Abstract: The instability of the mean wavelength of a superfluorescent fiber source (SFS) is reduced by randomizing the polarization of light from a pump source or by using polarization maintaining components. In one embodiment, the polarization of a pump source is made more random, leading to greater stability of the mean wavelength of the SFS, with an output mean wavelength that is stable to better than 3 ppm for full rotation of the pump polarization state. In another embodiment, the polarization of optical radiation throughout the device is kept substantially constant by using polarization maintaining fiber and components, thereby leading to enhanced mean wavelength stability of the SFS.

Abstract: The instability of the mean wavelength of a superfluorescent fiber source (SFS) is reduced by randomizing the polarization of light from a pump source or by using polarization maintaining components. In one embodiment, the polarization of a pump source is made more random, leading to greater stability of the mean wavelength of the SFS, with an output mean wavelength that is stable to better than 3 ppm for full rotation of the pump polarization state. In another embodiment, the polarization of optical radiation throughout the device is kept substantially constant by using polarization maintaining fiber and components, thereby leading to enhanced mean wavelength stability of the SFS.

Abstract: The instability of the mean wavelength of a superfluorescent fiber source (SFS) is reduced by randomizing the polarization of light from a pump source or by using polarization maintaining components. In one embodiment, the polarization of a pump source is made more random, leading to greater stability of the mean wavelength of the SFS, with an output mean wavelength that is stable to better than 3 ppm for full rotation of the pump polarization state. In another embodiment, the polarization of optical radiation throughout the device is kept substantially constant by using polarization maintaining fiber and components, thereby leading to enhanced mean wavelength stability of the SFS.

Abstract: The instability of the mean wavelength of a superfluorescent fiber source (SFS) is reduced by randomizing the polarization of light from a pump source or by using polarization maintaining components. In one embodiment, the polarization of a pump source is made more random, leading to greater stability of the mean wavelength of the SFS, with an output mean wavelength that is stable to better than 3 ppm for fall rotation of the pump polarization state. In another embodiment, the polarization of optical radiation throughout the device is kept substantially constant by using polarization maintaining fiber and components, thereby leading to enhanced mean wavelength stability of the SFS.

Abstract: The instability of the mean wavelength of a superfluorescent fiber source (SFS) is reduced by randomizing the polarization of light from a pump source or by using polarization maintaining components. In one embodiment, the polarization of a pump source is made more random, leading to greater stability of the mean wavelength of the SFS, with an output mean wavelength that is stable to better than 3 ppm for full rotation of the pump polarization state. In another embodiment, the polarization of optical radiation throughout the device is kept substantially constant by using polarization maintaining fiber and components, thereby leading to enhanced mean wavelength stability of the SFS.

Abstract: The present invention significantly improves the signal to noise ratio (SNR) in a passive optical array comprising sensors located in rungs between a distribution bus and a return bus. Erbium-doped optical fiber amplifiers are included in the buses proximate to each rung coupling to offset the coupler splitting losses. The gains of the amplifiers are selected to offset losses due to the couplings. The overall SNR can be maintained without significant degradation even for large numbers of sensors. In one aspect of the present invention, the amplifiers are located along the distribution and return buses directly after the couplers, except for the last coupler. In a second aspect, the amplifiers are located directly before each coupler. The optical amplifiers preferably are made of short lengths of erbium-doped fiber spliced into the distribution and return buses. Improvements can be made to the SNR when the distribution bus coupling ratios are set at optimal values.

Abstract: A new type of fiber filter is useable in optical communication systems. In particular, the fiber filter may be used to flatten the gain of erbium-doped fiber amplifiers (EDFAs). Such gain flattening is important for long-haul, dense (wavelength dependent multiplexed) WDM communication systems. The filter includes a periodic mechanical structure pressed against the side of a single-mode fiber to induce a wavelength-dependent loss in a signal propagating in the fiber core by coupling the signal to fiber cladding modes. The mechanical structure is a periodic comb of small ridges. Each ridge induces a local index change in the fiber via the photoelastic effect. For coupling to the right cladding modes, the period of the grating (and the comb) is in the range of few hundreds of microns. Thus, the grating is easy to fabricate with standard machining equipment.

Abstract: A fiber optic acoustic sensor array is based upon a Sagnac interferometer rather than being based upon Mach-Zehnder interferometers as in known acoustic sensor arrays. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the sensor array on the Sagnac interferometer rather than on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, has a larger dynamic range, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the Sagnac interferometer.

Abstract: The present invention significantly improves the signal to noise ratio (SNR) in a passive optical array comprising sensors located in rungs between a distribution bus and a return bus. Erbium-doped optical fiber amplifiers are included in the buses proximate to each rung coupling to offset the coupler splitting losses. The gains of the amplifiers are selected to offset losses due to the couplings. The overall SNR can be maintained without significant degradation even for large numbers of sensors. In one aspect of the present invention, the amplifiers are located along the distribution and return buses directly after the couplers, except for the last coupler. In a second aspect, the amplifiers are located directly before each coupler. The optical amplifiers preferably are made of short lengths of erbium-doped fiber spliced into the distribution and return buses. Improvements can be made to the SNR when the distribution bus coupling ratios are set at optimal values.

Abstract: The present invention significantly improves the signal to noise ratio (SNR) in a passive optical array by adding erbium-doped optical amplifiers between the sensor couplings to offset the coupler splitting losses. Optical amplifiers are inserted between the sensor couplings along the signal path, and the gain of the amplifiers is designed to offset losses due to the previous coupling. The overall SNR can be maintained without significant degradation even for large numbers of sensors. In a first aspect of the present invention, the amplifiers are located along the distribution and return buses directly after the couplers, except possibly for the last sensor. In a second aspect of the present invention, the amplifiers are located directly before the couplers. The optical amplifiers preferably are made of short lengths of erbium-doped fiber spliced into the distribution and return buses. Improvements can be made to the SNR when the distribution bus coupling ratios are set at optimal values.

