Single-mode fiber microlens with controllable spot size

Abstract

A novel method for fabricating microlenses on tapered single-mode fibers is shown to be able to control the lens spot size. The fiber cladding is first symmetrically tapered by etching it with an evaporating ammonium bifluoride solution. A hemispheric lens is then melted on the taper tip with a CO 2 laser. The lens can reduce the fiber mode radius to 40% of its original value. A theoretical calculation of the focused spot size agrees well with experimental results.

Focal properties of an aberration-free fiber micro-lens

“…It means the tapered clad don't affect on the mode of the SMF. This conclusion is agreed with the reported [8]. When the fiber micro-lens radius is larger than approximately twice the core radius, the mode is When the fiber micro-lenses radius is lager than twice the fiber core radius, an empirical formula for calculating the spot radius rsp ol is also obtained in Fig.6 r ,,!<,, /w = 0.54N,: -0.75N,: -O.4NII + I the formula provides the absolute value of relative error that is shown in Fig.7 is less than 6% for the micro lenses with clad radii of r=20 f.Lm and r=30 f.Lm , the relative error between the spot size calculated by (8) and by (3) in [8] is shown in Fig.8, and it is also less than 6%, this error can be accepted in laboratory and industry, it shows the empirical formula is valid.…”

“…Circle, plus sign, asterisk denote the simulated data, the calculated data by (8) and (3.2) in [4] respectively. An interesting result is observed.…”

“…The fiber has core and cladding retractive indices of 1.4575 and 1.453, respectively, and core diameters equal to 4.1 f.Lm , and the mode radius is 2.31 at 0.633 f.Lm . We present the results of the focal shift and the spot radius as a function of the Fresnel number Nw for tapered-cladding micro-lenses on the tip of the fiber in table 1 and 2, By comparing the simulation and the calculation results, it is shown that the empirical formulas (8) and (9) can accurately predict the focal shift and spot size of a tapered-cladding micro-lens.…”

Mode transforming properties of tapered single-mode fiber microlenses

“…Lenses are then formed by laser melting the ends of tapered fibers. 4 Figure 5 shows the experimental spot-size measurements. The theoretical curves are taken from Fig.…”

“…1(a). Alternatively, fibers may be tapered by acid etching, which results in a tapered-cladding lens, 4 as shown in Fig. 1(b).…”