Mid-infrared chalcogenide microfiber knot resonators

Abstract

A novel type of mid-IR microresonator, the chalcogenide glass (ChG) microfiber knot resonator (MKR), is demonstrated, showing easy fabrication, fiber-compatible features, resonance tunability, and high robustness. ChG microfibers with typical diameters around 3 μm are taper-drawn from As 2 S 3 glass fibers and assembled into MKRs in liquid without surface damage. The measured Q factor of a typical 824 μm diameter ChG MKR is about 2.84 × 10 4 at the wavelength of 4469.14 nm. The free spectral range (FSR) of the MKR can be tuned from 2.0 nm (28.4 GHz) to 9.6 nm (135.9 GHz) by tightening the knot structure in liquid. Benefitting from the high thermal expansion coefficient of As 2 S 3 glass, the MKR exhibits a thermal tuning rate of 110 pm · ° C − 1 at the resonance peak. When embedded in polymethyl methacrylate (PMMA) film, a 551 μm diameter MKR retains a Q factor of 1.1 × 10 4 . The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.

Batch Fabrication of High‐Quality Infrared Chalcogenide Microsphere Resonators

“…As shown in Figure 4a, a biconical As 2 S 3 fiber taper (see fabrication details in Figure S7 in the Supporting Information) is used for launching and collecting mid-IR light from a quantum cascade laser (QCL) light source (D11-00028-01, Daylight Solutions, ≈1 mW in power). [49,50] By coupling a 39.2-µm-diameter As 2 S 3 microsphere with a 1.6-µm-diameter As 2 S 3 fiber taper (inset of Figure 4a), a mid-IR transmission spectrum is obtained (Figure 4b). Lorentzian fitting to a resonance mode centered around 4521.67 nm leading to a loaded Q factor of 1.7 × 10 4 (Figure 4c, indicated by a red arrow in Figure 4b).…”

Chalcogenide Glass Microfibers for Mid-Infrared Optics

“…To ease the tapering system and obtain long MFs with uniform diameters with a large reduction ratio of fiber diameter between the preform fiber and the final MF, in 2020, Xie et al demonstrated a two-step taper-drawing process [45]. As schematically shown in Figure 1c1, commercial As 2 S 3 fiber was first heated and stretched bi-directionally with a low speed (0.4 mm•s −1 ).…”

“…In 2020, Xie et al demonstrated the first ChG MF-based resonator in the mid-IR region [45]. As 2 S 3 MFs with uniform diameters and long waists were fabricated via a two-step taper drawing process (Figure 1c1).…”

“…Furthermore, to increase the long-term stability of the MKR device and isolate it from contaminations, a 551-µm-diameter MKR was embedded in low-index polymer (PMMA) film while a Q factor of 1.1 × 10 4 around 4.5-µm wavelength was retained. In 2020, Xie et al demonstrated the first ChG MF-based resonator in the mid-IR region [45]. As2S3 MFs with uniform diameters and long waists were fabricated via a twostep taper drawing process (Figure 1c1).…”

“…The typical optical loss of ChG fibers in the mid-IR is around 0.1-10 dB/m [35], while the lowest loss, down to 0.012 dB/m at 3 µm, has been reported in multimode As 2 S 3 fibers [36]. Additionally, photonic devices based on ChG MFs, including resonators [37,38], gratings [39][40][41] and sensors [42,43], have been investigated in the visible (VIS) or near-infrared (near-IR) region and have recently extended to the mid-IR region [44][45][46]. In this review, combined with the latest progress in ChG MFs, we first introduce the fabrication and optical waveguiding properties of ChG MFs.…”