Comb Teeth Research Articles

Carrier-resolved real-field theory of multi-octave frequency combs

Optical frequency combs are pillars of precision spectroscopy, and their microresonator realization serves applications where miniaturization and large tooth separation are important. Microresonator combs cover an enormous range of time scales varying from the femtosecond periods of optical oscillations to milliseconds corresponding to the kilohertz linewidth of the comb teeth. Here, we develop and implement the carrier-resolved real-field model for multi-octave frequency combs, which allows for nearly ab initio capture of all the time scales involved. As an example, we consider a microresonator that has a mix of second- and third-order nonlinearities and uses periodic poling. By applying the real-field approach, we demonstrate how to surpass traditional limitations and model the spectral broadening and soliton mode-locking across three optical octaves.

Routing to mid-infrared microcomb via near-infrared direct pump.

Mid-infrared (MIR) microcomb provides a new way into the "molecular fingerprint" region. However, it remains rather a challenge to realize the broadband mode-locked soliton microcomb, which is often limited by the performance of available MIR pump sources and coupling devices. Here, we propose an effective approach towards broadband MIR soliton microcombs generation via a direct pump in the near-infrared (NIR) region, through full utilization of the second- and third-order nonlinearities in a thin-film lithium niobate microresonator. The optical parametric oscillation process contributes to conversion from the pump at 1550 nm to the signal around 3100 nm, and the four-wave mixing effect promotes spectrum expansion and mode-locking process. While the second-harmonic and sum-frequency generation effects facilitate simultaneous emission of the NIR comb teeth. Both the continuous wave and pulse pump sources with relatively low power can support a MIR soliton with a bandwidth over 600 nm and a concomitant NIR microcomb with a bandwidth of 100 nm. This work can provide a promising solution for broadband MIR microcombs by breaking through the limitation of available MIR pump sources, and can deepen the understanding of the physical mechanism of the quadratic soliton assisted by the Kerr effect.

梳刷式收获装置的研究现状及对物料的损伤机理综述

Mechanized harvesting of crops is very important in the field of agricultural engineering, then the brush harvesting is a common way. The comb brush device is divided into four types: comb tooth type, roller spring finger type, belt comb finger type, and rod comb finger type. The picking rate and breakage rate are the indexes to evaluate the effect of comb brush harvesting devices. How to improve the picking rate and reduce damage rate is of great significance to the popularization of the devices. To improve the picking rate, the design of comb teeth should conform to the growth characteristics of crops. In this study, the application of four comb brush devices in harvesting crops was introduced, then the working principles and results were summarized. Meanwhile, the research status of a variable finger spacing device was summarized. In addition, to study fruit damage caused by brush devices during harvesting, three common analysis methods were summarized. The application situations and key steps were listed, and the modeling methods of material fruit in simulation analysis were analyzed. The study is intended to provide a reference for improving the harvesting effect of comb brush device. In the future, with the deepening combination of agronomy and agricultural machinery technology, comb brush harvesters will be more widely applied.

Application of the Chebyshev mechanism in the design of the elements of mechanical devices for combing out the down of goats

The process of combing out down in goats still remains practically non-mechanized, and therefore very difficult for operators. For the successful development of the down goat breeding industry, it is necessary to conduct research in the development of mechanical devices that will significantly facilitate the work of operators and will increase their productivity. It is equally important to ensure careful combing of down, which will not cause injury to the animal and will improve the quality of the combed down. When developing a mechanical device for combing down in goats, it is necessary to repeat the process of manual combing of down as accurately as possible. To do this, an analysis of the trajectory of movement of the tip of the comb tooth during manual combing was carried out. Based on the results of the analysis, the scheme of a combing device based on the Chebyshev hinge-lever mechanism was proposed. Analytical equations linking the known parameters of the input (leading) link with the unknown parameters of the driving links are derived within the framework of the analytical method of the kinematic study of mechanisms. Using these equations, it is possible to calculate with a predetermined accuracy the necessary kinematic parameters (displacements, velocities, accelerations, both linear and angular) of the output link and driving links. Based on the results of full-scale modeling and theoretical calculations, the optimal dimensions of the main parts of the device were established. The use of the proposed mechanism will reduce physical effort and operator fatigue, increase productivity due to the abandonment of manual labor and improvement of the device.

