The stable long-distance transmission of radio-frequency (RF) signals holds significant importance from various aspects, including the comparison of optical frequency standards, remote monitoring and control, scientific research and experiments, and RF spectrum management. We demonstrate a scheme where an ultrastable frequency signal was transmitted over a 50 km coiled fiber. The optical RF signal is generated using a two-section distributed feedback (DFB) laser for direct modulation based on the reconstruction equivalent chirp (REC) technique. The 3-dB modulation bandwidth of the two-section DFB laser is 18 GHz and the residual phase noise of -122.87dBc/Hz is achieved at 10-Hz offset frequency. We report a short-term stability of 1.62×10-14 at an average time of 1 s and a long-term stability of 6.55×10-18 at the measurement time of 62,000 s when applying current to the front section of the DFB laser. By applying power to both sections, the stability of the system improves to 4.42×10-18 within a testing period of 56,737 s. Despite applying temperature variations to the transmission link, long-term stability of 8.63×10-18 at 23.9 h can still be achieved.

Neuromorphic photonic computing has emerged as a competitive computing paradigm to overcome the bottlenecks of the von-Neumann architecture. Linear weighting and nonlinear spike activation are two fundamental functions of a photonic spiking neural network (PSNN). However, they are separately implemented with different photonic materials and devices, hindering the large-scale integration of PSNN. Here, we propose, fabricate and experimentally demonstrate a photonic neuro-synaptic chip enabling the simultaneous implementation of linear weighting and nonlinear spike activation based on a distributed feedback (DFB) laser with a saturable absorber (DFB-SA). A prototypical system is experimentally constructed to demonstrate the parallel weighted function and nonlinear spike activation. Furthermore, a four-channel DFB-SA laser array is fabricated for realizing matrix convolution of a spiking convolutional neural network, achieving a recognition accuracy of 87% for the MNIST dataset. The fabricated neuro-synaptic chip offers a fundamental building block to construct the large-scale integrated PSNN chip.

Spiking neural networks (SNNs) utilize brain-like spatiotemporal spike encoding for simulating brain functions. Photonic SNN offers an ultrahigh speed and power efficiency platform for implementing high-performance neuromorphic computing. Here, we proposed a multi-synaptic photonic SNN, combining the modified remote supervised learning with delay-weight co-training to achieve pattern classification. The impact of multi-synaptic connections and the robustness of the network were investigated through numerical simulations. In addition, the collaborative computing of algorithm and hardware was demonstrated based on a fabricated integrated distributed feedback laser with a saturable absorber (DFB-SA), where 10 different noisy digital patterns were successfully classified. A functional photonic SNN that far exceeds the scale limit of hardware integration was achieved based on time-division multiplexing, demonstrating the capability of hardware-algorithm co-computation.

Modulation bandwidth enhancement in a directly modulated two-section distributed feedback (TS-DFB) laser based on a detuned loading effect is investigated and experimentally demonstrated. The results show that the 3-dB bandwidth of the TS-DFB laser is increased to 17.6 GHz and that chirp parameter can be reduced to 2.24. Compared to the absence of a detuned loading effect, there is a 4.6 GHz increase and a 2.45 reduction, respectively. After transmitting a 10 Gb/s non-return-to-zero (NRZ) signal through a 5-km fiber, the modulation eye diagram still achieves a large opening. Eight-channel laser arrays with precise wavelength spacing are fabricated. Each TS-DFB laser in the array has side mode suppression ratios (SMSR) > 49.093 dB and the maximum wavelength residual < 0.316 nm.

Wavelength-tunable organic semiconductor lasers based on mechanically stretchable polydimethylsiloxane (PDMS) gratings were developed. The intrinsic stretchability of PDMS was explored to modulate the period of the distributed feedback gratings for fine tuning the lasing wavelength. Notably, elastic lasers based on three typical light-emitting molecules show comparable lasing threshold values analogous to rigid devices and a continuous wavelength tunability of about 10 nm by mechanical stretching. In addition, the stretchability provides a simple solution for dynamically tuning the lasing wavelength in a spectral range that is challenging to achieve for inorganic counterparts. Our work has provided a simple and efficient method of fabricating tunable organic lasers that depend on stretchable distributed feedback gratings, demonstrating a significant step in the advancement of flexible organic optoelectronic devices.Wavelength-tunable organic semiconductor lasers based on mechanically stretchable polydimethylsiloxane (PDMS) gratings were developed. The intrinsic stretchability of PDMS was explored to modulate the period of the distributed feedback gratings for fine tuning the lasing wavelength. Notably, elastic lasers based on three typical light-emitting molecules show comparable lasing threshold values analogous to rigid devices and a continuous wavelength tunability of about 10 nm by mechanical stretching. In addition, the stretchability provides a simple solution for dynamically tuning the lasing wavelength in a spectral range that is challenging to achieve for inorganic counterparts. Our work has provided a simple and efficient method of fabricating tunable organic lasers that depend on stretchable distributed feedback gratings, demonstrating a significant step in the advancement of flexible organic optoelectronic devices.

在远距离相干测量系统中，分布反馈式半导体激光器（DFB-LD）以其直接高速调制特性、低成本、可批量生产等优势成为精密遥测系统的核心光源，因此对DFB-LD的窄线宽和短时频率稳定性提出了更高的要求。为了实现DFB-LD的频率稳定，通过边频锁定与光电反馈回路的方法将激光频率锁定在H¹³C¹⁴N气体吸收谱线1548.956 nm的一侧。将光电探测模块、后续误差信号生成与处理模块和激光器驱动模块集成在一块模拟电路板上，从而有效地降低了系统的噪声；使用除法器代替减法器来产生鉴频信号，大大提高了系统灵敏度和稳频精度；通过这两项技术的改进，将DFB-LD的秒级频率稳定度提高了两个数量级，从稳频前的秒级频率稳定度3.67 × 10⁻⁸提高到稳频后的秒级频率稳定度2.34×10⁻¹⁰。实验结果表明，该DFB-LD稳频方案具有高的稳频精度，且系统结构简单、体积小、可批量生产，适合于无人机机载应用场景，是远距离相干测量系统的理想光源。

提出并实验研究了一种宽带可调谐微波频率梳（MFC）的产生方案。首先，通过单频电信号调制一个分布反馈半导体激光器（DFB-SL1），可以得到包含多条梳线的种子光学频率梳（OFC）；然后，将种子OFC送入一个受同样单频信号驱动的相位调制器，可得到具有更多梳线的优化OFC；最后，将优化OFC注入到另一个DFB-SL（DFB-SL2）中，其输出通过光电转换后以获得宽带MFC。实验结果表明，采用频率为2.9 GHz的单频电信号，通过优化注入功率和两个DFB-SLs之间的频率失谐，可以获得幅度变化在±5 dB内带宽为55.1 GHz的MFC，且每条梳线的相位噪声均低于-98.66 dBc/Hz @ 10 kHz。通过改变单频电信号的频率并选择合适的工作参数，可以产生梳距可调谐的宽带MFC。