Brillouin Dynamic Grating Research Articles

Distributed discrimination of strain and temperature based on Brillouin dynamic grating in an optical fiber

This paper reviews distributed discrimination of strain and temperature by use of an optical fiber based on fiber optic nerve systems. The preliminary method based on multiple resonance peaks of the Brillouin gain spectrum in a specially-designed fiber is firstly introduced. The complete discrimination of strain and temperature based on the Brillouin dynamic grating in a polarization maintaining fiber is extensively presented. The basic principle and two experimental schemes of distributed discrimination based on fiber optic nerve systems are demonstrated. The performance of the high discriminative accuracy (0.1 °C–0.3°C and 5 μɛ–12μɛ) and high spatial resolution (∼10 cm) with the effective measurement points of about 50 for a standard system configuration or about 1000 for a modified one will be highly expected in real industry applications.

Fiber distributed Brillouin sensing with optical correlation domain techniques

Fiber distributed Brillouin sensing is discussed, focusing mainly on optical correlation domain techniques. By synthesizing a delta-function like optical coherence function between pump and probe lightwave traveling along an optical fiber in opposite directions, which is realized by modulating laser source frequency by an appropriate waveform, stimulated Brillouin scattering can be selectively excited at one specific position along the fiber. The selected position can easily be swept by changing the modulation frequency, so the distributed measurement can be achieved. In the system, Brillouin Optical Correlation Domain Analysis (BOCDA), the position to be measured can be selected randomly along the fiber, which is a special feature of the system. Spatial resolution of 1.6mm and measurement speed of 1000samples/s have already been demonstrated. With a similar way, distribution of spontaneous Brillouin scattering can also be measured along the fiber. Spatial resolution of 10mm and measurement speed of 50samples/s have already been demonstrated in the system, Brillouin Optical Correlation Domain Reflectometry (BOCDR). Brillouin dynamic grating (BDG), which is acoustic-wave generated refractive-index grating caused in the stimulated Brillouin scattering process, was found to cause a Bragg reflection for the orthogonally polarized lightwave in an polarization maintaining fiber. By measuring both the BDG and the Brillouin scattering, discriminative distributed measurement of strain and temperature has been realized by the BOCDA scheme with a 10mm spatial resolution.

Long-Range and High-Spatial-Resolution Distributed Birefringence Measurement of a Polarization-Maintaining Fiber Based on Brillouin Dynamic Grating

We report a long-range and high-spatial-resolution distributed measurement of the birefringence of a polarization-maintaining fiber based on Brillouin dynamic grating (BDG) through optimizing the pump and probe scheme in the time-domain. The optimal scheme includes a CW pump1, a long pump2 pulse, and a short probe pulse, where the long pump2 pulse can effectively excite a BDG with a relatively low power to avoid other nonlinear effects in a long-length fiber, and the short probe pulse is used to improve the spatial resolution. The numerical simulations verify that with this scheme the spatial resolution is determined by the duration of the probe pulse, while the BDG reflection spectrum width increases with shorting the duration of the probe pulse. In experiment, a measurement of a 500-m Panda polarization-maintaining fiber with a 20-cm resolution is realized by using a 20-ns pump2 pulse and a 2-ns probe pulse. The results clearly show the 49-cm spatial period of the birefringence variation caused by the uneven stress as winding the fiber around a spool. Besides, longer spatial periods of the birefringence variation are also observed, which could be caused by the residual stress during the fiber drawing and coating processes or the nonuniformity of fiber preform.

Applications of the Dynamic Brillouin Gratings to Ultrawideband Communications

Unconventional signal processing, such as all-optical signal time differentiation and true time reversal, can be realized on sub-nanosecond pulses, by exploiting dynamic Brillouin gratings in optical fibers. The performance of such optical processors, to generate ultrawideband (including high-order) Gaussian pulses and to implement an ultrawideband time reversal mirror, is numerically assessed.

All-optical generation of Brillouin dynamic grating based on multiple acoustic modes in a single-mode dispersion-shifted fiber

We demonstrate an all-optical generation of Brillouin dynamic grating (BDG) in a single-mode dispersion-shifted fiber (DSF). The feature of multiple-peak Brillouin gain spectrum (BGS) owing to the existence of the multiple acoustic modes in the single-mode DSF is utilized. Two inharmonic lock-in detections are newly introduced to characterize the BGS and the frequency-maintained or frequency-shifted BDG reflection. The frequency-shifted property of the BDG in the DSF with hundreds of MHz can find great potential applications in optical fiber sensing or all-optical signal processing.

