Vernier spectrometer using counterpropagating soliton microcombs

Abstract

Acquisition of laser frequency with high resolution under continuous and abrupt tuning conditions is important for sensing, spectroscopy and communications. Here, a single microresonator provides rapid and broad-band measurement of frequencies across the optical C-band with a relative frequency precision comparable to conventional dual frequency comb systems. Dual-locked counter-propagating solitons having slightly different repetition rates are used to implement a Vernier spectrometer. Laser tuning rates as high as 10 THz/s, broadly step-tuned lasers, multiline laser spectra and also molecular absorption lines are characterized using the device. Besides providing a considerable technical simplification through the dual-locked solitons and enhanced capability for measurement of arbitrarily tuned sources, this work reveals possibilities for chipscale spectrometers that greatly exceed the performance of table-top grating and interferometerbased devices.Frequency-agile lasers are ubiquitous in sensing, spectroscopy and optical communications 1-3 and measurement of their optical frequency for tuning and control is traditionally performed by grating and interferometerbased spectrometers, but more recently these measurements can make use of optical frequency combs 4-6 . Frequency combs provide a remarkably stable measurement grid against which optical signal frequencies can be determined subject to the ambiguity introduced by their equally spaced comb lines. The ambiguity can be resolved for continuously frequency swept signals by counting comb teeth 7 relative to a known comb tooth; and this method has enabled measurement of remarkably high chirp rates 8 . However, signal sources can operate with abrupt frequency jumps so as to quickly access a new spectral region or for switching purposes, and this requires a different approach. In this case, a second frequency comb with a different comb line spacing can provide a Vernier scale 9 for comparison with the first comb to resolve the ambiguity under quite general tuning conditions 9-11 . This Vernier concept is also used in dual comb spectroscopy 12,13 , but in measuring active signals the method can be significantly enhanced to quickly identify signal frequencies through a signal correlation technique 9 . The power of the Vernier-based method relies upon mapping of optical comb frequencies into a radio-frequency grid of frequencies, the precision of which is set by the relative line-by-line frequency stability of the two frequency combs. This stability can be guaranteed by self-referencing each comb using a common high-stability radio-frequency source or through optical locking of each comb to reference lasers whose relative stability is ensured by mutual locking to a common optical cavity.Here, a broad-band, high-resolution Vernier soliton microcomb spectrometer is demonstrated using a single miniature comb device that generates two mutuallyphase-locked combs. The principle of operation relies upon an optical phase locking effect observed in the generation of counter-pr...

Formation and Collision of Multistability-Enabled Composite Dissipative Kerr Solitons

“…On the other hand, DKSs exhibit a plethora of interesting phenomena such as Stokes solitons [14], soliton breathers [15][16][17], and soliton crystals [18]. Yet, to date, direct soliton interactions, including shortrange binding [19,20] and collision [21,22], have not been thoroughly investigated in DKSs, despite the fact that they hold critical importance, not only for understanding the fundamental soliton dynamics, but also for applications such as a vernier spectrometer using counterpropagating DKSs [23], as well as tricomb spectroscopy [24] with spatial multiplexing of DKSs [25]. The difficulty is threefold: first, solitons pumped by the same lasers have the same group velocity, which makes the control of the relative locations of solitons difficult; second, because of the low output power and the high repetition rate of microresonator DKSs, commonly employed imaging techniques including dispersive Fourier transformation technique [26] and electro-optic imaging technique [27] cannot be applied to image the close interaction of similar DKSs due to the limited temporal window or the coarse resolution; third, because of internal disturbances such as mode crossings [28], DKSs usually interact with other DKSs via long-range dispersive-wave-mediated effects [29][30][31][32], forming groups with large intersoliton separations, thus prohibiting the inception of direct binding and collision.…”

Advances in soliton microcomb generation

“…The Vernier spectrometer enhanced the capability for arbitrarily tuned source measurement. 118 High-performance dual-solitoncombs using two cascaded SiN microresonators with a single pump, which drastically reduces experimental complexity, have also been demonstrated. 119 In the mid-infrared region, molecular transitions are much higher (typically 10 to 1000 times) than that in the visible or near-IR, and a proof-of-principle mid-infrared DCS system based on silicon microrings was successfully realized through a thermal-controlled method.…”

Dirac solitons in optical microresonators

“…In microresonators, such Kerr solitons (KSs) have been realized in a wide range of geometries and material systems [7][8][9][10][11][12][13][14] . Soliton microcomb devices have been tested in diverse system demonstrations, including spectroscopy [15][16][17] , coherent communications 18 , range detection [19][20][21] , optical frequency synthesis 22 , exoplanet studies 23,24 , and optical clocks 25 . Progress towards integration of the microcomb with pump and other control functions is also being made [26][27][28] .…”