Optical Coupling System Optimization for Medical Laser Surgical Applications

Mirochnik, Karina; Lu, Zhuofan; Petropulos, Olivia; Brooks, Hannah

Student Work

Optical Coupling System Optimization for Medical Laser Surgical Applications

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In this report, we develop and optimize a compact, modular optical coupling system that couples light from an 400-μm-diameter Endostat fiber into a 200-μm-diameter multimode fiber, to enable steering for practical clinical use of endoscopic procedures for laryngeal lesions and other applications. The current commercial laser surgical systems were not able to effectively treat and reach all affected regions of the larynx due to their lack of steerability and efficiency, thus making them underutilized in clinical practices. The efficiency of the system determines how practical it can be during clinical use given the demand of medical needs. There has been a fiber coupling system in the lab from the previous year’s students, but the system was large, heavy, and not suitable for the aim of clinical applications. Therefore, we develop an optical fiber free-space coupling system - as a part of a robotic system - that channels light from a thick fiber in a commercial laser surgery system into a thinner multimode fiber to enable endoscope probe steering in confined spaces such as a larynx. Our work began by developing a smaller, portable, and more efficient coupling system through 12 design iterations. Prototypes for these design iterations were fabricated and tested via a power meter to determine the optical transmission efficiency of the system. A maximum efficiency of 53% was reached in the final design iteration. Besides the efficiency, the current system also achieved compactness in terms of the nearly 70% size reduction from the initial setup. After developing the new coupling system, the team progressed to biological testing on pig ears, larynges, and esophagi to determine the efficiency and compatibility of the system with human skin like tissues. The laser was tested on biological samples to determine how much damage can be done over a series of different exposure times. Exposure times tested ranged from 2 to 10 seconds, and the rest of the variables were held constant throughout. The average depth achieved for each exposure time is as follows: 2 seconds caused 461.08 μm of damage, 4 seconds caused 670.92 μm of damage, 6 seconds caused 907.09 μm of damage, 8 seconds cause 1284.26 μm of damage, and 10 seconds caused 1430.95 μm of damage. We found that the depth increases by about 200 μm with every 2 seconds of applied laser light. The depth values allows a clinician to estimate how long they need to hold the laser on a lesion depending on the lesion dimensions. The team also conducted testing on C2C12 cell samples. This study found that 2 seconds of 532 nm wavelength green light from the laser system produced 48.9% cellular detachment from the plate/death, 4 seconds produced 52.8% detachment, 6 second produced 53.3% detachment, 8 seconds produced 64,3% detachment and 10 seconds produced 70.8% detachment. This finding supports the idea that the energy put into the system shares a positive relationship with the damage done to the cells, in addition to demonstrating the capabilities of our coupling system for laser surgical applications. We believe that the efficiency and biological testing conducted in this report strongly support the conclusion that our optical free space coupling system is efficient and effective for coupling light to a customized thin fiber, which enables the surgical laser steering while retaining enough optical power for desired tissue damage, and our work has considerable potential in numerous clinical applications including laser surgeries and endoscopy.

This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.

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