High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical process and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectroscopy via supercontinuum generation, achieved using unprecedented nanophotonic dispersion engineering that allows for flat-envelope, ultra-broadband mid-IR comb spectra. The mid-IR dual-comb has an instantaneous bandwidth covering the functional group region from 2800-3600 1/cm, comprising more than 100,000 comb lines, enabling parallel gas-phase detection with a high sensitivity, spectral resolution, and speed. In addition to the traditional functional groups, their isotopologues are also resolved in the supercontinuum based dual-comb spectroscopy. Our approach combines well established fiber laser combs, digital coherent data averaging, and integrated nonlinear photonics, each in itself a state-of-the-art technology, signalling the emergence of mid-IR dual-comb spectroscopy for use outside of the protected laboratory environment.
Tapered and dispersion managed (DM) silicon nanophotonic waveguides are investigated for the generation of optimal ultra broadband supercontinuum (SC). DM waveguides are structures showing a longitudinally dependent group velocity dispersion that results from the variation of the waveguide width with the propagation distance. For the generation of optimal SC, a genetic algorithm has been used to find the best dispersion map. This allows for the generation of highly coherent supercontinuums that span over 1.14 octaves from 1300 nm to 2860 nm and 1.25 octaves from 1200 nm to 2870 nm at -20 dB le…
Tapered and dispersion managed (DM) silicon nanophotonic waveguides are investigated for the generation of optimal ultra broadband supercontinuum (SC). DM waveguides are structures showing a longitudinally dependent group velocity dispersion that results from the variation of the waveguide width with the propagation distance. For the generation of optimal SC, a genetic algorithm has been used to find the best dispersion map. This allows for the generation of highly coherent supercontinuums that span over 1.14 octaves from 1300 nm to 2860 nm and 1.25 octaves from 1200 nm to 2870 nm at -20 dB le…
We demonstrate an octave-spanning frequency comb with a spectrum covering wavelengths from 1,540 nm up to 3,200 nm. The supercontinuum is generated by pumping a 1-cm long dispersion engineered silicon wire waveguide by 70 fs pulses with an energy of merely 15 pJ. We confirm the phase coherence of the output spectrum by beating the supercontinuum with narrow bandwidth CW lasers. We show that the experimental results are in agreement with numerical simulations.
Si$_3$N$_4$ waveguides, pumped at 1550 nm, can provide spectrally smooth, broadband light for gas spectroscopy in the important 2 ${\mathrmμ}$m to 2.5 ${\mathrmμ}$m atmospheric water window, which is only partially accessible with silica-fiber based systems. By combining Er+:fiber frequency combs and supercontinuum generation in tailored Si$_3$N$_4$ waveguides, high signal-to-noise dual-comb spectroscopy (DCS) spanning 2 ${\mathrmμ}$m to 2.5 ${\mathrmμ}$m is demonstrated. Acquired broadband dual-comb spectra of CO and CO$_2$ agree well with database line shape models and have a spectral-signal…
Mid-infrared-to-ultraviolet supercontinuum generation in low-loss tantalum pentoxide nanophotonic waveguides
State Key Laboratory of Ultra-intense Laser Science and Technology, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences（中国科学院上海光学精密机械研究所）；Key Laboratory of Specialty Fiber Optics and Optical Access Networks, Shanghai University（上海大学）；The Extreme Optoelectromechanics Laboratory (XXL), School of Physics, East China Normal University（华东师范大学）；State Key Laboratory of Precision Spectroscopy, East China Normal University（华东师范大学）；Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences（中国科学院大学）；University College London（伦敦大学学院）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Hefei National Laboratory（合肥国家实验室）；Collaborative Innovation Center of Extreme Optics, Shanxi University（山西大学）；Collaborative Innovation Center of Light Manipulations and Applications, Shandong Normal University（山东师范大学）
Infrared spectroscopy is a powerful tool for basic and applied science. The molecular spectral fingerprints in the 3 um to 20 um region provide a means to uniquely identify molecular structure for fundamental spectroscopy, atmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise, coherent laser sources with broad, tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can enable the above-mentioned applicat…
