Fully integrated ultra-low power Kerr comb generation (1804.00357v1)

Abstract: Optical frequency combs are broadband sources that offer mutually-coherent, equidistant spectral lines with unprecedented precision in frequency and timing for an array of applications. Kerr frequency combs in microresonators require a single-frequency pump laser and have offered the promise of highly compact, scalable, and power efficient devices. Here, we realize this promise by demonstrating the first fully integrated Kerr frequency comb source through use of extremely low-loss silicon nitride waveguides that form both the microresonator and an integrated laser cavity. Our device generates low-noise soliton-modelocked combs spanning over 100 nm using only 98 mW of electrical pump power. Our design is based on a novel dual-cavity configuration that demonstrates the flexibility afforded by full integration. The realization of a fully integrated Kerr comb source with ultra-low power consumption brings the possibility of highly portable and robust frequency and timing references, sensors, and signal sources. It also enables new tools to investigate the dynamics of comb and soliton generation through close chip-based integration of microresonators and lasers.

• The paper introduces a fully integrated Kerr comb source achieving low-noise soliton-mode locked frequency combs with just 98 mW of electrical pump power.
• The authors demonstrate a novel dual-cavity design combining a III-V RSOA and Si₃N₄ laser cavity to enable stable comb generation at only 700 µW optical pump power.
• Experimental results highlight a high Q factor of 8.0×10⁶, up to 9.5 mW on-chip output power with 60 dB SMSR and a 40 kHz linewidth, paving the way for portable photonic systems.

Overview of Fully Integrated Ultra-Low Power Kerr Comb Generation

This paper presents a significant advancement in the field of optical frequency combs, detailing the development of a fully integrated Kerr frequency comb source. Optical frequency combs, with their ability to generate equidistant and mutually coherent spectral lines, are crucial in several high-precision applications such as spectroscopy, telecommunications, and timekeeping. This research introduces an innovative design that is compact, scalable, and notably consumes minimal power, opening new possibilities for portable photonic devices.

Technical Achievements

The authors have successfully integrated a Kerr comb source using silicon nitride (Si$_3$N$_4$) waveguides. These waveguides form both a microresonator and an integrated laser cavity. The integration leverages the low-loss properties of Si$_3$N$_4$, which allows for low-noise soliton-mode-locked combs that span over 100 nm utilizing merely 98 mW of electrical pump power. A novel dual-cavity configuration is employed here, showcasing the flexibility achievable through such full integration.

One of the primary achievements of this work is the production of a Kerr frequency comb via parametric four-wave mixing (FWM) under ultra-low power conditions. The research also demonstrates efficient comb generation along with soliton formation at just 700 µW of optical pump power, a remarkable feat given the typical power demands of non-integrated setups.

Experimental Results

The experimental setup is based on III-V Reflective Semiconductor Optical Amplifier (RSOA) coupled with a Si$_3$N$_4$ laser cavity that utilizes Vernier microring filters for wavelength tunability. The microresonator, demonstrating a high Q factor of $8.0 \times 10^6$, supports soliton comb generation using sub-milliwatt power levels.

The integrated device successfully achieved lasing with up to 9.5 mW on-chip output power, maintaining over 60 dB side-mode suppression ratio (SMSR), and a 40 kHz laser linewidth. The entire apparatus is capable of battery operation, marking an unprecedented low power consumption for Kerr frequency comb systems, thus allowing for mobile deployment.

Implications and Future Work

The realization of a low-power, fully integrated Kerr comb source could transform various applications, previously hindered by the onerous size and power requirements of traditional systems. The demonstrated integration approach also suggests a paradigm shift towards more robust, CMOS-compatible fabrication methods, leading to wider deployment possibilities in fields like metrology, communications, and waveform generation.

Future developments could explore enhancements in comb stability and further reductions in power consumption. Additionally, expanding the integrated photonic platform to include more versatile frequency comb configurations—such as those detailing exploitable multiple-soliton states—could bolster its application range. The scalability and resource efficiency of the demonstrated platform suggest promising avenues for extensive commercialization and integration into existing technological ecosystems.

In summary, this paper provides substantive advancements in integrated photonics, showcasing a practical approach to achieving low-power, compact frequency comb sources suitable for diverse high-precision applications.