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.     

Tunable optical comb generation based on carrier-suppressed intensity modulation and phase modulation

<正>An approach to generate a flat optical comb with tunable comb spacing and adjustable comb number is proposed.In the proposed approach,a Mach-Zehnder modulator(MZM),being biased to generate two carrier-suppressed first-order sidebands,is cascaded with a phase modulator.The two optical sidebands are then sent to the phase modulator to generate two identical,but frequency-shifted phase-modulated spectra.Thanks to the complementary nature of the two adjacent comb lines in the phase-modulated spectra,the overlapping of the two spectra would lead to the generation of a flat optical comb.Since only the phase modulation index or the microwave power is needed to be adjusted,the system is easy to be implemented with tunable comb spacing and adjustable comb number.Numerical simulations are performed,and the approach is verified by an experiment.     

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...     

Accuracy of optical frequency comb generation in optical fiber

We evaluated the accuracy of an optical frequency comb in optical fibers by measuring the frequency shift after a sideband from an electro-optic modulator had passed through the fiber. We found that a frequency drift of a few hertz was due largely to a variation in the ambient temperature that corresponded to an increase in the square root of the Allan variance to 0.66 Hz.     

Broadband optical frequency comb generation with a phase-modulated parametric oscillator

We introduce a novel broadband optical frequency comb generator consisting of a parametric oscillator with an intracavity electro-optic phase modulator. The parametric oscillator is pumped by 532-nm light and produces near-degenerate signal and idler fields. The modulator generates a comb structure about both the signal and the idler. Coupling between the two families of modes results in a dispersion-limited comb that spans 20 nm (5.3 THz). A signal-to-noise ratio of >30 dB in a 300-kHz bandwidth is observed in the beat frequency between individual comb elements and a reference laser.     

Dispersion compensation for terahertz optical frequency comb generation

We demonstrate dispersion compensation in a terahertz-span optical frequency comb generator by use of an intracavity prism pair. With partial compensation of the material dispersion of the lithium niobate modulator, the span of the comb increases from 3.0 to 4.3THz.     

Widely-tunable mid-infrared frequency comb source based on difference frequency generation

We report on a mid-IR frequency comb source of unprecedented tunability covering the entire 3-10 μm molecular fingerprint region. The system is based on difference frequency generation in a GaSe crystal pumped by a 151 MHz Yb:fiber frequency comb. The process was seeded with Raman-shifted solitons generated in a highly nonlinear suspended-core fiber with the same source. Average powers up to 1.5 mW were achieved at the 4.7 μm wavelength.     

Equal-amplitude optical comb generation using multi-frequency phase modulation in optical fibers

<正>We theoretically analyze and experimentally demonstrate a method of generating equal-amplitude optical comb exploiting multi-frequency phase modulation.The theoretical analysis shows that 4n-1 equal-amplitude spectral lines can be obtained when the modulation signal comprises n frequency components including the fundamental frequency and the odd harmonic frequencies,and 2n+1 equal-amplitude spectral lines can be obtained when the modulation signal comprises n frequency components including the fundamental frequency and the even harmonic frequencies.Then,we numerically simulate the spectra of 5,7,9,and 11 equal-amplitude spectral lines,respectively,which are also obtained in experiments with frequency separation of 30 MHz and flatness of better than 0.3 dB.     

Generation of flat optical frequency comb by fiber loop modulation

We propose a novel flat optical frequency comb generation system that employs fiber loop modulation and experimentally demonstrate its operation. Generally, when an external laser beam is injected into a fiber loop system including an optical modulator and an amplifying medium, multiple sidebands are generated exponentially. On the other hand, the fiber loop starts mode-locked oscillation at a center frequency to maximize the round-trip gain in the fiber loop from the seeds of the injected laser sidebands. By locking the sidebands from fiber loop modulation with the mode-locked oscillation in the fiber loop, the synchronous spectrum between the mode-locked oscillation and the sidebands can be shaped into a flat spectrum. Thus, a flat optical frequency comb with a flatness of about ±1 dB is obtained in the spectral bandwidth of about 1 THz.     

