Laparoscopic Photoacoustic Imaging System Based on Side-Illumination Diffusing Fibers.

OBJECTIVE: To develop a flexible miniaturized photoacoustic (PA) imaging probe for detecting anatomical structures during laparoscopic surgery. The proposed probe aimed to facilitate intraoperative detection of blood vessels and nerve bundles embedded in tissue not directly visible to the operating physician to preserve these delicate and vital structures. METHODS: We modified a commercially available ultrasound laparoscopic probe by incorporating custom-fabricated side-illumination diffusing fibers that illuminate the probe's field of view. The probe geometry, including the position and orientation of the fibers and the emission angle, was determined using computational models of light propagation in the simulation and subsequently validated through experimental studies. RESULTS: In wire phantom studies within an optical scattering medium, the probe achieved an imaging resolution of 0.43 ±0.09 mm and a signal-to-noise ratio of 31.2±1.84 dB. We also conducted an ex vivo study using a rat model, demonstrating the successful detection of blood vessels and nerves. CONCLUSION: Our results indicate the viability of a side-illumination diffusing fiber PA imaging system for guidance during laparoscopic surgery. SIGNIFICANCE: The potential clinical translation of this technology could enhance the preservation of critical vascular structures and nerves, thereby minimizing post-operative complications.

Highly accessible low-loss fiber tapering by the ceramic housed electric furnace (CHEF) and frequency-domain real-time monitoring.

Tapered optical fibers are versatile tools with a wide spectrum of applications, ranging from sensing to atomic physics. In this work, we developed a highly accessible and controllable fiber tapering system to fabricate tapered optical fibers with a routine optical transmission of 95% and above. With an optimal design, optical transmissions higher than 99% have been experimentally demonstrated. We achieved such results by developing two unique components in a traditional heat-and-pull system: a custom-made miniature heater named as the ceramic housed electric furnace (CHEF) and a real-time, frequency-domain monitoring method. The CHEF enables a well-controlled, uniform, and stable heating zone for an adiabatic tapering process, while the frequency-domain monitoring empowers one to reliably terminate the tapering right after the single-mode trigger. We designed and fabricated the CHEF using low-cost and readily accessible materials and equipment, in order to benefit a broader audience. We carried out a parametric study to systematically characterize the CHEF performance and provided guidelines for the CHEF design, fabrication, and operation. The frequency-domain monitoring method was developed based on our understanding of the dynamic evolution of optical modes in the tapered fiber. Such a method allows real-time visualization of the number of optical models and characterization of the taper adiabaticity during the tapering process, both of which are not available with the commonly used time-domain monitoring. The developed CHEF-based fiber tapering system will meet the urgent need of high-quality tapered optical fibers as well as opening doors to new applications of tapered optical fibers.

Transient response of a resonator fiber optic gyro with triangular wave phase modulation.

We present an in-depth analysis of the transient response of a resonator fiber optic gyro based on triangular wave phase modulation. Unusual effects have been observed in the process of tracking the resonant frequency of an optical fiber ring resonator (OFRR). There is a distortion phenomenon, unlike the ideally square wave or a pure DC output of the OFRR, but signal overshoot or undershoot occurs. A deep analysis of the influence of the nonideal square wave or pure DC output on gyro performance is fully developed for the first time, to the best of our knowledge. Further analysis shows that this is the transient response process after modulation by the triangular wave, and the process is related both to the parameters of the OFRR and the modulation frequency of the triangular wave. By sampling the steady-state signal of the distortion square wave, or by oversampling the distortion signal to get a number of data, and then accumulating and averaging these data to be demodulated, the distortion's effect can be considerably decreased.