Self-organized nanostructure formation during femtosecond-laser inscription of fiber Bragg gratings

Abstract

Periodic planar nanostructures are found in Type II-IR Bragg gratings produced in SMF-28 fiber by side-illuminating it with infrared femtosecond-laser pulses through a phase mask. The planar nanostructures are aligned perpendicular to the laser polarization, as demonstrated using scanning electron microscopy analysis of cleaved fiber samples. Dark field optical microscopy is employed for real-time monitoring of structural changes occurring inside the fiber during the inscription process.

Nano-ablation of silica by plasmonic surface wave at low fluence

“…Formation of deep-subwavelength structures is attracting the most interest. Research is focused on the evolution of ripples' period and orientation with laser power [6,13], pulse accumulation [6,14,15], laser polarization [16,17], and spin and angular momenta of photons [18]. Studies are focused on the lateral structure formation defined by polarization of the surface or perpendicular to the incoming laser beam [3,[19][20][21].…”

Through-the-coating femtosecond laser inscription of very short fiber Bragg gratings for acoustic and high temperature sensing applications

“…The intensity distribution after the phase mask M is visualized using direct imaging (DI) at λ = 800 nm. The fiber alignment is performed using nonlinear photoluminescence microscopy (NPM) at λ 1 ~400 nm [21]. Characterization of the resultant FBGs is performed using dark-field microscopy (DFM) at λ 2 = 637 nm [21].…”

“…Dark-field optical microscopy (DFM in Fig. 3) at λ 2 = 637 nm was employed for the visualization of laser-induced changes in the fiber under consideration [21]. Briefly, the DFM-technique is based on launching visible probe light into the fiber core and collecting scattered light originating from the laser-modified regions.…”

“…Using fs-lasers, FBGs can be produced i) by point-by-point [15], line-by-line [16], planeby-plane [17], and continuous writing [18], when the fs-laser beam induces changes in the fiber in a sequential fashion or ii) when a length of the fiber is irradiated simultaneously through a phase mask [19]. The latter technique is faster, more accurate and, importantly, allows one to fabricate both Type I or Type II FBGs using the same laser by simply changing its beam parameters (i.e., pulse duration and pulse energy) [20,21].…”

Fiber-Optic Multipoint Sensor System with Low Drift for the Long-Term Monitoring of High-Temperature Distributions in Chemical Reactors

“…gratings strongly decay at high temperatures [1,2]. Amongst others, type II FBGs inscribed with femtosecond (fs) lasers [3][4][5] and regenerated FBGs (RFBGs) [6][7][8] have been reported to be suitable for temperatures up to 1200 • C. Most often, type II FBGs are inscribed with high-intensity femtosecond laser beams by phase masks (type II-PM) [3,9] or by a point-by-point (type II-PbP) [10] technique, and their main features are a high grating reflectivity, inherent temperature stability, and high initial tensile strength. The disadvantages of type II FBGs arise from their polarization sensitivity [10,11] and strong cladding mode coupling [5,10], which can limit their multiplexing capabilities.…”