Brillouin optical time domain analysis (BOTDA) enhanced by the tailored compensation for the propagation loss of a pump pulse is experimentally demonstrated for long-distance and high-resolution distributed sensing. Distributed Brillouin amplification (DBA) of the pump pulse is applied in addition to an ordinary BOTDA configuration, where the frequency modulation with time-dependent amplitude variation is introduced to the DBA pump for tailored compensation for the propagation loss. In experiments, the distribution map of the Brillouin frequency along a 51.2 km test fiber is measured with a spatial resolution of 50 cm and a measurement error (σ) of less than 1 MHz.
Discriminative measurement of strain and temperature distribution is experimentally demonstrated by optical time-domain reflectometry of Brillouin dynamic grating (BDG-OTDR) in an elliptical core two-mode fiber (e-core TMF). The acoustic waves generated by the amplified spontaneous Brillouin scattering of LP01 mode in x-polarization are used to reflect the LP11 mode in x- and y-polarizations. Distribution maps of intermodal birefringence between the LP01 and LP11 modes with two different polarizations are measured to separate strain and temperature induced spectral shift of the BDG in a 95 m ecore TMF with 2.0 m spatial resolution. The strain and temperature sensitivities are measured to be ‒0.082 MHz/με and 6.8 MHz/°C for the pair of LP01y-LP11x modes, and ‒0.095 MHz/με and 3.9 MHz/°C for the pair of LP01 x-LP11x modes, respectively.
A Brillouin optical correlation domain analysis (BOCDA) system using time-domain data processing for concurrently interrogating a plurality of sensing positions is proposed, where the time-domain data processing combined with differential measurement effectively enhances the measurement range and measurement time as much as the spatial resolution of the BOCDA system. In the experiment, the distribution of the Brillouin gain spectra (BGS) along a 10.15 km test fiber is successfully obtained with a spatial resolution less than 5 cm by concurrently interrogating 980 correlation peaks.
Huge enlargement of the sensing range of Brillouin optical correlation domain analysis (BOCDA) is achieved by simultaneously applying double modulation and optical time gate on the basis of differential measurement scheme. The BOCDA system with a spatial resolution less than 1 cm and a sensing range over 10 km is experimentally demonstrated, which corresponds to distributed measurement with more than 1 million effective sensing points.
We measured the Brillouin frequency in fiber taper and identified the shift of the Brillouin frequency when strain and temperature changed. As taper diameter decreases, strain coefficient for Brillouin frequency decreases down to 0.0488 MHz/με while temperature coefficient is maintained.
Temperature dependence of birefringence in various types of polarization-maintaining fibers (PMF’s) is rigorously investigated by the spectral analysis of Brillouin dynamic grating (BDG). PANDA, Bowtie, and PM photonic crystal fibers are tested in the temperature range of -30 to 150 ºC, where nonlinear temperature dependence is quantified for each fiber to an accuracy of ±7.6 × 10-8. It is observed that the amount of deviation from the linearity varies according to the structural parameters of the PMF’s and the existence of acrylate jacket. Experimental confirmation of the validity of the BDG-based birefringence measurement is also presented in comparison to the periodic lateral force method.
We demonstrate a simplified Brillouin optical-time domain analysis system based on direct current modulation of a laser diode with an extended measurement range and an enhanced spatial resolution. Slow and periodic frequency dithering is additionally applied to the laser diode to suppress the noise originated from coherent Rayleigh scattering. The distribution of Brillouin gain spectra along a 25 km fiber is successfully measured with a 1 m spatial resolution and an accuracy of σ = 0.78 MHz, confirming its high practicality as a cost-effective solution.
Optical time-domain measurement and characterization of intermodal beat length in an elliptic-core two-mode fiber (ecore TMF) is demonstrated using Brillouin dynamic grating. A mode-selective coupler is used for selective launch and retrieval of different modes, and the operations of BDG for four different pairs of pump-probe (LP01 x-LP11 x, LP01x-LP11y, LP01y-LP11x, LP01y-LP11 y) are observed, representing a fine structure of modal birefringence in the e-core TMF. Distributed measurement of the BDG spectrum is performed for each pair of pump-probe with 1.5 m spatial resolution mapping the difference of the effective refractive indexes of spatial and polarization modes along a 75 m TMF.
We demonstrate a high-performance single-ended correlation-domain Brillouin sensor based on a phase modulation of Brillouin pump and a differential measurement scheme. Large DC noise induced by direct reflection of Brillouin pump was successfully removed by the phase modulation-based differential measurement as well as additional 4-fold enhancement in the spatial resolution. By applying an intentional loss to the end of a sensing fiber one of two correlation peaks within the fiber is suppressed, leading to double enlargement of the measurement range compared to former in-line reflector based systems. In the experimental confirmation a distributed strain measurement with a range of 100 m and a spatial resolution of 5 cm is presented.
