An optical interferometer based on multi-mode interference (MMI) devices includes an input port, an output port, a first MMI device connected to the input port at an input face of the first MMI device, a second MMI device connected to the first output port at an output face of the second MMI device. In the optical interferometer, an output face of the first MMI device and an input face of the second MMI device are directly connected, the first MMI device includes a first and a second self-imaging points at an interface between the first MMI device and the second MMI device, and a propagation axis of the second MMI device is tilted with respect to a propagation axis of the first MMI device, causing a path length difference between an upper optical path via the first self-imaging point and a lower optical path via the second self-imaging point.