Spin injection enhancement in CW VECSEL at room temperature using push-pull optical pumping.

We report the enhancement of spin injection efficiency in an external-cavity VCSEL based on a non-resonant pumping coupled with a polarized optical resonant illumination. This double pumping scheme allows both the injection of spin polarized electrons in the conduction band and the selection of the spin orientation for the electron/hole recombination laser process. Experimentally, a flip of the polarization state of the laser is achieved with an ellipticity of +31° (spin down) and -33° (spin up), so an increase of about 50% of the ellipticity is achieved in comparison to an optical non-resonant pumping alone.

Electrically pumped shot-noise limited class A VECSEL at telecom wavelength.

Class A shot-noise limited operation is achieved in an electrically pumped vertical external cavity surface emitting laser (VECSEL), opening the way for integration of such peculiar noiseless laser oscillation in applications where low power consumption and footprint are mandatory. The quantum well active medium is grown on an InP substrate to enable laser oscillation at telecom wavelengths. Single frequency class A operation is obtained by proper optimization of the cavity dimensions, ensuring at the same time a sufficiently long and high-finesse cavity without any intracavity filtering components. The laser design constraints due to electrical pumping are discussed as compared to optical pumping. The intensity noise spectrum of this laser is shown to be shot-noise limited, leading to a relative intensity noise of $-160\;{\rm dB/Hz}$ for 3.1 mA detected photocurrent.

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.

Orthogonality-breaking polarimetric sensing modalities for selective polarization imaging.

Polarimetric sensing/imaging by orthogonality breaking is a microwave-photonics-inspired optical remote sensing technique that was shown to be particularly suited to characterize dichroic samples in a direct and single-shot way. In this work, we expand the scope of this approach in order to gain sensitivity on birefringent and/or purely depolarizing materials by respectively introducing a circular or a linear polarization analyzer in the detection module. We experimentally validate the interest of these two new, to the best of our knowledge, induced orthogonality-breaking modalities in the context of infrared active imaging.

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.

Analytical modeling of dual-frequency solid-state lasers including a buffer reservoir for noise cancellation.

A theoretical model describing the dynamical behavior of dual-frequency solid-state lasers including a buffer reservoir (BR) is presented. It relies on the introduction of two additional coupled rate equations describing the interaction of the two laser modes with the BR. The relative intensity noise is derived by taking into account the fluctuations of both pump intensity and intra-cavity photons. This modelling approach accurately predicts the experimental noise spectra obtained with an Er,Yb:glass dual-frequency laser implemented in different cavity architecture configurations. The mode coupling strength in the BR is shown to rule the reduction efficiency of the excess noise lying at the in-phase and anti-phase frequencies.

VSPIN: a new model relying on the vectorial description of the laser field for predicting the polarization dynamics of spin-injected V(e)CSELs.

A new vectorial model (VSPIN) based on the Jones formalism is proposed to describe the polarization dynamics of spin injected V(e)CSELs. This general modelling framework accounts for spin injection effects as a gain circular dichroism in the active medium and provides guidelines for developing functional spin-controlled lasers. We investigate the detrimental role of phase anisotropy on polarization switching and show that it can be overcome by preparing the laser cavity to achieve efficient polarization switching under low effective spin injection. The VSPIN model predictions have been confirmed experimentally and explain the polarization behavior of spin-VCSELs reported in the literature.

Liquid crystal-based tunable photodetector operating in the telecom C-band.

Liquid crystal (LC) microcells monolithically integrated on the surface of InGaAs based photodiodes (PDs) are demonstrated. These LC microcells acting as tunable Fabry-Perot filters exhibit a wavelength tunability of more than 100 nm around 1550 nm with less than 10V applied voltage. Using a tunable laser operating in the S and C bands, photocurrent measurements are performed. On a 70 nm tuning range covered with a driving voltage lower than 7V, the average sensitivity for the PD is 0.4 A/W and the spectral linewidth of the LC filter remains constant, showing a FWHM of 1.5 nm. Finally, the emission spectrum from an Er-doped fiber is acquired by using this tunable PD as a micro-spectrometer.

