Imaging unit, camera head, method for manufacturing camera head, and method for attaching imaging unit

An imaging unit comprising:

• an optical element that is a gradient-index lens extending in a longitudinal direction and configured to adjust an optical path between an observation target and the imaging unit;
• a joint portion fixable to the optical element;
• and
• a camera head including a camera module, a light source disposed behind the camera module, a leading end portion that is close to the optical element and through which light from the optical element enters and light is emitted toward the optical element, and an optical fiber extending from the light source to the vicinity of the leading end portion,
• wherein the gradient-index lens, the joint portion, and the camera head are lined up along the longitudinal direction of the gradient-index lens,
• a male thread is formed around the leading end portion,
• the joint portion includes an attachment portion into which the male thread is screwed,
• the leading end portion is disposed inside the joint portion,
• the male thread and the attachment portion constitute an adjustment structure for adjusting a positional relationship between the leading end portion and the optical element in the longitudinal direction of the gradient-index lens,
• an end surface of a leading end portion of the optical fiber includes an inclined portion that is formed to incline rearward to be away from the leading end portion in the longitudinal direction of the gradient-index lens while extending outward from a center portion of the leading end portion in a direction perpendicular to the longitudinal direction of the gradient-index lens, the inclined portion being configured such that light guided from the light source is emitted from the inclined portion in a direction different from the longitudinal direction of the gradient-index lens, and
• the adjustment structure enables adjustment of the positional relationship between the leading end portion and the optical element in the longitudinal direction of the gradient-index lens such that a desired light emitting state or a desired light entering state is achieved between the optical element and the camera head.