Various embodiments relate to an optical detection element and GOI (Ge-on-insulator) device for ultra-small on-chip optical sensing, and a manufacturing method of the same. According to various embodiments, the optical detection element and the GOI device may be implemented on a GOI structure comprising a germanium (Ge) layer, and the GOI device may be implemented to have an optical detection element. Specifically, the GOI device may include a GOI structure with a waveguide region comprising a germanium layer, a light source element configured to generate light for the waveguide region, and at least one optical detection element configured to detect light coming from the waveguide region. At least one slot configured to collect light from the light source element may be formed in the germanium layer in the waveguide region. The light source element may generate light so as to be coupled to the germanium layer in the waveguide region. The optical detection element may detect heat generated as light is propagated from the germanium layer.