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. 2020 Apr 16;11(5):2607-2618.
doi: 10.1364/BOE.391980. eCollection 2020 May 1.

Photothermally tunable Fabry-Pérot fiber interferometer for photoacoustic mesoscopy

Bohua Chen  1 , Yuwen Chen  1 , Cheng Ma  1   2   3
Affiliations

Photothermally tunable Fabry-Pérot fiber interferometer for photoacoustic mesoscopy

Bohua Chen et al. Biomed Opt Express. .

Abstract

An optical fiber based Fabry-Pérot interferometer whose resonant wavelength can be dynamically tuned was designed and realized for photoacoustic mesoscopy. The optical path length (OPL) of the Fabry-Pérot cavity can be modulated by a photothermal heating process, which was achieved by adjusting the power of a 650 nm heating laser. The optical heating process can effectively change the thickness and refractive index of the polymer spacer of the sensor cavity. The robustness of the sensor can be greatly improved by proper packaging. The interferometer was interrogated by a relatively cheap wavelength-fixed 1550 nm laser for broadband and sensitive ultrasound detection, eliminating the requirement for an expensive tunable interrogation laser. The sensing module was then integrated into a photoacoustic mesoscopic imaging system. Two phantom imaging experiments and an ex vivo imaging experiment demonstrated the capability of such a miniature sensor. The interferometer has an acoustic detection bandwidth of up to 30 MHz and a noise equivalent pressure of 40 mPa/Hz1/2 (i.e., 220 Pa over the full detection bandwidth). The new tuning mechanism and the batch-production compatibility of the sensor holds promises for commercialization and parallelized detection.

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Conflict of interest statement

The authors declare that there are no conflicts of interest related to this article.

Figures

Fig. 1.
Fig. 1.
(a) Schematic of the interferometer. (b) Microscopic view of the sensor head. (c) Transmission spectrum of a 200 µm thick spacer sample doped with dark blue metal complex solvent dye. (d) Experimentally measured resonant wavelength versus power of the heating laser shows linear operation.
Fig. 2.
Fig. 2.
(a) Measured and simulated transfer function of a representative FPI, inset shows a zoom-in view around the resonant wavelength. (b) Fast Fourier Transform (FFT) of the temporal response obtained by a FPI (orange) and a commercial PVDF hydrophone (blue). The incident acoustic pulses were generated by a 50 MHz water immersion transducer. (c) COMSOL simulation and (d) measured spectral response of the FP sensor under different acoustic incident angle.
Fig. 3.
Fig. 3.
Schematic of the imaging system. OSA: Optical spectrum analyzer. PD: Photo detector. AC: Alternate current. DC: Direct current. DAQ: Data acquisition card. PC: Personal computer.
Fig. 4.
Fig. 4.
(a) MIP images of the reconstructed phantom made of human hairs and horse manes. Projections in the x-y, y-z, and x-z planes are provided. (b) Photograph of the phantom in (a). (c) MIP images of the reconstructed leaf vein phantom. (d) Photograph of the leaf vein phantom.
Fig. 5.
Fig. 5.
MIP images of an ex vivo mouse kidney shown in x-y, y-z, and x-z planes.
See this image and copyright information in PMC

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