Quasi-phase matched multispectral Kerr frequency comb

An optical channelized receiver (OCR) with a novel structure based on two coherent optical frequency combs (OFCs) and a Fabry-Perot (FP) filter has been proposed. Input wideband signals are multicasted in all optical channels by modulating one OFC. Then, different sub-frequency bands in all optical channels are filtered out by the FP filter. Finally, the sub-frequency bands are directly converted to intermediate frequency (IF) via coherent optical heterodyne with the LO provided by another OFC. Experiment results shows that the OCR works in X band with 8 channels, and the bandwidth of each channel is 500MHz, which means the instantaneous bandwidth of the OCR is 4GHz. The max power fluctuation between different channels is 4dB, which can be improved by adding proper attenuators to certain channels. The spurious free dynamic range (SFDR) of all channels is above 44dB under noise bandwidth of 1MHz, which equals to 84 dB·Hz2/3.

Globally, the long-haul transmission of ultra-high bandwidth data is enabled through coherent communications. Driven by the rapid pace of growth in interconnectivity over the last decade, long-haul data transmission has reached capacities on the order of tens to hundreds of terabits per second, over fiber reaches which may span thousands of kilometers. Data center communications operate in regimes featuring shorter reaches and higher cost sensitivity. While integrated microresonator frequency combs are poised to revolutionize light sources used for high-speed data transmission over fiber, recent progress has focused largely on coherent detection schemes. Furthermore, though state-of-the-art intensity modulators are advancing in speed, it has not been demonstrated in the literature if microresonator-based comb lines can accommodate higher intensity modulated direction data (IMDD) line rates in tandem with these advancements. In this manuscript, we demonstrate the use of microresonator frequency combs pumped with a single laser for the transmission of high-speed IMDD data. We demonstrate error-free transmission of 30 Gbs-1 per comb non-return-to-zero data over fiber lengths of 6 km, as well as bit error rates under the forward error correction limit for propagation through 20 km of optical fiber. 60 Gbs-1 and 42 Gbs-1 pulse modulation amplitude 4 (PAM4) data modulated on each frequency comb line is further quantified to have a bit error rate under the forward error correction limit for fiber reaches of up to 6 km and 20 km respectively. The results showcase CMOS-compatible microresonator frequency comb modulated using IMDD formats as a promising technology for high-speed transmission in the data center transceiver industry.

It has been difficult to use the measured dispersion data to determine which transverse mode is the best to use for producing optical frequency combs in microresonators. We propose a simulation method to do so.

Pulsed driving of Kerr microresonators represents a promising avenue for the\nefficient generation of soliton states associated with coherent optical\nfrequency combs. The underlying physics has not, however, yet been\ncomprehensively investigated. Here, we report on a numerical and theoretical\nstudy of the impact of de-synchronization between the periodic pump field and\nthe train of solitons circulating in the cavity. We show that\nde-synchronization can affect the soliton configurations that can be sustained\nfor given parameters, and that it can be leveraged to guarantee operation in\nthe attractive single-soliton regime. We also reveal that the interplay between\npump-resonator de-synchronization and stimulated Raman scattering can give rise\nto rich dynamics that explain salient features observed in recent experiments.\nOur work elucidates the dynamics of Kerr cavity solitons in the presence of\npulsed driving fields, and could facilitate the development of efficient\nmicroresonator frequency comb systems.\n

Multi-color solitons that are parametrically created in dual-pumped microresonators generate interleaved frequency combs that can be used to obtain combs at new frequencies and, when synchronized, can be used for low-noise microwave generation and potentially as an element in a chip-scale clockwork. Here, we first derive three-wave equations that describe multi-color solitons that appear in microresonators with a nearly quartic dispersion profile. These solitons are characterized by a single angular group velocity and different angular phase velocities. We then use these equations to explain the interleaved frequency combs that are observed at the output of the microresonator. Finally, we used these equations to describe the experimentally-observed soliton-OPO effect. In this effect, the pump frequency color interacts nonlinearly with a signal frequency color to create an idler frequency color in a new frequency range, somewhat analogous to an optical parametric oscillation (OPO) process, but in which the Kerr nonlinearity plays a role in matching the angular group velocity, analogous to soliton formation. These three colors then create an interleaved frequency comb in the output waveguide. We determine the conditions under which we expect this effect to occur. We anticipate that the three-wave equations and their extensions will be of use in designing new frequency comb systems and determining their stability and noise performance.

The aim of this work is to theoretically investigate the possibility of Kerr frequency combs in mechanical systems. In particular, whether microelectromechanical devices (MEMS) can be used to generate frequency combs in a manner that is analogous to the optical frequency combs generated in optical microresonators with Kerr-type nonlinearity. The analysis assumes a beam-like micromechanical structure, and starting from the Euler-Bernoulli beam equation derives the necessary conditions in parameter space for the comb generation. The chapter equally presents potential means for the physical implementation of mechanical Kerr combs.

