Structured Illumination System Research Articles

Miniaturization of a coherent monocular structured illumination system for future combination with digital holography

Holographic and 3D-measurement processes are an often-used tool in industry, medicine, and scientific applications. While small deviations of objects can be visualized by holographic means with high accuracy, optical systems with active structured illumination are a reliable source of absolute 3D-information in these fields. The combination of digital holography with structured illumination allows to simultaneously measure deformations and absolute 3D coordinates but also requires coherent light and has already been demonstrated in principle with a stereo camera setup. Multi-camera systems are limited to certain setup sizes given by the volume and distance of the detectors. Reducing the system to a one-camera (monocular) setup reduces space and acquisition costs. By using a multi-aperture illumination source an extremely high projection rate could be realized and reduced to a monocular approach with a novel voxel-calibration technique, while the projection system itself still requires a large amount of space. In this paper we present a miniaturized, monocular 3D-measurement system that works with repeatable, coherent speckles, generated by a fiber-coupled laser whose light was distributed by a fiber-switch to a diffuser plate connected with a measurement-head, also including a camera. By addressing different fibers through the switch, varying but repeatable patterns are generated. The size of the device (diameter < 3 cm) is now mainly limited by the volume of the camera. A first 3D-reconstruction of an object and an outlook for a combination of this system with digital holography is given, allowing absolute 3D-coordinates and relative deviations of object points to be measured simultaneously.

Simultaneous full-color single-pixel imaging and visible watermarking using Hadamard-Bayer illumination patterns

We present two novel techniques in single-pixel imaging (SPI): the first one is Hadamard-Bayer SPI in which the Hadamard-Bayer illumination patterns are employed for fast full-color SPI, with a sampling rate and computational complexity that are one-third of the full-sampling condition; the second one encodes spatial information of an image into time-varying factors in SPI and loads them into the illumination patterns, enabling high-quality single-pixel image fusion. Furthermore, we fuse these two techniques to achieve full-color visible watermarking while imaging. Theory, simulations, and experiments confirm the feasibility of the schemes. These techniques have high scalability and wide application prospects, and possess the potential to be applied in LED structured illumination systems, single-pixel multi-spectral imaging systems, and single-pixel broadcast systems.

Wollaston prism-based structured illumination microscope with tunable frequency.

This work proposes an alternative structured illumination (SI) system based on a Wollaston prism (WP) illuminated by the diffracted field of an incoherent linear source. The proposed WP-based SI system presents several advantages. First, the generated fringes can be approximated by a pure sinusoidal pattern; thereby, computational methods developed for sinusoidal SI can be used without the need for additional processing. Second, the SI pattern's period can be continuously varied up to the cutoff frequency of the native widefield system. Most significantly, the phase shifting of the SI pattern required for demodulation in SI microscopy can be easily accomplished using a de Sénarmont compensator, which provides accurate lateral displacement of the fringes independently of the lateral modulation frequency. Experimental verifications confirm the presented theoretical predictions.

Fast structured illumination microscopy using rolling shutter cameras

Spatial light modulators (SLM) update in a synchronous manner, whereas the data readout process in fast structured illumination systems is usually done using a rolling shutter camera with asynchronous readout. In structured illumination microscopy (SIM), this leads to synchronization problems causing a speed limit for fast acquisition. In this paper we present a configuration to overcome this limit by exploiting the extremely fast SLM display and dividing it into several segments along the direction of the rolling shutter of the sCMOS camera and displaying multiple SLM frames per camera acquisition. The sCMOS runs in continuous rolling shutter mode and the SLM keeps the readout-line always inside a dark region presenting different SIM patterns before and after the readout/start-exposure line.Using this approach, we reached a raw frame rate of 714 frames per second (fps) resulting in a two-beam SIM acquisition rate of 79 fps with a region of interest (ROI) of 16.5 × 16.5 μm2.

Grating imager systems for fluorescence optical-sectioning microscopy.

In fluorescence microscopy, optical sectioning is defined as the attenuation or removal of out-of-focus features from an image, and it is a prerequisite for quantitative analysis of three-dimensional structure or function within the specimen. Optical sectioning is most commonly performed by confocal scanning fluorescence microscopy or two-photon scanning fluorescence microscopy. However, structured illumination can be used in conventional fluorescence microscopes to obtain optical sectioning performance, and, in advanced systems, 3D superresolution. The simplest structured-illumination system uses a Ronchi grating as a mask to project parallel stripes within the sharp depth-of-focus of the objective to encode in-focus specimen features differently from out-of-focus features. By shifting the grating, the in-focus image component can be discriminated and separated by elementary image processing operations. This implementation of structured illumination, the fluorescence grating imager, uses a conventional light source, is compatible with all high-quality fluorescence filter sets, and provides high optical-sectioning performance when used to image specimens in which (1) the out-of-focus image component is not much brighter than the in-focus features and (2) there is no significant movement in the specimen during the grating shift and image capture process.

Enhanced extended range underwater imaging via structured illumination

In this article, the utility of structured illumination in order to enhance the contrast and subsequent range capability of an underwater imaging system is explored. The proposed method consists of transmitting a short pulse of light in a grid like pattern that consists of multiple, narrow, delta-function like beams. The grid pattern can be arranged in either a one-dimensional line or an area as a two-dimensional pattern. Scanning the pattern in time results in the sequential illumination of the entire scene. The receiving system architecture imposes the exact same, grid-like pattern sensitivity on the reflected light with a simple subsequent superposition of the time-sequenced images. The system can be viewed as a parallel implementation of a Laser Line Scan System where multiple beams are projected and received instead of a single one. The performance enhancement over more conventional systems that project either a sheet or an area of light is compared for a challenging underwater environment via computer simulations. The resulting images are analyzed as a function of the spacing between the projected light beams to characterize contrast and resolution. The results indicate that reasonable gains are obtainable for close spacing between the beams while quite significant gains are predicted for larger ones. Structured illumination systems can therefore collect images more rapidly than systems that scan a single beam; however with concomitant trade-offs in contrast and resolution.

Quantization of widefield fluorescence images using structured illumination and image analysis software

It is difficult to obtain precise quantitative measurements from fluorescent images captured from widefield microscopes. We wished to ascertain if reliable quantitative measurements of both biological and nonbiological specimens were possible using a widefield microscope equipped with a structured illumination system and image analysis software. In a nonbiological specimen, images were obtained from fluorescent beads of known intensity. For a biologically relevant model we used the uptake of fluorescently labeled transferrin by HeLa cells in culture. In the bead sample, the mean intensity of beads acquired with the structured illumination system showed relative intensities near to the predicted values without any further manipulation of data. In the transferrin uptake experiments, uptake and subsequent recycling of the labeled transferrin could be accurately and reproducibly measured. We conclude that using a combination of structured illumination and image processing algorithms accurate quantization of fluorescent images can be achieved in widefield microscopy.