A novel, sensitive, simple, and robust strain interrogation technique is analyzed and experimentally tested. By locking a laser wavelength to the midreflection wavelength of a standard fiber Bragg grating and measuring the error signal, we achieve high dynamic strain sensitivity of 45 picostrain/ radicalHz rms at 3 kHz, where the dominant noise in the experiment is the laser frequency noise.

Novel and highly sensitive static strain interrogation technique is demonstrated, where the sensing element is a fiber-Bragg grating (FBG) and the light source is a frequency-locked diode laser. Locking the laser frequency to the center of an absorption line (atomic line of potassium in our experiment) eliminates the slow frequency drift of the laser. The stabilized laser source is used to measure low frequency ("static") strain, with a sensitivity of 1.2 nanostrain/ p Hz rms at 1.5 Hz.Index Terms-Gratings, optical fiber devices, strain measurement. and physics, from the Hebrew University, Jerusalem, Israel, in 1969 and the M.Sc. degree in applied physics from the Weizmann Institute of Science, Rehovot, Israel, in 1972, where he investigated electromagnetic wave propagation in cholesteric liquid crystals. After spending five years in the Israeli Defense Forces, he attended the Faculty of Engineering of Tel-Aviv University, Tel-Aviv, Israel, and received the Ph.D. degree in 1981.His research there involved analytical, numerical and experimental investigations of wave propagation through random media, as well as fiber-optic communication systems. During the academic years 1981-1983, he was a Postdoctoral fellow (1981)(1982) and then a Research Associate (1982)(1983) at the Information System Laboratory and the Edward L. Ginzton Laboratory of Stanford University, Stanford, CA. At the Information System Laboratory, he studied speckle phenomena, various theories of wave propagation in random media, and asymptotic solutions of the fourth moment equation. At the Ginzton Laboratory, he participated in the development of new architectures for single-mode fiber-optic signal processing and investigated the effect of laser phase noise on such processors. He is presently a Professor of Electrical Engineering and Chairman of the Department of Interdisciplinary Studies in the Faculty of Engineering at Tel-Aviv University, Tel-Aviv, Israel, where he established a fiber-optic sensing laboratory. He has authored or coauthored more than 150 journal and conference technical papers with recent emphasis on fiber-optic bit rate limiters, fiber lasers, fiber-optic sensor arrays, the statistics of phase-induced intensity noise in fiber-optic systems, fiber sensing in smart structures, fiber Bragg gratings, polarization mode dispersion, and advanced fiber-optic communication systems.Dr. Tur is a Fellow of the Optical Society of America (OSA).

No abstract

The effects of hard apertures on the transversal mode distribution and the output near and far field distributions are investigated both theoretically and experimentally. Wavefronts propagating in different directions inside a CO(2) laser cavity were measured at the same plane and found to have different transversal amplitude profiles. The influence of intracavity aperture's location and diameter on the near field distribution and far field beam quality were measured and calculated. Quantitative figures of merit are introduced to evaluate the departure of the transversal mode patterns from ideal Gaussians.

No abstract