빅셀(VCSEL)의 온도 의존성을 이용한 파장 가변 형 광섬유 격자 온도센서

Fiber Bragg Grating Temperature Sensor by the Wavelength Tuning Using the Temperature Dependence of VCSEL

Abstract

본 논문에서는 광섬유 브래그 격자(FBG)를 이용한 광온도센서를 제작하였으며 광원은 출력 파장의 온도 의존성을 가지는 저가형 VCSEL이 사용되며 FBG에서 반사되는 빛의 파장을 분석하는 interrogator는 VCSEL에서 변화되는 출력 파장을 VCSEL의 내부 온도로 확인하는 방법을 적용하여 저가격의 광온도센서를 구현하였다. VCSEL의 내부온도를 $52.2^{\circ}C$에서 $14^{\circ}C$까지 조절하면서 출력 파장을 1519.90 nm에서 1524.25 nm까지 총 4.35 nm 파장을 변화시켰으며 온도 조절에 따른 파장 변화 반복도 오차는 ${\pm}0.003nm$이며 온도 측정 오차는 ${\pm}0.18^{\circ}C$로 측정되었다. 광온도센서를 사용하여 $22.3{\sim}194.2^{\circ}C$의 온도를 측정한 결과 인가한 온도 ${\Delta}T$에 따른 광원 내부 온도 변화 값은 $0.146^{\circ}C/{\Delta}T$이고 인가한 온도 ${\Delta}T$에 따른 온도 프로브 반사 파장 변화 값(${\Delta}{\lambda}_{\beta}T/{\Delta}T$)은 $16.64pm/^{\circ}C$로 측정되었으며 센서의 측정 오차는 ${\pm}1^{\circ}C$로 나타났다. VCSEL의 출력 파장은 온도에 의존성을 가지고 있어 좁은 범위의 출력 파장을 변화시키기 위한 광원으로 사용하기에 매우 적합하다.

In this paper, a low-cost optical temperature sensor is implemented, using a fiber Bragg grating (FBG) as the temperature probe and a low-cost VCSEL with temperature-dependent output wavelength as the light source. To analyze the wavelength of the reflected light from the FBG, an interrogation was applied using a method of referring to the internal temperature according to the output wavelength of the VCSEL. When the temperature of the VCSEL was adjusted from 14 to $52.2^{\circ}C$, the output wavelength varied from 1519.90 to 1524.25 nm. The degree of wavelength tuning according to temperature was $0.114nm/^{\circ}C$. The variable wavelength repeatability error according to temperature was ${\pm}0.003nm$, and the temperature measurement error was ${\pm}0.18^{\circ}C$. As a result of measuring the temperatures from 22.3 to $194.2^{\circ}C$, the value of the internal temperature change of the light source according to the applied temperature ${\Delta}T$ was $0.146^{\circ}C/{\Delta}T$, the change in reflected wavelength of the temperature probe according to applied temperature ${\Delta}T$ was measured at $16.64pm/^{\circ}C$. and the temperature measurement error of the sensor was ${\pm}1^{\circ}C$.

Fig. 5. The graph about the error and the measured temperature of the optical temperature sensor according to the applied temperature of temperature probe.

Fig. 1. (a) The construction of tunable wavelength optical temperature sensors using temperature dependence of VCSEL. (b) The structure of VCSEL package and the graph about the value of the internal temperature change of the VCSEL to tune the wavelength and the value of the measured power of the reflected light from the FBG.

Fig. 2. (a) The graph about the output wavelength according to internal application temperature of light source (applied temperature range: 14~52.2℃, output wavelength range: 1519.90~1524.25 nm). (b) Graph about output wavelength repeatability according to internal temperature of light source (output wavelength at 14℃ and 52.2℃: 1519.90 nm, 1524.25 nm, maximum repeatability error: ±0.003 nm).

Fig. 3. (a) The photograph of fabricated temperature probe. (b) The graph about the reflection wavelength of the temperature probe (temperature of the probe: 21.17℃, the center optical wavelength: 1520.93 nm, 3-dB bandwidth: 0.11 nm).

Fig. 4. (a) The graph about the measured temperature of the light source and the reflection wavelength of the probe according to the applied temperature of temperature probe (measurement temperature range: 22.3~194.2℃). (b) The graph about the measured value of internal temperature of the light source when the power of the reflected wavelength according to the applied temperature is the maximum value (The value of the reflected wavelength change of the temperature probe according to applied temperature ΔΤ: 16.64 pm/℃).