KEYWORDS: Sensors, Acoustics, Signal detection, Rayleigh scattering, Demodulation, Sensing systems, Nonlinear optics, Fiber Bragg gratings, Analog to digital converters, Vibration
A low-noise φ-OTDR sensor is developed by adding a 2-stage pre-amplification system mixing linear and nonlinear amplification in a 3x3 Michelson interferometric configuration. Its performance is evaluated by deploying it as a distributed acoustic sensing system in a survey well (sampling rate: 10 kHz), showing noise floor levels below 1 nε
In this work, we present an enhanced design for a Brillouin Ring Laser (BRL) based on a doubly-resonant cavity (DRC) with short fiber length, paired with a heterodyne-based wavelength-locking system, to be employed as pump-probe source in Brillouin sensing applications. The enhanced source is compared with the long-cavity (LC) (~ 2 km) BRL pump-probe source that we have recently demonstrated, showing a significantly lower relative intensity noise (~-145 dB/Hz in the whole 0-800 MHz range), a narrower linewidth (10 kHz), combined with large tunability features and an excellent pumpprobe frequency stability (~200 Hz) which is uncommon for fiber lasers. The measurement of intensity noise on the novel BRL signal yielded an improved signal-to-noise ratio (SNR) of about 22 dB with respect to LC-BRL schemes that is expected to lead to a temperature/strain resolution enhancement in BOTDA applications up to 5.5 dB.
In this work, we present an enhanced design for a Brillouin Ring Laser (BRL) based on a doubly-resonant cavity (DRC) with short fiber length, paired with a heterodyne-based wavelength-locking system, to be employed as pump-probe source in Brillouin sensing applications. The enhanced source is compared with the long-cavity (LC) (~ 2 km) BRL pump-probe source that we recently demonstrated, showing a significantly lower relative intensity noise (~ -145 dB/Hz in the 0-800 MHz range), a narrower linewidth (10 kHz), combined with large tunability features and an excellent pumpprobe frequency stability (~200 Hz) which is uncommon for fiber lasers. The measurement of intensity noise on the novel BRL signal yielded an improved signal-to-noise ratio (SNR) of about 22 dB with respect to LC-BRL schemes that is expected to lead to a temperature/strain resolution enhancement in BOTDA applications up to 5.5 dB.
Brillouin distributed optical fiber sensors have proved to be a powerful technology for real-time detection of strain and temperature. In such sensors the optical fiber is interrogated along its full length with a resolution down to decimeters and a frequency-encoding of the measurement data that is not affected by variation of the optical attenuation. The fiber sensing cable plays a key role, since it must provide accurate strain transfer, robustness and durability. In this paper, a novel, suitably designed fiber cable for achieving optimal strain measurement performance is presented. The concept and development phases are illustrated, together with results on the strain transfer capability.
In this work we report the results of a theoretical and experimental study that we have carried out on a Brillouin optical time domain analysis (BOTDA) sensing scheme using a novel low-noise actively-stabilized fiber Brillouin ring laser (BRL) as probe source. The BRL laser is based on a short-cavity (SC), < 4 meters long, layout achieving double-resonance (DR) operation for both pump and probe signals; an active wavelength-locking circuit is used to stabilize the signal and tune the signal frequency over a range of ̴ 200 MHz range. The wavelength-locked SC-DR BRL shows spectral linewidth of approximately 10 kHz and RIN values of ~-145 dB/Hz across the (0-600) MHz range; pump-probe frequency shift can be efficiently tuned across the entire Brillouin gain spectrum of the sensing fiber with sub-kHz precision (200 Hz) and high temporal stability for timescale of BOTDA measurements (more than 100 ms). A preliminary BOTDA measurement using a wavelength-locked long-cavity (LC) BRL yielded a Brillouin frequency shift (BFS) uncertainty of 1,5 MHz corresponding to temperature and strain sensitivity values of 1 K and 25 με, respectively, and a spatial resolution of 5 m for 50 ns-long pump pulses.
