Colour simplex coding for brillouin distributed sensors

Abstract

The possibility to customize Simplex coding for long range Brillouin Optical Time Domain Analysis is demonstrated by "colouring" the sequences in the frequency domain. The coding gain is identical to the traditional intensity-modulated Simplex code, though with much simplified series of sequences. The frequency-hopping pulses in return-to-zero intensity-modulated format are generated with a Direct-Digital Synthesizer. The proof-of-concept is experimentally demonstrated with measurements over a 50 km range (100 km fibre-loop) and a 2 meter spatial resolution.

Novel Brillouin Optical Time-Domain Analyzer for Extreme Sensing Range Using High-Power Flat Frequency-Coded Pump Pulses

“…Moreover, such coding techniques can be applied as long as the accumulated information, taken from the pump pulses to the probe, keeps a linear amplification. In other words, if the code length is long (to be able to get a high code gain), the pump power has to be reduced to avoid distortion [9].…”

Increasing robustness of bipolar pulse coding in Brillouin distributed fiber sensors

“…While coding schemes based on incoherent pulse compression [19,20] have efficiently been used in high spatial resolution sensors, demonstrations in long-range BOTDA have been classically based on unipolar sequences, such as Simplex [9] or Golay [11] codes. Two kinds of pulse coding schemes have been recently proposed as a new breach in long range sensing: bipolar codes [12] and time/frequency or colored codes [13][14][15]. Both coding schemes offer improved SNR enhancement in comparison to traditionally-used unipolar coding schemes [9][10][11].…”

“…Besides enhancing BOTDA systems for long range [9][10][11][12][13][14][15], optical pulse coding has also be applied to high spatial resolution Brillouin sensors, based for instance in correlation-domain [19]. While coding schemes based on incoherent pulse compression [19,20] have efficiently been used in high spatial resolution sensors, demonstrations in long-range BOTDA have been classically based on unipolar sequences, such as Simplex [9] or Golay [11] codes.…”

“…On the probe wave side, the power of the CW probe is ultimately limited by the onset of amplified spontaneous Brillouin scattering, which also eventually sets a limit to the SNR on the measurements [5]. To overcome all those limitations to the performance of long-range Brillouin sensors, alternative solutions such as distributed Raman amplification [6][7][8] and optical pulse coding [9][10][11][12][13][14][15] have been proposed, providing a huge improvement in the sensor performance, especially when both techniques are combined in the same system [16,17]. The situation becomes even more critical and demanding in terms of SNR when the real remoteness of the sensor is extended using a linear fiber-loop configuration [17,18], in which half of the fiber is used for sensing while the second half, paired to the sensing segment, is used to convey the probe to the most remote sensing location, i.e.…”

Novel Concepts and Recent Progress in Distributed Optical Fiber Sensing

“…Different types of code sequences can be implemented, the simplest being the Simplex code [12,13], while higher SNR can be obtained using more sophisticated codes, such as the bipolar Golay code -where "-1" and "+1" elements can be practically realized by pulses inducing Brillouin loss and gain processes, respectively [14] -or the colored codes, in which each pulse has a different optical frequency [15].…”