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1.
Opt Express ; 32(8): 14705-14712, 2024 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-38859407

RESUMO

Tomographic Volumetric Additive Manufacturing (TVAM) allows printing of mesoscopic objects within seconds or minutes. In TVAM, tomographic patterns are illuminated onto a rotating glass vial which contains a photosensitive resin. Current pattern optimization is based on a ray optical assumption which ultimately leads to limited resolution around 20 µm and varying throughout the volume of the 3D object. In this work, we introduce a rigorous wave-based optical amplitude optimization scheme for TVAM which shows that high-resolution printing is theoretically possible over the full volume. The wave optical optimization approach is based on an efficient angular spectrum method of plane waves with custom written memory efficient gradients and allows for optimization of realistic volumes for TVAM such as (100µm)3 or (10 mm)3 with 5503 voxels and 600 angles. Our simulations show that ray-optics start to produce artifacts when the desired features are 20 µm and below and more importantly, the amplitude modulated TVAM can reach sub 20 µm features when optimizing the patterns using a full wave model.

2.
Opt Lett ; 49(2): 322-325, 2024 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-38194559

RESUMO

We demonstrate the fabrication of volume holograms using two-photon polymerization with dynamic control of light exposure. We refer to our method as (3 + 1)D printing. Volume holograms that are recorded by interfering reference and signal beams have a diffraction efficiency relation that is inversely proportional to the square of the number of superimposed holograms. By using (3 + 1)D printing for fabrication, the refractive index of each voxel is created independently and thus, by digitally filtering the undesired interference terms, the diffraction efficiency is now inversely proportional to the number of multiplexed gratings. We experimentally demonstrated this linear dependence by recording M = 50 volume gratings. To the best of our knowledge, this is the first experimental demonstration of distributed volume holograms that overcome the 1/M2 limit.

3.
Opt Lett ; 48(20): 5249-5252, 2023 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-37831839

RESUMO

Neural networks (NNs) have demonstrated remarkable capabilities in various tasks, but their computation-intensive nature demands faster and more energy-efficient hardware implementations. Optics-based platforms, using technologies such as silicon photonics and spatial light modulators, offer promising avenues for achieving this goal. However, training multiple programmable layers together with these physical systems poses challenges, as they are difficult to fully characterize and describe with differentiable functions, hindering the use of error backpropagation algorithm. The recently introduced forward-forward algorithm (FFA) eliminates the need for perfect characterization of the physical learning system and shows promise for efficient training with large numbers of programmable parameters. The FFA does not require backpropagating an error signal to update the weights, rather the weights are updated by only sending information in one direction. The local loss function for each set of trainable weights enables low-power analog hardware implementations without resorting to metaheuristic algorithms or reinforcement learning. In this paper, we present an experiment utilizing multimode nonlinear wave propagation in an optical fiber demonstrating the feasibility of the FFA approach using an optical system. The results show that incorporating optical transforms in multilayer NN architectures trained with the FFA can lead to performance improvements, even with a relatively small number of trainable weights. The proposed method offers a new path to the challenge of training optical NNs and provides insights into leveraging physical transformations for enhancing the NN performance.

4.
Opt Express ; 30(16): 28601-28613, 2022 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-36299052

RESUMO

Shifted Excitation Raman Difference Spectroscopy (SERDS) is a non-destructive chemical analysis method capable of removing the fluorescence background and other disturbances from the Raman spectrum, thanks to the independence of the fluorescence with respect to the small difference in excitation wavelength. The spectrum difference is computed in a post-processing step. Here, we demonstrate the use of a lock-in camera to obtain an on-line analog SERDS spectra allowing longer exposure times and no saturation, leading to an improved Signal-to-Noise Ratio (SNR) and reduced data storage. Two configurations are presented: the first one uses a single laser and can remove excitation-independent disturbances, such as ambient light; the second employs two-wavelength shifted sources and removes fluorescence background similarly to SERDS. In both cases, we experimentally extrapolate the expected SNR improvement.