Chirped Brillouin dynamic gratings for storing and compressing light

We demonstrate theoretically that chirped dynamic gratings can be created in optical fibers through stimulated Brillouin scattering with frequency-chirped "signal" and "write" pulses. When the grating is interrogated with a third pulse of the opposite chirp, a compressed signal pulse is retrieved. This provides a method to regenerate stored pulses and enhance signal levels for communications applications.

All-optical signal processing using dynamic Brillouin gratings

The manipulation of dynamic Brillouin gratings in optical fibers is demonstrated to be an extremely flexible technique to achieve, with a single experimental setup, several all-optical signal processing functions. In particular, all-optical time differentiation, time integration and true time reversal are theoretically predicted, and then numerically and experimentally demonstrated. The technique can be exploited to process both photonic and ultra-wide band microwave signals, so enabling many applications in photonics and in radio science.

A method for refractive index measurement of a liquid in a suspended core fiber using Brillouin dynamic grating

A novel method is proposed to measure the refractive index change of a liquid around a fiber using a dynamic grating generated by stimulated Brillouin scattering. Two pump waves are used to generate a dynamic grating along a polarization-maintaining fiber. The grating is then read by a probe wave. It is shown numerically that the frequency deviation of the pump and probe waves depends on the refractive index of liquid around the fiber. We consider three- and four-hole suspended core fibers, in which one or two holes are filled with liquid, and investigate the change in the birefringence and the frequency deviation of the Brillouin dynamic grating due to the variation of the refractive index of liquid. The effects of fiber parameters on the sensitivity of frequency deviation as a function of liquid refractive index are discussed. We predict that a resolution of can be obtained using this method.

Observation of Brillouin dynamic grating in a photonic chip

We report demonstration of a Brillouin dynamic grating (BDG) in a photonic chip. A BDG was characterized in a 6.5 cm long chalcogenide (As(2)S(3)) rib waveguide using CW pumps in x polarization and read using a CW probe in y polarization. The measured reflectivity, on-off ratio, and 3 dB bandwidth (f(3 dB)) for the BDG were 0.4%, ~28 dB, and ~6 GHz, respectively.

High contrast, low noise selection and amplification of an individual optical frequency comb line

We present a frequency-selective amplifier for optical frequency combs based on stimulated Brillouin scattering and the effect of a Brillouin dynamic grating. A user defined individual frequency comb line is amplified while the other comb lines are efficiently suppressed, rendering a frequency-stable clean-up oscillator unnecessary. A measured signal to noise ratio of 89 dBc/Hz proves the suitability of the method for phase coherent measurements. The overall noise figure is 6 dB.

Low-noise delays from dynamic Brillouin gratings based on perfect Golomb coding of pump waves

A method for long variable all-optical delay is proposed and simulated, based on reflections from localized and stationary dynamic Brillouin gratings (DBGs). Inspired by radar methods, the DBGs are inscribed by two pumps that are comodulated by perfect Golomb codes, which reduce the off-peak reflectivity. Compared with random bit sequence coding, Golomb codes improve the optical signal-to-noise ratio (OSNR) of delayed waveforms by an order of magnitude. Simulations suggest a delay of 5 Gb/s data by 9ns, or 45bit durations, with an OSNR of 13dB.

High-sensitivity optical time-domain reflectometry based on Brillouin dynamic gratings in polarization maintaining fibers

A high-sensitivity optical time-domain reflectometry based on Brillouin dynamic grating (BDG) is proposed and experimentally demonstrated in polarization-maintaining fibers, where a single-end access to a fiber under test is applied with co-propagation of pump and probe pulses for the operation of BDG. Distributed measurements of the BDG spectra are presented with 80 cm spatial resolution in 935 m range, showing strain and temperature sensitivities of 1.37 MHz/με and -57.48 MHz/°C, respectively.

All-optical Brillouin dynamic grating generation in few-mode optical fiber

We report, for the first time (to our knowledge), generation of Brillouin dynamic gratings (BDGs) in few-mode optical fibers. A moving acoustic grating is generated by stimulated Brillouin scattering using a writing beam in one fiber mode, which is used to reflect a reading beam at a different wavelength in another fiber mode. With single-end pumping, a BDG with a tunable reflectance of up to 0.1% is demonstrated in a 15km specially designed two-mode optical fiber.

