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Photoacoustics Volume 32, August 2023, 100527

Michael Nagli, Ron Moisseev, Nathan Suleymanov, Eitan Kaminski, Yoav Hazan, Gil Gelbert, Ilya Goykhman, Amir Rosenthal Abstract: Silicon photonics is an emerging platform for acoustic sensing, offering exceptional miniaturization and sensitivity. While efforts have focused on silicon-based resonators, silicon nitride resonators can potentially achieve higher Q-factors, further enhancing sensitivity. In this work, a 30 µm silicon nitride microring resonator was fabricated and coated with an elastomer to optimize acoustic sensitivity and signal fidelity. The resonator was characterized acoustically, and its capability for optoacoustic tomography was demonstrated. An acoustic bandwidth of 120 MHz and a noise-equivalent pressure of ∼ 7 mPa/Hz^1/2 were demonstrated. The spatially dependent impulse response agreed with theoretical predictions, and spurious acoustic signals, such as reverberations and surface acoustic waves, had a marginal impact. High image fidelity optoacoustic tomography of a 20 µm knot was achieved, confirming the detector’s imaging capabilities. The results show that silicon nitride offers low signal distortion and high-resolution optoacoustic imaging, proving its versatility for acoustic imaging applications. Fig. 3D optoacoustic reconstruction of a surgical suture. (a) 2D maximum amplitude projection image of the suture. (b) Photograph of the suture showing the similarity between the reconstruction and the imaged object. (a) and (b) are the same scale. (c) 2D slice along the white dashed line shown in (a); shows the cross-section of the suture and demonstrates the lateral and axial resolutions. Read more –Photoacoustics Volume 32, August 2023, 100527 Michael Nagli, Ron Moisseev, Nathan Suleymanov, Eitan Kaminski, Yoav Hazan, Gil Gelbert, Ilya Goykhman, Amir Rosenthal

© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement© 2019 Optics Express, OSA publishing.

Abstract
Ultrasound detection via optical resonators can achieve high levels of miniaturization and sensitivity as compared to piezoelectric detectors, but its scale-up from a single detector to an array is highly challenging. While the use of wideband sources may enable parallel interrogation of multiple resonators, it comes at the cost of reduction in the optical power, and ultimately in sensitivity, per channel. In this work we have developed a new interferometric approach to overcome this signal loss by using high-power bursts that are synchronized with the time window in which ultrasound detection is performed. Each burst is composed of a train of low-noise optical pulses which are sufficiently wideband to interrogate an array of resonators with non-overlapping spectra. We demonstrate our method, termed burst-mode pulse interferometry, for interrogating a single resonator in which the optical power was reduced to emulate the power loss per channel that occurs in parallel interrogation of 20 to 200 resonators. The use of bursts has led to up 25-fold improvement in sensitivity without affecting the shape of the acoustic signals, potentially enabling parallel low-noise interrogation of resonator arrays with a single source.

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Fig. The optical signal at the CM (blue) and BM (red) of the CRF output in the transition from the unlocked stated, in which the CRF blocks the optical pulses, to the locked state in which the CRF transmits the optical pulses and blocks only the ASE. Each of the spikes in the locked BM channel represents a burst with a width of 10 µs, shown in detail in Fig. 2(d), where the burst repletion rate was 8 kHz.

Oleg Volodarsky, Yoav Hazan, Michael Nagli, and Amir Rosenthal.
Optics Express, Volume 30, Issue 6, Pages 8959-8973
https://opg.optica.org/oe/abstract.cfm?URI=oe-30-6-8959

 

source: © 2018 Optical Society of America

Coherence-restored pulse interferometry (CRPI) is a recently developed method for optical detection of ultrasound that achieves shot-noise-limited sensitivity and high dynamic range. In principle, the wideband source employed in CRPI may enable the interrogation of multiple detectors by using wavelength multiplexing. However, the noise-reduction scheme in CRPI has not been shown to be compatible with wideband operation. In this work, we introduce a new scheme for CRPI that relies on a free-space Fabry-Pérot filter for noise reduction and a pulse stretcher for reducing nonlinear effects. Using our scheme, we demonstrate that shot-noise-limited detection may be achieved for a spectral band of 80 nm and powers of up to 5 mW. [Read More…]

