Nanophotonics of optical fibers

Abstract

This review is concerned with nanoscale effects in highly transparent dielectric photonic structures fabricated from optical fibers. In contrast to those in plasmonics, these structures do not contain metal particles, wires, or films with nanoscale dimensions. Nevertheless, a nanoscale perturbation of the fiber radius can significantly alter their performance. This paper consists of three parts. The first part considers propagation of light in thin optical fibers (microfibers) having the radius of the order of 100 nanometers to 1 micron. The fundamental mode propagating along a microfiber has an evanescent field which may be strongly expanded into the external area. Then, the cross-sectional dimensions of the mode and transmission losses are very sensitive to small variations of the microfiber radius. Under certain conditions, a change of just a few nanometers in the microfiber radius can significantly affect its transmission characteristics and, in particular, lead to the transition from the waveguiding to non-waveguiding regime. The second part of the review considers slow propagation of whispering gallery modes in fibers having the radius of the order of 10-100 microns. The propagation of these modes along the fiber axis is so slow that they can be governed by extremely small nanoscale changes of the optical fiber radius. This phenomenon is exploited in SNAP (surface nanoscale axial photonics), a new platform for fabrication of miniature super-low-loss photonic integrated circuits with unprecedented sub-angstrom precision. The SNAP theory and applications are overviewed. The third part of this review describes methods of characterization of the radius variation of microfibers and regular optical fibers with sub-nanometer precision.

Optical bottle microresonators

“…1(c)), the axial radius can be made much greater than the azimuthal radius, ax az r r >> . For example, BMRs fabricated in SNAP (Surface Nanoscale Axial Photonics) technology [19][20][21][22][23][24][25][26][27][28] may have the axial radius exceeding a kilometre [23,24]. For this reason, the characteristic variation length of WGMs along the axis of a BMR can be much greater than that of spherical and toroidal microresonators.…”

Surface nanoscale axial photonics structures introduced by bending of optical fibers

“…Surface Nanoscale Axial Photonics (SNAP) is the ultraprecise platform for fabrication of miniature optical structures at the surface of optical fibers [1]. In SNAP structures, whispering gallery modes (WGMs) circulate around the optical fiber surface and undergo slow axial propagation.…”

“…The propagation is described by the one-dimensional Schrödinger equation. SNAP devices can be manufactured with unprecedented sub-angstrom precision [2] by local annealing with focused CO2 laser radiation [1] and by the femtosecond laser inscription [3]. The subangstrom fabrication precision of SNAP devices and their ultralow loss allows one to create complex miniature photonic circuits having promising applications in communication technologies, quantum computing, optomechanics, microfluidics, and sensing.…”

“…Remarkably, due to the positive sign of the ERV, this local bending introduces a SNAP optical bottle resonator [1] which parameters can be tuned by variation of the bending radius. Generally, more complex ERV can be introduced by advanced manipulation of the fiber ends.…”

Surface nanoscale axial photonics (SNAP) at the silica microcapillary with ultrathin wall

“…The Surface Nanoscale Axial Photonics (SNAP) platform [1] enables fabrication of resonant ultralow loss photonics structures at the surface of an optical fiber with unprecedented precision currently approaching 0.1 angstrom [2]. The idea of SNAP consists in exploring whispering gallery modes (WGMs) which slowly propagate along the surface of an optical fiber.…”