A two-stage optical frequency comb generator based on Mach-Zehnder modulator and Re-circulating frequency shifter

We propose a novel scheme to generate optical frequency comb by using a two-stage generator based on Mach-Zehnder modulator and re-circulating frequency shifter. Based on the Mach-Zehnder modulator a light source including 2 flat and stable frequency spectrum lines is generated at the first stage, and the light source is then used as the seed light in the re-circulating frequency shifter loop at the second stage. The scheme can greatly reduce the accumulated noise of the system. Through theoretical analysis and simulation it is shown that the proposed theoretical model of the two-stage system is proved in good agreement with simulation results.     

High flatness optical frequency comb generator based on the chirping of modulators

A novel scheme for generation of an optical frequency comb (OFC) based on the chirping of two cascaded modulators is proposed. The first modulator is a dual-electrode Mach–Zehnder modulator (MZM), while the other modulator is an integrated MZM composed of two parallel MZMs that increases the number of comb lines. Our modified scheme can generate a large number of frequency lines with excellent flatness by simply modifying the chirp factor, and it is shown that up to 54 frequency lines could be observed. Theoretical analysis and simulation results show that under the variety of conditions that can be used in this scheme, the power fluctuations of the OFC lines are less than 0.5 dB in all cases; these results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness. Additionally, our modified scheme has the merit of tunable frequency spacing, which is practical for experimental realization of the OFC.     

Generation and noise analysis of a wide-band optical -frequency comb based on recirculating frequency shifter

By optimizing the gain configuration and length of the loop, a 90-tone optical frequency comb （OFC） is successfully generated based on recirculating frequency shifter structure. The peak-to-peak power fluctuation of the 90-tone OFC is 4.26 dB and the tone-to-noise ratio is higher than 19.17 dB. To further analyze the noise accumulation feature of the tones when travelling around the loop, linewidth of the tones is measured by delayed self-heterodyne interferometer structure. The result shows the linewidth of the tones deteriorates little during the recirculating process, indicating that the generated OFC is an ideal multi-wavelength source for high-speed communication svstems.     

A tunable frequency-decuple optoelectronic oscillator based on frequency comb and stimulated Brillouin scattering

An optically tunable frequency-decuple optoelectronic oscillator based on optical frequency comb (OFC) and stimulated Brillouin scattering has been proposed and theoretically analyzed. In the proposed structure, the OFC is generated using a cascaded Mach–Zehnder modulator and a dual-parallel Mach–Zehnder modulator (DPMZM), and multi-pump lights could be obtained instead of one pump. A quintuple Brillouin frequency shift oscillation signal generated by using Brillouin gain-loss compensation principle and carrier phase-shifted double sideband modulation is realized by using the DPMZM to double the oscillation frequency. As a consequence, a decuple frequency shift microwave signal is achieved. Profit from the wavelength-dependent nature of Brillouin frequency shift, a frequency-decuple signal at 10 \(f_{b}\) which could be tunable from 87.9750 to 94.4750 GHz by simply tuning the wavelength of the tunable laser source is obtained in theory.     

Simulation of a flat optical frequency comb using a single-drive multi-RF Mach–Zehnder modulator in a cascaded intensity modulator chain

We proposed a scheme based on two cascaded lithium niobate intensity modulators to generate an optical frequency comb with very high flatness. Single-drive multi-RF waveforms are used for driving the first intensity modulator, and 9 lines within 1 dB power variation can be obtained. When cascading with another intensity modulator, by specially adjusting the DC bias and the drive amplitudes of the RF signals of the two intensity modulators, 27 or 45 comb lines with a spectral power variation about 1 dB are obtained. The scheme is relatively simple and adjustable, and the frequency interval of the OFC varies with microwave frequency applied on modulators.     

Terahertz optical frequency comb generation with optimized cascaded difference frequency generation

Optical Review - A novel scheme that generates terahertz optical frequency comb (THz OFC) based on optimized cascaded difference frequency generation (OCDFG) with an aperiodically poled lithium...     

Ultraflat and broadband optical frequency comb generator based on cascaded two dual-electrode Mach–Zehnder modulators

Optical Review - A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach–Zehnder modulators (DE-MZM)....     

Scheme for generation of flat top and high signal-to-noise ratio optical frequency comb

We demonstrate a new scheme for generation of optical frequency comb(OFC) based on cascade modulators, 23 comb lines within 0.5 d B spectral power variation are obtained. An optical finite impulse response(FIR) filter is introduced for suppression of amplified spontaneous emission noise. It is shown that carrier-to-noise-ratio of the OFC generated by this scheme can be as high as 38.8 d B with 12 d B improvement by using a 16-tap FIR filter, and the error vector magnitude performances of loaded Nyquist-16 quadrature amplitude modulation signal is improved from 14.20% to 7.44%.     

