Resonance‐Induced Dispersion Tuning for Tailoring Nonsolitonic Radiation via Nanofilms in Exposed Core Fibers

Abstract

Efficient supercontinuum generation demands for fine‐tuning of the dispersion of the underlying waveguide. Resonances introduced into waveguide systems can substantially improve nonlinear dynamics in ultrafast supercontinuum generation via modal hybridization and formation of avoided crossings. Using the example of exposed core fibers functionalized by nanofilms with sub‐nanometer precision both zero‐dispersion and dispersive wave emission wavelengths are shifted by 227 and 300 nm, respectively, at tuning slopes higher than 20 nm/nm. The presented concept relies on dispersion management via induced resonances and can be straightforwardly extended to other deposition techniques and film geometries such as multilayers or 2D materials. It allows for the creation of unique dispersion landscapes, thus tailoring nonlinear dynamics and emission wavelengths and for making otherwise unsuitable waveguides relevant for ultrafast nonlinear photonics.

Understanding Nonlinear Pulse Propagation in Liquid Strand-Based Photonic Bandgap Fibers

“…Figure 1b shows the spectral distribution of the GVD parameter β 2 = ∂ 2 β/∂ω 2 (with the propagation constant β = n eff (ω) × ω/c, effective refractive index n eff , angular frequency ω, and speed of light in vacuum c) in three transmission bands, which is essential for the SCG process and shows a characteristic evolution within each band with a different sign of β 2 . This type of behavior is in qualitative accordance with the dispersion of anti-resonance hollow-core fibers [15,28] suggesting a conceptual similarity that results from the general concept of including resonances into the waveguide system for dispersion manipulation, which was also recently demonstrated on the example of dielectric nano-films located on the core of an exposed core fiber [13]. In the present case, the zero dispersion wavelengths (ZDWs) are 553, 689 and 962 nm within these three transmission bands.…”

“…Due to the strong wavelength dependence of this interference effect, PBG fibers (PBGFs) are highly suitable for the spectral filtering of multiple selected wavelengths, with extinction ratios as high as 60 dB/cm [9], or for ultrahigh sensitivity sensors to measure temperature [11] or strain [12]. In addition, the inclusion of resonances into the waveguiding system imposes a unique dispersion landscape [13] that strongly differs from its non-resonant counterpart [14,15] and that for instance leads to a massive increase in the group velocity dispersion (GVD) in close proximity to the edge of the transmission bands. This allowed for the observation of sophisticated nonlinear optical effects in PBGFs, examples of which include the extreme deceleration of the soliton self-frequency shift (SSFS) or the cancellation of the SSFS at the long-wavelength edge of the bandgap regions [16,17].…”

Tailored Multi‐Color Dispersive Wave Formation in Quasi‐Phase‐Matched Exposed Core Fibers

“…This does not increase the potential bandwidth, as this can also be achieved by shifting the DW 0 using an appropriate constant nanofilm thickness. [ 34 ] The situation changes, however, for the QPM peaks at long wavelengths: Here, the second ZDW at λ ≈ 2.7 µm is spectrally too far away to produce a zero‐order long‐wavelength DW by conventional means with our laser, so QPM is the only way to broaden the spectrum at low input energy.…”

“…[ 16 ] As shown, for example, in ref. [ 34 ], the inclusion of nano‐films enables waveguide systems to be used for nonlinear frequency conversion (through the creation of a zero‐dispersion wavelength [ZDW] near the pump), which typically do not work for this application. To establish the periodic modulation within the context of this work, we realize a periodic nano‐film on the core of an exposed core fiber (ECF) ( Figure 1 a –c).…”

“…The technique allows for simultaneous energy transfer into multiple regimes that cannot be reached with classical DW generation. This versatile generation process could be unlocked by extending our recently developed dispersion modulation scheme [ 24 , 34 ] that applies high refractive index nano‐films on the exposed side of a suspended‐core fiber. [ 35 , 36 , 37 , 38 ] Here, we mastered the process to obtain periodic longitudinal patterns to achieve for the first time wavelength‐tailored QPM for the efficient higher‐order DW generation in fibers with femtosecond pump pulses, uniquely leading to distinct narrowband spectral features with sub‐picosecond durations as suggested by realistic nonlinear pulse propagation simulations.…”