A passive bias-free ultrabroadband optical isolator based on unidirectional self-induced transparency

TL;DR

This paper proposes a passive, bias-free ultrabroadband optical isolator using unidirectional self-induced transparency, enabling broadband nonreciprocal transmission for femtosecond laser pulses without external magnetic fields.

Contribution

It introduces a novel mechanism of unidirectional self-induced transparency for all-optical isolation, achieving high contrast and ultrabroad bandwidth without gain or external bias.

Findings

Achieves ~14.3 dB transmission contrast for femtosecond pulses.

Provides an ultrabroad bandwidth of 200 THz.

Comparable bandwidth to magneto-optical isolators.

Abstract

Achieving a broadband nonreciprocal device without gain and any external bias is very challenging and highly desirable for modern photonic technologies and quantum networks. Here, we theoretically propose a passive and bias-free all-optical isolator for a femtosecond laser pulse by exploiting a new mechanism of unidirectional self-induced transparency, obtained with a nonlinear medium followed by a normal absorbing medium at one side. The transmission contrast between the forward and backward directions can reach ~14.3 dB for a 2\pi 5 fs laser pulse, implying isolation of a signal with an ultrabroad bandwidth of 200 THz. The 20 dB bandwidth is about 57 nm, already comparable with a magneto-optical isolator. This cavity-free optical isolator may pave the way to integrated nonmagnetic isolation of ultrashort laser pulses.