This PDF file contains the front matter associated with SPIE Proceedings Volume 11739, including the Title Page, Copyright information, and Table of Contents.

Single crystal fiber has a wide range of applications spanning from high temperature sensing, radiation sensing in harsh environment, high power laser and power delivery, medical and chemical application, and imaging applications. Nevertheless, the potential of single crystal fiber has not been fully explored in part because of the limited facilities available for custom growth of high quality, low loss, and custom fiber chemistries and geometries. The presentation provides an overview of recent work and current state of the art on growth of single crystal oxide fibers using various techniques. A discussion of recent progress in applications of single crystal fibers was also presented spanning harsh environment sensing, radiation sensing, and fiber lasers. In this paper, we also overview establishment of a Laser Heated Pedestal Growth system at University of Pittsburgh including the online monitoring of the fiber growth process and discuss important process parameters for future process optimization. We demonstrate the growth of single crystal fiber from a polycrystalline source rod which may be a more affordable and flexible method in the future.

Surface plasmon polaritons have been employed in a wide spectrum of sensing applications. However, as a surface plasmon polariton propagates along the surface of a metal-dielectric interface it rapidly diffracts and is absorbed reducing the sensitivity of a measurement. Attempts to prevent diffraction have included waveguides of many types but these require precise fabrication to mitigate dissipative losses. We propose using space-time surface plasmon polaritons for sensing. Our calculations show that proper selection of spatial frequency and temporal frequency correlations will produce a wave packet that propagates without diffraction or dispersion. This is possible without any waveguides or surface patterning.

Here, we demonstrate a multimode fiber Rayleigh-based sensor that can make quantitative strain measurements by tracking the amplitude of the backscattered speckle pattern recorded on a high-speed camera. The diversity of spatial modes provides sufficient information to recover both the magnitude and algebraic sign of the strain. Amplitude-measuring multimode fiber Rayleigh sensors have reduced sensitivity to laser phase noise, have higher thresholds for nonlinear effects, improving noise performance, and are completely immune to interference fading. The sensor presented here achieves pε/√Hz-level noise, over 10 kHz of bandwidth, and operates at a range of up to 2 km.

This article presents a contactless measurement technique of the rotor temperature of small rotating machines using Near-Infrared Fiber Bragg Gratings (FBGs) sensors. This principle allows localizing heat spots in the rotor of electrical machines. The temperature information can be used to protect the machine by stopping its operation due to a heat spot. The concept is to measure the wavelength shift due to temperature changes for several FBGs integrated into a rotor. First, the temperature response of the FBG is simulated using Matlab. Then, a test bench is designed including a geometrically small electrical motor, a mechanical coupler, two bearings and a 3D printed cylinder. It has a rotational speed equivalent to a real electrical machine. The measurement principle uses a super-luminescent diode (815-855 nm) which is continuously coupled into an FBG embedded onto the rotor using suitable optics. The heating system is calibrated using a T-type thermocouple (class A: +/- 1 °C). Then, the Fiber Bragg Grating is heated while rotating the cylinder. The reflected signals are detected by a spectrometer. Finally, wavelength shifts due to temperature variations (10°C steps from 20 °C up to 70 °C) are experimentally measured up to 754 RPM. A temperature sensibility of 4.7 pm/°C is experimentally reached. As future work, the system with several gratings will be integrated into a small power rotating machine (kW) suitable for automotive applications. Reflected signals that correspond to temperature variations will be detected while rotating the FBGs to measure high temperatures ~ 150 °C for 1500 RPM.

Coherent nanosecond pulses with high peak powers in the 2μm region are in demand for applications such as LIDAR and atmospheric sensing. In this paper we present a PM pulsed laser based on a MOPA configuration providing up to 50W of peak power. The 2039nm seed laser is a pre-amplified DFB-FBG laser with <10kHz linewidth. Nanosecond pulses produced by an acousto-optic modulator are amplified by a single booster stage amplifier using a double clad PM thulium-doped fiber. We demonstrate >10W of output peak power for 50ns pulses over repetition rates from 50kHz to 2MHz. For 4-μs pulses and a repetition rate of 50kHz, our MOPA delivers 28μJ of pulse energy.

We present a novel Brillouin based dynamic strain sensor that is immune to most of the technical and environmental noise sources that limit existing Brillouin sensors. In particular, we introduce a modified slope-assisted Brillouin optical time domain analysis (SA-BOTDA) system that combines information from the complex Stokes and anti-Stokes interactions to extract the Brillouin frequency shift while suppressing noise and cross-talk due to fluctuations in the power, frequency, or polarization state of the pump and probe beams. This approach enables a strain noise of 15.6 nε/Hz1/2 in ~1 km of fiber with 4 m resolution and 25 kHz bandwidth.

