A Low Power Threshold, Ultrathin Optical Limiter Based on a Nonlinear Zone Plate

TL;DR

This paper proposes a novel ultrathin optical limiter using a nonlinear zone plate embedded with saturable absorbing materials, achieving a low threshold intensity suitable for miniaturized optical systems.

Contribution

The work introduces a theoretical and computational design of an ultrathin optical limiter with a low threshold using a nonlinear zone plate with embedded saturable absorbers, demonstrating significant improvements over existing limiters.

Findings

Device thickness of 0.5 μm

Optical limiting threshold as low as 0.45 kW/cm²

Flexible design adaptable to different wavelengths

Abstract

Ultrathin optical limiters are needed to protect light sensitive components in miniaturized optical systems. However, it has proven challenging to achieve a sufficiently low optical limiting threshold. In this work, we theoretically show that an ultrathin optical limiter with low threshold intensity can be realized using a nonlinear zone plate. The zone plate is embedded with nonlinear saturable absorbing materials that allow the device to focus low intensity light, while high intensity light is transmitted as a plane wave without a focal spot. Based on this proposed mechanism, we use the finite-difference time-domain method to computationally design a zone plate embedded with InAs quantum dots as the saturable absorbing material. The device has a thickness of just 0.5 $\mu m$ and exhibits good optical limiting behavior with a threshold intensity as low as 0.45 kW/$cm^2$, which is several orders of magnitude lower than current ultrathin flat-optics-based optical limiters. This design can be optimized for different operating wavelengths and threshold intensities by using different saturable absorbing materials. Additionally, the diameter and focal length of the nonlinear zone plate can be easily adjusted to fit different systems and applications. Due to its flexible design, low power threshold, and ultrathin thickness, this optical limiting concept may be promising for application in miniaturized optical systems.