Optical coherence tomography (OCT) has wide applications in diagnosing diseases, benefitting from its non-invasive, high-resolution, and real-time visualization of tissue microstructures. Still, this technology faces the mutual constraint between transverse resolution and depth of focus. Metalens can modulate the light fields at subwavelength scales, effectively enhancing the depth of focus of an OCT system. In this paper, a metalens designed for the OCT system is proposed. The metalens with different structures can generate various phase modulation outcomes. Using the finite-difference time-domain (FDTD) simulation, the impacts of the nanopillar parameters (e.g. height, diameter, and spacing) and the materials (e.g. Si, SiO2, and TiO2) on phase modulation have been analyzed. Based on the simulation results, the phase modulation capability of nanopillars is compromised at reduced heights, while excessively tall structures can adversely decrease transmittance. With a constant height, the radius of the nanopillars can be manipulated to achieve a phase delay of 2π. Furthermore, the propagation efficiency and the typical depth of focus were calculated from the results of the beam intensity distribution, indicating an enhanced imaging performance of the OCT system. The results provide a basis for designing the metalens used in the OCT systems.
Optical coherence tomography (OCT) is widely used in ophthalmology and has been a standard method for diagnosing ocular diseases. Improving spatial resolution is crucial for the visualization of ocular microstructure. In conventional OCT systems, enhanced transverse resolution typically results in a reduction of depth of field (DOF). In our study, we designed four metalenses with different microstructures and then integrated them into the sample arm of an OCT imaging system. The metalens can modulate the amplitude and the phase of incident light in the sample. In this way, the depth of focus in the OCT system can be effectively enhanced while maintaining the transverse resolution. Also, the impact of different parameters, such as the size and the spacing of micro-units, has been discussed for OCT imaging. Finally, the experiment on the glass slides has been conducted to validate the performance of OCT imaging. The results demonstrate that the metalens with a specific microstructure could effectively enhance the DOF of OCT imaging. Furthermore, the enhanced depth of focus of the OCT system opens up new opportunities for investigating tissue morphology and function.
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