Reflection spectrum analysis of stimulated Brillouin scattering dynamic grating

The reflection spectrum of Brillouin dynamic grating is calculated by a numerical method called piecewise approach. A sawtooth frequency modulation is proposed to be used in Brillouin dynamic grating localization along a fiber. It is shown that the reflection spectrum has a flat band where its linewidth depends on the amplitude of frequency modulation. The maximum reflection of dynamic grating can be adjusted by the amplitude of modulation and the power of pump waves, which generates the grating. This grating can be useful as a fiber laser cavity mirror.

Effects of induced birefringence on Brillouin dynamic gratings in single-mode optical fibers

The effects of linear or circular birefringence on the operation of Brillouin dynamic grating are experimentally investigated where the birefringence is induced by bending or twisting a single-mode optical fiber, respectively. Experimental results show that the reflection spectrum of the dynamic grating in a 5 m fiber is split by bend-induced linear birefringence with the separation frequency dependent on the bending diameter, matching well with the theoretical model. Meanwhile, the spectrum is almost immune to circular birefringence induced by twist with a rate of up to 24 turns/m.

Distributed fiber sensing technology: Currents and challenge

In this paper, distributed fiber sensing technologies are explained, showing principles and applications. Time domain technologies have been developed, at first, as ways to analyze the distributed information along the fiber. For example, in distributed strain measurement through the nature of scattering, basic systems showed limitation in spatial resolution of about 1m. However, novel phenomena and new systems have recently been proposed, and the resolution has been much improved. Optical correlation domain techniques, in which interference of continuous lightwaves is manipulated to obtain the distributed information, have already realized superior performances, such as 1.6 mm spatial resolution and 1 kHz sampling rate, in the fiber Brillouin distributed strain sensing. Applications, such as aircraft health monitoring, have also been demonstrated. Recently, Brillouin dynamic grating in a polarization maintaining fiber has been studied, and created various novel applications, including simultaneous distributed measurement of strain and temperature. With the correlation domain technique, other schemes, such as multiplexing systems for long-length FBG distributed sensors, have also been developed.

Tunable and reconfigurable multi-tap microwave photonic filter based on dynamic Brillouin gratings in fibers

We propose and experimentally demonstrate new architectures to realize multi-tap microwave photonic filters, based on the generation of a single or multiple dynamic Brillouin gratings in polarization maintaining fibers. The spectral range and selectivity of the proposed periodic filters is extensively tunable, simply by reconfiguring the positions and the number of dynamic gratings along the fiber respectively. In this paper, we present a complete analysis of three different configurations comprising a microwave photonic filter implementation: a simple notch-type Mach-Zehnder approach with a single movable dynamic grating, a multi-tap performance based on multiple dynamic gratings and finally a stationary grating configuration based on the phase modulation of two counter-propagating optical waves by a common pseudo-random bit sequence (PRBS).

Dynamic Brillouin gratings permanently sustained by chaotic lasers

A method to induce only one permanent and localized dynamic Brillouin grating in polarization maintaining optical fibers is introduced. The generation of the grating exploits the thumbtack correlation of the chaotic laser signals. A numerical calculation, corroborated by a theoretical analysis, is performed and the grating properties, length, and reflectance determined.

布里渊动态光纤光栅及其在分布式传感中的应用

布里渊动态光纤光栅及其在分布式传感中的应用

Sub-Centimeter Spatial Resolution in Distributed Fiber Sensing Based on Dynamic Brillouin Grating in Optical Fibers

Optical fiber sensors based on stimulated Brillouin scattering in optical fibers have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements. The fiber is used as sensing element and a value for temperature and/or strain can be obtained from any point along the fiber. While the spatial resolution of classical configurations is practically limited to 1 meter by the phonon lifetime, novel approaches have been demonstrated these past years that can overcome this limit. In this paper, this could be achieved by two physical processes: prior activation of a steady acoustic wave through the classical Brillouin interaction between two Brillouin pumps, and interrogation by Bragg reflection on the acoustic wave using a distinct ultra-short pulse in a highly birefringent fiber. We could achieve a spatial resolution below one centimeter, while preserving the full accuracy on the determination of temperature and strain.