窄线宽激光器的线宽表征方式通常采用延时自外差法测量技术。该技术是通过延时光纤差拍产生一个与待测激光线宽相关的洛伦兹频谱,因此该频谱只具有单一的线宽表现形式。为了能够观察到激光器的线宽和频率噪声在其傅里叶频率分布下的完...窄线宽激光器的线宽表征方式通常采用延时自外差法测量技术。该技术是通过延时光纤差拍产生一个与待测激光线宽相关的洛伦兹频谱,因此该频谱只具有单一的线宽表现形式。为了能够观察到激光器的线宽和频率噪声在其傅里叶频率分布下的完整特性,报道了一种基于β算法计算窄线宽激光器线宽的方法。该方法是结合频率噪声中的白噪声和1/ f 噪声分别诱导不同激光线型的理论,从而确定激光线宽。首先,对β算法的基本原理进行了详细的分析说明。通过基于维纳-辛钦定理,分析了窄线宽激光器不同频率范围内的频率噪声和激光线宽的依赖关系。阐明了在截止频率趋于0和无穷大的两个范围条件时,激光频谱特性从高斯线型向洛伦兹线型演变。同时推导出使两种线型转换的截止频率表达式,并将其转换为频率噪声函数,该函数定义为β分子线。此时频率噪声分量中高斯线型的总和即为激光线宽计算公式;其次,对窄线宽激光器的频率噪声和激光线型进行数值仿真。将通过OEwaves公司的OE4000互相关零差相位/频率噪声自动测试系统测得的频率噪声谱密度,带入β算法理论公式中。结果显示: 1/ f 噪声导致激光呈现高斯线型,线宽随截止频率的增加而增大。而白噪声将导致洛伦兹线型,线宽不再随截止频率而改变。此外,在低频区域,频率噪声电平远大于其傅里叶频率,噪声调制系数较高,该部分噪声可以决定线宽大小。因此,高斯线型区域对应的频率噪声的积分,即为待测激光器的线宽;在高频区域,频率噪声电平与其傅里叶频率相差较小,频率波动较快,噪声对线宽影响可以忽略。并且频率带宽在截止频率范围内,计算的线宽误差较小。最后,实验上运用β算法对RIO公司的1 550 nm低噪声窄线宽激光器的频率噪声功率谱密度进行积分计算,成功获得了其不同傅里叶频率�展开更多
We report a low noise continuous-wave （CW） single-frequency 1.5-μm laser source obtained by a singly resonant optical parametric oscillator （SRO） based on periodically poled lithium niobate （PPLN）. The SRO was ...We report a low noise continuous-wave （CW） single-frequency 1.5-μm laser source obtained by a singly resonant optical parametric oscillator （SRO） based on periodically poled lithium niobate （PPLN）. The SRO was pumped by a CW single-frequency Nd：YVO4 laser at 1.06μm. The 1.02 W of CW single-frequency signal laser at 1.5 μm was obtained at pump power of 6 W. At the output power of around 0.75 W, the power stability was better than ±l.5% and no mode-hopping was observed in 30 min and frequency stability was better than 8.5 MHz in 1 min. The signal wavelength could be tuned from 1.57 to 1.59 μm by varying the PPLN temperature. The 1.5-μm laser exhibits low noise characteristics, the intensity noise of the laser reaches the shot noise limit （SNL） at an analysis frequency of 4 MHz and the phase noise is less than 1 dB above the SNL at analysis frequencies above 10 MHz.展开更多
Frequency combs with equally spaced frequency lines show great potentials for applications in spectroscopy,imag-ing,communications,and so on.In the terahertz frequency region,the quantum cascade laser(QCL)is an ideal ...Frequency combs with equally spaced frequency lines show great potentials for applications in spectroscopy,imag-ing,communications,and so on.In the terahertz frequency region,the quantum cascade laser(QCL)is an ideal radiation source for frequency comb and dual-comb operation.The systematic evaluation of phase noise characteristics of terahertz QCL frequency comb and dual-comb sources is of great importance for high precision measurements.In this work,we present detailed measurements and analysis of the phase noise characteristics of terahertz QCL frequency comb and dual-comb sources emitting around 4.2 THz with repetition frequencies of~6.2 GHz.The measurement results for the current noise of the direct