Abstract
In this paper a novel single-pixel method for coherent imaging through an endoscopic fiber bundle is presented. The use of a single-pixel detector allows greater sensitivity over a wider range of wavelengths, which could have significant applications in endoscopic fluorescence microscopy. First, the principle of lensless focussing at the distal end of a coherent fiber bundle is simulated to examine the impact of pixelation at microscopic scales. Next, an experimental optical correlator system using spatial light modulators (SLMs) is presented. A simple contrast imaging method of characterizing and compensating phase aberrations introduced by fiber bundles is described. Experimental results are then presented showing that our phase compensation method enables characterization of the optical phase profile of individual fiberlets. After applying this correction, early results demonstrating the ability of the system to electronically adjust the focal plane at the distal end of the fiber bundle are presented. The structural similarity index (SSIM) between the simulated image and the experimental focus-adjusted image increases noticeably when the phase correction is applied and the retrieved image is visually recognizable. Strategies to improve image quality are discussed.
Highlights
E NDOSCOPES are powerful tools for diagnosis of a range of diseases in the gastrointestinal and respiratory tracts, particular cancers
When the measured reference phase image is used to correct the sample image phase as in Fig. 6(c), it is seen that this ripple pattern disappears and the phase profile becomes patches of approximately constant phase corresponding to individual fiberlets
It is shown experimentally that the system is able to measure the phase of the wavefront emerging at the proximal end of a fiber bundle and is able to estimate and correct phase aberrations therein
Summary
E NDOSCOPES are powerful tools for diagnosis of a range of diseases in the gastrointestinal and respiratory tracts, particular cancers. In the case of a coherent fiber bundle, if all the fibers are single mode at a given wavelength and there is negligible coupling between fiberlets, this measurement reduces to determining the random phase shift introduced by each fiberlet due to variation in optical path lengths In reality, these fiberlets are not single mode, typically exhibiting at least three spatial modes and a small amount of coupling between adjacent fibrelets in the 700–900 nm range [11]. Single-pixel methods have the advantage of being able to use low-cost sensors (single photodiodes) that work over a wide range of wavelengths These detectors can be extremely sensitive, for example photomultiplier tubes. An SLM-based single-pixel imaging technique is adapted to measure both the amplitude and phase profiles of light in individual fiberlets of a coherent fiber bundle and demonstrate dynamic lenseless focus shifting.
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