Acoustic desensitization of single-mode fibers utilizing nickel coatings.

The pressure sensitivity of the phase of light propagating in a single-mode fiber coated with a thin nickel jacket is determined both analytically and experimentally. The measured acoustic response of the fiber is found to be 1 order of magnitude lower than that of the bare fiber, in agreement with analytical predictions. The technique thus appears to be a promising way for desensitizing optical-fiber leads for use with fiber-optic sensors.

Fiber-optic acoustic sensors with increased sensitivity by use of composite structures.

Fiber-optic acoustic sensors having sensitivity nearly 2 orders of magnitude greater than that of sensors using bare fiber are reported. These new devices utilize a composite structure wherein the fiber is embedded in a material of lower elastic modulus that serves to increase the stress, and hence the optical phase shift, in the fiber for a given pressure.

Fiber-optic sensing of pressure and temperature.

The use of a fiber-optic Mach-Zehnder interferometer to measure differences in temperature or pressure between two single-mode fiber arms is described. Temperature or pressure changes are observed as a motion of an optical interference fringe pattern. Values are calculated for the pressure and temperature dependence of the fringe motion. Pressure and temperature measurements are made with the interferometer, and the experimental values for sensitivity are in good agreement with those calculated.

Fiber optic acoustic sensors with composite structure: an analysis.

Fiber optic acoustic sensors with composite structures are analyzed and shown to offer greatly increased acoustic sensitivity. The composite structure consists of an optical fiber coated with or embedded in an elastic material of lower elastic modulus. Sensitivity increases of 10-100 times are indicated. Important advantages of this technique in practical acoustic sensors are also described.

Unidirectional star coupler for single-fiber distribution systems.

The design and construction of a unidirectional star coupler for single-fiber distribution systems are described. A rectangular mixing section is required to obtain uniform output distribution. Four-port stars have been constructed with losses only (1/2) to 1 dB greater than packing fraction. For any given input, outputs are uniform to within about +/-1 dB.

Mode dispersion in diffused channel waveguides by the effective index method.

The effective index method for calculating waveguide mode dispersion is reviewed and applied to uniform rectangular optical waveguides with both small and large index differences. The results are shown to be at least as accurate as other approximate techniques. The effective index method is then applied to channel waveguides assuming 1-D and 2-D diffusion. Channel waveguides without sideways diffusion are shown to be described by the method using a normalized notation and previously published universal dispersion curves. Two-dimensional diffusion theory is applied to treat the case of isotropic sideways diffusion. A new, normalized, 1-D universal chart is obtained which in conjunction with previous results defines waveguide mode dispersion in isotropically diffused 2-D channels.