current(DC)sources(that are used to electrically pump the terahertz QCLs)indicate that at 100 Hz,the current noise for DC-1 and DC-2 is 0.3895 and 0.0982 nA/Hz1/2,respectively.Such levels of current noise can be safely disregarded.The phase noise of radio frequency(RF)generators(that are employed for injection locking and phase locking),intermode beatnotes,and dual-comb signals with and without phase-locked loop(PLL)are all measured and compared.The experimental results show that in the free-running mode,the phase noise of the intermode beatnote signals is always lower than that of the dual-comb sig-nals across all frequencies.Additionally,the phase noise induced by the RF generators is negligible.By employing the phase lock-ing technique,the phase noise of the intermode beatnote and dual-comb signals in the low offset frequency band can be signifi-cantly suppressed.At an offset frequency of 100 Hz,the measured phase noise values of the dual-comb line without and with phase locking are 15.026 and-64.801 dBc/Hz,respectively.展开更多
给出了利用全光纤环形谐振器实现对激光器频率噪声抑制的原理和实验结果。采用Pound-Drever-Hall的方法对锁定在铷原子吸收谱线上的激光进行稳频,实现了饱和吸收光谱与光纤环形谐振器双回路锁定。通过外差式马赫-曾德干涉仪来测量锁定...给出了利用全光纤环形谐振器实现对激光器频率噪声抑制的原理和实验结果。采用Pound-Drever-Hall的方法对锁定在铷原子吸收谱线上的激光进行稳频,实现了饱和吸收光谱与光纤环形谐振器双回路锁定。通过外差式马赫-曾德干涉仪来测量锁定后的激光器频率噪声发现,在频率100 Hz时,光纤环形谐振器对频率噪声的抑制度超过了40 d B。在1 Hz处,稳频激光器的频率噪声小于100 d B Hz2/Hz,其抑制度达到60 d B。展开更多
文摘窄线宽激光器的线宽表征方式通常采用延时自外差法测量技术。该技术是通过延时光纤差拍产生一个与待测激光线宽相关的洛伦兹频谱,因此该频谱只具有单一的线宽表现形式。为了能够观察到激光器的线宽和频率噪声在其傅里叶频率分布下的完整特性,报道了一种基于β算法计算窄线宽激光器线宽的方法。该方法是结合频率噪声中的白噪声和1/ f 噪声分别诱导不同激光线型的理论,从而确定激光线宽。首先,对β算法的基本原理进行了详细的分析说明。通过基于维纳-辛钦定理,分析了窄线宽激光器不同频率范围内的频率噪声和激光线宽的依赖关系。阐明了在截止频率趋于0和无穷大的两个范围条件时,激光频谱特性从高斯线型向洛伦兹线型演变。同时推导出使两种线型转换的截止频率表达式,并将其转换为频率噪声函数,该函数定义为β分子线。此时频率噪声分量中高斯线型的总和即为激光线宽计算公式;其次,对窄线宽激光器的频率噪声和激光线型进行数值仿真。将通过OEwaves公司的OE4000互相关零差相位/频率噪声自动测试系统测得的频率噪声谱密度,带入β算法理论公式中。结果显示: 1/ f 噪声导致激光呈现高斯线型,线宽随截止频率的增加而增大。而白噪声将导致洛伦兹线型,线宽不再随截止频率而改变。此外,在低频区域,频率噪声电平远大于其傅里叶频率,噪声调制系数较高,该部分噪声可以决定线宽大小。因此,高斯线型区域对应的频率噪声的积分,即为待测激光器的线宽;在高频区域,频率噪声电平与其傅里叶频率相差较小,频率波动较快,噪声对线宽影响可以忽略。并且频率带宽在截止频率范围内,计算的线宽误差较小。最后,实验上运用β算法对RIO公司的1 550 nm低噪声窄线宽激光器的频率噪声功率谱密度进行积分计算,成功获得了其不同傅里叶频率�
基金supported by the National Natural Science Foundation of China(Grant No.60878003)the Science Fund for Excellent Research Team of the National Natural Science Foundation of China(Grant No.60821004)the National Basic Research Program of China(Grant No.2010CB923101)
文摘We report a low noise continuous-wave （CW） single-frequency 1.5-μm laser source obtained by a singly resonant optical parametric oscillator （SRO） based on periodically poled lithium niobate （PPLN）. The SRO was pumped by a CW single-frequency Nd：YVO4 laser at 1.06μm. The 1.02 W of CW single-frequency signal laser at 1.5 μm was obtained at pump power of 6 W. At the output power of around 0.75 W, the power stability was better than ±l.5% and no mode-hopping was observed in 30 min and frequency stability was better than 8.5 MHz in 1 min. The signal wavelength could be tuned from 1.57 to 1.59 μm by varying the PPLN temperature. The 1.5-μm laser exhibits low noise characteristics, the intensity noise of the laser reaches the shot noise limit （SNL） at an analysis frequency of 4 MHz and the phase noise is less than 1 dB above the SNL at analysis frequencies above 10 MHz.
