The present disclosure relates optical imaging devices and methods useful in biological and medical imaging applications. In one embodiment, an optical imaging device includes a flexible lightguide having a first end and a second end, the output of the source of pulsed infrared radiation being optically coupled to the first end of the flexible lightguide; a lens assembly attached to and optically coupled to the second end of the flexible lightguide, the lens assembly comprising a variable-focus lens element, the a variable-focus lens element having a tunable focal length; and a photodetector coupled to the flexible lightguide to detect radiation propagating from the second end toward the first end of the flexible lightguide. The optical imaging devices and methods can be used in both confocal and multi-photon techniques.