We demonstrate a route to supercontinuum generation in gas-filled hollow-core anti-resonant fibers through the creation of a broad vibrational Raman frequency comb followed by continuous broadening and merging of the comb lines through either rotational Raman scattering or the optical Kerr effect. Our demonstration experiments, utilizing a single pump pulse with 20 ps duration at 532 nm in a nitrogen-filled fiber, produce a supercontinuum spanning from 440 nm to 1200 nm, with an additional deep ultraviolet continuum from 250 nm to 360 nm. Numerical results suggest that this approach can produc…
There are several mechanisms by which the frequency spectrum of a laser broadens when it propagates at near-relativistic-intensity in tenuous plasma. Focusing on one dimensional effects, we identify two strong optical nonlinearities, namely, four-wave mixing (FWM) and forward Raman scattering (FRS), for creating octave-wide spectra. FWM dominates the interaction when the laser pulse is short and intense; Its combination with phase modulation produces a symmetrically broadened supercontinuum. FRS dominates when the laser pulse is long and relatively weak; It broadens the laser spectrum mainly t…
We demonstrate mid-infrared (mid-IR) supercontinuum generation (SCG) with instantaneous bandwidth from 2.2 to 5 μm at 40 dB below the peak, covering the wavelength range desirable for molecular spectroscopy and numerous other applications. The SCG occurs in a tapered As2S3 fiber prepared by in-situ tapering and is pumped by femtosecond pulses from the subharmonic of a mode-locked Er-doped fiber laser. Interference with a narrow linewidth c.w. laser verifies that the coherence properties of the near-IR frequency comb have been preserved through these cascaded nonlinear processes. With this appr…
Using aluminum-nitride photonic-chip waveguides, we generate optical-frequency-comb supercontinuum spanning from 500 nm to 4000 nm with a 0.8 nJ seed pulse, and show that the spectrum can be tailored by changing the waveguide geometry. Since aluminum nitride exhibits both quadratic and cubic nonlinearities, the spectra feature simultaneous contributions from numerous nonlinear mechanisms: supercontinuum generation, difference-frequency generation, second-harmonic generation, and third-harmonic generation. As one application of integrating multiple nonlinear processes, we measure and stabilize …
We demonstrate a broad, flat, visible supercontinuum spectrum that is generated by a dispersion-engineered tapered photonic crystal fiber pumped by a 1 GHz repetition rate turn-key Ti:sapphire laser outputting $\sim$ 30 fs pulses at 800 nm. At a pulse energy of 100 pJ, we obtain an output spectrum that is flat to within 3 dB over the range 490-690 nm with a blue tail extending below 450 nm. The mode-locked laser combined with the photonic crystal fiber forms a simple visible frequency comb system that is extremely well-suited to the precise calibration of astrophysical spectrographs, among oth…
Frequency combs with mode spacing in the range of 10 to 20 gigahertz (GHz) are critical for increasingly important applications such as astronomical spectrograph calibration, high-speed dual-comb spectroscopy, and low-noise microwave generation. While electro-optic modulators and microresonators can provide narrowband comb sources at this repetition rate, a significant remaining challenge is a means to produce pulses with sufficient peak power to initiate nonlinear supercontinuum generation spanning hundreds of terahertz (THz) as required for self-referencing in these applications. Here, we pr…
All-optical signal processing is envisioned as an approach to dramatically decrease power consumption and speed up performance of next-generation optical telecommunications networks. Nonlinear optical effects, such as four-wave mixing (FWM) and parametric gain, have long been explored to realize all-optical functions in glass fibers. An alternative approach is to employ nanoscale engineering of silicon waveguides to enhance the optical nonlinearities by up to five orders of magnitude, enabling integrated chip-scale all-optical signal processing. Previously, strong two-photon absorption (TPA) o…
Supercontinuum generation using chip-integrated photonic waveguides is a powerful approach for spectrally broadening pulsed laser sources with very low pulse energies and compact form factors. When pumped with a mode-locked laser frequency comb, these waveguides can coherently expand the comb spectrum to more than an octave in bandwidth to enable self-referenced stabilization. However, for applications in frequency metrology and precision spectroscopy, it is desirable to not only support self-referencing, but also to generate low-noise combs with customizable broadband spectra. In this work, w…
