Abstract
Holographic wavefront manipulation enables converting hair-thin multimode optical fibers into minimally invasive lensless imaging instruments conveying much higher information densities than conventional endoscopes. Their most prominent applications focus on accessing delicate environments, including deep brain compartments, and recording micrometer-scale resolution images of structures in close proximity to the distal end of the instrument. Here, we introduce an alternative “far-field” endoscope capable of imaging macroscopic objects across a large depth of field. The endoscope shaft with dimensions of 0.2 × 0.4 mm2 consists of two parallel optical fibers: one for illumination and the other for signal collection. The system is optimized for speed, power efficiency, and signal quality, taking into account specific features of light transport through step-index multimode fibers. The characteristics of imaging quality are studied at distances between 20 mm and 400 mm. As a proof-of-concept, we provide imaging inside the cavities of a sweet pepper commonly used as a phantom for biomedically relevant conditions. Furthermore, we test the performance on a functioning mechanical clock, thus verifying its applicability in dynamically changing environments. With the performance reaching the standard definition of video endoscopes, this work paves the way toward the exploitation of minimally invasive holographic micro-endoscopes in clinical and diagnostics applications.
Highlights
Holographic endoscopes harnessing controlled light transport through hair-thin multimode optical fibers have recently emerged as powerful technological candidates for minimally invasive observations in biomedical applications.1–5 The concept spun-out from groundbreaking research on photonics of complex media,6–10 utilizing empirical quantification of optical propagation through a random medium,11 heralding a new era of applications that cannot be met by conventional endoscopes
With the performance reaching the standard definition of video endoscopes, this work paves the way toward the exploitation of minimally invasive holographic micro-endoscopes in clinical and diagnostics applications
The endoscope exploits the principle of raster-scan imaging, whereby images are reconstructed from the local response of an object to a scanning beam preshaped by the holographic modulator and delivered by a multimode optical fiber
Summary
Holographic endoscopes harnessing controlled light transport through hair-thin multimode optical fibers have recently emerged as powerful technological candidates for minimally invasive observations in biomedical applications. The concept spun-out from groundbreaking research on photonics of complex media, utilizing empirical quantification of optical propagation through a random medium, heralding a new era of applications that cannot be met by conventional endoscopes. The concept spun-out from groundbreaking research on photonics of complex media, utilizing empirical quantification of optical propagation through a random medium, heralding a new era of applications that cannot be met by conventional endoscopes Their recognized potential to obtain detailed imagery from large depths of sensitive tissue structures has recently been exploited in in vivo neuroscience studies, where neurones and processes of neuronal circuits have been acquired in living animal models through fibers having footprints of ∼0.01 mm. The aspiration of this work is to extend the applicability of holographic endoscopes into clinical environments, where reduction of instrument’s footprint is desired, yet the demands on imaging performance differ considerably from those of in vivo neuroscience This relates to spatial resolution and frame rate but importantly to the working distance and field of view, which have to be significantly enhanced before the concept can be accepted as a credible strategy for new minimally invasive diagnostics and surgery-assisting instrumentation. Compressive sensing or machine-learning algorithms could accelerate imaging or eliminate inherently speckled nature of the images, all our results are presented as raw measurements with their original contrast in order to avoid any biases
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