Abstract: An all-optical fiber switch is implemented within a short Mach-Zehnder interferometer configuration. The Mach-Zehnder switch is constructed to have a high temperature stability so as to minimize temperature gradients and other thermal effects which result in undesirable instability at the output of the switch. The Mach-Zehnder switch of the preferred embodiment is advantageously less than 2 cm in length between couplers to be sufficiently short to be thermally stable, and full switching is accomplished by heavily doping one or both of the arms between the couplers so as to provide a highly nonlinear region within one or both of the arms. A pump input source is used to affect the propagation characteristics of one of the arms to control the output coupling ratio of the switch. Because of the high nonlinearity of the pump input arm, low pump powers can be used, thereby alleviating difficulties and high cost associated with high pump input powers.

Abstract: The present invention significantly improves the signal to noise ratio (SNR) in a passive optical array by adding erbium-doped optical amplifiers between the sensor couplings to offset the coupler splitting losses. Optical amplifiers are inserted between the sensor couplings along the signal path, and the gain of the amplifiers is designed to offset losses due to the previous coupling. The overall SNR can be maintained without significant degradation even for large numbers of sensors. In a first aspect of the present invention, the amplifiers are located along the distribution and return buses directly after the couplers, except possibly for the last sensor. In a second aspect of the present invention, the amplifiers are located directly before the couplers. The optical amplifiers preferably are made of short lengths of erbium-doped fiber spliced into the distribution and return buses. Improvements can be made to the SNR when the distribution bus coupling ratios are set at optimal values.

Abstract: A superfluorescent fiber source outputs highly polarized light without a substantial decrease in output power efficiency. According to one embodiment, a polarizer is spliced within the superfluorescent fiber at a selected location along the length of the fiber (e.g., near the middle of the fiber). According to another embodiment, the entire length of the superfluorescent fiber is polarizing to thereby assure that one of the polarizations of light is substantially extinguished while the other polarization of light is nearly double the power which that polarization would have if the polarizer were not present within the superfluorescent fiber. In this manner, superfluorescent sources can be adapted especially for use in fiber optic gyroscopes, or the like, which require highly polarized light, without a substantial reduction in efficiency.

Abstract: A fiber optic array having a plurality of subarrays of optical sensors, the subarrays being spaced apart along and optically connected to input and output buses through associated input and output optically actuated optical switches in series in the input and output buses. First and second light signal pulse trains are applied to one and other ends of the input bus and a third light signal pulse train is applied to one end of the output bus. The input switches are sequentially responsive to each first light signal pulse on the input bus for passing to an associated subarray a pulse of second light signal that is simultaneously present at that input switch such that second light signal pulses of the same magnitude are applied to each subarray. Associated output switches are sequentially responsive to third light signal pulses for passing trains of second light signal pulses from the arrays onto the output bus and to processing equipment.

Abstract: A fiber optic array having a plurality of subarrays of optical sensors, the subarrays being spaced apart along and optically connected to input and output buses through associated input and output optically actuated optical switches in series in the input and output buses. First and second light signal pulse trains are applied to one and other ends of the input bus and a third light signal pulse train is applied to one end of the output bus. The input switches are sequentially responsive to each first light signal pulse on the input bus for passing to an associated subarray a pulse of second light signal that is simultaneously present at that input switch such that second light signal pulses of the same magnitude are applied to each subarray. Associated output switches are sequentially responsive to third light signal pulses for passing trains of second light signal pulses from the arrays onto the output bus and to processing equipment.

Abstract: A ladder architecture comprises an input optical fiber bus and an output optical fiber bus. A plurality of input optical couplers couple light between the input bus and a plurality of branching fibers. A plurality of output couplers couple light from the branching fibers to the output bus. The input bus and the branch fibers may be single mode optical fibers while the output bus a multimode optical fiber. The input couplers may be symmetrical, single mode devices, and the output couplers may be asymmetrical and single mode to multimode devices. The input bus may also be a multimode fiber, and the input couplers may also be multimode to single mode devices. The asymmetrical coupling reduces the amount of signal lost at fiber ends.

Abstract: A lattice includes a transmit bus formed of a single mode optical fiber and a return bus formed of a multimode optical fiber. An optical transmitter applies input signals to the transmit bus, and an optical receiver receives the signals guided by the return bus. The return fiber is looped around the couplers so that the signal output from each segment of the lattice passes through all the preceding segments before reaching the receiver. The optical couplers have asymmetric coupling efficiencies so that recirculating light is attenuated.

Abstract: A fiber optic rotation sensor utilizes multimode optical fiber to improve power coupling and reduce coherent back scattering. A multimode light source such as a light emitting diode can be used. The system is economical and environmentally stable.

Abstract: An acoustic scanning apparatus is described having an acoustic grating for scattering waves into a focused beam. Surface acoustic waves are generated by a chirp signal generator and are introduced along one surface of the scanning apparatus. These waves propagate along the surface, are scattered by the acoustic grating and are thereby converted into bulk acoustic waves. The bulk acoustic waves converge into a focused beam inwardly directed at an angle to the surface acoustic waves. The focused beam scans at substantially the same speed as the surface acoustic waves traveling along the surface of the apparatus. The acoustic grating can also be used to convert bulk waves to surface acoustic waves as either a variable chirp rate generator or a variable pulse compression filter.