基金supported by the Innovation Program for Quantum Science and Technology (2023ZD0301000)the National Science Fund for Distinguished Young Scholars (62325509)+3 种基金the National Natural Science Foundation of China (62235019,61875220,61927813,61991430,62035005,62105351,62275258,62035014,and 62305364)Science and Technology Commission of Shanghai Municipality (21ZR1474600)the"From 0 to 1"Innovation Program of the Chinese Academy of Sciences (ZDBS-LY-JSC009)the CAS Project for Young Scientists in Basic Research (YSBR-069).
文摘Frequency combs with equally spaced frequency lines show great potentials for applications in spectroscopy,imag-ing,communications,and so on.In the terahertz frequency region,the quantum cascade laser(QCL)is an ideal radiation source for frequency comb and dual-comb operation.The systematic evaluation of phase noise characteristics of terahertz QCL frequency comb and dual-comb sources is of great importance for high precision measurements.In this work,we present detailed measurements and analysis of the phase noise characteristics of terahertz QCL frequency comb and dual-comb sources emitting around 4.2 THz with repetition frequencies of~6.2 GHz.The measurement results for the current noise of the direct current(DC)sources(that are used to electrically pump the terahertz QCLs)indicate that at 100 Hz,the current noise for DC-1 and DC-2 is 0.3895 and 0.0982 nA/Hz1/2,respectively.Such levels of current noise can be safely disregarded.The phase noise of radio frequency(RF)generators(that are employed for injection locking and phase locking),intermode beatnotes,and dual-comb signals with and without phase-locked loop(PLL)are all measured and compared.The experimental results show that in the free-running mode,the phase noise of the intermode beatnote signals is always lower than that of the dual-comb sig-nals across all frequencies.Additionally,the phase noise induced by the RF generators is negligible.By employing the phase lock-ing technique,the phase noise of the intermode beatnote and dual-comb signals in the low offset frequency band can be signifi-cantly suppressed.At an offset frequency of 100 Hz,the measured phase noise values of the dual-comb line without and with phase locking are 15.026 and-64.801 dBc/Hz,respectively.
文摘给出了利用全光纤环形谐振器实现对激光器频率噪声抑制的原理和实验结果。采用Pound-Drever-Hall的方法对锁定在铷原子吸收谱线上的激光进行稳频,实现了饱和吸收光谱与光纤环形谐振器双回路锁定。通过外差式马赫-曾德干涉仪来测量锁定后的激光器频率噪声发现,在频率100 Hz时,光纤环形谐振器对频率噪声的抑制度超过了40 d B。在1 Hz处,稳频激光器的频率噪声小于100 d B Hz2/Hz,其抑制度达到60 d B。
