Frequency Comb Generation by Bloch Gain Induced Giant Kerr Nonlinearity.

Nikola Opačak,Johannes Hillbrand,Sandro Dal Cin,Benedikt Schwarz

doi:10.1103/physrevlett.127.093902

Abstract

Optical nonlinearities are known to coherently couple amplitude and phase of light, which can result in the formation of periodic waveforms. Such waveforms are referred to as optical frequency combs. Here we show that Bloch gain-a nonclassical phenomenon that was first predicted in the 1930s-can play an essential role in comb formation. We develop a self-consistent theoretical model that considers all aspects of comb dynamics: band structure, electron transport, and cavity dynamics. In quantum cascade lasers, Bloch gain gives rise to a giant Kerr nonlinearity, which enables frequency modulated combs and serves as the physical origin of the linewidth enhancement factor. Bloch gain also triggers the formation of solitonlike structures in ring resonators, paving the way toward electrically driven Kerr combs.

Highlights

Bloch and Zener predicted charge oscillations in a periodic potential under a constant electric field in the 1930s [1,2], a phenomenon which is referred to as Bloch oscillations
The Green’s function [15] formalisms. They generalized the concept of the Bloch gain and showed that it can appear between any two states in semiconductor heterostructures, such as quantum cascade lasers (QCLs)
We show that a dominant Bloch gain contribution is present in any operating QCL and causes a giant Kerr nonlinearity at the laser wavelength

Summary

Introduction

Bloch and Zener predicted charge oscillations in a periodic potential under a constant electric field in the 1930s [1,2], a phenomenon which is referred to as Bloch oscillations. We show that a dominant Bloch gain contribution is present in any operating QCL and causes a giant Kerr nonlinearity at the laser wavelength. The induced nonlinearity plays an essential role in the laser cavity dynamics as it is a requirement for self-starting optical frequency combs [22].

Results

Conclusion