Graded-index (GRIN) lenses have been widely used for developing compact imaging devices due to the small dimensions and simple optics designs. GRIN lenses, however, have intrinsic aberration which causes a distortion of the image and thus are subject to limited resolution and blurred imaging quality. Here, we employ the high-precision wavefront measurement technique for compensation of the distortion of a GRIN lens to obtain a high-resolution and high-contrast image. In doing so, we demonstrate a high-resolution and ultra-thin endo-microscope using a GRIN. A reflection-type interferometric microscope through a GRIN lens was constructed using multiple lasers (473 nm, 532 nm, and 633 nm) as light sources. The characteristics of the aberration of the GRIN lens were measured using the digital holographic method. The distortion of the GRIN lens was removed by numerical image processing with the prior information from the pre-calibration. We apply this technique to a reflection image of biological tissues acquired by our custom-built GRIN lens probe. Consequently, a diffraction limited lateral resolution as well as improved axial resolution can be achieved. Our approach will facilitate the use of GRIN lenses for compact imaging devices without compromising optical resolution and image quality.
Hyung-Jin Kim, Kwan Jun Park, Taeseok D. Yang, Wonshik Choi, Beop-Min Kim, and Youngwoon Choi, "High-resolution image reconstruction for GRIN rod lens probe (Conference Presentation)," Proc. SPIE 10040, Endoscopic Microscopy XII, 100400T (Presented at SPIE BiOS: January 30, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2251768.5369883830001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon