Search

We report the presence of surface acoustic wave (SAW) band gap on acoustic superlattice (ASL) in a single-crystal lithium niobate structure. The band gap behavior is determined by calculating the SAW band structure and also by simulating the transmission of an acoustic wave through a finite length section of ASL using finite element analysis. The calculated band gap appears at a frequency twice the value expected from purely acoustic Bragg scattering. We have identified the band gap as originating from a polariton-based mechanism due to the coupling between the electromagnetic wave and the surface vibrations. We have examined the influence of the band gap on SAW generation with the ASL and have shown that the calculated frequency resonance of the SAW lies in the vicinity of the upper stop-band edges. This results in the localization of the SAW in the ASL. Experimental confirmation is achieved through direct measurement of the SAW displacement by laser vibrometry on an actual ASL SAW transducer. The localization of generated SAW to the ASL transducer is observed confirming the prediction of the existence of a band gap. © 2013 AIP Publishing LLC.

This study deploys the application of Fiber Bragg Gratings (FBGs) in physiological pressure monitoring by integrating an elastomeric, biocompatible coating ranging from 300-500μm, designed to improve sensor functionality for in-vivo pressure monitoring applications. FBGs are favored for their sensitivity, immunity to electromagnetic interference, and compact size, making them ideal for embedding within medical devices such as catheters and guidewires. However, their use has been limited by low inherent pressure sensitivity (3.14 pm/MPa) and the impracticality of thicker coatings described in previous studies. Our approach demonstrates that this unique coating not only boosts the pressure sensitivity significantly—surpassing 1.63 orders of magnitude (43.10 times)—but also enhances the signal-to-noise ratio of the optical signal. These advancements enable potential applications in high-resolution manometry, gastrointestinal pressure monitoring, intracranial and intracoronary blood pressure measurements, marking a significant step forward in medical diagnostics and monitoring.

Bioresorbable photonic implants are emerging as potential material choice for interstitial theranostic and monitoring applications. They gradually dissolve within the physiological environment in a clinically relevant period, eliminating the need for extraction surgeries. In the present study, we tested the suitability of in-house fabricated bioresorbable optical fibres based on calcium phosphate (CaP) glass for diffuse correlation spectroscopic (DCS) and diffuse fluorescence tomographic (DFT) applications. The results represent the potential of bioresorbable fibers for the monitoring of interstitial microvascular blood flow and the spatial distribution of fluorescent photosensitizer drugs that are administered prior to therapies. Together or separate, the continuous monitoring of these parameters can have significant implications in planning, optimizing and in predicting or monitoring the outcomes in interstitial photodynamic therapy (PDT).

Domain inversion (DI) is applied to traveling-wave integrated electrooptic (EO) LiNbO3 modulators to achieve predefined EO frequency response and improved performance with respect to standard single-domain (not domain-inverted) counterparts, including lower driving voltages and larger modulation bandwidths. In particular, when an appropriate poling (DI) is performed along the interaction length, two novel configurations are envisaged. 1) An apodised longitudinal poling profile is used in non-velocity-matched (NVM) modulators to achieve a desired EO response, such as amplitude modulation with intrinsic third-order Bessel-type optical filtering for duobinary transmission. 2) Two- section longitudinal poling is used to counteract the detrimental microwave loss effect in VM modulators and to increase the bandwidth to driving voltage ratio, achieving a value up to 50% larger than that of single-domain (unpoled) structure. [ABSTRACT FROM PUBLISHER]

Electric-field domain inversion cannot be performed in z-cut LiNbO3 after waveguide fabrication using common Ti-indiffusion techniques. In this work we show that an appropriate combination of low indiffusion temperature, dry O2 and Li enriched atmosphere during waveguide fabrication allows subsequent domain inversion without the need for any surface grinding, which would dramatically increase the risk of LiNbO3 substrate breakage during its processing. The proposed technique allows a simplified, robust and high yield processing over full wafer scale (up to 4”) with sub-micron resolution. [ABSTRACT FROM AUTHOR]