Linearization of the frequency sweep of a frequency-modulated continuous-wave semiconductor laser radar and the resulting ranging performance

Abstract

The performance of a frequency-modulated continuous-wave (FMCW) semiconductor laser radar has been examined. Frequency modulation (linear chirp) has been studied experimentally in detail. To create a linear frequency sweep, we modified the modulating function according to the measured frequency response of the laser, using an arbitrary function generator. The measurements indicate the possibility of achieving a spectral width of the signal peak that is transform limited rather than limited by the frequency modulation response of the laser, which permits the use of a narrow detection bandwidth. The narrow width results in a relatively high signal-to-noise ratio for low output power and thus also in relatively long-range and high-range accuracy. We have performed measurements of a diffuse target to determine the performance of a test laser radar system. The maximum range, range accuracy, and speed accuracy for a semiconductor laser with an output power of 10 mW and a linewidth of 400 kHz are presented. The influence of the laser's output power and coherence length on the performance of a semiconductor-laser-based FMCW laser radar is discussed.

Advantages of a new modulation scheme in an optical self-mixing frequency-modulated continuous-wave system

“…Several other authors, for instance in Ref. 11, have built and reported on systems using a fiber optical coupler in a similar way, as we have done in our experiments. A second attractive alternative is to use a fiber optical circulator instead of a coupler.…”

“…Others have also reported this effect, as well as the problem caused by larger Doppler shifts. 11 Some laser diodes also have a built in low-pass filter to protect the diode from spikes in the drive current. This, of course, also limits f mod .…”

Doppler lidar sensor for precision landing on the Moon and Mars

“…The main factors determining the precision of the Doppler lidar measurement are the spectral linewidth of laser, the linearity of the modulation waveform, the signal-to-noise ratio, and the signal processor frequency resolution [7,8]. Fortunately, the advances in single-frequency fiber laser, high quantum efficiency detector, high-speed analog electronics, and powerful processor technologies have enabled the development a system with sufficient precision and operational range for a number of applications including planetary landing.…”

Linear FMCW Laser Radar for Precision Range and Vector Velocity Measurements

“…Laser line-width limits the IF measurement resolution, and waveform linearity limits signal to noise ratio (SNR) [8,9]. The system to be installed and field-tested aboard a helicopter uses a frequency stabilized, fiber laser with a spectral line width that is less than 10 KHz full width, at half maximum.…”