Single-shot multiple-depth macroscopic imaging by spatial frequency multiplexing

We present a low-coherence interferometric imaging system designed for 3-dimensional (3-D) imaging of a macroscopic object through a narrow passage. Our system is equipped with a probe-type port composed of a bundle fiber for imaging and a separate multimode optical fiber for illumination. To eliminate the need for mechanical depth scanning, we employ a spatial frequency multiplexing method by installing a 2-D diffraction grating and an echelon in the reference arm. This configuration generates multiple reference beams, all having different path lengths and propagation directions, which facilitates the encoding of different depth information in a single interferogram. We demonstrate the acquisition of 9 depth images at the interval of 250 µm for a custom-made cone and a plaster teeth model. The proposed system minimizes the need for mechanical scanning and achieves a wide range of depth coverage, significantly increasing the speed of 3-D imaging for macroscopic objects.