Wavelength Tuning of a 2 µm Tm-Ho fiber laser based CO2 Sensor Marjorie Dallmann, Renjie Zhou, and Prof. Lynford Goddard Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign Goals Theory Design and build a stretch tuning fiber Bragg grating (FBG) circuit Tune the output wavelength of a 2 µm Tm-Ho fiber laser by stretching the FBG Use wavelength modulation absorption spectroscopy (WMAS) to measure CO2 concentration for monitoring spoilage of stored grain FBG – a reflector inside an optical fiber that selectively reflects one wavelength and transmits all others The highest absorption peak for CO2 with low-cost fiber is around 2.005 µm, the 2 µm fiber laser must be tuned to ~1 nm around this peak for WMAS By stretching the FBG, the fiber laser output wavelength can be changed to allow for WMAS and CO2 concentration measurement FBG Stretching Set-Up 12V power source Fiber Bragg Grating 90o Rotation Stepper Motor Both motors are fixed on a stationary base Arduino Uno Stepper Motor Driver Experimental Results 1.5 µm FBG tuning Arduino Control Code Main Body Rotation function void rotateDeg(float deg, float vel){ int dir = (deg > 0)? HIGH:LOW; digitalWrite(dirpin, dir); int steps = abs(deg)*(1/0.225); float usDelay = (1/vel) * 70; for(int i=0; i < steps; i++){ digitalWrite(steppin, HIGH); delayMicroseconds(usDelay); digitalWrite(steppin, LOW); delayMicroseconds(usDelay);} } int dirpin = 2; int steppin = 3; void rotateDeg(float deg, float vel); void setup() { pinMode(dirpin, OUTPUT); pinMode(steppin, OUTPUT); rotateDeg(90, 1); } void loop() {} Original transmission spectrum Transmission spectrum after tuning Future Work Perform wavelength modulation with 2 µm FBG and test setup Begin to test the device for CO2 concentration measurement References Arduino Function Code: http://bildr.org/2011/06/easydriver/ Stepper Motor, Arduino, and Easy Driver Picture: http://bildr.org/blog/wp-content/uploads/2011/05/EasyDriver-Stepper-Motor-Driver2.png R. Zhou et al, CO2 sensing with a 2005 nm thulium holmium co-doped fiber laser, Optical Sensors, OSA Technical Digest, paper STh2B.4, 2012.