Femtosecond Inscription of a Fiber Bragg Grating Spectral Array in the Same Spatial Location.

A five fiber Bragg grating (FBG) array is inscribed at the same spot with a single uniform phase-mask (PM). The inscription setup consists of a near-infrared femtosecond laser, a PM, a defocusing spherical lens and a cylindrical focusing lens. The tunability of the center Bragg wavelength is achieved by a defocusing lens, and by translating the PM, which results in a different magnification of the PM.

Step-Index (Semi-Immersed) Model for Photonic Nanojet and Experimental Characterization via Near-Field Optical Microscopy with Microcylinder.

Experimental limitations such as design complexity and low optical throughput have prevented photonic nanojet (PNJ) and photonic hook (PH) measurements from demonstrating and characterizing the implementation of narrow intense electromagnetic beams generated from dielectric microelements with circular symmetry. Near-fields optical microscopy can mitigate these limitations and still present a capability of detecting a highly localized electromagnetic beam for applications in step-index media. Here we model a localized PNJ and PH formation in step-index media.

Green-Graphene Protective Overlayer on Optical Microfibers: Prolongs the Device Lifetime.

Optical microfibers find new applications in various fields of industry, which in turn require wear resistance, environmental friendliness and ease of use. However, optical microfibers are fragile. Here we report a new method to prolong the microfiber lifetime by modifying its surface with green-extracted graphene overlayers.

Femtosecond Bragg grating inscription in an Yb-doped large-mode-area multicore fiber for high-power laser applications.

We demonstrate a direct inscription of a fiber Bragg grating (FBG) in the active cores of an Yb-doped large mode area multicore fiber (MCF). An ultrashort pulsed laser is used to inscribe the FBG simultaneously in all six cores. In order to validate the FBG reflection and uniformity, the FBG is incorporated as a rear mirror in a fiber laser oscillator setup.

Surface roughness-induced absorption acts as an ovarian cancer cells growth sensor-monitor.

Uncontrolled growth of ovarian cancer cells is the fifth leading cause of female cancer deaths since most ovarian cancer patients are diagnosed at an advanced stage of metastatic disease. Here, we report on the sensor for monitoring the cancer treatment efficiency in real-time. We measure the optical interaction between the evanescent fields of microfiber and ovarian cancer inter-cellular medium at different treatment stages.

Femtosecond inscription of fiber Bragg gratings through the coating with a Low-NA lens.

Fiber Bragg grating (FBG) inscription in standard fibers with femtosecond (fs) laser pulses was first reported nearly two decades ago. FBG fs inscription through the fiber polymer coating was recently demonstrated with a phase mask (PM) and High Numerical Aperture (High-NA) cylindrical lenses. In this work, we report on a new technique for FBG inscription through the acrylate polymer coating of optical fibers using a Low-NA lens and the PM.

Characterizing the effect of femtosecond photo-treatment on the center wavelength of fiber Bragg gratings.

Various types of pre- and post-treatments to optical fibers are typically used to improve and/or change the properties of fiber Bragg grating (FBG). Here, we investigate experimentally the effects of NIR femtosecond (fs) laser pulses used for pre- and post-treatment on the refractive index of the fiber, and the resulting center wavelength shift of an fs inscribed FBG. We observe "red"-shift when applying a suitable pre-treatment, and both "blue"- and "red"-shifts when applying post-treatment.

Strain-assisted femtosecond inscription of phase-shifted gratings.

Two slightly shifted gratings are inscribed, one over the other, while exploiting fiber strain in a single-mode fiber. The inscription is done with a near-infrared femtosecond laser, a phase mask, and a cylindrical focusing lens. The first fiber Bragg grating (FBG) is inscribed under normal fiber tension, while the second overlapping FBG is inscribed under higher fiber tension.

Ns-duration transient Bragg gratings in silica fibers.

We demonstrate, for the first time to our knowledge, fast all-optical switching in standard silica fibers, based on a transient Bragg grating. The grating is implemented in the fiber using an immunization photo-pretreatment process, followed by side illumination with femtosecond laser pulses through a suitable phase mask. Each pulse is nonlinearly absorbed, creating a thermal grating that is washed out by thermal diffusion.

Properties of light reflected from road signs in active imaging.

Night vision systems in vehicles are a new emerging technology. A crucial problem in active (laser-based) systems is distortion of images by saturation and blooming due to strong retroreflections from road signs. We quantify this phenomenon.