As the national research laboratory for the Navy, the US Naval Research Laboratory has been at the forefront of development of materials for fiber optics as well as fiber production processes necessary to take full advantage of those materials. NRL has conducted research into fluorides, chalcogenides, crystalline materials, silica and polymers to name a few. Each poses specific fiber fabrication challenges. NRL has implemented at least six distinct fiber-making methodologies to address those challenges including standard silica/MCVD, rod in tube, and double crucible draw techniques as well as extrusion, single crystal fiber growth and 3D printing techniques. NRL continues to expand upon its capabilities as evidenced by recent achievements of high efficiency active as well as low loss passive IR fibers, expanded wavelength coverages and unique all-new fiber optic functionalities.

Two barium gallo-germanate glass series were elaborated to investigate the effect of the yttrium introduction on the glass physicochemical properties and crystallization behavior. Through differential scanning calorimetry and X-ray diffraction analyses, it was found that competition occurs between the gallo-germanate zeolite-type phase and the yttrium-containing phase. From 13 mol% of YO3/2, the yttrium introduction impedes the formation of surface crystallization in these glasses. Then, different dehydration methods were studied in order to reduce the water and OH content in gallo-germanate glasses. Two dehydration agents were tested under different synthesis conditions, namely the atmosphere, types of gas and the concentration of the dehydration agents. The combination of argon and dry oxygen with the use of ammonium difluoride appears to be effective in reducing the water and OH content in BGG glasses

We report the development of a phase-stable mid-IR Er:fibre laser-amplifier system operating at a 76 MHz repetition rate. A train of ultrashort mid-IR pulses is generated by a difference frequency mixing between a portion of the 1.55-mm output of an Er:fibre master oscillator and a dispersive branch of a supercontinuum driven by the second portion. This scheme yields a high-brightness mid-IR frequency comb with automatically zeroed carrier-envelope offset frequency, motivated by applications in spectroscopy of trace gases and nanophotonics.

We studied numerically 1000 nm, 1 ps pulse width propagation in a PT-symmetric nonlinear directional coupler in the form of dual-core photonic crystal fiber. The base material of the fiber is phosphate glass, while gain and loss channels are implemented by ytterbium-based and copper-based doping, respectively. The propagation models were based on coupled generalized nonlinear Schrödinger equations solved with the Split-Step method: 1) extended model including coupling coefficient dispersion, self-steepening nonlinearity and its spectral dependence, stimulated Raman contribution, cross-phase modulation and Gaussian-like gain and loss coefficient frequency function; 2) simplified model with second-order dispersion term, linear coupling and first-order nonlinearity. We predicted two states of light propagation: 1) linear pulse energy oscillation between gain and loss channels (PT-symmetry state) at 100 pJ; 2) retention of the pulse in the excited gain channel (broken PT-symmetry) at 445 pJ. The presented results open perspective on the demonstration of fiber-based all-optical switching devices.

In this paper gallium based oxyhalides suitable for radiation detectors, lasers, and acousto-optic devices for mid-infrared (MWIR) and long wave infrared (LWIR} operations are discussed. Low temperature solution and flux growth methods have demonstrated that these materials are very anisotropic and belong to hexagonal class. In this paper, we will describe the details of effect of anisotropy and its importance in nonlinearity in optical applications.

Highly efficient and narrow-band red phosphors with blue or near-UV excitation are strongly required to improve the color rendering property and luminous efficacy of the existing white LEDs. With this aim in view, the Eu3+-doped YSiO2N oxynitride phosphor was developed, whose charge transfer excitation band was located at the near-UV region (~320–340 nm) due to covalent N 2p orbitals. To investigate the effect of the mixed-anion coordination around Eu3+ ions, the relationship between the luminescence properties and the local environments was investigated with site-selective and time-resolved spectroscopy. The Eu3+ luminescence properties in Y3+ sites that differ in terms of centrosymmetric were characterized, and the results suggest that thermal distortion with a lack of the inversion center induces the electronic dipole transition, resulting in a shorter luminescence lifetime.

In this investigation, two techniques of epitaxial growth of GaSb quantum dots on silicon substrates are explored. The first method involves the direct nucleation of GaSb islands on the Silicon (100) substrate and an AlSb barrier layer. The second method combines selective-area epitaxy (SAE) with Vapor-Liquid-Solid (VLS) growth principles in order to achieve suitable growth temperatures for antimonides. Our analysis focuses on the presence of pseudomorphic strain due to the high mismatch in lattice constant between the dots and the substrate. Transmission electron microscopy and photoluminescence spectroscopy are used to characterize the dots analyzed in these studies.