Microcombs are optical frequency combs in microresonators [1], [2]. Laser cavity-soliton (LCS) states can be achieved in a system comprising a nonlinear Kerr microresonator nested in a fibre laser [3], resulting in a self-emergent, robust [4], and efficient [5] microcomb. Generally, the platform generally produces a broader variety of states depending on the specific parameter settings of the system. The two critical experimental parameters that need to be adjusted to achieve solitary oscillation via self-emergence [4] are the gain, which controls the state energy, and the length of the main cavity, which governs the group velocity mismatch between the two cavities. When searching for solitary oscillations, these parameters must be spanned over large ranges. While detailed information can be obtained through accurate but time-consuming methods like laser scanning spectroscopy and interferometry, real-time approaches are preferable when handling large datasets. In this work, we introduce a rapid method to distinguish typical lasing states, including soliton states, based on simple experimental properties. Specifically, our approach utilises radiofrequency (RF) data and spectral analysis to map states within nonlinear optical systems in real time, with minimal computational effort when handling large datasets.

We study theoretically and demonstrate experimentally generation of coherent optical frequency combs in a sapphire whispering gallery mode resonator. We verify phase locking of the comb harmonics by demodulating the comb on a fast photodiode and by observing the production of a spectrally pure radio frequency signal. Because of excellent optical and superior mechanical properties of the material, the sapphire resonator is an excellent candidate for the on-chip device integration of the comb oscillator.

Optical resonator-based Kerr frequency combs allow an ultra-precise time and frequency measurements for a wide range of applications including ranging, biosensing, high-capacity communications, and quantum information technology. Kerr solitons are coherent frequency combs that are crucial for frequency synthesizer and chronometric instruments. The behavior of the soliton is determined by multiple factors while the key challenge for stable operation is to maintain thermal equilibrium in the resonator. In this work, owing to the stabilizing thermal effect caused by a neighboring auxiliary mode (TE10), we demonstrate the generation of octave-spanning (1100-2380 nm) single-soliton within a wide laser detuning range (up to 16 GHz) by pumping the TE00 mode. The influence of temperature on the microcombs behavior is also explored. Firstly, diverse two-solitons are achieved by adjusting the temperature. Secondly, the soliton access possibility is reduced when further increasing the temperature due to the avoided mode crossing between the pump mode (TE00) and another adjacent fundamental transverse-magnetic mode. At the same time, the spectral bandwidth of the microcomb that originates from TM00 modes is significantly enhanced. Finally, we show that the carrier offset frequency, which is evaluated to be ∼30-40 GHz, increases as the temperature is increased.

Generation of coherent frequency combs in optical microresonators at normal GVD is a challenging task. It is well known that they can be generated in the form of the flat-top solitonic pulses, platicons, via controllable mode interaction or modulated pump. However, such methods are rather complicated, requiring either sophisticated mode interactions, complex two-cavity systems or high-frequency modulators. Recent investigations have shown that the self-injection locking effect provides interesting possibilities for frequency comb generation. It has been shown that this effect not only provides laser stabilization due to the resonant backscattering of laser radiation from the high-quality-factor microresonator but also leads to the nontrivial nonlinear dynamics in the same microresonator. First, this has been demonstrated for bright solitons with an ordinary laser diode as a pump source. Recently, it has been shown experimentally that such approach is also applicable for platicon generation and does not require additional equipment. In our work we study this process in detail and identify different generation regimes depending on the combination of the pump power and the backscattering coefficient providing the self-injection locking effect. The range of parameters necessary for the efficient platicon generation is found. We also report a novel mechanism of platicon generation based on the thermal effects inevitable in real-life systems. We show that it is possible if thermal effects are negative (the direction of the thermal shift of the microresonator resonance is opposite to the direction of the nonlinear shift) and the ratio of the thermal relaxation time to photon lifetime is small enough. Different generation regimes are found, and the possibility of the turn-key operation regime is demonstrated.

Kerr frequency combs in optical passive microresonators promise new breakthrough in photonics. Such combs result from multiple hyper-parametric four-wave mixing processes. The report presents the results of recent theoretical and experimental studies, leading to the development of compact and integrated coherent frequency comb sources.

We phase-lock a frequency comb based on a few-cycle Cr:ZnS laser oscillator to its narrow-linewidth optical pump, creating a set of mutually coherent optical frequency combs that span from the visible to the long-wave IR.

Generating coherent optical frequency combs in micro-ring resonators with Kerr nonlinearity has remarkably advanced the fundamental understanding and applications of temporal dissipative solitons. However, the spectrum of such soliton combs is restricted to the conventional definition of combs as phase-locked, equidistant lines in frequency. Here, we introduce a new class of floquet topological soliton combs that emerge in two-dimensional arrays of strongly coupled resonators engineered using floquet topology. Specifically, we demonstrate incommensurate combs where the comb lines are not equidistant but remain phase-locked. These incommensurate combs are generated by self-organized, phase-locked floquet topological soliton molecules that circulate the edge of the array. We show that these floquet topological solitons are robust and they navigate around defects, allowing for agile tunability of the comb line spacing. Our results introduce a new paradigm in using floquet engineering to generate unconventional frequency combs beyond those achievable with single or weakly coupled resonators.

We determine the regions in the parameter space of microresonators where cnoidal waves (Turing rolls) are stable. Solitons are included as a special limit. We identify conditions to efficiently obtain broadband frequency combs.

Optical frequency combs function as extremely broad bandwidth photonic synthesizers, capable of generating ultra-low noise signals from radio frequency to optical domains. We present synthesis results with both mode-locked laser and microresonator frequency combs.