Flexible lensless endoscope with a conformationally invariant multi-core fiber

Abstract

The lensless endoscope represents the ultimate limit in miniaturization of imaging tools: an image can be transmitted through a (multi-mode or multi-core) fiber by numerical or physical inversion of the fiber's premeasured transmission matrix. However, the transmission matrix changes completely with only minute conformational changes of the fiber, which has so far limited lensless endoscopes to fibers that must be kept static. In this letter we report for the first time a lensless endoscope which is exempt from the requirement of static fiber by designing and employing a custom-designed conformationally invariant fiber. We give experimental and theoretical validations and determine the parameter space over which the invariance is maintained.

BPM-Matlab: an open-source optical propagation simulation tool in MATLAB

“…These results are congruous with the earlier observations stated in Ref. [59], demonstrating that BPM-Matlab models twisted fibers correctly. Fig.…”

“…However, the aperiodicity of patterns such as the Fermat's golden spiral core pattern [58] and pseudo-random or random patterns [54] have all been shown to reduce the side-lobes. Recent theoretical and experimental studies have shown that a conformationally invariant (bending resilient) MCF can be fabricated with twisted cores, thereby providing promising fibers for lensless endoscopes [59].…”

“…The simulated intensity profiles of the focal spot pattern made in free space near the distal end of a 41 cm long MCF demonstrated in Ref. [59] using BPM-Matlab are presented in Fig. 5 in the presence and absence of fiber bending and fiber twisting.…”

Guidestar-free image-guided wavefront shaping

“…For leached fiber bundles that do not have a shared clad for all cores, such as the ones used in our experiments, fiber bending may cause strong decorrelation of the wavefront, which will require faster optimization. Recently introduced MCF designs feature significantly reduced bend sensitivity ( 41 )and are especially attractive for applying our approach.…”

Real-time holographic lensless micro-endoscopy through flexible fibers via Fiber Bundle Distal Holography (FiDHo)

“…Alternative, speckle based incoherent imaging approaches [11,12,13,14], suffer from very low contrast of the acquired images. MCFs with bend-insensitive intercore phase relations have been fabricated [28]. However, these rely on a relatively small number of single-mode cores, suffering from low collection-efficiency and fill-factor.…”