Intensity noise correlations in a two-frequency VECSEL

Modeling the Lamb mode-coupling constant of quantum well semiconductor lasers

We theoretically compute the coupling constant C between two emission modes of an extended cavity laser with a multiple quantum-well active layer. We use an optimized Monte Carlo model based on the Markov chain that describes the elementary events of carriers and photons over time. This model allows us to evaluate the influence on C of the transition from a class A laser to a class B laser and illustrates that the best stability of dual-mode lasers is obtained with the former. In addition, an extension of the model makes it possible to evaluate the influence of different mode profiles in the cavity as well as the spatial diffusion of the carriers and/or the inhomogeneity of the temperature. These results are in very good agreement with previous experimental results, showing the independence of C with respect to the beating frequency and its evolution versus the spatial mode splitting in the gain medium.

Direct measurement of the spectral dependence of Lamb coupling constant in a dual frequency quantum well-based VECSEL

Spectral dependence of Lamb coupling constant C is experimentally investigated in an InGaAlAs Quantum Wells active medium. An Optically-Pumped Vertical-External-Cavity Surface-Emitting Laser is designed to sustain the oscillation of two orthogonally polarized modes sharing the same active region while separated in the rest of the cavity. This laser design enables to tune independently the two wavelengths and, at the same time, to apply differential losses in order to extract without any extrapolation the actual coupling constant. C is found to be almost constant and equal to 0.84 ± 0.02 for frequency differences between the two eigenmodes ranging from 45 GHz up to 1.35 THz.

Non-equilibrium dynamics in the dual-wavelength operation of vertical external-cavity surface-emitting lasers

Microscopic many-body theory coupled with Maxwell's equation is used to study dual-wavelength operation in vertical external-cavity surface-emitting lasers. The intrinsically dynamic nature of coexisting emission wavelengths in semiconductor lasers is associated with characteristic non-equilibrium carrier dynamics, which causes significant deformations of the quasi-equilibrium gain and carrier inversion. Extended numerical simulations are employed to efficiently investigate the parameter space to identify the regime for dual-wavelength operation. Using a frequency selective intracavity etalon, two families of modes are stabilized with dynamical interchange of the strongest emission peaks. For this operation mode, anti-correlated intensity noise is observed in agreement with the experiment. A method using effective frequency selective filtering is suggested for stabilization of genuine dual-wavelength output.

Ultra-low noise dual-frequency VECSEL at telecom wavelength using fully correlated pumping

An ultra-low intensity and beatnote phase noise dual-frequency vertical-external-cavity surface-emitting laser is built at telecom wavelength. The pump laser is realized by polarization combining two single-mode fibered laser diodes in a single-mode fiber, leading to a 100% in-phase correlation of the pump noises for the two modes. The relative intensity noise is lower than -140  dB/Hz, and the beatnote phase noise is suppressed by 30 dB, getting close to the spontaneous emission limit. The role of the imperfect cancellation of the thermal effect resulting from unbalanced pumping of the two modes in the residual phase noise is evidenced.

Independence between intensity and phase noise of superluminescent diodes in the low-frequency domain

We theoretically and experimentally demonstrate a method for measuring the phase and intensity noise and their correlation in superluminescent diodes. A Michelson interferometer containing strongly unbalanced paths has been developed to measure the noise. By the spectral analysis of the photocurrents in detectors, the intensity noise is about twice the value of the phase noise in the superluminescent diode. The more interesting result we obtained is the experimental evidence that the intensity noise and the phase noise are mutually independent. The correlation coefficient of the intensity noise and the phase noise fluctuates between -0.08 and 0, which shows scarcely any sign of amplitude-phase noise correlation. The results offer a basic premise for the analysis of broadband light sources.

Laser Refrigeration of Ytterbium-Doped Sodium-Yttrium-Fluoride Nanowires

Sodium yttrium fluoride (β-NaYF₄ ) nanowires (NWs) with a hexagonal crystal structure are synthesized using a low-cost hydrothermal process and are shown to undergo laser refrigeration based on an upconversion process leading to anti-Stokes (blueshifted) photoluminescence. Single-beam laser trapping combined with forward light scattering is used to investigate cryophotonic laser refrigeration of individual NWs through analysis of their local Brownian dynamics.

Reduction of residual excess noise in class-A lasers using two-photon absorption

We demonstrate experimentally a significant reduction of the remaining excess intensity noise in a class-A semi-conductor laser. This is obtained by inserting into the laser cavity a buffer reservoir mechanism based on two-photon absorption in GaAs. The excess noise peaks at the laser-free spectral range, induced by the beating between the lasing mode and the amplified spontaneous emission in the adjacent non-oscillating modes, is reduced by 20 dB, while preserving the class-A dynamical behavior of the laser cavity.

Class-A dual-frequency VECSEL at telecom wavelength

We report class-A dual-frequency oscillation at 1.55 μm in a vertical external cavity surface emitting laser with more than 100 mW optical power. The two orthogonal linear polarizations of different frequencies oscillate simultaneously as their nonlinear coupling is reduced below unity by spatially separating them inside the active medium. The spectral behavior of the radio frequency beatnote obtained by optically mixing two polarizations and the phase noise of the beatnote have been explored for different coupling strengths between the lasing modes.