A microelectromechanical systems (MEMS) device comprising: an optical directional coupler comprising: at least one light source configured to provide a light beam; at least one substrate; a first waveguide formed on the at least one substrate, the first waveguide having a first end and the second end, wherein the first end of the first waveguide is coupled to the at least one light source, wherein the light beam is introduced into the first end of the first waveguide; a second waveguide formed on the substrate, the second waveguide having a third end and a fourth end, wherein the first waveguide and the second waveguide are positioned adjacent to each other at a central region of the optical directional coupler at a distance such that the light beam is at least partially evanescently coupled between the first waveguide and the second waveguide in the central region when the light beam is introduced into the first end of the first waveguide; a first photodetector coupled to a second end of the first waveguide, wherein the first photodetector is configured to detect a first optical power in the light beam propagating through the first waveguide at the second end; and a second photodetector coupled to a fourth end of the second waveguide, wherein the second photodetector is configured to detect a second optical power in the light beam propagating through the second waveguide at the fourth end; at least one vibrating proof mass positioned adjacent to the optical directional coupler in a first direction from the optical directional coupler, wherein the at least one vibrating proof mass is equidistant from the first waveguide and the second waveguide, wherein when one or more inertial forces are applied to the MEMS device in at least one of the first and a second direction, the at least one vibrating proof mass is configured to move in the first direction; at least one processor coupled to the first photodetector and the second photodetector, wherein the processor is configured to determine the displacement of the at least one proof mass from the optical directional coupler as a function of the first optical power and the second optical power. an optical directional coupler comprising: at least one light source configured to provide a light beam; at least one substrate; a first waveguide formed on the at least one substrate, the first waveguide having a first end and the second end, wherein the first end of the first waveguide is coupled to the at least one light source, wherein the light beam is introduced into the first end of the first waveguide; a second waveguide formed on the substrate, the second waveguide having a third end and a fourth end, wherein the first waveguide and the second waveguide are positioned adjacent to each other at a central region of the optical directional coupler at a distance such that the light beam is at least partially evanescently coupled between the first waveguide and the second waveguide in the central region when the light beam is introduced into the first end of the first waveguide; a first photodetector coupled to a second end of the first waveguide, wherein the first photodetector is configured to detect a first optical power in the light beam propagating through the first waveguide at the second end; and a second photodetector coupled to a fourth end of the second waveguide, wherein the second photodetector is configured to detect a second optical power in the light beam propagating through the second waveguide at the fourth end; at least one light source configured to provide a light beam; at least one substrate; a first waveguide formed on the at least one substrate, the first waveguide having a first end and the second end, wherein the first end of the first waveguide is coupled to the at least one light source, wherein the light beam is introduced into the first end of the first waveguide; a second waveguide formed on the substrate, the second waveguide having a third end and a fourth end, wherein the first waveguide and the second waveguide are positioned adjacent to each other at a central region of the optical directional coupler at a distance such that the light beam is at least partially evanescently coupled between the first waveguide and the second waveguide in the central region when the light beam is introduced into the first end of the first waveguide; a first photodetector coupled to a second end of the first waveguide, wherein the first photodetector is configured to detect a first optical power in the light beam propagating through the first waveguide at the second end; and a second photodetector coupled to a fourth end of the second waveguide, wherein the second photodetector is configured to detect a second optical power in the light beam propagating through the second waveguide at the fourth end; at least one vibrating proof mass positioned adjacent to the optical directional coupler in a first direction from the optical directional coupler, wherein the at least one vibrating proof mass is equidistant from the first waveguide and the second waveguide, wherein when one or more inertial forces are applied to the MEMS device in at least one of the first and a second direction, the at least one vibrating proof mass is configured to move in the first direction; at least one processor coupled to the first photodetector and the second photodetector, wherein the processor is configured to determine the displacement of the at least one proof mass from the optical directional coupler as a function of the first optical power and the second optical power.