This review presents an overview of “Lab on Fiber” technologies and devices with special focus on the design and development of advanced fiber optic nanoprobes for biological applications. Depending on the specific location where functional materials at micro and nanoscale are integrated, “Lab on Fiber Technology” is classified into three main paradigms: Lab on Tip (where functional materials are integrated onto the optical fiber tip), Lab around Fiber (where functional materials are integrated on the outer surface of optical fibers), and Lab in Fiber (where functional materials are integrated within the holey structure of specialty optical fibers).

This work reviews the strategies, the main achievements and related devices developed in the “Lab on Fiber” roadmap, discussing perspectives and challenges that lie ahead, with special focus on biological sensing applications.

Lab on Fiber Technology for biological sensing applications

The flat tip of an optical fiber is a unique and unconventional platform for micro and nanotechnologies The small cross-section and large aspect ratio of the fiber provide an inherently light-coupled substrate that is uniquely suited to remote, in vivo and in situ applications However, these same characteristics challenge established fabrication technologies, which are best suited to large planar substrates This review presents a broad overview of strategies for patterning the flat tip of an optical fiber Techniques discussed include self-assembly, numerous lithographies, through-fiber patterning, hybrid techniques, and strategies for mass manufacture, while the diverse applications are discussed in context throughout

The Optical Fiber Tip: An Inherently Light-Coupled Microscopic Platform for Micro- and Nanotechnologies

Light-induced rotation of absorbing microscopic particles by transfer of angular momentum from light to the material raises the possibility of optically driven micromachines. The phenomenon has been observed using elliptically polarized laser beams or beams with helical phase structure. But it is difficult to develop high power in such experiments because of overheating and unwanted axial forces, limiting the achievable rotation rates to a few hertz. This problem can in principle be overcome by using transparent particles, transferring angular momentum by a mechanism first observed by Beth in 1936, when he reported a tiny torque developed in a quartz waveplate due to the change in polarization of transmitted light. Here we show that an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers. Depending on the polarization of the incident beam, the particles either become aligned with the plane of polarization (and thus can be rotated through specified angles) or spin with constant rotation frequency. Because these microscopic particles are transparent, they can be held in three-dimensional optical traps at very high power without heating. We have observed rotation rates in excess of 350 Hz.

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Optical alignment and spinning of laser-trapped microscopic particles

The flat endface of an optical fiber tip is an emerging light-coupled microscopic platform that combines fiber optics with planar micro- and nanotechnologies. Since different materials and structures are integrated onto the endfaces, optical fiber tip devices have miniature sizes, diverse integrated functions, and low insertion losses, making them suitable for all-optical networks. In recent decades, the increasing demand for multifunctional optical fibers has created opportunities to develop various structures on fiber tips. Meanwhile, the unconventional shape of optical fibers presents challenges involving the adaptation of standard planar micro- and nanostructure preparation strategies for fiber tips. In this context, researchers are committed to exploring and optimizing fiber tip manufacturing techniques, thereby paving the way for future integrated all-fiber devices with multifunctional applications. First, we present a broad overview of current fabrication technologies, classified as “top-down,” “bottom-up,” and “material transfer” methods, for patterning optical fiber tips. Next, we review typical structures integrated on fiber tips and their known and potential applications, categorized with respect to functional structure configurations, including “optical functionalization” and “electrical integration.” Finally, we discuss the prospects for future opportunities involving multifunctional integrated fiber tips.

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Multifunctional integration on optical fiber tips: challenges and opportunities

I analyze physical approximations and mathematical tools used when modeling diffractive optics elements and devices. Examples of the numerical simulation of focusing optical elements and a space-based Offner hyperspectral imaging spectrometer (hyperspectrometer) are presented. The design of the hyperspectrometer features the use of a diffractive optical element on curved surfaces. The modeling results show that the hyperspectrometer under study offers optical characteristics superior to those of a similar device based on spectral filters.

Modeling diffractive optics elements and devices

We fabricated and experimentally studied diffractive optical elements intended to focus near IR light into a ring and a twin-spot Fabrication technology and the performances of the fabricated optical elements are discussed

Fabricating and testing diffractive optical elements focusing into a ring and into a twin-spot

The fabrication of diamond-based optical elements for high-power CO2 lasers is of particular interest because of low optical absorption, high thermal conductivity and weak temperature dependence of the refractive index of diamond. In earlier publications, we presented the results of the implementation of ion-chemical etching technology for generating a diffraction grating on the surface of a diamond film. The results on generating diamond diffractive optical elements and a sub-wavelength antireflection structure by plasma etching were also presented. In this paper, we study the generation of the grating on the diamond surface by ion-chemical etching. The choice of (Ar+O2) mixture as a working gas and use of niobium as a masking layer are substantiated. The results of studying a diffraction microrelief generated on the diamond-film surface through ion-chemical etching are discussed.

Formation of diffractive microrelief on diamond film surface

We discuss experiments on micromanipulation in the higher-order Bessel beams generated by diffractive optical elements (DOEs). Comparison is made of the rotation efficiency in the Bessel beams of the fifth and tenth order. We show that a two-fold increase in the Bessel beam number results in about a two-fold increase of the linear velocity of the microparticle circular movement, despite the fact that the laser beam intensity shows over a three-fold decrease.

Micromanipulation in higher-order Bessel beams

A technology for fabricating a diffractive microrelief on an end face of a polycrystalline IR fiber (PIR-fiber) is studied. We discuss how fabrication imperfections of a beam-splitter implemented on the fiber’s output end face could affect the specified intensity distribution of diffraction orders. Recommendations for improving the characteristics of the microrelief to manufacture are worked out.

Studying fabrication errors of the diffraction grating on the end face of a silver-halide fiber

We discuss a method for generating a diffractive optical microrelief by plasmochemical etching with the use of a masking copper layer.

A. V. Volkov

Papers

Fabricating and testing diffractive optical elements focusing into a ring and into a twin-spot

Formation of diffractive microrelief on diamond film surface

Micromanipulation in higher-order Bessel beams

Studying fabrication errors of the diffraction grating on the end face of a silver-halide fiber

Thin copper film for plasma etching of quartz