Microresonator-based spectral translation of a gain-switched semiconductor laser comb.

Gain-switched semiconductor laser technology provides a simple and low-cost method to generate optical frequency combs. However, the spectral coverage of these compact comb sources has been limited to the near-infrared range. Here, we combine a gain-switched laser comb with a continuous-wave translation laser within a periodically poled lithium niobate microresonator and demonstrate efficient and broadband sum-frequency conversion, spectrally translating the near-infrared comb to the visible domain. The broadband nature of the nonlinear conversion arises from a chirping of the domain inversion grating period along the microresonator circumference. We also validate the coherence of the visible-wavelength comb teeth which underlines the general applicability of this spectral translation approach.

Free‐Electron‐Driven Frequency Comb

AbstractFree‐electron radiations prompt numerous advanced applications such as particle detectors, biological imaging, and light sources from microwave to X‐ray. While their polarization, directionality, and phase could be shaped with prosperous metamaterials, their natural broad spectra have not been tailored to yield frequency combs, which are state‐of‐the‐art technology in metrology, spectroscopy, and precision frequency synthesis. Here, the frequency comb directly emitted from the free‐electron radiation is demonstrated by simultaneously exciting a series of modes with equidistant spectral lines. Both the offset and repetition frequencies are readily adapted by structural parameters, and relative spectrum intensities between the comb teeth are customizable based on selective coupling, thus permitting flexible tunability over broadband. Moreover, the repetition rate is experimentally verified at the microwave regime. The proposed methodology implies that swift electrons present a natural and versatile platform for generating frequency combs, facilitating the development of metrology and spectroscopy in the terahertz band.

Narrow linewidth optical frequency comb based on a directly modulated microcavity laser with optical feedback.

A narrow linewidth optical frequency comb (OFC) based on a directly modulated microcavity laser with external optical feedback is investigated numerically and demonstrated experimentally. Based on the numerical simulations with rate equations, the evolution of the optical and electrical spectra is presented for the direct-modulated microcavity laser with increased feedback strength, and the linewidth property is improved at suitable feedback conditions. The simulation results also show good robustness for the generated OFC in terms of feedback strength and phase. Moreover, the OFC generation experiment is performed by combining with the dual-loop feedback structure to suppress the side mode, and an OFC with a side-mode suppression ratio of 31 dB is realized. Thanks to the high electro-optical response of the microcavity laser, a 15-tone OFC with a frequency interval of 10 GHz is obtained. Finally, the linewidth of each comb tooth is measured to be around 7 kHz under the feedback power of 47 µW, which indicates an enormous compression of approximately 2000 times compared with the free-running continuous-wave microcavity laser.

Rydberg-Atom-Based Electrometry Using a Self-Heterodyne Frequency-Comb Readout and Preparation Scheme

Atom-based radio-frequency (rf) electromagnetic field sensing using atomic Rydberg states is a promising technique that has recently attracted significant interest. Its unique advantages, such as extraordinary bandwidth, self-calibration, and all-dielectric sensors, are a tangible improvement over antenna-based methods in applications such as test and measurement and development of broad-bandwidth receivers. Here, we demonstrate how an optical-frequency comb can be used to acquire data in the Autler-Townes regime of Rydberg-atom-based electrometry in a massively parallel fashion, eliminating the need for laser scanning. Two-photon electromagnetically induced transparency readout and preparation of cesium is used for the demonstration. A flat quasicontinuous optical comb is generated with the probe laser at 852 nm using an electro-optic modulator and arbitrary waveform generator. A single-frequency coupling laser at 509 nm is tuned to the Rydberg launch state. An enhanced transmission signal is obtained using self-heterodyne spectroscopy, where the comb signal is beat against a local oscillator derived from the single-frequency probe laser on a fast photodiode. The transmission of each probe-laser comb tooth is observed. We resolve electromagnetically induced transparency peaks with line widths below 5 MHz, with and without laser locking. Radio-frequency electromagnetic fields as low as $66\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{Vcm}}^{\ensuremath{-}1}$ are detected, with sensitivities of $2.3\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{Vcm}}^{\ensuremath{-}1}{\mathrm{Hz}}^{\ensuremath{-}1/2}$. The method offers a significant advantage for reading out electromagnetically induced transparency and Autler-Townes splitting, as neither laser needs to be scanned and slow frequency drifts can be tolerated in some applications. The method enables the detection of the amplitude of a pulsed rf electromagnetic field when the incoming pulse Autler-Townes splits the electromagnetically induced transparency peak.