基于飞秒锁模光纤激光脉冲基频光的差频产生红外光梳

报道了一种基于飞秒锁模光纤激光脉冲基频光的光纤型差频产生(DFG)红外光梳及其研制技术.基于自主研制的重频锁定200 MHz飞秒锁模掺铒光纤激光器,经啁啾脉冲光纤放大与超连续谱产生技术,优化近零色散OFS光纤(型号:OFS-980-20)长度,结合可调延时线,获得了精准同步的基频双色脉冲;以GaSe为非线性晶体,利用光整流技术,产生了可在6—10μm范围内宽带调谐的DFG红外光梳,光梳最大光谱宽度可达1.3μm.这种光纤型远红外光梳可望在分子光谱精密测量等领域发挥重要作用.     

一种提高基于循环频移器的多载波光源光信噪比的方案

频率锁定多载波光源是实现太比特系统传输的关键器件之一, 目前已成为光纤通信领域的研究热点.基于循环频移技术产生的频率锁定 多载波光源因具有驱动电压低、串扰小、平坦度高的优点而受到重视, 但是其输出质量容易受到调制器固有的高阶谐波串扰的影响,特别是三阶谐波串扰. 为了减小三阶串扰的影响,本文提出了在I/Q调制器两支路上再加载另一频率为3f_m的射频信号的方案, 用其产生的一阶信号来抑制三阶串扰.通过理论分析与数值仿真,得到了载波数为24、 载波间最大功率差小于0.1 dB的多载波光源输出.与未采用三阶串扰抑制方案的结果比较, 光源输出有效光信噪比提高了2 dB. 结果表明,采用本文的改进方案,可以有效地提高多载波光源的输出平坦度和有效光信噪比.     

Optoelectronic oscillator using a LiNbO3 phase modulator for self-oscillating frequency comb generation

Optical frequency comb generation by using a novel optoelectronic oscillator (OEO) is proposed and demonstrated with the emphasis placed on self-oscillating operation. In the OEO, a wideband LiNbO3 phase modulator is driven with a large-amplitude radio-frequency (RF) feedback signal to generate a deeply phase-modulated light wave; accordingly, an optical frequency comb with a bandwidth greater than the RF signal is generated by self-oscillation. Although it generates multifrequency components, the OEO exhibits characteristics of a single-mode oscillator. Its operation is stable and self-starting. An optical frequency comb with a 120 GHz bandwidth and 9.95 GHz frequency spacing was successfully generated by self-oscillation at a single frequency.     

一种基于电光调制光频梳光谱干涉的绝对测距方法

提出了一种基于电光调制光学频率梳的光谱干涉测距方法.理论分析了电光调制光学频率梳的数学模型和光谱扩展原理,并分析得出了光谱干涉测距方法的非模糊范围和分辨力的影响因素.在实验中,使用三只级联的电光相位调制器调制单频连续波激光生成了40多阶高功率梳齿状边带,并通过单模光纤和高非线性光纤对电光调制器输出的激光进行光谱扩展,得到重复频率为10 GHz,光谱宽度达30 nm的光学频率梳.将该光频梳作为光谱干涉测距装置的光源,可以实现无"死区"的绝对距离测量.另外,使用等频率间隔重采样和二次方程脉冲峰值拟合算法对测量结果进行数据处理,可以修正系统误差,提升测距精度.实验结果表明,在1 m的测量范围内,使用该装置可以在任意位置达到±15μm以内的绝对测距精度.     

High-resolution spectroscopy using interleaved 100 GHz optical frequency comb scanned by phase modulator

A high-resolution spectroscopy technique is proposed with an optical phase modulator combined with an interleaved optical frequency comb. The optical phase modulator and a frequency-locked laser light guarantee a spectral resolution less than 1 MHz on an absolute frequency axis. A wide measurement frequency range was realized using a 25 GHz optical frequency comb lying over a 4 THz frequency region. An extraction of single tooth intensity from the comb was realized by a heterodyne technique with a frequency-tunable laser used as a local oscillator. Also, the 25 GHz optical frequency comb was interleaved to generate four 100-GHz combs for removing the crosstalk from the 25 GHz neighboring sidebands in the teeth. This proposed spectroscopy technique was experimentally demonstrated with a resonator of less than 1 MHz linewidth and a H¹³C¹⁴N gas cell. Thus, a measurement frequency range higher than 4 THz (1530 nm-1560 nm) was confirmed with an effective spectral resolution 100 kHz order. In addition, the characteristics of the proposed system were compared with those of the previous system with a single-sideband (SSB) optical modulator.     

