Leonbredahl3286

This work offers a simple and effective route to realize all-silica mid-IR lasers based on enhanced optical nonlinearity in WGM microresonators.Superposed constellation for spatial multiplexing visible light communication (VLC) systems has recently attracted significant attention as a promising method to alleviate the effect of nonlinearity on light-emitting diodes (LEDs) that has achieved significant performance improvements in VLC systems. learn more A large minimum Euclidean distance (ED) value of the superposed signals can be achieved at the receiver side by employing optimal power ratios transmitted from different LEDs. However, the power allocation strategy using fixed shaped sub-constellations at the LEDs has the inherent limitation of low optimization dimensions. In this paper, we propose optimizing the sub-constellations at individual LEDs instead of just the power allocation coefficients to further increase the minimum ED value. Moreover, intra-ED and inter-ED terms are used to reduce the complexity of the optimization solving process. The simulation results show that the proposed constellation design scheme can improve the symbol error rate performance compared to the conventional one, and the right choice of pre-defined shape of the sub-constellations at the LEDs has an important role in the optimization process.The Faraday effect due to the cyclotron resonance of conduction electrons in semiconductor InSb allows for nonreciprocity of transmitted light in our Faraday THz isolator operating in the presence of a small magnetic field. We select InSb as an efficient medium for our isolator due to its high electron mobility, low electron effective mass, and narrow band gap. Experimental measurements of the isolator performance indicate a maximum achieved isolation power of 18.8 dB with an insertion loss of -12.6 dB. Our optical analysis of the device points to a remarkable nonreciprocal Fabry-Perot effect in the magneto-optical InSb layer as the origin of the multi-fold isolation enhancement. This nonreciprocity occurs as the Fabry-Perot reflections in the forward direction add constructively and enhance the transmittance at certain frequencies, while the Fabry-Perot reflections in the backward direction add destructively and suppress the transmittance at the same frequencies.In the field of silicon photonics, germanium (Ge) is an attractive material for monolithic light sources. Tensile strain is a promising means for Ge based light sources due to enhancing direct band gap recombination. We investigated strain engineering in Ge using silicon nitride (SiNx) stressors. We found that microfabricated Ge greatly improves the tensile strain because SiNx on the Ge sidewalls causes a large tensile strain in the direction perpendicular to the substrate. Tensile strain equivalent to an in-plane biaxial tensile strain of 0.8% at maximum was applied, and the PL emission intensity was improved more than five times at the maximum.Slow tool servo diamond turning has widespread application in fabricating freeform optics. Previous studies are focused on the methods of the tool path generation and verification of zero-rake-angle tools. However, these methods are unsuitable for non-zero-rake tools that are used for machining hard-and-brittle materials. This paper presents a universal location-point-drive tool path generation method, which caters to arbitrary rake angle tools and the steady X movement feature, and the corresponding universal tool interference check method. Systematic analysis and ultra-precision machining experiments confirmed the feasibility of our methods and present better surface quality and form accuracy compared to the traditional method.Metasurfaces, the promising artificial micro-nano structures with the ability to manipulate the wavefront of light, have been widely studied and reported in recent years. However, dynamic control of the wavefront using dielectric metasurfaces remains a great challenge. Here, unlike the previously reported reconfigurable metasurfaces that offer only binary functions or limited switchable states, we propose and numerically demonstrate an active dielectric metasurface with the metamolecule unit-cell design that enables full-range phase or amplitude tuning in the telecommunications band using the phase-change material Ge2Sb2Se4Te1 (GSST). Selective control of the phase transition of each GSST nanopillar in the metamolecule allows multi-level modulation of the phase and amplitude of the light to be achieved. The functionalities of the structure are validated through the generation of optical vortices, phase-only hologram, and pure amplitude modulation. Benefiting from its dynamic wavefront control capability, the proposed metasurface offers major potential for use in future applications including complex beam steering, optical communications, 3D holograms, and displays.Automatic modulation recognition (AMR) is an integral part of an intelligent transceiver for future underwater optical wireless communications (UOWC). In this paper, an orthogonal frequency division multiplexing (OFDM) based progressive growth meta-learning (PGML) AMR scheme is proposed and analyzed over UOWC turbulence channels. The novel PGML few-shot AMR framework, mainly suffering from the severe underwater environments, can achieve fast self-learning for new tasks with less training time and data. In the PGML algorithm, the few-shot classifier, which works in the presence of Poisson noise, is fed with constellations of noisy signals in bad signal-to-noise ratio (SNR) scenarios directly. Moreover, the data augmentation (DA) operation is adopted to mitigate the impact of light-emitting diode (LED) distortion, yielding further classification accuracy improvements. Simulation results demonstrate that the proposed PGML scheme outperforms