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Using the quasiprobability positive P of phase space representation, we examine the features of squeezing over two octaves of frequency difference with each octave integrating two-channel nonlinear waveguides. The second harmonic coupling of the light fields is taken into account in the current arrangement. We discovered that single-mode squeezing is decreased by second harmonic coupling.

Broadband and low-noise microresonator frequency combs (microcombs) are critical for deployable optical frequency measurements. Here we expand the bandwidth of a microcomb far beyond its anomalous dispersion region on both sides of its spectrum through spectral translation mediated by mixing of a dissipative Kerr soliton and a secondary pump. We introduce the concept of synthetic dispersion to qualitatively capture the system’s key physical behavior, in which the second pump enables spectral translation through four-wave mixing Bragg scattering. Experimentally, we pump a silicon nitride microring at 1063 nm and 1557 nm to enable soliton spectral translation, resulting in a total bandwidth of 1.6 octaves (137–407 THz). We examine the comb’s low-noise characteristics, through heterodyne beat note measurements across its spectrum, measurements of the comb tooth spacing in its primary and spectrally translated portions, and their relative noise. These ultra-broadband microcombs provide new opportunities for optical frequency synthesis, optical atomic clocks, and reaching previously unattainable wavelengths. Integrated optical frequency measurements, benefit from broadband on-chip frequency combs. Here the authors present a low-noise microcomb whose span extends from telecom to near-visible wavelengths. Here the authors present a dissipative Kerr soliton formation approximated by introducing the concept of synthetic dispersion.

A coherent, compact and robust light source with coverage from the ultraviolet to the infrared is desirable for heterodyne super-resolution imaging1, broadband infrared microscopy2, protein structure determination3 and standoff trace-gas detection4. To address these demanding problems, frequency combs5 combine absolute frequency accuracy with sub-femtosecond timing and waveform control to enable high-resolution, high-speed and broadband spectroscopy6–9. Here we demonstrate a scalable source of near-single-cycle pulses from robust and low-noise erbium fibre (Er:fibre) technology. With a peak power of 0.56 MW we generate a comb spanning six octaves, from the ultraviolet (350 nm) to the mid-infrared (22,500 nm), achieving a resolving power of 1010 across 0.86 PHz of bandwidth. Second-order nonlinearities in LiNbO3, GaSe and CdSiP2 provide phase-stable infrared ultrashort pulses with simultaneous brightness exceeding a synchrotron10, while cascaded nonlinearities in LiNbO3 yield four octaves simultaneously (0.350–5.6 μm). We anticipate that these advances will be enabling for basic and applied spectroscopy, microscopy and phase-sensitive nonlinear optics.Ultralow-noise erbium:fibre comb technology allows the generation of a comb spanning six octaves, from the ultraviolet (350 nm) to the mid-infrared (22,500 nm), with a resolving power of 1010 across 0.86 PHz of bandwidth.

The availability of high-energy pulses with durations shorter than the period of their carrier frequency (sub-cycle) will reveal new regimes of strong-field light–matter interactions. Parametric waveform synthesis (that is, the coherent combination of carrier-envelope-phase-stable pulses that emerge from different optical parametric amplifiers) is a promising technology for the realization of tailored optical waveforms with scalable spectral bandwidth, energy and average power. Here we use parametric waveform synthesis to generate phase-controlled sub-cycle waveforms at the millijoule energy level with excellent stability. Full control over the synthesized waveforms (currently spanning 1.7 octaves with full-width at half-maximum durations down to 2.8 fs, that is, 0.6 optical cycles at a central wavelength of 1.4 μm) enables the creation of extreme ultraviolet isolated attosecond pulses via high-harmonic generation without the need for additional gating techniques. The synthesized electric field is directly measured by attosecond-resolution sampling, which also showcases the waveform stability.Optical waveforms with a 1.7 octave spectrum and 0.6 optical cycle duration are generated at a central wavelength of 1.4 μm by parametric waveform synthesis. The output pulse energies amount to >500 μJ with fluctuations of 1% r.m.s. over 1,000 shots.

High-brightness sources of coherent and few-cycle-duration light waveforms with spectral coverage from the ultraviolet to the terahertz would offer unprecedented versatility and opportunities for a wide range of applications from bio-chemical sensing1 to time-resolved and nonlinear spectroscopy, and to attosecond light-wave electronics2,3. Combinations of various sources with frequency conversion4,5 and supercontinuum generation6–9 can provide relatively large spectral coverage, but many applications require a much broader spectral range10 and low-jitter synchronization for time-domain measurements11. Here, we present a carrier-envelope-phase (CEP)-stable light source, seeded by a mid-infrared frequency comb12,13, with simultaneous spectral coverage across seven optical octaves, from the ultraviolet (340 nm) into the terahertz (40,000 nm). Combining soliton self-compression and dispersive wave generation in an anti-resonant-reflection photonic-crystal fibre with intra-pulse difference frequency generation in BaGa2GeSe6, the spectral brightness is two to five orders of magnitude above that of synchrotron sources. This will enable high-dynamic-range spectroscopies and provide numerous opportunities in attosecond physics and material sciences14,15.Using a gas-filled anti-resonant-reflection photonic-crystal fibre, a high-brightness table-top source of coherent carrier-envelope-phase-stable waveforms is demonstrated across seven octaves (340 nm to 40,000 nm) with ultraviolet peak powers up to 2.5 MW and terahertz peak powers of 1.8 MW, without the need for changing nonlinear crystals.

