Leland Stanford Junior University

Litton Systems, Inc.

Novera Optics, Inc.

Benjamin J Vakoc

Michel J F Digonnet

Gordon S Kino

Michel J Digonnet

Byoung Yoon Kim

H John Shaw

Craig W Hodgson

A folded Sagnac fiber optic sensor array uses a common delay path to reduce distributed pickup in downlead fibers. The sensor array is used to detect perturbations (e.g., acoustic waves in water). By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of sensors can be multiplexed into the architecture of the sensor array. In one particularly preferred embodiment, the sensor array is configured with couplers and amplifiers selected to direct substantially equal portions of an input light signal to each sensor in the array. In another particularly preferred embodiment, first and second delay paths are provided for light at first and second wavelengths to increase the dynamic range of the sensors.

Amplified tree structure technology for fiber optic sensor arrays

Apparatus and method for processing optical signals from two delay coils to increase the dynamic range of a sagnac-based fiber optic sensor array

An optical apparatus includes an optical fiber. A plurality of individual optical fiber deformation structures are positioned adjacent along a length of the optical fiber. Each of an individual optical fiber deformation structure introduces a mechanical or index deformation of a portion of the optical fiber to create perturbation in the optical modes in the fiber and provide a coherent coupling between two modes in the optical fiber.

Gain flattening tunable filter

An apparatus and a method provide gain flattening in communications systems wherein a large number of optical signals at different wavelengths must be amplified while maintaining signal power within an acceptable range. Because of differences in gain of typical optical amplifiers as a function of wavelength and input power, the signals at different wavelengths are not amplified by the same amounts. Thus, when amplified multiple times, certain signals tend to become severely attenuated to the point of being no longer useable. The present gain flattening apparatus and method cause signals having higher gain-power products to be attenuated by a greater amount in response to Kerr-induced phase shifting such that after multiple stages of amplification, all the signal powers converge toward a small range of acceptable output powers. The apparatus provides amplification, multiple times, of a series of signals with a plurality of wavelengths covering a very wide spectral range, while maintaining the power of all the signals within a small range. The spread of this signal power range is robust against changes in the signal power, against changes in the number of signals, and, to some degree, against changes in the amplifier's pump power. The apparatus design is also robust against manufacturing changes in the parameters of the apparatus' components. The apparatus and invention are preferably implemented as multiple nonlinear Sagnac amplifiers having erbium-doped fiber amplifiers positioned asymmetrically in an interferometer loop.

Gain flattening with nonlinear sagnac amplifiers

Gain flattening with nonlinear Sagnac amplifiers

An acoustic array includes amplifiers and sensor subarrays, both of which are placed along rungs that connect a return distribution bus with both a signal distribution bus and a pump distribution bus. By placing the amplifiers along the rungs, separate buses can be used for distributing the optical signal and the pump energy for the amplifiers, thereby facilitating the use of standardized couplers. Time division multiplexed sensor subarrays are advantageously connected to unique combinations of laser signal sources and signal return buses, in which the laser signal sources generate different optical wavelengths that are multiplexed on the signal return buses. Optical sources include intensity modulators on either side of an amplifier to eliminate extraneous noise between optical pulses. In addition, amplified spontaneous emission (ASE) filters may be advantageously used to reduce optical noise at wavelengths other than those of interest.

Large scale WDM/TDM sensor array employing erbium-doped fiber amplifiers

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.

Fiber optic acoustic sensor array based on Sagnac interferometer

A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, 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 folded Sagnac fiber optic acoustic array.

Growing community of inventors

Palo Alto, CA, United States of America

Benjamin J Vakoc