We present detailed studies of the coherence properties of an ultra-broadband super-continuum, enabled by a new approach involving continuous wave laser sources to independently probe both the amplitude and phase noise quadratures across the entire spectrum. The continuum coherently spans more than 1.5 octaves, supporting Hz-level comparison of ultrastable lasers at 698 nm and 1.54 μm. We present the first numerical simulation of the accumulated comb coherence in the limit of many pulses, in contrast to the single-pulse level, with systematic experimental verification. The experiment and numer…
Optical frequency comb is an enabling technology for a multitude of applications from metrology to ranging and communications. The tremendous progress in sources of optical frequency combs has mostly been centered around the near-infrared spectral region while many applications demand sources in the visible and mid-infrared, which have so far been challenging to achieve, especially in nanophotonics. Here, we report frequency combs tunable from visible to mid-infrared on a single chip based on ultra-widely tunable optical parametric oscillators in lithium niobate nanophotonics. Using picosecond…
Dissipative solitons formed in Kerr microresonators may enable chip-scale frequency combs for precision optical metrology. Here we explore the creation of an octave-spanning, 15-GHz repetition-rate microcomb suitable for both f-2f self-referencing and optical-frequency comparisons across the near infrared. This is achieved through a simple and reliable approach to deterministically generate, and subsequently frequency stabilize, soliton pulse trains in a silica-disk resonator. Efficient silicon-nitride waveguides provide a supercontinuum spanning 700 to 2100 nm, enabling both offset-frequency …
For the first time, we demonstrated that a hyper-broadband from 2μm to 10μm can be generated with a high spectral flatness by using a ~4 um pump and an As2Se3 photonic crystal fiber. The broad and flat dispersion profile and the low guiding loss of the endlessly single-mode As2Se3 photonic crystal fibers combining with the high nonlinearity and wide mid-infrared transparent window of As2Se3 chalcogenide glass are essential for this high performance mid-infrared laser source.
In supercontinuum generation, various propa- gation effects combine to produce a dramatic spec- tral broadening of intense ultrashort optical pulses with far reaching possibilities. Different applications place highly divergent and challenging demands on source characteristics such as spectral coverage from the ultraviolet (UV) across the visible (VIS) to the near-infrared (NIR), and into the mid-infrared (MIR). Shot-to-shot repeatability, high spectral energy density, an absence of complicated or non-deterministic pulse splitting are also essential for many applications. Here we present an "a…
Directly accessing the middle infrared, the molecular functional group spectral region, via supercontinuum generation processes based on turn-key fiber lasers offers the undeniable advantage of simplicity and robustness. Recently, the assessment of the coherence of the mid-IR dispersive wave in silicon nitride waveguides, pumped at telecom wavelength, established an important first step towards mid-IR frequency comb generation based on such compact systems. Yet, the spectral reach and efficiency still fall short for practical implementation. Here, we experimentally demonstrate for the first ti…
Supercontinuum (SC) generation via femtosecond (fs) pumping in all-normal-dispersion (ANDi) fiber is predicted to offer completely coherent broadening mechanisms, potentially allowing for substantially reduced noise levels in comparison to those obtained when operating in the anomalous dispersion regime. However, previous studies of SC noise typically treat only the quantum noise, typically in the form of one-photon-per-mode noise, and do not consider other technical noise contributions, such as the stability of the pump laser, which become important when the broadening mechanism itself is coh…
Detection and identification of lipids are highly coveted for the interrogation of chronic diseases such as atherosclerosis and myocardial infarction. Intravascular photoacoustic imaging (IVPA) and deep tissue imaging are modern techniques, which rely on complex near infrared (NIR) optical parametric oscillators (OPOs) and other high-power solid-state laser systems for the diagnosis, which in turn make the systems bulky and expensive. In this work, we propose a cost-effective directly modulated high pulse energy supercontinuum source (operating in kHz regime) based on a standard optical fiber …