Real-time pH monitoring of cement can improve maintenance schedules and predict early failures for wellbores, which is beneficial for wellbore integrity monitoring in oil and gas production and carbon dioxide sequestration. Metal oxideenabled fiber optic pH sensors offer a solution for real-time distributed pH monitoring at high temperature high pressure conditions in the wellbores, and such harsh conditions disable many other pH sensing techniques. Our previous investigation revealed that a fiber optic sensor with sol-gel coated titanium oxide (TiO₂) is capable of pH sensing in the high alkaline range at 80 °C, relevant for the wellbore cement conditions. Atomic layer deposition (ALD) approach provides uniform conformal films on complex surfaces, which could enhance the TiO₂ film stability on the optical fiber. This work presents detailed characterization and testing of ALD TiO₂ thin films for pH sensing by measuring the pHdependent transmission of the coated fiber optic sensors at room temperature and 80 °C. ALD TiO₂ has demonstrated enhanced sensing performance compared to sol-gel TiO₂ in terms of sensitivity, reversibility, and stability.

In this paper, we demonstrate a fading noise reduction in the phase-optical time domain reflectometry (Φ-OTDR) based on a wavelength diversity technique. In the proposed wavelength diversity technique, multiple wavelengths are injected into the sensing fiber, while the wavelength selective time delay is induced to avoid the temporal overlapping. The proofof- concept experimentally demonstrated with three pump wavelengths in the proposed system using a 2 km sensing fiber with 1 m spatial resolution. In the proposed wavelength diversity Φ-OTDR system, the amplitude standard deviations are significantly minimized, thus reduced fading errors. At the end of the 2 km, the vibration frequencies from 100 Hz to 10 kHz are demonstrated. In addition, a simple, low-cost self-mixing demodulation technique has been employed in a proposed wavelength diversity Φ-OTDR system to eliminate the frequency offset between the electrical local oscillator and the beat signal. The proposed fading noise-free system will be attractive for practical applications such as oil and gas pipeline monitoring.

We report the use of a femtosecond infrared (fs-IR) laser to produce random grating structures in optical fibers for fiber sensor and fiber laser applications. The plane-by-plane method of inscribing various gratings is presented. We review our experimental results over the past 5 years of the applications of fiber random gratings for distributed temperature measurements, fiber lasers and fiber laser sensors. The potential applications of fs-IR laser processed optical fibers in structure health monitoring, harsh environment sensing, perimeter intrusion detection and encrypted communication will be discussed.

It is important to monitor and locate internal corrosion along natural gas pipelines to prevent methane leaks and catastrophic failures. Corrosion proxy materials enable optical fiber sensors to provide insight into corrosive environments where the pipeline materials tend to corrode. A distributed optical fiber corrosion sensor was demonstrated using a metallic film-coated, single-mode optical fiber interrogated with an optical backscatter reflectometer (OBR), based on strain changes during metallic film dissolution. Electroless plating leads to inherent internal stress in the metallic coating and therefore induces strains on optical fibers. As the metallic film gets dissolved or corroded, the internal stress will be released and cause opposite changes in strain, which can be used for corrosion monitoring. The microstrains induced solely by electroless plating or metal dissolution were measured in situ and in real time using the OBR, and interferences from temperature changes and water-induced swelling were compensated through comparison between the treated section (sensitized and activated) and an untreated control section. High-pH Ni plating had a faster deposition rate with branching on the film and induced negative microstrains, whereas low-pH Ni plating had a slower deposition rate with smooth coating and induced negligible (near-zero) strains. Eletroless Fe plating with high pH didn’t cause significant microstrains. When exposed to corrosive HCl solutions, dissolution of high-pH Ni plated films induced positive microstrains, opposite to the Ni plating. The OBR allows for distributed monitoring of strain changes due to Ni dissolution, demonstrating the capability of identifying corrosion locations along the optical fiber.

Reliable, secure, and resilient electricity distribution requires continuous health monitoring of electrical assets including power transformers. Among all sensing parameters, temperature is of utmost importance. Using optical fiber sensors for temperature monitoring has various advantages over traditional methods as they are inherently immune to electromagnetic interference, are good insulators at high-voltage levels, and are easy to install due to their small size and flexibility. Measuring the temperature of different parts of a power transformer core can help to detect hotspots and predict imminent device health issues. In this paper, a low-cost temperature sensor based on plasmonic-enabled optical fiber is demonstrated in multiple arrangements. The simplest arrangement would cost ~ $100 with potential for further cost reductions through reductions in the cost of the detection and excitation circuitry and optical components. By functionalizing an optical fiber with Au-Silica thin-films, the sensor was also demonstrated to measure the temperature of an energized transformer core in real-time. Repeatability and reliability of the proposed sensor were confirmed by running multiple cycles.

