Towards high-power, high-coherence, integrated photonic mmWave platform with microcavity solitons

Abstract

Millimetre-wave (mmWave) technology continues to draw great interest due to its broad applications in wireless communications, radar, and spectroscopy. Compared to pure electronic solutions, photonic-based mmWave generation provides wide bandwidth, low power dissipation, and remoting through low-loss fibres. However, at high frequencies, two major challenges exist for the photonic system: the power roll-off of the photodiode, and the large signal linewidth derived directly from the lasers. Here, we demonstrate a new photonic mmWave platform combining integrated microresonator solitons and high-speed photodiodes to address the challenges in both power and coherence. The solitons, being inherently mode-locked, are measured to provide 5.8dB additional gain through constructive interference among mmWave beatnotes, and the absolute mmWave power approaches the theoretical limit of conventional heterodyne detection at 100GHz. In our free-running system, the soliton is capable of reducing the mmWave linewidth by two orders of magnitude from that of the pump laser. Our work leverages microresonator solitons and high-speed modified uni-traveling carrier photodiodes to provide a viable path to chip-scale, high-power, low-noise, high-frequency sources for mmWave applications. Millimetre waves: soliton solutions in optical microcavityPowerful high-frequency radio waves can be generated by shining laser-driven resonating microcavity solitons onto tiny photodiodes, researchers in the USA have shown. Millimetre-waves (mmWaves), at the top end of the radio spectrum, will improve bandwidth and resolution for future telecommunication technologies, and recent breakthroughs promise ways to generate mmWaves through photonic, rather than electronic, methods. Now, Beichen Wang at the University of Virginia and co-workers have directed laser light into a microscopic ring-shaped silicon nitride resonator, generating solitary wave packets (solitons) that illuminate a tiny photodiode to produce 100 Gigahertz mmWaves at one of the highest powers ever reported. The researchers believe their system could be modified to generate higher-frequency mmWaves of several hundred Gigahertz. Moreover, the microresonator absorbs only a small portion of the laser power, which could be recycled to drive other microresonators.