In this paper we show a Brillouin optical time-domain analysis (BOTDA) sensing system experiment employing a tunable narrow-linewidth dual pump-probe source based on modified Brillouin ring laser technology. The developed cost-effective source generates a pump-locked and tunable probe light, with wavelength shift and a large tuning range (~200 MHz), narrow linewidth (<2.5 MHz) and adequate power (~0.5 mW). The developed source was hence employed in BOTDA system experiments providing distributed sensing over ~10 km single mode optical fiber, and attaining strain and temperature resolutions of ~10με and ~0.5 °C respectively, indicating the pump-probe source as an efficient and cost-effective solution for BOTDA avoiding high-frequency signal generators or complex locking techniques.
We present a tunable narrow-linewidth dual pump-probe optical source based on modified Brillouin ring laser technology aimed at Brillouin-based sensing. The developed source exhibits a narrow linewidth and allows for a large tuning range, attaining <2.5 MHz bandwidth, ~200 MHz tuning range and ~0.5 mW power, thus constituting an efficient and cost-effective solution for sensing interrogators.
In this work we report the results of both theoretical and experimental strain analysis of Silicon waveguides and
couplers. Simulations of induced stress and strain distributions on photonic structures (waveguides with 450 × 220 nm
cross section) have been performed taking into account a ~375 nm thick Si3N4 straining layer. The Convergent Beam
Electron Diffraction (CBED) technique has also been employed to provide locally accurate strain measurements on
fabricated silicon rib and coupling structures across the nitride-to-silicon interface, showing a good match between
multiphysics simulations and measurements along the rib cross-section, resulting in notable attained strain levels.
In this paper we present a giant-area fiber-optic gyroscope (GAFOG) combining a Raman distributed temperature sensor (RDTS) for metrological monitoring of Earth rotation rate fluctuations. The GAFOG exhibits sensitivity limits in Earth rotation sensing associated to temperature variations along the fiber. Distributed temperature measurements providing an accurate fiber temperature mapping, enable tracking of the signal phase drifts. This allows reduction of the phase noise at low Fourier frequencies, and a corresponding enhancement of the Earth rotation rate variation sensitivity beyond the currently achieved 2•nrad/s for integration times of 1000 s.
Differential pulse-width-pair BOTDA technique is combined with bi-directional Raman amplification and Simplex
coding to achieve sub-meter spatial resolution over very long sensing distances. Numerical simulations are used to
optimize the power levels of the Raman pumps, avoiding nonlinear effects and pump depletion. Distortions in the
Brillouin gain spectrum due to acoustic-wave pre-excitation are also avoided by numerical optimization of the pulse
width and duty cycle of return-to-zero Simplex coding, providing significant SNR enhancement. We demonstrate 50 cm
spatial resolution over 93 km of standard SMF with a strain/temperature accuracy of 34με/1.7 °C, respectively.
We propose and experimentally demonstrate a hybrid fiber optic sensing technique that effectively combines Brillouin
optical time-domain analysis and a time-domain multiplexing interrogation technique for Fiber Bragg Gratings (FBGs).
The highly-integrated proposed scheme employs broadband apodized low-reflectivity FBGs with a single optical source
and a shared receiver block, allowing for simultaneous measurements of distributed static and discrete dynamic
temperature and strain, over the same sensing fiber.
In this paper we demonstrate distributed Raman temperature sensing (RDTS) in a loop scheme employing anti-Stokes
light intensity only. Using a single-channel receiver and anti-Stokes traces measured in loop configuration, we
implement RDTS with inherent compensation of fiber wavelength-dependent losses, as well as local external
perturbations. Experimental results show a signal-to-noise ratio enhancement with respect to a standard RDTS in loop
configuration, providing a robust and reliable high-performance sensor for long sensing ranges.
In this paper we propose the use of optimized bi-directional distributed Raman amplification to enhance the operating
range of Brillouin optical time-domain analysis (BOTDA) sensors. In particular by combining high-power fiber-Raman
lasers and polarization-multiplexed Fabry-Pérot lasers operating at 1450 nm with low relative-intensity-noise (RIN), we
demonstrate distributed sensing (using first-order Raman amplification) over 120 km of standard single-mode fiber with
2 meter spatial resolution and with a strain/temperature accuracy of 45με/2.1°C respectively.
