Development of an All-Fiber Coherent Laser Radar for Precision Range and Velocity Measurements

Abstract

An all-fiber coherent laser radar system capable of high-resolution range and line of sight velocity measurements is under development with a goal to aid NASA's new Space Exploration initiative for manned and robotic missions to the Moon and Mars. Precision range and velocity data are key parameters to navigating planetary landing pods to the pre-selected site and achieving autonomous safe soft-landing. By employing a combination of optical heterodyne and linear frequency modulation techniques [1-3] and utilizing state-of-the-art fiber optic technologies, highly efficient, compact and reliable laser radar suitable for operation in a space environment is being developed.The all-fiber coherent laser radar has several important advantages over more conventional pulsed laser altimeters or range finders. One of the advantages of the coherent laser radar is its ability to directly measure the platform velocity by extracting the Doppler shift generated by the platform motion. The Doppler velocity measurement is about two orders of magnitude more accurate than the velocity estimates obtained by laser altimeters using the rate of change in range [4]. Another advantage is continuous-wave operation that allows the use of highly efficient and reliable commercial off-the-shelf fiber optic telecommunication components. This paper will describe the design and operation of this laser radar sensor and discuss its projected performance. A laboratory breadboard system has already been developed as a step toward a flight prototype. The experimental data representing the potentials of this laser radar system will be reported.

Development of a Multimode Field Deployable Lidar Instrument for Topographic Measurements of Unsaturated Soil Properties: Instrument Description

“…Among laser altimetry methods, coherent, frequency modulated continuous waveform (FMCW) lidar has been widely pursued [35][36][37][38][39][40][41][42]. A pulse compression technique has been applied to FMCW lidar systems, whereby a linear frequency sweep or "chirp" with a large bandwidth is used to modulate the optical carrier signal.…”

Narrow-linewidth semiconductor laser with highly-linear frequency modulation response for coherent sensing

“…Distributed acoustic sensing (DAS) systems [1] rely on ultra-narrow-linewidth lasers to achieve system range up to a hundred kilometers with minimal impact on the distance resolution. Depending on the application and system architecture, one may also benefit from modulating the laser frequency to extract positioning and doppler information, as it is the case in frequency modulated continuous wave (FMCW) lidar [2]. Frequency modulation of narrow linewidth laser sources is also beneficial to reach high spatial resolution in fiber sensing systems based on Rayleigh scattering to perform strain, temperature, and vibration measurements [1].…”

Laser Altimeter Based on Random Code Phase Modulation and Heterodyne Detection

“…The common advantages of coherent detection are high sensitivity and high tolerance to the background noise. In [13]- [15], the systems adopt coherent detection and chirp modulation. Distance resolution is in inversely proportional to chirp bandwidth.…”

“…Distance resolution is in inversely proportional to chirp bandwidth. In [13], chirp modulation is realized by controlling the cavity length of the laser through a piezo actuator. The internal modulation achieves gigahertz chirp bandwidth easily.…”