Blue Green Emission From a Cu$^{+}$ -Doped Transparent Material Prepared by Sintering Porous Glass

A colorless transparent, blue green emission material was fabricated by sintering porous glass impregnated with copper ions. The emission spectral profile obtained from Cu⁺ -doped high silica glass (HSG) by 267-nm monochromatic light excitation matches that obtained by pumping with an 800-nm femtosecond laser, indicating that the emissions in both cases come from an identical origin. The upconversion emission excited by 800-nm femtosecond laser is considered to be a three-photon excitation process. A tentative scheme of upconverted emission from Cu⁺ -doped HSG was also proposed. The glass materials presented herein are expected to find application in lamps, high density optical storage, and three-dimensional color displays.     

光纤飞秒光梳频率精密控制的研究

新一代光纤飞秒光梳在精密测量和基础物理研究领域中有着广阔的前景,一种通过数字电荷泵锁相环和温控电路相结合的方法可以精密控制光纤飞秒光梳。在实验中,我们成功搭建了光纤飞秒光梳系统。光梳的重复频率为129MHz,初始频率大约为33MHz。我们通过自主研发的温控和数字电荷泵锁相环成功地把光纤飞秒光梳成功地锁定在了由Agilent PSG Analog Singal Generator提供的标准微波信号上,锁定时间至少长达1天。锁定后的重复频率的抖动标准差为0.78mHz,与基准源同一个数量级且很接近,锁定后的初始频率的抖动标准差可达8.98Hz。     

飞秒光学频率梳在精密测量中的应用

飞秒光学频率梳通过锁定飞秒锁模激光的重复频率和偏置频率至微波频率基准,在时域上得到重复频率稳定的飞秒脉冲激光,在频域上得到频率间隔稳定的激光频率梳。飞秒光学频率梳作为微波频率与光学频率的桥梁,可以实现对激光频率的直接精密计量,同时作为一种有别于传统连续波稳频激光的特殊激光光源,在激光频率标尺、绝对距离测量和精密光谱测量等光学精密测量领域都有着重要应用。综述了飞秒光学频率梳在若干光学精密测量应用中的研究进展、关键技术和研究动向,分析了其在未来光学测量中的重要作用。     

Phase locking of a continuous-wave optical parametric oscillator to an optical frequency comb for optical frequency synthesis

A continuous-wave optical parametric oscillator (OPO) was phase locked to an optical frequency comb in the 830-nm region. The optical frequency of the OPO was controlled by changing the cavity length of the pump laser. The residual phase noise under phase locking was 220 mradrms and the energy concentration to the carrier was 95%. Furthermore, the optical frequency fluctuations of a free-running OPO were measured by using an optical frequency comb that was phase locked to an atomic clock. The measured fluctuations were around 10 MHz in an hour.     

Laser-cooled neutral atom frequency standards

The authors review the prospects for a frequency standard based on what is called the atomic fountain. Atomic fountain frequency standards have better signal-to-noise ratios than ion standards, but suffer from larger systematic effects. An analysis of a Cs microwave fountain predicts potential stability and accuracy improvements of a factor of 100 over other laboratory standards, with an ultimate accuracy near 10 ^-16. An optical frequency standard based on a two-photon transition in xenon is analyzed and shown to have potential stability 5 orders of magnitude better than conventional Cs standards, and a possible accuracy of 10^-18. Neutral atom frequency standards will have much better signal-to-noise ratios than ion standards, but suffer from larger systematic effects, making the two technologies complementary in many ways     

Wide-span optical frequency comb generator for accurate opticalfrequency difference measurement

An optical frequency comb (OFC) generator was realized for accurate optical frequency difference measurement of 1.5 μm wavelength semiconductor lasers by using a high frequency LiNbO₃ electrooptic phase modulator which was installed in a Fabry-Perot cavity. It was confirmed that the span of the OFC was wider than 4 THz. By using semiconductor lasers whose spectrum linewidths were narrowed to 1 kHz and a sensitive optical balanced-mixer-receiver for measuring beat signal between the sideband of the comb and the laser, we demonstrated a frequency difference measurement up to 0.5 THz with a signal-to-noise ratio higher than 61 dB, and a heterodyne optical phase locking with a heterodyne frequency of 0.5 THz in which the residual phase error variance was less than 0.01 rad². The maximum measurable frequency difference, which was defined as the sideband frequency with the signal-to-noise ratio of 0 dB, was estimated to be 4 THz     

