title: Optical temperature sensor and thermal expansion measurement using a femtosecond micromachined grating in 6H-SiC.
abstract: An optical temperature sensor was created using a femtosecond micromachined diffraction grating inside transparent bulk 6H-SiC, and to the best of our knowledge, this is a novel technique of measuring temperature. Other methods of measuring temperature using fiber Bragg gratings have been devised by other groups such as Zhang and Kahrizi [in MEMS, NANO, and Smart Systems (IEEE, 2005)]. This temperature sensor was, to the best of our knowledge, also used for a novel method of measuring the linear and nonlinear coefficients of the thermal expansion of transparent and nontransparent materials by means of the grating first-order diffracted beam. Furthermore the coefficient of thermal expansion of 6H-SiC was measured using this new technique. A He-Ne laser beam was used with the SiC grating to produce a first-order diffracted beam where the change in deflection height was measured as a function of temperature. The grating was micromachined with a 20 microm spacing and has dimensions of approximately 500 microm x 500 microm (l x w) and is roughly 0.5 microm deep into the 6H-SiC bulk. A minimum temperature of 26.7 degrees C and a maximum temperature of 399 degrees C were measured, which gives a DeltaT of 372.3 degrees C. The sensitivity of the technique is DeltaT=5 degrees C. A maximum deflection angle of 1.81 degrees was measured in the first-order diffracted beam. The trend of the deflection with increasing temperature is a nonlinear polynomial of the second-order. This optical SiC thermal sensor has many high-temperature electronic applications such as aircraft turbine and gas tank monitoring for commercial and military applications.
authors.affiliation: AT&T Government Solutions, Wright-Patterson Air Force Base, Ohio 45433, USA. george.desautels@wpafb.af.mil
authors.forename: G Logan
authors.initials: GL
authors.lastname: DesAutels
authors.forename: Peter
authors.initials: P
authors.lastname: Powers
authors.forename: Chris
authors.initials: C
authors.lastname: Brewer
authors.forename: Mark
authors.initials: M
authors.lastname: Walker
authors.forename: Mark
authors.initials: M
authors.lastname: Burky
authors.forename: Gregg
authors.initials: G
authors.lastname: Anderson