Active illumination using a digital micromirror device for quantitative phase imaging

Abstract

We present a powerful and cost-effective method for active illumination using a digital micromirror device (DMD) for quantitative phase imaging techniques. Displaying binary illumination patterns on a DMD with appropriate spatial filtering, plane waves with various illumination angles are generated and impinged onto a sample. Complex optical fields of the sample obtained with various incident angles are then measured via Mach-Zehnder interferometry, from which a high-resolution two-dimensional synthetic aperture phase image and a three-dimensional refractive index tomogram of the sample are reconstructed. We demonstrate the fast and stable illumination control capability of the proposed method by imaging colloidal spheres and biological cells, including a human red blood cell and a HeLa cell.Quantitative phase imaging (QPI) has emerged as an invaluable tool for imaging small transparent objects, such as biological cells and tissues [1,2]. QPI employs various interferometric microscopy techniques, including quantitative phase microscopy [2] and digital holographic microscopy [3], to quantitatively measure the optical phase delay of samples. In particular, the measured optical phase delay provides information about the morphological and biochemical properties of biological samples at the single-cell level. Recently, QPI techniques have been widely applied to study the pathophysiology of various biological cells and tissues, including red blood cells (RBCs) [4][5][6][7], white blood cells [8], bacteria [9][10][11], neurons [12][13][14], and cancer cells [15,16].Controlling the illumination beam is crucial in QPI. Especially for measuring 3-D refractive index (RI) tomograms [17] or 2-D highresolution synthetic aperture images [18], angles of plane wave illumination impinging onto a sample should be systematically controlled, and the corresponding light field images of the sample should be measured. Traditionally, galvanometer-based rotating mirrors have been used to control the angle of the illumination beam. A galvanometer-based rotating mirror located at the plane that is conjugate to a sample can control the angle of the incident beam by tilting the mirror with a certain electric voltage.The use of galvanometers, however, has several disadvantages. Inherently, there exists mechanical instability due to position jittering induced by electric noise and positioning error at high voltages. When a two-axis galvanometer is used, the rotational surfaces of each axis cannot be simultaneously conjugate to a sample due to its geometry, and this may induce unwanted additional quadratic phase distribution on the illumination beam that can limit the accurate measurements of 3-D RI tomograms. To solve this optical misalignment, two one-axis galvanometers can be placed at separate conjugate planes, but it requires a bulky optical setup with a long optical path, which can deteriorate phase noise. More importantly, galvanometers cannot generate acomplex wavefront; only tilting of a plane wave is permitted. Recently, a spatial lig...

Refractive index tomograms and dynamic membrane fluctuations of red blood cells from patients with diabetes mellitus

“…A miniaturised QPI unit 57–59 can convert conventional bright field microscopy into a QPI system by simply attaching the unit to a microscope body with light source adjustment. QPI techniques employing DMD-based illumination schemes 60 or graphic-processing units 61 allow real-time visualisation of a 3-D microscopic object, and are expected to become an attractive imaging tool for investigating live cell dynamics. A white-light diffraction tomography 62 is free from the problem of speckle noise by using a low-coherent light source and can obtain 3-D images of individual cells with high axial resolutions.…”

Confocal retinal imaging using a digital light projector with a near infrared VCSEL source

“…DMD diffraction has been characterized in the design of laser-based custom projection systems used for wavelength tuning, 19 tunable fiber lasers, 20 quantitative phase imaging, 21 and fluorescent microscopy. 22 It is generally desired to couple as much of the illumination power into the zero order diffracted output (the specular reflection) of the micromirror when tilted into an ON state.…”

GPU-based deep convolutional neural network for tomographic phase microscopy with ℓ1 fitting and regularization

“…[4][5][6] The label-free and noninvasive character makes it attractive in biomedical imaging, especially for cultured cells. 7,8 However, most of the current methods require around 50 quantitative phase images acquired at different angles [9][10][11] or different depths 6 for optical tomography. This speed limitation greatly restricts its field of applications.…”