We newly propose and experimentally demonstrate a differential lock-in detection scheme for the enhancement of
Brillouin optical correlation domain analysis (BOCDA), where additional phase modulation is applied to the Brillouin
pump wave and the on-off control on which is used for data acquisition. The theoretical model and the experimental
results show that at least three-fold improvement is obtained in the spatial resolution of the distributed measurements and
the Brillouin gain spectrum (BGS) with much narrower 3dB bandwidth than that of conventional BOCDA systems is
acquired by the differential lock-in detection.
KEYWORDS: Reflectometry, Signal processing, Polarization maintaining fibers, Polarization, Spatial resolution, Data acquisition, Optical amplifiers, Fiber Bragg gratings, Structured optical fibers, Signal to noise ratio
We newly propose and experimentally demonstrate high-sensitivity optical time-domain reflectometry based on
Brillouin dynamic grating in polarization maintaining fiber. Distributed measurements with strain sensitivity as high as
~ 1 MHz/με is demonstrated in a 110 m fiber under test with 0.8 m spatial resolution. The operation principle with the
condition for proper measurement of the grating spectrum and the advantageous features such as low operating power,
high signal to noise ratio, and simple data-acquisition process are explained in comparison with ordinary Brillouin
optical time-domain reflectometry, which is verified by the experimental results.
A novel kind of high repetition-rate distributed Brillouin sensor is proposed and
experimentally demonstrated based on optical correlation-domain analysis with differential
frequency modulation, where the optical frequencies of the pump and the probe waves are
modulated at slightly different RF frequencies so that the temporal position of the
measurement is continuously and repeatedly swept along a fiber under test. A distribution
map of Brillouin frequency variation along a 100 m optical fiber is acquired at a repetition
rate of 20 Hz with an accuracy of ± 2.5 MHz and a spatial resolution of about 80 cm.
A novel kind of Brillouin optical time-domain sensor based on direct modulation of a laser
diode (LD) is demonstrated which is free from the use of any microwave device. The
Brillouin pump and the probe waves are alternately generated by the LD modulation, and an
optical time-domain analysis adopted for distributed measurement. Maps of Brillouin
frequency shift are obtained with a spatial resolution of 2 m and an accuracy of ±2 MHz in a
2 km optical fiber.
A novel kind of all-optical dynamic grating with the reflectance and the center wavelength controlled by another optical
wave can be realized based on Brillouin scattering in polarization-maintaining optical fibers. This grating, called
Brillouin dynamic grating (BDG), has proved to be useful based on its unique characteristics in several applications such
as high performance distributed sensors and optically-tunable delay lines.
We propose and experimentally demonstrate the highest-resolution BOTDA system ever
reported using Brillouin dynamic grating in a polarization-maintaining fiber (PMF). Acoustic
waves containing the information of local Brillouin frequency are generated by a long pump
pulse in one polarization, and read out by a short probe pulse in the orthogonal polarization at
a clearly distinct optical frequency from the pump. In the experiment, a distributed strain
measurement with 1 cm spatial resolution is performed over a 20 m fiber.
We demonstrate a novel kind of tunable optical delays based on dynamic grating generated
by Brillouin scattering in an optical fiber. An axial strain gradient is applied to a 15 m section
of a polarization-maintaining fiber, and the Brillouin reflection grating is generated positionselectively
by controlling the optical frequencies of Brillouin pump waves. Tunable time
delays of up to 132 ns are achieved with an 82 ns Gaussian pulse.
We report a novel kind of all-optical dynamic grating based on Brillouin scattering in
polarization maintaining fiber (PMF). A moving acoustic grating is generated by stimulated
Brillouin scattering between optical waves in one polarization, and used to reflect
orthogonally polarized waves at different wavelength. A 3-dB bandwidth of ~ 100 MHz is
observed with the tunable reflectivity of up to 2% in a 30 m PMF.
The distribution of temperature-induced changes in Brillouin frequency shift and that of birefringence-determined
frequency deviation in the spectrum of SBS-generated dynamic grating in a PMF have been measured with 1.2-meter
spatial resolution and 110-meter measurement range. Synchronously controlled sinusoidal frequency-modulations are
applied into two laser sources that are used for pump (probe) light and readout light, respectively, enabling distributed
generation and detection of the dynamic grating.
We demonstrate distributed measurement of dynamic strain with 1 kHz sampling rate, the highest speed ever reported in
Brillouin-based fiber sensors, using the simplified Brillouin optical correlation domain analysis system. Pump and probe
waves are generated by direct current modulation of a laser diode applying a pre-compensated rectangular waveform at
100 kHz, and an unbalanced Mach-Zehnder delay line is introduced to the probe wave for the suppression of noise in
high speed lock-in detection. Brillouin gain spectrum of single position is acquired at the sampling rate of 1 kHz with
position-selectivity, and several kinds of strain variations up to 200 Hz are successfully measured with 10 cm spatial
resolution and 20 m measurement range.
Effects of intensity modulation of light source on fiber distributed sensors based on Brillouin optical correlation domain
analysis (BOCDA) are analyzed by numerical simulation, and the results are compared with reported experimental
results. We show that the shape of the Brillouin gain spectrum in the BOCDA system has a particular dependence on the
optical spectrum of the light source, and that it can be controlled and tailored by a proper modification of the optical
spectrum using the intensity modulation.
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.