Craig W. Hodgson

Large-scale interferometric fiber sensor arrays with multiple optical amplifiers

We report what we believe to be the first laboratory prototype of a fiber sensor array using multiple low-gain (5dB) remotely pumped amplifiers in a 10-rung ladder structure. Incorporating amplifiers improves the system noise figure to less than 20dB, compared with 32dB in an optimized passive array of the same size. Scalability to more than 300sensors per fiber pair while a high dynamic range (1microrad/ sensitivity) is maintained is demonstrated.

Acoustic fiber sensor arrays

The acoustic fiber sensor arrays that have been developed over the past two decades for oil exploration and other applications can support hundreds of fiber hydrophones per fiber pair and exhibit exceptional properties, including shot-noise-limited sensitivities better than 1 μrad/√Hz, high stability, and dynamic ranges well in excess of 130 dB. This article reviews the main configurations reported to date, which are based on ladder architectures utilizing either Mach-Zehnder or Sagnac interferometric sensors and time-domain multiplexing. The emphasis is placed on their principles, performance characteristics, and relative advantages regarding such key issues as signal fading, polarization-induced fading, frequency response, sensitivity, and the number of sensors that can be multiplexed on a given pair of fibers.

Novel fiber sensor arrays using erbium-doped fiber amplifiers

We examine the signal-to-noise ratio (SNR) performance of a novel type of time domain multiplexed sensor arrays in which low gain (1-10 dB) fiber amplifiers are incorporated to compensate for splitting losses between sensors. The system noise figure for passive and amplified sensor arrays is presented, along with expressions to optimize the array parameters for high SNRs. We show that practical amplified sensor arrays exhibit low system noise figures that allow much larger arrays (hundreds of sensors) than passive arrays.

Optimization of large-scale fiber sensor arrays incorporating multiple optical amplifiers. I. Signal-to-noise ratio

We report on optimizing the signal-to-noise ratio (SNR) of large-scale fiber sensor arrays employing erbium-doped fiber amplifier (EDFA) telemetry with respect to the number of sensors per rung, the number of amplifiers per array, and the coupling ratio between the fiber buses and the rungs. Broad optimum regions are found, providing design flexibility to minimize pump power requirements. Simulations predict that 300 sensors can be multiplexed on a fiber pair while maintaining a high sensitivity (1 /spl mu/rad//spl radic/(Hz)) for all sensors with a moderate input pump power (<1 W).

Optimization of large-scale fiber sensor arrays incorporating multiple optical amplifiers. Part II: pump power

For part I see, ibid., p. 218, 1998. We discuss how to minimize the pump power required for large-scale fiber sensor arrays employing erbium-doped fiber amplifier (EDFA) telemetry with respect to the number of amplifiers per bus, number of sensors per rung, and the gain per amplifier. For a large array, the pump power requirement is dominated by passive component losses along the array. We investigate several methods, including alternative array topologies, to reduce the power requirement while minimizing the impact on the signal-to-noise ratio (SNR). We define an optimum topology which requires less than 1 W of 1480 nm pump power per bus to support 200 high sensitivity (1 /spl mu/rad//spl radic/(Hz)) sensors on a pair of fiber buses, a power requirement that is reasonable and attainable with available laser diodes.

Large-scale fiber interferometric sensor arrays with multiple optical amplifiers

Many applications require using common input and output fibers to support a large number of interferometric fiber sensors located far from the receiving electronics. Passive multiplexing of sensors is limited by splitting and dissipative losses to approximately 10 sensors per pair of fibers. A large scale array (200-1000 sensors) will thus require 40-200 telemetry fibers, which is unmanageable in practice. We report a novel method for multiplexing hundreds of sensors per pair of fibers, which incorporates fiber amplifiers into a time-domain multiplexed array with a ladder topology.

Phase-sensitivity measurement of a 10-sensor array with erbium-doped fiber amplifier telemetry.

We report what are believed to be the first measurements of the phase sensitivity of a fiber sensor array using multiple low-gain remotely pumped amplifiers with an interferometric sensor inserted. The measured phase sensitivities for individual rungs average 5.7 microrad(rms)/ radicalHz and exhibit no dependence on rung number, in agreement with predictions.