A probe with optimized focal depth, working distance and axial intensity uniformity

Abstract

The invention provides a probe with optimized focal depth, working distance and uniformity of axial light intensity. Gradient-index fiber, large-core fiber for generating mode interference field (MIF) and regulating phase difference between modes, No. 2 gradient-index fiber for amplifying MIF, coreless fiber, and No. 3 gradient-refractive fiber for focusing Composition of fiber optics. The invention optimizes the uniformity of axial light intensity and prolongs the working distance while expanding the focal depth. The invention does not require phase stability, does not require mechanical scanning, and uses the same optical path to realize illumination and detection, which is very beneficial to the miniaturization design of the probe; the invention allows greater manufacturing errors and reduces manufacturing costs.

Description

technical field [0001] The invention belongs to the field of optical coherence tomography (OCT, Optical coherence tomography), in particular to a probe that utilizes mode interference in an optical fiber to simultaneously realize focal depth extension, working distance extension, and axial light intensity uniformity optimization. [0002] technical background [0003] OCT is an important imaging method that can obtain high-resolution three-dimensional structural information and functional information of living internal tissues through the endoscopic probe [1]. Compared with conventional optical imaging methods, the axial resolution of OCT has nothing to do with the lateral resolution, but depends on the coherence length of the light source. Using the most advanced broadband light source at present, its axial resolution can reach 1-5 microns [2]. However, if the lateral resolution is increased to the same level, the effective imaging range of OCT will be limited by the extrem...

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Problems solved by technology

However, some of the above methods require phase stability, some require mechanical scanning, and some require two optical paths for illumination and detection respectively.

Therefore, these methods are difficult to apply to miniaturized probes

by chemical corrosion [7] or grinding and polishing [8] Fabricated miniature axicon mirrors, miniature binary phase plates fabricated by soft lithography [9] Has been used to extend the depth of focus of the probe, but these miniature optics have limited ability to extend the depth of focus of the probe compared to benchtop systems

On the other hand, a phase-mask-based scheme that requires no other processing than cutting and splicing a series of fibers has been reported. [10] , but this scheme based on the phase mask has high requirements on the cutting accuracy of the fiber

Another approach to depth-of-focus extension in all-fiber probes exploits higher-order modes in step-index fibers [11,12] , but the interference and destructive phenomenon in the depth of focus area leads to the uneven distribution of the light intensity of the outgoing beam in the axial direction, which has a negative impact on the overall imaging effect

Recently, we observed that by modulating the multimode interference field in a fiber-type pupil filter can be used to extend the depth of focus of an all-fiber probe [13] , however, the original probe design has a limited working distance

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