Spectral Broadening in a Continuously Pumped Singly Resonant Second-Harmonic Cavity

Optical frequency comb synthesizers with a wide spectral range are an essential tool for many research areas such as spectroscopy, precision metrology, optical communication, and sensing. Recent studies have demonstrated the direct generation of frequency combs, via second-order processes, that are centered on two different spectral regions separated by an octave. Here, we present the capability of optical quadratic frequency combs for broad-bandwidth spectral emission in unexplored regimes. We consider comb formation under phase-matched conditions in a continuous-wave pumped singly resonant second-harmonic cavity, with large intracavity power and control of the detuning over several cavity line widths. The spectral analysis reveals quite distinctive sidebands that arise far away from the pump, singularly or in a mixed regime together with narrowband frequency combs. Notably, by increasing the input power, the optical frequency lines evolve into widely spaced frequency clusters, and at maximum power, they appear in a wavelength range spanning up to 100 nm. The obtained results demonstrate the power of second-order nonlinearities for direct comb production within a wide range of pump wavelengths.

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Optical Frequency Combs in Quadratically Nonlinear Resonators

Micromachines ◽

10.3390/mi11020230 ◽

2020 ◽

Vol 11 (2) ◽

pp. 230 ◽

Cited By ~ 8

Author(s):

Iolanda Ricciardi ◽

Simona Mosca ◽

Maria Parisi ◽

François Leo ◽

Tobias Hansson ◽

...

Keyword(s):

Continuous Wave ◽

Frequency Comb ◽

Second Harmonic ◽

Theoretical Work ◽

Optical Frequency ◽

Pump Frequency ◽

Optical Frequency Combs ◽

Frequency Combs ◽

New Class ◽

Parametric Processes

Optical frequency combs are one of the most remarkable inventions in recent decades. Originally conceived as the spectral counterpart of the train of short pulses emitted by mode-locked lasers, frequency combs have also been subsequently generated in continuously pumped microresonators, through third-order parametric processes. Quite recently, direct generation of optical frequency combs has been demonstrated in continuous-wave laser-pumped optical resonators with a second-order nonlinear medium inside. Here, we present a concise introduction to such quadratic combs and the physical mechanism that underlies their formation. We mainly review our recent experimental and theoretical work on formation and dynamics of quadratic frequency combs. We experimentally demonstrated comb generation in two configurations: a cavity for second harmonic generation, where combs are generated both around the pump frequency and its second harmonic and a degenerate optical parametric oscillator, where combs are generated around the pump frequency and its subharmonic. The experiments have been supported by a thorough theoretical analysis, aimed at modelling the dynamics of quadratic combs, both in frequency and time domains, providing useful insights into the physics of this new class of optical frequency comb synthesizers. Quadratic combs establish a new class of efficient frequency comb synthesizers, with unique features, which could enable straightforward access to new spectral regions and stimulate novel applications.

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Kerr optical frequency combs: theory, applications and perspectives

Nanophotonics ◽

10.1515/nanoph-2016-0013 ◽

2016 ◽

Vol 5 (2) ◽

pp. 214-230 ◽

Cited By ~ 53

Author(s):

Yanne K. Chembo

Keyword(s):

Continuous Wave ◽

Frequency Comb ◽

Kerr Nonlinearity ◽

Optical Frequency Comb ◽

Optical Frequency ◽

Optical Frequency Combs ◽

Frequency Combs ◽

Comprehensive Survey ◽

Microwave Signal Generation ◽

Mode Locked Lasers

AbstractThe optical frequency comb technology is one of the most important breakthrough in photonics in recent years. This concept has revolutionized the science of ultra-stable lightwave and microwave signal generation. These combs were originally generated using ultrafast mode-locked lasers, but in the past decade, a simple and elegant alternativewas proposed,which consisted in pumping an ultra-high-Q optical resonator with Kerr nonlinearity using a continuous-wave laser. When optimal conditions are met, the intracavity pump photons are redistributed via four-wave mixing to the neighboring cavity modes, thereby creating the so-called Kerr optical frequency comb. Beyond being energy-efficient, conceptually simple, and structurally robust, Kerr comb generators are very compact devices (millimetric down to micrometric size) which can be integrated on a chip. They are, therefore, considered as very promising candidates to replace femtosecond mode-locked lasers for the generation of broadband and coherent optical frequency combs in the spectral domain, or equivalently, narrow optical pulses in the temporal domain. These combs are, moreover, expected to provide breakthroughs in many technological areas, such as integrated photonics, metrology, optical telecommunications, and aerospace engineering. The purpose of this review article is to present a comprehensive survey of the topic of Kerr optical frequency combs.We provide an overview of the main theoretical and experimental results that have been obtained so far. We also highlight the potential of Kerr combs for current or prospective applications, and discuss as well some of the open challenges that are to be met at the fundamental and applied level.

