Wire Array Infrared Metamaterial Fibres: Fabrication and Applications

Metamaterials are artificial composite materials that exhibit exotic properties due to their components and sub-wavelength structure. During the past decades, several new materials have emerged from this research field with exciting new optical properties and applications. However, the fabrication of certain meta-structures remains a challenge, particularly with low cost and in large volumes. Fibre drawing is an attractive alternative to overcome such problems, but currently fabrication constraints restrict the size of the metal/dielectric drawn structures, limiting their operation to THz frequencies. In this context, this thesis concerns the fabrication, characterization, and use of new soft-glass based wire array metamaterials fibres for applications in the infrared. Numerical modelling of wire array structures is presented to understand which material combinations and structural parameters are more appropriate for infrared metamaterial fibres. The co-drawing process used is described, focusing on the adaptations used to minimize fluctuation of the structure due to fluid dynamics. Metamaterial fibres with uniform structures containing wire diameter and spacing on the order of few hundreds of nm are produced, which are compatible with operation at mid-infrared frequencies. The fabrication of metamaterial fibre tapers with steep transitions, generating hyperlenses, is also demonstrated. Far field imaging is attempted and the challenges regarding subdiffraction imaging are discussed. Feasible alternatives for future far field super-resolution imaging are proposed based on our numerical modelling and the typical structural transitions fabricated. Since the operational range of our hyperlenses is not limited to the infrared, subdiffraction focusing of 1/176 of the operational wavelength is reported at THz frequencies, achieved by combining a polymer hyperlens with our new infrared hyperlens

Fiber-Drawn Metamaterial for THz Waveguiding and Imaging

In this paper, we review the work of our group in fabricating metamaterials for terahertz (THz) applications by fiber drawing. We discuss the fabrication technique and the structures that can be obtained before focusing on two particular applications of terahertz metamaterials, i.e., waveguiding and sub-diffraction imaging. We show the experimental demonstration of THz radiation guidance through hollow core waveguides with metamaterial cladding, where substantial improvements were realized compared to conventional hollow core waveguides, such as reduction of size, greater flexibility, increased single-mode operating regime, and guiding due to magnetic and electric resonances. We also report recent and new experimental work on near- and far-field THz imaging using wire array metamaterials that are capable of resolving features as small as λ/28

Mid-infrared frequency modulation spectroscopy of NO detection in a hollow-core antiresonant fiber

Mid-infrared frequency modulation spectroscopy (FMS) in a tellurite hollow-core antiresonant fiber (HC-ARF) is investigated for gas detection. The spectroscopic system is demonstrated for nitric oxide (NO) detection by exploiting its strong absorption line at 1900.08 cm−1 with a quantum cascade laser (QCL). By modulating the injection current of the QCL at 250 MHz and measuring NO in a 35 cm long HC-ARF, we achieve a noise equivalent concentration of 67 ppb at an averaging time of 0.1 s. Compared to direct absorption spectroscopy with a low-pass filter for etalon noise reduction, the FMS technique shows an improvement factor of 22. The detection limit of FMS can be further improved to 6 ppb at a longer averaging time of 100 s, corresponding to a noise equivalent absorption coefficient of 1.0 × 10−7 cm−1.</p

Mid-infrared absorption spectroscopy of ethylene at 10.5 µm using a chalcogenide hollow-core antiresonant fiber

We demonstrate the mid-infrared absorption spectroscopy with a chalcogenide glass IG3 hollow-core antiresonant fiber (HC-ARF) for gas sensing at 10.5 µm. A continuous-wave quantum cascade laser (CW-QCL) is adopted to detect the strong absorption line of ethylene (C2H4) centered at 949.5 cm−1 by coupling the laser beam into a chalcogenide HC-ARF of 22 cm in length. Both direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) are performed in this study for comparison. At the integration time of 0.1 s, the noise equivalent absorption (NEA) coefficient is determined to be 4.7 × 10-5 cm−1 for DAS and 5.1 × 10-6 cm−1 for WMS, respectively. Based on the Allan-Werle deviation analysis, the NEA coefficient of WMS can be further improved to 4.0 × 10-7 cm−1 by using a longer integration time of 80 s. The combination of QCLs and chalcogenide glass HC-ARFs provides a promising platform for mid-infrared gas sensing applications.</p

Data base for: Numerical modelling of a hybrid hollow-core fiber for enhanced mid-infrared guidance

This dataset supports the publication &#39;Numerical modelling of a hybrid hollow-core fiber for enhanced mid-infrared guidance&#39; in Optics Express.</span

