The Photonic Lantern

Photonic lanterns are made by adiabatically merging several single-mode cores into one multimode core. They provide low-loss interfaces between single-mode and multimode systems where the precise optical mapping between cores and individual modes is unimportant.Comment: 45 pages; article unchanged, accepted for publication in Advances in Optics and Photonic

The ultrafast laser inscription of photonic devices for integrated optical applications

A study of some key areas in which ultrafast laser inscription may usefully be employed is presented. The thesis includes waveguide inscription in a variety of substrates including passive glass, doped glass and a nonlinear crystal. The work contained can be split into three studies, with some overlap between them. Firstly fused silica glass is used, both in planar substrates and as flat fibre, for the inscription of two sensing elements. The planar substrate is used for a device similar in design to a side-polished fibre and the flat fibre is used for the fabrication of a Bragg grating waveguide array. In the second study, waveguides are inscribed in the nonlinear crystal monoclinic bismuth borate, and used for guided mode second harmonic generation. A novel waveguide design is employed to increase overlap between the pump and second harmonic waveguide modes. The remainder of the thesis investigates the applicability of ultrafast laser inscription to the fabrication of compact modelocked lasers. Lasing is demonstrated, both continuous wave and modelocked, using a laser inscribed erbium doped bismuthate glass waveguide as the gain element. A study is then undertaken into methods of integrating carbon nanotubes, used as saturable absorbers to modelock lasers, into laser inscribed waveguides

Advanced fibre gratings in near- and mid-infrared region and their applications for structure monitoring and biosensing

This thesis emphasises an elaborate research finding on the fabrication, analysis of resonance spectral response and sensing applications in various fields using different type of optical fibre grating devices over an entire wavelength range from near- to mid-infrared (IR). Firstly, the major contribution described in the thesis is a thorough investigation of sensor structures, detailed in respect to writing techniques for optical fibre gratings irradiated by a frequency-doubled Argon ion laser. Thereafter spectral modulation for these UV-inscribed fibre Bragg gratings (FBGs), long period gratings (LPGs) and tilted fibre gratings (TFGs) of small and large angled structures are analysed. Special LPG devices with both dual peaks and 1st&2nd orders, and excessively tilted TFGs (Ex-TFGs) are also achieved with the resonances in the mid-IR range for enhanced sensitivity. Investigations of different sensing measurements, such as temperature, strain, bending and surrounding refractive index (SRI) for these fibre grating devices are performed. Another important contribution is the study on experimental investigation for the fabrication of FBGs into multicore fibre such as four core fibre (4CF) with two different core spacings and seven core fibre (7CF) are explained. A selective inscription method is utilised for inscribing FBGs into different cores of multicore fibre (MCF). The measurement performance with vector bend/twist sensing results in an enhanced sensitivity for FBGs in the distributed cores around the circumference of 4CF and 7CF is analysed in detail, showing the effective detection of both amplitude and direction. Whereas, in 7CF the central core FBG acts as the temperature reference having low bending sensitivity of -8.83 pm/m-1, presenting extra function for eliminating temperature cross-talk effect. The application for these grating devices is largely associated to structural monitoring in astronomy, biomedical sciences, and robotics. Finally, I have investigated different enzyme functionalised and nano-deposited LPG devices for bio and environmental sensing applications. The experimental findings for these sensors are discussed in glucose sensing measurements by observing resonance wavelength shift. Whereas LPGs fabricated with mono or multi-layered deposition of 2D nanomaterials, such as graphene oxide (GO) solution and single walled carbon nanotubes (SWCNT) are demonstrated with SRI measurement. Here, the fabricated devices show a significant intensity change into the transmission spectrum. The resonance response is observed in the near- to mid-IR ranges. This enhanced sensitivity is utilised for haemoglobin sensing in the detection of anaemia in human body and relative humidity sensing for monitoring environmental condition respectively. All demonstrated optical fibre grating based sensors have potential for a wide range of future applications in industry, medical and environmental sectors

