Boon Kwee Lee

Self-Aligned Single-Mode Polymer Waveguide Interconnections for Efficient Chip-to-Chip Optical Coupling

Single-mode (SM) ultrashort optical interconnections between the fibers and waveguides using self-forming polymeric waveguides with low optical losses at 1300 and 1550 nm were demonstrated. The localized refractive index in the SM regime is estimated by measuring the surface topography induced by monomer diffusion during the waveguide formation. A loss less than -1 dB can be obtained from self-aligning SM-to-multimode (MM) fibers and SM-to-SM fibers interconnections, respectively. A self-formed waveguide-to-fiber interconnection is fabricated and measured with loss less than 0.2 dB at 1550 nm. The polymer waveguide relaxes the positioning requirements for single-mode chip-to-chip optical interconnections, showing great potential to improve the short-term yield and long-term reliability

High-Density Fiber Optical Sensor and Instrumentation for Gas Turbine Operation Condition Monitoring

Gas turbine operation control is normally based on thermocouple-measured exhaust temperatures. Due to radiation shielding and bulky package, it is difficult to provide high spatial resolution for measuring can-to-can combustion temperature profile at the exhaust duct. This paper has demonstrated that wavelength-division-multiplexing-based fiber Bragg grating sensors could provide high spatial resolution steady and dynamic temperature measurements. A robust sensor package can be designed with either circumferential sensing cable or radial sensing rake for quasi-distributing multiple fiber sensors in the gas turbine environment. The field validations have demonstrated that quasi-distributed fiber sensors have not only demonstrated its temperature measurement accuracy compared to existing thermocouple sensors but also shown its unique dynamic response amplitude and power spectra that could be utilized for gas turbine transient operation condition monitoring and diagnostics.

Online compositional analysis in coal gasification environment using laser-induced plasma technology

Integrated Gasification Combined Cycle (IGCC) power plants have great potential for future clean-coal power generation. Today, the quality of coal is measured by sampling coal using various offline methods, and the syn-gas composition is determined by taking samples downstream of the gasifier and measured by gas chromatograph (GC). Laser induced plasma technology has demonstrated high sensitivity for elementary detection. The capability of free space transmission and focusing of laser beam makes laser induced plasma a unique technology for online compositional analysis in coal gasification environment and optimization control.

Characterization and calibration of Raman based distributed temperature sensing system for 600°C operation

Fiber optic distributed temperature sensing based on Raman scattering of light in optical fibers has become a very attractive solution for distributed temperature sensing (DTS) applications. The Raman scattered signal is independent of strain within the fiber, enabling simple packaging solutions for fiber optic temperature sensors while simultaneously improving accuracy and robustness of temperature measurements due to the lack of strain-induced errors in these measurements. Furthermore, the Raman scattered signal increases in magnitude at higher fiber temperatures, resulting in an improved SNR for high temperature measurements. Most Raman DTS instruments and fiber sensors are designed for operation up to approximately 300˚C. We will present our work in demonstrating high temperature calibration of a Raman DTS system using both Ge doped and pure silica core multi-mode optical fiber. We will demonstrate the tradeoffs involved in using each type of fiber for high temperature measurements. In addition, we will describe the challenges of measuring large temperature ranges (0 – 600˚C) with a single DTS interrogator and will demonstrate the need to customize the interrogator electronics and detector response in order to achieve reliable and repeatable high temperature measurements across a wide temperature range.

Fiber-optic photo-acoustic spectroscopy sensor for harsh environment gas detection

Photo-acoustic spectroscopy (PAS) has been successfully applied to detect various gases and chemicals due to its high selectivity and sensitivity. However, the performance of the conventional acoustic sensors prohibits the application of PAS for harsh environment gas species real-time monitoring. By replacing conventional acoustic sensors, such as microphone and piezo-transducers, with a high-temperature Fiber Bragg Grating (FBG) vibration sensor, we developed a fiber-optic PAS sensing system that can be used in high-temperature and high-pressure harsh environments for gas species identification and concentration measurement. A resonant acoustic chamber is designed, and FBG vibration sensor is embedded in the molybdenum membrane. An OPO laser is used for spectrum scanning. Preliminary test on water vapor has been conducted, and the result is analyzed. This sensing technology can be adapted into harsh environments, such as Integrated Gasification Combined Cycle (IGCC) power plant, and provide on-line real-time monitoring of gases species, such as CO, H2O, and O2. Presently, our FBG-based vibration sensor can withstand the high temperature up to 800°C.

Temperature-dependent fiber optic hydrogen gas sensor response characteristics

Dynamic response characteristics of silica fiber long-period grating with a modified cladding, composed of ∼10-100 nm nanoparticle palladium oxides thin film material prepared by a magnetron sputtering technique, have been investigated at several elevated temperatures with a 2%H2/98%N2 mixing gas concentration. The fiber cladding modified grating, without cladding chemical etching process, demonstrates 540 pm per 1% H2 sensitivity, a better than 1sec response times at 160oC, respectively. The thermal responses of the prototype have demonstrated increased dynamic wavelength shift while reducing response time simultaneously. The observed thermal dependence of the prototype could be attributed to a combined effect of thermal dependent hydrogen atoms diffusion rate and hydrogen atoms solubility.

Drift in high-temperature FBG sensors

Fiber Bragg gratings are reported that are optimized for low wavelength drift, making them suitable for high- accuracy temperature measurements over extended periods of time. Our gratings show drift in the order of a few 10s of pm over 1,300 h at up to 650°C.

Self-assembled 3-D Polymer Micro/nano Wire and Its Applications

Based on a novel light-induced local diffusion in polymer, we have demonstrated a self-aligned 3-D SM polymer waveguide for efficient optical coupling. The polymer waveguide relaxes the positioning requirements for single-mode chip-to-chip optical interconnections

Sapphire-fiber-based pyrometer for harsh environment applications

It is very critical to develop sensor that can operate in high temperature and chemically harsh environments. Sapphire (Al2O3) material, which possesses a melting point of 2050°C and a wide transmission wavelength region as high as ~3.5μm, has been demonstrated to be an ideal candidate for high temperature fiber-based environmental sensing applications. Under harsh environment, the performance of conventional blackbody radiation based sapphire fiber high temperature sensor could be easily affected due to the lack of cladding. In this paper, a fiber-optic temperature sensor with a single-crystal sapphire fiber as the light guide and a high temperature ceramic coating as the sensing element as well as the protection layer was presented. The radiance emitted from the ceramic coating is used to measure the temperature, and it is transmitted to optical receiver through the sapphire fiber. This ceramic coating greatly improved the stability and dynamical range of pyrometer. Preliminary experimental results demonstrated that the sensor is very promising for measuring ultra-high temperature up to 1900°C in the harsh environment.