Proposed Research Statement
Shayne X. Short
Texas A&M University

"Optical fiber Sagnac interferometry for space platform and other smart structure applications"

Continuing Plans of Research

This fellowship and research application proposes to continue to investigate applications of in-line Sagnac interferometry for space platform applications. This technology possesses many advantages for both current sensing and distributed strain sensing. The sensing head of this fiber-optic sensor consists of a single lead extending from the light source and signal processing electronics. This one unique advantage allows for great flexibility in aerospace applications. The sensing fiber portion of the sensor can be embedded in a structure allowing for distributed strain characterization along the continuous fiber length. This would provide more precise information for feedback control in such an aerospace system to dampen undesirable and potentially catastrophic mechanical oscillations. To perform this distributed strain sensing we propose to build a slightly mod)fied version of the present in-line Sagnac interferometer. This proposed model in shown in Fig. 1.

In addition to the promise of performing distributed strain sensing, the in-line Sagnac interferometer has been shown to provide superb performance for current sensing. In line with the development of distributed strain sensing is the development of the in-line Sagnac interferometer for current sensing. Such a dielectrically isolated current sensor with only one fiber lead extending from the source electronics can provide many desirable applications for both aerospace platform and terrestrial applications. Of particular interest are extremely small size and weight, and the intrinsic dielectric properties of fiber. The current sensor topology which we are presently constructing and modeling is shown in Fig. 2. We plan to continue pursuing this particular topology of the in-line Sagnac interferometer current sensor in the coming years.

Current year's activities

This past year's activities have centered largely around the in-line Sagnac interferometer for current sensing applications. In our laboratory, we have a proto-type of the in-line current sensor. In modeling this sensor, we have looked at various design considerations such as the effects of imperfect optical components within the design. This has been in an effort to determine how robust the design is. We have performed comparative analysis between the in-line Sagnac sensor and other traditional polarimetric type current sensors. The experimental results have helped confirm our predictions of robustness in design. The Sagnac type sensor does not possess such strict requirements for high quality optical fiber components. This suggests that a commercial venture to produce this sensor could be made at lower cost with wider tolerances of precision components.

Also, we have invested sign)ficant effort into investigating various environmental effects such as thermal transients and acoustic vibrations on various fiber-optic components of the sensor as compared to polarimetric type sensors. Again, our sensor possesses much greater immunity to environmental perturbations than the previous polarimetric type sensors.

This work has resulted in the publication of two papers:

S. X. Short, P. Tantaswadi, R. T. de Carvalho, B. D. Russell, and J. Blake, "Environmental Sensitivity Comparison of In-line Sagnac and Polarimetric Type Current Sensors," submitted for publication, OFS-II, Eleventh International Conference on Optical Fiber Sensors, Sapporo, Japan, May 21-24,1996.

S. X. Short, P. Tantaswadi, R. T. de Carvalho, B. D. Russell, and J. Blake, "Experimental Verification of Acoustic Vibration Effects in Optical Fiber Current Sensors," 96 W M 229-5 PWRD, presented at the 1996 IEEE PES Winter Meeting, Baltimore, MD, Jan. 21-25,1996.

We are presently in the process of developing a test to demonstrate electronic compensation for a very wide tolerance in quarter waveplate stability in our sensor. Assuming this demonstration is successful, it will provide further evidence of the ability of our sensor to be constructed with not only fiber-optic components of much less stringent tolerance requirements, but also the ability to perform feedback compensation to ensure proper function in the event of extreme component instability for long-term applications.


Last Modified: August 9, 2001