Thermo-tunable hybrid photonic crystal fiber based on solution-processed chalcogenide glass nanolayers

The possibility to combine silica photonic crystal fiber (PCF) as low-loss platform with advanced functional materials, offers an enormous range of choices for the development of fiber-based tunable devices. Here, we report a tunable hybrid silica PCF with integrated As2S3 glass nanolayers inside the air-capillaries of the fiber based on a solution-processed glass approach. The deposited high-index layers revealed antiresonant transmission windows from ~500 nm up to ~1300 nm. We experimentally demonstrate for the first time the possibility to thermally-tune the revealed antiresonances by taking advantage the high thermo-optic coefficient of the solution-processed nanolayers. Two different hybrid fiber structures, with core diameter 10 and 5 μm, were developed and characterized using a supercontinuum source. The maximum sensitivity was measured to be as high as 3.6 nm/°C at 1300 nm. The proposed fiber device could potentially constitute an efficient route towards realization of monolithic tunable fiber filters or sensing elements.


Scanning Electron Microscopy
After the chalcogenide glass integration inside the holes of the silica PCFs, the end facets were cleaved using a ceramic cleaving tile. The SEM images in every case were taken with a FEI Quanta 200 ESEM FEG Electron Microscope using an accelerating voltage of 2-20 kV combined with energy dispersive X-ray Spectroscopy (EDX) (using an Oxford Instruments 80 mm 2 X-Max silicon drift detector) in order to confirm the existence of the two main elements of the chalcogenide nanofilms, Arsenic (As) and Sulfide (S). In addition to Fig. 1 in the manuscript, we imaged the hybrid LMA-5 PCF after the glass deposition and post-annealing treatment to confirm the presence of the chalcogenide glass films in the holes of the fiber. Figure S1 (a) shows the initial LMA-5 silica PCF used in our experiments and Fig. S1 (b) shows the core section of the fiber after integration of As 2 S 3 glass indicating the formation of the glass nanolayers in the air-holes of the fiber. It should be noted that Fig. S2 (b) is slightly distorted as the angled cleave of the fiber introduced strong electron charging inside the holes of the fiber (white areas). Figure S1: (a)Scanning Electron Microscope image of the initial LMA-5 silica PCF and (b) after the deposition of the As 2 S 3 glass nanolayers.

Amine solvent absorption measurements
The most widely amine solvents used for dissolving chalcogenide glass are n-butylamine, npropylamine and ethylenediamine (EDA). As the dissolution kinetics form a glass-solvent network, the solvent itself contributes to the total absorption of the solution. Figure S2 shows for the first time (to the best of our knowledge) the absorption spectra of the three amine solvents (n-butylamine, n-propylamine and ethylenediamine) used to develop dissolvedderived chalcogenide glasses from 550 nm up to 1750 nm. The measurements were performed using a liquid cell (cuvette), a supercontinuum source and an integrating sphere similar to the configuration used for the measurement in Fig 2 (a) (see Methods). EDA has the strongest absorption peak at ~1050 nm compared to n-butylamine and n-propylamine. However, the main advantage of EDA is that homogeneous dissolution of the bulk As 2 S 3 glass can be achieved within a few hours while n-butylamine and n-propylamine require several weeks under stirring. Furthermore, the three solvents are highly transparent in the visible range (550 -750 nm) and therefore their loss levels are close to the background noise as shown in

Power stability and device repeatability measurements
For our experiments we used a commercially available supercontinuum source (SuperK Versa).
We measured the intensity stability of our source versus time. Figure S3 shows that the power of the source is not fully stable over time (5 hours). This can explain the small spectral Figure S3: Intensity characterization of the SuperK Versa supercontinuum source (NKT Photonics) over 5 hours using a thermal head detector, a power meter and a computer.
The repeatability of the hybrid LMA-10 device was tested by heating and cooling the fiber over two full cycles. The following Fig. S4 (a) and (b) shows the long-edge response of the fiber by tracking the resonance at ~1300 nm. Figure S4: Resonance shift of the hybrid LMA-10 As 2 S 3 /silica PCF at ~1300 nm for (a) the 1 st full heating/cooling cycle and (b) 2 nd full heating/cooling cycle.