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Collard L, Piscopo L, Pisano F, Zheng D, De Vittorio M, Pisanello F. Optimizing the internal phase reference to shape the output of a multimode optical fiber. PLoS One 2023; 18:e0290300. [PMID: 37682976 PMCID: PMC10490902 DOI: 10.1371/journal.pone.0290300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 08/04/2023] [Indexed: 09/10/2023] Open
Abstract
Pre-shaping light to achieve desired amplitude distributions at the tip of a multimode fiber (MMF) has emerged as a powerful method allowing a wide range of imaging techniques to be implemented at the distal facet. Such techniques rely on measuring the transmission matrix of the optically turbid waveguide which scrambles the coherent input light into an effectively random speckle pattern. Typically, this is done by measuring the interferogram between the output speckle and a reference beam. In recent years, an optical setup where the reference beam passes through the MMF has become an attractive configuration because of the high interferometric stability of the common optical path. However, the merits and drawbacks of an internal reference beam remain controversial. The measurement of the transmission matrix is known to depend on the choice of internal reference and has been reported to result in "blind spots" due to phase singularities of the reference beam. Here, we describe how the focussing efficiency of the calibration can be increased by several percent by optimising the choice of internal reference beam.
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Affiliation(s)
- Liam Collard
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- RAISE Ecosystem, Genova, Italy
| | - Linda Piscopo
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- Dipartimento di Ingegneria Dell’Innovazione, Università del Salento, Lecce, Italy
| | - Filippo Pisano
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- Department of Physics and Astronomy “G. Galilei”, University of Padova, Padova, Italy
| | - Di Zheng
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
| | - Massimo De Vittorio
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- RAISE Ecosystem, Genova, Italy
- Dipartimento di Ingegneria Dell’Innovazione, Università del Salento, Lecce, Italy
| | - Ferruccio Pisanello
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- RAISE Ecosystem, Genova, Italy
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Pikálek T, Stibůrek M, Simpson S, Čižmár T, Trägårdh J. Suppression of the non-linear background in a multimode fibre CARS endoscope. BIOMEDICAL OPTICS EXPRESS 2022; 13:862-874. [PMID: 35284193 PMCID: PMC8884213 DOI: 10.1364/boe.450375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 01/07/2022] [Accepted: 01/07/2022] [Indexed: 06/14/2023]
Abstract
Multimode fibres show great potential for use as miniature endoscopes for imaging deep in tissue with minimal damage. When used for coherent anti-Stokes Raman scattering (CARS) microscopy with femtosecond excitation sources, a high band-width probe is required to efficiently focus the broadband laser pulses at the sample plane. Although graded-index (GRIN) fibres have a large bandwidth, it is accompanied by a strong background signal from four-wave mixing and other non-linear processes occurring inside the fibre. We demonstrate that using a composite probe consisting of a GRIN fibre with a spliced on step-index fibre reduces the intensity of the non-linear background by more than one order of magnitude without significantly decreasing the focusing performance of the probe. Using this composite probe we acquire CARS images of biologically relevant tissue such as myelinated axons in the brain with good contrast.
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Affiliation(s)
- Tomáš Pikálek
- Institute of Scientific Instruments of the Czech Academy of Sciences, Královopolská 147, 61264 Brno, Czech Republic
| | - Miroslav Stibůrek
- Institute of Scientific Instruments of the Czech Academy of Sciences, Královopolská 147, 61264 Brno, Czech Republic
| | - Stephen Simpson
- Institute of Scientific Instruments of the Czech Academy of Sciences, Královopolská 147, 61264 Brno, Czech Republic
| | - Tomáš Čižmár
- Institute of Scientific Instruments of the Czech Academy of Sciences, Královopolská 147, 61264 Brno, Czech Republic
- Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745 Jena, Germany
- Institute of Applied Optics, Friedrich Schiller University Jena, Fröbelstieg 1, 07743 Jena, Germany
| | - Johanna Trägårdh
- Institute of Scientific Instruments of the Czech Academy of Sciences, Královopolská 147, 61264 Brno, Czech Republic
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Zhao T, Ourselin S, Vercauteren T, Xia W. Focusing light through multimode fibres using a digital micromirror device: a comparison study of non-holographic approaches. OPTICS EXPRESS 2021; 29:14269-14281. [PMID: 33985150 PMCID: PMC8240458 DOI: 10.1364/oe.420718] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Focusing light through a multimode fibre (MMF) has attracted significant research interest, mainly driven by the need for miniature endoscopes in biomedicine. In recent years, digital micromirror devices (DMD) have become increasingly popular as a high-speed alternative to liquid-crystal spatial light modulators for light focusing via wavefront shaping based on binary amplitude modulations. To exploit the potentials and limitations of the state-of-the-art DMD-based wavefront shaping methods, in this study, for the first time, we compared four representative, non-holographic and DMD-based methods that are reported so far in literature with the same experimental and simulation conditions, including a real-valued intensity transmission matrix (RVITM)-based algorithm, a complex-valued transmission matrix (TM)-based algorithm, a conditional probability algorithm and a genetic algorithm. We investigated the maximum achievable peak-to-background ratio (PBR) in comparison to theoretical expectations, and further improved the performance of the RVITM-based method. With both numerical simulations and experiments, we found that the genetic algorithm offered the highest PBR but suffered from the lowest focusing speed, while the RVITM-based algorithm provided a comparable PBR to that of the genetic algorithm, and the highest focusing speed.
