We present a novel photonic structure on the end-face of a polarization-maintaining single-mode optical fiber for broadband vector beam generation, specifically radially and azimuthally polarized beams and modes. The structure, micro-3D printed using 2-photon lithography, is sub-mm long, and features a unique design comprising complex sequential sections. Our unprecedented design enables spatial control over light's intensity profile and polarization at the optical fiber’s output, with potential significant implications for fields such as optical communications, optical trapping, microscopy, and material processing.
Bessel beams (BBs) were first introduced by Durnin in 1987 and have a transverse intensity distribution dictated by the Bessel function. BBs are characterized by their diffraction-free propagation and self-healing nature. The family of BBs is categorized into two sets - zeroth-order Bessel beams (ZOBBs) with narrow high-intensity center and high-order Bessel beams (HOBBs) with phase singularity and dark center. HOBBs are vortex beams as they carry orbital angular momentum (OAM). Several approaches to generate BBs have been devised; some of them include transforming a narrow annular beam with a lens, using an axicon, or using spatial light modulators. Nevertheless, these techniques involve space-consuming and expensive table-top diffractive optical elements. In recent years, the on-fiber generation of BBs has gained prominence as it offers miniaturized optical probes that can find exciting applications in different fields, ranging from bio-imaging to communications. Here, we present on-fiber 3D printed complex photonic structures that convert the Gaussian-like mode from single-mode fibers into BBs of various orders. Remarkably, we report for the first time the generation of HOBBs from optical fibers. Our technique is inspired by Durnin's approach of generating BBs due to the transformation of an annular beam through a lens. Our novel design has three sections; the first and second sections contain photonic crystal waveguides that convert the input Gaussian-like mode into an annular beam of arbitrary radius and width, which is then transformed into BBs with the help of a micro-lens. To generate HOBBs, we also integrated a spiral phase plate in the stacked structure. We compared the experimentally generated BB parameters with what predicted from theory and found an excellent match. For HOBBs, we performed modal decomposition to confirm the existence of OAM. Overall, we showcase the results of various BBs with orders up to 20.
The conventional way of generating Bessel beams (BBs) is based on axicon and other diffractive optical elements such as light modulators. These methods involve space-consuming optics. To overcome this limitation, over the past years, efforts were made to create BBs using miniaturized optics and generation of BBs directly from optical fibers. We propose a novel photonic structure 3D micro-printed on the end-face of an optical fiber, generating BBs of various orders. With our approach, we report for the first time the generation of high-order BBs from optical fibers. The results showcase Bessel beams ranging from orders zero- to 20.
Optical tweezers based on single optical fibers are typically fabricated with methods that grant only limited design flexibility in the trapping geometry. Here, we present a novel hybrid micro-optical structure 3D printed in a single step on a standard single-mode optical fiber, to create an ultra-compact fiber tweezer. The structure is made of stacked refractive, reflective, and waveguiding optical elements. Our approach allows an easy and independent tuning of trapping parameters as the numerical aperture and the working distance of the optical trap. We experimentally illustrate the 3D trapping capabilities of the proposed fiber optical tweezers.
We study the near-infrared properties of spherical multishell nanoparticles comprising a loss-less dielectric core enclosed by a concentric layering of metallic–dielectric–metallic nanoshells. The coupling between the metallic shells induces plasmon resonance redshifts and peak splitting in the absorption spectra of the layered particle relative those of the metallic constituents. We use full-wave electromagnetic analysis to investigate changes in the absorption spectra as a function of key parameters including the material properties of the inner and outer metallic shells and the aspect ratio of their inner and outer radii. We systematically vary the aspect ratios and quantify the degree of plasmonic coupling between the metallic nanoshells. Our analysis reveals conditions under which the spectral resonance peaks blueshift and/or redshift. We consider bimetallic particles with gold and silver nanoshells and determine the dependency of plasmon resonance peak shifting and splitting as a function of the order of these material layers, i.e., as inner or outer shells.
Tunable LASER source is a device which emits a particular light wavelength based on the tuning done. The tuning depends on certain characteristic of the LASER source which makes it customised within a gamut of wavelengths. Most Conventional LASER sources in the market are bulky and complex. The Tunable LASER source designed is established on the simple idea that Optical Amplifier can act as a broadband source, and temperature and strain sensitive Fiber Bragg Grating can be used to filter the required wavelength. This makes the design very light and elementary.
Pressure and temperature are fundamental properties of the oceanic water. They have varying effects on the processes that take place in oceans be they biological, physical or chemical while pressure always increases with respect to surface when you go down, temperature has a more complex variation with respect to the depth. Various tools and techniques are available to measure these properties. A combination sensor with high accuracy and response time would enable better measurements of these two parameters. This paper presents a novel structure based on simultaneous measurement of temperature and pressure sensing using Fiber Bragg grating (FBG) sensors. For this, proposed sensor heads for both temperature and pressure. Temperature measurement, two different types of sensor heads has been designed for this implementation. The first sensor head consists of a FBG which is fixed between ceramic block on one side and a bimetallic strip made up of aluminum and copper on the other. The second sensor head consists of the FBG which is fixed between two bimetallic strips. For pressure, in first type the FBG is fixed between silicon rubber foil and sensor head wall. In second method the FBG is fixed between two silicone rubber foils. The pressure on walls of silicon rubber foils elongates FBG, which results in shift of wavelength. Theoretical studies carried out on these proposed sensor heads resulted in an increase in temperature sensitivity of about six times greater than that of bare FBG sensor and pressure sensitivity of about eight times greater than that of bare FBG. Further, the proposed sensors have shown good linearity and stability.
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