Fiber optic sensors are __________ sensors that use fiber optic filaments to send and receive light.

• A. Proximity
• B. Ultrasonic
• C. Thermal
• D. Photoelectric

Answer: (D)

Fiber optic sensors rely on light sent and received through optical filaments to detect changes or the presence of an object. That use of light guided by a fiber fits the photoelectric sensing approach, where a light source and a detector work together to sense targets or environmental changes. In fiber optic versions, the light travels along the fiber to the sensing point and back, enabling remote sensing and electrical isolation while remaining immune to many forms of interference. Proximity sensors, ultrasonic sensors, and thermal sensors are based on different physical principles—fields or contactless detection, sound waves, and temperature changes, respectively—which is why they don’t describe fiber optic sensing.