We experimentally analyse the impact of pulse modulation format on BOTDA sensors exploiting Simplex coding. A
careful optimisation of modulation format is required to avoid spurious oscillations causing severe penalties in the
measurement accuracy.
KEYWORDS: Spatial resolution, Sensors, Signal to noise ratio, Single mode fibers, Temperature metrology, Modulation, Optical amplifiers, Fiber optics sensors, Scattering
In this paper we demonstrate a long-range distributed strain and temperature optical fiber sensor using Brillouin optical
time-domain analysis in conjunction with optical pulse coding. Compared to standard BOTDA, pulse coding provides
higher signal-to-noise ratio at the same pump peak power, overcoming the limitations induced by pump depletion and
modulation instability, and allowing to achieve a record of 1 meter spatial resolution over 50 km of standard single mode
fiber with temperature and strain resolution of 2.2 °C and 44 με respectively.
In this paper we propose the use of multi-longitudinal mode lasers, such as Fabry-Pérot (FP) lasers, for simultaneous
distributed strain and temperature sensing based on hybrid Brillouin and Raman scattering. Fabry-Pérot lasers allow for
high-power Raman intensity measurement and the simultaneous detection of the Brillouin frequency shift parameter for
all FP longitudinal modes, by using a self-heterodyne detection scheme based on a multi-wavelength optical local
oscillator. Experiments point out significant improvement in hybrid sensor performance, also suggesting further potential
benefits when combining the use of FP lasers with optical coding techniques and/or optical amplification.
In this paper, we will briefly outline our contributions for the physical realization of coded OTDR, along with its
principles and also highlight recent key results related with its applications. For the communication network application,
we report a multi-port / multi-wavelength, high-speed supervisory system for the in-service monitoring of a bidirectional
WDM-PON system transmission line up to 16 ports x 32 nodes (512 users) capacity. Monitoring of individual branch
traces up to 60 km was achieved with the application of a 127-bit simplex code, corresponding to a 7.5dB SNR coding
gain effectively reducing the measurement time about 30 times when compared to conventional average mode OTDR.
Transmission experiments showed negligible penalty from the monitoring system to the transmission signal quality, at a
2.5Gbps / 125Mbps (down / up stream) data rate. As an application to sensor network, a Raman scattering based coded-OTDR distributed temperature sensor system will be presented. Utilizing a 255-bit Simplex coded OTDR together with
optimized sensing link (composed of cascaded fibers with different Raman coefficients), significant enhancement in the
interrogation distance (19.5km from coding gain, and 9.6km from link-combination optimization) was achieved to result
a total sensing range of 37km (at 17m/3K spatial/temperature resolution), employing a conventional off-shelf low power
(80mW) laser diode.
KEYWORDS: Temperature metrology, Spatial resolution, Temperature sensors, Time metrology, High temperature raman spectroscopy, Multimode fibers, Raman spectroscopy, Receivers, Raman scattering, Fiber lasers
The performance of distributed temperature sensor systems based on spontaneous Raman scattering and coded OTDR
are investigated. The evaluated DTS system, which is based on correlation coding, uses graded-index multimode fibers,
operates over short-to-medium distances (up to 8 km) with high spatial and temperature resolutions (better than 1 m and
0.3 K at 4 km distance with 10 min measuring time) and high repeatability even throughout a wide temperature range.
KEYWORDS: Raman spectroscopy, Wavelength division multiplexing, Fiber lasers, Optical amplifiers, Interference (communication), High power lasers, Single mode fibers, Signal to noise ratio, Amplifiers, Polarization
In this paper we describe advanced bi-directional Raman pumping schemes for extending the maximum reach achievable in long-span unrepeated WDM transmission systems operating at 10 Gb/s. We describe both first- and higher-order bi-directional Raman pumping schemes, pointing out that co-pumping, although critical in terms of noise transfer from pump to WDM signals, can be very effective in extending the maximum system reach. New co-propagating Raman pump lasers, characterized by high power levels and low relative intensity noise, are also proposed to further increase the maximum achievable span loss, avoiding transmission penalties induced by relative intensity noise transfer.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.