Hon Man Chan

Fabrication and Mode Identification of Compact Long-Period Gratings Written by CO

We report highly compact (1.2 cm) long-period fiber gratings (LPGs) exhibiting strong grating effect (>30-dB loss) and low insertion loss (<0.25 dB) inscribed by a continuously scanned CO2 laser. The LPG resonances are also probed using traveling acoustic gratings with variable period. Our results show that these CO2 laser side-exposed LPGs predominantly couple to antisymmetrical cladding modes.

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A compact high-temperature fiber-optic sensor is demonstrated by fusion splicing a 3.25mm-long two-mode fiber (TMF) between two single mode fibers (SMFs) to form an all-fiber Mach-Zehnder interferometer (MZI). Under optimized splicing conditions, a strong interference is achieved with high extinction ratio (~10dB). Two methods are applied to detect temperature changes from temperature induced wavelength shift and intensity change of a probing light source. Experimental results show the device is capable of monitoring temperature change from 25degC to 425degC with temperature sensitivity of 58pm/degC and 0.45muW/degC with 360muW of input power, respectively, and a theoretical temperature range from 25degC up to 1000degC

Laser

An overview of the research and technological development of the fiber-optic sensing system (FOSS) at the National Aeronautics and Space Administration Armstrong Flight Research Center (NASA AFRC) is presented. Theory behind fiber Bragg grating (FBG) sensors, as well as interrogation technique based on optical frequency domain reflectometry (OFDR) is discussed. Assessment and validation of FOSS as an accurate measurement tool for structural health monitoring is realized in the laboratory environment as well as large-scale flight deployment.

A compact Mach-Zehnder two-mode fiber-optic interferometer for high temperature sensing

We demonstrate a compact, all-fiber frequency shifter by cascading a CO2-written long-period grating with a flexural acoustic-wave-induced microbending grating on a single-mode fiber. Carrier and image sideband suppressions of 30.0 and 28.1 dB, respectively, are measured. An all-fiber vibrometer based on this frequency shifter capable of nanometer resolution at frequencies up to megahertz is also demonstrated.

Fiber-optic sensing system: Overview, development and deployment in flight at NASA

A new method to inscribe a long-period grating (LPG) with strong grating (>25 dB loss), short grating length (1.2 cm) and low insertion loss (<1.0 dB) by using a programmable sinusoidal-dithering, linearly scanned CO2 laser beam is reported.

A Compact All-Fiber LPG-AOTF Frequency Shifter on Single-Mode Fiber and Its Application to Vibration Measurement

A 2015 NASA Aeronautics Mission “Seedling” Proposal is described for a Severe-Environment UAV (SE-UAV) that can perform in-situ measurements in hazardous atmospheric conditions like lightning, volcanic ash and radiation. Specifically, this paper describes the design of a proof-of-concept vehicle and measurement system that can survive lightning attachment during flight operations into thunderstorms. Elements from three NASA centers draw together for the SE-UAV concept. 1) The NASA KSC Genesis UAV was developed in collaboration with the DARPA Nimbus program to measure electric field and X-rays present within thunderstorms. 2) A novel NASA LaRC fiber-optic sensor uses Faraday-effect polarization rotation to measure total lightning electric current on an air vehicle fuselage. 3) NASA AFRC’s state-of-the-art Fiber Optics and Systems Integration Laboratory is envisioned to transition the Faraday system to a compact, light-weight, all-fiber design. The SE-UAV will provide in-flight lightning electric-current return stroke and recoil leader data, and serve as a platform for development of emerging sensors and new missions into hazardous environments. NASA’s Aeronautics and Science Missions are interested in a capability to perform in-situ volcanic plume measurements and long-endurance UAV operations in various weather conditions. (Figure 1 shows an artist concept of a SE-UAV flying near a volcano.) This paper concludes with an overview of the NASA Aeronautics Strategic Vision, Programs, and how a SE-UAV is envisioned to impact them. The SE-UAV concept leverages high-value legacy research products into a new capability for NASA to fly a pathfinder UAV into hazardous conditions, and is presented in the SPIE DSS venue to explore teaming, collaboration and advocacy opportunities outside NASA.

Ultra-Compact Long-Period Fiber Grating and Grating Pair Fabrication using a Modulation-Scanned CO 2 Laser

A new method to create a long-period fiber grating utilizing a scanning CO2 laser with varying scanning velocities is reported that results in strong grating (>30dB loss) with extremely short grating length (1.1-cm) all achieved with low insertion loss (<2dB).