Irina Veretennicoff

Polarization switching in VCSEL's due to thermal lensing

We demonstrate a new mechanism for polarization switching in slightly anisotropic vertical-cavity surface-emitting lasers (VCSELs) based on index guiding due to the effect of thermal lensing. This polarization switching takes place when the laser operates on the short-wavelength side of the gain maximum. The two orthogonal linear polarizations correspond to slightly different wavelengths and switching occurs from shorter toward longer laser wavelength as the drive current increases. Polarization modulation has been observed up to 50 MHz with a polarization contrast ratio of 20:1.

Optical feedback induces polarization mode hopping in vertical-cavity surface-emitting lasers.

Vertical-cavity surface-emitting lasers subjected to weak polarization-insensitive optical feedback are studied experimentally and theoretically. We find that the feedback induces random anticorrelated hopping between the two orthogonal linearly polarized modes. This polarization mode hopping is accompanied by rapid anticorrelated oscillations in the linearly polarized intensities at the external-cavity frequency. The study of a simple stochastic delay differential equation suggests that these oscillations generated by the delay are typical of any hopping phenomenon between states.

Effect of photon-energy-dependent loss and gain mechanisms on polarization switching in vertical-cavity surface-emitting lasers

We have analyzed the effect of the photon energy and temperature dependence of both the gain and the total losses inside the cavity to understand the polarization behavior of vertical-cavity surface-emitting lasers. The assumption that the losses are dominated by free-carrier absorption in the p-doped mirror is made. Developing a new theoretical approach, we are able to predict different polarization switching regimes in which switching occurs from the high- to the low-frequency mode, from the low- to the high-frequency mode, or both consecutively. All these predictions have been experimentally verified by our measurements on GaAs/AlGaAs proton-implanted vertical-cavity surface-emitting lasers.

Slab plasmon polaritons and waveguide modes in four-layer resonant semiconductor waveguides

This paper presents a detailed study of the waveguide and plasmon polariton properties of four-layer systems involving highly doped semiconductor material. The dispersion relations of waveguide and plasmon polariton modes are calculated for different geometrical parameters and material properties. Special attention is paid to the transition region between the latter modes, which exhibits a complex behavior. Slab plasmon polaritons at wavelengths slightly larger than the plasma wavelength, yielding a positive real part of the permittivity, have been found. Finally, applications at wavelengths near the transition region and near the plasma wavelength are proposed and discussed.

Impact of in-plane anisotropic strain on the polarization behavior of vertical-cavity surface-emitting lasers

We experimentally demonstrate that the presence of switching between two fundamental modes with orthogonal linear polarization in vertical-cavity surface-emitting lasers and the current at which this phenomenon occurs depend on both the magnitude and the orientation of an externally induced in-plane anisotropic strain. We interpret this behavior by considering the anisotropy in gain and in refractive index, both induced by the in-plane strain, and by accounting for a redshift of the two gain curves as a result of current-induced heating.

Minimal rate equations describing polarization switching in vertical-cavity surface-emitting lasers

Intensity rate equations for two nearly degenerate modes are derived for current driven polarization switching (PS) in vertical-cavity surface-emitting lasers (VCSELs). We show that the introduction of a current-dependent gain that saturates with increasing optical power leads to a minimal description of a PS experiment. The main advantage of these rate equations compared to more sophisticated model equations is the possibility to describe analytically the PS dynamical phenomenon. We obtain a simple expression for the switching time which agrees with experimental observations.

Negative diffraction pattern dynamics in nonlinear cavities with left-handed materials

We study a ring cavity filled with a slab of a right-handed material and a slab of a left-handed material. Both layers are assumed to be nonlinear Kerr media. First, we derive a model for the propagation of light in a left-handed material. By constructing a mean-field model, we show that the sign of diffraction can be made either positive or negative in this resonator, depending on the thicknesses of the layers. Subsequently, we demonstrate that the dynamical behavior of the modulation instability is strongly affected by the sign of the diffraction coefficient. Finally, we study the dissipative structures in this resonator and reveal the predominance of a two-dimensional up-switching process over the formation of spatially periodic structures, leading to the truncation of the homogeneous hysteresis cycle.

Enhancing Optical Gradient Forces with Metamaterials

We demonstrate how the optical gradient force between two waveguides can be enhanced using transformation optics. A thin layer of double-negative or single-negative metamaterial can shrink the interwaveguide distance perceived by light, resulting in a more than tenfold enhancement of the optical force. This process is remarkably robust to the dissipative loss normally observed in metamaterials. Our results provide an alternative way to boost optical gradient forces in nanophotonic actuation systems and may be combined with existing resonator-based enhancement methods to produce optical forces with an unprecedented amplitude.

Two-dimensional plastic microlens arrays by deep lithography with protons: fabrication and characterization

We present a quantitative study of the fabrication process of two-dimensional plastic microlens arrays fabricated using deep lithography with protons. Our process involves the proton irradiation of a PMMA (poly(methyl methacrylate)) sample in regions with a circular footprint followed by a diffusion of MMA vapour into the bombarded zones to cause a lens-shaped volume expansion. In the first part of this paper we give a detailed description of our fabrication technique and of the calibration procedure that goes with it. We demonstrate the flexibility of our approach with the fabrication of different types of array: highly uniform microlens arrays and arrays of microlenses with varying sags (maximum height of the spherical lenscap) and pitches. All lenses under test feature diameters of 200 ± 2µm, root-mean-square (RMS) roughnesses on the top of the lenses of λ/30 @ 632 nm and lens sags ranging from 10 to 70 µm. We also present the optical performances and the aberrations of the microlenses, measured using a dedicated transmission Mach–Zehnder interferometer. The focal lengths of the lenses under study range from 166 to 1444 µm, corresponding to a range of sags between 9.77 and 69.73 µm and to focal numbers between 0.83 and 7.22. Typical values for the RMS and peak-to-valley aberrations of 0.209λ and 1.057λ respectively were observed. To conclude, we analyse and discuss the strengths and weaknesses of this fabrication method.

Polarization behavior of vertical-cavity surface-emitting lasers: Experiments, models and applications

Due to the emission of light perpendicular to the surface of the quantum well and the usually symmetric vertical resonator there is a priori no intrinsic polarization anisotropy mechanism in VCSELs. Small residual strain explains the emission of linearly polarized light with a common orientation along [110] or [1–10] crystallographic directions. These two modes of linear polarization are strongly anti-correlated. Experimentally, polarization switching between them can be observed with increasing the injection current. It could happen from shorter to longer wavelength mode (type 1) or in the opposite way—from longer to shorter wavelength mode (type II). The polarization switching happens through a region of mode hopping or hysteresis. In the first case, the dwell time (the average time the laser spends in one mode) scales in several orders of magnitude. Thermal (carrier) effects influence the polarization behavior of VCSELs through the red (blue) shift of the gain maximum and through the dependence of the ...