5.
Biomacromolecules ; 23(12): 5007-5017, 2022 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-36379034

RESUMO

The surgical treatments of injured soft tissues lead to further injury due to the use of sutures or the surgical routes, which need to be large enough to insert biomaterials for repair. In contrast, the use of low viscosity photopolymerizable hydrogels that can be inserted with thin needles represents a less traumatic treatment and would therefore reduce the severity of iatrogenic injury. However, the delivery of light to solidify the inserted hydrogel precursor requires a direct access to it, which is mostly invasive. To circumvent this limitation, we investigate the approach of curing the hydrogel located behind biological tissues by sending near-infrared (NIR) light through the latter, as this spectral region has the largest transmittance in biological tissues. Upconverting nanoparticles (UCNPs) are incorporated in the hydrogel precursor to convert NIR transmitted through the tissues into blue light to trigger the photopolymerization. We investigated the photopolymerization process of an adhesive hydrogel placed behind a soft tissue. Bulk polymerization was achieved with local radiation of the adhesive hydrogel through a focused light system. Thus, unlike the common methods for uniform illumination, adhesion formation was achieved with local micrometer-sized radiation of the bulky hydrogel through a gradient photopolymerization phenomenon. Nanoindentation and upright microscope analysis confirmed that the proposed approach for indirect curing of hydrogels below the tissue is a gradient photopolymerization phenomenon. Moreover, we found that the hydrogel mechanical and adhesive properties can be modulated by playing with different parameters of the system such as the NIR light power and the UCNP concentration. The proposed photopolymerization of adhesive hydrogels below the tissue opens the prospect of a minimally invasive surgical treatment of injured soft tissues.


Assuntos
Hidrogéis , Nanopartículas , Adesivos , Materiais Biocompatíveis , Polimerização
6.
Appl Opt ; 61(9): F34-F46, 2022 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-35333224

RESUMO

Lensless inline holography can produce high-resolution images over a large field of view (FoV). In a previous work [Appl. Opt.60, B38 (2021)APOPAI0003-693510.1364/AO.414976], we showed that (i) the actual FoV can be extrapolated outside of the camera FoV and (ii) the effective resolution of the setup can be several times higher than the resolution of the camera. In this paper, we present a reconstruction method to recover high resolution with an extrapolated FoV image of the phase and the amplitude of a sample from aliased intensity measurements taken at a lower resolution.

7.
Macromol Rapid Commun ; 42(10): e2000660, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33834552

RESUMO

Attaching hydrogels to soft internal tissues is crucial for the development of various biomedical devices. Tough sticky hydrogel patches present high adhesion, yet with lack of injectability and the need for treatment of contacting surface. On the contrary, injectable and photo-curable hydrogels are highly attractive owing to their ease of use, flexibility of filling any shape, and their minimally invasive character, compared to their conventional preformed counterparts. Despite recent advances in material developments, a hydrogel that exhibits both proper injectability and sufficient intrinsic adhesion is yet to be demonstrated. Herein, a paradigm shift is proposed toward the design of intrinsically adhesive networks for injectable and photo-curable hydrogels. The bioinspired design strategy not only provides strong adhesive contact, but also results in a wide window of physicochemical properties. The adhesive networks are based on a family of polymeric backbones where chains are modified to be intrinsically adhesive to host tissue and simultaneously form a hydrogel network via a hybrid cross-linking mechanism. With this strategy, adhesion is achieved through a controlled synergy between the interfacial chemistry and bulk mechanical properties. The functionalities of the bioadhesives are demonstrated for various applications, such as tissue adhesives, surgical sealants, or injectable scaffolds.


Assuntos
Hidrogéis , Adesivos Teciduais , Adesivos , Polímeros , Medicina Regenerativa
8.
Opt Express ; 28(22): 33767-33783, 2020 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-33115036

RESUMO

The phase sensitivity limit of Differential Phase Contrast (DPC) with partially coherent light is analyzed in details. The parameters to tune phase sensitivity, such as the diameter of illumination, the numerical aperture of the objective, and the noise of the camera are taken into account to determine the minimum phase contrast that can be detected. We found that a priori information about the sample can be used to fine-tune these parameters to increase phase contrast. Based on this information, we propose a simple algorithm to predict phase sensitivity of a DPC setup, which can be performed before the setup is built. Experiments confirm the theoretical findings.

9.
Opt Express ; 28(16): 23433-23438, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32752340

RESUMO

We demonstrate the first all-fiber multimode spatiotemporally mode-locked laser. The oscillator generates dissipative soliton pulses at 1036 nm with 12 mW average power, 6.24 ps duration, and 24.3 MHz repetition rate. The reported pulse energy (0.5 nJ) represents ∼4 times improvement over the previously reported single-mode all-normal dispersion mode-locked lasers with multimode interference-based filtering. Numerical simulations are performed to investigate the cavity and spatiotemporal mode-locking dynamics. The all-fiber oscillator we present shows promise for practical use since it can be fabricated simply.

