Matthew A. Cooper

We present results from development of a photonic Quantum-Inspired Imager (QI2) providing source reconstruction below the optical/NIR diffraction limit through atmospheric turbulence without adaptive optics. Our group has demonstrated a photonic spatial mode sorter quantum-sensing device in practice — a photonic lantern — with capabilities in both spatial and spectral diversity, as well as future extensions to polarization sensitivity. Our team has developed high-efficiency photonic lantern mode-sorting/multiplexing devices fabricated in optical fibers. Our proposed passive imaging system is therefore based on three main innovations: (i) photonic lantern spatial mode sorters with spatial and spectral diversity, (ii) atmospheric blur removal enabled by mode-/wavelength-resolution, (iii) quantum-inspired image reconstruction techniques.

Antiresonant hollow-core fibers (AR-HCFs) have opened up exciting possibilities for high-energy and high-power laser delivery because of their exceptionally low nonlinearities and high damage thresholds. While these fiber designs offer great potential for handling kilowatt-class powers, it is crucial to investigate their performance at multi-kW power levels. Until now, transmission of narrow-linewidth single-mode lasers at multi-kW power levels through a HCF has not been demonstrated, to our knowledge. Here, we present the delivery of a record 2.2 kW laser power with an input spectral linewidth of 86 GHz, centered at 1080 nm, while maintaining 95% transmission efficiency and beam quality (M²) of 1.03. This was achieved via a 104.5 m single-mode five-tube nested AR-HCF with 0.79 dB/km loss. Furthermore, we show power delivery of 1.7 kW with a spectral linewidth as narrow as 38 GHz through the same fiber. Our results could lead to a new generation of fiber-based laser beam delivery systems with applications in precision machining, nonlinear science, directed energy, and power beaming over fiber.

High-Energy light in the UV-visible regime has seen an amazing boom of R&D primarily in the communities of the micro-machining and welding of highly reflective metals such as copper and aluminum, as well as in the areas of medical lasers and underwater sensing. Transport in the UV-visible range is extremely affected by the wavelength-dependent material dispersion and absorption of the transport optics. By utilizing the air core in a nested anti-resonant hollow core fiber (NANF) one can enable high confinement of the fundamental mode to achieve low-loss transmission in many environments. This paper presents a numerical study following the development process and initial experiments of a novel NANF designed for UV-vis transmission.

Multimode (MM) laser light has a vast application history spanning from laser pump sources, to high-speed optical links, to imaging systems but can suffer enormous inefficiencies when coupled through a solid core optical fiber for long transmission path lengths. One way to improve the MM transmission is by replacing the traditional solid-core fibers with uniquely tailored nested antiresonant hollow-core fibers (NANFs). By improving upon previous design methods, one can extend the application of the HCF to 100s of modes and beyond while maintaining low loss thus enabling novel concepts such as power beaming through fiber and the transmission of spatiotemporal tailored ultrafast wavepackets. We report a uniquely designed, fabricated, and tested MM NANF that enables low-loss transmission of 100s of modes.

Hollow-core core fibers with an anti-resonant nodeless structure are showing an incredible ability for mode confinement within the realm of optical transport. A subset of this application, high-energy laser beam delivery, requires extremely finite tolerances and precise design constraints in what are the traditional solid-core fiber solutions whereas nested antiresonant hollow-core fibers (NANF) allow for significantly more flexibility in both design and application. Increasing the number of capillaries in a NANF increases the number of allowed optical modes to propagate through the fiber thus reaching the few-mode and multi-mode regime, however increasing the modal count in propagation is not always desired. This study presents a comparison between experimental and simulated performance in the kW regime of a NANF with an internal structure consisting of five nested capillaries.

Anti-Resonant Hollow Core Fibers (AR-HCFs) are an emerging technology with a number of applications in low-latency communications, mid-IR transmission, and power delivery. Current R&D applications of AR-HCFs utilize free-space optics to obtain results in a timely and cost-effective manner. However, this approach exposes the HCFs to contaminants entering the HCF microstructures and if unmitigated can cause loss and potentially damage to the fiber. End-capping HCFs can protect the interfaces from damage, dust, and debris while simultaneously increasing their robustness and allowing for long-term use. Here, we present a novel endcap technique that allows low-loss transmission through a robust end-capped AR-HCF.

Anti-resonant hollow core fibers (AR-HCF) have been investigated for several use cases relating to high power transmission. Single mode, low-loss operation is needed in high-speed telecommunications and in high-energy beam delivery applications. In these fibers, higher order modes leak out of the core through the surrounding capillaries and subsequently are highly attenuated upon propagation resulting in effective mode filtering. With regards to CW operation, 900W have been delivered through a single resonant ring AR-HCF, and 1kW through a nested AR-HCF. This study presents an experimentally derived performance comparison of the spatial, spectral, and loss metrics between these two types of fibers when using an identical 1kW laser source.

We demonstrate a fast and versatile approach to analyze the modal content of a high power fiber amplifier using a low-loss photonic lantern. By monitoring the first three modes of the photonic lantern on a photodetector we can directly determine the modal content of a laser beam, enabling real time diagnostics of the output and its corresponding beam quality factor, M². We first investigate the beam quality and modal content of the output of a passive LMA double clad fiber commonly used as a delivery fiber in high power fiber laser amplifiers. The output of the fiber is analyzed by both a 6-mode mode-selective photonic lantern and a conventional M² setup utilizing a translation stage and beam profiler. The modal content and beam quality measurements produced in real-time by the photonic lantern are compared to the M² measurements resulting in an RMS error less than 0.098 across M² values between 1.020 to 2.260. We then conduct a follow on experiment using the same photonic lantern to monitor modal instability in a large mode area fiber laser amplifier. In this case, we compare our photonic lantern mode analysis approach versus the commonly used RIN/pinhole method evaluating modal instabilities. Not only does the photonic lantern estimate the modal content and beam quality in real-time but the modal content trends with the RIN metric as the fiber laser amplifier progresses from stable regime below 300W through the chaotic transverse modal instability regime above 400W.

SPIE Digital Library Proceedings

A low-NA Yb-doped LMA gain fiber is fabricated to increase bend insensitivity and is presented for the first time. The design study shows that incorporating segmented-trenches decrease the low-loss bend diameter by up to 30%.