FBG Temperature Sensitivity and Multi-point Sensing Solutions for Wafer Temperature Measurement
Problem Description
A user inquired about the temperature sensitivity of Fiber Bragg Gratings (FBG) for temperature measurement. Subsequently, the user had a project requirement to measure temperature at 10 points on a 25 cm wafer, with temperatures not exceeding 100°C. The user also sought guidance on the necessary equipment beyond just the sensors.
Technical Analysis
Fiber Bragg Grating (FBG) temperature measurement is based on the principle that the Bragg wavelength of the FBG drifts as temperature changes. This phenomenon arises from the thermo-optic effect and thermal expansion effect within the fiber material, leading to alterations in the effective refractive index and the grating period, which in turn causes the Bragg wavelength to shift.
Typically, the temperature sensitivity of a standard FBG is approximately 10-12 pm/℃. This means that for every 1°C change in temperature, the grating’s central wavelength will drift by 10 to 12 picometers (pm). However, the precise value can be influenced by factors such as the fiber material, the grating fabrication process, and the sensor’s packaging method. For instance, OFSCN® sensors undergo precise temperature calibration at the factory, providing corresponding temperature-wavelength calibration formulas (often binomial) to ensure measurement accuracy.
For multi-point sensing, a single FBG sensor fiber can incorporate multiple grating elements (e.g., 10 sensing points). These multiple points can be efficiently monitored and read through a single channel of an FBG interrogator.
Solution & Recommendation
-
Sensor Selection: For accurate temperature measurement at 10 points on a 25 cm wafer, where temperatures do not exceed 100°C, the OFSCN® 100°C FBG Temperature Sensor is recommended.
-
Sensor Configuration for 10-point Wafer Measurement: To optimally distribute 10 sensing points across a 25 cm wafer, the following preliminary planning is suggested:
- Lead-in length (L1): 2 cm, designated for fiber connection and initial securing.
- Spacing between sensing points (L2): 2.3 cm. With 10 sensing points, there will be 9 gaps, distributing the sensors roughly evenly over 20.7 cm.
- Pigtail length (L3): 2 cm, reserved for fiber end processing and buffering.
- The total approximate length would be L1 + (9 * L2) + L3 = 2 cm + (9 * 2.3 cm) + 2 cm = 24.7 cm, which is highly suitable for a 25 cm wafer.
-
Interrogator Selection: In addition to the sensor, a Fiber Bragg Grating (FBG) interrogator is essential to acquire the wavelength data from the sensor and convert it into meaningful temperature values.
- A single OFSCN® FBG Interrogator with 8 channels is recommended.
- Crucially, even if a single optical fiber sensor contains multiple grating sensing points (e.g., 10 points in this case), it typically only requires connection to one channel of the FBG interrogator. This setup allows the interrogator to read and process the wavelength data from all gratings on that single fiber, while also providing capacity for future expansion or additional sensors.
Recommended Product
OFSCN® 100°C FBG Temperature Sensor: 100℃ Fiber Bragg Grating Temperature Sensor - FBG Thermometer - Fiber Optic Grating Temperature Sensor - Customizable - Model Parameter Picture - Manufacturer Brand Price - DCYS - ofscn.net
OFSCN® FBG Interrogator: https://www.ofscn.net/fbg-products/fbg-interrogator.html
(Source Discussion / 原帖讨论: 光纤光栅灵敏度的问题？)