Coherent supercontinuum generation up to 23 µm in all-solid soft-glass photonic crystal fibers with flat all-normal dispersion

Abstract

Supercontinuum spanning over an octave from 900 - 2300 nm is reported in an all-normal dispersion, soft glass photonic crystal fiber. The all-solid microstructured fiber was engineered to achieve a normal dispersion profile flattened to within -50 to -30 ps/nm/km in the wavelength range of 1100 - 2700 nm. Under pumping with 75 fs pulses centered at 1550 nm, the recorded spectral flatness is 7 dB in the 930 - 2170 nm range, and significantly less if cladding modes present in the uncoated photonic crystal fiber are removed. To the best of our knowledge, this is the first report of an octave-spanning, all-normal dispersion supercontinuum generation in a non-silica microstructured fiber, where the spectrum long-wavelength edge is red-shifted to as far as 2300 nm. This is also an important step in moving the concept of ultrafast coherent supercontinuum generation in all-normal dispersion fibers further towards the mid-infrared spectral region.

Coherent supercontinuum bandwidth limitations under femtosecond pumping at 2 µm in all-solid soft glass photonic crystal fibers

“…ANDi SC pumped at around 1.55 µm and extending past 2.0 µm with their redshifted side-band have already been reported [14,15]. The all-solid glass approach to photonic crystal fiber (PCF) fabrication [16] allows broadband flattening of the ANDi profile, as shown in oxide soft glass fibers [15,17]. A hybrid ZBLAN-chalcogenide ANDi PCF was also demonstrated to generate an SC spectrum spanning 1.2-2.7 µm under pumping around 1.9 µm with 100 fs pulses [18], where ZBLAN is the well-known ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF heavy-metal fluoride glass composition.…”

“…Both fibers have a hexagonal lattice layout, in which the air-holes of the photonic cladding were replaced with another glass, thermally matched to the glass in the lattice and the core. The original design of fibers, reported previously and in this work labeled NL21C2 and NL21C4, consisted of a lattice and core made from F2 glass from Schott, with the lattice holes filled with inclusions made from in-house boron-silicate glass [15,17]. The refractive indices of the F2 and the boron-silicate glass, measured at 1550 nm, are 1.5948 (core and lattice glass) and 1.5113 (lattice inclusions).…”

“…This enables recompression close to the single-cycle limit using phase-compensation methods [13]. ANDi SC pumped at around 1.55 µm and extending past 2.0 µm with their redshifted side-band have already been reported [14,15]. The all-solid glass approach to photonic crystal fiber (PCF) fabrication [16] allows broadband flattening of the ANDi profile, as shown in oxide soft glass fibers [15,17].…”

“…This fiber is confronted in context of ANDi supercontinuum generation with the design reported earlier [15,17]. Both fiber types were made from silicate soft glasses and specifically the photonic lattice of the new ANDi PCF was composed of two commercially available glasses F2 and SF6 (Schott).…”

Group Delay measurements of ultrabroadband pulses generated in highly nonlinear fibers

“…On the other hand, stable and repeatable supercontinua are generated in all normal dispersion fibers where newly generated spectral components constantly recede from each other, and thus do not have the chance to interact for longer times [7]. Spectral broadening mechanisms have been investigated with the Cross-correlation Frequency Resolved Optical Gating (XFROG) technique [8] by several research groups [9][10][11].…”