Design of optical fiber sensors and interrogation schemes

[ES] Las fibras ópticas son dispositivos muy utilizados en el campo de las telecomunicaciones desde su descubrimiento. En las últimas décadas, las fibras ópticas comenzaron a utilizarse como sensores fotónicos. Los primeros trabajos se centraron en la medición de unas dimensiones físicas en un punto específico. Posteriormente, surgió la posibilidad de medir las propiedades de la fibra óptica en diferentes puntos a lo largo de la fibra. Este tipo de sensores se definen como sensores distribuidos. Los componentes optoelectrónicos fueron desarrollados e investigados para telecomunicaciones. Los avances en las telecomunicaciones hicieron posible el desarrollo de sistemas de interrogación para sensores de fibra óptica, creciendo en paralelo con los avances de las telecomunicaciones. Se desarrollaron sistemas de interrogación de fibra óptica que permiten el uso de una única fibra óptica monomodo estándar como sensor que puede monitorear decenas de miles de puntos de detección al mismo tiempo. Los métodos que extraen la información de detección de la señal reflejada en la fibra óptica son los más empleados debido a la facilidad de acceso al sensor y la flexibilidad de estos sistemas. Los más estudiados son la reflectometría en dominios de tiempo y frecuencia. La reflectometría óptica en el dominio del tiempo (OTDR) fue la primera técnica utilizada para detectar la posición de los fallos en las redes de comunica-ción de fibra óptica. El OTDR sensible a la fase hizo posible detectar la elongación y la temperatura en una posición específica. Paralelamente, los gratings de Bragg (FBG) se convirtieron en los dispositivos más utilizados para implementar sensores en fibra óptica discretos. Se desarrollaron técnicas de multiplexación para realizar la detección en múltiples puntos utilizando FGBs. La reflectometría realizada interrogando arrays de FBG débiles demuestra que mejora el rendimiento del sistema en comparación al uso de una fibra monomodo. Los sistemas de interrogatorio actuales tienen algunos inconvenientes. Algunos de ellos son velocidad de interrogatorio limitada, grandes dimensiones y alto costo. En esta tesis doctoral se desarrollaron nuevos sistemas de interrogación y sensores de fibra óptica para superar algunos de estos inconvenientes. Los sensores de fibra óptica de plástico demuestran ser una plataforma innovadora para desarrollar nuevos sensores y sistemas de interrogación de bajo costo y fáciles de implementar para fibras de plástico comerciales. Se investigó la reflectometría en el dominio del tiempo y las técnicas fotónicas de microondas para la interrogación de una matriz de rejillas débiles que permitieron simplificar el sistema de interrogación para la detección de temperatura y vibración.[CA] Les fibres òptiques són dispositius molt utilitzats en el camp de les telecomunica-cions des del seu descobriment. En les últimes dècades, les fibres òptiques van començar a utilitzar-se com a sensors fotònics. Els primers treballs es van centrar en el mesurament d'unes dimensions físiques en un punt específic. Posteriorment, va sorgir la possibilitat de mesurar les propietats de la fibra òptica en diferents punts al llarg de la fibra. Aquest tipus de sensors es defineixen com a sensors distribüits. Els components optoelectrònics van ser desenvolupats i investigats per a telecomunicacions. Els avanços en les telecomunicacions van fer possi-ble el desenvolupament de sistemes d'interrogació per a sensors de fibra òptica, creixent en paral·lel amb els avanços de les telecomunicacions. Es van desenvolupar sistemes d'interrogació de fibra òptica que permeten l'ús d'una única fibra òptica monomodo estàndard com a sensor que pot monitorar desenes de milers de punts de detecció al mateix temps. Els mètodes que extreuen la informació de detecció del senyal reflectit en la fibra òptica són els més utilitzats a causa de la facilitat d'accés al sensor i la flexibilitat d'aquests sistemes. Els més estudiats són la reflectometría en dominis de temps i freqüència. La reflectometría òptica en el domini del temps (OTDR) va ser la primera tècnica utilitzada per a detectar la posició de les fallades en les xarxes de comunicació de fibra òptica. El OTDR sensible a la fase va fer possible detectar l'elongació i la temperatura en una posició específica. Paral·lelament, els gratings de Bragg (FBG) es van convertir en els dispositius més utilitzats per a implementar sensors en fibra òptica discrets. Es van desenvolupar tècniques de multiplexació per a realitzar la detecció en múltiples punts utilitzant FGBs. La reflectometría realitzada interrogant arrays de FBG febles demostra que millora el rendiment del sistema en comparació a l'ús d'una fibra monomodo. Els sistemes d'interrogatori actuals tenen alguns inconvenients. Alguns d'ells són velocitat d'interrogatori limitada, voluminositat i alt cost. En aquesta tesi doctoral es van desenvolupar nous sistemes d'interrogació i sensors de fibra òptica per a superar alguns d'aquests inconvenients. Els sensors de fibra òptica de plàstic demostren ser una plataforma innovadora per a desenvolupar nous sensors i siste-mes d'interrogació de baix cost i fàcils d'implementar per a fibres de plàstic comercials. Es va investigar la reflectometría en el domini del temps i les tècniques fotòniques de microones per a la interrogació d'una matriu de reixetes febles que van permetre simplificar el sistema d'interrogació per a la detecció de temperatura i vibració.[EN] Optical fibers are devices largely used in telecommunication field since their discovery. In the last decades, optical fibers started to be used as photonic sensors. The first works were focused on the measurement of physical dimensions to a specific point. Afterward, emerged the possibility to measure the optical fiber properties at different locations along the fiber. These kinds of sensors are defined as distributed sensors. The optoelectronic components were developed and investigated for telecommunications. The progress in telecommunication made possible the development of optical fiber sensors interrogation systems, growing in parallel with the advances of telecommunications. Optical fiber interrogation systems were developed to use a single standard monomode optical fiber as a sensor that can monitor tens of thousands of sensing points at the same time. The methods that extract the sensing information from the backscattered signal in the optical fiber are widely employed because of the easiness of access to the sensor element and the flexibility of these systems. The most studied are the reflectometry in time and frequency domains. The optical time domain reflectometry (OTDR) was the first technique used to detect the position of the failures in the optical fiber communication networks. Using phase sensitive OTDR it is possible to sense strain and temperature at a specific position. In parallel, fiber Bragg gratings (FBGs) became the most widely used devices to implement discrete optical fiber sensors. Multiplexing techniques were developed to perform multi points sensing using these gratings. The reflectometry performed interrogating weak FBGs arrays demonstrate to improve the performance of the system employing a single mode fiber. The interrogation systems nowadays have some drawbacks. Some of them are limited speed of interrogation, bulkiness, and high cost. New interrogation systems and optical fiber sensors were developed in this doctoral thesis to overcome some of these drawbacks. Plastic optical fiber sensors demonstrate to be an innovative platform to develop both new sensors and low cost, easy to implement interrogation systems for commercial plastic fibers. Reflectometry in time domain and microwave photonic techniques were investigated for the interrogation of weak gratings array allowed to simplify the interrogation system for the sensing of temperature and vibration.I would like to greatly thank the European Union’s Horizon 2020 Research and Innovation Program that funded the research described in this thesis under the Marie Sklodowska-Curie Action Grant Agreement 722509.Sartiano, D. (2021). Design of optical fiber sensors and interrogation schemes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/161357TESI