the classical meta-learning (ML) approach in training efficiency, robustness against Poisson noise and generalization performance on a new task.In this paper, we analyse the performance of a silicon nano-opto-electro-mechanical system (NOEMS) applied as an optical modulator, based on a suspended slot waveguide driven by electrostatic forces. The analysis is carried out with the help of the finite element analysis (FEA) method involving the influences from Casimir force, optical force and electrostatic force. The performance of the modulator are analysed from aspects of actuating modes, actuating voltage, modulating frequency, effective index, phase change, and energy consumption using the FEA method. Simulation results show that a suspended slot modulator has the advantages of low actuation voltage, low power consumption, as well as large effective index and phase change compared with modulators based upon other approaches. The performance of such a modulator can fill the performance gap between the carrier-based approach and micro-opto-electro-mechanical system (MOEMS) approach for modulation.A broadband and compact TE0-TE1 mode converter for a mode division multiplexing system designed using a wavefront matching method is realized. We present the first experimental demonstration of a silicon waveguide device designed by a wavefront matching method. In order to achieve broadband operation of the silicon mode converter, seven wavelengths are considered in its optimization process. The designed silicon mode converter is fabricated via a standard complementary metal-oxide-semiconductor technology, which enables low-cost mass production. Measurements performed using the fabricated mode converter correlate strongly with the calculated results.In this study, AlGaInP red light emitting diodes with sizes ranging from 5 to 50 micrometers were fabricated and characterized. The atomic layer deposition technology is applied to coat a layer of silicon dioxide for passivation and protection. The top emission area is covered by ITO layer to maximize the optical output. From the optical measurement, the linewidth and emission peaks shift very little among different current levels (from 30 to 150 A/cm2). High current level lifetests are performed and a 15 µm ALD device can last 27 hours of continuous operation at 100 A/cm2 before their diode junction failed. A much shorter lifetime of 5.32 hours was obtained when the driving current is raised to 400 A/cm2. When the same condition was applied to 15 µm PECVD devices, 25 hours and 4.33 hours are registered for 100 A/cm2 and 400 A/cm2 tests, respectively. The cross-sectional SEM reveals the voids, defects, and dark lines developed during the aging tests, and most of them are caused by top contact failure. The surface layers of ITO and SiO2 were melted and the dark lines which were originated from the top surface propagated through the device and led to the eventual failure of the diode. The optical intensity degradation slopes of different sizes of devices indicate a large device can last longer in this accelerated aging test. The efficiencies of the devices are also evaluated by the ABC model and the fitted bimolecular coefficient ranges from 1.35 to 3.40×10-10 cm3/s.Squeezed light is a quantum resource that can improve the sensitivity of optical measurements. However, existing sources of squeezed light generally require high powers and are not amenable to portability. Here we theoretically investigate an alternative technique for generating squeezing using degenerate four-wave-mixing in atomic vapors. We show that by minimizing excess noise, this technique has the potential to generate measurable squeezing with low powers attainable by a small diode laser. We suggest experimental techniques to reduce excess noise and employ this alternative nonlinear optical process to build a compact, low-power source of squeezed light.Designing freeform optics for illuminating hard-to-reach areas is a challenging and rewarding issue. The current designs of freeform illumination optics are mostly valid in the applications in which the region of interest is easily accessible. What we present here is a general formulation of designing freeform lenses for illuminating hard-to-reach areas. In this method, the freeform lens consists of two elaborately designed surfaces, by which both the intensity distribution and wave-front of the light beam are manipulated in a desired manner. The light beam after refraction by the freeform lens is further guided through a light-guiding system to produce a prescribed illumination on a target plane which is inaccessible. The properties of the light-guiding system are taken into account in the tailoring of the freeform lens profiles to guarantee the prescribed illumination on the target plane. Two examples are presented to demonstrate the elegance of this method in designing freeform optics for illuminating hard-to-reach areas.A digital micro-mirror device is one of the most frequently used spatial light modulators for holographic three-dimensional displays due to its fast refresh rate. The modulation by the digital micro-mirror device is, however, limited to the binary amplitude modulation, and it degrades the reconstruction image quality. In this paper, we propose a novel binary hologram encoding technique which applies the error diffusion algorithm considering the carrier wave of the hologram. The error diffusion weights designed for the hologram carrier wave suppress the binarization noise around the carrier wave where the most signal energy is concentrated, which enhances the reconstruction quality. The combination with the time-multiplexing enables speckless enhanced-quality three-dimensional reconstruction with shallow depth of focus. The proposed technique is verified by simulations and optical experiments.