High power, ultrashort pulse control through a multi-core fiber for ablation

Ultrashort pulse ablation has become a useful tool for micromachining and biomedical surgical applications. Implementation of ultrashort pulse ablation in confined spaces has been limited by endoscopic delivery and focusing of a high peak power pulse. Here we demonstrate ultrashort pulse ablation through a thin multi-core fiber (MCF) using wavefront shaping, which allows for focusing and scanning the pulse without requiring distal end optics and enables a smaller ablation tool. The intensity necessary for ablation is significantly higher than for multiphoton imaging. We show that the ultimate limitations of the MCF based ablation are the nonlinear effects induced by the pulse in the MCFs cores. We characterize and compare the performance of two devices utilizing a different number of cores and demonstrate ultrashort pulse ablation on a thin film of gold.

Three-dimensional microfabrication through a multimode optical fiber

3D printing based on additive manufacturing is an advanced manufacturing technique that allows the fabrication of arbitrary macroscopic and microscopic objects. Many 3D printing systems require large optical elements or nozzles in proximity to the built structure. This prevents their use in applications in which there is no direct access to the area where the objects have to be printed. Here, we demonstrate three-dimensional microfabrication based on two-photon polymerization (TPP) through an ultra-thin printing nozzle of 560 µm in diameter. Using wavefront shaping, femtosecond infrared pulses are focused and scanned through a multimode optical fiber (MMF) inside a photoresist that polymerizes via two-photon absorption. We show the construction of arbitrary 3D structures built with voxels of diameters down to 400 nm on the other side of the fiber. To our knowledge, this is the first demonstration of microfabrication through a multimode optical fiber. The proposed printing nozzle can reach and manufacture micro-structures in otherwise inaccessible areas through small apertures. Our work represents a new area which we refer to as endofabrication.

Calibration-free imaging through a multicore fiber using speckle scanning microscopy

The images produced by multicore endoscopes are pixelated, and their resolution is limited by the core-to-core spacing. Lenses can be used to improve the resolution, but this reduces the field of view proportionally. Lensless endoscopy through multicore fibers can be achieved by using wavefront shaping techniques. This requires a calibration step, and the conformation of the fiber must remain constant over time. Here we demonstrate that, without a calibration step and in the presence of core-to-core coupling, we can obtain fluorescence images with a resolution better than the core-to-core spacing. This is accomplished by taking advantage of the memory effect present in these kinds of fibers.

Lensless two-photon imaging through a multicore fiber with coherence-gated digital phase conjugation

We performed near-diffraction limited two-photon fluorescence (TPF) imaging through a lensless, multicore-fiber (MCF) endoscope utilizing digital phase conjugation. The phase conjugation technique is compatible with commercially available MCFs with high core density. We demonstrate focusing of ultrashort pulses through an MCF and show that the method allows for resolution that is not limited by the MCF core spacing. We constructed TPF images of fluorescent beads and cells by digital scanning of the phase-conjugated focus on the target object and collection of the emitted fluorescence through the MCF.

Towards new applications using capillary waveguides

In this paper we demonstrate the enhancement of the sensing capabilities of glass capillaries. We exploit their properties as optical and acoustic waveguides to transform them potentially into high resolution minimally invasive endoscopic devices. We show two possible applications of silica capillary waveguides demonstrating fluorescence and optical-resolution photoacoustic imaging using a single 330 μm-thick silica capillary. A nanosecond pulsed laser is focused and scanned in front of a capillary by digital phase conjugation through the silica annular ring of the capillary, used as an optical waveguide. We demonstrate optical-resolution photoacoustic images of a 30 μm-thick nylon thread using the water-filled core of the same capillary as an acoustic waveguide, resulting in a fully passive endoscopic device. Moreover, fluorescence images of 1.5 μm beads are obtained collecting the fluorescence signal through the optical waveguide. This kind of silica-capillary waveguide together with wavefront shaping techniques such as digital phase conjugation, paves the way to minimally invasive multi-modal endoscopy.

Light control in a multicore fiber using the memory effect

Endoscopic imaging through a multicore fiber (MCF) is widely used but is affected by pixelated images, which limits its resolution to a few micrometers. This is due to the spacing between the cores in the MCF, which is large enough to avoid core-to-core light coupling. Wavefront shaping techniques have been shown to focus light to a resolution finer than the inter core spacing, however a long calibration procedure is needed. Moreover the calibration depends on the optical fiber conformation. Here, we show a calibration method using only one digital hologram. The method is based on digital phase conjugation and the memory effect of the MCF to focus and scan a spot. In addition, we show how simple patterns can be projected using the same multicore fiber.

Enhanced resolution in a multimode fiber imaging system

Multimode fibers have recently been demonstrated to be a promising candidate for ultrathin and high resolution endoscopy. However, this method does not offer depth discrimination for fluorescence imaging and the numerical aperture of the fiber limits its resolution. In this paper we demonstrate optical sectioning and enhanced resolution using saturated excitation and temporal modulation. Using a continuous wave laser excitation, we demonstrate improved resolution in all three dimensions and increased image contrast by rejecting out of focus light.

Optimal control for SIRC epidemic outbreak

In this paper the mathematical SIRC epidemic model is considered. It efficiently describes diseases in which a cross immune class (C) is present, along with the susceptible (S), the infected (I) and the removed (R) ones. Controlling epidemic diseases corresponds to the introduction of vaccination, quarantine and treatment strategies; generally only one of these actions is considered. In this paper the possibility of optimal controls both over the susceptible and the infected subjects is assumed, taking into account also limitations of resources. A suitable cost index is introduced and via the Pontryagin's Minimum Principle the optimal control strategy is determined and the existence of the optimal solution is assessed. Numerical results are developed analyzing the effects of different control strategies.