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.

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.

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.

Dual frequency laser with two continuously and widely tunable frequencies for optical referencing of GHz to THz beatnotes.

A dual-frequency 1.55 µm laser for CW low noise microwave, millimeter and sub millimeter wave synthesis is demonstrated, where frequency stabilization is possible on each wavelength independently. The solid state Er:Yb laser output power is 7 mW. The amplitude noise is -150 dBc/Hz at 1 MHz offset frequency. In free running regime, the frequency noise is 3.10(5)/f Hz/sqrt(Hz) (800 Hz on a 1µs timescale), better than commercial fibered or semi-conductor sources at this wavelength.

Long-range polarimetric imaging through fog.

We report an experimental implementation of long-range polarimetric imaging through fog over kilometric distance in real field atmospheric conditions. An incoherent polarized light source settled on a telecommunication tower is imaged at a distance of 1.3 km with a snapshot polarimetric camera including a birefringent Wollaston prism, allowing simultaneous acquisition of two images along orthogonal polarization directions. From a large number of acquisitions datasets and under various environmental conditions (clear sky/fog/haze, day/night), we compare the efficiency of using polarized light for source contrast increase with different signal representations (intensity, polarimetric difference, polarimetric contrast, etc.). With the limited-dynamics detector used, a maximum fourfold increase in contrast was demonstrated under bright background illumination using polarimetric difference image.

Polarimetric imaging beyond the speckle grain scale.

We address an experimental Stokes imaging setup allowing one to explore the polarimetric properties of a speckle light field with spatial resolution well beyond the speckle grain scale. We detail how the various experimental difficulties inherent to such measurements can be overcome with a dedicated measurement protocol involving a careful speckle registration step. The setup and protocol are then validated on a metallic reference sample, and used to measure the state of polarization (SOP) of light in each pixel of highly resolved speckle patterns (>2000 pixels per speckle grain) resulting from the scattering of an incident coherent beam on samples exhibiting different polarimetric properties. Evolution of the SOP with spatial averaging and across adjacent speckle grains is eventually addressed.