Fig. 1 A schematic of CRPI. EDFA is erbium-doped fiber amplifier; PZ is piezoelectric fiber stretcher; CRF is coherence-restoring filter; and π-FBG is π-phase-shifted fiber Bragg grating. The pulse train from the laser is filtered to a bandwidth of 0.4 nm, amplified, and further filtered by the CRF. Shifts of resonance of the π-FBG are measured by optical demodulator, implemented by a Mach-Zehnder interferometer locked to quadrature.

Oleg Volodarsky, Yoav Hazan, and Amir Rosenthal, “Ultrasound detection via low-noise pulse interferometry using a free-space Fabry-Pérot,” Opt. Express 26, 22405-22418 (2018)

source: © 2018 Light: Science & Applications

Originally developed for diagnostic ultrasound imaging, piezoelectric transducers are the most widespread technology employed in optoacoustic (photoacoustic) signal detection. However, the detection requirements of optoacoustic sensing and imaging differ from those of conventional ultrasonography and lead to specifications not sufficiently addressed by piezoelectric detectors. Consequently, interest has shifted to utilizing entirely optical methods for measuring optoacoustic waves. All-optical sound detectors yield a higher signal-to-noise ratio per unit area than piezoelectric detectors and feature wide detection bandwidths that may be more appropriate for optoacoustic applications, enabling several biomedical or industrial applications. Additionally, optical sensing of sound is less sensitive to electromagnetic noise, making it appropriate for a greater spectrum of environments. In this review, we categorize different methods of optical ultrasound detection and discuss key technology trends geared towards the development of all-optical optoacoustic systems. We also review application areas that are enabled by all-optical sound detectors, including interventional imaging, non-contact measurements, magnetoacoustics, and non-destructive testing.[Read More…]

Fig. 1 a Intensity-sensitive detection of refractive index. b Single-beam deflectometry. c Phase-sensitive ultrasound detection with a Schlieren beam. d Phase-sensitive ultrasound detection with a decoupled optoacoustic source. AL acoustic lens, CMOS CMOS camera, FP Fourier plane, L lens, LA laser, P prism, PD photodiode, QPD quadrant photodiode, SB Schlieren beam, SF spatial filter, US ultrasound

Georg Wissmeyer, Miguel A. Pleitez, Amir Rosenthal & Vasilis Ntziachristos ,”Looking at sound: optoacoustics with all-optical ultrasound detection”, in Light: Science & Applications volume 7, Article number: 53 (2018)

source: © 2018 Optical Society of America

In the optical detection of ultrasound, resonators with high Q-factors are often used to maximize sensitivity. However, increasing the Q-factor of a resonator may reduce the linear range of the interrogation scheme, making it more susceptible to strong external perturbations and incapable of measuring strong acoustic signals. In this Letter, a passive-demodulation scheme for pulse interferometry was developed for high dynamic-range measurements. The passive scheme was based on an unbalanced Mach–Zehnder interferometer and a 90° optical hybrid, which was implemented in a dual-polarization all-fiber setup. We demonstrated the passive scheme for detecting ultrasound bursts with pressure levels for which the response of conventional, active interferometric techniques became nonlinear. [Read More…]

Fig. 1. (a) Schematic drawing of the system used for pulse interferometry. (b) Active-demodulation scheme consists of an unbalanced Mach–Zehnder interferometer (MZI) stabilized to quadrature using a wideband feedback circuit. PZ is piezoelectric fiber stretcher, and FC is 50/50 fused fiber coupler. (c) Passive-demodulation scheme consists of a dual-polarization unbalanced MZI, implementing a 90° optical hybrid. PBS is polarization beam splitter.

Yoav Hazan and Amir Rosenthal, “Passive-demodulation pulse interferometry for ultrasound detection with a high dynamic range,” Opt. Lett. 43, 1039-1042 (2018)