10.
Opt Express ; 27(2): 1090-1098, 2019 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-30696180

RESUMO

We report on a sapphire fiber Raman imaging probe's use for challenging applications where access is severely restricted. Small-dimension Raman probes have been developed previously for various clinical applications because they show great capability for diagnosing disease states in bodily fluids, cells, and tissues. However, applications of these sub-millimeter diameter Raman probes were constrained by two factors: first, it is difficult to incorporate filters and focusing optics at such small scale; second, the weak Raman signal is often obscured by strong background noise from the fiber probe material, especially the most commonly used silica, which has a strong broad background noise in low wavenumbers (<500-1700 cm-1). Here, we demonstrate the thinnest-known imaging Raman probe with a 60 µm diameter Sapphire multimode fiber in which both excitation and signal collection pass through. This probe takes advantage of the low fluorescence and narrow Raman peaks of Sapphire, its inherent high temperature and corrosion resistance, and large numerical aperture (NA). Raman images of Polystyrene beads, carbon nanotubes, and CaSO4 agglomerations are obtained with a spatial resolution of 1 µm and a field of view of 30 µm. Our imaging results show that single polystyrene bead (~15 µm diameter) can be differentiated from a mixture with CaSO4 agglomerations, which has a close Raman shift.

11.
Methods ; 136: 17-23, 2018 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-29162547

RESUMO

Phase imaging provides intensity contrast to visualize transparent samples such as found in biology without any staining. Among them, digital holographic microscopy (DHM) is a well-known quantitative phase method. Lensfree implementations of DHMs offer the added advantage to provide large field of views (several mm2 compared to several hundred µm2) and more compact setups that traditional DHM which have high quality microscope objectives. In this article, a lensfree DHM is presented using a side illumination technique in order to further reduce the device size. Its practical use is described and results on a transparent (phase only) sample are shown.


Assuntos
Holografia/métodos , Lentes , Microscopia/métodos , Humanos , Processamento de Imagem Assistida por Computador
12.
Opt Express ; 26(6): 6785-6795, 2018 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-29609366

RESUMO

The observation of retinal cellular structures is fundamental to the understanding of eye pathologies. However, except for rods and cones, most of the retinal microstructures are weakly reflective and thus difficult to image with state of the art reflective optical imaging techniques such as optical coherence tomography. Recently, we demonstrated the possibility of obtaining the phase contrast of retinal cells in the eye using oblique illumination of the retina. Indeed, by illuminating the eye with incoherent oblique illumination, we obtain a secondary oblique illumination from the backscattered light which can then be used to obtain phase contrast in an effective transmission-like configuration. In this technique, a weak phase signal is modulated over an intense background. Maximizing this phase contrast is thus crucial for the image quality. Here, we investigate the parameters that affect phase contrast by modelling image formation with the backscattered light. We find that the key parameter for maximizing contrast is the intensity profile of the backscattered light. Specifically, the gradient of the profile is found to be proportional to the phase contrast. We validate the model by comparing simulations with experimental results on ex-vivo retina samples.


Assuntos
Microscopia de Contraste de Fase , Retina/diagnóstico por imagem , Retina/efeitos da radiação , Espalhamento de Radiação , Animais , Humanos , Luz , Suínos
13.
Opt Express ; 26(2): 1766-1778, 2018 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-29402046

RESUMO

Two-photon polymerization (TPP) processes have enabled the fabrication of advanced and functional microstructures. However, most TPP platforms are bulky and require the use of expensive femtosecond lasers. Here, we propose an inexpensive and compact alternative to TPP by adapting an endoscopic imaging system for single-photon three-dimensional microfabrication. The wavefront of a visible continuous-wave laser beam is shaped so that it focuses into a photoresist through a 5 cm long ultra-thin multimode optical fiber (∅70 µm, NA 0.64). Using this device, we show that single-photon polymerization can be confined to the phase-controlled focal spot thanks to the non-linearity of the photoresist, likely due to oxygen radical scavenging. Thus, by exploiting this non-linearity with a specific overcuring method we demonstrate single-photon three-dimensional fabrication of solid and hollow microstructures through a multimode fiber with a 1.0-µm lateral and 21.5-µm axial printing resolution. This opens up new possibilities for advanced and functional microfabrication through endoscopic probes with inexpensive laser sources.

14.
Opt Lett ; 43(8): 1654-1657, 2018 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-29652332

RESUMO

We report on a method to increase the spatial resolution in a compact lensless microscope. A compact side illumination is fabricated to illuminate the sample with a collimated beam by diffraction from a volume phase grating. The wavelength of a semi-conductor laser source (vertical-cavity surface-emitting laser) is tuned with the injection current to alter the illumination direction by wavelength selective diffraction from the volume phase grating. The angle tuning is such that several subpixel shifted digital inline holograms are obtained. The stack of holograms is then processed in a pixel super-resolution reconstruction algorithm. The amplitude of the sample is reconstructed with subpixel resolution over a large field of view (FOV). The technique is demonstrated on a 1951 USAF test target. A resolution of ∼2.76 µm, over a FOV of ∼28 mm2, is demonstrated for a device of <2 cm height. The original pixel size was 5.2 µm demonstrating the subpixel resolution.

