Abdelkrim El Amili

Nonreciprocal lasing in topological cavities of arbitrary geometries

Topological lasing Resonant cavities that confine light are crucial components of lasers. Typically, these cavities are designed to high specification to get the best possible output. That, however, can limit their integration into photonic devices and optical circuits. Bahari et al. fabricated resonant cavities of arbitrary shape within a hybrid photonic crystal structure. The confinement of light to topologically protected edge states resulted in lasing at communication wavelengths. Relaxing the resonant cavity design criteria should be useful in designing photonic devices. Science, this issue p. 636 Resonant cavities of arbitrary shape can be designed to provide lasing into topically protected edge states. 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.

Experimental evidence and theoretical modeling of two-photon absorption dynamics in the reduction of intensity noise of solid-state Er:Yb lasers

A theoretical and experimental investigation of the intensity noise reduction induced by two-photon absorption in a Er,Yb:Glass laser is reported. The time response of the two-photon absorption mechanism is shown to play an important role on the behavior of the intensity noise spectrum of the laser. A model including an additional rate equation for the two-photon-absorption losses is developed and allows the experimental observations to be predicted.

Phase Noise of the Radio Frequency (RF) Beatnote Generated by a Dual-Frequency VECSEL

We analyze, both theoretically and experimentally, the phase noise of the radio frequency (RF) beatnote generated by optical mixing of two orthogonally polarized modes in an optically pumped dual-frequency vertical external cavity surface emitting laser (VECSEL). The characteristics of the RF phase noise within the frequency range of 10 kHz-50 MHz are investigated for three different nonlinear coupling strengths between the two lasing modes. In the theoretical model, we consider two different physical mechanisms responsible for the RF phase noise. In the low frequency domain (typically below 500 kHz), the dominant contribution to the RF phase noise is shown to come from the thermal fluctuations of the semiconductor active medium induced by pump intensity fluctuations. However, in the higher frequency domain (typically above 500 kHz), the main source of RF phase noise is shown to be the pump intensity fluctuations which are transferred to the intensity noises of the two lasing modes and then to the phase noise via the large Henry factor of the semiconductor gain medium. For this latter mechanism, the nonlinear coupling strength between the two lasing modes is shown to play an important role in the value of the RF phase noise. All experimental results are shown to be in good agreement with theory.

Experimental demonstration of a dual-frequency laser free from antiphase noise.

A reduction of more than 20 dB of the intensity noise at the antiphase relaxation oscillation frequency is experimentally demonstrated in a two-polarization dual-frequency solid-state laser without any optical or electronic feedback loop. Such behavior is inherently obtained by aligning the two orthogonally polarized oscillating modes with the crystallographic axes of a (100)-cut neodymium-doped yttrium aluminum garnet active medium. The antiphase noise level is shown to increase as soon as one departs from this peculiar configuration, evidencing the predominant role of the nonlinear coupling constant. This experimental demonstration opens new perspectives on the design and realization of extremely low-noise dual-frequency solid-state lasers.

Dynamic hysteresis in a coherent high-β nanolaser

The quest for an integrated light source that promises high energy efficiency and a fast modulation for high-performance photonic circuits has led to the development of room-temperature telecom-wavelength nanoscale lasers with a high spontaneous emission factor β. The coherence characterization of this type of laser using the conventional measurement of output light intensity versus input pump intensity is inherently difficult due to the diminishing kink in the measurement curve. We demonstrate that the transition from incoherent 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 peak that shrinks below and broadens above the threshold. Our photon fluctuation study, the first ever reported for this type of nanolaser, confirms the validity of this measurement technique. Additionally, we show that the width variation above the threshold results from the delayed threshold phenomenon, providing the first observation of dynamical hysteresis in a nanolaser.

Noise reduction in solid-state lasers using a SHG-based buffer reservoir.

The cancellation of resonant intensity noise, from a few kHz up to several GHz, is reported using a second-harmonic generation (SHG) buffer reservoir in a Nd:YAG solid-state laser. This approach is shown to be well suited and easily optimizable for reducing the excess noise lying at the laser relaxation oscillations as well as that originating from the beating between the lasing mode and nonlasing adjacent longitudinal modes. A thorough analysis of noise spectra of both laser and SHG signals confirms definitely that noise reduction is a consequence of a deep laser dynamics modification rather than noise evacuation mechanism.

Buffer reservoir approach for cancellation of laser resonant noises

The introduction of a buffer reservoir mechanism with optimized time-constants and cross sections in a laser system enables breaking any resonant exchange between the population inversion and photon population over an extremely wide bandwidth. The associated noise cancellation, including the excess noise at relaxation oscillations and spontaneous-signal beating, is experimentally evidenced up to 16 GHz in an Er,Yb laser comprising a GaAs two-photon absorber. Such approach is shown to preserve the laser linewidth quality and is advantageously implemented for optical distribution of frequency references.

Coupling in a dual metallo-dielectric nanolaser system

To achieve high packing density in on-chip photonic integrated circuits, subwavelength scale nanolasers that can operate without crosstalk are essential components. Metallo-dielectric nanolasers are especially suited for this type of dense integration due to their lower Joule loss and nanoscale dimensions. Although coupling between optical cavities when placed in proximity to one another has been widely reported, whether the phenomenon is induced for metal-clad cavities has not been investigated thus far. We demonstrate coupling between two metallo-dielectric nanolasers by reducing the separation between the two cavities. A split in the resonant wavelength and quality factor is observed, caused by the creation of bonding and anti-bonding supermodes. To preserve the independence of the two closely spaced cavities, the resonance of one of the cavities is detuned relative to the other, thereby preventing coupling.

In-phase and antiphase self-intensity regulated dual-frequency laser using two-photon absorption.

A 25 dB reduction of resonant intensity noise spectra is experimentally demonstrated for both the antiphase and in-phase relaxation oscillations of a dual-frequency solid-state laser operating at telecommunication wavelengths. Experimental results demonstrate that incorporation of an intracavity two-photon absorber that acts as a buffer reservoir reduces efficiently the in-phase noise contribution, while it is somewhat ineffective in lowering the antiphase noise contributions. A slight spatial separation of the two modes in the nonlinear two-photon absorber reduces the antiphase resonant intensity noise component. These experimental results provide a new approach in the design of ultra-low noise dual-frequency solid-state lasers.

Self-regulated intensity noise dual-frequency laser using the buffer reservoir approach

Dual-frequency (DF) solid-state lasers provide very interesting characteristics for application in Radar-Lidar, metrology or microwave photonics systems. Indeed, such lasers sustaining the oscillation of two cross-polarized modes with different frequencies provide stable and tunable optically carried microwave beat-notes [1, 2]. Nevertheless, solid-state DF lasers suffer from resonant excess intensity noise due to their class-B dynamics. The introduction of a slight nonlinear absorption, such as two-photon absorption (TPA), inside the cavity of a single frequency laser has proved to be a powerful solution to cancel out the excess intensity noise at the laser relaxation oscillation frequency. By acting as a buffer reservoir (BR), the nonlinear losses deeply change the dynamical behavior of the laser leading to a self-regulation of its intensity [3]. By proposing a new design intended to cancel out both in-phase and anti-phase excess noise, we tailor here the BR approach to solid-state DF lasers.