Silica-based photonic crystal fibre has proven highly successful for supercontinuum generation, with smooth and flat spectral power densities. However, fused silica glass suffers from strong material absorption in the mid-infrared (>2,500 nm), as well as ultraviolet-related optical damage (solarization), which limits performance and lifetime in the ultraviolet (<380 nm). Supercontinuum generation in silica photonic crystal fibre is therefore only possible between these limits. A number of alternative glasses have been used to extend the mid-infrared performance, including chalcogenides, fluorides and heavy-metal oxides, but none has extended the ultraviolet performance. Here, we describe the successful fabrication (using the stack-and-draw technique) of a ZBLAN photonic crystal fibre with a high air-filling fraction, a small solid core, nanoscale features and near-perfect structure. We also report its use in the generation of ultrabroadband, long-term stable, supercontinua spanning more than three octaves in the spectral range 200–2,500 nm. A low-loss ZBLAN micro-structured fibre is used to generate a supercontinuum spanning from the UV to the mid-IR (200 nm–2,500 nm). The material has high resistance even after extended operation and can withstand large spectral power densities.

Modern communication and sensing technologies connect the optical domain with the microwave domain. Accessing the terahertz region from 100 GHz to 10 THz is critical for providing larger bandwidths capabilities. Despite progress in integrated electronics, they lack a direct link to the optical domain, and face challenges with increasing frequencies ( > 1 THz). Electro-optic effects offer promising capabilities but are currently limited to bulk nonlinear crystals, missing out miniaturization, or to sub-terahertz bandwidths. Here, we address these challenges by realizing photonic circuits that integrate terahertz transmission lines on thin-film lithium niobate (TFLN). By providing terahertz field confinement and phase-matched interaction with optical fields, our miniaturized devices support low-noise and broad bandwidth terahertz generation and detection spanning four octaves (200 GHz to  > 3 THz). By leveraging photonics’ advantages in low-loss and high-speed control, our platform achieves control over the terahertz spectrum and its amplitude, paving the way for compact and power-efficient devices with applications in telecommunications, spectroscopy, quantum electrodynamics and computing. Terahertz transmission lines are integrated with photonic integrated circuits, achieving phase matching over extended bandwidths up to 3.5 THz, and laying the foundation for broadband integrated terahertz photonics. The authors demonstrate emitters, detectors, and cavities in the terahertz regime on a scalable thin-film lithium niobate platform.

We present the comprehensive characterization of a series of harmonic fields generated in a ZnO crystal by a few-cycle MIR driving pulse that spans the visible to mid-infrared (MIR) spectral region. The characterization is conducted using the recently developed Plasma-Induced Frequency Resolved Optical Switching (PI-FROSt) technique. We demonstrate the ability of this method to accurately characterize the MIR driving field (λ = 3.2 μm), as well as both odd and even harmonics up to the fifth order. The total spectral bandwidth extends over an exceptionally wide range of 2.6 octaves. All assessments validate the high precision of the field reconstructions and confirm the suitability of the PI-FROSt method for the metrology of over-octave-spanning waveforms. The results offer valuable insights into the fundamental mechanisms governing harmonic generation and emphasize the crucial influence of propagation and cascading.

Tailoring the electric-field waveform of ultrashort light pulses forms the basis for controlling nonlinear optical phenomena on their genuine, attosecond timescale. Here we extend waveform control from the visible and near-infrared—where it was previously demonstrated—to the mid-infrared spectral range. Our approach yields single-cycle infrared pulses over several octaves for the first time. Sub-10-fs pulses from a carrier-envelope-phase-stabilized, Kerr-lens-mode-locked, diode-pumped Cr:ZnS laser drive cascaded intrapulse difference-frequency generation and control the electric-field evolution of the resulting coherent emission over 0.9–12.0 μm. Sub-cycle field control in this wavelength range will be instrumental for launching and steering few-femtosecond electron/hole wavepackets in low-gap materials, extending the bandwidth of electronic signal processing to multi-terahertz frequencies, as well as for electric-field-resolved molecular fingerprinting of biological systems.Continuously adjustable single-cycle waveform spanning from 0.9 to 12.0 μm is obtained by cascaded intrapulse difference-frequency generation in a ZnGeP2 crystal. The cascade-associated phase response—distinct for different spectral bands—provides a new tuning parameter for waveform adjustment.

Multimode optical fibers have recently reemerged as a viable platform for addressing a number of long-standing issues associated with information bandwidth requirements and power-handling capabilities. As shown in recent studies, the complex nature of such heavily multimoded systems can be effectively exploited to observe altogether novel physical effects arising from spatiotemporal and intermodal linear and nonlinear processes. Here, we study for the first time, accelerated nonlinear intermodal interactions in core-diameter decreasing multimode fibers. We demonstrate that in the anomalous dispersion region, this spatiotemporal acceleration can lead to relatively blue-shifted multimode solitons and blue-drifting dispersive wave combs, while in the normal domain, to a notably flat and uniform supercontinuum, extending over 2.5 octaves. Our results pave the way towards a deeper understanding of the physics and complexity of nonlinear, heavily multimoded optical systems, and could lead to highly tunable optical sources with very high spectral densities. Multimode optical fibers can be used to observe complex intermodal processes like optical solitons. Here, Eftekhar et al. study accelerated nonlinear interaction in multimode fibers with a tapered core diameter and its effect on the temporal and spectral behavior of the multimode solitons.