End-capped optical fiber, fiber array, light source device, and wavelength beam combining device

An end-capped optical fiber comprising:

• an optical fiber comprising:
• a first portion comprising a first core, and a first cladding surrounding the first core, and
• a second portion comprising a second core, and a second cladding surrounding the second core, the second core being adjacent to the first core, and the second cladding being adjacent to the first cladding;
• and
• a first end cap having a first face and a second face, the first face being connected to an end face of the second portion of the optical fiber, and the second face being located on opposite side of the first face;
• wherein:
• a diameter of the first core is constant along an optical axis of the first core;
• a diameter of the second core gradually increases toward the first end cap;
• the first end cap comprises a convex lens;
• the second surface includes a convex lens surface of the convex lens;
• and
• a thickness of the first end cap on an optical axis of the convex lens is less than a distance from an apex of the convex lens to a focal point of the convex lens.