This paper solves the challenge of precise dual-frequency laser control in Airborne Coherent Doppler LiDAR systems by implementing an innovative laser driver architecture, which integrates compact hardware design with cascade Proportional-Integral-Derivative (PID) control and a frequency–temperature compensation mechanism. The experimental results demonstrate eminent performance with long-term temperature fluctuation below 0.007 °C, temperature stabilizing time under 4 s and long-term power fluctuation of the linear constant current source being <1%. The system enables wide-range temperature–frequency adjustment for individual lasers and dynamically adjusts the dual-laser beat frequencies between −1 GHz and +2 GHz, achieving the frequency difference fluctuation within 3 MHz. These achievements greatly enhance LiDAR performance and create possibilities for broader applications in dynamic environmental sensing, atmospheric monitoring, deep-space exploration, and autonomous systems.

Pipeline conflicts arising from data dependencies are a common issue encountered in the hardware implementation of layered QC-LDPC decoders. This paper proposes an efficient layered decoding architecture to reduce pipeline conflicts without introducing stall cycles, by reordering the processing order offline and using the patch method based on variable-to-check message. The experimental results on the LDPC code of the IEEE802.16 standard in the OFDM-PON system demonstrate that the proposed architecture has a sensitivity improvement of 0.125 dBm and 0.375 dBm, respectively, compared with our previous work and the method described in the other work.

The high standard of communication quality in optical access networks makes forward error correction (FEC) schemes, such as LDPC, an integral part of the system. However, pipeline conflict arising from data dependencies is a common issue encountered in the hardware implementation of layered QC-LDPC decoders. This paper proposes an efficient layered decoding architecture to reduce pipeline conflicts without introducing stall cycles. It can solve some of the pipeline conflicts by flexibly reordering the processing order of inter-layer and intra-layer submatrices offline. In addition, the patch method, based on variable-to-check messages, allows for the delayed use of gains between layer iterations, which can further minimize the performance loss caused by the remaining pipeline conflicts. The experimental results on the LDPC code of the IEEE802.16 standard in the OFDM-PON system demonstrate that the proposed architecture has sensitivity improvements of 0.125 dBm and 0.375 dBm, respectively, compared with our previous work and the method described in the other work. The optimized architecture improves the reliability of the decoder and can also make a contribution to efficient PON systems.

On carrierless phase retrieval (PR) receivers based on direct detection, bandwidth limitation of electrical-to-optical (E/O) conversion at the transmitter side (Tx) distorts the modulated optical signal. In this paper, we propose the Gercheberg-Saxton (GS)-aided and the data-aided estimation method in order to know the complex-valued of E/O channel response in the absence of phase information. Furthermore, we compare four channel estimation schemes based on the mean square error (MSE) between the estimated and preset channel response in numerical simulation, which are generated by combining least mean square (LMS) or least square (LS) with the proposed GS-aided or data-aided methods. In order to compensate the distortion from E/O frequency response, two compensation schemes including pre-equalization processing at the Tx and post-equalization processing at the Rx are implemented and compared by simulations and experiments. In the experiment, we transmit a single-polarization 30GBaud QPSK signal including a training sequence of 2048 symbols to estimate the E/O conversion frequency response over 55-km single-mode fiber (SMF). The received signal is detected by a PR receiver employing different estimation (LMS/LS) and equalization (pre-/post-) schemes to compare their performance. The experimental results demonstrate that all estimation schemes successfully estimate the frequency response in the absence of phase information, and PR employing pre-equalization with GS-aided-LMS estimation exhibits good robustness, resulting in a received optical power improvement of 0.69 dB to achieve 20% forward-error correction (FEC) threshold.

For the first time, a highly energy-efficient 32-parallel 64-point FFT scheme for IMDD OFDM-PON is proposed and implemented on a Xilinx ML605 platform. By experimentally verifying the power consumption model for the FPGA logic resources utilized in the FFT, the relationship between FFT calculating consumption and FPGA logic resource usage is established. Based on this relationship, we derive a resource selection principle for the FFT bit resolution optimization to minimize power consumption under different levels of received optical power. Consequently, the proposed FFT achieves a 76.1% reduction in power consumption compared to the traditional Spiral FFT at a received optical power of −21 dBm. Based on the proposed FFT, the real-time OFDM-PON receiver power consumption can save up to 43% compared with traditional OFDM-PON system.