Dual-Comb Ranging

Absolute distance measurement is a fundamental technique in mobile and large-scale dimensional metrology.Dual-comb ranging is emerging as a powerful tool that exploits phase resolution and frequency accuracy for high-precision and fast-rate distance measurement.Using two coherent frequency combs,dual-comb ranging allows time and phase response to be measured rapidly.It breaks through the limitations related to the responsive bandwidth,ambiguity range,and dynamic measurement characteristics of conventional ranging tools.This review introduces dual-comb ranging and summarizes the key techniques for realizing this ranging tool.As optical frequency comb technology progresses,dualcomb ranging shows promise for various professional applications.

Review of low timing jitter mode-locked fiber lasers and applications in dual-comb absolute distance measurement

Passively mode-locked fiber lasers emit femtosecond pulse trains with excellent short-term stability. The quantum-limited timing jitter of a free running femtosecond erbium-doped fiber laser working at room temperature is considerably below one femtosecond at high Fourier frequency. The ultrashort pulse train with ultralow timing jitter enables absolute time-of-flight measurements based on a dual-comb implementation, which is typically composed of a pair of optical frequency combs generated by femtosecond lasers. Dead-zone-free absolute distance measurement with sub-micrometer precision and kHz update rate has been routinely achieved with a dual-comb configuration, which is promising for a number of precision manufacturing applications, from large step-structure measurements prevalent in microelectronic profilometry to three coordinate measurements in large-scale aerospace manufacturing and shipbuilding. In this paper, we first review the sub-femtosecond precision timing jitter characterization methods and approaches for ultralow timing jitter mode-locked fiber laser design. Then, we provide an overview of the state-of-the-art dual-comb absolute ranging technology in terms of working principles, experimental implementations, and measurement precisions. Finally, we discuss the impact of quantum-limited timing jitter on the dual-comb ranging precision at a high update rate. The route to highprecision dual-comb range finder design based on ultralow jitter femtosecond fiber lasers is proposed.

Digitally calibrated broadband dual-comb gases absorption spectral measurements

From the perspective of error compensation in the sampling process, a digital calibration algorithm was studied for the processing of spectral data in dual-comb spectroscopy. In this algorithm, dynamic adaptation to phase fluctuations maintained constant measurement results of spectral line positions and intensities. A mode-resolved broadband absorption spectrum was obtained over the full-spectral range of the comb with a Hertz linewidth of radio frequency comb mode.The measured spectrum spanned over 10 THz, which covered the multiplexed absorption regions of mixed gases, such as CO2 and N2 O. The calibrated interferograms were also capable of direct coherent averaging in the time domain. The transmittance obtained deviated from the theoretical calculation by no more than 2% in the whole spectral span.

Optical frequency comb technology: from ground to space

Optical frequency combs,as powerful tools for precision spectroscopy and research into optical frequency standards,have driven continuous progress and significant breakthroughs in applications such as time-frequency transfer,measurement of fundamental physical constants,and high-precision ranging,achieving a series of milestone results in ground-based environments.With the continuous maturation and evolution of femtosecond lasers and related technologies,optical frequency combs are moving from ground-based applications to astronomical and space-based applications,playing an increasingly important role in atomic clocks,exoplanet observations,gravitational wave measurements,and other areas.This paper,focusing on astronomical and space-based applications,reviews research progress on astronomical frequency combs,optical clock time-frequency networks,gravitational waves,dark matter measurement,dual-comb large-scale absolute ranging,and high-resolution atmospheric spectroscopy.With enhanced performance and their gradual application in the field of space-based research,optical frequency combs will undoubtedly provide more powerful support for astronomical science and cosmic exploration in the future.

