Harnessing Spatial Intensity Fluctuations for Optical Imaging and Sensing

Properties of light such as amplitude and phase, temporal and spatial coherence, polarization, etc. are abundantly used for sensing and imaging. Regardless of the passive or active nature of the sensing method, optical intensity fluctuations are always present! While these fluctuations are usually regarded as noise, there are situations where one can harness the intensity fluctuations to enhance certain attributes of the sensing procedure. In this thesis, we developed different sensing methodologies that use statistical properties of optical fluctuations for gauging specific information. We examine this concept in the context of three different aspects of computational optical imaging and sensing. First, we study imposing specific statistical properties to the probing field to image or characterize certain properties of an object through a statistical analysis of the spatially integrated scattered intensity. This offers unique capabilities for imaging and sensing techniques operating in highly perturbed environments and low-light conditions. Next, we examine optical sensing in the presence of strong perturbations that preclude any controllable field modification. We demonstrate that inherent properties of diffused coherent fields and fluctuations of integrated intensity can be used to track objects hidden behind obscurants. Finally, we address situations where, due to coherent noise, image accuracy is severely degraded by intensity fluctuations. By taking advantage of the spatial coherence properties of optical fields, we show that this limitation can be effectively mitigated and that a significant improvement in the signal-to-noise ratio can be achieved even in one single-shot measurement. The findings included in this dissertation illustrate different circumstances where optical fluctuations can affect the efficacy of computational optical imaging and sensing. A broad range of applications, including biomedical imaging and remote sensing, could benefit from the new approaches to suppress, enhance, and exploit optical fluctuations, which are described in this dissertation

Hybrid confinement of optical and mechanical modes in a bullseye optomechanical resonator

Optomechanical cavities have proven to be an exceptional tool to explore fundamental and technological aspects of the interaction between mechanical and optical waves. Such interactions strongly benefit from cavities with large optomechanical coupling, high mechanical and optical quality factors, and mechanical frequencies larger than the optical mode linewidth, the so called resolved sideband limit. Here we demonstrate a novel optomechanical cavity based on a disk with a radial mechanical bandgap. This design confines light and mechanical waves through distinct physical mechanisms which allows for independent control of the mechanical and optical properties. Our device design is not limited by unique material properties and could be easily adapted to allow large optomechanical coupling and high mechanical quality factors with other promising materials. Finally, our demonstration is based on devices fabricated on a commercial silicon photonics facility, demonstrating that our approach can be easily scalable.Comment: 16 pages, 11 figure

Two-scale envelope-domain analysis of injected chirped oscillators

The response of chirped oscillators under the injection of independent signals, for spectrum sensing in cognitive radio, and under self-injection, for radio frequency identification, is analyzed in detail. The investigation is performed by means of a semianalytical formulation, based on a realistic modeling of the free-running oscillator, extracted from harmonic-balance simulations or from experimental measurements, through a new characterization technique. In the new formulation, the oscillator is linearized about a free-running solution that varies with the control voltage. This enables its application to oscillators having a frequency characteristic that deviates from the linear one. In the case of injection by independent signals, the two-scale envelope-domain formulation will enable an efficient handling of the difference between the slow chirp frequency and the beat frequency. The input carriers can be detected from their dynamic synchronization intervals or, at lower input-power levels, from the dynamics of the beat frequency. Noise perturbations are introduced into the formulation, which enables an estimation of the minimum detectable signal. In the case of a self-injected oscillator for radio frequency identification, an insightful formulation is derived to predict the propagation and tag-resonance effects on the instantaneous oscillation frequency. The tag-resonance signature gives rise to a distinct modulation of the oscillation frequency during the chirp period, which can be detected from the variation of the oscillator bias current. The analysis methods are illustrated through their application to a chirped oscillator, operating in the band 2-3 GHz.This work was supported by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (ERDF/FEDER) under Project TEC2014-60283-C3-1-R and Project TEC2017-88242-C3-1-

Microscale sensing with NV centers in diamond

Elektroniskā versija nesatur pielikumusNegatīvi lādētais slāpekļa vakances (NV) centrs dimantā ir cietvielu defekts, kam piemīt izcilas spina koherences īpašības pat istabas temperatūrā un kura spina stāvokli iespējams viegli nolasīt optiski. Šajā darbā tika pētīta NV centra relaksācijas īpašības, un defekta-kā-sensora veiktspēja. Eksperimentālie dati liecināja par spēcīgu NV-NV dipola-dipola mijiedarbības lomu T1 relaksācijas procesos augstas koncentrācijas NV centros. Tika identificēti vairāki uzlabojumi NV magnētiskā mikroskopa eksperimentālajā dimantā un visbeidzot tika uzņemts pirms divdimensiju KMR spektrs ar NV KMR spektrometru spiniem, kas atrodas ārpus dimanta matricas. Cik es zinu, šis ir pirmais publicētais šāda tipa eksperimentālais rezultāts. Atslēgas vārdi: cietvielu defekts, kvantu metroloģija, kodolu magnētiskā rezonanse, NV centriThe negatively charged nitrogen vacancy (NV) center in diamond is a solid state defect that possesses both high-spin coherence time at room temperature and a robust optical readout of the spin state. In this work the relaxation dynamics and sensing performance of the nitrogen-vacancy (NV) center were investigated. Strong evidence of NV-NV dipole-dipole couplings playing an important role in T1 relaxation processes in high NV concentration diamonds was found, several key experimental design improvements in a NV diamond magnetic microscope were identified and finally a two-dimensional NMR spectra with a NV NMR spectrometer on an external analyte was observed; the first result of this kind to be reported in literature to the best of my knowledge. Keywords: solid state defects, quantum sensing, nuclear magnetic resonance, NV center

Fabrication and Simulation of Nanomagnetic Devices for Information Processing

Nanomagnetic devices are highly energy efficient and non-volatile. Because of these two attributes, they are potential replacements to many currently used information processing technologies, and they have already been implemented in many different applications. This dissertation covers a study of nanomagnetic devices and their applications in various technologies for information processing – from simulating and analyzing the mechanisms behind the operation of the devices, to experimental investigations encompassing magnetic film growth for device components to nanomagnetic device fabrication and measurement of their performance. Theoretical sections of this dissertation include simulation-based modeling of perpendicular magnetic anisotropy magnetic tunnel junctions (p-MTJ) and low energy barrier nanomagnets (LBM) – both important devices for magnetic device-based information processing. First, we propose and analyze a precessionally switched p-MTJ based memory cell where data is written without any on-chip magnetic field that dissipates energy as low as 7.1 fJ. Next, probabilistic (p-) bits implemented with low energy barrier nanomagnets (LBMs) are also analyzed through simulations, and plots show that the probability curves are not affected much by reasonable variations in either thickness or lateral dimensions of the magnetic layers. Experimental sections of this dissertation comprise device fabrication aspects from the basics of material deposition to the application-based demonstration of an extreme sub-wavelength electromagnetic antenna. Magnetic tunnel junctions for memory cells and low barrier nanomagnets for probabilistic computing, in particular, require ultrathin ferromagnetic layers of uniform thickness, and non-uniform growth or variations in layer thickness can cause failures or other problems. Considerable attention was focused on developing methodologies for uniform thin film growth. Lastly, micro- and nano-fabrication methods are used to build an extreme sub-wavelength electromagnetic antenna implemented with an array of magnetostrictive nanomagnets elastically coupled to a piezoelectric substrate. The 50 pW signal measured from the approximately 250,000-nanomagnet antenna sample was 10 dB above the noise floor