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We report on photodetection in deep subwavelength Ge(Sn) nano-islands on Si nano-pillar substrates, in which self-aligned nano-antennas in the Al contact metal are used to enhance light absorption by means of local surface plasmon resonances. The impact of parameters such as substrate doping and device geometry on the measured responsivities are investigated and our experimental results are supported by simulations of the three-dimensional distribution of the electromagnetic fields. Comparatively high optical responsivities of about 0.1 A W−1 are observed as a consequence of the excitation of localized surface plasmons, making our nano-island photodetectors interesting for applications in which size reduction is essential.

A comparative study of two different Photonic Integrated Circuits (PICs) structures for continuous-wave generation of millimeter-wave (MMW) signals is presented, each using a different approach. One approach is optical heterodyning, using an integrated dual-wavelength laser source based on Arrayed Waveguide Grating. The other is based on ModeLocked Laser Diodes (MLLDs). A novel building block-Multimode Interference Reflectors (MIRs)-is used to integrate on-chip both structures, without need of cleaved facets to define the laser cavity. This fact enables us to locate any of these structures at any location within the photonic chip. As will be shown, the MLLD structure provides a simple source for low frequencies. Higher frequencies are easier to achieve by optical heterodyne. Both types of structures have been fabricated on a generic foundry in a commercial MPW PIC technology.

A set of rate equations is derived describing the deterministic multi-mode dynamics of a semiconductor laser. Mutual interactions among the lasing modes, induced by high-frequency modulations of the carrier distribution, are described by carrier-inversion moments and lead to special spectral content of each spatial mode. The diffusion of carriers is shown to play an important role in determining the spectral properties of the field. The Bogatov effect of asymmetric gain suppression in semiconductor lasers will be derived. We will explicitly discuss the nontrivial relationship between the modes of the nonlinear cavity and the optical spectrum of the laser output and illustrate this for a two and three-mode laser. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Semiconductor lasers often make use of external optical feedback, for various reasons, like single-mode selection, stabilization or linewidth narrowing. A draw-back of such method is that delayed feedback can easily lead to sustained relaxation oscillations (RO). The occurrence of the RO is sensitive to, among other things, the applied settings of the phase of the feedback light. It is known from early studies that the onset of ROs already occurs with weak feedback. However, the onset of ROs is shifted to higher feedback strengths under resonance conditions, i.e. when the product of RO-frequency and external delay time equals an integer. This finding was based upon certain numerical and analytical considerations, but no simple explanation was given. From a theoretical analysis based on the Lang and Kobayashi equations, the existence of RO-free bias-current intervals of substantial width will be demonstrated for realistic pumping values, irrespective of the feedback phase. It will be shown that for conventional semiconductor lasers with weak optical feedback under RO-resonance condition the laser with feedback behaves as if no feedback is present. Therefore, under these conditions the RO is damped, hence will be suppressed. This result is valid in the regime of sufficiently weak feedback, such that the RO frequency is not deviating significantly from its value in the solitary laser and is supported by calculations of the RIN spectrum. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Single quantum dots embedded in tapered nanowire waveguides have emerged as leading candidates for designing high efficiency single-photon and entangled photon sources, with efficiencies exceeding 90%. Here we have developed a bottom-up growth approach that allows for independent control of boththe quantum dot size, and position, as well as the nanowire shape. Importantly, by design, the single quantum dot is always found perfectly on the nanowire axis. By integrating a gold mirror at the base of a tapered nanowire waveguide we obtain a 20-fold enhancement in the single-photon flux in comparison to no waveguide. The 20-fold enhancement is accompanied by a shortening of the exciton lifetime as the quantum emitter couples to the fundamental waveguide mode with an increased rate. Finally, the optical quality of the emitter is drastically improved by removing the nanowire stacking faults in the vicinity of the quantum dot. As a result, we demonstrate very pure single-photon emission with a probability of multi-photon emission below 1%, and an emission line width that is reduced by at least an order of magnitude (, Physics and Simulation of Optoelectronic Devices XXI, February 4-7, 2013, San Francisco, CA, USA, Series: Proceedings of SPIE; no. 8619

