Ultrafast manipulation of single photons using dispersion and sum-frequency generation

Single photons provide a natural platform for quantum communication and quantum networking, as they can be entangled in many degrees of freedom and maintain coherence over long-distance links. However, while their minimal interactions with the environment isolate them from detrimental noise, it can make them difficult to measure and manipulate. In particular, manipulation on the ultrafast timescale is necessary to fully exploit the energy-time (or spectral) photonic degree of freedom. Full control over the spectral properties of single photons is key to many quantum technologies and opens the door to natural high-dimensional quantum encodings. In this thesis, we theoretically and experimentally examine the use of nonlinear optical processes mediated by strong laser pulses as a method to control the spectral properties of ultrafast single photons. By mixing single-photon pulses with strong escort pulses that have been shaped through dispersion in a nonlinear crystal, the shape of the escort is imprinted on the photon, resulting in a custom-tailored upconverted pulse. We theoretically examine this process for quadratic spectral phases and show that it has the potential to be simultaneously effective and efficient for the customization of single-photon spectral waveforms, and can be performed in an entanglement-conserving manner. We then experimentally demonstrate the range of this technique through three applications. First, we show that sum-frequency generation with shaped pulses can be used to coherently measure time-bin encoded photons with bin separations on the order of picoseconds, well below the timing resolution of our detectors. Secondly, we show that this technique can be adapted to convert a train of pulses to a frequency comb, which can be read out in a straightforward manner using diffraction-based spectrometry. We also show here that this process can be performed in a polarization-maintaining fashion, and demonstrate that entanglement with a partner photon is conserved with high fidelity. Finally, we show that this process can be viewed as a time lens, which modulates a temporal waveform in an analogous fashion to a lens focusing a beam of light. We apply the time lens to a photon from an energy-time entangled pair, and show negative magnification of the joint spectrum through a reversal of the spectral correlations. Such processes could find application in quantum state engineering and high-speed single-photon measurement

Ultrafast manipulation of single photons using dispersion and sum-frequency generation

Single photons provide a natural platform for quantum communication and quantum networking, as they can be entangled in many degrees of freedom and maintain coherence over long-distance links. However, while their minimal interactions with the environment isolate them from detrimental noise, it can make them difficult to measure and manipulate. In particular, manipulation on the ultrafast timescale is necessary to fully exploit the energy-time (or spectral) photonic degree of freedom. Full control over the spectral properties of single photons is key to many quantum technologies and opens the door to natural high-dimensional quantum encodings. In this thesis, we theoretically and experimentally examine the use of nonlinear optical processes mediated by strong laser pulses as a method to control the spectral properties of ultrafast single photons. By mixing single-photon pulses with strong escort pulses that have been shaped through dispersion in a nonlinear crystal, the shape of the escort is imprinted on the photon, resulting in a custom-tailored upconverted pulse. We theoretically examine this process for quadratic spectral phases and show that it has the potential to be simultaneously effective and efficient for the customization of single-photon spectral waveforms, and can be performed in an entanglement-conserving manner. We then experimentally demonstrate the range of this technique through three applications. First, we show that sum-frequency generation with shaped pulses can be used to coherently measure time-bin encoded photons with bin separations on the order of picoseconds, well below the timing resolution of our detectors. Secondly, we show that this technique can be adapted to convert a train of pulses to a frequency comb, which can be read out in a straightforward manner using diffraction-based spectrometry. We also show here that this process can be performed in a polarization-maintaining fashion, and demonstrate that entanglement with a partner photon is conserved with high fidelity. Finally, we show that this process can be viewed as a time lens, which modulates a temporal waveform in an analogous fashion to a lens focusing a beam of light. We apply the time lens to a photon from an energy-time entangled pair, and show negative magnification of the joint spectrum through a reversal of the spectral correlations. Such processes could find application in quantum state engineering and high-speed single-photon measurement

