## 1 Introduction  
Visible light communication (VLC) is an attractive and promising technology for future wireless communication systems [1]. VLC is a kind of optical wireless communication (OWC) using visible light spectrum for communication. Due to the advances of light emitting diode (LED) development, VLC systems can be based on existing lighting infrastructure to provide illumination and communication at the same time [2]. Due to the highly directional feature of the optical light beam, VLC could provide highly directional and high privacy transmission, at the same time being immune to radio-frequency (RF) electromagnetic interference (EMI) [3]. Different VLC technologies have been studied in ref. [4]. Due to the many unique advantages offered by VLC, it has been considered as one of the potential candidates for beyond 5G or 6G mobile and wireless communication [5]. There are many potential applications of VLC systems, such as vehicle to vehicle communication [6], visible light positioning (VLP) [7], robot navigation in hospitals [8], underwater communication [9], optical camera communication (OCC) [10], display and sign board communication [11]. One popular VLC transmitter (Tx) is the LED [12]. A phosphor-based LED Tx for both lighting and VLC has been reported [13]. As the data rate of the LED based VLC system is limited by the relaxation time of the yellow phosphor, schemes include pre/post-equalization [14], multiple-input multiple-output (MIMO) [15], etc. [PERSON] et al. reporteda 1.1 Gbit/s white-light VLC system based on 3 \(\times\) 3 MIMO [15]. [PERSON] et al. reported a 3.4 Gbit/s VLC system based on wavelength division multiplexing of red green blue (RGB) LEDs [16]. Besides, [PERSON] et al. also reported a 3.375 Gbit/s RGB LEDs based WDM VLC system using high level modulation (i.e., eight levels of pulse amplitude modulation, PAM 8) [17]. To further enhance the modulation bandwidth, micro-LEDs can also be employed [18]. [PERSON] et al. reported a 3 Gbit/s VLC link using a blue gallium nitride (GaN) micro-LED and high spectral efficient orthogonal frequency division multiplexing (OFDM) format [19]. Recently, [PERSON] et al. reported a 1 Gbit/s on-off-keying (OOK) VLC system using a violet micro-LED [20]. By growing the micro-LED in non-polar or semi-polar orientations, the quantum confined stark effect (QCSE) can be reduced and a higher modulation bandwidth can be achieved. [PERSON] et al. reported a 4.343 Gbit/s VLC transmission based on a green semipolar micro-LED array [21]. To suppress the LED efficiency droop [22] and enhance the modulation bandwidth, the laser diode (LD) can also be a promising candidate for VLC. LD based VLC is one of the best choices for high-speed data transmission, such as simultaneous lighting and communication [23], machine to machine communication [24], underwater communication [25], and mobile back-haul transmission [26]. [PERSON] et al. demonstrated a 6.915 Gbit/s white-light illumination and VLC system using blue LD with yellow phosphor [27] and these can be used for illumination and communication simultaneously. In order to further increase the transmission capacity, multiplexing schemes in different physical dimensions, including time, frequency, modulation quadrature, polarization, and space, can be employed. [PERSON] et al. reported a VLC system using WDM RGB LDs operated at 8 Gbit/s [28] and [PERSON] et al. illustrated a LD based VLC system combining WDM and polarization division multiplexing (PolDM) which operated at 40.665 Gbit/s [29]. Moreover, [PERSON] et al. also illustrated an LD based VLC system for color-shift-keying (CSK) [30]. Besides the physical domain multiplexing schemes, digital domain multiplexing schemes such as OFDM [31] can also enhance the total system capacity by allowing a certain degree of signal spectral overlapping to maximize the bandwidth utilization. The OFDM system divides the data signal into several lower bit rate subcarriers, which are orthogonal to each other.