The present invention is directed to an achromatic capsule endoscope with diffractive optics. A micromotor (or a broadband rotary joint) and a custom 800 nm SD-OCT system make ultrahigh-resolution 3D volumetric imaging over a large area possible. The diffractive microlens is used directly with other miniature lens including but not limited to a GRIN lens, making the capsule endoscope design simpler and cost effective. Preliminary ex vivo 3D intraluminal imaging was performed with the distal-scanning capsule endoscope in conjunction with a home-built broadband spectral-domain OCT system, demonstrating the performance of the diffractive capsule. Considering the miniature OCT capsule imaging probe is an attractive component for using the OCT technology for esophagus imaging (or other internal organs), the proposed approach will have a broad impact on endoscopic OCT imaging by improving OCT resolution in any applications that involve a capsule OCT probe, such as gastrointestinal (GI) tract imaging, airway imaging etc.