Measurements of Noise-seeded Dynamics in Nonlinear Fiber Optics

Nonlinear physical systems are ubiquitous in nature - formation of sand dunes, currents occuring in a rapidly flowing river or a simple double rod pedulum are just a few examples from everyday life. Studying and understanding these systems has interested scientists for decades. Because these nonlinear systems might be chaotic, measurements of such systems need to be performed on a real-time basis and by statistical analysis methods.The propagation of short and intense pulses in optical fibers are another well-known example of nonlinear systems. However, the rapid fluctuations of optical fields has prohibited studying these systems on a real-time basis, until recent years. This thesis demonstrates the use of state-of-the-art real-time measurement techniques to capture the stochastic dynamics of noise-seeded nonlinear processes in optical fibers allowing for novel insights and interpretation within analytical frameworks.In particular, we characterize noisy picosecond pulse train emerging from spontaneous modulation instability using a time lens system. The experimental results are compared with analytical Akhmediev breather solutions showing remarkable agreement, allowing to understand the complex dynamics from an analytical viewpoint. An experimental demonstration of a high dynamic range real-time spectral measurement system for spontaneous modulation instability is also introduced to study the random breather structures in the spectral domain, paving the way for possible indirect optical rogue wave detection schemes.By combining real-time temporal and spectral measurements unforeseen details of transition dynamics of a mode-locking of a fiber laser are also reported. The simultaneous spectro-temporal acquisition allows for complete electric field reconstruction with numerical algorithms, which has not been possible before at megahertz repetition rates with sub-picosecond and sub-nanometer resolutions demonstrated here.Supercontinuum generation is one of the most well-known examples of nonlinear fiber optics that is also becoming widely spread in applications. The details of the complex and noise driven dynamics are now well-known, but the connection of the stability of such light sources with traditional coherence theory was only derived recently. Experimental measurement of supercontinuum stability in the framework of second-order coherence theory is demonstrated, filling a gap in characterization of non-stationary light sources.Finally, an application of supercontinuum generation is proposed in terms of all-optical signal amplification. This is based on the inherently sensitive nature of the nonlinear process to any input fluctuations. The potential of such a highly nonlinear system for a practical application is demonstrated and the underlying dynamics leading to this sensitivity are explained

Photons & Phonons: A room-temperature diamond quantum memory

This thesis presents demonstrations of the storage and manipulation of single photons in a room-temperature diamond quantum memory using a Raman memory protocol. We report on results from four experiments. In the first we demonstrate single photon storage and, upon retrieval, verify the quantum nature of the light with a Hanbury Brown Twiss measurement of g^(2)(0) = 0.65±0.07. A measurement of g^(2)(0) < 1 is indicative of quantum light. This is the first demonstration of single photon storage where the bandwidth of the stored light is greater than 1 THz. The diamond memory stores light for over 13 times the duration of the input wavepacket. In the second experiment, we report the storage and retrieval of polarization-encoded qubits and demonstrate qubit storage above a classical bound. We also verify that entanglement between the input photon and an auxiliary persists through storage and retrieval. We then turn to additional uses of a Raman quantum memory. We demonstrate that a photon stored in the diamond memory can, upon retrieval, have its frequency and bandwidth converted. We report frequency conversion over a range of 4.2 times the bandwidth of the input photon (4.1 nm, 2.3 THz), and bandwidth modulation between 0.5 to 1.9 times the bandwidth of the input. We verify that the output light from storage and spectral manipulation is still non-classical in nature. Finally, we demonstrate both single- and two-photon quantum interference mediated by the diamond memory, where the memory acts as a beamsplitter between photon and optical phonon modes in the diamond lattice. In a first experiment, a single photon is split into two time-bins. The first time-bin is stored in the memory, then recalled and made to interfere with the second time-bin producing fringes. In a second experiment, a photon from a weak coherent state is stored in the memory and, upon retrieval, undergoes Hong- Ou-Mandel interference with a second photon. We measure Hong-Ou-Mandel interference with a visibility of 59% giving a signature of non-classical interference (> 50%). This collection of experiments establishes the diamond memory as a prime candidate for certain quantum communication and processing applications. These results demonstrate the potential for the diamond memory to be an integrated platform for photon storage, spectral conversion, and information processing

