We present advances in InGaN-based laser diodes, photodiodes, and systems leveraging these devices. A wide range of laser diode (LD) innovations will be reviewed including high power blue and violet LDs, ultrashort cavity LDs, and the potential for a manufacturable distributed feedback LDs. In addition, we present advances in photodiodes for optical power transfer and communication, andsystems enabled by these devices will be discussed. This new class of GaN devices and systems are applicable to a wide variety of applications including: AR/VR, HUDs, non-lethal deterrents, undersea and spaced-based optical communication & power transfer, directed energy, rangefinding, LIDAR and quantum computing.

Tm-doped fiber amplifiers are good sources for high energy laser, DIRCM, LIDAR, remote sensing and spectroscopy. The reported Tm-doped amplifiers have efficiencies between 55% to 65%. The diode lasers that are commercially available at 793 nm produce about 35% ex-fiber efficiency. Therefore, the power conversion efficiency of Tm-doped amplifiers is only in the range of 20% - 23% which is less than half that of Yb-doped amplifiers. One straightforward way to improve the e-o power conversion efficiency of Tm-doped fiber amplifiers is to boost the efficiency of 793 nm diode pump from 35% to >55%. This will enable >36% efficient Tm-doped fiber amplifiers. With improvement in epitaxial design, we have demonstrated 64% at 15.5 W producing fiber-coupled package with 400 W in 225-μm/0.22 NA and 54% ex-fiber efficiency in packages with <0.63 kg/kW and <0.49 cc/W specific mass and specific volume, respectively. Further improvement is underway and we will update the latest results.

Watt-class semiconductor optical amplifiers (SOAs) at 1550 nm are an attractive alternative to replace erbium-doped fiber amplifiers (EDFAs) in various applications including remote sensing, optical communications, illumination, and LIDAR, with the potential to be more efficient, compact, and cost-effective. We report a world record of a single mode fiber-coupled packaged semiconductor optical amplifier delivering >30 dBm (1.2 W) of continuous wave ex-fiber power at 1550 nm, enabled by recent advancements in diffraction-limited output from tapered diode laser amplifiers. This result is achieved with an input seed power of 30 mW (~15 dBm), corresponding to an overall gain of ~16 dB. Reliability data will be presented for our tapered laser chips, as will progress towards demonstration of high performance SOAs in an optical link. Watt-class SOAs are available and being shipped to customers now.

The optical properties of rare-earth (RE) activated materials have been extensively investigated for their potential as solid-state laser gain media. More recently, mid-IR gain and lasing from RE3+ (Tb3+, Pr3+, Ce3+) doped low-phonon selenide-based chalcogenide glasses have sparked further development of this class of materials which have shown lifetimes on the order of millisecond for mid-IR transitions. In this work, mid-IR (3 - 5 micron) spectroscopic study was performed on the Ho3+ doped low-phonon sulfide and selenide-based chalcogenides glasses as well as indium fluoride glasses, which were prepared by melt quenching technique.

With the goal of developing new mid-IR laser sources, Rare-earth doped low-phonon crystals and sulfide-based chalcogenide glasses are being explored. Low maximum phonon energy materials are necessary to minimize competing non-radiative decay processes such as multi-phonon relaxation (MPR). This work presents the results of a comprehensive mid-IR spectroscopic study on Dy3+ doped sulfide-based chalcogenide glasses, as well as comparative results from similarly doped chloride and fluoride crystals. Spectroscopic results will focus on absorption, fluorescence, and decay characteristics. From these measurements, laser relevant parameters such as cross sections and radiative lifetimes are calculated.

Combinable high average power fiber amplifiers with diffraction-limited beam that is suitable for High Energy Laser (HEL) applications is currently primarily limited in output power by TMI and SBS. SBS is better understood and numerous methods have been shown to be effective for scaling power to several kilowatt levels. Currently, TMI limits output power to ~3-kW for approximately 20-µm core conventional step-index dual-clad fiber amplifiers. We report on the use of low-quantum defect pumping scheme to increase the TMI threshold. We have demonstrated 5kW and further power-scaling is underway and the latest results will be presented.

Rare-earth-doped fibers with single-crystal cores have the potential for 10x higher TMI threshold than their glass counterparts and are a promising candidate for use as gain media in high-power laser systems. Their utility has been limited by parasitic optical losses and difficulty in fabrication. This paper explores methods to reduce the losses in these fibers in the core, in the cladding and at the core-cladding interface and an overview of the work done at NRL in this area.

This conference presentation was prepared for SPIE Defense + Commercial Sensing, 2023.

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.

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.

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.

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.

Freeform optics offer many advantages when performing complex beam shaping for directed energy applications. A number of design methods are presented utilizing radial basis functions, the Monge Ampere solution to optimal transport theory, as well as a novel phase wrapping approach. These methods allow for the precise manufacturing of singular optical elements such as collimation arrays and phase flatteners. This design study also outlines a modular solution in which multiple of these optics can be combined into a single, low-SWaP housing producing an array of aligned and collimated beams with a simulated power in the bucket of more than 80%.