Single-Arm Frequency-Shifted Interferometry Using a Bidirectional Electro-Optic Modulator

Abstract

Multiplexing fiber-optic sensors is an effective way to perform large-area quasi-distributed sensing. Among many sensor multiplexing and interrogation methods, frequency-shifted interferometry (FSI) emerges as a unique low-cost technique that is capable of resolving sensor locations using a continuous-wave broadband source, a bidirectional optical frequency shifter, and a slow photo detector. An acousto-optic modulator is typically used as the frequency shifter in FSI due to its high modulation efficiency and bidirectional operation. But its relatively low modulation bandwidth results in low spatial resolution, on the order of meters. To improve spatial resolution, single-arm FSI (SA-FSI) that employs an electro-optic modulator (EOM) as the frequency shifter was proposed, but the EOM's broad modulation bandwidth cannot be fully utilized because conventional EOMs cannot support bidirectional modulation at gigahertz frequencies due to the speed mismatch between the optical wave and the applied RF wave, especially when the two are counter propagating. In this paper, we modified a commercial EOM to increase the modulation efficiency of the counter-propagating optical wave and used it to interrogate 15 weak fiber Bragg gratings (FBGs) in an array, achieving a spatial resolution of ∼3 cm and a sensing range of >1 km. A signal-to-noise ratio as high as ∼18 dB was obtained with a 15-mW broadband amplified spontaneous emission source without any optical amplification. This is the first demonstration of both spatially resolved and spectrally resolved SA-FSI, and it is the first time that FBGs are interrogated with the SA-FSI technique.

Polarization–frequency hyperentangled photons: generation, characterization, and manipulation

“…Conversely, negligible frequency conversion occurs in the opposite direction due to the phase mismatch between the two counterpropagating fields. 36,37 Under optimal RF driving conditions, 20 photons in the original frequency bin are depleted, while conversion efficiency to the desired bin is 27% (excluding insertion loss)-a consequence of employing a single EOM driven by sinusoidal modulation. Photons scattered into sidebands outside the computational space can be removed with an additional spectral filter.…”

Diagnostics of Internal Defects in Composite Overhead Insulators Using an Optic E-Field Sensor

“…However, recent developments have achieved extremely compact designs, which are also promising in terms of bandwidth [ 13 ]. Interferometric methods [ 14 , 15 , 16 ] are based on the splitting of a laser beam into two paths, travelling along two different arms. The properties of the light guides are chosen so that, as the light is recombined, interference effects occur, leading to the possibility of detecting the electric field.…”

Arbitrary Phase Access for Stable Fiber Interferometers

“…In particular, many free-space components or alreadydeveloped interferometer designs do not have accessible counterparts in fiber and generally, deployed optical fiber systems suffer from larger phase drifts. Several works towards reconstructing and stabilizing phase in fiber interferometers have thus been introduced, [27][28][29][30][31][32][33] featuring impressive milestones accomplished through diverse experimental approaches. These include, for example, the injection of single-frequency reference lasers, [27] variants of the Pound-Drever-Hall method, [32] modulation of an interferometer arm, [29][30][31]33] and explorations of weak references for phase reconstruction.…”

“…Several works towards reconstructing and stabilizing phase in fiber interferometers have thus been introduced, [27][28][29][30][31][32][33] featuring impressive milestones accomplished through diverse experimental approaches. These include, for example, the injection of single-frequency reference lasers, [27] variants of the Pound-Drever-Hall method, [32] modulation of an interferometer arm, [29][30][31]33] and explorations of weak references for phase reconstruction. [28,34] However, present phase-retrieval Here, the resulting fields are described by Ψ A (solid green line) and Ψ B (solid orange line), respectively.…”