For the first time ever, a combination of industry and academia has achieved optical coherence tomography (OCT) imaging of cubic meters of volume. Thanks to the OCT's ability to provide inaccessible information on material composition, subsurface structure, coating, surface roughness, and other properties, this advance opens up many new OCT uses in industry, manufacturing and medicine. This achievement also represents an important advance in the development of high-speed, low-cost OCT systems on a single integrated circuit chip.
"Our results create a world record in cubic meter volumetric imaging, at least an order of magnitude greater in depth and volume than previous 3D OCT demonstration models," James G. of the Massachusetts Institute of Technology (Massachusetts) said. Fujimoto said. "These results provide a rationale for the use of OCT in this new field."
OCT, the OCT technology first invented by Fujimoto's research group and its collaborators in the 1990s, has now become the standard test in the field of ophthalmology and is increasingly used in heart disease and gastrointestinal disorders . Although OCT provides a useful three-dimensional image with micrometer-scale resolution, its imaging depth is limited to a few millimeters to a few centimeters.
A new 3D OCT technique for imaging large human bodies such as this life-size human body model and board.
In the Journal of Optics, a high-impact research journal for the American Optical Society, the researchers reported high-speed 3D OCT with 15-micron resolution over a 1.5-meter area. They demonstrated their new OCT imaging method by imaging a human body model, a bicycle, and a model of the human brain and skull. They also measured objects that range in size from meters to microns.
Long range of a variety of scales
In addition to the advantages of high speed and high resolution, OCT enables imaging, profile and distance measurements at multiple depths to be performed simultaneously without stray light.
"Long-range OCT is a new class of work that requires very high-performance light sources, integrated optical receivers and signal processing," said Fujimoto. The range referred to in the OCT is the range of depth over which measurements can be made simultaneously. It is possible to place the center of the OCT range in a position very close or very far from the imaging instrument.
This new technology is particularly useful for industrial and manufacturing environments where it can be used to monitor processes, perform technical measurements and non-destructive evaluation of materials. Macro-scale OCT can also enhance medical imaging, for example, providing three-dimensional measurements during laparoscopy or providing mapping of the upper respiratory tract.
Advances in telecommunications have brought OCT technology improvements
A light source that enables OCT on a meter scale is a tunable vertical cavity surface emitting laser (VCSEL) developed by Thorlabs and Praevium Research. It employs MEMS devices to perform so-called sweep source optical coherence tomography with rapid changes over time or by scanning the wavelength of the laser.
"Our research at the Massachusetts Institute of Technology and our collaborators from Thorlabs and Praevium Research Inc. shows that the coherence length of VCSEL light sources is several orders of magnitude longer than other suitable scanning laser techniques for OCT, suggesting that long-range OCT imaging "Said Ben Potsaid of MIT and Thorlabs, one of the co-authors of the paper.
Although MIT researchers have been experimenting with VCSEL light sources for many years, light detection and data acquisition remain a challenge. These obstacles are overcome by advanced optics designed for telecom applications.
In this new work, researchers used a new silicon photonic coherent optical receiver developed by Acacia Communications to replace several with a tiny, low-cost, single-chip photonic integrated circuit (PIC) Large volume OCT components. More importantly, the PIC receiver supports the very high electrical frequencies and the very wide optical wavelength range required to scan the source OCT, while allowing for so-called quadrature detection, which allows OCT at a given data acquisition rate Imaging range has doubled.
"The development of OCT technology in the early 1990s benefited from the devices and methods used in optical fiber communications," said Fujimoto. "Twenty-five years later, advances in the optical communications industry continue to drive OCT technology."
In the paper, the researchers demonstrated that OCTs in the meter range can obtain strong signals from different shapes and material surfaces. Their experiments also show that the performance of the technology has not reached the principle limits of a VCSEL laser source or a PIC receiver.
On-chip OCT
Researchers are working to develop and utilize cheaper and faster components to speed up data acquisition and processing steps. This may eventually make real-time OCT imaging with custom integrated circuit chips possible.
"As PIC technology continues to evolve, one can expect OCT systems to be integrated onto a single chip in the next five years, dramatically reducing size and cost," said Chris Doerr of Acacia Communications, a co-author of the paper one. "It will benefit more people around the world from OCT technology and open up new applications."
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