Abstract
The current fiber-based illumination systems of laparoscopes are unable to uniformly illuminate a large enough area in abdomen due to the limited numerical aperture (NA) of the fiber bundle. Most energy is concentrated in a small region at the center of the illumination area. This limitation becomes problematic in laparoscopes which require capturing a wide field of view. In this paper, we propose an aspherical lens array which is used to direct the outgoing rays from the fiber bundle of laparoscope to produce a more uniformly illuminated, substantially larger field coverage than standalone fiber source. An intensity feedback method is developed to design the aspherical lens unit for extended non-Lambertian sources, which is the key to the design of this lens array. By this method, the lens unit is obtained after only one iteration, and the lens array is constructed by Boolean operation. Then, the ray-tracing technique is used to verify the design. Further, the lens array is fabricated and experimental tests are performed. The results clearly show that the well-illuminated area is increased to about 0.107m(2) from 0.02m(2) (about 5x larger than a standard fiber illumination source). More details of the internal organs can be clearly observed under this improved illumination condition, which also reflects the significant improvement in the optical performance of the laparoscope.
Highlights
Laparoscopes, which have unparalleled ability to visualize lesions within internal organs with high resolution, allow doctors to perform both minor and complex surgeries with a few small cuts in the abdomen
As the experimental tests will show, the performance of the illumination system is significantly improved by the aspherical lens array, and the organs can be well illuminated under this new illumination method, which allows the imaging system of the laparoscope to capture more details of internal organs
An aspherical lens array along with an aperture array is placed adjacent to the end surface of the laparoscope, which redistributes the outgoing beam from the fiber bundle of the laparoscope to produce a uniform illumination over an extended area
Summary
Laparoscopes, which have unparalleled ability to visualize lesions within internal organs with high resolution, allow doctors to perform both minor and complex surgeries with a few small cuts in the abdomen. The concentrated non-uniform illumination problem present a severe challenge in laparoscopes whose imaging systems are designed to capture a large surgical area or the objectives of the laparoscopes have large numerical aperture for higher light efficiency. As shown later in this paper [see Fig. 9(c)], most part of the organ cannot be clearly observed due to the poor performance of such an illumination system, especially at the center and the edge of the organ With such an illumination system, any attempt to improve the optical performance of laparoscopes by increasing the resolution of the imaging system might be in vain. As the experimental tests will show, the performance of the illumination system is significantly improved by the aspherical lens array, and the organs can be well illuminated under this new illumination method, which allows the imaging system of the laparoscope to capture more details of internal organs.
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