Microresonator Soliton Dual-Comb Spectroscopy (1607.08222v1)

Abstract: Rapid characterization of optical and vibrational spectra with high resolution can identify species in cluttered environments and is important for assays and early alerts. In this regard, dual-comb spectroscopy has emerged as a powerful approach to acquire nearly instantaneous Raman and optical spectra with unprecedented resolution. Spectra are generated directly in the electrical domain and avoid bulky mechanical spectrometers. Recently, a miniature soliton-based comb has emerged that can potentially transfer the dual-comb method to a chip platform. Unlike earlier microcombs, these new devices achieve high-coherence, pulsed mode locking. They generate broad, reproducible spectral envelopes, which is essential for dual-comb spectroscopy. Here, dual-comb spectroscopy is demonstrated using these devices. This work shows the potential for integrated, high signal-to-noise spectroscopy with fast acquisition rates.

• The paper demonstrates the integration of soliton microcombs in dual-comb spectroscopy for chip-scale, high-fidelity spectral measurements.
• It employs high-Q silica wedge microresonators to generate phase-locked femtosecond pulses, achieving 30 nm optical bandwidth and 22 GHz resolution.
• The system attains over 30 dB SNR and paves the way for compact, integrated spectroscopic devices and future advancements in diverse applications.

Microresonator Soliton Dual-Comb Spectroscopy

Introduction

The paper "Microresonator Soliton Dual-Comb Spectroscopy" explores advancements in dual-comb spectroscopy, emphasizing the integration of soliton microcombs. Dual-comb spectroscopy is recognized for its potential to perform rapid, high-resolution optical and vibrational spectroscopy. This paper showcases a novel implementation using soliton-based microresonators, providing an efficient pathway for chip-scale spectroscopy with considerable implications for real-world applications.

Technical Overview

Dual-comb spectroscopy leverages the coherence properties of two frequency combs with slightly different repetition frequencies to allow the measurement of broad-band spectra with high resolution. Traditional systems are often bulky with substantial mechanical requirements, but advances in microresonator technology represent a significant departure from these limitations by transitioning to a chip-scale platform.

The microcombs in this paper, generated via soliton mode-locking in microresonators, provide phase-locked femtosecond pulses. These pulses maintain a well-defined and reproducible spectral shape essential for achieving high signal-to-noise ratio (SNR) in dual-comb spectroscopy. The experimental setup exploits two microresonators to produce distinct soliton pulse trains, which are then combined for interferogram generation.

Results

This paper reports the realization of dual-comb spectroscopy using soliton microcombs. High-Q silica wedge microresonators, fabricated with precise lithographic control, are employed, which maintain a repetition rate difference that is carefully matched to achieve a comprehensive optical bandwidth measurement within a limited electrical bandwidth. This is a crucial aspect of enabling broad-band spectral analysis with high fidelity.

Numerically, the system demonstrated a spectral coverage over 30 nm in optical C-band, with an optical resolution of 22 GHz and an electrical bandwidth below 500 MHz. The soliton microcomb-based dual-comb spectroscopy system achieved a SNR in excess of 30 dB, highlighting superior performance characteristics that support its potential integration into compact devices.

Implications and Future Work

The practical implications of this work are noteworthy. Soliton microcombs provide a promising route to realize dual-comb spectroscopy systems that are not only compact but also capable of being integrated with other devices on a chip. The potential to extend the spectral coverage using fiber nonlinear broadening or internal resonator dispersive wave generation is considerable. Further, advancements could lead to the development of chip-based dual-comb coherent anti-Stokes Raman spectroscopy (CARS), broadening the application scope of this technology.

Work could also expand into covering other spectral ranges by modifying the resonator dispersion, which, in turn, could leverage a wide range of mid-infrared microcomb-enabling materials. Such work could dramatically enhance the usability of this technology for various applications, including atmospheric testing, chemical assays, and potentially dynamic process analysis, such as observing real-time chemical reactions.

Conclusion

This paper effectively demonstrates the capabilities of soliton microcombs in dual-comb spectroscopy, marking a significant advance towards integrated spectroscopic systems. The work highlights both strong technical accomplishments and provides a roadmap for future research and development, emphasizing the transition from laboratory-scale apparatus to practical chip-based devices suitable for diverse applications.