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Dispersion engineering and measurement of whispering gallery mode microresonator for Kerr frequency comb generation

Nanophotonics ◽

10.1515/nanoph-2019-0497 ◽

2020 ◽

Vol 9 (5) ◽

pp. 1087-1104 ◽

Cited By ~ 2

Author(s):

Shun Fujii ◽

Takasumi Tanabe

Keyword(s):

Continuous Wave ◽

Frequency Tuning ◽

Frequency Comb ◽

Whispering Gallery Mode ◽

High Repetition Rate ◽

Power Efficient ◽

Frequency Combs ◽

Dispersion Engineering ◽

Whispering Gallery ◽

Wide Range

AbstractDesigning and engineering microresonator dispersion are essential for generating microresonator frequency comb. Microresonator frequency combs (microcombs, Kerr frequency combs) offer the potential for various attractive applications as a new type of coherent light source that is power efficient and compact and has a high repetition rate and a broad bandwidth. They are easily driven with a continuous-wave pump laser with adequate frequency tuning; however, the resonators must have a high quality (Q) factor and suitable dispersion. The emergence of cavity enhanced four-wave mixing, which is based on third-order susceptibility in the host material, results in the generation of broadband and coherent optical frequency combs in the frequency domain equivalent to an optical pulse in the time domain. The platforms on which Kerr frequency combs can be observed have been developed, thanks to intensive efforts by many researchers over a few decades. Ultrahigh-Q whispering gallery mode (WGM) microresonators are one of the major platforms since they can be made of a wide range of material including silica glass, fluoride crystals and semiconductors. In this review, we focus on the dispersion engineering of WGM microresonators by designing the geometry of the resonators based on numerical simulation. In addition, we discuss experimental methods for measuring resonator dispersion. Finally, we describe experimental results for Kerr frequency combs where second- and higher-order dispersions influence their optical spectra.

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Coherent control of acoustic phonons in a silica fiber using a multi-GHz optical frequency comb

Communications Physics ◽

10.1038/s42005-021-00581-9 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Mamoru Endo ◽

Shota Kimura ◽

Shuntaro Tani ◽

Yohei Kobayashi

Keyword(s):

Coherent Control ◽

Continuous Wave ◽

Frequency Comb ◽

Effective Interaction ◽

Interaction Strength ◽

Single Mode ◽

Optical Frequency Comb ◽

Material Structure ◽

Optical Frequency ◽

Acoustic Phonons

AbstractMulti-gigahertz mechanical vibrations that stem from interactions between light fields and matter—known as acoustic phonons—have long been a subject of research. In recent years, specially designed functional devices have been developed to enhance the strength of the light-matter interactions because excitation of acoustic phonons using a continuous-wave laser alone is insufficient. However, the strength of the interaction cannot be controlled appropriately or instantly using these structurally-dependent enhancements. Here we show a technique to control the effective interaction strength that does not operate via the material structure in the spatial domain; instead, the method operates through the structure of the light in the time domain. The effective excitation and coherent control of acoustic phonons in a single-mode fiber using an optical frequency comb that is performed by tailoring the optical pulse train. This work represents an important step towards comb-matter interactions.

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Repetition frequency locking of a terahertz quantum cascade laser emitting at 4.2 THz

Terahertz Science and Technology ◽

10.1051/tst/2020131032 ◽

2020 ◽

Vol 13 (1) ◽

pp. 32-40

Author(s):

Wen Guan ◽

Ziping Li ◽

Kang Zhou ◽

Wenjian Wan ◽

Xiaoyu Liao ◽

...

Keyword(s):

Quantum Cascade Laser ◽

Continuous Wave ◽

Frequency Comb ◽

Signal To Noise Ratio ◽

Phase Lock Loop ◽

Wave Mode ◽

Repetition Frequency ◽

Frequency Locking ◽

Frequency Combs ◽

Quantum Cascade

The electrically-pumped terahertz quantum cascade laser (QCL) is characterized by high power emission, compact, broad frequency coverage, and so on, which shows abilities for frequency comb operations. Although free-running QCLs can work as frequency combs by designing the laser structure with small group velocity dispersions and/or inserting mirrors to compensate laser intrinsic dispersions, the ideal comb operation can only be obtained by firmly locking the repetition frequency and carrier frequency of a laser. In this work, we have reported a repetition frequency locking of a terahertz QCL emitting around 4.2 THz. When the 6-mm-long laser is operated in continuous wave mode without any locking techniques, the repetition frequency is measured to be ~6.15 GHz with a linewidth of hundred kilohertz. Once a phase lock loop (PLL) is applied to dynamically control the drive current of the QCL, we have demonstrated a successful repetition frequency locking of the laser with a signal to noise ratio of 80 dB. This technique can be employed for the frequency comb and dual-comb operations of terahertz QCLs for high-resolution applications.