Characterization of wavelength tunable lasers for use in wavelength packet switched networks

The telecom industry's greatest challenge, and the optical systems and components vendors' biggest opportunity is enabling providers to expand their data services. The solution lies in making optical networks more responsive to customer needs, i.e., making them more rapidly adaptable. One possible technique to achieve this is to employ wavelength tunable optical transmitters. The importance of tunability grows greater every year, as the average number of channels deployed on DWDM platforms increases. By deploying tunable lasers it is much easier to facilitate forecasting, planning and last minute changes in the network. This technology provides with solution for inventory reduction. It also offers solution for fast switching at packet level. The conducted research activities of the project was divided in two work packages: 1. Full static characterization-the laser used in the experiment was a butterfly-packaged Sampled Grating DBR laser with four electrically tunable sections. LabView programme was developed for distant control of the equipment and the laser itself. The parameters required for creating a look-up table with the exact currents for the four sections of the laser, namely wavelength, side mode suppression ratio and output power, were transferred to tables. Based on those tables the currents were defined for each of the 96 different accessible channels. The channel allocation is based on the 50 GHz spacing grid. A detailed analysis of the tuning mechanisms is provided. 2. Dynamic characterization and BER performance in wavelength packet switched WDM systems-a commercially available module was used supplied with the software package for controlling the wavelength channels and setting the laser to switch between any accessible channel. The laser is DBR laser without SOA integration so the dynamic tunability can be investigated. As the switching in the nanosecond regime is executed in the electrical domain, analysis of the switching parameters concerning the electrical circuit as well as laser structure is provided. The actual switching time was defined. The degradation in system performance due to spurious wavelength signals emitted from the tunable module during the switching event and their interference with other active channels was demonstrated by examining the presence of an error floor in the BER rate against received power measurements

Sistemas de transmissão ópticos com amplificação de Raman

Doutoramento em Engenharia ElectrónicaO presente trabalho tem como objectivo analisar a amplificação de Raman no contexto dos sistemas de comunicação ópticos. Para tal, inicialmente é feita uma análise das diferentes formas do espalhamento da luz em fibras ópticas, nomeadamente espalhamento de Rayleigh, espalhamento de Brillouin e espalhamento de Raman. No âmbito deste trabalho são feitas medições destes três tipos de espalhamento. A modelação do coeficiente de atenuação para diferentes fibras ópticas é realizada. O espalhamento de Brillouin e o espalhamento de Raman são observados em fibras ópticas. Posteriormente é apresentado um modelo para o amplificador de Raman a funcionar no modo estacionário. Este modelo é descrito através de um sistema de equações diferenciais acopladas cuja resolução numérica é efectuada pelo método da análise em potências médias. Os valores para o coeficiente do ganho de Raman são obtidos experimentalmente e é encontrada uma função analítica para os descrever. Este modelo é validado experimentalmente para três configurações do amplificador de Raman: co - propagante, contra - propagante e bidireccional, e para sistemas com um ou múltiplos lasers de bombeamento. Um modelo para descrever o ruído gerado pela emissão espontânea amplificada é apresentado. Este modelo descreve o ruído não-branco. O dimensionamento de um amplificador de Raman para sistemas CWDM para três canais é efectuado usando o modelo previamente desenvolvido. No desenvolvimento deste protótipo as potências e os comprimentos de onda dos lasers de bombeamento foram optimizados para a obtenção da curva do ganho necessária para o sistema proposto. O ganho obtido apresenta uma diferença máxima igual a 1 dB relativamente ao valor especificado para a janela espectral utilizada (60 nm). Experiências foram realizadas para validar o protótipo desenvolvido. O efeito transitório no amplificador de Raman é observado devido à adição e remoção de canais no sistema de transmissão. Um modelo para representar o comportamento do efeito transitório, utilizando o modelo para o regime estacionário com a inclusão da dependência temporal no sistema de equações de propagação, é apresentado. Este modelo é validado experimentalmente.The aim of this work is to analyze the Raman amplification in the context of optical communication systems. For this purpose, it is initially performed an analysis of the different types of the light scattering in optical fiber namely Rayleigh, Brillouin and Raman scattering. In this work, measurements of these three scattering processes are made. The modeling of the attenuation coefficient for different optical fibers is realized. The Brillouin scattering and the Raman scattering are observed in optical fibers. Subsequently, it is presented a model for the Raman amplifier operating at steady-state mode. This model is described using a system of coupled differential equations, and it is numerically solved by the average power analysis method. The values for the Raman gain coefficient are obtained experimentally and it is found an analytic function to describe them. This model is validated experimentally for three configurations of the Raman amplifier: forward, backward and bidirectional, and for systems using one or multiple pumps. A model to describe the noise generated by amplified spontaneous emission is presented. This model describes the non-white noise. The dimensioning of a Raman amplifier for CWDM systems for three channels is realized using the previously validated model. For the development of the prototype, the powers and the wavelengths of the pump lasers were optimized to obtain the required gain curve for the system. The obtained gain presents a maximum difference of 1 dB relatively to the specified value for the used spectral window (60 nm). Experiments were realized to validate the developed prototype. The transient effect using the Raman amplifier is observed due to the add and drop of channels in the transmission system. A model to describe the behavior of the transient effect, obtained by including a time dependent term in the system of propagation equations used for the steady-state regime, is presented. This model is validated experimentally

