Abstract
Two multi-path interferometers were developed using cleaved silica microspheres. A microsphere on top of a singlemode fiber tip was cleaved with a focused ion beam. The asymmetry introduced in the structure generates a new set of optical paths due to random reflections inside the microsphere. The obtained reflection spectrum presents a random-like interferometric behavior with strong spectral modulation of around 3 dB amplitude. Two distinct regions can be observed when a fast Fourier transform is applied. The first involves two cavities at a lower frequency and the second region involves a band of frequencies that is originated by the random interferometric reflections. These two spectral characteristics can be separated using low-pass and high-pass filters, respectively. A correlation method was used to obtain a temperature response from the two-cavity component. A similar structure was also created in a microsphere of multimode fiber. The microsphere was cleaved by polishing the structure with a certain angle. The interference between the different optical paths can be seen as the superposition of several two-wave interferometers, which can be discriminated through signal processing. Temperature sensing was also explored with this structure. The sensitivity to temperature is more than 3-fold for smaller cavities. Moreover, a sensitivity enhancement is also verified if a correlation method is used.

Abstract

Abstract
This paper will review the fabrication of monolithic integrated optical devices by laser direct writing with femtosecond pulsed laser sources, starting with the description of experimental procedures and optimal conditions to fabricate low loss optical waveguides, directional couplers, Y-junctions and first order Bragg gratings by point-by-point writing methods. Finally, the characterization results of a fully operational Add-Drop filter in pure fused silica substrate are described.

Abstract
Optical coherence tomography (OCT) systems have huge potential for applications beyond the traditional ophthalmology as a general-purpose medical instrument for optical biopsy. The widening of the range of applications is expected to significantly increase production volume and, consequently, puts pressure on unit cost. This trend calls for a flexible and miniaturized system fabricated in a batch process. In this paper, the different OCT configurations are compared for suitability in such an implementation. The required flexibility favors operation in the spectral domain, using a broadband light source in combination with a spectrometer, while the miniaturization and low unit-cost in batch fabrication can be achieved using silicon micro-system technologies. The feasibility of miniaturizing OCT components has already been demonstrated, amongst others a beam splitter using 45 degrees saw dicing of a glass substrate and appropriate thin-film coating the integration of the essential components into a single OCT microsystem remains a challenge. In this paper, the wafer-level fabrication of a Michelson interferometer for a miniaturized OCT system is presented, using an improved 45 degrees saw dicing process, which is suitable for wafer-level co-integration of also the other components of the OCT microsystem.

Abstract
Optical analog experiments have captured a lot of interest in recent years by offering a strategy to test theoretical models and concepts that would be otherwise untestable. The approach relies on the similarity between the mathematical model for light propagation in nonlinear optical media and the model to be mimicked. In particular, the analogy between light and a quantum fluid with superfluidlike properties has been studied extensively. Still, while most of these studies use thermo-optical media to perform these experiments, the possibility of using nematic liquid crystals to perform such optical analog experiments remains to be analyzed. This work explores how this medium can constitute an alternative to materials more commonly used in optical analogs, such as thermo-optical media, and how its tunable properties can be advantageous to explore and better control fluidlike properties of light. Moreover, we explore the analogy between the propagation of light and a quantum fluid, and propose a pump-probe experiment to measure the dispersion relation of the superfluid analog.

Abstract