High-resolution spectroscopy based on optical phase modulator and optical frequency comb

A phase modulation of an optical frequency comb has been applied to measure a fine spectrum in the 1.5 μm wavelength range by the optical heterodyne-detection method. The measurement frequency range covered 25 GHz, which satisfies the frequency interval of the optical frequency comb, with a spectral resolution of 1 MHz.     

Carrier suppression in quadruple frequency modulation by cascaded optical external modulators for millimeter-wave generation

The optical carrier suppression in optical quadruple frequency modulation by cascaded external modulators is investigated theoretically and experimentally. Theoretical analysis demonstrates that the optical carrier suppression ratio is related with not only the initial phase difference of electrical signals applied on the two modulators, but also the optical phase shift between the two modulators. The maximum suppression ratio can be achieved when the total phase difference is equal to nπ＋π/2 （n = 1, 2,…）, which is verified by experiments. By properly controlling the total phase shift, 40-GHz millimeter-wave is generated by using a 10-GHz radio frequency （RF） source and the modulators.     

Flat optical frequency comb generation using polarization modulator and frequency shifter with double recirculating frequency shifting loops

A scheme to generate ultra-flat and stable optical frequency comb (OFC) based on multi-wavelength optical seed source and polarization-modulator-based complementary frequency shifter (PCFS) has been proposed and demonstrated. The OFC generation scheme includes two stages: 5-carrier light source is generated by utilizing a polarization modulator at the first stage, and the light source is then used as the seed light in the PCFS at the second stage. Compared with the previous flat OFC generator based on a recirculation frequency shifter, the proposed scheme can greatly reduce the recirculation times, and such a property makes the accumulated noise of the system enormously decrease. In order to achieve the frequency comb with the best flatness, the optical amplifier gain, filter stop-band attenuation and modulator drive voltage are optimized. Experiment simulations show that high-quality OFC with hundreds of frequency lines and power fluctuation within 2 dB can be achieved without direct-current bias control and wavelength-selective-switch.     

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.     

Design of waveguide-integrated semiconductor laser sources for optical frequency comb generation

A numerical study of threshold gain and modal dispersion in integrated semiconductor laser optical frequency comb sources is presented. We consider an example device where one of the cleaved facets of the laser is replaced by a short Bragg grating section and show that as many as 16 modes can be selected at the first harmonic of the underlying Fabry-Perot cavity. An intracavity approach to limiting the grating-induced dispersion that can be implemented directly through the grating profile is demonstrated.     

Parallel generation of quadripartite cluster entanglement in the optical frequency comb

Scalability and coherence are two essential requirements for the experimental implementation of quantum information and quantum computing. Here, we report a breakthrough toward scalability: the simultaneous generation of a record 15 quadripartite entangled cluster states over 60 consecutive cavity modes (Q modes), in the optical frequency comb of a single optical parametric oscillator. The amount of observed entanglement was constant over the 60 Q modes, thereby proving the intrinsic scalability of this system. The number of observable Q modes was restricted by technical limitations, and we conservatively estimate the actual number of similar clusters to be at least 3 times larger. This result paves the way to the realization of large entangled states for scalable quantum information and quantum computing.     

Sweep optical frequency synthesizer with a distributed-Bragg-reflector laser injection locked by a single component of an optical frequency comb

A sweep optical frequency synthesizer is demonstrated by using a frequency-stabilized optical frequency comb and injection-locked distributed-Bragg-reflector (DBR) laser diode. The injection-locked DBR laser acts as a single-frequency filter and, simultaneously, a high-gain amplifier of the optical frequency comb. The frequency instability of the heterodyne beat signal between two independently injection-locked DBR lasers is measured to be 2.3 x 10(-16) at 1 s averaging time. The output frequency of the sweep optical frequency synthesizer can be precisely tuned over 1 GHz, and a saturated absorption spectrum of the Cs D2 line at 852 nm is recorded by the injected DBR laser.     