15.
Opt Express ; 25(14): 16652-16659, 2017 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-28789166

RESUMO

Current compact lensless holographic microscopes are based on either multiple angle in-line holograms, multiple wavelength illumination or a combination thereof. Complex computational algorithms are necessary to retrieve the phase image which slows down the visualization of the image. Here we propose a simple compact lensless transmission holographic microscope with an off-axis configuration which simplifies considerably the computational processing to visualize the phase images and opens the possibility of real time phase imaging using off the shelf smart phone processors and less than $3 worth of optics and detectors, suitable for broad educational dissemination. This is achieved using a side illumination and analog hologram gratings to shape the reference and signal illumination beams from one light source. We demonstrate experimentally imaging of cells with a field of view (FOV) of ~12mm2, and a resolution of ~3.9µm.

16.
Opt Express ; 25(6): 6263-6273, 2017 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-28380979

RESUMO

Light propagation in multimode fibers is typically assumed to be extremely sensitive to changes in geometry. We study here a particular configuration where an S-shaped bend is translated between two sections of fiber. In this sliding bend configuration, we show that nearly constant propagation characteristics can be obtained in certain fibers. Several fibers were tested using a bend with a peak radius of curvature of 25 mm. We found large differences in bending behavior between fibers of varying core diameters and numerical apertures. Fibers with a large numerical aperture are found to be more stable. In several fibers, the bend can be translated over a distance of 25 mm with a limited impact on imaging performance. The experimental results are confirmed using simulations. Our findings shed a new light on bending sensitivity in multimode fibers, and open up more possibilities for their use as imaging devices.

17.
Opt Express ; 25(4): 4438-4445, 2017 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-28241646

RESUMO

Lensless quantitative phase imaging is of high interest for obtaining a large field of view (FOV), typically the size of the camera chip, to observe biological cell material with high contrast. It has the potential to be widely spread due to its inherent simplicity. However, the tradeoff is the added complexity due to the illumination. Current illumination systems are several centimeters away from the sample, use mechanics to obtain super resolution (i.e., smaller than the detector pixel size) or different illumination directions, and block the view to the sample. In this paper, we propose and demonstrate a side illumination system which reduces the height by an order of magnitude while providing an unobstructed view of the sample. We achieve this by shaping the illumination using multiplexed analog holograms that produce 9 illumination angles. We demonstrate experimentally imaging of phase samples with a FOV of ~17mm2.

18.
Opt Express ; 25(10): 11491-11502, 2017 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-28788714

RESUMO

Ultrashort pulse ablation has become a useful tool for micromachining and biomedical surgical applications. Implementation of ultrashort pulse ablation in confined spaces has been limited by endoscopic delivery and focusing of a high peak power pulse. Here we demonstrate ultrashort pulse ablation through a thin multi-core fiber (MCF) using wavefront shaping, which allows for focusing and scanning the pulse without requiring distal end optics and enables a smaller ablation tool. The intensity necessary for ablation is significantly higher than for multiphoton imaging. We show that the ultimate limitations of the MCF based ablation are the nonlinear effects induced by the pulse in the MCFs cores. We characterize and compare the performance of two devices utilizing a different number of cores and demonstrate ultrashort pulse ablation on a thin film of gold.

19.
Opt Express ; 25(6): 7031-7045, 2017 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-28381044

RESUMO

3D printing based on additive manufacturing is an advanced manufacturing technique that allows the fabrication of arbitrary macroscopic and microscopic objects. Many 3D printing systems require large optical elements or nozzles in proximity to the built structure. This prevents their use in applications in which there is no direct access to the area where the objects have to be printed. Here, we demonstrate three-dimensional microfabrication based on two-photon polymerization (TPP) through an ultra-thin printing nozzle of 560 µm in diameter. Using wavefront shaping, femtosecond infrared pulses are focused and scanned through a multimode optical fiber (MMF) inside a photoresist that polymerizes via two-photon absorption. We show the construction of arbitrary 3D structures built with voxels of diameters down to 400 nm on the other side of the fiber. To our knowledge, this is the first demonstration of microfabrication through a multimode optical fiber. The proposed printing nozzle can reach and manufacture micro-structures in otherwise inaccessible areas through small apertures. Our work represents a new area which we refer to as endofabrication.

20.
Opt Express ; 24(24): 27791-27804, 2016 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-27906347

RESUMO

We demonstrate the potential of spatial light modulators for the spectral control of a broadband source in digital holographic microscopy. Used in a 'pulse-shaping' geometry, the spatial light modulator provides a versatile control over the bandwidth and wavelength of the light source. The control of these properties enables adaptation to various experimental conditions. As a first application, we show that the source bandwidth can be adapted to the off-axis geometry to provide quantitative phase imaging over the whole field of view. As a second application, we generate sequences of appropriate wavelengths for a hierarchical optical phase unwrapping algorithm, which enables the measurement of the topography of high-aspect ratio structures without phase ambiguity. Examples are given with step heights up to 50 µm.

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