We propose two distinctive designs of metamaterials demonstrating antireflective properties in the optical and near infrared region and, simultaneously, a high reflectivity in the mid-infrared. Since the emissivity is related to the absorption of a material, our structures would then offer a high emissivity in the visible and near infrared. Beyond those wavelengths, the emissivity would be quite low. Usually, such systems find their applications in the field of thermophotovoltaics, where the goal is to convert radiation from the visible up to 2.5 microns into electrons, while limiting the emissivity for the larger wavelengths. A particular interest in the field of optoelectronics is found as well, especially for optical detection. Here, the major difficulty is to offer a metal thick enough to be considered as mirror across the electromagnetic radiation spectrum that possesses at the same time an anti-reflective character within a range of several microns. Thus, we have summoned the exceptional physical properties of the material patterning. Numerical analysis has been performed on commonly used metamaterial designs: a perforated metallic plate and a metallic cross grating. Through all these structures, we have demonstrated the various physical phenomena contributing to a reduction in the reflectivity in the optical and near infrared region. By showing realistic geometric parameters, the structures were not only designed to demonstrate a good optical response but were also meant to be feasible on large surfaces by lithographic methods such as micro contact printing or nano-imprint lithography.

Achieving a broadband antireflection property from material surfaces is one of the highest priorities for those who want to improve the efficiency of solar cells or the sensitivity of photo-detectors. To lower the reflectance of a surface, we have decided to study the optical response of a top-flat cone shaped silicon grating, based on previous work exploring pyramid gratings. Through rigorous numerical methods, such as Finite Different Time Domain or Rigorous Coupled-Wave Analysis, we then designed several structures theoretically demonstrating an antireflective character within the middle infrared region. From the opto-geometrical parameters such as period, depth and shape of the pattern determined by numerical analysis, these structures have been fabricated using controlled slope plasma etching processes. Afterwards, optical characterizations of several samples were carried out. The reflectance of the grating in the near and middle infrared domains has been measured by Fourier Transform Infrared spectrometry and a comparison with numerical analysis has been made. As expected, those structures offer a fair antireflective character in the region of interest. Further numerical investigations led to the fact that patterning the top of the cone could enlarge the antireflective domain to the visible region. Thus, as with the simple cone grating, a comparison of the numerical analysis with the experimental measurements is made. Finally, diffracted orders are studied and compared between both structures. Those orders are critical and must be limited as one wants to avoid crosstalk phenomena in imaging systems.

Recent calculations of the eigenmodes in waveguides grown on semipolar GaN suggest that the optical polarization of the emitted light as well as the optical gain depends on the orientation of the resonator. Our measurements on separate confinement heterostructures on semipolar (1122) and (10 12) GaN show that for laser resonators along the semipolar [1123] and [0111] directions (i.e. the projection of the c-axis onto the plane of growth) the threshold for amplified spontaneous emission is lower than for the nonpolar direction and that the stimulated emission is linearly polarized as TE mode. For the waveguide structures along the nonpolar [1 100] or [1120] direction on the other hand, birefringence and anisotropy of the optical gain in the plane of growth leads not only to a higher threshold but alsoto a rotation of the optical polarization which is not any more TE- or TM-polarized but influenced bythe ordinary and extraordinary refractive index of the material. We observe stimulated emission into a mode which is linearly polarized in extraordinarydirection nearly parallel to the c-axis.

A microscopic theory is used to analyze optical gain in InGaN/GaN quantum wells (QW). Experimental data are obtained from Hakki–Paoli measurements on edge-emitting lasers for different carrier densities. The simulations are based on the solution of the quantum kinetic Maxwell–Bloch equations, including many-body effects and a self-consistent treatment of piezoelectric fields. The results confirm the validity of a QW gain description for this material system with a substantial inhomogeneous broadening due to structural variation. They also give an estimate of the nonradiative recombination rate.