基于双环混频光电振荡器的可调谐微波频率梳产生

随着无线通信的速率提升和微蜂窝趋势,光载微波技术已经成为重要的发展趋势,而光生多载波系统是光载微波的最重要的技术之一.本文提出了一种基于双环混频光电振荡器（OEO）的可调谐光载微波频率梳产生方案,可同时实现多频段微波信号产生,从而高效低成本地为无线节点提供光生微波载波.方案采用混频双环OEO系统,通过工作在增益开关状态的直调激光器,利用其非线性动态特性产生多频率光载微波频率梳信号,并采用双路微波滤波器分别滤出两个相邻频率的微波信号,并利用二者的差频反馈注入直调激光器构成光电谐振.利用偏振双环结构抑制长谐振腔引起的边模问题,提高了输出信号的噪声特性.经过实验分析,得到了低相噪的多路微波信号,并最终实现了间隔797.4 MHz的稳定的微波频率梳信号,一阶载波相位噪声低于-101.7 dBc/Hz@10 kHz,-115.2 dBc/Hz@50 kHz.因此该方案产生的光载微波频率梳信号具有低噪声的优点,适用于光载微波通信系统.     

飞秒光频梳的任意长绝对测距

高精度测距在工业、航空航天、科学研究等方面都具有重要应用, 而不断发展的激光测距技术始终处于前沿研究领域. 本文研究飞秒光频梳绝对测距技术, 拓展光梳在长度测量领域的应用. 在利用脉冲激光进行任意绝对长度测量中常用到飞行时间法, 然而其测量分辨力受限于电子器件的带宽, 仅为毫米量级. 为克服这一缺点, 本文研究了光梳多脉冲序列之间的时间相干性, 结合多脉冲序列干涉法和飞行时间法提出了任意长绝对测距的方法, 搭建了基于改进型Michelson干涉原理的任意绝对测长系统, 通过同时测量多脉冲序列的一阶和二阶互相关信号, 可以分别计算出飞行时间的时间差, 即可得到被测距离. 利用光梳作为光源进行了0.6m的绝对测距实验, 将测量结果与高精度激光位移传感器的测量值进行比较, 实验结果表明本系统具有良好的测量线性度, 并且测距精度可达±0.5μm. 关键词： 飞秒光频梳 任意长绝对测距 飞行时间法 多脉冲序列干涉法     

Quantum-noise-limited optical frequency comb spectroscopy

We achieve a quantum-noise-limited absorption sensitivity of 1.7×10(-12) cm(-1) per spectral element at 400 s of acquisition time with cavity-enhanced frequency comb spectroscopy, the highest demonstrated for a comb-based technique. The system comprises a frequency comb locked to a high-finesse cavity and a fast-scanning Fourier transform spectrometer with an ultralow-noise autobalancing detector. Spectra with a signal-to-noise ratio above 1000 and a resolution of 380 MHz are acquired within a few seconds. The measured absorption line shapes are in excellent agreement with theoretical predictions.     

基于飞秒光频梳的双频He-Ne激光器频率测量

利用光纤飞秒光频梳和外腔可调谐半导体激光器, 建立了一套双频He-Ne激光器频率测量系统. 选用铷钟作为系统的频率基准, 通过将外腔半导体激光锁定至光频梳使得其频率溯源至铷钟, 再利用外腔可调谐半导体激光与双频He-Ne激光器输出的正交偏振激光拍频, 同时测量两路正交偏振激光频率. 将可调谐半导体激光器锁定至光频梳第1894449个梳齿, 其绝对频率为473612190000.0±2.7 kHz, 相对不确定度为5.7×10^-12. 对商品双频He-Ne激光器进行频率测量实验, 双频He-Ne激光器水平方向偏振激光频率均值为473612229934 kHz, 竖直方向偏振激光频率均值为473612232111 kHz, 平均时间为1024 s的相对Allan标准差为5.2×10^-11, 频差均值为2.177 MHz, 标准偏差为2 kHz.