This Letter presents an all-optical high-temperature flow sensor based on hot-wire anemometry. High-attenuation fibers (HAFs) were used as the heating elements. High-temperature-stable regenerated fiber Bragg gratings were inscribed in HAFs and in standard telecom fibers as temperature sensors. Using in-fiber light as both the heating power source and the interrogation light source, regenerative fiber Bragg grating sensors were used to gauge the heat transfer from an optically powered heating element induced by the gas flow. Reliable gas flow measurements were demonstrated between 0.066 m∕s and 0.66 m∕s from the room temperature to 800°C. This Letter presents a compact, low-cost, and multiflexible approach to measure gas flow for high-temperature harsh environments. Gas flow measurement plays important roles in various industrial sectors. It provides vital information for a large number of applications such as process controls, fossil fuel and nuclear electric power generation, transportation, and environment monitoring. To perform flow measurements, a large number of flow sensors based on various mechanical, electronic, and microelectromechanical system (MEMS) structures [1] have been developed. These sensors can perform effective flow measurements at room temperature or slightly elevated temperatures (e.g., <200°C). However, a number of industrial and aerospace applications demand flow sensors with much higher operational temperatures (>500°C). These are not attainable by current state-of-the-art technology, such as MEMS. To address this technical challenge, this Letter presents a low-cost and compact all-optical-fiber flow sensing technique that can provide rapid and accurate gas flow measurements from room temperature to 800°C. This is, to our best knowledge, the highest operational temperature for a flow sensor. Fiber-optic sensors are well-known for their resilience in many harsh conditions including in high-temperature, corrosive, and strong electromagnetic environments. Over the last decade, various optical-fiber-based flow sensors have been reported, largely based on two schemes: fiber optical interferometry Compared with electrically heated HWA flow sensors, fiber-optic sensors can also be heated optically to perform flow measurements. Using various optical coupling schemes In this Letter, we demonstrate an all-fiber hightemperature flow sensor using the optical HWA rated for 800°C operation. The sensor consists of an in-fiber optical heating element using high-attenuation fibers (HAFs). High-temperature-stable regenerated FBGs (RFBG