Intensity noise cancellation in solid-state laser at 1.5 µm using SHG depletion as a buffer reservoir.

An absorption mechanism based on second-harmonic generation (SHG) is successfully implemented as a buffer reservoir in a solid-state Er,Yb:Glass laser emitting at the telecom wavelength. We show that a slight absorption mechanism based on SHG rate conversion of 0.016% using a beta barium borate crystal enables the canceling out of the excess intensity noise at the relaxation oscillation frequency, i.e., 35 dB reduction, as well as canceling the amplified spontaneous emission beating at the free spectral range resonances of the laser lying in the gigahertz range. Laser robustness is discussed.

Class-A operation of an optically-pumped 1.6 µm-emitting quantum dash-based vertical-external-cavity surface-emitting laser on InP.

A continuous-wave 1.6 µm-emitting InAs Quantum Dash-based Optically-Pumped Vertical-External-Cavity Surface-Emitting Laser on InP is demonstrated. The laser emits in the L-band with a stable linear polarization. Up to 163 mW output power has been obtained in multi-transverse mode regime. Single-frequency regime is achieved in the 1609-1622 nm range, with an estimated linewidth of 22 kHz in a 49 mm cavity, and a maximum emitted power of 7.9 mW at 1611 nm. In such conditions, the laser exhibits a Class-A behavior, with a cut-off frequency of 800 kHz and a shot-noise floor of -158 dB/Hz for 2 mA of detected photocurrent.

Generation of a coherent light beam with precise and fast dynamic control of the state and degree of polarization.

Recent developments of polarized light sources with tunable state and degree of polarization (SOP and DOP) inherently provide a temporally incoherent beam, which makes them unsuitable for applications like interferometry. We present a method for generating a coherent beam with full, precise, and independent control of the SOP and DOP. Our approach is based on an imbalanced dual-frequency dual-polarization light source. We demonstrate that it offers three different working regimes, respectively providing perfectly depolarized light, DOP modulated light, or fully polarized light with a deterministic SOP trajectory. A simple implementation of this versatile approach is described and experimentally validated.

Free-space active polarimetric imager operating at 1.55 µm by orthogonality breaking sensing.

We report the design and optimization of an active polarimetric imaging demonstrator operating at 1.55 µm that is based on the orthogonality breaking technique. It relies on the use of a fibered dual-frequency dual-polarization source raster scanned over the scene. A dedicated opto-electronic detection chain is developed to demodulate the optical signal backscattered at each location of the scene in real time, providing multivariate polarimetric image data in one single scan with limited acquisition time. We experimentally show on a homemade scene that contrast maps can be built to reveal hidden dichroic objects over a depolarizing background, as well as their orientation. Finally, experiments through air turbulence illustrate the benefit of such an imaging architecture over standard polarimetric techniques requiring multiple image acquisitions.

Compensation of the residual linear anisotropy of phase in a vertical-external-cavity-surface-emitting laser for spin injection.

We report on the compensation of the linear anisotropy of phase in a vertical-external-cavity surface-emitting laser from 21 to 0.5 mrad with an intracavity PLZT electro-optical ceramic. It allows dynamic and accurate control of the laser linear anisotropy, as well as dynamic control of the laser polarization eigenstates. At the birefringence compensation point, we observe an elliptical polarization state with 41° of ellipticity, rotated from its initial position of 32°. The experimental observations are in close agreement with the theoretical predictions. Finally, we are able to demonstrate control of the polarization state with spin injection.

Orthogonality-breaking sensing model based on the instantaneous Stokes vector and the Mueller calculus: erratum.

For J. Opt. Soc. Am. A33, 434 (2016)JOAOD60740-323210.1364/JOSAA.33.000434, a corrected version of Eq. (9) is provided owing to typographical errors in the original article. The original full article text and calculations are unchanged. Another typo is corrected in Eq. (A5) of Appendix A.