Relative timing jitter compression in a Fabry-Pérot cavity-assisted free-running dual-comb interferometry

Dual-comb interferometric systems with high time accuracy have been realized for various applications.The flourishing ultralow noise dual-comb system promotes the measurement and characterization of relative timing jitter,thus improving time accuracy.With optical solutions,introducing an optical reference enables 105 harmonics measurements,thereby breaking the limit set by electrical methods;nonlinear processes or spectral interference schemes were also employed to track the relative timing jitter.However,such approaches operating in the time domain either require additional continuous references or impose stringent requirements on the amount of timing jitter.We propose a scheme to correct the relative timing jitter of a free-running dual-comb interferometry assisted by a Fabry-Pérot(F-P)cavity in the frequency domain.With high wavelength thermal stability provided by the F-P cavity,the absolute wavelength deviation in the operating bandwidth is compressed to<0.4 pm,corresponding to a subpicosecond sensitivity of pulse-to-pulse relative timing jitter.Also,Allan deviation of 10^(-10) is obtained under multiple coherent averaging,which lays the foundation for mode-resolved molecular spectroscopic applications.The spectral absorption features of hydrogen cyanide gas molecules at ambient temperature were measured and matched to the HITRAN database.Our scheme promises to provide new ideas on sensitive measurements of relative timing jitter.

基于点-轴系统理论的池州区域空间整合

池州市属于安徽省的欠发达地区,处于"T"型开发战略长江轴线上皖江经济带的波谷,区域中心城镇规模小,点-轴系统形成晚、成长较快。基于点-轴系统理论,吸纳双核结构模式观点,提出以"梳"型空间结构作为池州区域发展的空间结构模式。"梳"型空间结构是以皖江经济带池州段作为发展主轴,池州城-蓉城镇、池州城-梅街镇、殷汇镇-仁里镇、大渡口镇-尧渡镇-东流镇等双核结构与之耦合而形成的一种空间结构形式,"梳"型空间结构利于整合区域发展空间,加强城镇体系建设,推动区域经济发展,促进生态环境保护。

Sub-femtometer-resolution absolute spectroscopy with sweeping electro-optic combs

Optical frequency comb with evenly spaced lines over a broad bandwidth has revolutionized the fields of optical metrology and spectroscopy.Here,we propose a fast interleaved dual-comb spectroscopy with sub-femtometer-resolution and absolute frequency,in which two electro-optic frequency combs are swept.Electrically-modulated stabilized laser enables ultrahigh resolution of 0.16 fm(or 20 k Hz in optical frequency)and single-shot measurement in 90 ms.Total 20 million points are recorded spanning 3.2 nm(or 400 GHz)bandwidth,corresponding to a spectral sampling rate of 2.5×10^(8)points/s under Nyquist-limitation.Besides,considering the trade-off between the measurement time and spectral resolution,a fast single-shot measurement is also realized in 1.6 ms with 8 fm(or 1 MHz)resolution.We demonstrate the 25-averaged result with 30.6 d B spectral measurement signal-to-noise ratio(SNR)by reducing the filter bandwidth in demodulation.The results show great prospect for precise measurement with flexibly fast refresh time,high spectral resolution,and high SNR.

基于飞秒光学频率梳的乙炔气体光谱测量

双光梳光谱分析技术近年来凭借高分辨率、高灵敏度、宽光谱覆盖和快速测量的优势,在分子和原子光谱分析领域得到了快速的发展。首先简要介绍双光梳光谱测量技术的基本原理,然后根据实验室现有条件,建立相应的双光梳光谱测量装置,并针对乙炔气体进行可行性验证。

Compact mid-infrared dual-comb spectrometer over 3-4μm via intra-pulse difference frequency generation in LiNbO_(3) waveguides

