An optical sensing device configured to detect an object or features of the object is provided. The optical sensing device includes a structured light projector and a sensor. A structured light projector is configured to project a structured light to the object and includes a light source and at least one tunable liquid crystal diffractive optical element (LCDOE). The light source is configured to emit a light beam. The at least one tunable LCDOE is disposed on a path of the light beam and configured to convert the light beam into the structured light to form a structured light pattern on the object. The LCDOE is capable of controlling the structured light pattern by controlling voltage distribution to a liquid crystal layer in the LCDOE. The sensor is configured to sense a reflected light formed by the object reflecting the structured light. Besides, a structured light projector is also provided.