The field of integrated photonics has expanded since the last century due to the need for even smaller devices, finding numerous applications in areas such as sensing, communications, and information technology. Particularly, the use of optical sensors has increased in recent years due to advantages over classical sensors, including versatility, minimal sample quantities, and label-free quantitative detection of chemical and biological samples. One technique employed for creating integrated photonic structures is ultrashort laser inscription, enabling the fabrication of optical waveguides in transparent materials without the need for masks or chemical processes. This work presents significant advancements in the design, fabrication, and characterization of Mach-Zehnder interferometers (MZIs) based on optical waveguides, utilizing the femtosecond direct laser writing (FDLW) technique. These interferometers have enabled the creation of integrated systems and their application in detecting physical variables such as temperature changes and variations in the refractive index of solutions with varying concentrations, including urea. We manufactured an embedded Mach-Zehnder interferometer in soda-lime glass, exhibiting sensitivity comparable to Silicon-on-Insulator (SOI) devices. A substantial enhancement in sensitivity (~54 pm/°C) was achieved, thanks to the unique three-dimensional (3D) capabilities provided by FDLW, surpassing the typically low thermo-optic coefficient of soda-lime glass. As a proof of concept, we also applied the first FDLW-fabricated MZI for concentration changes detection through evanescent field interaction in fused silica, demonstrating a sensitivity of ~1.22 nm/mM. Such miniaturized structures will significantly impact the development of compact and highly sensitive integrated photonic devices.
We have investigated the ability to monitor the dynamics transition phase of various substances by resonant probe light. Such a specific Micro-Total Analysis Systems (μTAS) can be used in food, cosmetic and biology applications. Such labon- chip sensors present the possibility of data treatment with an embedded system. The serial of transduced spectra are then acquired with an optical spectrum analyzer linked to a computer on which Matlab software record and process the data in real time. Then specific quantities can be linked to the intrinsic physico-chemical characteristics of the substances. As an example (not exhaustive) the development and the ability of an optical integrated polymeric resonator, acting as a surface light probe, for monitoring temperature-induced supramolecular phase transitions will be presented. The homogeneous detection of the transitions between different self-assembled structures in an aqueous solution of fatty acids (12-hydroxystearic acid, in association with amino-pentanol) was studied by investigating the coupling between the solution and the integrated photonic micro-cavity. Tuning the self-organized assemblies of surfactant is very attractive for many applications, such as cosmetic products, food, drug delivery and medical, and the development of alternative tools - especially those requiring minute amount of solution - to monitor their structural changes are essential. These original studies at temperatures ranging from 17 to 24 °C, based on a statistical treatment of optical resonance spectra, have evidenced the thermoresponsive nature of the optical features, and that different regimes occur with temperature. The optical results were corroborated with the measurement of the solution viscosity as a function of temperature, confirming that we can ascribe the optically-detected regimes to a surfactant assembly shifting reversibly from a tubular shape to a micellar one. The comparison between the optical and the rheological responses showed different accuracies: while the viscosity data exhibited a rather smooth and monotonous transition, the behavior changes were sharper and non-monotonous in terms of optical properties, allowing us to unambiguously identify in intermediate regime between 18.5 and 20°C. These morphological transition experiments represent a unique opportunity to extend the numbers of available techniques studying these systems through integrated optical techniques with potential opportunities of real time detection and working on low sampling volume. Other examples will be developed as the detecting of phase transition of sphingomyelin in biology and health corroborate by differential scanning calorimetry.
Optical cavities are able to confine and store specific wavelengths of light, acting as optical amplifiers at those wavelengths. Because the amount of amplification is directly related to the cavity quality factor (Q) (or the cavity finesse), frequency comb research has focused on high-Q and ultra-high Q microcavities fabricated from a range of materials using a variety of methods. In all cases, the comb generation relies on a nonlinear process known as parametric frequency conversion which is based on a third order nonlinear interaction and which results in four wave mixing (FWM). Clearly, this approach requires significant optical power, which was the original motivation for using ultra-high-Q cavities. In fact, the majority of research to date has focused on pursuing increasingly high Q factors. However, another strategy is to improve the nonlinearity of the resonator through intelligently designing materials for this application. In the present work, a suite of nanomaterials (organic and inorganic) have been intelligently designed with the explicit purpose to enhance the nonlinearity of the resonator and reducing the threshold for frequency comb generation in the near-IR. The nanomaterials do not change the structure of the comb and only act to reduce the comb threshold. The silica microcavity is used as a testbed for initial demonstration and verification purposes. However, the fundamental strategy is translatable to other whispering gallery mode cavities.
The following work presents the linear and nonlinear optical (NLO) properties for two ligands (L1-L2) derived from cinnamaldehyde and their corresponding boron complexes (B1-B2). These organic molecules have a backbone with electronic π-systems possessing different "push-pull" features. The structure confirmation of compounds L1 and B1 was made through X-ray diffraction analysis, wherein is observed that planar conformation is conserved after boron complexation on B1. Linear absorption of ligands and boron complexes shows a red shift after boron complexation which could be attributed to more efficient intramolecular charge transfer. Second and third-order NLO responses were performed by Electric Field Induced Second Harmonic (EFISH) Generation technique at 1.9 μm and Third-Harmonic Generation (THG) at 1.9 and 1.067 μm, respectively. Experimental results showed an increment on the hyperpolarizabilities values from ligands to boron complexes which are attributed to N→B coordinative bond. The first hyperpolarizability increased by factors of 3 and 2 from L1 to B1 and L2 to B2, respectively. Individually, these studies demonstrate that B1 is the strongest NLO compound, showed values of first hyperpolarizability 126×10-24 and second hyperpolarizability 35×10-24.
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