Numerical Simulation of a lightwave synthesized frequency sweeper incorporating an optical SSB Modulator composed of four optical phase Modulators

We describe the numerical analysis of a lightwave synthesized frequency sweeper (LSFS) that uses an optical single-sideband (SSB) modulator composed of four optical phase modulators. The SSB modulator realizes a large frequency shift in the LSFS. This means that we can reduce the number of pulse circulations in the LSFS cavity to cover a given frequency sweep range. We propose a frequency-domain analysis method for the LSFS, in which a general optical modulator is expressed by using a matrix that includes optical phase terms. We employ this method to simulate the LSFS for several different phaseand group-velocity dispersion values in the lightpaths in the LSFS cavity. The results indicate that we can realize a linear frequency sweep by adjusting the phase change of the modulation signal during the cavity round-trip time.     

Microwave signal generation using an optical self-heterodyne technique

A new technique for mixing optical waves to generate microwave-frequency signals using an injection laser diode and a fibre-optic interferometer is reported. A beat signal is produced by interfering light from the laser with light from the same laser emitted earlier at a different frequency. The interferometer consists of an evanescent-field fibre coupler joined to a length of single-mode optical fibre. The laser is tuned by pulsed or bipolar current waveforms superimposed on a DC bias current. Feedback from an external cavity stabilises the laser frequency and reduces its linewidth. Efficient mixing at difference frequencies from 250 MHz to 2 GHz is obtained, with spectral widths of less than 1% of the centre frequency.     

Microwave harmonic generation in a plasma capacitor

Microwave harmonic generation in a plasma capacitor is investigated both theoretically and experimentally. Deficiencies of previous harmonic generation theories are pointed out and a nonlinear one-dimensional mathematical model, which includes the reactive nonlinearities due to the spatial variation of E, is developed. This nonlinear plasma capacitor model indicates that under certain electron-density and capacitor-plate spacing conditions strong harmonic resonances and an antiresonance are present. The antiresonance occurs when nω= ωpand the resonances occur when nω≳ ωp, where ωp=plasma frequency, ω= the fundamental frequency, and n is the harmonic number. Harmonic generation in a number of gases is investigated experimentally in a coaxial discharge structure. Third-harmonic (9-GHz) efficiencies of up to 13 percent, and third-harmonic output power in excess of 600 mW are reported. Double-probe and microwave-scattering measurements show that enhanced harmonic generation occurs at the above resonances and, hence, substantiate the non-linear plasma capacitor theory. In order to explain the harmonic output power variations that occur with pressure variation and gas type, a graphical method of analysis based on experimental fact and pressure-collision frequency-electron energy curves is presented. This method of analysis not only yields results that compare qualitatively with experimental observations, but it may also possibly be used to design and predict the performance of future plasma frequency multipliers.     

Second harmonic generation in optical fibers

We describe second harmonic generation in silica based optical fibers as a function of time and the preliminary explanations published so far in the literature. The latter deal essentially with the electromagnetic aspect of the phenomenon. By a different way of analysis (closer to material science), we emphasize on the structural defects active in this non-linear property.     

基于级联相位调制器和光衰减器的光频梳产生研究

提出了一种基于级联相位调制器和光衰减器的光 频梳产生方案,建立了方案的理论模型并进行了 系统验证,研究了射频(radio frequency,RF) 信号幅度和光衰减器衰减系数对光频梳平坦度的影响。结果表明数值 计算与实验 结果一致性较好,通过调整RF驱动信号幅度和光衰减器衰减系数可产生梳线数量为15条、平坦度为 0.8 dB,边模抑制比(side-mode suppression ratio,SMSR) 为5.05 dB的光频梳。方 案中引入滤波器后,在梳线数量保持不变的前 提下,其平坦度和SMSR可分别提高62.5%和61.4%。     

DWDM optical millimeter-wave generation for radio-over-fiber using an optical phase modulator and an optical interleaver

We have proposed and experimentally demonstrated a novel scheme to generate a dense wavelength-division multiplexing (DWDM) optical millimeter-wave source by using an optical phase modulator and an optical interleaver. The stability of the DWDM optical millimeter wave generation is largely improved because we use an optical phase modulator without a dc-bias controller and an optical interleaver is subsequently employed to suppress the optical carrier of the DWDM source, which is not as temperature sensitive as a fiber Bragg grating. Moreover, the limitation of chromatic dispersion is greatly reduced due to avoiding the generation of higher order sidebands via driving the phase modulator with optimized RF signal.     

常用双轴晶体连续调谐倍频时的相位匹配特性

本文讨论了常用双轴晶体ＫＴＰ、ＬＢＯ、ＫＮ在基频光波长连续调谐时的倍频相位匹配特性，给出了这三种晶体在不同波长倍频时的最佳相位匹配角的有效倍频极化系数，并纠正了以往计算中的不正确作法。     

Resonant optical second harmonic generation and mixing

Experimental and theoretical results are described on the enhancement of optical second harmonic generation (SHG) and mixing in KDP by the use of optical resonance. Both resonance of the harmonic and of the fundamental are considered. Large enhancements are possible for resonators with low loss. Using a planoconcave harmonic resonator containing 1.23 cm of KDP, the authors achieved a loss < 4 percent per pass. This resulted in an enhancement of ∼ 500 times the harmonic power internal to the resonator and ∼ 10 times external to the resonator. When resonating, the fundamental enhancements of ∼ 5 were observed. The theory includes the effect of double refraction. This results in a coupling coefficient of the generated harmonic power to the transverse modes of the harmonic resonator. The experimental results are in substantial agreement with the theory.     

