Full-span reversible space-time birefringence

TL;DR

This paper introduces a novel method to control birefringence in optical crystals by programming the spatiotemporal spectral phase of incident light, enabling continuous, broad, and rapid tuning beyond conventional limits.

Contribution

It presents a new approach for manipulating birefringence through spectral phase programming, surpassing traditional physical and external stimulus methods in tunability and speed.

Findings

Achieves over 100-fold broader birefringence tuning spectrum.

Enables continuous birefringence tuning from positive to negative values.

Operates independently of the crystal's inherent optical sign.

Abstract

Birefringence, the polarization-dependent splitting of light in anisotropic crystals, enables diverse optical phenomena and advanced functionalities such as optical communication, nonlinear optics, and quantum optics. However, conventional methods for controlling birefringence typically rely on engineering the optical crystal structure or applying external stimuli such as electric fields, mechanical stress or thermal variations, which are often constrained by limited tunability, challenges in integration with compact photonic devices or slow response time. Here, we introduce a new degree of freedom to manipulate the birefringence of light propagation in optical crystals through programming the spatiotemporal spectral phase of the incident light wave. We demonstrate this approach achieves continuous tuning of birefringence across a spectrum more than 100 times broader than that achievable with conventional birefringence tuning, spanning from positive through zero to negative values, irrespective of the crystal's optical sign and without inherent physical limitations. This unique optical behavior provides a versatile platform for investigating the complex dynamics of wave flow in anisotropic media, while the broad tunability of this space-time birefringence will spur innovations in ultrafast optical manipulation, optical computation, and quantum information processing-applications that demand rapid and flexible device reconfiguration.