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Dynamics of microresonator frequency comb generation: models and stability

Nanophotonics ◽

10.1515/nanoph-2016-0012 ◽

2016 ◽

Vol 5 (2) ◽

pp. 231-243 ◽

Cited By ~ 11

Author(s):

Tobias Hansson ◽

Stefan Wabnitz

Keyword(s):

Continuous Wave ◽

Temporal Dynamics ◽

Frequency Comb ◽

Modulational Instability ◽

Theoretical Models ◽

Light Sources ◽

Generation Process ◽

Modal Expansion ◽

Frequency Combs ◽

Comb Generation

AbstractMicroresonator frequency combs hold promise for enabling a new class of light sources that are simultaneously both broadband and coherent, and that could allow for a profusion of potential applications. In this article, we review various theoretical models for describing the temporal dynamics and formation of optical frequency combs. These models form the basis for performing numerical simulations that can be used in order to better understand the comb generation process, for example helping to identify the universal combcharacteristics and their different associated physical phenomena. Moreover, models allow for the study, design and optimization of comb properties prior to the fabrication of actual devices. We consider and derive theoretical formalisms based on the Ikeda map, the modal expansion approach, and the Lugiato-Lefever equation. We further discuss the generation of frequency combs in silicon resonators featuring multiphoton absorption and free-carrier effects. Additionally, we review comb stability properties and consider the role of modulational instability as well as of parametric instabilities due to the boundary conditions of the cavity. These instability mechanisms are the basis for comprehending the process of frequency comb formation, for identifying the different dynamical regimes and the associated dependence on the comb parameters. Finally, we also discuss the phenomena of continuous wave bi- and multistability and its relation to the observation of mode-locked cavity solitons.

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Stable continuous-wave THz vector imaging based on an optical frequency comb

10.1117/12.2604690 ◽

2021 ◽

Author(s):

Zuomin Yang ◽

Zijie Lu ◽

Shiwei Wang ◽

Hongqi Zhang ◽

Lu Zhang ◽

...

Keyword(s):

Continuous Wave ◽

Frequency Comb ◽

Optical Frequency Comb ◽

Optical Frequency

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Ultrastable Offset-Locking Continuous Wave Laser to a Frequency Comb with a Compound Control Method for Precision Interferometry

Sensors ◽

10.3390/s20051248 ◽

2020 ◽

Vol 20 (5) ◽

pp. 1248

Author(s):

Ruitao Yang ◽

Haisu Lv ◽

Jing Luo ◽

Pengcheng Hu ◽

Hongxing Yang ◽

...

Keyword(s):

Continuous Wave ◽

Control Method ◽

Frequency Comb ◽

Frequency Control ◽

Beat Frequency ◽

Laser Interferometry ◽

Optical Frequency ◽

Interference Signal ◽

Compound Control ◽

Cw Laser

A simple and robust analog feedforward and digital feedback compound control system is presented to lock the frequency of a slave continuous wave (CW) laser to an optical frequency comb. The beat frequency between CW laser and the adjacent comb mode was fed to an acousto-optical frequency shifter (AOFS) to compensate the frequency dithering of the CW laser. A digital feedback loop was achieved to expand the operation bandwidth limitation of the AOFS by over an order of magnitude. The signal-to-noise ratio of the interference signal was optimized using a grating-based spectral filtering detection unit. The complete system achieved an ultrastable offset-locking of the slave CW laser to the frequency comb with a relative stability of ±3.62 × 10−14. The Allan deviations of the beat frequency were 8.01 × 10−16 and 2.19 × 10−16 for a gate time of 10 s and 1000 s, respectively. The findings of this study may further improve laser interferometry by providing a simple and robust method for ultrastable frequency control.

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Relationship between the voltage applied to MZM arms and the generation of optical frequency comb

International Journal of Engineering & Technology ◽

10.14419/ijet.v7i4.15.23026 ◽

2018 ◽

Vol 7 (4.15) ◽

pp. 405

Author(s):

Yousif I. Hammadi ◽

Tahreer S. Mansour

Keyword(s):

Continuous Wave ◽

Frequency Comb ◽

Optical Frequency Comb ◽

Laser Source ◽

Optical Frequency ◽

High Data ◽

Rate Transmission ◽

Rf Signals ◽

Rf Signal ◽

Data Rate Transmission

In this study, an optical frequency comb source (OFCS) based on a dual-drive Mach–Zehnder modulator (MZM) is constructed and theoretically demonstrated. A mathematical model of the constructed OFCS is then built to investigate the effect of the peak-to-peak radio frequency (RF) signals applied to the MZM arms on the generated optical frequency comb (OFC) lines at the MZM output. A dual-drive MZM, a continuous wave laser source, and an RF signal source are included in the OFCS. The chirp parameter can be controlled and 64 comb lines generated at a comb spacing of 25 GHz by regulating voltages applied to the MZM arms. The developed OFCS is relatively simple but valuable. The generated OFC lines can be used for high data-rate transmission.

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