Theoretical optimal modulation frequencies for scattering parameter estimation and ballistic photon filtering in diffusing media.

The efficiency of using intensity modulated light for the estimation of scattering properties of a turbid medium and for ballistic photon discrimination is theoretically quantified in this article. Using the diffusion model for modulated photon transport and considering a noisy quadrature demodulation scheme, the minimum-variance bounds on estimation of parameters of interest are analytically derived and analyzed. The existence of a variance-minimizing optimal modulation frequency is shown and its evolution with the properties of the intervening medium is derived and studied. Furthermore, a metric is defined to quantify the efficiency of ballistic photon filtering which may be sought when imaging through turbid media. The analytical derivation of this metric shows that the minimum modulation frequency required to attain significant ballistic discrimination depends only on the reduced scattering coefficient of the medium in a linear fashion for a highly scattering medium.

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.

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.

Mode-hopping suppression in long Brillouin fiber laser with non-resonant pumping.

We propose a reliable method for stabilizing narrow linewidth Brillouin fiber lasers with non-resonant pumping. Mode-hopping is suppressed by means of a phase-locked loop that locks the pump-Stokes detuning to a local radio-frequency (RF) oscillator. Stable single-mode operation of a 110-m-long Brillouin fiber laser oscillating at 1.55 µm is demonstrated for several hours. The beat note between two independent Stokes waves presents a phase noise level of -60 dBc/Hz at 100 Hz with a -20 dB/decade slope, and a FWHM linewidth lower than 50 Hz.

Orthogonality-breaking sensing model based on the instantaneous Stokes vector and the Mueller calculus.

Polarimetric sensing by orthogonality breaking has been recently proposed as an alternative technique for performing direct and fast polarimetric measurements using a specific dual-frequency-dual-polarization (DFDP) source. Based on the instantaneous Stokes-Mueller formalism to describe the high-frequency evolution of the DFDP beam intensity, we thoroughly analyze the interaction of such a beam with birefringent, dichroic, and depolarizing samples. This allows us to confirm that orthogonality breaking is produced by the sample diattenuation, whereas this technique is immune to both birefringence and diagonal depolarization. We further analyze the robustness of this technique when polarimetric sensing is performed through a birefringent waveguide, and the optimal DFDP source configuration for fiber-based endoscopic measurements is subsequently identified. Finally, we consider a stochastic depolarization model based on an ensemble of random linear diattenuators, which makes it possible to understand the progressive vanishing of the detected orthogonality-breaking signal as the spatial heterogeneity of the sample increases, thus confirming the insensitivity of this method to diagonal depolarization. The fact that the orthogonality-breaking signal is exclusively due to the sample dichroism is an advantageous feature for the precise decoupled characterization of such an anisotropic parameter in samples showing several simultaneous effects.

Orthogonality breaking through few-mode optical fiber.

Polarization sensing and imaging through optical fibers is a technological challenge motivated by promising applications for in vivo, in situ polarimetric endoscopy for biomedical diagnosis. Among the recent approaches proposed to solve this issue, the depolarization/dichroism sensing by polarization orthogonality breaking (DSOB) technique was shown to perform remotely through single-mode optical fibers for depolarization/diattenuation measurements. In this article, we investigate the applicability of such a technique in slightly multimode waveguides. Through theoretical modeling and numerical simulations, we evidence the conditions required for the polarization orthogonality to be preserved after propagation in a few-mode fiber, notably in terms of detection geometry of the spatial modes. Original experiments realized in few-mode fibers both in transmission and reflection configurations are also reported and validate the theoretical predictions. These results allow us to analyze the influence of the experimental parameters, such as detection geometry, sample tilt, or fiber length, on orthogonality preservation and on the measurement dynamics of the DSOB technique in slightly multimode waveguides.