Mathematical model of potential distribution in a pinned photodiode of an indirect time offlightCMOS image sensor.

This paper focuses on the rapid charge transfer of lock-in pixels in time of flight 3D image sensors. Through the principal analysis, a mathematical model of potential distribution in a pinned photodiode (PPD) in different comb shapes is established. Based on this model, the influence of different comb shapes on the accelerating electric field in PPD is analyzed. The semiconductor device simulation tool SPECTRA is applied to verify the effectiveness of the model, and the simulation results are analyzed and discussed. When the width of comb tooth is in narrow and medium range, the potential changes more obviously with the increase of comb tooth angle α, whereas the potential becomes stable even if the comb tooth angle α increases sharply with the wide comb tooth width. The proposed mathematical model contributes to instructing the design of pixel transferring electrons rapidly and resolving image lag.

Gene-poor Y-chromosomes substantially impact male trait heritabilities and may help shape sexually dimorphic evolution.

How natural selection facilitates sexually dimorphic evolution despite a shared genome is unclear. The patrilineal inheritance of Y-chromosomes makes them an appealing solution. However, they have largely been dismissed due to their gene-poor, heterochromatic nature and because the additive genetic variation necessary for adaptive evolution is theoretically difficult to maintain. Further, previous empirical work has revealed mostly Y-linked sign epistatic variance segregating within populations, which can often impede adaptive evolution. To assess the evolutionary impact of Y-linked variation, we established replicate populations in Drosophila simulans containing multiple Y-chromosomes (YN populations) or a single Y-chromosome variant (Y1 populations) drawn from a single population. We estimated male and female heritabilities for several traits known to be influenced by Y-chromosomes, including the number of sternopleural bristles, abdominal bristles, sex comb teeth, and tibia length. A decrease in YN heritabilities compared with Y1 would be consistent with Y-chromosome variation being sign epistatic. A decrease in Y1 heritabilities would be consistent with Y-chromosome variation being additive, though additive-by-additive epistatic variation cannot be entirely dismissed. Female heritability estimates served as controls and were not expected to differ. We found male Y1 populations exhibited lower heritabilities for all traits except tibia length; consistent with Y-linked additivity (on average YN trait heritabilities were 25% greater than Y1). Female estimates showed no difference. These data suggest Y-chromosomes should play an important role in male trait evolution and may even influence sexually dimorphic evolution by shaping traits shared by both sexes.

Free-running Yb:KYW dual-comb oscillator in a MOPA architecture.

