Brillouin spectroscopy of a hybrid silicon-chalcogenide waveguide with geometrical variations

Computed tomography for distributed Brillouin sensing

A method to reconstruct the spatial distribution of Brillouin gain spectrum from its Radon transform is proposed, which is a type of optical computed tomography. To verify the concept, an experiment was performed on distributed Brillouin fiber sensing, which succeeded in detecting a 55-cm strain section along a 10-m fiber. The experimental system to obtain the Radon transform of the Brillouin gain spectrum is based on a Brillouin optical correlation-domain analysis with a linear frequency-modulated continuous-wave laser. Combining distributed fiber sensing with computed tomography, this method can realize a high signal-to-noise ratio Brillouin sensing.

Phase-coded Brillouin optical correlation domain analysis with 2-mm resolution based on phase-shift keying

We report a phase-coded Brillouin optical correlation-domain analysis (BOCDA) based on phase-shift keying (PSK), in which the pseudo-random binary sequence (PRBS) phase coding is realized using a Mach-Zehnder modulator (MZM). Unlike the conventional phase-coded BOCDA using a phase modulator, which suffers from the non-rectangular transition in the encoded phase, the PSK can realize perfect phase switches between 0 and π with zero-width edges. It is not sensitive to the bandwidth of the modulator and the power of the radio-frequency modulation signal. Numerical simulations and experimental results prove that it can effectively suppress the Brillouin amplification in the off-peak positions. In experiment, a 2-mm spatial resolution sensing is realized using only a 20-GHz bandwidth MZM.

High Resolution Brillouin Sensing of Micro-Scale Structures

Brillouin distributed measurement techniques have been extensively developed for structural health monitoring using fibre optic nerve systems. The recent advancement in the spatial resolution capabilities of correlation-based Brillouin distributed technique have reached the sub-mm regime, making this approach a suitable candidate for monitoring and characterizing integrated photonic devices. The small dimension associated with the short length of these devices—on the order of the cm- and mm-scale—requires high sensitivity detection techniques and sub-mm spatial resolution. In this paper, we provide an overview of the different Brillouin sensing techniques in various micro-scale structures such as photonic crystal fibres, microfibres, and on-chip waveguides. We show how Brillouin sensing is capable of detecting fine transverse geometrical features with the sensitivity of a few nm and also extremely small longitudinal features on the order of a few hundreds of μ m . We focus on the technique of Brillouin optical correlation domain analysis (BOCDA), which enables such high spatial resolution for mapping the opto-acoustic responses of micro-scale waveguides.