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.
Highlights
Photoacoustic tomography (PAT), an imaging modality with high-resolution, optical contrast and deep penetration [1], has potential applications in clinical practices such as breast [2,3,4], dermatologic [5,6,7,8,9], and vascular imaging [10,11,12]
Image resolution and fidelity hinge on the richness of the temporal and spatial frequencies in the detected PA signals
The laser light passes through a 3-port fiber circulator and a fiber coupler (Thorlabs, DC1300LEFA) to illuminate the FPI
Summary
Photoacoustic tomography (PAT), an imaging modality with high-resolution, optical contrast and deep penetration [1], has potential applications in clinical practices such as breast [2,3,4], dermatologic [5,6,7,8,9], and vascular imaging [10,11,12]. Larger bandwidth), and its penetration extends much beyond optical-resolution PA microscopy (i.e., higher sensitivity) Due to their potential broadband and sensitive acoustic detection ability, optical ultrasound sensors including interferometric [17,18,19,20,21,22,23] and non-interferometric sensors [24,25,26] have been designed and applied in PA imaging and other ultrasound applications. For the fiber based FPI, each sensing element requires a high-power, wavelength-tunable, narrow-linewidth and mode-hopping-free continuous wave (CW) laser for interrogation This kind of laser is much more expensive than ordinary single mode laser diodes (LD), making paralleled detection costly. We obtained good-quality PA mesoscopic images of two different phantoms and an ex vivo mouse kidney
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