We utilize silicon-nitride waveguides to self-reference a telecom-wavelength fiber frequency comb through supercontinuum generation, using 11.3 mW of optical power incident on the chip. This is approximately ten times lower than conventional approaches using nonlinear fibers and is enabled by low-loss (<2 dB) input coupling and the high nonlinearity of silicon nitride, which can provide two octaves of spectral broadening with incident energies of only 110 pJ. Following supercontinuum generation, self-referencing is accomplished by mixing 780-nm dispersive-wave light with the frequency-doubled …
We phase-coherently measure the frequency of continuous-wave (CW) laser light by use of optical-phase modulation and f-2f nonlinear interferometry. Periodic electro-optic modulation (EOM) transforms the CW laser into a continuous train of picosecond optical pulses. Subsequent nonlinear-fiber broadening of this EOM frequency comb produces a supercontinuum with 160 THz of bandwidth. A critical intermediate step is optical filtering of the EOM comb to reduce electronic-noise-induced decoherence of the supercontinuum. Applying f-2f self-referencing with the supercontinuum yields the carrier-envelo…
Frequency microcombs, successors to mode-locked laser and fiber combs, enable miniature rulers of light for applications including precision metrology, molecular fingerprinting, and exoplanet discoveries. To enable the frequency ruling function, microcombs must be stabilized by locking their carrier-envelop offset frequency. So far, the microcomb stabilization remains compounded by the elaborate optics external to the chip, thus evading its scaling benefit. To address this challenge, here we demonstrate a nanophotonic chip solution based on aluminum nitride thin films, which simultaneously off…
Ultraviolet frequency combs enable applications ranging from precision spectroscopy to atomic clocks by addressing the electronic transitions of atoms and molecules. Access to ultraviolet light via integrated nonlinear optics is usually hampered by the strong material dispersion and large waveguide attention in the ultraviolet region. Here we demonstrate a simple route to chip-scale ultraviolet comb generators, simultaneously showing a gap-free frequency span of ~128 terahertz and supercontinuum sourced by an ultrafast fiber laser. The simultaneous cubic and quadratic nonlinear processes are i…
A tapered semiconductor amplifier is injection seeded by a femtosecond optical frequency comb at 780 nm from a mode-locked Ti:sapphire laser. Energy gains over 17 dB (12 dB) are obtained for 1 mW (20 mW) of average input power when the input pulses are stretched into the picosecond range. A spectral window of supercontinuum light generated in a photonic fiber has also been amplified. Interferometric measurements show sub-hertz linewidths for a heterodyne beat between the input and amplified comb components, yielding no detectable phase-noise degradation under amplification. These amplifiers ca…
Periodically poled lithium niobate (PPLN) waveguide is a powerful platform for efficient wavelength conversion. Conventional PPLN converters however typically require long device lengths and high pump powers due to the limited nonlinear interaction strength. Here we use a nanostructured PPLN waveguides to demonstrate an ultrahigh normalized efficiency of 2600%/W-cm$^2$ for second-harmonic generation of 1.5-$μ$m radiation, more than 20 times higher than that in state-of-the-art diffused waveguides. This is achieved by a combination of sub-wavelength optical confinement and high-fidelity periodi…
Quantum memories for light are important components for future long distance quantum networks. We present on-chip quantum storage of telecommunications band light at the single photon level in an ensemble of erbium-167 ions in an yttrium orthosilicate photonic crystal nanobeam resonator. Storage times of up to 10 $μ$s are demonstrated using an all-optical atomic frequency comb protocol in a dilution refrigerator under a magnetic field of 380 mT. We show this quantum storage platform to have high bandwidth, high fidelity, and multimode capacity, and we outline a path towards an efficient erbium…
The integration of neutral atoms with nanophotonic structures offer significant potential as a versatile platform to explore fundamental light-matter interactions as well as realizing novel quantum-optical devices. Here, we investigate the possibility of creating low-threshold micro-scale lasers in hybrid systems based on integrating room-temperature atomic gases with both dielectric and metallic nanophotonic systems. We particularly focus on studying two different devices resulting from incorporating an optically-pumped Rb-ethane mixture in a dielectric ring resonator and a plasmonic lattice.…