Active and passive mid-infrared photonic devices in ZnSe based materials

The work described in this thesis details the development of mid-infrared waveguide laser sources created through the fabrication of waveguide structures in Cr2+: ZnSe using ultrafast laser inscription (ULI). Current quantum cascade laser (QCL) technology in the 2 – 5 μm region offer compact and robust sources suited to use outside the laboratory but the technology does not offer the high average powers, >100 mW, and wide tuneability, 2 – 3.3 μm of Cr2+: ZnSe laser sources. The development of a Cr2+: ZnSe waveguide laser source provides an environmentally robust product with access to powers and tuneable ranges greater than that provided by QCL systems. The first phase of the investigation produced the first successful refractive index modification of ZnSe using ULI. Both positive and negative refractive index changes were achieved and utilised to fabricate a range of waveguides in ZnSe and Cr2+: ZnSe. Low loss near-infrared waveguides were demonstrated through exploitation of the positive refractive index change. Low loss mid-infrared depressed cladding waveguides were subsequently demonstrated utilising the negative refractive index change. These waveguides were characterised at wavelengths of 1928, 2300 and 3390 nm as representative of pump and signal wavelengths in Cr2+: ZnSe laser systems. Finally, the newly fabricated Cr2+: ZnSe waveguides were constructed into waveguide laser cavities and pumped with a thulium fibre laser source operating at 1928 nm. Laser operation is demonstrated in both waveguides devices at wavelengths of 2573 and 2486 nm with a maximum achieved output power of 285 mW and a slope efficiency of 45%. Furthermore, a tuneable laser source is constructed in the Littman-Metcalf configuration exhibiting a maximum tuning range of 510 nm, 2330-2840 nm, with output powers exceeding 25 mW across the full range. These waveguide laser devices offer an environmentally robust and compact source in the 2 – 3 μm region with improvements upon maximum power and tuneability ranges in current quantum cascade laser sources. The waveguide laser sources reported open the door to products offering the robust nature of QCL sources with the higher powers and 2 – 3 μm tuneability associated with current bulk Cr2+: ZnSe laser systems.Engineering and Physical Sciences Research Council (EPSRC