Chongfan Technology
News
03
2025
-
03
Optoelectronic technology for microcavity optical frequency comb synchronization
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With the rapid development of technologies such as 6G communication, autonomous driving, and intelligent computing, the demand for high-frequency, broadband, and low-latency signal processing has surged sharply. Traditional electronic systems rely on crystal oscillators to generate clock signals, but their frequencies are usually limited to hundreds of megahertz, requiring complex frequency conversion circuits to cover the microwave to terahertz bands. This solution brings a series of problems such as high power consumption, narrow bandwidth, and signal distortion.
Although optoelectronic technology can directly synthesize microwave or even terahertz signals through optical carriers, in practical systems, it is difficult for optical signals to synchronize with the clock of electronic devices. If the system is not synchronized, frequency and phase errors will occur between system sources, reducing processing accuracy and information transmission speed. Existing locking methods for optoelectronic systems, such as the Pound–Drever–Hall locking method, frequency doubling and injection locking method, and f-2f self-referencing locking method, although effective in reducing digital signal processing (DSP) to some extent, usually require additional hardware and operations. The complexity and cost of these methods limit their widespread application.
Recently, to solve this problem,the research team led by Chang Lin at Peking Universityin collaboration withthe Aerospace Information Innovation Research Institute of the Chinese Academy of Sciencesproposed a photonic clock chip based on an on-chip microcavity optical frequency comb. Based on ultra-high Q value resonators, it utilizes self-injection locking microcavity optical frequency comb technology to achieve a low-noise microwave photonic oscillator without the assistance of electronic devices. This oscillator can synthesize microwave signals from MHz to over 100 GHz and naturally synchronize optical synthesized signals and electronic devices by providing a shared time-frequency reference. This strategy can achieve extremely high data processing accuracy, thereby eliminating coherent DSP algorithms in data transmission. In addition, it can integrate different functions across various frequency bands through a set of shared hardware and has completed application verification for integrated sensing.
The team developed a frequency synthesizer based on a microcavity optical frequency comb, which consists of a Si3N4micro-resonator and a commercial indium phosphide DFB laser. Through self-injection locking, a coherent microcavity optical frequency comb state with a repetition frequency of 35.3 GHz was achieved. This microcavity optical frequency comb has low noise characteristics. In addition, this microcavity optical frequency comb can be directly turned on and off through a simple laser switch without any auxiliary control or feedback electronic devices. By combining single-sideband modulation and injection locking technology, the synthesized signal supports seamless coverage from UHF to W-band signals, with the synthesized broadband signal (bandwidth 2 GHz) having a power flatness better than 1.3 dB.
The research team also utilized the microcavity optical frequency comb to provide clock references for the entire optoelectronic system. By frequency dividing the repetition rate of the microcavity optical frequency comb, a clock signal based on the microcavity optical frequency comb was generated, with a frequency of 10 MHz. This clock signal can meet the synchronization needs of electronic devices and can be remotely synchronized through low-loss optical fibers. The research team validated the effectiveness of this optoelectronic synchronization technology through trigger tests, pulse compression, and wireless communication experiments.
In the trigger test, under electronic clock synchronization, the trigger signal and the triggered signal have no fixed phase relationship, and the phase of the triggered signal is randomly distributed, resulting in disorder after waveform superposition. Under microcavity optical frequency comb synchronization, the trigger signal and the triggered signal achieve phase coherence, with the phase jitter of the triggered signal <0.15 rad, resulting in stable waveforms.
In the pulse compression experiment, under electronic clock synchronization, the measurement error of the delay gradually increases over time (-2~100 ns), accompanied by significant random oscillation. In contrast, under microcavity optical frequency comb synchronization, the measured delay error remains stable (±2 ns), reducing by about 25 times.
In wireless transmission, under electronic clock synchronization, the constellation diagram can be restored after using the complete DSP algorithm, but when the carrier recovery and phase recovery DSP algorithms are removed, the constellation diagram cannot be resolved. In comparison, under microcavity optical frequency comb synchronization, the signal can restore the constellation diagram without coherent DSP algorithms, with the error vector magnitude (EVM) at 13.2%, close to the 12.3% of full DSP processing, indicating that this method can effectively save computational resources.
The microcavity optical frequency comb synchronized optoelectronic system can integrate various functions across different frequency bands into a shared hardware platform, achieving a multifunctional system for communication, sensing, frequency measurement, navigation, and more. In sensing mode, it can utilize linear frequency-modulated signals for target detection and imaging; in communication mode, it can achieve high-speed data transmission. This multifunctionality not only improves the efficiency of the system but also reduces its complexity and cost. To demonstrate the potential of this technology, the team constructed a joint sensing and communication (JSAC) system based on microcavity optical frequency comb synchronization, providing a unified reference clock for communication and sensing modules, eliminating frequency mismatches.
In sensing mode, adjacent teeth of the optical frequency comb (spacing 35.3 GHz) were selected to generate Ka-band linear frequency-modulated sensing signals with a bandwidth of 2 GHz, achieving a distance resolution of 6.7 cm, completing imaging of simulated point targets, two-point targets on a turntable, and surface targets, with both range and azimuth resolutions reaching the centimeter level, and detecting a 24-meter high building at a distance of 38 meters; in communication mode, data transmission was completed in the Ka band (30.3 GHz) using 16-QAM, 64-QAM, and 256-QAM, with their vector error magnitudes all below 4.5%. Among them, the result with a symbol rate of 100 MBd/s and modulation format of 256-QAM had a bit error rate (BER) as low as 1.1×10-3, meeting the forward error correction threshold.
The emergence of microcavity optical frequency comb synchronized optoelectronic technology brings new opportunities to the field of information processing. It not only enhances the performance of traditional optoelectronic system applications but also provides new technical means for emerging fields such as intelligent computing, terahertz communication, GPS-free navigation, and quantum sensing. Furthermore, with the continuous development of photonic integrated circuits and CMOS electronic chips, optoelectronic systems based on microcavity optical frequency combs are expected to achieve full-chip integration, further promoting the miniaturization and high performance of information systems.
In summary, the emergence of microcavity optical frequency comb synchronized optoelectronic technology marks an important breakthrough in the field of information processing. It not only solves the synchronization problem between optical synthesized signals and electronic clocks but also provides a new direction for the future development of high-performance, low-power, and multifunctional information systems. As this technology continues to mature and be applied, we have reason to believe that it will play an important role in the future digital age, bringing more convenience and innovation to the development of human society.
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