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Ross CA, MacLachlan DG, Smith BJE, Beck RJ, Shephard JD, Weston N, Thomson RR. A Miniature Fibre-Optic Raman Probe Fabricated by Ultrafast Laser-Assisted Etching. MICROMACHINES 2020; 11:mi11020185. [PMID: 32053957 PMCID: PMC7074630 DOI: 10.3390/mi11020185] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Revised: 02/06/2020] [Accepted: 02/08/2020] [Indexed: 01/20/2023]
Abstract
Optical biopsy describes a range of medical procedures in which light is used to investigate disease in the body, often in hard-to-reach regions via optical fibres. Optical biopsies can reveal a multitude of diagnostic information to aid therapeutic diagnosis and treatment with higher specificity and shorter delay than traditional surgical techniques. One specific type of optical biopsy relies on Raman spectroscopy to differentiate tissue types at the molecular level and has been used successfully to stage cancer. However, complex micro-optical systems are usually needed at the distal end to optimise the signal-to-noise properties of the Raman signal collected. Manufacturing these devices, particularly in a way suitable for large scale adoption, remains a critical challenge. In this paper, we describe a novel fibre-fed micro-optic system designed for efficient signal delivery and collection during a Raman spectroscopy-based optical biopsy. Crucially, we fabricate the device using a direct-laser-writing technique known as ultrafast laser-assisted etching which is scalable and allows components to be aligned passively. The Raman probe has a sub-millimetre diameter and offers confocal signal collection with 71.3% ± 1.5% collection efficiency over a 0.8 numerical aperture. Proof of concept spectral measurements were performed on mouse intestinal tissue and compared with results obtained using a commercial Raman microscope.
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Affiliation(s)
- Calum A. Ross
- Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK
- Correspondence:
| | - David G. MacLachlan
- Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK
| | | | - Rainer J. Beck
- Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Jonathan D. Shephard
- Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK
| | | | - Robert R. Thomson
- Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK
- EPSRC IRC Hub, MRC Centre for Inflammation Research, Queen’s Medical Research Institute (QMRI), University of Edinburgh, Edinburgh EH16 4TJ, UK
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Amitonova LV, de Boer JF. Sensitivity analysis of Raman endoscopy with and without wavefront shaping. OPTICS EXPRESS 2020; 28:3779-3788. [PMID: 32122039 DOI: 10.1364/oe.383801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 01/13/2020] [Indexed: 06/10/2023]
Abstract
Vibrational spectroscopy is a powerful method for the label-free identification of molecules. Spontaneous Raman spectroscopy integrated with an ultra-thin fiber-based endoscope can provide remote, local, and minimally invasive chemical analysis in many fields from biomedical diagnostics to the materials industry. Miniaturization of the probe in combination with a large field of view (FOV) and high sensitivity would be beneficial for a broad class of applications. Here we quantitatively analyze signal-to-noise ratio (SNR) and the sensitivity improvement due to wavefront shaping. We show that wavefront shaping in an ultra-thin single-fiber probe allows to decrease the total measurements time up to several orders of magnitude even without any prior knowledge of the Raman particle location. Such a fiber probe is well suited for minimally-invasive endoscopy in biological and medical applications.
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Trägårdh J, Pikálek T, Šerý M, Meyer T, Popp J, Čižmár T. Label-free CARS microscopy through a multimode fiber endoscope. OPTICS EXPRESS 2019; 27:30055-30066. [PMID: 31684259 DOI: 10.1364/oe.27.030055] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Multimode fibres have recently been employed as high-resolution ultra-thin endoscopes, capable of imaging biological structures deep inside tissue in vivo. Here, we extend this technique to label-free non-linear microscopy with chemical contrast using coherent anti-Stokes Raman scattering (CARS) through a multimode fibre endoscope, which opens up new avenues for instant and in-situ diagnosis of potentially malignant tissue. We use a commercial 125 µm diameter, 0.29 NA GRIN fibre, and wavefront shaping on an SLM is used to create foci that are scanned behind the fibre facet across the sample. The chemical selectivity is demonstrated by imaging 2 µm polystyrene and 2.5 µm PMMA beads with per pixel integration time as low as 1 ms for epi-detection.
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Pikálek T, Trägårdh J, Simpson S, Čižmár T. Wavelength dependent characterization of a multimode fibre endoscope. OPTICS EXPRESS 2019; 27:28239-28253. [PMID: 31684580 DOI: 10.1364/oe.27.028239] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 09/01/2019] [Indexed: 06/10/2023]
Abstract
Multimode fibres have recently shown promise as miniature endoscopic probes. When used for non-linear microscopy, the bandwidth of the imaging system limits the ability to focus light from broadband pulsed lasers as well as the possibility of wavelength tuning during the imaging. We demonstrate that the bandwidth is limited by the dispersion of the off-axis hologram displayed on the SLM, which can be corrected for, and by the limited bandwidth of the fibre itself. The selection of the fibre is therefore crucial for these experiments. In addition, we show that a standard prism pulse compressor is sufficient for material dispersion compensation for multi-photon imaging with a fibre endoscope.
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