As an excellent material platform for integrated photonics, thin film lithium niobate (TFLN) boots the performance of various integrated photonic devices such as integrated electro-optic modulators, integrated optical frequency combs, and nonlinear wavelength converters. The performance of these devices is highly dependent on the quality of nanofabrication method. Despite the fact that conventional inductively coupled plasma–reactive ion etching can achieve TFLN microrings with intrinsic quality factor (Q-factor) as high as 10 million, this method still shows high cost, poor reproducibility, and low throughput. Here, we achieved z-cut TFLN micro-racetrack with an intrinsic Q-factor over 11.9 million using we etching method. This method can facilitate the mass production of high-performance integrated TFLN devices with low cost, high reproducibility, and high throughput.

Fabry-Perot (FP) etalons play a central role in many industrial and research applications including spectroscopy. In the context of filters and frequency comb generators, they are typically illuminated with nominally collimated light with the intent of achieving a well-behaved, high-finesse spectral response. Few studies have analyzed the transmission profile of defect-limited fused silica FP etalons subjected to a range of illumination conditions. This paper presents such a comprehensive analysis, demonstrating quantitative agreement between theory, experiment, numerical analysis, and ray-tracing analysis. In particular, we predict and characterize the asymmetry and widening of the transmission peaks for the cases of small diameter gaussian beams at normal incidence and near-flat-top incoherent beams at non-normal incidence. Among other applications, we expect our work to support the development of high-performance frequency combs based on low-cost incoherent broadband sources for spectroscopy.

Although optical fiber is efficient for transmitting light, its functionality is limited by the dielectric material of the core and nonlinear-optical responses and has a dielectric diffraction limit. Therefore, the optical properties of the optical fiber cannot be altered after the fiber drawing fabrication, thus limiting the development of novel in-fiber devices. In this talk, I will present our recent development of “Meta”-optical fiber, an advanced optical fiber integrated with emerging nanophotonic concepts such as optical metasurfaces, plasmonic nanowires, and zero-index photonics. I will present the development of ultrathin optical metalens which is cascaded on the facet of a photonic crystal fiber that enables light focusing. I will also discuss the first experimental demonstration of zero-index resonance excitation in an optical fiber coated with AZO nanolayer and the excitation of plasmonic resonances on holey optical fiber for advanced optical sensing and tip-enhanced Raman spectroscopy. These advanced “meta”-optical fibers open a pathway to revolutionary in-fiber lasers/spectroscopies, optical imaging/sensing, and optical communication devices.

Silicon-based Schottky barrier photodetectors (SBPDs) have become a popular choice for near-infrared (NIR) applications due to their cost-effectiveness and compatibility with the CMOS fabrication process. This work provides a quantitative analysis of the external quantum efficiency in platinum/copper bilayer SBPDs, extending the conventional single-layer analyses. We conducted a systematic investigation of optical losses, energy distribution losses, and momentum mismatch losses, successfully matching our theoretical predictions to experimental results. Our study also demonstrates the long-term stability of bilayer SBPDs in the NIR region. These findings have significant implications for affordable NIR photodetection technologies.

In this work, we present the results of our recent spectroscopic investigation on Dy3+-doped Ga2Ge5S13 (Dy:GGS) glass, aiming to explore its potential for mid-infrared (3-5 µm) laser applications. Under 910 nm excitation, the studied Dy:GGS glass displayed broad emission bands centered at ~2.9 µm and ~4.35 µm corresponding to 6H13/2 --> 6H15/2 and 6H11/2 --> 6H13/2, respectively. The measured fluorescence decay time of the 6H11/2 manifold (upper laser level for 4.35 µm laser transition) was found to be in the millisecond range, demonstrating similarity to other sulfide glasses doped with Dy3+. Spectroscopic results and data modeling including the temperature dependent emission and decay dynamics, concentration dependent studies, Judd-Ofelt analysis, and transition cross-sections, will be presented.

We present new designs of optical silica fibers tailored for sensing applications. Highly versatile MCVD technology allows co-doping of fused silica in a large variety of elements and the deposition of differently doped layer structures. Co-doping of Ge/B- or Ge/Al enables tuning the refractive index and thus adapting the mode field of the fibers. Ge/Ce co-doping allows tuning the photosensitive properties for Fiber Bragg grating inscription. Combining Ge- and Al-doping modifies the fiber properties for improved distributed sensing applications. We report realization of the designs and present first results of fiber properties. Work is supported by German BMBF contract 03RU1U071J.

