We describe a method to image objects through scattering media based on single-pixel detection and microstructured illumination. Spatial light modulators are used to project a set of microstructured light patterns onto the sample. The image is retrieved computationally from the photocurrent fluctuations provided by a single-pixel detector. This technique does not require coherent light, raster scanning, time-gated detection or a-priori calibration process. We review several optical setups developed by our research group in the last years with particular emphasis in a new optical system based on a double-pass configuration and in the combination of single-pixel imaging with Fourier filtering.
There are several ophthalmic devices to image the retina, from fundus cameras capable to image the whole fundus to
scanning ophthalmoscopes with photoreceptor resolution. Unfortunately, these devices are prone to a variety of ocular
conditions like defocus and media opacities, which usually degrade the quality of the image. Here, we demonstrate a
novel approach to image the retina in real-time using a single pixel camera, which has the potential to circumvent those
optical restrictions. The imaging procedure is as follows: a set of spatially coded patterns is projected rapidly onto the
retina using a digital micro mirror device. At the same time, the inner product’s intensity is measured for each pattern
with a photomultiplier module. Subsequently, an image of the retina is reconstructed computationally. Obtained image
resolution is up to 128 x 128 px with a varying real-time video framerate up to 11 fps. Experimental results obtained in
an artificial eye confirm the tolerance against defocus compared to a conventional multi-pixel array based system.
Furthermore, the use of a multiplexed illumination offers a SNR improvement leading to a lower illumination of the eye
and hence an increase in patient’s comfort. In addition, the proposed system could enable imaging in wavelength ranges
where cameras are not available.
One challenge that has long held the attention of scientists is that of clearly seeing objects hidden by turbid media, as smoke, fog or biological tissue, which has major implications in fields such as remote sensing or early diagnosis of diseases. Here, we combine structured incoherent illumination and bucket detection for imaging an absorbing object completely embedded in a scattering medium. A sequence of low-intensity microstructured light patterns is launched onto the object, whose image is accurately reconstructed through the light fluctuations measured by a single-pixel detector. Our technique is noninvasive, does not require coherent sources, raster scanning nor time-gated detection and benefits from the compressive sensing strategy. As a proof of concept, we experimentally retrieve the image of a transilluminated target both sandwiched between two holographic diffusers and embedded in a 6mm-thick sample of chicken breast.
Precise control of light propagation through highly scattering media is a much desired goal with major technological implications. Since interaction of light with turbid media results in partial or complete depletion of ballistic photons, it is in principle impossible to transmit images through distances longer than the extinction length. In biomedical optics, scattering is the dominant light extinction process accounting almost exclusively for the limited imaging depth range. In addition, most scattering media of interest are dynamic in the sense that the scatter centers continuously change their positions with time. In our work, we employ single-pixel systems, which can overcome the fundamental limitations imposed by multiple scattering even in the dynamically varying case. A sequence of microstructured light patterns codiﬁed onto a programmable spatial light modulator are used to sample an object and measurements are captured with a single-pixel detector. Acquisition time is reduced by using compressive sensing techniques. The patterns are used as generalized measurement modes where the object information is expressed. Contrary to the techniques based on the transmission matrix, our approach does not require any a-priori calibration process. The presence of a scattering medium between the object and the detector scrambles the light and mixes the information from all the regions of the sample. However, the object information that can be retrieved from the generalized modes is not destroyed. Furthermore, by using these techniques we have been able to tackle the general problem of imaging objects completely embedded in a scattering medium.
Despite imaging systems that scan a single-element benefit from mature technology, they suffer from acquisition times linearly proportional to the spatial resolution. A promising option is to use a single-pixel system that benefits from data collection strategies based on compressive sampling. Single-pixel systems also offer the possibility to use dedicated sensors such as a fiber spectrometer for multispectral imaging or a distribution of photodiodes for 3D imaging. The image is obtained by lighting the scene with microstructured masks implemented onto a programmable spatial light modulator. The masks are used as generalized measurement modes where the object information is expressed and the image is recovered through algebraic optimization. The fundamental reason why the bucket detection strategy can outperform conventional optical array detection is the use of a single channel detector that simultaneously integrates all the photons transmitted through the patterned scene. Spatial frequencies that are not transmitted through this low-quality optics are demonstrated to be present in the retrieved image. Our work makes two specific contributions within the field of single-pixel imaging through patterned illumination. First, we demonstrate that single-pixel imaging improves the resolution of conventional imaging systems overcoming the Rayleigh criterion. An analysis of resolution using a low NA microscope objective for imaging at a CCD camera shows that single-pixel cameras are not limited at all by the optical quality of the collection optics. Second, we experimentally demonstrate the capability of our technique to properly recover an image even when an optical diffuser is located in between the sample and the bucket detector.
In computational imaging by pattern projection a sequence of microstructured light patterns codified onto a programmable spatial light modulator is used to sample an object. The patterns are used as generalized measurement modes where the object information is expressed. Our paper makes two specific contributions within the field of single-pixel imaging through patterned illumination. First, we perform an analysis of the optical resolution of the computational image. This resolution is shown not to be limited at all by the optical quality of the collection optics. This result is proved by using a low NA microscope objective for imaging at a CCD camera. Spatial frequencies that are not transmitted through this low quality optics are demonstrated to be present in the retrieved image through patterned illumination. Second, we experimentally demonstrate the capability of our technique to properly recover an image even when an optical diffuser is located in between the sample and the single-pixel detector.