Abstract: Methods for coating an optical fiber with optical fiber Bragg grating (FBG) with a hermetic coating, particularly a coating of carbon, are employed to avoid ingress of gases, vapors or fluids in the ambient environment. This ingress can be from water or hydrogen, which can diffuse in the fiber glass and cause deviation/drift in the measured Bragg measurements. Bragg gratings that maintain the grating strength at temperatures in excess of 1000° C. are used and can be formed by heating the fiber above 1000° C. in a chamber with a reactive gas that produces deposition of carbon.

Abstract: Method for coating an optical fibre with optical fibre Bragg grating (FBG) with a hermetic coating, particularly a coating of carbon, to avoid ingress of gases, vapours or fluids in the ambient environment. This can be water or hydrogen, which can diffuse into the fibre glass and cause deviation/drift in the measured Bragg measurements. Bragg grating that maintain the grating strength at temperatures in excess of 1000° C. is used, which is heated to above 1000 ° C. in a chamber with a reactive gas that produces deposition of carbon.

Abstract: Signal cable for transmission of optical signals, especially in oil and gas wells, includes at least one elongated optical fiber, and an elongated, generally tubular container within which the optical fiber is disposed, the container having an inner wall and an outer wall, a space being defined between the optical fiber and the inner wall. At least one of the inner wall and the outer wall has a thin continuous surface coating of gold or a gold alloy.

Abstract: Signal cable for transmission of optical signals in oil and gas wells, said cable comprising one or more optical fibers (1) wrapped in at least one pressure- and temperature-resistant, hollow and generally channel-shaped, protection means (2), optionally placed near, or integrated with, a cable construction. The protection means (2) is provided with a thin continuous surface coating (3) of gold to passivate the formation of hydrogen, and to prevent or reduce the diffusion of hydrogen through the protection means and into the optical fiber, and accordingly prevent resulting loss of signal in the fiber.

Abstract: A photoacoustic method of simultaneously determining optical bulk and surface absorption coefficients in solids in which a transducer is attached to the solid for measuring the amplitude of the acoustic wave generated by a beam of incident radiation as a function of distance of the transducer to the incident beam at a wavelength where bulk and surface losses, respectively, are heavily dominant. The transducer is chosen so as to give different functional dependencies for the bulk and surface absorption curves, respectively. The solid sample is also calibrated at wavelengths where bulk and surface absorption, respectively, are known. The output versus position or distance is measured at the wavelength of interest, and values of surface and bulk absorption coefficients are fitted to the respective pure curves so that they will add up to the experimentally generated composite curve.

Abstract: An apparatus for producing efficient second harmonic generation and frequency mixing having at least one crystal slice of predetermined thickness and preselected orientation mounted in optical alignment with an incoming laser beam. The proper orientation of the crystal slice together with the choice of laser polarization leads to efficient non-linear optical coupling with low reflection losses.