The mid-infrared optical frequency comb is a powerful tool for gas sensing.In this study,we demonstrate a simple midinfrared dual-comb spectrometer covering 3±4μm in Li Nb O_(3)waveguides.Based on a low-power fiber laser system,the mid-infrared comb is achieved via intra-pulse difference frequency generation in the Li Nb O_(3)waveguide.We construct pre-chirp management before supercontinuum generation to control spatiotemporal alignment for pump and signal pulses.The supercontinuum is directly coupled into a chirped periodically poled Li Nb O_(3)waveguide for the 3±4μm idler generation.A mid-infrared dual-comb spectrometer based on this approach provides a 100 MHz resolution over25 THz coverage.To evaluate the applicability for spectroscopy,we measure the methane spectrum using the dualcomb spectrometer.The measured results are consistent with the HITRAN database,in which the root mean square of the residual is 3.2%.This proposed method is expected to develop integrated and robust mid-infrared dual-comb spectrometers on chip for sensing.

Dual-comb soliton rains based on polarization multiplexing in a single-walled carbon nanotube mode-locked Er-doped fiber laser

We experimentally demonstrate tunable dual-comb soliton rains in a polarization multiplexing fiber laser based on a singlewalled carbon nanotube.The repetition frequency difference of dual-comb pulses is about 39 Hz,with a maximum extinction ratio of 29 dB.With suitable polarization states,one of the dual-comb pulses switches into soliton rain sequence with chirped isolating soliton trains.The signal-to-noise ratio reaches 61 dB,which is 11 dB higher than that of the normal dual-comb pulses.The intervals between chirped isolating solitons are distributed progressively,and the number of isolating solitons can be flexibly tuned from 2 to 11 by adjusting polarization state or pump power.Our work will provide support for further understanding of interaction dynamics of solitons and give a new route to the application of precision measurement.

Adaptive cavity-enhanced dual-comb spectroscopy

Resolution and bandwidth are critical for cavity-enhanced dual-comb spectroscopy(CE-DCS). Here, we pioneer an adaptive approach in CE-DCS to improve the broadband as well as the resolution. Postcorrections to dualcomb interferograms adaptively compensate the relative phase jitters of the optical frequency combs and result in both a mode-resolved spectral resolution and a signal-to-noise ratio of 440:1 in 1 s. Meanwhile, an adaptive combcavity locking scheme exploits more than 90% of the comb modes, covering 340 cm-1(10 THz) at 6450 cm-1. For a single dual-comb interferogram, more than 40,000 comb teeth spaced by 250 MHz are measured in less than7.5 ms, contributing to a noise equivalent absorption per spectral element of 2 × 10-10 cm-1·Hz-1∕2. This adaptive cavity-enhanced dual-comb spectroscopy technique provides an attractive spectroscopic tool that may be utilized in trace-gas sensing, breath and cancer analysis, and engine combustion diagnosis.

Adaptive-sampling near-Doppler-limited terahertz dual-comb spectroscopy with a free-running single-cavity fiber laser

Dual-comb spectroscopy(DCS)is an emerging spectroscopic tool with the potential to simultaneously achieve a broad spectral coverage and ultrahigh spectral resolution with rapid data acquisition.However,the need for two independently stabilized ultrafast lasers significantly hampers the potential application of DCS.We demonstrate mode-resolved DCS in the THz region based on a free-running singlecavity dual-comb fiber laser with the adaptive sampling method.While the use of a free-running single-cavity dual-comb fiber laser eliminates the need for two mode-locked lasers and their frequency control,the adaptive sampling method strongly prevents the degradation of spectroscopic performance caused by the residual timing jitter in the free-running dual-comb laser.Doppler-limit-approaching absorption features with linewidths down to 25 MHz are investigated for low-pressure acetonitrile/air mixed gas by comb-mode-resolved THz spectroscopy.The successful demonstration clearly indicates its great potential for the realization of lowcomplexity,Doppler-limited THz spectroscopy instrumentation.

