Multiplexing of fiber-optic ultrasound sensors via swept frequency interferometry

Abstract

The use of fiber-optic sensors for ultrasound (US) detection has many advantages over conventional piezoelectric detectors. However, the issue of multiplexing remains a major challenge. Here, a novel approach for multiplexing fiber-optic based US sensors using swept frequency interferometry is introduced. Light from a coherent swept source propagates in an all-fiber interferometric network made of a reference arm and a parallel connection of N sensing arms. Each sensing arm comprises a short polyimide coated sensing section (~4cm), which is exposed to the US excitation, preceded by a delay of different length. When the instantaneous frequency of the laser is linearly swept, the receiver output contains N harmonic beat components which correspond to the various optical paths. Exposing the sensing sections to US excitation introduces phase modulation of the harmonic components. The US-induced signals can be separated in the frequency domain and be extracted from their carriers by common demodulation techniques. The method was demonstrated by multiplexing 4 sensing fibers and detecting microsecond US pulses which were generated by a 2.25MHz ultrasound transducer. The pulses were successfully measured by all sensing fibers without noticeable cross-talk.

Looking at sound: optoacoustics with all-optical ultrasound detection

“…Advances in parallelized all-optical detection have been recently demonstrated, in particular in the fabrication and simultaneous interrogation of interferometric detector arrays 89 , 91 , 134 – 136 . However, piezoelectric detector arrays remain the key technology for real-time optoacoustic imaging in most applications.…”

“…Generally, if each sensor operates at a different wavelength, the same number of lasers as sensors is needed to achieve simultaneous read-out. This need for hardware scale-up can be mitigated by tuning all read-out interferometers to the same wavelength as the laser 88 or by using frequency-modulation schemes that rely on the sinusoidal spectrum of the interferometers 89 – 91 .…”

“…A major challenge for optical ultrasound sensors in optoacoustic tomography remains the parallelized read-out of multiple sensors without duplicating the read-out system. Solutions to this problem may be possible using fiber-based MZIs 59 , 89 . Moreover, the broad bandwidth achieved by optical sound detection makes optical sound detectors a ubiquitous technology for different implementations of acoustic-resolution optoacoustic imaging, spanning from optoacoustic microscopy to optoacoustic macroscopy applications 1 .…”

Error Analysis in Determination of Density and Temperature of Saline Solution Using Fiber Optic Photoacoustic Transducer Coated with MoS2-PDMS Composite

“…Nonetheless, it can be concluded from those previously reported works [14,15,17,18] that at present piezoelectric transducers (PZTs) are employed to generate ultrasound waves for density detection due to much higher signal-to-noise at a comparable bandwidth. Despite their excellent attributes, these sensors also suffer from several inherent disadvantages, such as electromagnetic interference (EMI) caused by electrical contacts, detection sensitivity restricted by the sensing element area and larger size [19]. In particular, fabrication of broadband electrical transducers with millimeter-scale lateral dimensions and integration into compact devices with meter-scale longitudinal dimensions can be challenging and expensive [20].…”

Fiber Segment Interferometry for Dynamic Strain Measurements

“…Dynamic strain measurement applications feasible with the current implementation include vibration-based condition monitoring [8], [9], cyclic load estimation [10], rotor imbalance detection [11] and the monitoring of transient strain events, such as quench detection in superconducting magnets [12] or impact detection [13], [14]. Also applications in fiber-optic ultrasound detection using integrating long-gauge length sensors [15], [16] could be envisaged.…”