RESUMO
The stimulated Brillouin scattering (SBS) gain efficiencies were measured in the LP(08) and LP(01) modes of a higher-order-mode optical fiber. Gain efficiencies C(B) of 0.0085 and 0.20 (m-W)(-1) were measured for the LP(08) and LP(01) modes at 1083 nm, respectively. C(B) is inversely proportional to the optical effective area Aeff and the same core-localized acoustic phonon seeds the SBS process in each case. An acoustic modal analysis and a distributed phenomenological model are presented to facilitate the data analysis and interpretation. The LP(08) mode exhibits a threshold powerlength product of 2.5 kW-m.
RESUMO
Suppression of stimulated Raman scattering (SRS) is demonstrated in a cladding-pumped fiber amplifier. The Yb-doped amplifier fiber design incorporates a high-index ring that resonantly couples SRS wavelengths out of the gain material, thus filtering the gain. Modeling shows that fiber asymmetry plays an important role in the filtering spectrum.
RESUMO
The bichromatic optical frequency correlation function for Rayleigh backscattering from a pulse of laser light propagating along a single-mode optical fiber has been calculated and measured. It is shown that the optical correlation frequency, Dnu(c) , is equal to the reciprocal of pulse width T(w) . These results are important for the development of wavelength diversity techniques for the reduction of coherent Rayleigh noise in distributed Rayleigh backscattering single-mode optical fiber sensors.
RESUMO
A closed-form expression is developed for the infrared solar glint clutter radiance generated by the nearhorizon ocean surface. The clutter radiance is calculated as a function of water temperature, wind speed, wind direction, and solar position and agrees well with midwave infrared imagery measurements.
RESUMO
A novel dual-air-gap fiber-optic Mach - Zehnder interferometer is proposed for the direct measurement of the atmospheric optical turbulence structure constant C(n)(2). The shot-noise-limited minimum detectable structure constant is estimated to be 4.5 x 10(-20) m(-2/3), which is more than 2 orders of magnitude below a typical value of 10(-17) m(-2/3) for weak turbulence. This sensor is suitable for the measurement of atmospheric turbulence over land and ocean surfaces.
RESUMO
A statistical analysis is presented for the mean and the clutter radiance emitted by the ocean surface near the horizon and in the absence of direct solar illumination. The calculated midwave and long-wave radiances are given as functions of the environmental and optical parameters and agree with experimentally measured radiance profiles to within 20%. A simple expression for the calculated radiance as a function of wind speed and look direction is obtained by linearizing the radiance as a function of the wave slope.
RESUMO
An analytic model is developed for the mean and clutter infrared radiance emitted from the ocean surface near the horizon and in the presence of solar glint. The model is based on the identification of a characteristic facet dimension over which the ocean surface is essentially flat. Fluctuations in the facet orientation generated by the water wave motion are modeled by a parameterized wave height power spectral density that provides the two orthogonal wave slope variances. The mean and root-meansquare facet radiances are calculated with Gaussian probability-density functions for the wave slopes. One can determine the number of facets within the field of view of a single detector by estimating the exposed ocean area and dividing by the facet area. This estimation takes into account shadowing effects of the swell wave, the swell wavelength, and the transverse detector field of view. The number of exposed facets together with the central-limit theorem permits computation of the radiance clutter as a function of look-down angle below the horizon. Vertical radiance profiles, parameterized by the azimuthal offset from the solar position, are calculated over a sensor look-down angle range of ±50 mrad about the horizon. The results of this analysis are compared with infrared radiance measurements of the ocean surface near the horizon and in the presence of solar glint. Agreement between the measured and calculated values of the mean and clutter radiances is good.
RESUMO
A two-element single-mode optical fiber goniometer that uses graded-index microlens receivers is presented that measures the angular orientation of a remote laser. The goniometer exhibits a sensitivity of 1.0 V/mrad and a calculated shot-noise-limited angular resolution of 1.0 nrad/ radicalHz.
RESUMO
A 1 x 2 single-mode fiber-optic heterodyne array is presented that simultaneously measures the radial and angular Doppler velocities of a target. This heterodyne array also provides an amplitude-dependent error signal suitable for angular tracking.
RESUMO
Characteristics of a fiber-optic sensor for the detection of external electric fields are presented. This device utilizes a single-mode fiber that is embedded in a poled vinylidene fluoride-tetrafluoroethylene copolymer film and incorporated as the sensor arm of a Mach-Zehnder interferometer. A low-frequency intrinsic sensitivity of (0.20 +/- 0.03) x 10(-12) m/V is measured which compares well with our projected theoretical static sensitivity. This sensitivity implies a minimum detectable field of 33 microAV/m for a 1.0-km length of activated fiber and a 10(-7)-rad phase-shift detection capability.
RESUMO
The detection of electric fields with a piezoelectric polymer-jacketed single-mode optical fiber is proposed. The polymer-jacketed fiber is incorporated as the sensing arm of a Mach-Zehnder fiber-optic interferometer. Calculations are presented for the fractional phase change/unit electric field strength of monochromatic light propagating in a poly(vinylidene fluoride)-jacketed fiber as a function of jacket radius. A minimum detectable field strength of 6.0 microV/m is estimated for a 1-km length of jacketed fiber.
