Complex-optical-field lidar system for range and vector velocity measurement

Abstract

A coherent lidar system based on the measurement of complex optical field is demonstrated for the first time. An electro-optic inphase/quadrature (I/Q) modulator is used in the lidar transmitter to realize carrier-suppressed complex optical field modulation in which the positive and the negative optical sidebands can carry independent modulation waveforms. A fiber-optic 90° hybrid is used in the lidar receiver for coherent heterodyne detection and to recover the complex optical field. By loading a constant modulation frequency on the lower optical sideband and a wideband linear frequency chirp on the upper sideband, vector velocity and target distance can be measured independently. The wide modulation bandwidth of this lidar system also enabled unprecedented range resolution and the capability of measuring high velocity unambiguously.

Coherent laser radar with dual-frequency Doppler estimation and interferometric range detection

“…They are widely used for atmospheric sensing [11], wake vortex risk mitigation [12], and more besides. Nevertheless the speckle noise, induced by target's roughness and atmospheric turbulence [13], causes spectral broadening of the backscattered light, thus limiting the resolution of the system [14]. In order to reach high robustness against the speckle noise, dual-frequency lidar (DFL) architectures [15] resort to the detection of the differential Doppler shifts among two phase locked continuous waves.…”

Bandwidth efficient coherent lidar based on phase-diversity detection

“…Various different modulation and detection techniques can be used for a lidar altimeter, and the range resolution is generally determined by ΔR c∕2B, where c is the speed of light, and B is the modulation bandwidth [2]. A frequency-modulated continuous-wave (FMCW) lidar uses linearly frequency-chirped optical pulses with relatively long pulse duration, and thus the peak power of each optical pulse is much lower than that in a shortpulsed lidar with comparable range resolution [5][6][7]. Detection sensitivity, another important parameter of a lidar system, depends on the receiver configuration.…”

“…We show that the chirp bandwidth of the optical signal can be twice as wide as that of the RF chirp when an in-phase/quadrature (I∕Q) modulator is employed for electro-optic modulation, and the I and Q components can be separately detected with coherent homodyne detection based on a 90-degree optical hybrid [5,6]. More specifically, we demonstrate that 7 GHz continuous optical chirping, corresponding to a range resolution of approximately 1.28 cm, can be achieved with 3.5 GHz RF bandwidth.…”

Modeling PN Modulation In-Car Laser Radar for Range and Velocity Measurement

“…Another factor for in-car laser radar is the cost. Recently, Gao& [5] proposed a new FMCW approach utilizing the measurement of complex-optical-field for range and velocity measurement with high accuracy(3.2cm and 0.5m/s). However, the cost of electro-optic I/Q modulator used in this method is very expensive and the calculating quantity is so large that it's difficult for this method to be applied in in-car laser radar.…”

“…The velocity of the Doppler frequency shift can be either positive or negative depending on the 4th International Conference on Computer, Mechatronics, Control and Electronic Engineering (ICCMCEE 2015) direction of the velocity (moving toward or away from the observer). Nevertheless, dilemma has to be considered as the method used in pulsed Doppler radar, that is, a good choice of PRF (Pulse Repetition Frequency) to achieve a large unambiguous range will be a poor choice to achieve a large unambiguous velocity [5]. Thus, in traditional pulsed Doppler laser radar system, a tradeoff between the velocity resolution and ranges resolution has to be made.…”