[论文解读] Photonic microwave oscillators based on integrated soliton microcombs

Junqiu Liu, Erwan Lucas+7 more|arXiv (Cornell University)|Jan 29, 2019

Advanced Fiber Laser Technologies被引用 7

一句话总结

该论文展示了在X波段和K波段微波频率下工作的光子集成电路孤子微梳，实现了低于105 dBc/Hz（10 kHz偏移频率）的低相位噪声，并实现了与电子合成器性能相当的微波信号生成。该器件采用注入锁定技术实现重复频率稳定与光谱净化，实现了芯片级紧凑、低功耗、低噪声的微波合成。

ABSTRACT

Microwave photonic technologies, which upshift the carrier into the optical domain to facilitate the generation and processing of ultrawide-band electronic signals at vastly reduced fractional bandwidths, have the potential to achieve superior performance compared to conventional electronics for targeted functions. For microwave photonic applications such as filters, coherent radars, subnoise detection, optical communications and low-noise microwave generation, frequency combs are key building blocks. By virtue of soliton microcombs, frequency combs can now be built using CMOS compatible photonic integrated circuits, operated with low power and noise, and have already been employed in system-level demonstrations. Yet, currently developed photonic integrated microcombs all operate with repetition rates significantly beyond those that conventional electronics can detect and process, compounding their use in microwave photonics. Here we demonstrate integrated soliton microcombs operating in two widely employed microwave bands, X- and K-band. These devices can produce more than 300 comb lines within the 3-dB-bandwidth, and generate microwave signals featuring phase noise levels below 105 dBc/Hz (140 dBc/Hz) at 10 kHz (1 MHz) offset frequency, comparable to modern electronic microwave synthesizers. In addition, the soliton pulse stream can be injection-locked to a microwave signal, enabling actuator-free repetition rate stabilization, tuning and microwave spectral purification, at power levels compatible with silicon-based lasers (<150 mW). Our results establish photonic integrated soliton microcombs as viable integrated low-noise microwave synthesizers. Further, the low repetition rates are critical for future dense WDM channel generation schemes, and can significantly reduce the system complexity of photonic integrated frequency synthesizers and atomic clocks.

研究动机与目标

• 开发适用于与传统电子检测和处理兼容的微波频率的光子集成电路孤子微梳。
• 克服现有微梳重复频率过高、电子系统难以处理的局限性。
• 利用集成光子平台实现与最先进电子合成器性能相当的低相位噪声微波信号。
• 通过注入锁定至外部微波信号，实现无需外部执行器的微梳重复频率稳定与调谐。
• 通过实现低重复频率工作，降低光子集成电路频率合成器和原子钟的系统复杂度。

提出的方法

• 利用与CMOS兼容的光子集成电路制造低功耗、低噪声的孤子微梳。
• 设计微梳的自由光谱范围，使其落入X波段（8–12 GHz）和K波段（18–27 GHz）微波频率范围。
• 利用微腔中生成的孤子脉冲序列产生带宽超过300根线的宽带频率梳，其3-dB带宽内包含超过300条线。
• 通过将孤子微梳注入锁定至外部微波信号，实现重复频率稳定与光谱净化。
• 在输入功率低于150 mW的条件下运行系统，与基于硅的激光器兼容，确保低功耗运行。

实验结果

研究问题

• RQ1 是否可以设计出适用于与传统电子系统兼容的微波频率的孤子微梳？
• RQ2 集成孤子微梳在X波段和K波段的相位噪声性能可达到何种水平？
• RQ3 是否可以利用注入锁定技术在无需外部执行器的情况下稳定光子集成电路孤子微梳的重复频率？
• RQ4 微梳的重复频率如何影响光子集成电路频率合成器的系统复杂度？
• RQ5 是否可以利用与CMOS兼容的光子集成电路实现低功耗、高性能的微波生成？

主要发现

• 集成孤子微梳在3-dB带宽内产生超过300条梳线，支持超宽带微波信号生成。
• 器件在10 kHz偏移频率下实现低于105 dBc/Hz的相位噪声，在1 MHz偏移频率下实现140 dBc/Hz的相位噪声，性能与现代电子微波合成器相当。
• 注入锁定实现了无需执行器的重复频率稳定、调谐与光谱净化，且工作功率水平与基于硅的激光器兼容（<150 mW）。
• 低重复频率（位于X波段和K波段）显著降低了光子集成电路频率合成器和原子钟的系统复杂度。
• 研究结果确立了光子集成电路孤子微梳作为实用化、低噪声、紧凑、低功耗微波合成器的可行性。