Recently a group of scientists from the Dresden University of Technology has presented a developed compact self-calibrating endoscope based on the fiber optic technology that offers to capture 3D images of objects smaller than a single cell. The composition of such an optical fiber endoscope does not include a lens or any optical, electrical, or mechanical components, herewith, the tip of the fiber optic system is just 200 μm across.
The operation of a self-calibrating fiber optic endoscope became possible due to the addition of a 150-μm-thick glass plate to the tip of a coherent fiber optic bundle that is considered to be a type of optical fiber that is generally used for endoscopic applications. It should be noted that the width of the fiber bundle is about 350 μm, and this fiber optic technology includes 10,000 cores.
The principle of optical fiber operation is the following: at the moment when the central optical fiber core is illuminated, it produces a beam that is returned into the fiber optic bundle. Additionally, the beam operates there as a reference point for measuring the transfer of light, which offers the required information for the endoscopic fiber bundle to calibrate itself as necessary.
Also, the developed fiber optic technology includes a spatial light modulator for manipulation of the light direction resulting in remote focusing and a camera that captures the back-reflected light from the fiber optic bundle. The back-reflected light, in its turn, is superimposed with a reference wave to gage the light phase. The thing is that the beam position that is reflected in the endoscopic fiber bundle points the focus of the fiber optic system with a minimum diameter of the focus of about 1 μm.
An adaptive lens and a 2D galvometer mirror to change the focus and allow scanning at various depths are required for the production of the optical fiber device. The new fiber optic technology was tested by using the endoscope to image a 3D specimen under a 140-μm-thick coverslip. According to the researchers, “when scanning the image plane in 13 steps over 400 μm with an image rate of 4 cycles per second, the endoscopic fiber bundle successfully imaged particles at the top and bottom of the 3D specimen”.
Although the focus of the optical fiber endoscope deteriorated as the galvometer mirror’s angle increased, this obstacle could be overcome in future improvements. Additionally, the fiber optic technology applying a galvometer scanner with a higher frame rate advances faster image acquisition.
Finally, the minimally invasive fiber optic device offers high-contrast imaging and reliable stimulation, while its self-calibration opportunities will enable to withstand bending or twisting of the optical fiber. Therefore, this endoscopic fiber optic bundle can be employed in optogenetics to stimulate cellular activity and during medical procedures to monitor cells and tissue.
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