Modern Applications in Optics and Photonics: From Sensing and Analytics to Communication

Optics and photonics are among the key technologies of the 21st century, and offer potential for novel applications in areas such as sensing and spectroscopy, analytics, monitoring, biomedical imaging/diagnostics, and optical communication technology. The high degree of control over light fields, together with the capabilities of modern processing and integration technology, enables new optical measurement systems with enhanced functionality and sensitivity. They are attractive for a range of applications that were previously inaccessible. This Special Issue aims to provide an overview of some of the most advanced application areas in optics and photonics and indicate the broad potential for the future

Diseño y desarrollo de un sistema optoacústico de múltiples longitudes de onda basado en fuentes de diodos láseres de alta potencia: generación de señales optoacústicas con nanopartículas para aplicaciones biomédicas

Durante los últimos años, el rápido avance de las tecnologías ópticas para la obtención de imágenes biomédicas hace posible revelar importantes informaciones biológicas a partir de la interacción entre la luz y el tejido. El interés emergente en nuevas técnicas de obtención de imágenes biomédicas está motivado por la necesidad de detectar células malignas y otras enfermedades durante las etapas precoces de evolución. La limitada profundidad de penetración de la energía óptica en medios biológicos se debe principalmente al alto nivel de dispersión óptica. Además, la difusión de la luz en los tejidos biológicos limita la resolución espacial de las imágenes adquiridas. La técnica optoacústica sobresale estos problemas combinando el alto contraste de la imagen óptica con la alta resolución espacial de los sistemas de ultrasonido en los tejidos profundos. Asimismo, la baja dispersión de las ondas ultrasónicas producidas en los tejidos biológicos facilita la adquisición de imágenes de alta resolución. Dos importantes aspectos a considerar demás en las aplicaciones optoacústicas para una imagen funcional son el uso de agentes de contraste óptico para mejorar la absorción de energía óptica en aquellas áreas donde la dispersión es dominante y la cantidad de energía óptica suministrada por las fuentes láseres para penetrar en profundidad. La necesidad de fuentes láseres compactas y de bajo coste con las características requeridas por las aplicaciones optoacústicas ha impulsado los estudios presentados en esta tesis, proponiendo el uso de diodos láseres de alta potencia en lugar de los clásicos láseres de estado sólido. Generalmente, los láseres de estado sólido como el Nd:YAG y los osciladores ópticos paramétricos se utilizan para la generación de señales optoacústicas, pero su uso en el ambiente clínico está limitado por sus altos costes, bajas frecuencias de repetición y tamaños voluminosos. Por otro lado, los diodos láseres de alta potencia emergen como una potencial alternativa, debido a sus relativamente bajos costes, altas frecuencias de repetición requeridas para una rápida adquisición de imágenes y tamaños compactos. Sin embargo, la potencia de los diodos láseres de alta potencia es todavía relativamente baja en comparación con los láseres de estado sólido y por esta razón se necesita combinarlos para conseguir la cantidad de potencia óptica requerida para las aplicaciones optoacústicas. Un sistema optoacústico basado en diodos láseres de alta potencia ha sido implementado y mejorado a lo largo de los estudios presentados en esta tesis. Se han realizado experimentos optoacústicos a diferentes longitudes de onda utilizando varios tipos de absorbentes colocados en cubeta de cuarzo u hospedados dentro de un “phantom” que simula la dispersión óptica de un tejido blando. Soluciones de nanotubos de carbono, óxido de grafeno y nanoparticulas de oro se han utilizado como absorbentes a lo largo de los experimentos. Los primeros experimentos realizados en espacio libre para enfocar la luz en los absorbentes se han mejorado mediante el uso de fibras ópticas en una segunda etapa. Por último, se han propuesto barras de diodos láseres comercialmente disponibles para sustituir los diodos láseres de alta potencia con el objetivo de aumentar la potencia óptica para futuras implementaciones