Christian Rosenberg Petersen

ZBLAN, a heavy-metal fluoride glass fiber, achieves demonstrably better transmission in the mid-infrared range compared to silica fibers and is predicted to outperform their optical performance across the ultraviolet to mid-infrared spectrum; however, achieving this potential is hindered by crystallization during terrestrial fabrication. In this study, we leverage the microgravity environment aboard the International Space Station (ISS) to explore conditions that enable high-fidelity fiber drawing with reduced optical loss. We produced ~12 km of ZBLAN fiber on the ISS, marking the first time sufficient space-drawn material is available for comprehensive characterization. An international consortium of 5 organizations evaluated ~2.1 km length of samples with highest diameter uniformity from the produced fibers. Comparative analyses reveal that space-drawn fibers with a step-index core-and-clad structure exhibit lower optical attenuation and enhanced mechanical performance relative to their ground-based counterparts. These results demonstrate that microgravity manufacturing enables high-performance ZBLAN fiber production for near- and mid-infrared applications while opening new opportunities for advanced photonic materials in space-based industry.

Combining near-infrared (NIR) and mid-infrared (MIR) spectroscopy to cover both the fundamental and overtone combination molecular vibrational resonances allows more robust analytical methods to be used, such as two-dimensional correlation spectroscopy. However, due to the strong differences in molar absorption coefficients and transparency of the optical material, it is inherently difficult to perform NIR and MIR spectroscopy on aqueous samples using a single instrument. Combining spectra from different instruments and sample presentations can result in unwanted spectral variations, which can influence the prediction models and mitigate the advantages of the combination approaches. In this work, a more consistent instrument response is achieved by combining a single supercontinuum (SC) laser spanning from 1000 to 4000 nm as the light source, with an attenuated total reflection crystal and a transmission cuvette in a single-path configuration. Using this approach, NIR–MIR correlation spectroscopy is demonstrated using a set of 22 aqueous samples with varying concentrations of ethanol, sucrose, and ʟ-proline.

Mid-infrared supercontinuum (SC) sources can benefit from low-cost pumps with center wavelength longer than the zero-dispersion wavelength of fluoride fibers (∼1600nm). This makes thulium-doped lasers an attractive technology, but their relative intensity noise (RIN) is typically not characterized. Furthermore, is low pump noise even a requirement for SC applications? With focus on low cost, we have developed a three-stage amplified 1946 nm gain-switched diode (GSD) demonstrating 12% RIN and flexible repetition rate control, which crucially allows the user to optimize SC performance specific to the application. We demonstrate a maximum −10dB bandwidth of 1873–3986 nm at 2 MHz and a minimum RIN of 6.1% at 1900 nm, 10.4% at 2300 nm, and 16.6% at 3250 nm at 1 MHz. We define a figure of merit for operation between the 3000 and 3500 nm region and demonstrate that it is maximized at 3 MHz, showcasing the power of this control in optimizing specific performance metrics. This performance is compared with a SC spanning 1900–3796 nm, pumped by an amplified thulium-doped mode-locked fiber laser operating at 5.8 MHz with <0.11% RIN. Despite the vastly superior pump noise, comparative SC RIN values of 2.0% at 1900 nm, 9.5% at 2300 nm, and 8.5% at 3250 nm were obtained, indicating that the modulational instability driven SC generation process dominates noise performance, thereby reducing the need for low pump noise.

Mid‐infrared (IR) supercontinuum (SC) lasers are important in applications such as pollution detection, stand‐off detection, and non‐destructive testing. The performance in many applications is limited by the noise level of the supercontinuum laser. High noise typically results in low sensitivities or a need for long integration times. In this paper, a simple technique to reduce the noise of high noise soliton‐based SC sources is introduced by adding a short piece of normal dispersion fiber to force the spectrally distributed solitons to spectrally broaden through self‐phase modulation and thereby overlap to average out the noise. The noise reduction is demonstrated experimentally and numerically using a ZBLAN fiber based mid‐IR SC source and adding a short piece of highly nonlinear arsenic‐sulfide fiber. However, the method is generally applicable to any soliton‐based near‐IR or mid‐IR SC source. Its efficiency is underlined by experimentally comparing it to SC generation in fibers in which a second zero‐dispersion wavelength provides the spectral alignment noise reduction mechanism.

