Frequency-Modulated Chirp Signals for Single-Photodiode Based Coherent LiDAR System

Abstract

In this paper, we investigate two categories of linear frequency-modulated chirp signals suitable for singlephotodiode based coherent light detection and ranging (Li-DAR) systems, namely, the frequency-modulated continuouswave (FMCW) single-sideband (SSB) signal and the amplitudemodulated 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 signalbased 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.

Impact of Laser Phase Noise on Ranging Precision Within and Beyond Laser Coherence Length in FMCW LiDAR

“…The light was then externally modulated using an in-phase and quadrature modulator (IQM), avoiding the impact of modulation nonlinearity or limited tuning speed suffered from using directlymodulated laser sources. The single-sideband (SSB) FMCW signal was generated by independently modulating the in-phase (I) and quadrature(Q) arms of the IQM by [6]:…”

“…The receiver comprised a 3-dB coupler combining the local oscillator (LO) and the delayed SSB FMCW signal, followed by a single-ended photodiode, previously shown to be a strong candidate for low-cost and low-complexity coherent LiDAR systems [6]. The received FMCW signal was first aligned with the LO using a polarization controller.…”

Energy-Efficient Forward-Biased PIN Silicon Mach–Zehnder Modulator With 50 μm Active Phase Shifter Length

“…Up to now, in the field of optical communications, the preference has been predominantly towards the reversedbiased configuration, since these modulators can provide high bandwidths and therefore, high-speed communications [6][7][8][9]. However, in addition to their applications in optical communications, MZMs have attracted a lot of attention to be utilized in various other fields like microwave photonics [10], LiDAR [11][12], quantum key distribution [13][14], optical switches [15][16], optical computing like reservoir computing [17][18], etc. Some of these fields, for example, LiDAR do not require high bandwidth or modulation speed in the GHz range and should be operated with low power consumption [11][12].…”

“…However, in addition to their applications in optical communications, MZMs have attracted a lot of attention to be utilized in various other fields like microwave photonics [10], LiDAR [11][12], quantum key distribution [13][14], optical switches [15][16], optical computing like reservoir computing [17][18], etc. Some of these fields, for example, LiDAR do not require high bandwidth or modulation speed in the GHz range and should be operated with low power consumption [11][12]. However, they need large-scale integration.…”