Numerical modelling of a hybrid hollow-core fiber for enhanced mid-infrared guidance

We propose a novel design of hollow-core fiber for enhanced light guidance in the mid-infrared. The structure combines an arrangement of non-touching antiresonant elements in the air core with a multilayer glass/polymer structure in the fiber’s cladding. Through numerical modeling, we demonstrate that the combination of antiresonant/inhibited-coupling and photonic bandgap guidance mechanisms can decrease the optical loss of a tubular antiresonant fiber by more than one order of magnitude. More specifically, our simulations demonstrate losses of the HE11 mode in the few dB/km level, which can be tuned through mid-infrared wavelengths (5 µm-10.6 µm) by carefully optimizing the structural parameters of both structures. We also show that the hybrid hollow-core fiber design is more robust to bend-induced loss than an equivalent tubular antiresonant fiber or a Bragg/OmniGuide fiber. As a result, if successfully fabricated, the hybrid hollow-core fiber will offer low-loss, high beam-quality, effectively single-mode operation, and low bending losses, potentially solving many of the problems that affect all known mid-infrared fiber types

Trace gas detection in a hollow-core antiresonant fiber with heterodyne phase-sensitive dispersion spectroscopy

Laser dispersion spectroscopy provides an attractive way of gas sensing by measuring refractive index rather than absorption. The previous dispersion gas sensors were mostly developed with free-space optics. In this work, we demonstrated heterodyne phase-sensitive dispersion spectroscopy (HPSDS) for sensitive nitric oxide (NO) detection in a hollow-core fiber to take advantage of the enhanced light-gas interaction in a compact setup. A quantum cascade laser (QCL) at 5.26 µm was coupled into a 35 cm tellurite hollow-core antiresonant fiber to exploit the strong absorption line of NO. The injection current of the QCL was modulated at 1 GHz to generate the three-tone beam for dispersion measurements. We achieved a noise equivalent concentration (NEC) of 0.8 ppm at the measurement time of 80 s. A comparative study of HPSDS with wavelength modulation spectroscopy (WMS) was also conducted to evaluate these two methods in terms of sensitivity and dynamic range.</p

Tellurite hollow-core antiresonant fiber-coupled quantum cascade laser absorption spectroscopy

Mid-infrared absorption spectroscopy for gas detection is reported in this study using a quantum cascade laser (QCL) coupled with a custom-made tellurite hollow-core antiresonant fiber (HC-ARF). The HC-ARF is fabricated from tellurite glass by extrusion and subsequent fiber drawing. The QCL emitting at 5.26 μm is coupled into the 21-cm long HC-ARF. As a proof-of-concept, this spectroscopic system is demonstrated for nitric oxide (NO) detection by exploiting its strong absorption line at 1900.08 cm-1. By quickly filling gas mixtures into the HC-ARF, we first conduct direct absorption spectroscopy of NO and achieve a noise equivalent absorption (NEA) of 2.1 × 10-5 cm-1. Besides, we also conduct wavelength modulation spectroscopy to improve sensing performance. A minimum detection limit of 6 ppb NO is achieved at the integration time of 30 s, corresponding to 1.0 × 10-7 cm-1 in NEA. The HC-ARF is tested to show a response time of only 0.3 s when applying a pressure difference of 11 kPa between the two fiber ends. Such a tellurite HC-ARF-coupled QCL spectroscopic system makes it attractive for developing optical gas sensors with compact size, fast response, and high sensitivity. </p

Mid-infrared photothermal gas sensor enabled by core-cladding mode interference in a hollow-core fiber

Photothermal spectroscopy provides an attractive way of sensitive gas detection with a large dynamic range. Previous photothermal gas sensors normally use an optical interferometer for measuring the slight phase change caused by gas absorption. However, an active opto-mechanical stabilization system is required in the photothermal interferometry, making the sensor complex, bulky and hard for field applications. Here, we report a new mid-infrared photothermal gas sensor based on core-cladding mode interference in a tellurite hollow-core antiresonant fiber (HC-ARF). This method relies on the co-propagation of the HE11 mode of a mid-infrared pump laser and the core-cladding modes of a probe laser in the tellurite HC-ARF. As a proof-of-principle demonstration, we detect nitric oxide in the 35 cm long fiber by using a quantum cascade laser (5.2 μm, 21.7 mW) as the pump laser. We achieve a noise equivalent concentration of 50 ppbv, corresponding to a normalized noise equivalent absorption coefficient of 8.6 × 10-9 cm-1WHz-1/2. Our technique has long-term stability without using any active stabilization devices and holds promise for fast, sensitive and background-free gas detection with a simplified configuration. </p