Leading edge erosion of wind turbine blades is one of the most critical issues in wind energy production, resulting in lower efficiency, as well as increased maintenance costs and downtime. Erosion is initiated by impacts from rain droplets and other atmospheric particles, so to protect the blades, special protective coatings are applied to increase their lifetime without adding significantly to the weight or friction of the blade. These coatings should ideally absorb and distribute the force away from the point of impact; however, microscopic defects, such as bubbles, reduce the mechanical performance of the coating, leading to cracks and eventually erosion. In this work, mid‐infrared (MIR) Optical Coherence Tomography (OCT) is investigated for non‐destructive, contactless inspection of coated glass‐fiber composite samples to identify subsurface coating defects. The samples were tested using rubber projectiles to simulate rain droplet and particle impacts. The samples were subsequently imaged using OCT, optical microscopy, and X‐ray tomography. OCT scanning revealed both bubbles and cracks below the surface, which would not have been detected using ultrasonic or similar non‐destructive methods. In this way, OCT can complement the existing quality control in turbine blade manufacturing, help improve the blade lifetime, and reduce the environmental impact from erosion.

Leading edge erosion of wind turbine blades is one of the most critical issues in wind energy production, resulting in lower efficiency, as well as increased maintenance costs and downtime. Erosion is initiated by impacts from rain droplets and other atmospheric particles, so to protect the blades special protective coatings are applied to increase their lifetime without adding significantly to the weight or friction of the blade. These coatings should ideally absorb and distribute the force away from the point of impact, however, microscopic defects, such as bubbles, reduce the mechanical performance of the coating, leading to cracks and eventually erosion. In this work, Optical Coherence Tomography (OCT) is investigated for non-destructive, contactless inspection of coated glass-fiber composite samples to identify subsurface coating defects. The samples were tested using rubber projectiles to simulate rain droplet and particle impacts. The samples were subsequently imaged using both OCT, optical microscopy, and X-ray tomography. OCT scanning revealed both bubbles and cracks below the surface, which would not have been detected using ultrasonic or similar non-destructive methods. In this way, OCT can complement the existing quality control in turbine blade manufacturing, help improve the blade lifetime, and reduce the environmental impact from erosion.

In industrial paper production, online monitoring of a range of quality parameters is essential for ensuring that the performance and appearance of the final product is suitable for a given application. In this article, two optical sensing techniques are investigated for non-destructive, non-contact characterization of paper thickness, surface roughness, and production defects. The first technique is optical coherence tomography based on a mid-infrared supercontinuum laser, which can cover thicknesses from ~20–90 μm and provide information about the surface finish. Detection of subsurface voids, cuts, and oil contamination was also demonstrated. The second technique is terahertz time domain spectroscopy, which is used to measure paper thicknesses of up to 443 μm. A proof-of-concept thickness measurement in freely suspended paper was also demonstrated. These demonstrations highlight the added functionality and potential of tomographic optical sensing methods towards industrial non-contact quality monitoring.

We report on mid-infrared optical coherence tomography (OCT) at 4 µm based on collinear sum-frequency upconversion and promote the A-scan scan rate to 3 kHz. We demonstrate the increased imaging speed for two spectral realizations, one providing an axial resolution of 8.6 µm, and one providing a record axial resolution of 5.8 µm. Image performance is evaluated by sub-surface micro-mapping of a plastic glove and real-time monitoring of C O 2 in parallel with OCT imaging.

Numerical modeling of cascaded mid-infrared (IR) supercontinuum generation (SCG) is used to study how an ensemble of spectrally and temporally distributed solitons from the long-wavelength part of an SC evolves when coupled into the normal dispersion regime of a highly nonlinear chalcogenide fiber. This has revealed a novel phenomenon—the generation of a high-energy rogue wave in the normal dispersion regime in the form of a strong self-phase-modulation (SPM) chirped pulse. This SPM rogue wave is generated by swallowing the energy of many sufficiently closely spaced pulses through inter-pulse Raman amplification and is a key effect behind efficient cascaded mid-IR SCG.

A hybrid optical fiber comprising metal electrodes, high performance polymers, and a highly nonlinear glass core is presented in this work as a novel, to the best of our knowledge, platform for mid-infrared nonlinear devices. The fiber allows for electrical tuning of the temperature by joule heating using a set of embedded tungsten wires. Unlike temperature tuning by an external heater, this results in a strong modulation, which introduces alternating signs of its dispersion. Enhanced spectral broadening through supercontinuum generation in the mid-infrared due to this modulation is investigated numerically.