Abstract
In this paper, we investigate two categories of linear frequency-modulated chirp signals suitable for single-photodiode based coherent light detection and ranging (LiDAR) systems, namely, the frequency-modulated continuous-wave (FMCW) single-sideband (SSB) signal and the amplitude-modulated double-sideband (DSB) signal, and compare their achievable receiver sensitivity performance. The DSB signal requires a simpler transmitter design, as it is real-valued and can be generated using a single-drive Mach-Zehnder modulator (MZM), while the SSB signal, which is frequency/phase modulated, requires an in-phase and quadrature modulator (IQM)-based transmitter. A theoretical analysis of direct-detection (DD) beating interference (BI) especially the local oscillator (LO) beating with itself, known as LO-LO BI, is presented. Both Monte Carlo simulations and experimental demonstrations are carried out. Good agreement between simulations and experiments is achieved. In comparison with the SSB system, the DSB signal-based system is affected by laser phase noise-induced power fluctuation, and also suffers a significant sensitivity penalty due to nonlinear LO-LO BI. A spectral guard band for mitigating LO-LO BI is necessary for the DSB signal, achieved at the expense of requiring a larger electrical bandwidth. In system tests with a delay line of 385 m, the SSB signal outperforms the DSB signal with a 10 dB better receiver sensitivity in the case with a guard band, and 25 dB better sensitivity without a guard band.
Highlights
L IGHT detection and ranging (LiDAR) systems have been widely studied for numerous applications such as autonomous vehicles, 3D imaging and anemometry [1]– [6]
We first employed a sufficiently wide guard band to ensure local oscillator (LO)-LO BI terms fell at frequencies outside the desired signal band (i.e., f1 = 2 GHz), and the system performance was limited by LO-amplified spontaneous emission (ASE) beating interference
We evaluated the performance of two linear frequencymodulated chirp signals: the frequency-modulated continuouswave SSB signal and the amplitude-modulated DSB signal in coherent LiDAR systems with single-photodiode detection
Summary
L IGHT detection and ranging (LiDAR) systems have been widely studied for numerous applications such as autonomous vehicles, 3D imaging and anemometry [1]– [6]. Through both Monte Carlo simulations and experimental demonstrations, we investigate a low-cost and lowcomplexity coherent LiDAR receiver with single-photodiode detection in which the LO is a frequency-modulated chirp signal, and compare the receiver sensitivity performance difference between two chirp waveforms: 1) the frequencymodulated complex-valued SSB signal, and 2) the amplitudemodulated real-valued DSB signal. The DSB signal is susceptible to laser phase noise as it is converted to amplitude noise after squarelaw detection on reception, leading to a power fluctuation of the desired beat frequency Both simulation and experimental results indicate that with a delay line of 385 m, when LOLO BI is mitigated through the use of a guard band, the SSB FMCW signal offers 10 dB better receiver sensitivity than the DSB signal.
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