Photothermally tunable Fabry-Pérot fiber interferometer for photoacoustic mesoscopy

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/Hz 1/2 (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.

Ultrasonic signal detection based on Fabry–Perot cavity sensor

“…In addition, a coating fixture was designed to coat the end surface of the double-clad fiber with a high-reflection film by thermal evaporation. This helps to increase the adhesion of the F–P cavity on the end face of the fiber and increases the number of round-trips of the light in the cavity, which, once again, results in a higher Q factor and a higher cavity transfer function at the periodic damage [ 16 ]. The incident acoustic wave modulates the optical thickness of the F–P cavity, produces an optical phase shift between the optical fields reflected from both sides of the F–P cavity, and produces corresponding reflection intensity modulation.…”

Adaptive optics enhanced all-optical photoacoustic tomography

“…Utilizing active wavefront shaping devices with more active elements such as spatial light modulators (SLMs) could allow to correct for higher order aberrations and thus to further improve the sensitivity of the FPI. Eventually, future gains in overall sensitivity will likely also require advanced manufacturing techniques that can actively alter the cavity structure locally [17,18] and/or can ensure high thermal stability of the FPI cavity. Finally, we note that our work also indirectly explores the possibilities of wavefront shaping.…”

A Review of Endogenous and Exogenous Contrast Agents Used in Photoacoustic Tomography with Different Sensing Configurations

“…By using the FPI-based PAM system, researchers have demonstrated in vivo imaging for human palm vasculature [ 148 , 149 ], human peripheral limb arteries [ 150 ], mouse brain vasculature [ 146 ], and human placental vasculature [ 147 ]. Optical fiber-based FPIs have also been developed with high sensitivity, broadband, small footprint, and wide detection angels [ 151 , 152 , 153 ]. Chen et al developed a tunable fiber-based FPI into PA mesoscopy, which can tune the resonant wavelength by using an additional 650 nm heating laser in real-time, achieving a high detection bandwidth of 30 MHz and a low NEP of 40 mPa/Hz 1/2 [ 153 ].…”

“…Optical fiber-based FPIs have also been developed with high sensitivity, broadband, small footprint, and wide detection angels [ 151 , 152 , 153 ]. Chen et al developed a tunable fiber-based FPI into PA mesoscopy, which can tune the resonant wavelength by using an additional 650 nm heating laser in real-time, achieving a high detection bandwidth of 30 MHz and a low NEP of 40 mPa/Hz 1/2 [ 153 ]. Similarly, with the advantage of small size, Ansari et al promoted fiber-based FPI into a PA endoscopy probe with an outer diameter of 3.2 mm [ 152 ].…”