High-quality manipulable fiber-microsphere for super-resolution microscopy.

Despite the gain in resolution brought by microsphere (MS)-assisted microscopy, it has always faced several limitations, such as a limited field of view, surface defects, low contrast, and lack of manipulability. This Letter presents a new type of MS created at the tip of an optical fiber, which we call a fiber microsphere (fMS). The fMS is made from a single-mode or coreless fiber, molten and stretched, ensuring high homogeneity and a sphere diameter smaller than the fiber itself. In addition, the connection between the fMS and the fiber makes scanning the sample a simple task, offering a solution to the difficulties of handling. The fabrication procedure of the fMS and the optical system used in the study are detailed. Our measurements show a clear superiority of the fMS over the soda-lime MS in resolving power and imaging performance.

Molded high curvature core-aligned micro-lenses for single-mode fibers.

A polymer-based fiber micro-lens molding fabrication technique with, to our knowledge, unprecedented performances is presented along with its advantages and applications. This technique is a fast and affordable tool to achieve a wide variety of possible spherical and aspherical micro-lens sizes and curvatures. The alignment of the micro-lens mold with the fiber core receiving the lens is done optically, which allows high precision. Using the proposed technique, different micro-lenses are fabricated. Then the output beams of two different micro-lenses on single-mode fibers are characterized. Fiber micro-lenses with curvature as small as 5 µm are achieved. This shows how low curvature micro-lenses can achieve collimation and how high curvature ones on single-mode fibers lead to high focusing (FWHM=λ) that is much smaller than what most conventional commercial techniques can reach. Given that this technique imposes no stress and causes no damage to the fiber receiving the micro-lens, it presents a significant potential for compatibility with non-silica-based and micro-structured fibers such as photonic crystal and quasi-crystal fibers.

Direct imaging of a photonic jet at shaped fiber tips.

This Letter presents, to our knowledge, the first direct measurement of the three-dimensional distribution of photonic jets (PJs) generated by shaped-tip multimode optical fibers. A PJ at the distal end of optical fibers makes it easier to scan a sample, for lithography or optical analysis, for example, with a spot smaller than the diffraction limit. The backscattered light can also be easily collected. In this study, the volume of the PJ has been reconstructed using a stack of image planes and compared to numerical simulations. For the first time, the power distribution of the non-fundamental mode around the PJ has been observed, giving a better understanding of PJ-based laser etching using multimode optical fibers. An original 50/125 fiber with a microlens fitting just on its core has made it possible to strongly reduce the power spread compared to the thermoformed 100/140 fibers used in our previous works.