Volumetric 3D display allows a wide range of applications in air traffic control, medical imaging, automotive and aerospace design, visualisation in weather or defence monitoring. Previous work in this area has examined the use of upconversion in low-phonon-energy fluoride glasses and single crystals as the imaging chamber material. However, these glasses and crystals are difficult to produce at a sufficient size and quality. We will report on our examination of a range of low-phonon-energy glasses. This study identified tellurite glass as a promising candidate with high fluorescence efficiency for display and up-scalability of the imaging chamber size.

Near-infrared photodetection is promising for real-time imaging, surveillance, and spectroscopy. We propose an array photodetector using an ultra-thin gold (Au) film on Si, based on hot-carrier injection in a Schottky junction. Au thin films (<5 nm) with a large extinction coefficient enhance hot carrier injection from Au to Si, while thick Au films (>100 nm) primarily reflect light. The device employs thin Au films as active areas and thick ones as electrodes, eliminating the need for insulating materials. Photocurrent properties and operation speed are investigated, showing a rapid response (7.5/8 μs rise/fall time), comparable to commercial Germanium (Ge) photodiodes.

BaTiO3 (BTO) has emerged as an electro-optic (EO) material in integrated photonics, offering advantages over traditional materials such as LiNbO3 due to larger Pockels coefficients. BTO thin films on oxide substrates have been extensively studied for on-chip EO modulators that manipulate light properties in waveguides. One application is in compact laser systems for atomic gravity sensors, where BTO-based single-sideband (SSB) modulators reduce cost and power consumption by suppressing sidebands. This research presents the fabrication of an SSB modulator using BTO film on MgO substrate, operating at 780 and 1560 nm wavelengths. The modulator uses a Mach-Zehnder interferometer to convert a 1560 nm light source into a 6.8 GHz optical signal. This work advances integrated photonics by exploring the potential of BTO in compact laser systems for atomic gravity sensors.

Chalcogenide glasses have attracted attention for sensing applications due to their high transparency in the infrared range, their ability to be fabricated into thin films by PVD and to be processed into integrated photonic components by photolithography and etching. We will present the development of a chalcogenide-based mid-infrared platform dedicated to mid-infrared spectroscopy using evanescent waves. This study represents an important step towards the development of an optical sensor in the MIR spectral range using chalcogenide materials for the detection of organic molecules in water.

The dispersion uniformity of a commercially available and a custom-fabricated photonic crystal fiber (PCF) was characterized with a white light interferometry (WLI) setup between 900 - 1100 nm. The custom-fabricated PCFs displayed up to 1.5 times less variation in β2 and β3 for neighboring 50 cm long pieces and the largest variation between two 50-cm long pieces within a 5m long fiber section. As changes in dispersion can be caused by fabrication tolerances, this can be regarded as an effective metric to evaluate fiber fabrication uniformity.

We report the appearance of reversible photodarkening (solarisation) in anti-resonant hollow-core optical fibres transmitting ultraviolet light in spectral bands down to 195 nm. Over time the effect reduces transmission in a band of wavelengths centred around 325 nm, with a 50% reduction in transmission after 4 hours in 4.85 m of fibre carrying 100-200 nW of continuous-wave broadband UV light. Transmission at the affected wavelengths recovers over days and weeks, in contrast to the well-known permanent photodarkening of solid-core fibres.

Chalcogenide fibers are known for their large transparency window and their high nonlinear optical properties. Indeed, they can be transparent from the visible region up to the mid-infrared (mid-IR) until 12 µm..For these reasons, chalcogenide glass fibers are well suited for generating mid-IR supercontinuum source. The management of dispersion profile is of fundamental importance for supercontinuum generation. In order to address this problem, we have developed for the first-time chalcogenide graded index fibers with a nanostructured core composed by two different glass compositions

An approach to create a ROHS-compliant NDIR-type gas sensing multichannel module based on a fully configurable design. Parameters, advantages, and possibilities will be presented and discussed. Demonstration of exemplary applications in order to get an overview of possibilities. Finally, a few words about the plans for further development of this product line in terms of miniaturizing the whole system.

Aspheric optical lens surface is getting incorporated more into optical systems for improving different aspects of the system such as resolution, aberration corrections, weight, size etc. However, in comparison to a spherical lens, an aspheric lens poses new challenges in the alignment of the optic as the aspheric geometry consist of a single axis of rotational symmetry in comparison with a sphere which is radially symmetric at any point on the surface. This paper is intended to describe different methods which can be used to specify the centration of an aspheric lens component and how these methods should be chosen according to the intended assembly process.