The Idaho National Laboratory (INL) is engaged in research and development activities for the development of nuclear instrumentation that provides crosscutting support to US Department of Energy Nuclear Energy (DOE-NE) programs. The combined application of laser and optical fiber technologies has the potential to offer innovative measurement solutions that could accelerate research and development activities and improve the competitiveness of advanced nuclear energy system. This paper discusses the main challenges encountered in the deployment of optical fiber sensors for nuclear applications based on the results of recent irradiation experiments in Material Test Reactors (MTRs) at INL and collaborating Organizations.

Recent advancements in fiber optic manufacturing, sensor design, and fiber optic interrogators have provided significant opportunities towards the development of cross-cutting fiber optic sensing solutions across the nuclear industry. The addressable harsh nuclear environment markets include Gen II, II+ and IV nuclear reactors, fusion reactors, and accelerator systems. In this work the authors present a series of developments towards the implementation of singlefiber, multipoint, temperature and pressure sensors, test results in high-temperature and high-radiation environments, cryogenic environments, material compatibility studies for sensor packaging, and future development needs to address technical challenges towards sensor commercialization.

Optical fiber-based sensors show unique advantages for high temperature and harsh environment sensing, with off-the-shelf silica fibers being relevant for application environments at temperatures approaching approximately 800oC. Through the integration of oxide-based sensing layers with the optical fiber platform in an evanescent field sensing approach, the optical response of a sensing layer which is modified in response to changing ambient conditions can be directly correlated to the sensor environment. Numerous deposition techniques have been explored in prior publications including sol-gel based wet chemistry deposition and sputtering. As an alternative, atomic layer deposition (ALD) allows for deposition of high quality, nanometer-scale thin films and is uniquely suited for coating of optical fiber-based sensors due to a lack of directionality during the deposition process and compatibility with scalable coating of optical fiber samples. In the current publication, ALD coated TiO₂ sensing layers are demonstrated to show a pronounced optical absorption in the visible range which depends upon subsequent processing temperatures and chemical environments. More specifically, the ALD deposition conditions result in the formation of initially amorphous TiO₂ layers which show a broad absorption band across the visible range due to the amorphous structure. A reversible temperature dependent response is observed, and above a critical temperature (~400-500°C), crystallization of the TiO₂ results in an irreversible change in optical absorption with a sharpened absorption peak associated with the band edge for which the temperature dependence is consistent with prior experiments and theoretical results. Following crystallization of the initially amorphous TiO2 layer, a strong and stable H2 sensing response is also demonstrated for H2 concentrations of various levels ranging from 0-3.9% H₂ in nitrogen balance, and at temperatures up to 800°C. Particularly attractive responses are shown in the telecom wavelengths (1550 nm) indicating potential application for distributed sensing with commercially available techniques.

Indoor illumination is generally characterized by artificial lighting and light-emitting diodes (LEDs). However, in order to reduce energy consumption, two potential alternatives are solar power and daylighting. Daylighting redirects sunlight to illuminate an indoor space, which also provides potential health benefits to long-term indoor workers through the use of natural light. This paper discusses the use of daylighting as an alternative to traditional, electrical lighting. In the first part of this work, an active daylighting system that follows the sun’s position is proposed. By inputting the location, date, and time variables, the sun’s azimuth and elevation angles are calculated (source code available through the link https://github.com/azhang7740/SolarPositionCalculator), and the results have been verified through an observational experiment. However, the program is unable to adjust for minute differences in the sun’s position from weather and other factors, suggesting that a tracking component may be necessary for direct alignment with the sun. In the second part of this paper, we introduce a sun redirecting prototype system which includes three main components: a light concentrator, transmitter, and diffuser. The light concentrator collects sunlight, and Fresnel lenses, parabolic troughs, and compound parabolic concentrators are considered. Optic fiber cables, which can transmit light through long distances, are a viable option for light transmission. Finally, the diffuser disperses light in order to achieve comfortable viewing, and a combination of lenses are considered for this mechanism. The current study evaluates the feasibility of the proposed method, while our future work will incorporate further quantitative theoretical and experimental analysis.