A spurious frequencies suppression method for optical frequency comb based microwave photonic filter

The traditional optical frequency comb (OFC) based microwave photonic filters (MPFs) are rigidly restricted to be operated in a single “Nyquist zone”, as varieties of spurious frequencies signals coexist in the output. Here, a method for spurious frequencies suppression in the OFC‐based MPF is proposed and experimentally demonstrated. The method is achieved by applying group velocity dispersion on the carrier combs to separate the filter transfer functions of the spurious frequencies from that of the input radio frequency signal. It is fairly simple and effective, and has no effect on the filter characteristic. With this method, the filter pass band can be freely tuned without the limitation of the “Nyquist zone”. It can be considered as a step forward for the practical application of the OFC‐based MPF.     

Second-harmonic generation of an optical frequency comb at 1.55 microm with periodically poled lithium niobate

To expand the span of the optical frequency comb (OFC), we generated the second harmonics of an OFC at 1.55microm , using a multiperiod periodically poled lithium niobate (PPLN) crystal. A coupled-cavity OFC generator with an average output power of 0.2 mW was amplified and expanded with a fiber amplifier and a dispersion-flattened fiber. The fundamental OFC average power and span were 100 mW and 45 THz, respectively. The second-harmonic comb's span was 3.2 THz; however, we tuned the center frequency over 30 THz by changing the poling period. We also demonstrated that the second-harmonic comb can be used for frequency-difference measurement.     

Generation of very flat optical frequency combs from continuous-wave lasers using cascaded intensity and phase modulators driven by tailored radio frequency waveforms

We demonstrate a scheme based on a cascade of lithium niobate intensity and phase modulators driven by specially tailored RF waveforms to generate an optical frequency comb with very high spectral flatness. In this Letter, we demonstrate a 10 GHz comb with 38 comb lines within a spectral power variation below 1 dB. The number of comb lines that can be generated is limited by the power handling capability of the phase modulator, and this can be scaled without compromising the spectral flatness. Furthermore, the spectral phase of the generated combs in our scheme is almost purely quadratic, which, as we will demonstrate, allows for high-quality pulse compression using only single-mode fiber.     

Optimized amplification of femtosecond optical pulses by dispersion management for octave-spanning optical frequency comb generation

We report a method for optimizing the amplification of femtosecond optical pulses by using dispersion management. The amount of dispersion provided to the seed optical pulse of an erbium-doped fiber (EBF) has an optimal region that enhances the output power of an amplifier. The power enhancement is accompanied by spectral broadening, which originates from adiabatic narrowing in the erbium-doped fiber. The amplified optical pulses can be used to generate an octave-spanning optical frequency comb (OFC) by employing a highly nonlinear fiber (HNLF).     

All polarization-maintaining Er:fiber-based optical frequency comb for frequency comparison of optical clocks

We demonstrate an optical frequency comb (OFC) based on a turnkey mode-locked laser with a figure-9-shape structure and polarization-maintaining fibers, for the comparison of frequency among optical clocks with wavelengths of 698 nm, 729 nm, 1068 nm, and 1156 nm. We adopt a multi-branch approach in order to produce high power OFC signals at these specific wavelengths, enabling the signal-to-noise ratio of the beatnotes between the OFC and the clock lasers to exceed 30 dB at a resolution bandwidth of 300 kHz. This approach makes the supercontinuum spectra much easier to be generated than a single branch OFC. However, more out-of-loop fibers degrade the long-term frequency instability due to thermal drift. To minimize the thermal drift effect, we set the fiber lengths of different branches to be similar, and we stabilize the temperature as well. The out-of-loop frequency instability of the OFC due to the incoherence of the multi-branch is about 5.5×10^-19 for 4000 s, while the in-loop frequency instability of f_ceo and that of f_beat are 7.5×10^-18 for 1 s and 8.5×10^-18 for 1 s, respectively. The turnkey OFC meets the requirement for the comparison of frequency between the best optical clocks.     

All optical arbitrary waveform generation by optical frequency comb based on cascading intensity modulation

We propose and experimentally demonstrate an all optical arbitrary waveform generation by optical frequency comb (OFC) based on cascading intensity modulation. By selecting spectral lines of interest from OFC through optical filters, 10 GHz, 20 GHz, and 60 GHz sinusoidal signals with low phase noise and more complex waveforms, including ultra-short pulse, half-wave cosine, and single frequency modulated MMW signals, are generated easily.     

基于相位调制偏振态QKD系统的量子信道校正发送方案

提出了一种基于相位调制偏振态QKD系统的量子信道校正发送的新方案—采用波导型相位调制器研制成电控连续可调光学相移器,它可随相位调制器输入电压的连续改变而产生连续的相移,从而控制输出的偏振态;在其前放置一个半波片,即可校正接收端偏振态量子态在信道中所发生的改变,从而保证信道传送密钥的可用性.通过理论推导和实验研究验证了基于相位调制偏振态QKD系统的量子信道校正发送方案的核心部件的可行性.由于本方案能实现高速调制（GHz）,为解决光纤传输的偏振编码QKD系统中偏振态漂移问题提供了一种新的途径.