en los sistemas optoacústicos. Las simulaciones ópticas han demostrado la posibilidad de enfocar el haz emitido por barras de diodos láseres de diferentes longitudes de onda en fibras ópticas por medio de microlentes cilíndricas. En una segunda etapa, las barras de diodos láseres han sido ensambladas en un único sistema para simular un sistema de múltiples longitudes de onda. Los haces han sido combinados por medio de espejos dicroicos y enfocados en una fibra óptica multimodo. Este trabajo de investigación ha abierto nuevas líneas de investigación en el desarrollo de fuentes láser de alta potencia para la endoscopia optoacústica y la tomografía en aplicaciones biomédicas.Over last few years, the rapid growth of optical technologies for biomedical imaging makes possible to reveal important biological information of tissues from light-tissue interaction. The emerging interest on new biomedical imaging techniques is motivated by the necessity to detect malignant cells and other diseases at early growth stages. The limited penetration depth of optical energy in biological media is primarily due to the high level of optical scattering. In addition, the diffusion of light in biological tissues limits the spatial resolution of the images acquired. The optoacoustic technique overcomes these issues combining the high contrast of optical imaging with the high spatial resolution of ultrasound systems in deep tissues. As well, the low scattering of the ultrasound waves produced in the biological tissues facilitates the acquisition of high-resolution images. Two more important aspects to be considered in optoacoustic applications for a functional imaging are the use of optical contrast agents to increase the absorption of optical energy in those areas where the scattering is dominant, and the amount of optical energy delivered by laser sources to penetrate in depth. The necessity of compact and cost-effective laser sources with the characteristics required by optoacoustic applications has encouraged the studies presented in this thesis, proposing the use of high-power diode lasers instead of the classical solid state lasers. Generally, solid-state lasers like Nd:YAG and optical parametric oscillators are used for the generation of optoacoustic signals, but their use in clinical environment is limited by their high costs, low repetition rates and bulky sizes. On the other hand, high-power diode lasers emerge as a potential alternative, due to their relatively low costs, high repetition rates required for fast image acquisition and compact sizes. However, the power of high-power diode lasers is still relatively low compared to solid-state lasers and for this reason they need to be combined in arrays to reach the amount of the optical power required for optoacoustic applications. An optoacoustic setup based on small arrays of high-power diode lasers has been implemented and improved along the studies presented in this thesis. Optoacoustic experiments have been performed at different wavelengths using several kinds of absorbers hosted in a quartz cuvette or embedded within a phantom that simulates the optical scattering of a soft tissue. Solutions of carbon nanotubes, graphene oxide and gold nanorods have been used as absorbers in the experiments. The first experiments done in free space to focus the light in the absorbers have been improved by using optical fibers in a second stage. Lastly, some commercially available diode laser bars have been proposed to replace the high-power diode lasers with the aim to increase the optical power for future implementations in the optoacoustic systems. Optical simulations have demonstrated the possibility to focus the beam of diode laser bars operating at different wavelengths into optical fibers by means of cylindrical microlenses. In a second step, the diode laser bars have been assembled together to simulate a multi-wavelength system. The beams have been combined by dichroic mirrors and focused in a multi-mode optical fiber. This research work has opened up new lines of investigation in the development of high-power laser sources for optoacoustic endoscopy and tomography in biomedical applications.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Alexander A. Oraevsky.- Secretario: José Antonio García Souto.- Vocal: Ana Pilar González Marco

