Order of Magnitude Improvement in Feedback Stability of Nanolasers by Inclusion of a Fano Resonance-Based Mirror

Due to the extraordinary sensitivity of semiconductor lasers to external optical feedback [1,2], optical isolators are necessary for stable operation in most applications. This is a critical issue for the use of semiconductor nanolasers as light sources in photonic integrated circuits for e.g. on-chip optical signal processing, where optical isolators are notoriously difficult to incorporate, so recently a number of ideas for solutions to this problem have been proposed [3,4]. Here we demonstrate that the recently realised [5] photonic crystal Fano laser (FL) may intrinsically be exceedingly stable towards external feedback, improving upon conventional nanolasers by orders of magnitude. Figure 1 (top right) shows a schematic of the Fano laser, in which one laser mirror is realised by Fano interference between a continuum of modes in a line-defect waveguide and a discrete mode in a nearby side-coupled nanocavity. This interference yields a narrow, highly dispersive reflection, which, when combined with a termination of the waveguide at one end, yields a laser cavity. The Fano laser showed a number of remarkable properties, including pinned single-mode lasing and the first demonstration of self-pulsing in a microscopic laser [5]. In this work we study the behaviour of the Fano laser when subjected to external optical feedback, using a generalised version of the conventional Lang-Kobayashi model which also accounts for the field stored in the nanocavity, and compare the results to those of a conventional Fabry-Perot (FP) laser.