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Register a new userDual-comb correction with spectrally broadened fiber lasers
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Authors
Philippe Guay
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The phase information provided by the beat note between frequency combs and two continuous-wave lasers is used to extrapolate the phase evolution of comb modes found in a spectral region obtained via nonlinear broadening. This thereafter enables using interferogram self-correction to fully retrieve the coherence of a dual-comb beat note between two independent fiber lasers. This approach allows to forego the $f - 2f$ self-referencing of both combs, which is a significant simplification. Broadband near-infrared methane spectroscopy has been conducted as a demonstration of the simplified systems preserved performance.
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Precision frequency and phase synchronization between distinct fiber interconnected nodes is critical for a wide range of applications, including atomic timekeeping, quantum networking, database synchronization, ultra-high-capacity coherent optical communications and hyper-scale data centers. Today, many of these applications utilize precision, tabletop laser systems, and would benefit from integration in terms of reduced size, power, cost, and reliability. In this paper we report a record low 3x10^-4 rad^2 residual phase error variance for synchronization based on independent, spectrally pure, ultra-high mutual coherence, photonic integrated lasers. This performance is achieved with stimulated Brillouin scattering lasers that are stabilized to independent microcavity references, realizing sources with 30 Hz integral linewidth and a fractional frequency instability less than or equal to 2x10^-13 at 50 ms. This level of low phase noise and carrier stability enables a new type of optical-frequency-stabilized phase-locked loop (OFS-PLL) that operates with a less than 800 kHz loop bandwidth, eliminating traditional power consuming high bandwidth electronics and digital signal processors used to phase lock optical carriers. Additionally, we measure the residual phase error down to a received carrier power of -34 dBm, removing the need to transmit in-band or out-of-band synchronized carriers. These results highlight the promise for a path to spectrally pure, ultra-stable, integrated lasers for network synchronization, precision time distribution protocols, quantum-clock networks, and multiple-Terabit per second coherent DSP-free fiber-optic interconnects.
Dual-comb lasers from which asynchronous ultrashort pulses can be simultaneously generated have recently become an interesting research subject. They could be an intriguing alternative to the current dual-laser optical-frequency-comb source with highly sophisticated electronic control systems. If generated through a common light path traveled by all pulses, the common-mode noises between the spectral lines of different pulse trains could be significantly reduced. Therefore, coherent dual-comb generation from a completely common-path, unidirectional lasing cavity would be an interesting territory to explore. In this paper, we demonstrate such a dual-comb lasing scheme based on a nanomaterial saturable absorber with additional pulse narrowing and broadening mechanisms concurrently introduced into a mode-locked fiber laser. The interactions between multiple soliton formation mechanisms result in unusual bifurcation into two-pulse states with quite different characteristics. Simultaneous oscillation of pulses with four-fold difference in pulsewidths and tens of Hz repetition rate difference is observed. The coherence between these spectral-overlapped, picosecond and femtosecond pulses is further verified by the corresponding asynchronous cross-sampling and dual-comb spectroscopy measurements.
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Philippe Guay
, Alex Tourigny-Plante
, Vincent Michaud-Belleau andn Nicolas Bourbeau Hebert
2021
The impact of photodetector nonlinearity on dual-comb spectrometers is described and compared to that of Michelson-based Fourier transform spectrometers (FTS). The optical sampling occurring in the dual-comb approach, being the key difference with FTS, causes optical aliasing of the nonlinear spectral artifacts. Measured linear and nonlinear interferograms are presented to validate the model. Absorption lines of H$^{13}$CN are provided to understand the impact of nonlinearity on spectroscopic measurements.
Dual-comb spectroscopy utilizes two sets of comb lines with slightly different comb-tooth-spacings, and optical spectral information is acquired by measuring the radio-frequency beat notes between the sets of comb lines. It holds the promise as a real-time, high-resolution analytical spectroscopy tool for a range of applications. However, the stringent requirement on the coherence between comb lines from two separate lasers and the sophisticated control system to achieve that have confined the technology to the top metrology laboratories. By replacing control electronics with an all-optical dual-comb lasing scheme, a simplified dual-comb spectroscopy scheme is demonstrated using just one dual-wavelength, passively mode-locked fiber laser. Dual-comb pulses with a repetition-frequency difference determined by the intracavity dispersion are shown to be sufficiently stable against common-mode cavity drifts and noises. As sufficiently low relative linewidth is maintained between two sets of comb lines, capability to resolve RF beat notes between comb teeth and picometer-wide optical spectral features is demonstrated using a simple data acquisition and processing system in an all-fiber setup. Possibility to use energy-efficient, free-running fiber lasers with a small comb-tooth-spacing could enable the realization of low-cost dual-comb spectroscopy systems affordable to more applications.
We demonstrate 14.3-attosecond timing jitter [integrated from 10 kHz to 94 MHz offset frequency] optical pulse trains from 188-MHz repetition-rate mode-locked Yb-fiber lasers. In order to minimize the timing jitter, we shorten the non-gain fiber length to shorten the pulsewidth and reduce excessive higher-order nonlinearity and nonlinear chirp in the fiber laser. The measured jitter spectrum is limited by the amplified spontaneous emission limited quantum noise in the 100 kHz - 1 MHz offset frequency range, while it was limited by the relative intensity noise-converted jitter in the lower offset frequency range. This intrinsically low timing jitter enables sub-100-attosecond synchronization between the two mode-locked Yb-fiber lasers over the full Nyquist frequency with a modest 10-kHz locking bandwidth. The demonstrated performance is the lowest timing jitter measured from any free-running mode-locked fiber lasers, comparable to the performance of the lowest-jitter Ti:sapphire solid-state lasers.
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