Fabrication and characterization of periodically patterned silica fiber structures for enhanced second-order nonlinearity

Abstract

We develop and characterize a UV ablation technique that can be used to pattern soft materials such as polymers and nonlinear molecules self-assembled over silica microstructures. Using this method, we fabricate a spatially periodic coating of nonlinear film over a thin silica fiber taper for second harmonic generation (SHG). Experimentally, we find that the second harmonic signal produced by the taper with periodic nonlinear coating is 15 times stronger than the same taper with uniform nonlinear coating, which suggests that quasi-phase-matching is at least partially achieved in the patterned nonlinear silica taper. The same technique can also be used to spatially pattern other types of functional nanomaterials over silica microstructures with curved surfaces, as demonstrated by deposition of gold nanoparticles in patterned structures.

Second harmonic generation in thin optical fibers via cladding modes

“…For coating the fiber with nonlinear film, the ionic self -assembled multilayer (ISAM) technique is used. This technique is fully described in [12][13][14]. The one bilayer is composed of positively charged polyelectrolyte which is poly (allylamine hydrochloride) (PAH) followed by negatively charged polyelectrolyte which is the nonlinear nanomaterial (Procion Brown (PB)).…”

“…Recently [14], the QPM technique was applied in nonlinear fiber tapers in order to solve the problem of mismatching between pump and second harmonic modes [12,13]. Under 400 W of pump power, the SHG efficiency is enhanced theoretically to ~10%, and experimentally to ~10 -4 %.…”

“…The efficiency through SMF under pump power 3 W is higher than MMF under pump power of 400 W. Table 4 is introduced to compare our results with other reports considering the main parameters such as input power, fiber dimensions, and interaction length. Although fiber taper model [12][13][14] introduces the idea of using traditional optical fibers to produce SHS with acceptable efficiency, the model has many practical problems such as the assumption of higher input pump mode and difficulties to reach fiber taper with such dimensions. We figure out that, the maximum total efficiency of our model is around 10 2fold enhancement compared with that calculated from nonlinear fiber taper [12,13] without the need to apply the QPM technique.…”

“…This coated fiber taper can produce SHS with theoretical efficiency of order 10 -3 % [12,13]. Recently, C. Daengngam et al [14] implemented Quasi Phase Matching (QPM) in nonlinear fiber tapers that enhance the SHG efficiency to reach the order of 10%.…”

“…Furthermore, the efficiency of SHG is quite low due to the phase mismatching between the fundamental core mode and generated SHS, and the small area of interaction between fundamental core mode and the nonlinear material. QPM can solve the phase mismatching issue but still concerns about the small diameter and the efficiency itself [14].…”