arXiv subjects

Muralidhar Madabhushi Balaji

Publications and source records attributed to Muralidhar Madabhushi Balaji.

5 recordsLinked to original sources

arXiv2026

Lensless wide-field 3D fiber endoscopy through scattering media using synthetic wavelength holography

Minimally invasive imaging with fiber optic endoscopes is crucial for in vivo visualization of tissue morphology, as it supports applications such as early detection of tumors. However, imaging performance of conventional fiber endoscopes is limited when scattering layers are present between target and the distal end of endoscope. This limitation is particularly relevant in biomedicine, where targets such as early stage lesions or blood clots can be obscured by scattering tissue. To address this challenge, we present a lensless endoscopic imaging approach based on synthetic wavelength holography (SWH). SWH is a computational imaging technique in which two optical fields acquired at closely spaced wavelengths are combined to synthesize a field at a longer synthetic wavelength. As the field at longer wavelengths is less sensitive to path length perturbations, this approach can enable endoscopic recovery of holographic information despite scattering in the intervening tissue. In addition, because the synthetic field is assembled from scattered optical fields with larger optical étendue, our approach can extend the field of view (FoV) beyond the numerical aperture of the fiber. In this paper, we present the first demonstration of an SWH-based lensless endoscope using a multicore multimode fiber. We experimentally recover three-dimensional images of objects hidden behind scattering layers and through real biological tissue, with a spatial resolution of $\approx 500~μm$. We further demonstrate recovery of object information over an extended FoV of 46° without any distal optics. These results suggest a practical path toward extending fiber endoscopy for wide-field, three-dimensional imaging through scattering media.

physics.optics↗

arXiv2026

Synthetic Light-in-Flight

Light-in-flight (LiF) measurements enable the visualization of light paths through arbitrary, volumetric scenes, making light-matter interactions at ultrafast timescales visible. Traditionally, LiF measurements require specialized equipment, such as ultrashort pulse light sources and high-speed electronics, often limited by low spatial resolution. Herein, we introduce a novel computational approach, "Synthetic Light-in-Flight" (SLiF), that overcomes these constraints by relying solely on tunable, continuous wave (CW) lasers and off-the-shelf CMOS cameras. From multiple CW scene measurements at different optical wavelengths, we create multiple "synthetic fields," each at a "synthetic wavelength," which is the beat wave of two respective optical waves. These synthetic fields are robust to speckle and environmental fluctuations, enabling us to combine multiple synthetic fields into a "synthetic light pulse" that sections the volumetric scene at much lower instantaneous peak illumination power than a comparable physical light pulse. We experimentally demonstrate the generation of synthetic pulses with 1 ps-scale width and show that their complex synthetic pulse fields can be freely manipulated in the computer after their acquisition, allowing for spatial and temporal shaping of different sets of pulses from the same set of measurements to maximize the decoded information output for each scene. Finally, we show that the recovered time-of-flight information can be used to characterize physical scene properties, such as depth and refractive indices.

physics.optics↗

arXiv2025

Intensity-Correlation Synthetic Wavelength Imaging in Dynamic Scattering Media

Imaging through dynamic scattering media, such as biological tissue, presents a fundamental challenge due to light scattering and the formation of speckle patterns. These patterns not only degrade image quality but also decorrelate rapidly, limiting the effectiveness of conventional approaches, such as those based on transmission matrix measurements. Here, we introduce an imaging approach based on second-order correlations and synthetic wavelength holography (SWH) to enable robust image reconstruction through thick and dynamic scattering media. By exploiting intensity speckle correlations and using short-exposure intensity images, our method computationally reconstructs images from a hologram without requiring phase stability or static speckles, making it inherently resilient to phase noise. Experimental results demonstrate high-resolution imaging in both static and dynamic scattering scenarios, offering a promising solution for biomedical imaging, remote sensing, and real-time imaging in complex environments.

physics.optics↗

arXiv2025

A Multisensory Approach to Probing Scattering Media

Non-invasive detection of objects embedded inside an optically scattering medium is essential for numerous applications in engineering and sciences. However, in most applications light at visible or near-infrared wavebands is scattered by the medium resulting in the obscuration of the embedded objects. Existing methods to overcome scattering generally rely on point-by-point scanning strategies, which limit spatial sampling density. In this work, we address the sampling limitations by drawing inspiration from multisensory integration mechanisms observed in nature, wherein distinct sensing modalities work together to enhance the perception of the surroundings. Our multisensory approach leverages the unique advantages of coherent light by combining the sensitivity of an interferometric LiDAR with a wide field neuromorphic sensor to probe objects inside a densely scattering medium. The neuromorphic camera provides wide field spatial cues of the embedded object, by monitoring the fluctuations in the speckle patterns produced by tuning the laser frequency. These spatial cues are used to guide a point-scanning FMCW LiDAR to retrieve high-resolution images. Using this approach, we imaged objects embedded within an 8 cm thick (>100 transport mean free paths), tissue-like scattering medium with a 10x improvement in sampling density compared to traditional uniform sampling.

physics.optics↗

arXiv2025

Fiber Endoscopy Using Synthetic Wavelengths for 3D tissue imaging

Fiber-based endoscopes utilizing multi-core fiber (MCF) bundles offer the capability to image deep within the human body, making them well-suited for imaging applications in minimally invasive surgery or diagnosis. However, the optical fields relayed through each fiber core can be significantly affected by phase scrambling from height irregularities at the fiber ends or potential multi-mode cores. Moreover, obtaining high-quality endoscopic images commonly requires the fiber tip to be placed close to the target or relies on the addition of a lens. Additionally, imaging through scattering layers after the fiber tip is commonly not possible. In this work, we address these challenges by integrating Synthetic Wavelength Imaging (SWI) with fiber endoscopy. This novel approach enables the endoscopic acquisition of holographic information from objects obscured by scattering layers. The resulting endoscopic system eliminates the need for lenses and is inherently robust against phase scrambling caused by scattering and fiber bending. Using this technique, we successfully demonstrate the endoscopic imaging of features approximately 750micrometers in size on an object positioned behind a scattering layer. This advancement represents significant potential for enabling spatially resolved three-dimensional imaging of objects concealed beneath tissue using fiber endoscopes, expanding the capabilities of these systems for medical applications.

physics.optics↗