30-THz span optical frequency comb generation by self-phasemodulation in an optical fiber

The width of an optical frequency comb (OFC) was increased to 30 THz by using self-phase modulation (SPM) in an optical fiber. This value is 2.7 times larger than the maximum OFC span obtained by the OFC generator alone. We compare the resulting spectrum to numerical simulations to confirm that the SPM and the higher order dispersion of the fiber contribute to broaden the spectral profile     

Microwave phase shifter using optical waveguide structure

A microwave phase shifter with an integrated optics structure with high efficiency is discussed. The structure and the performance of the device are discussed. Microwave phase shifting was carried out using the fabricated phase shifter of titanium diffused LiNbO₃ optical waveguides. The measured voltage to obtain halfwave phase shift for a 800 MHz microwave signal was 7.0 V. The input microwave power was 21 dBm, and the detected output microwave power was -24 dBm, so the microwave insertion loss was calculated to be approximately -45 dB. The optical insertion loss of the device was -12 dB     

Achromatic phase matching for second harmonic generation offemtosecond pulses

A scheme is proposed by which the phase matching bandwidth can be increased by adjusting higher-order terms in frequency shift in the phase-matching condition. This is achieved by introducing a spectral angular dispersion so that the different spectral components propagate at their phase-matching angles. This is equivalent to canceling the group velocity mismatch. The equations describing the requirements on the angular dispersion are discussed and applied to the particular case of type I phase matching. A possible experimental setup is shown that would meet all the conditions required     

Temperature dependence of second harmonic generation in germania-doped silica optical fibres

Seeded second harmonic generation (SHG) is compared between room temperature (RT) and liquid N/sub 2/ temperature (LNT) in GeO/sub 2/-doped silica fibres. At RT the SH power grows much more rapidly. The corresponding conversion efficiency after seeding for 2 h is over 20 times larger than at LNT.<>     

二次谐波产生的光学倍频腔自锁定系统

二次谐波产生技术能有效扩展现有的激光波段,被广泛应用于原子分子物理、光物理、生物医学等多个领域。倍频腔的长期锁定是倍频技术中的一项关键技术,它直接关系到输出激光的功率稳定性和可靠性,目前的商用二次谐波产生激光器都会存在不同程度上的失锁状态。提出了一种基于积分扫描来实现连续激光倍频器自锁定的方案,能在没有人为调节的情况下连续工作,不需要额外的功率监测和扫描信号,失锁后可自动恢复锁定,最终实现了长期稳定的二次谐波产生激光输出。     

Photoelectric instability in optical fibre resulting in spontaneous second harmonic generation

The self-organised second harmonic generation (SHG) in optical fibres is explained as a consequence of a convective instability leading to spontaneous formation of the chi /sup (2)/ grating due to the growth of small fluctuations. The authors show that the observed SHG should be interpreted as amplification of noise.<>     

基于相位调制器倍频技术产生56GHz毫米波的光载无线通信系统

提出并实验研究了一种基于光相位调制器(PM)倍频技术产生56GHz毫米波的光载无线通信(RoF)系统。在中心站,通过28GHz射频(RF)信号驱动PM产生了56GHz光毫米波,并将下行的2.8Gb/s开关键控(OOK)信号调制到该光载波上,然后经过20km标准单模光纤(SSMF)传输至基站,最后由天线进行发射。用户终端接收后,采用相干解调恢复出基带信号。实验结果表明,56GHz光载毫米波信号经SSMF传输20km后其功率代价小于1dB,通过无线方式传输1.1m后其功率代价小于2.5dB。     

Optical generation and distribution of continuously tunable millimeter-wave signals using an optical phase modulator

In this paper, we propose an approach to generate and distribute two wide bands of continuously tunable millimeter-wave (mm-wave) signals using an optical phase modulator and a fixed optical notch filter. We demonstrate theoretically that the odd-order electrical harmonics are cancelled and even-order electrical harmonics are generated at the output of a photodetector when the optical carrier is filtered out from the phase-modulated optical spectrum. Analysis shows that dispersion compensation is required in order to maintain the suppression of the odd-order electrical harmonics, in order to eliminate signal fading of the generated electrical signal when the optical signal is distributed using conventional single-mode optical fiber. It is experimentally demonstrated that, when the electrical drive signal is tuned from 18.8-25 GHz, two bands of mm-wave signals from 37.6 to 50 GHz and from 75.2 to 100 GHz with high signal quality are generated locally and remotely. This approach does not suffer from the direct current (dc) bias-drifting problem observed when an optical intensity modulator is used.     

基于载波和边带相位控制的微波光子移相器

为了实现一种360°相移新型微波光子移相器，通过使用一个相位调制器、延迟线和光学滤波器来控制载波和边带的相位，最终控制射频信号的相位。相位调制器只需控制一个电压来调节移相角度，减少了使用复杂双平行马赫-曾德尔调制器所导致的漂移带来的影响，具有结构简单、成本较低等优点。结果表明，仿真验证的微波光子移相器可以在0GHz~40GHz频率范围内实现从0°~360°的全相移范围，并且在同一输出相位情况下，频率在0GHz~40GHz范围内，功率基本保持不变。此研究对微波光子移相器技术有一定参考意义。     

基于单个电吸收调制器产生超平坦双光梳

为产生频率间隔相同而又平坦的光频梳,基于单个多量子阱电吸收调制器强度调制特性,设计出一种新型超平坦双光梳产生方案。通过在电吸收调制器前置矩形滤波器,精密控制多量子阱电吸收调制器的反向偏置电压与射频驱动信号幅度,滤除频谱的中心谱线后,得到了平坦度为0.01dB的双光梳。利用Optisystem7.0软件进行仿真,其对不同线宽(100kHz、10 MHz和20 MHz)的激光光源均可产生位于中心谱线两侧对称的、带宽均为300 GHz、谱线均为15条、谱线间距均为20GHz以及平坦度可达0.01dB的双光梳。