The development and application of dual-comb spectroscopy in analytical chemistry

Analytical chemistry plays an important role in the qualitive and quantitative analysis for molecules in the various circumstances,especially for the high-resolution analysis.The dual-comb spectroscopy(DCS)technology with the characteristics of high resolution,high sensitivity and instantaneous sampling exhibited a great potential in high-resolution in-situ spectral methods and has been active in the fields of spatial ranging,air composition analysis,reaction monitoring and so on.In this review,we will summarize the principle of DCS according to the different wavelength coverage and overview the applications of DCS in analytical chemistry.

大尺寸计量中双光梳绝对测距方法的研究进展

大尺寸计量中广泛采用增量式激光干涉仪作为量值传递的计量标准,在测量过程中易发生断光影响,严重限制测量灵活性。近年来,以飞秒光学频率梳为光源的高精度绝对测距方法得到了迅猛发展,特别是双光梳异步光学采样绝对测距方法,利用具有微弱重频差的两台飞秒光学频率梳能够实现大量程、高精度和高更新率的绝对距离测量。以大尺寸激光绝对测距和飞秒光学频率梳绝对测距为切入点,详细综述了现阶段大尺寸双光梳绝对测距的研究进展;针对大尺寸计量场景分析了双光梳绝对测距现存的瓶颈,并对此开展了双光梳光源搭建与优化、测距精度优化、测距系统设计和测距性能验证等深入研究,最后对双光梳绝对测距在大尺寸计量中未来的应用方向提出了展望。

Scanning dual-microcomb spectroscopy

Dual-comb spectroscopy(DCS) is a powerful tool in molecular spectroscopy benefiting from the advantages of high resolution and short measurement time. The recently developed soliton microcomb(SMC) can potentially transfer the dual-comb method to an on-chip platform. In this paper, we demonstrate DCS using two frequency scanning SMCs, termed scanning dual-microcomb spectroscopy(SDMCS). The two SMCs are generated by an auxiliary-assisted thermal balance scheme, and the pump laser frequency sweeps over one free spectral range of the microresonator(~49 GHz) using a feedback control system. The proposed SDMCS has a spectral resolution of 12.5 MHz, which is determined by the minimum sweeping step of the pump laser. Using this SDMCS system, we perform three types of gas molecule absorption spectroscopy recognition and gas concentration detection.This study paves the way for integrated DCS with a high signal-to-noise ratio, high spectral resolution, and fast acquisition rate.

Generation of dual and quad‑optical frequency combs in the injected radiation free mode‑locked frequency‑shifted feedback laser

The results of an optoelectronic system—frequency-shifted feedback(FSF)laser experimental examination are presented.The considered FSF laser is seeded only with optical amplifer spontaneous emission(ASE)and operates in the mode-locked regime,whereby the output radiation is sequence of short pulses with a repetition rate determined by the delay time in its optical feedback circuit.In the frequency domain,the spectrum of such a pulse sequence is an optical frequency comb(OFC).These OFCs we call initial.We consider the possibility of tunable acousto-optic(AO)dual and quad-comb frequency spacing downconversion in the FSF laser seeded with ASE and operating in the mode-locked regime.The examined system applies a single frequency shifting loop with single AO tunable flter as the frequency shifter that is fed with several radio frequency signals simultaneously.The initial OFCs with frequency spacing of about 6.5 MHz may be obtained in the wide spectral range and their width,envelope shape and position in the optical spectrum may be tuned.The dual-combs are obtained with a pair of initial OFCs aroused by two various ultrasound waves in the acousto-optic tunable flter(AOTF).The dual-combs frequency spacing is determined by the frequency diference of the signals applied to the AOTF piezoelectric transducer and can be tuned simply.The quad-combs are obtained with three initial OFCs,forming a pair of dual-combs,appearing when three ultrasound frequencies feed the AOTF transducer.The quad-combs frequency spacing is defned by the diference between the frequency spacing of dual-combs.Quad-combs with more than 5000 spectral lines and tunable frequency spacing are observed.The successive frequency downconversion gives the possibility to reduce the OFC frequency spacing form several MHz for initial OFC to tens of kHz for quad-combs.