A Newcomer\u27s Guide to Functional Near Infrared Spectroscopy Experiments

This review presents a practical primer for functional near-infrared spectroscopy (fNIRS) with respect to technology, experimentation, and analysis software. Its purpose is to jump-start interested practitioners considering utilizing a non-invasive, versatile, nevertheless challenging window into the brain using optical methods. We briefly recapitulate relevant anatomical and optical foundations and give a short historical overview. We describe competing types of illumination (trans-illumination, reflectance, and differential reflectance) and data collection methods (continuous wave, time domain and frequency domain). Basic components (light sources, detection, and recording components) of fNIRS systems are presented. Advantages and limitations of fNIRS techniques are offered, followed by a list of very practical recommendations for its use. A variety of experimental and clinical studies with fNIRS are sampled, shedding light on many brain-related ailments. Finally, we describe and discuss a number of freely available analysis and presentation packages suited for data analysis. In conclusion, we recommend fNIRS due to its ever-growing body of clinical applications, state-of-the-art neuroimaging technique and manageable hardware requirements. It can be safely concluded that fNIRS adds a new arrow to the quiver of neuro-medical examinations due to both its great versatility and limited costs

Development of non-invasive, optical methods for central cardiovascular and blood chemistry monitoring.

Cardiovascular disease and sepsis are leading causes of mortality, morbidity and high cost in hospitals around the world. Failure of the circulatory system during cardiogenic shock and sepsis both can significantly impair the perfusion of oxygen through organs, resulting in poor patient outcome if not detected and corrected early. Another common disorder which goes hand-in-hand with cardiovascular disease is Diabetes Mellitus. Diabetes is a metabolic disorder resulting from the inability of the body to regulate the level of glucose in the blood. The prevalence of diabetes worldwide is increasing faster than society’s ability to manage cost effectively, with an estimated 9% of the world population diagnosed with metabolic disease. The current gold standard measurements for venous oxygen saturation, arterial pulse wave velocity (PWV), and diabetes management through blood glucose concentration monitoring are all invasive. Invasive measurements increase risk of infection and com- plications, are often high cost and disposable, and have a low patient compliance to regular measurements. The aim of this thesis is to develop non-invasive methods of monitoring these important dynamic physiological variables, including, venous oxygen saturation, pulse wave velocity, and blood glucose concentration. A novel photoplethysmography-based NIR discrete wavelength spectrometer was developed using LEDs to both emit light, and detect the light reflected back through the tissue. Using LEDs to detect light simplifies sensing circuit design, lowering hardware costs, allowing adaptable sensing specific to the needs of the user. A reflectance pulse oximeter was developed to measure the oxygen saturation at both the external jugular vein, and carotid artery. Measuring the jugular venous pulse (JVP) allows estimation of the venous oxygen saturation through either the JVP, or through breathing induced variation of the JVP. In addition to oxygenation, the de- vice developed is capable of adapting the sensing layout to measure the arterial pulse waveform at multiple sites along a peripheral artery, such as the carotid or radial. The PWV local to the carotid artery, and radial artery can then be measured, providing key information of cardiovascular risk. A novel algorithm for PWV measurement over multiple pulse waveforms was also developed. Expanding the sensor to use multiple different wavelength LEDs allow discrete spectroscopy in pulsatile blood. An absorption model of components in blood at specific wavelengths was created to isolate the spectral fingerprint of glucose. The sensor successfully measured the oxygen saturation at the carotid artery, and external jugular vein across 15 subjects, giving mean oxygen saturations of 92% and 85% respectively, within the expected physiological ranges. Venous oxygen saturation calculated using breathing induced changes to JVP was 3.3% less than when calculated on the JVP alone, with a standard deviation of 5.3%, compared to 6.9%. Thus, future work on the sensor will focus on extraction of the breathing induced venous pulse, rather than measuring from the JVP itself. The PWV on the carotid and radial artery was successfully measured within the ex- pected physiological ranges, with the novel phase difference algorithm proving more robust to noise than the gold standard foot-foot method. The phase difference method returned a mean PWV at the radial artery of 4.7 ±0.6 m s−1, and a mean CoV of 20%, compared to 4.0 ±1.4 m s−1, and a moan CoV of 58% for the foot-foot method. The proof of concept PWV sensor gives promising results, but needs to be calibrated against invasive gold standards, such as aorta and femoral pressure catheters. A glucose trial involving adult and neonatal subjects provided validation of the NIR non-invasive pulse glucometer. The sensor has an R2 of 0.47, and a mean absolute relative difference (MARD) of 19% compared to gold standard reference measurements. Clarke error grid analysis returns 85% of measurements in Zone A, 11% in Zone B, and 4% in Zone C. While the sensor is not as accurate as the gold standard invasive measurements, the ability to constantly measure without any pain or discomfort will help increase measurement compliance, improving user quality of life, plus further development may improve this. Overall, this thesis provided novel contributions in non-invasive venous oxygen saturation, PWV, and glucose concentration monitoring. The adaptability of the sensor shows promise in helping reduce the pain and inconvenience of the current invasive measurements, especially in diabetes management, where the sensor has the most potential for impact

Optical Diagnostics in Human Diseases

Optical technologies provide unique opportunities for the diagnosis of various pathological disorders. The range of biophotonics applications in clinical practice is considerably wide given that the optical properties of biological tissues are subject to significant changes during disease progression. Due to the small size of studied objects (from μm to mm) and despite some minimum restrictions (low-intensity light is used), these technologies have great diagnostic potential both as an additional tool and in cases of separate use, for example, to assess conditions affecting microcirculatory bed and tissue viability. This Special Issue presents topical articles by researchers engaged in the development of new methods and devices for optical non-invasive diagnostics in various fields of medicine. Several studies in this Special Issue demonstrate new information relevant to surgical procedures, especially in oncology and gynecology. Two articles are dedicated to the topical problem of breast cancer early detection, including during surgery. One of the articles is devoted to urology, namely to the problem of chronic or recurrent episodic urethral pain. Several works describe the studies in otolaryngology and dentistry. One of the studies is devoted to diagnosing liver diseases. A number of articles contribute to the studying of the alterations caused by diabetes mellitus and cardiovascular diseases. The results of all the presented articles reflect novel innovative research and emerging ideas in optical non-invasive diagnostics aimed at their wider translation into clinical practice