摘要
双光梳光谱技术的测量分辨率取决于光频梳的脉冲重复频率,重复频率越低,测量分辨率越高。然而传统的低噪声锁模光频梳的重复频率被腔长限制在百MHz量级,这限制了双光梳光谱技术的分辨率。提出了一种基于电光强度调制脉冲拾取的高分辨率双光梳光谱技术。通过将电光强度调制器的偏置点稳定在其功率传输曲线的最低值处,利用电光强度调制器对锁模光频梳的时域脉冲进行特定周期的选取,成功将重复频率为250 MHz的锁模光频梳的重复频率降低到31.25 MHz。利用此高分辨率光频梳测量了H^(13)C^(14)N气体的P10吸收峰,光谱分辨率为31.25 MHz,吸收谱线分辨率提高了8倍,验证了该方法的可行性。
Objective Optical frequency combs(OFCs)exhibit a comblike structure in the frequency domain,characterized by equally spaced frequency intervals.Due to the properties of this comblike structure,OFCs have become ideal light sources for precision spectral measurements.The resolution of comb spectroscopy is determined by the line spacing of the comb,which corresponds to the pulse repetition rate.Modelocked frequency combs typically operate in the range of hundreds of megahertz to gigahertz.A smaller repetition rate results in a reduced frequency interval between spectral sampling points,thereby enhancing spectral resolution.However,for modelocked frequency combs,achieving a low repetition rate generally necessitates an increase in cavity length,which consequently enlarges the physical dimensions of the modelocked comb and hampers its applicability for outdoor spectral measurements.On the other hand,microcombs typically exhibit repetition rates exceeding gigahertz,which limits the spectral resolution due to the large frequency spacing.Considering the advantages of both modelocked combs and microcombs,obtaining low repetition rate outputs from high repetition rate combs with pulse picking is one method toward achieving highresolution frequency combs.Dualcomb spectroscopy employs two frequency combs with slightly repetition rate difference to transfer spectral information from the optical frequency domain to the radio frequency domain,offering benefits such as high coherence and sensitivity.When combined with pulse picking technology,dualcomb spectroscopy can obtain highresolution frequency comb spectra.Methods In this study,we conducted timedomain pulse picking using two modelocked OFCs with repetition rates of 250 MHz and 249.92 MHz.An arbitrary waveform generator(AWG)generated rectangular wave signals at frequencies of 31.25 MHz and 31.24 MHz with a duty cycle of 12.5%,which were used to drive an electrooptic amplitude modulator(EOAM).By actively controlling the bias point of the EOAM,we selected one pulse from every eight pulses produced by the two OFCs,while suppressing the remaining pulses.This approach effectively increased the pulse period of the combs to eight times the original duration,resulting in a corresponding reduction in the repetition rate to oneeighth of the original,while the number of comb teeth increased eightfold.Both the frequency combs and the AWG were synchronized to a rubidium atomic clock.Following pulse picking,the highresolution OFCs passed through a gas absorption cell,and the resulting radio frequency spectrum,obtained through multiheterodyne detection,contained information regarding the gas absorption characteristics.A photodetector recorded the timedomain interferograms(IGMs),which was then processed using a lowpass filter(LPF)with a cutoff frequency of 13 MHz.Subsequently,coherence was restored through a selfcorrection algorithm based on the crossambiguity function.Results and Discussions After pulse picking,the period of the IGMs increased from 12.5μs to 100μs(Fig.4),corresponding to a spectral interval in the radio frequency spectrum that changed from 80 kHz to 10 kHz(Fig.5),consistent with theoretical analysis.Since the optical bandpass filter used after the combination of the dualcomb exhibits a Gaussian line shape,we performed a Gaussian fit on the regions of the radio frequency spectrum outside absorption as a reference.The ratio of the measured value to the reference represents the spectral transmittance.The minimum value of the radio frequency spectrum was fixed at the H13C14N gas P10 absorption peak,specifically at 193.45 THz.By multiplying the frequency axis of the radio frequency spectrum by the conversion factor,we obtained the transmittance spectrum in the optical frequency domain,with a measurement point spacing of 31.25 MHz.Compared to the 250 MHz spacing before pulse picking,this represents an eightfold improvement in resolution.Voigt fitting was performed on both sets of spectral lines,yielding fitted curves with residuals for both cases below 0.05(Fig.6),thereby demonstrating accurate measurement of the H^(13)C^(14)N P10 absorption peak spectrum.Conclusions We proposed a method for achieving highresolution dualcomb spectra based on pulse picking,which actively controls the bias point of the EOAM.An AWG drives the EOAM to output rectangular wave signals with specific frequencies and duty cycles for timedomain pulse picking of the OFCs.This approach resulted in an eightfold increase in both the number of radio frequency comb teeth and the spectral resolution.By measuring the P10 absorption peak of gas,we obtained accurate results with a resolution of 31.25 MHz,thereby validating the feasibility of this method.This approach provides a method and experimental evidence for obtaining highresolution spectra from high repetition rate modelocked microcombs,and the dualcomb system is not complex,facilitating outdoor spectral measurements.The subsequent work may focus on reducing the modulation frequency or applying this method to higher repetition rate comb sources to demonstrate its broad adaptability and explore the limits of resolution.
作者
马湘泽
龙玮
程杰
黄腾
汲煜佳
陈迪俊
Ma Xiangze;Long Wei;Cheng Jie;Huang Teng;Ji Yujia;Chen Dijun(Aerospace Laser Technology and System Department,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China;Hangzhou Institute for Advanced Study,University of Chinese Academy of Sciences,Hangzhou 310024,Zhejiang,China;Center of Materials Science and Optoelectronics Engineering,University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《中国激光》
北大核心
2025年第11期235-241,共7页
Chinese Journal of Lasers
基金
国家重点研发计划(2020YFC2200300)。
关键词
光频梳
双光梳光谱
电光调制
脉冲拾取技术
optical frequency comb
dualcomb spectroscopy
electrooptic modulation
pulse picking technology
