Artificial distributed-index media fabricated by zero-order gratings

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Zero-order gratings feature periods significantly smaller than the wavelength of incident light.
• These gratings primarily allow the zero diffraction order (directly transmitted or reflected light) to propagate, behaving like a homogeneous material.
• The effective refractive index of such gratings can be tuned by altering their material composition or duty cycle.

Purpose of the Study:

• To propose and demonstrate the concept of distributed-index elements based on artificial materials.
• To explore the tunability of effective refractive index in zero-order gratings by varying the duty cycle.
• To validate the physical principle using a water wave analogy.

Main Methods:

• Utilizing zero-order gratings with sub-wavelength periods.
• Modulating the grating's duty cycle to control its effective refractive index.
• Employing a water wave system to physically demonstrate the concept of distributed index.

Main Results:

• Demonstrated that zero-order gratings can mimic homogeneous materials with an effective refractive index.
• Showcased that varying the duty cycle allows for continuous control over the effective refractive index.
• Successfully illustrated the principle of distributed index using water waves, confirming the theoretical basis.

Conclusions:

• Zero-order gratings with tunable duty cycles can be engineered as artificial materials with distributed refractive indices.
• This principle enables the design of novel distributed-index optical elements.
• The water wave analogy provides a clear physical intuition for the behavior of these artificial materials.