Optical coupling techniques between an optical fiber and another optical device, such as a planar optical waveguide, or a probed region are disclosed. An optical fiber for lateral optical coupling includes a cladding, a core disposed in the cladding, a reflecting structure inclined relative to the fiber axis, and a light-converging structure embedded in the cladding. The reflecting structure is configured to reflect light between the core and a lateral coupling path extending and providing lateral optical coupling between the core and an exterior of the fiber. The cladding-embedded light-converging structure is configured to intercept and converge light traveling along the lateral coupling path. In some implementations, the optical fiber is a fiber-optic transition coupled between a main optical fiber and another optical device or a probed region. A coupled optical system including an optical fiber coupled to another optical device is also disclosed.