Super-fast lensless images through a thin fiber
A smart signal processing technique combined with ultra-thin optical fiber and just a single light sensitive sensor could revolutionise endoscopy (looking inside) methods. Scientists at the Vrije University of Amsterdam for the first time demonstrated compressive endo-microscopy: Super-sharp video-mode images via ultrathin probe.
11/06/2018 | 11:25 AM
Optical imaging via ultrathin probes is the only way to look deep inside the human body in a minimally invasive manner. The traditional methods of endoscopy use a flexible tube with a light and camera attached to it and can only examine the interior of a hollow organ of the body. Modern endoscopes are based on a fiber-bundle and have a much broader range of applications. Unfortunately, the resolution of such endoscopes is several micrometres at best. This is not enough to see fine features within biological cells. An alternative is endoscopes based on 'multimode' fibers, which uses only a large single core to transmit an entire image. Unfortunately, the image becomes scrambled as it passes through the fiber and requires a complex, slow and expensive elements (spatial light modulators) to perform this unscrambling.
VENI laureate Dr Lyubov Amitonova and Prof Dr Johannes de Boer have now shown that these limitations can be overcome. They have demonstrated super-sharp ultra-high speed images through a tiny single-core fiber with no lens, spatial light modulators or camera needed.
One of the key component of novel endoscopy method is compressive sensing: an imaging paradigm that goes against the common view in data acquisition. We use compression in everyday life often without noticing, for example, to store images with modern codecs such as JPEG-2000. Compressive imaging implements such compression already at the signal acquisition stage. The image data that would be discarded in compression are never measured, leading to a significant speed-up of the imaging process. It also means that we can recover images from far fewer measurements than traditional methods in use.
Scientists showed that the light fields generated in a multimode fiber represent an excellent basis for compressive sensing. Using compressive sensing approach in combination with a multimode fiber probe they have succeeded in high-resolution imaging in endoscopic format with the total number of measurements 20 times less than is required for the standard raster scanning approach. This revolutionary endoscopy method has a number of advantages. Firstly, the tiny amount of data is required to retrieve an image. It allows to speed-up imaging process more than an order of magnitude keeping the same spatial resolution. Second, without a lens, these images suffer none of the aberrations and focusing problems associated with lenses. Finally, it doesn’t require expensive instruments and complex procedures of fiber characterizations for ‘unscrambling’.
This research has been made possible by funding from the Netherlands Organisation for Scientific Research (NWO) (VENI 15872).
Examples of the illumination patterns (left) used for conventional raster scanning endoscopy (top) and novel compressive endoscopy (bottom) and received images of a sample.
Dr. Lyubov Amitonova
Lyubov V. Amitonova and Johannes F. de Boer, “Compressive imaging through a multimode fiber” Optics Letters 43, 5427 (2018)