Single-cavity dual-combs comprise a rapidly emerging technology platform suitable for a wide range of applications like optical ranging, equivalent time sampling, and spectroscopy. However, it remains a challenging task to develop a dual-comb system that exhibits low relative frequency fluctuations to allow for comb line resolved measurements, while simultaneously offering high average power and short pulse durations. Here we combine a passively cooled and compact dual-comb solid-state oscillator with a pair of core-pumped Yb-fiber-based amplifiers in a master-oscillator power-amplifier (MOPA) architecture. The Yb:KYW oscillator operates at 250 MHz and uses polarization multiplexing for dual-comb generation. To the best of our knowledge, this is the first demonstration of a single-cavity dual-comb based on this gain material. As the pulse timing characteristics inherent to the oscillator are preserved in the amplification process, the proposed hybrid approach leverages the benefit of both the ultra-low noise solid-state laser and the advantages inherent to fiber amplifier systems such as straight-forward power scaling. The amplifier is optimized for minimal pulse broadening while still providing significant amplification and spectral broadening. We obtain around 1 W of power per output beam with pulses then compressed down to sub-90 fs using a simple grating compressor, while no pre-chirping or other dispersion management is needed. The full-width half-maximum (FWHM) of the radio-frequency comb teeth is 700 Hz for a measurement duration of 100 ms, which is much less than the typical repetition rate difference, making this passively stable source well-suited for indefinite coherent signal averaging via computational phase tracking.

Generation and Evolution of Phononic Frequency Combs via Coherent Energy Transfer between Mechanical Modes

Phononic frequency combs represent the mechanical analog of optical frequency combs. Several independent experimental studies have demonstrated the onset and evolution frequency comb response in a variety of micro- and nanoelectromechanical devices in recent years. A theoretical basis for exploring and understanding the conditions for comb generation and evolution with varying driving parameters is essential to enable future practical applications. Here, we present the comparison between modeling and experimental results on the generation and evolution mechanism of phononic frequency combs in a nonlinear micromechanical resonator from the perspective of coherent energy transfer between two mechanical modes. Phononic frequency combs emerge in a strong coupling regime involving nonlinear resonances when the amplitudes and phases of two coupled mechanical modes are modulated via coherent energy transfer. The spacing and number of comb teeth can be analytically estimated based on modeling the nature of the interaction of the coupled modes under the specified driving conditions. As the driving conditions are varied, the phononic frequency comb evolves into different forms and a phenomenological model for the system is established to accurately predict the evolution of phononic frequency combs. The alignment between experiment and model provides a basis for the engineering of this phenomenon in future device applications.

Optical frequency comb generation based on spectral broadening of a phase locked dual-wavelength microcavity laser

A highly coherent optical frequency comb (OFC) based on spectral broadening of a phase-locked dual-wavelength microcavity laser is presented. By directly modulating the microcavity laser to generate multiple sidebands, the cross-injection locking of the dual modes is achieved and the beat-signal linewidth is improved from 13.5 MHz to less than 100 Hz. Subsequently, 21 flat comb teeth in a ±3 dB power variation are achieved by combining a phase modulator. Finally, an OFC with a bandwidth of 16 nm is successfully realized by narrowing the optical pulse and spectral broadening in a commercial nonlinear optical fiber. The repetition rate has a low phase noise of −102 dBc Hz−1 at 10 kHz offset, demonstrating the generated OFC has a high degree of coherence.

Observation of modulation instability Kerr frequency combs in a fiber Fabry-Pérot resonator.

We report the experimental observation of a modulation instability induced Kerr frequency comb in an all fiber Fabry-Pérot resonator. We fully characterized, in intensity and phase, the frequency comb using a commercial 10 MHz resolution heterodyne detection system to reveal more than 125 comb teeth within each of the modulation instability sidelobes. Moreover, we were able to reveal the fine temporal structure in phase and intensity of the output Turing patterns. The experimental results are generally in good agreement with numerical simulations.

