Abstract
Dual frequency comb (DFC) spectroscopy using electro-optic comb generators stands out for its flexibility, easy implementation, and low cost. Typically, two combs with different line spacing are generated from a common laser using independent electro-optic comb generators. This approach minimizes the impact of laser phase noise; however, the distinct paths followed by the two combs ultimately limit the attainable signal-to-noise ratio and long-term stability of the system. In this work, a common-path DFC is generated using a single modulator driven by an arbitrary waveform generator, thus enabling a remarkable increase of the system stability (up to 0.8 s of integration time) while maintaining high flexibility. The proposed technique is experimentally validated by implementing a dual frequency comb with 3000 lines, covering an optical bandwidth of 4.5 GHz, and demonstrating an optical-to-radiofrequency compression factor of 7500. Our system is able to measure extremely narrowband optical features (in the MHz range) with an accuracy only limited by the master laser stability.
Highlights
O PTICAL frequency combs (OFCs) have become a groundbreaking technology in a variety of applications, such as precision spectroscopy [1], distance ranging [2] and telecommunications [3], to name just a few
We propose a method to generate a singlepath dual-comb based on a single electro-optic modulator, fed by a low phase noise CW laser, and driven by an arbitrary waveform generator (AWG)
The main features of the Brillouin gain/loss spectrum can be resolved with high resolution in the electrical domain, with a compression factor (CF) = 7500, as expected from the Dual frequency comb (DFC) settings
Summary
O PTICAL frequency combs (OFCs) have become a groundbreaking technology in a variety of applications, such as precision spectroscopy [1], distance ranging [2] and telecommunications [3], to name just a few. Mode-locked fiber lasers [18], [19], a mode-locked integrated external-cavity surface emitting laser [20] and dissipative Kerr solitons counter-propagating in a microresonator [21] These schemes generally present limited flexibility to tune both the comb line spacing and the down-conversion factor, some of these restrictions have been recently alleviated by the use of a bidirectional frequency-shifting loop seeded with a CW laser [22]. In all the described dual-comb schemes, the two generated frequency combs propagate along different arms before interfering, even when they are originated from the same cavity or fiber loop In this way, thermal fluctuations or any uncorrelated noise between the two arms imposes an ultimate limit to the mutual coherence between the combs. With the current AWG technology, this method can be engineered to resolve extremely sharp optical features, in the order of MHz or below, as demonstrated hereafter
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