Resonant cavities are essential building blocks governing many wave-based phenomena, but their geometry and reciprocity fundamentally limit the integration of optical devices. We report, at telecommunication wavelengths, geometry-independent and integrated nonreciprocal topological cavities that couple stimulated emission from one-way photonic edge states to a selected waveguide output with an isolation ratio in excess of 10 decibels. Nonreciprocity originates from unidirectional edge states at the boundary between photonic structures with distinct topological invariants. Our experimental demonstration of lasing from topological cavities provides the opportunity to develop complex topological circuitry of arbitrary geometries for the integrated and robust generation and transport of photons in classical and quantum regimes.

We present an experimental and theoretical study of the intensity noise correlation between the two orthogonally polarized modes in a dual frequency Vertical External Cavity Surface Emitting Laser (VECSEL). The dependence of the noise correlation spectra on the non-linear coupling between the two orthogonally polarized modes is put into evidence. Our results show that for small coupling the noise correlation amplitude and phase spectra remain nearly flat (around -6 dB and 0° respectively) within the frequency range of our interest (from 100 kHz to 100 MHz). But for higher values of the coupling constant the low frequency behaviors (below 1-2 MHz) of the correlation amplitude and phase spectra are drastically changed, whereas above this cut-off frequency (1-2 MHz) the correlation spectra are almost independent of coupling strength. The theoretical model is based on the assumptions that the only source of noise in the frequency range of our interest for the two modes are pump noises, which are white noises of equal amplitude but partially correlated.

The quest for an integrated light source that promises high energy efficiency and fast modulation for high-performance photonic circuits has led to the development of roomtemperature telecom-wavelength nanoscale laser with high spontaneous emission factors, β. The coherence characterization of this type of lasers is inherently difficult with the conventional measurement of output light intensity versus input pump intensity due to the diminishing kink in the measurement curve. We demonstrate the transition from chaotic to coherent emission of a high-β pulse-pump metallo-dielectric nanolaser can be determined by examining the width of a second order intensity correlation, ) ( 2  g , peak, which shrinks below and broadens above threshold. Photon fluctuation study, first one ever reported for this type of nanolaser, confirms the validity of this measurement technique. Additionally, we show that the width variation above threshold results from the delayed threshold phenomenon, providing the first indirect observation of dynamical hysteresis in a nanolaser. Main Text:Nanocavity lasers with high spontaneous emission factors, β, have attracted considerable attention in the past decade in light of their technical applications ranging from optical interconnects (1), bio-sensing (2), chemical detection (3) and nonlinear optical microscopy (4) to fundamental research on thresholdless lasers (5-8) and cavity quantum electrodynamics (9-10).Theoretically a high-β nanolaser is more energy efficient as most spontaneous emission is funneled into the lasing mode, resulting in an extremely low lasing threshold (5). Additionally,

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