梳刷气吸复合式亚麻（胡麻）蒴果收获试验台设计与试验

In view of the problem of plant entanglement threshing roller in the process of mechanized flax harvesting, a comb-brush air-suction composite flax capsule harvesting test stand was designed based on the harvesting method of harvesting capsules independently and then breaking the capsules to thresh them. The following four parameters were selected as experimental factors: the shape of comb tooth cross-section, the rotational speed of comb roller, the relative speed of machine travel and the air volume of centrifugal fan. The following four indicators were chosen as the experimental indicators: capsule removal rate, capsule breakage rate, capsule collection rate and plant winding rate. A four-factor and three-level orthogonal test was conducted. The results showed that the optimal combination of test factors was as follows: the shape of comb tooth cross-section was rectangular, the rotational speed of the brush roller was 90 rad/min, the speed of machine travel relative to the plant was 80 mm/s and the air volume of centrifugal fan was 6000 m3/h. Under the condition of better experiment parameters combination, the capsule removal rate was 96.45%, capsule shell breaking rate was 98.79%, capsule collection rate was 95.65% and flax plants winding rate was 2.52%. The comb-brush air-suction composite flax capsule harvesting test bench provided the feasibility scheme for the problem of plant winding thresher roller and capsule collection.

All-fiber acetylene-referenced optical frequency comb

We demonstrated an all-fiber compact Erbium-doped optical frequency comb based on optical reference. Compared with the traditional RF reference, the whole system adopts the all-fiber design of optical reference. Comb stabilization is achieved by simultaneously locking the repetition rate (fr) to an RF reference and an optical comb tooth to a CW reference. The standard deviation of the fr frequency in 4.5 hours was recorded as 0.37 mHz, leading to a fraction instability of 4.3 ×10−12 at 1 s gate time and 2.8 ×10−13 at 10 s gate time. The locking of single comb tooth is achieved by locking the optical comb and the beat note of the CW laser. We used the P(16) overtone transition line of 13C2H2 as the CW reference and optimized the stabilization by choosing appropriate lock point on the Doppler-limited absorption transition. The comb was able to achieve stable locking for almost five hours. The short-term fraction instability of the optical frequency was measured to be 6.56 ×10−10 at 1 s gate time, which is mostly from the CW reference. Our approach of acetylene-stabilized fiber comb offers a feasible solution to help fiber combs move from laboratory to outdoors applications based on fiber sensing, laser stabilization and spectrum analysis.

Analysis and Design of Operating Parameters of Floor-Standing Jujube Pickup Device Based on Discrete Element Method

In view of the problem whereby the floor-standing jujube pickup device designed by the research group has a large resistance when the comb teeth (CT) enter the soil, the strip brush can easily bend, and the operation effect is poor. In this paper, the structural parameters of the CT and bar brush in the mechanical floor date-picking device are determined by theoretical analysis. EDEM software was used to establish the discrete element simulation model of the floor-standing jujube soil–jujube pickup device. According to the simulation results, it is determined that the angle of the CT entering the soil (ACT) can change freely within 30–33° and meet the operation requirements. Through the single-factor test on the pickup rate of jujube and the soil hilling quantity, it is determined that the value range of the CT working speed (CWS) is 0.2–0.4 m/s, and the value range of the CT entering the soil (DCS) is 5–45 mm. Simulation and field verification tests were carried out on the determined operation parameter range. It was found that when the CWS was 0.2 m/s and the DCS was 5 mm, the pickup rates in the simulation test and the field verification test were 84.17% and 91.23%, respectively, and the relative error was the largest but not more than 8%. The result shows that the operation parameters and range determined by the discrete element method were reliable. This study is expected to provide the working parameter basis for the subsequent design of a floor-standing jujube pickup device.

Broadband EO-Comb Generation Based on Two-Stage Nonlinear System

Optical frequency comb (OFC) has attracted growing interest in various fields, such as frequency metrology, absorption spectroscopy, and instrumental calibrations. Electro-optic modulation (EOM) is one of the main comb-generating methods with the advantageous features of adjustable repetition frequency, high optical signal-to-noise ratio, and intrinsic coherence of the comb teeth. However, the spectral range of the EO-comb is limited by the modulation depth. In this paper, a two-stage nonlinear system is built to broaden a 12.5 GHz EO-comb, namely the fiber-based stage and the on-chip stage. In the fiber-based stage, the pulse width of the comb is compressed to 52 fs from ∼3 ps, meanwhile, the peak power is amplified to 2053 W and the comb spectrum is moderately broadened. In the on-chip stage, the comb is further broadened by an integrated Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> waveguide spanning from 1200 nm up to 2000 nm. It is worth mentioning that the characteristic absorption lines of water vapor can also be observed in the broadened spectrum. These results indicate that the built system may have great application prospects in the field of parallel gas detection.

