SFML is indeed an alternative to SDL, but at the same level. None of these options include features of a higher level engine (things like a game loop, object/entity management, data-driven definitions, physics, input abstraction, etc...).
OpenGL is lower level library and only handles graphics, it's not an alternative to SDL/SFML per se, however if one wants an OpenGL-centric alternative to these libraries, I'd recommend checking GLFW.