We show that bulk rhenium diselenide, ReSe2 is characterized by record high value of the refractive index exceeding 5 in near-infrared frequency range. We use back focal plane reflection spectroscopy to extract the components of the ReSe2 permittivity tensor and reveal its extreme biaxial anisotropy. We also demonstrate the good agreement between the experimental data and the predictions of the density functional theory. The combination of the large refractive index and giant optical anisotropy makes ReSe2 a perspective material for all-dielectric nanophotonics in the near-infrared frequency r…
We introduce and experimentally demonstrate a new class of electrically driven thermal emitter based on globally aligned carbon nanotube metamaterials patterned as nanoscale ribbons. The metamaterial ribbons exhibit electronic and photonic properties with extreme anisotropy, which enable low loss, wavelength-compressed hyperbolic photonic modes along one axis and high electrical resistivity and efficient Joule heating along the other axis. Devices batch-fabricated on a single chip emit linearly polarized thermal radiation with peak wavelengths dictated by their hyperbolic resonances, and their…
A global trend to miniaturization and multiwavelength performance of nanophotonic devices drives research on novel phenomena, such as bound states in the continuum and Mietronics, as well as the survey for high-refractive index and strongly anisotropic materials and metasurfaces. Hexagonal boron nitride (hBN) is one of promising materials for the future nanophotonics owing to its inherent anisotropy and prospects of high-quality monocrystals growth with atomically flat surface. Here, we present highly accurate optical constants of hBN in the broad wavelength range of 250-1700 nm combining the …
We report on a mode-locked laser design using Yb-doped fiber lasers for low-noise frequency-comb generation. The frequency comb covers the spectral range from $700$ to $1400$ nm. Although this range is more practical for many measurements than that produced by the more commonly used Er-fiber lasers, it has been addressed in only a handful of reports, mainly due to the difficulty of generating a fully coherent supercontinuum at $1\;μ$m. We overcome this difficulty by a tailored design of the mode-locking dynamics that succeeds in generating energetic 33 fs-long pulses without even using higher-…
An infrared high-brightness light source based on supercontinuum generation through a SF6 photonic crystal fiber seeded by a Cr^4+:YAG femtosecond oscillator is developed for high resolution multiplex spectroscopy in the 1.5 $μ$m region. Moreover, a multiplex high resolution approach based on a Cr^4+:YAG frequency comb enables to probe large spectral domains, with simultaneous sensitive measurement of the absorption and the dispersion associated with all individual spectral features.
Non-volatile phase-change materials with large optical contrast are essential for future tunable nanophotonics. Antimony trisulfide (Sb2S3) has recently gained popularity in this field due to its low absorption in the visible spectral region. Although several Sb2S3 deposition techniques have been reported in the literature, none of them was optimized with respect to the lowest possible absorption and largest optical contrast upon the phase change. Here, we present a comprehensive multi-parameter optimization of pulsed laser deposition of Sb2S3 towards this end. We correlate the specific deposi…
Using the ultraviolet autofluorescence of tryptophan aminoacids offers fascinating perspectives to study single proteins without the drawbacks of fluorescence labelling. However, the low autofluorescence signals have so far limited the UV detection to large proteins containing several tens of tryptophan residues. This limit is not compatible with the vast majority of proteins which contain only a few tryptophans. Here we push the sensitivity of label-free ultraviolet fluorescence correlation spectroscopy (UV-FCS) down to the single tryptophan level. Our results show how the combination of nano…
We have specifically investigated the free-space mode locking dynamics of erbium-doped fiber (EDF) mode-locked ultrafast lasers via nonlinear polarization rotation (NPR) in the normal dispersion regime. To do so, we built a passively mode-locked fiber laser based on NPR with a repetition rate of 89 MHz producing an octave-spanning spectrum due to supercontinuum (SC) generation in highly nonlinear fiber (HNLF). Most significantly, we have achieved highly stable self-starting NPR mode-locked femtosecond fiber laser based frequency comb which has been running mode locked for the past one year wit…