Third International Workshop on Squeezed States and Uncertainty Relations

The purpose of these workshops is to bring together an international selection of scientists to discuss the latest developments in Squeezed States in various branches of physics, and in the understanding of the foundations of quantum mechanics. At the third workshop, special attention was given to the influence that quantum optics is having on our understanding of quantum measurement theory. The fourth meeting in this series will be held in the People's Republic of China

Development and application of fluorescence lifetime imaging and super-resolution microscopy

This PhD thesis reports the development and application of fluorescence imaging technologies for studying biological processes on spatial scales below the diffraction limit. Two strategies were addressed: firstly fluorescence lifetime imaging (FLIM) to study molecular processes, e.g. using Förster resonance energy transfer (FRET) to read out protein interactions, and secondly direct imaging of nanostructure using super-resolution microscopy (SRM). For quantitative FRET readouts, the development and characterisation of an automated multiwell plate FLIM microscope for high content analysis (HCA) is described. Open source software was developed for the data acquisition and analysis, and approaches to improve the performance of time-gated imaging for FLIM were evaluated including different methods to despeckle the laser illumination and testing of an enhanced detector. This instrument was evaluated using standard fluorescent dye samples and cells expressing fluorescent protein-based FRET constructs. It was applied to an assay of live cells expressing a FRET biosensor and to FRET readouts of aggregation of a membrane receptor (DDR1) in fixed cells. A novel instrument, combining structured illumination microscopy (SIM) with FLIM, was developed to explore the combination of SRM and FLIM-FRET readouts. This enabled the simultaneous mapping of molecular readouts with FLIM and super-resolved imaging. The SIM+FLIM system was applied to image collagen-stimulated DDR1 aggregation in cells, to image DNA structures during the cell cycle and to explore interactions between cell organelles. A novel SRM approach based on a stimulated emission of depletion (STED) microscope incorporating a spatial light modulator (SLM) was developed to provide straightforward robust alignment with collinear excitation/depletion beams, aberration correction, an extended field of view and multiple beam scanning for faster STED image acquisition. The performance of easySLM-STED was evaluated by imaging bead samples, labelled vimentin in Vero cells and the synaptonemal complex in homologs of C. elegans germlines.Open Acces