Kwang-Yong Song

Correlation-based distributed measurement of a dynamic grating spectrum generated in stimulated Brillouin scattering in a polarization-maintaining optical fiber.

We study the principle of correlation-based distributed generation and readout of dynamic grating spectrum generated in stimulated Brillouin scattering in a polarization-maintaining optical fiber. The experimental validation is demonstrated by applying synchronous sinusoidal frequency modulations to two orthogonally polarized laser sources that serve as the Brillouin pump-probe light and readout light of the dynamic grating, respectively. Temperature-induced opposite changes in the Brillouin frequency shift and in the birefringence-determined optical frequency deviation are clearly observed with 1.2 m spatial resolution and a 110 m measurement range.

Enlargement of measurement range in a Brillouin optical correlation domain analysis system using double lock-in amplifiers and a single-sideband modulator

We demonstrate a novel technique to enlarge the measurement range of a correlation-based fiber Brillouin distributed sensing system using double lock-in amplifiers and a single-sideband (SSB) modulator. In our work, the lock-in detection is applied to both a probe and a pump waves at different frequencies to effectively remove the noise induced by the backward reflection of the pump waves, and the SSB modulator is used to purify the probe wave by suppressing the other first-order sideband component. A 300-m measurement range with a 20-cm spatial resolution is achieved successfully without any optical filter

Effects of Intensity Modulation of Light Source on Brillouin Optical Correlation Domain Analysis

The effects of the intensity modulation (IM) of light source on fiber-distributed sensors based on Brillouin optical correlation domain analysis (BOCDA) are analyzed by numerical simulation, and the results are experimentally confirmed. We show that the shape of the Brillouin gain spectrum in the BOCDA system has a particular dependence on the optical spectrum of light source and that it can be controlled and tailored by proper modification of the optical spectrum using an additional IM. In the experiments, we applied several IM waveforms based on the simulation results for confirmation. Additionally, a distributed strain measurement along a 1-km optical fiber with a 30-cm spatial resolution is demonstrated by applying a proper IM scheme, which is the longest range reported using the BOCDA system

Brillouin Optical Correlation Domain Analysis in Linear Configuration

We demonstrate a novel type of Brillouin optical correlation domain analysis system based on linear configuration. The Brillouin pump and the probe waves are propagated in the same direction to be reflected at the end of a fiber under test, and beat lock-in detection is applied for the signal acquisition. In experiments, a 40-m-range distributed strain measurement is demonstrated with 16-cm spatial resolution for the confirmation of the novel scheme.

Brillouin gain-coefficient measurement for bismuth-oxide-based photonic crystal fiber under significant beam reflection at splicing points

We investigate a six-air-hole bismuth-oxide-based photonic crystal fiber (Bi-PCF) in terms of Brillouin characteristics. One huge challenge in measuring the Brillouin properties of the Bi-PCF is the nonnegligible beam reflection at the splicing points, which can be attributed to the mirroring effect caused by different refractive indices of silica and bismuth fibers. To solve the problem we propose a method that is based on the combination of a pump-probe beat lock-in scheme and a normalized gain curve-fitting technique. Using this method, successful characterization of Brillouin properties for a 1.16-m-long Bi-PCF is experimentally demonstrated. With the measured Brillouin gain coefficient and the known chi((3)) nonlinearity parameters, the Kerr nonlinearity figure-of-merit (F(nl-SBS)), including the stimulated Brillouin scattering-caused pump-power limit, is also estimated for the Bi-PCF.

All-optical dynamic grating generation based on Brillouin scattering in polarization maintaining fiber

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.

Distributed fiber strain sensor with 1 kHz sampling rate based on Brillouin optical correlation domain analysis

We report the highest speed distributed sensing of dynamic strain based on stimulated Brillouin scattering in optical fibers. A sampling rate of 1 kHz, more than an order of magnitude higher than the former best result, is achieved by applying a simplified Brillouin optical correlation domain analysis with optimized time gates and an unbalanced Mach-Zehnder delay line. In experiments, we present the measurement of various dynamic strains at the maximum frequency of 200 Hz with 10-cm spatial resolution and 20-m measurement range.

Correlation-based distributed measurement of SBS-generated dynamic grating spectrum in a polarization-maintaining fiber

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.

SBS slow light in optical fibers with 25-GHz-bandwidth

Broadband slow light is demonstrated using stimulated Brillouin scattering in optical fibers based on double Brillouin pump. A 25-GHz bandwidth is achieved, resulting in a variable time delay up to 10.9 ps with 37-ps pulses.

Analysis of Brillouin frequency shift and acoustic waves in a hollow optical fiber

We propose and demonstrate a new method to manipulate the Brillouin frequency shift in silica optical fiber by introducing a silica hollow optical fiber (HOF) waveguide structure. Propagation characteristics of acoustic waves guided along the HOF were theoretically analyzed, and the corresponding Brillouin frequency shifts were measured by a Brillouin optical-correlation domain-analysis system. We experimentally observed that Brillouin frequency shift v(B) monotonically increases as a function of the central air-hole radius, which showed good agreement with the simulation results. We confirmed that a precise control of Brillouin frequency shift can be obtained by controlling the waveguide parameters of the HOF.