Using a discrete thermal model to obtain a linear frequency ramping in a frequency-modulated continuous-wave system

Daniel Nordin Kalevi Hyyppä Luleå University of Technology EISLAB SE-971 87, Luleå, Sweden E-mail: [email protected] Abstract. The lasing wavelength of a single-section distributed feedback DFB laser diode can be modulated by modulating the drive current. This makes it possible to utilize the DFB laser diode in a frequencymodulated continuous wave FMCW range and velocity measuring system. In FMCW, the frequency of the laser is ramped, and the frequency difference between the reflected wave and a local-oscillator wave is monitored. For maximum performance the frequency ramping should be linear. Due to thermal phenomena, a linear ramping of the current seldom results in a linear ramping of the optical frequency. We have derived a discrete thermal model, using resistors and capacitors, of our laser module. The thermal model was then used as a starting point to model the frequency behavior of the laser and to derive modulation currents that resulted in a linear frequency ramping at some different modulation frequencies. © 2005 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.1949205