reflection in thin film light guides at steps of varying film thickness.
• To demonstrate experimental evidence of these phenomena using Zinc Sulfide (ZnS) films on glass.
• To explore applications of these thin film guides as optical components like prisms and lenses for guided light.

Main Methods:

• Utilizing geometrical optics to model light propagation and effective refractive index (N).
• Conducting experimental demonstrations with Zinc Sulfide (ZnS) thin films deposited on glass substrates.
• Analyzing light behavior at thickness-step discontinuities within the thin film guides.

Main Results:

• Observed and explained light refraction and total reflection at film thickness steps, consistent with Snell's law.
• Demonstrated the functionality of thin film prisms and lenses for manipulating guided light beams.
• Showcased the ability to achieve significant positive or negative wavelength dispersion, including achromatic refraction, by controlling film thicknesses.

Conclusions:

• Thin film light guides offer tunable optical properties based on film thickness.
• These guides can be engineered into functional optical elements for guided light.
• Precise control over film thickness allows for tailored refractive and dispersive characteristics, opening avenues for advanced optical devices.