19 research outputs found
Observing distant objects with a multimode fibre-based holographic endoscope
Holographic wavefront manipulation enables converting hair-thin multimode
optical fibres 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 micrometre-scale resolution images of
structures in close proximity to the distal end of the instrument. Here, we
introduce an alternative 'farfield' endoscope, capable of imaging macroscopic
objects across a large depth of field. The endoscope shaft with dimensions of
0.20.4 mm consists of two parallel optical fibres, one for
illumination and the second 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 fibres. The
characteristics of imaging quality are studied at distances between 20 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.
Further, we test the performance on a functioning mechanical clock, thus
verifying its applicability in dynamically changing environments. With
performance reaching the standard definition of video endoscopes, this work
paves the way towards the exploitation of minimally-invasive holographic
micro-endoscopes in clinical and diagnostics applications.Comment: 9+6 pages, 4+5 figure
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Observing distant objects with a multimode fiber-based holographic endoscope
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. © 2021 Author(s)
Robustness of Light-Transport Processes to Bending Deformations in Graded-Index Multimode Waveguides
Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to bending, conserving the structure of propagation-invariant modes. Moreover, we show that changes to the transmission matrix of parabolic-index fibers due to bending can be expressed with only two free parameters, regardless of how complex a particular deformation is. We provide detailed analysis of experimentally measured transmission matrices of a commercially available graded-index fiber as well as a gradient-index rod lens featuring a very faithful parabolic refractive index profile. Although parabolic-index fibers with a sufficiently precise refractive index profile are not within our reach, we show that imaging performance with standard commercially available graded-index fibers is significantly less influenced by bending deformations than step-index types under the same conditions. Our work thus predicts that the availability of ultraprecise parabolic-index fibers will make endoscopic applications with flexible probes feasible and free from extremely elaborate computational challenges
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Comparison of nematic liquid-crystal and DMD based spatial light modulation in complex photonics
Digital micro-mirror devices (DMDs) have recently emerged as practical spatial light modulators (SLMs) for applications in photonics, primarily due to their modulation rates, which exceed by several orders of magnitude those of the already well-established nematic liquid crystal (LC)-based SLMs. This, however, comes at the expense of limited modulation depth and diffraction efficiency. Here we compare the beam-shaping fidelity of both technologies when applied to light control in complex environments, including an aberrated optical system, a highly scattering layer and a multimode optical fibre. We show that, despite their binary amplitude-only modulation, DMDs are capable of higher beam-shaping fidelity compared to LC-SLMs in all considered regimes
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Robustness of Light-Transport Processes to Bending Deformations in Graded-Index Multimode Waveguides
Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to bending, conserving the structure of propagation-invariant modes. Moreover, we show that changes to the transmission matrix of parabolic-index fibers due to bending can be expressed with only two free parameters, regardless of how complex a particular deformation is. We provide detailed analysis of experimentally measured transmission matrices of a commercially available graded-index fiber as well as a gradient-index rod lens featuring a very faithful parabolic refractive index profile. Although parabolic-index fibers with a sufficiently precise refractive index profile are not within our reach, we show that imaging performance with standard commercially available graded-index fibers is significantly less influenced by bending deformations than step-index types under the same conditions. Our work thus predicts that the availability of ultraprecise parabolic-index fibers will make endoscopic applications with flexible probes feasible and free from extremely elaborate computational challenges
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High-fidelity multimode fibre-based endoscopy for deep brain in vivo imaging
Progress in neuroscience relies on new techniques for investigating the complex dynamics of neuronal networks. An ongoing challenge is to achieve minimally invasive and high-resolution observations of neuronal activity in vivo inside deep brain areas. Recently introduced methods for holographic control of light propagation in complex media enable the use of a hair-thin multimode optical fibre as an ultranarrow imaging tool. Compared to endoscopes based on graded-index lenses or fibre bundles, this new approach offers a footprint reduction exceeding an order of magnitude, combined with a significant enhancement in resolution. We designed a compact and high-speed system for fluorescent imaging at the tip of a fibre, achieving a resolution of 1.18 ± 0.04 µm across a 50-µm field of view, yielding 7-kilopixel images at a rate of 3.5 frames/s. Furthermore, we demonstrate in vivo observations of cell bodies and processes of inhibitory neurons within deep layers of the visual cortex and hippocampus of anaesthetised mice. This study paves the way for modern microscopy to be applied deep inside tissues of living animal models while exerting a minimal impact on their structural and functional properties
Comparison of nematic liquid-crystal and DMD based spatial light modulation in complex photonics
Digital micro-mirror devices (DMDs) have recently emerged as practical spatial
light modulators (SLMs) for applications in photonics, primarily due to their modulation rates,
which exceed by several orders of magnitude those of the already well-established nematic liquid
crystal (LC)-based SLMs. This, however, comes at the expense of limited modulation depth and
diffraction efficiency. Here we compare the beam-shaping fidelity of both technologies when
applied to light control in complex environments, including an aberrated optical system, a highly
scattering layer and a multimode optical fibre. We show that, despite their binary amplitude-only
modulation, DMDs are capable of higher beam-shaping fidelity compared to LC-SLMs in all
considered regime