Quadratic phase coding for SNR improvement in time-expanded phase-sensitive OTDR
Miguel Soriano-Amat, Hugo F. Martins, Vicente Durán, Sonia Martín‐López, Miguel González‐Herráez, María R. Fernández‐Ruiz
Abstract
Time-expanded phase-sensitive optical time-domain reflectometry ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">T</mml:mi> <mml:mi mathvariant="normal">E</mml:mi> </mml:mrow> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">Φ</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">O</mml:mi> <mml:mi mathvariant="normal">T</mml:mi> <mml:mi mathvariant="normal">D</mml:mi> <mml:mi mathvariant="normal">R</mml:mi> </mml:mrow> </mml:math> ) is a dual-comb-based distributed optical fiber sensing technique capable of providing centimeter scale resolution while maintaining a remarkably low (MHz) detection bandwidth. Random spectral phase coding of the dual combs involved in the fiber interrogation process has been proposed as a means of increasing the signal-to-noise ratio (SNR) of the sensor. In this Letter, we present a specific spectral phase coding methodology capable of further enlarging the SNR of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">T</mml:mi> <mml:mi mathvariant="normal">E</mml:mi> </mml:mrow> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">Φ</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">O</mml:mi> <mml:mi mathvariant="normal">T</mml:mi> <mml:mi mathvariant="normal">D</mml:mi> <mml:mi mathvariant="normal">R</mml:mi> </mml:mrow> </mml:math> . This approach is based on the use of a quadratic spectral phase to precisely control the peak power of the comb signals. As a result, an SNR improvement of up to 8 dB has been experimentally attained with respect to that based on the random phase coding previously reported.