Harvest

Harvest Kieron Walquist (bio) [ See PDF for formatting of the poem. ] I. Chanterelle You cut the mushroom head + leave it overnight face down then a chanterelle spore print on tinfoil— a soft firework a white fern— you show me how to scrape the murmur with a pocketknife to score the little life into a mason jar inoculated ryegrass you can be patient easy with me II. Oyster It shone florescentin the bathroom along the carpet + bathtub border— we washed the outside off only for the mushroom to jungle in when you yanked the inch-high stem as if it were a teenager's boombox cord I unzipped part of me thanked you your willingness [End Page 45] + the other part had lost a comfort— to imagine the oyster an umbrella keeping an unseeable being dry after my shower III. Trumpet Once after sex we laughed about being fruiting bodiesyour breath a warm whistle across the bottle-mouth of my collarbone you said we should flush throughout this season before we were found + picked clean but that night we were boundless you were my comb tooth + I was your trumpet IV. Honey Fungus Their mycelium reaches for milessleeps across state lines you tell me while we hunt in early Junefor coral that if I'm lost among the trees don't look for the sun but the fungi Press your ear to the ground Listen for its pulse Let the orchard orient you I ask [End Page 46] if I were lost where would you be V. Golden Teacher A generous pinch of psilocybin brought me to worship I was a dancer in wool socks the world met me in that melting the bite + beauty of a tongue kiss to a battery something like that how I adored every layer of clothing you took off of me until I realized your hands were my hands slowly defeathering myself VI. Shiitake From an oak older than I'll ever be to the kitchen stove stir-fry shiitakes take on taste you tell me a shadow of other ingredients but it's only texture tough works the jaw like jerky smells of a sore one looks at after ripping [End Page 47] off a band-aid when you turn away I spit VII. Poison Cups A bouquet of night tossed down the log no longer a dead elm but a flute again + again I asked you why were they poisonous no reason you said some are just born bad VIII. Morels In an issue of Missouri Conservationist a nine or ten-year-old me is posing shirtless a dried-apricot-complexion my nipples two dirty pennies I'm wearing morels as fingernails my mouth giving its best grrrthere I'm severe or sassy or stoked or scared I can't tell anymore the title reads Monster Morels the title reads Monster it's your favorite picture [End Page 48] Kieron Walquist Kieron Walquist is a queer, neurodivergent writer and MFA candidate at Washington University in St. Louis. His work appears, or is forthcoming, in Bennington Review, GASHER, Gulf Coast, The Missouri Review, Puerto del Sol, Small Orange, and elsewhere. He lives in Missouri. Copyright © 2022-2023 Pleiades and Pleiades Press

Study on the throwing mechanism and loss characteristics of three-dimensional disturbance comb

To reduce rice harvest loss and explore the performance of different combs for threshing prior to cutting, a three-dimensional tip disturbance comb and a three-dimensional bionic disturbance comb were designed. Based on high-speed camera technology and bench tests, the throwing mechanisms, distribution characteristics and loss rates of three kinds of combs, including primitive plane angular combs, were explored. Through comparative analysis of the material diffusion angle and throwing mechanism, it was obtained that the average material diffusion angle of the three combs decreased gradually with increasing rotating speed and that the material diffusion angle and stability of the three-dimensional bionic disturbance comb performed best. At the same rotating speed, the fitting slope ratio of the three-dimensional bionic disturbance comb was the largest, and the effect of throwing and transporting materials was the best. The total loss rates of three kinds of comb teeth were obtained by analyzing the falling grain loss rate and uncombed loss rate: three-dimensional tip disturbance comb > primitive plane angular comb > three-dimensional bionic disturbance comb; the corresponding minimum total loss rates were 6.17 %, 5.76 % and 2.71 %.