Mr. Vinh Tran Profile

Vinh Tran

PhD student at Nanyang Technological Univ

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Publications (3)

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Proceedings Article | 4 March 2019 Presentation

Utilizing the randomness of light propagation through scattering media for sensing application (Conference Presentation)

Vinh Tran, Sujit Sahoo, Dong Wang, Cuong Dang

Proceedings Volume 10890, 108900M (2019) https://doi.org/10.1117/12.2509829

KEYWORDS: Light scattering, Scattering media, Refractive index, Speckle pattern, Diffraction, Glasses, Environmental sensing, Scattering, Optical sensors, Cameras

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As widely known, random diffraction effect due to refractive index inhomogeneity is considered as an annoying factor for propagating light through scattering media. Here, instead of overcoming the random diffraction, we utilize the natural randomness of strongly scattering media and their sensitivity to inhomogeneity of refractive index to develop a novel optical sensor. Unlike various sensing technologies with trade-off among complexity, sensitivity and stability, here we demonstrate a very simple sensing technique which uses scattering media to achieve super sensitivity, speedy response time and possibly high stability. In our sensing principle, a lasing beam passing through a turbid medium creates a speckle pattern on a camera due to interference of random refracted light off the scattering media. Light is scattered multiple times at multiple interfaces between ground glass and the surrounding environment creating a speckle pattern which is sensitive to the environment’s refractive index. The correlation of speckle patterns indicates the change of refractive index around the scattering medium. Simply placing the rough surface of ground glass in contact with sensing solutions, we are able to measure glucose, or sodium chloride concentration with sensitivity in the order of micro grams per liter. More interestingly, the sensitivity of the proposed approach could be improved simply by adding more scattering surfaces in contact with the target medium. Therefore, our simple technique could be very useful for prominent applications in refractive index sensing such as measuring solution concentration, distinguishing different gases, detecting pressure change and so on.

Proceedings Article | 20 February 2019 Paper

Utilizing optical conjugate plane to enhance 3D focusing and forming shapes behind turbid media

Vinh Tran, Sujit Sahoo, Dongliang Tang, Cuong Dang

Proceedings Volume 10886, 108861C (2019) https://doi.org/10.1117/12.2509998

KEYWORDS: Spatial light modulators, Scattering, Cameras, Light scattering, Laser scattering, Diffusers, Phase shifts, Biomedical optics, Modulation, Optical storage

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Inner diffraction phenomenon is known as the major obstacle of light transmission through scattering media such as ground glasses, skin or biological tissue. Recently, the most effective and convenient solution is wave-front shaping technique which modulates the field profile of incident light by using a spatial light modulator (SLM). For practical and advanced biomedical applications, requirement of speedy response, high accuracy and large energy delivery are necessary. In our previous work, we presented a wave-front shaping technique and utilized optical memory effect for swiftly drawing various 2 dimensional (2D) shapes or contours through a scattering medium without any mechanical movement. However, with process of scanning angle phase profile and shifting phase pattern on SLM, the accuracy and beam energy utilization are still very much restricted. Here, we present an exceeding improvement from previous technique by establishing optical conjugate planes between SLM and scattering medium surface, which is also known as 4F system. With only one phase profile for creating a focus spot behind scattering medium, we are able to swiftly move focus spot in 3D space or draw any 3D contours through turbid medium without scanning or shifting process. The new approach allows us to deliver laser energy through a scattering medium to any spot within 3D memory effect space with very fast response, high accuracy and more importantly, fully utilized laser beam energy. Our approach demonstrates a practical method to control light through scattering media for prominent applications such as opto-genetic excitation, minimal invasive laser surgery and other related fields.

Proceedings Article | 23 February 2018 Presentation + Paper

Swiftly moving focus points and forming shapes through the scattering media

Vinh Tran, Sujit Kumar Sahoo, Dongliang Tang, Cuong Dang

Proceedings Volume 10502, 105020N (2018) https://doi.org/10.1117/12.2289747

KEYWORDS: Spatial light modulators, Scattering, Light scattering, Cameras, Scattering media, Laser scattering, Phase shifts, Alternate lighting of surfaces, Optical storage, Light wave propagation

Read Abstract +

Propagation of light through scattering media such as ground glass or biological tissue limits the quality and intensity of focusing point. Wave front shaping technique which uses spatial light modulator (SLM) devices to reshape the field profile of incoming light, is considered as one of the most effective and convenient methods. Advanced biomedical or manufacturing applications require drawing various contours or shapes quickly and precisely. However, creating each shape behind the scattering medium needs different phase profiles, which are time consuming to optimize or measure. Here, we demonstrate a technique to draw various shapes or contours behind the scattering medium by swiftly moving the focus point without any mechanical movements. Our technique relies on the existence of speckle correlation property in scattering media, also known as optical memory effect. In our procedure, we first modulate the phase-only SLM to create the focus point on the other side of scattering medium. Then, we digitally shift the preoptimized phase profile on the SLM and ramp it to tilt the beam accordingly. Now, the incoming beam with identical phase profile shines on the same scattering region at a tilted angle to regenerate the focus point at the desired position due to memory effect. Moreover, with linear combination of different field patterns, we can generate a single phase profile on SLM to produce two, three or more focus points simultaneously on the other side of a turbid medium. Our method could provide a useful tool for prominent applications such as opto-genetic excitation, minimally invasive laser surgery and other related fields.

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