用飞秒锁模激光测量光的频率

介绍了2005年诺贝尔物理学奖的获奖工作-用锁模飞秒激光光梳去测量光的频率.飞秒激光光梳技术大大简化了光频的测量.锁模飞秒激光通过光子晶体光纤时,由于自相位调制,在可见光和近红外区能够产生上百万等间隔的梳状频率,其频率间隔等于锁模脉冲的重复率.利用光频梳和倍频技术,把对光频的测量变为对射频的测量,这样就能够很容易地测出光的频率.使得光频测量精度和原子钟精度达到前所未有的高度,从而对物理学和计量学的发展有重要意义.     

Rapid, Precise, and Stable Control of Optical Frequency for SG-DBR LD Using Quartz Etalon

This paper presents rapid, precise, and stable control of optical frequency for sampled-grating distributed Bragg reflector (SG-DBR) laser diode (LD) using a Z-cut quartz etalon supported at the middle point. The optical frequency of SG-DBR LD was controlled by the mode-hop-free three-electrode control method. As a result, stable mode operation and wide continuous tuning range without mode hopping have been realized. A 0.2-ms optical frequency tuning speed with a 4.35-THz tuning range and a 130-MHz control error of the optical frequency was demonstrated. A 1.1-MHz Allan deviation was reached at an integration time of 12 times 10³ s.     

The optically pumped rubidium maser

The optically pumped rubidium maser oscillator is the most recent addition to a growing number of atomic frequency standards. It is the first atomic frequency standard which is small enough and simple enough to be considered as a replacement for crystal oscillators. These factors and the extreme phase stability which results from the maser action make this device unique among all frequency standards. The device generates a microwave output at the ground-state hyperfine frequency of Rb⁸⁷(6835 Mc/s). The maser consists of a microwave cavity filled with Rb⁸⁷vapor and nitrogen gas. Oscillation occurs when the vapor is illuminated with filtered rubidium resonance radiation. The power output of the maser is 10^-10watts, and higher powers can be expected. In this paper the physical principles and construction of the device are described. The effects of optical pumping, buffer gas, and temperature on the maser are discussed, and experimental results are given. The short-term stability for observation times of about one second is expected to be about one part in 10¹². This may be increased by an order of magnitude by increasing the powser output to 10^-8watts. The long-term stability is expected to be comparable to that obtained in the passive rubidium standard (about one part in 10¹¹per month). These slow fluctuations arise from pressure shifts, light shifts, cavity pulling, and changes in the chemical composition of the buffer gas. The long-term stability can be improved by using the rubidium maser as the flywheel for an atomic beam frequency standard. Such a combination could be expected to have both long-term and short-term stabilities as great as one part in 10¹³.     

Limitations of atomic beam frequency standards

Atomic beam frequency standards may be placed into two categories: field standards and laboratory standards. While this distinction is somewhat artificial, because the two types of standards are interdependent, each category does have different requirements of accuracy, size, and cost. Despite this separation, generally the developments which produce the best laboratory standards eventually give rise to improved field standards. Existing field standards are limited in long term fractional frequency stability to σ_y (τ) 3 x 10^-13, for τ 6 months. A laboratory standard such as NBS-6, the U.S. primary cesium standard, is limited in inaccuracy to Δ_y 8 x 10^-14. Proposed new cesium field standards are expected to yield long term stabilities of σ_y(τ) 1 x 10^-14 (τ = 6 months). Stored ion standards, prime candidates for new laboratory frequency standards, are expected to have better than Δy = 1 x 10^-15 inaccuracy. As other approaches to atomic beam frequency standards are considered, they should attempt to compete favorably with these emerging technologies.     

Spectral-Amplitude-Coded OCDMA Optimized for a Realistic FBG Frequency Response

We develop a methodology for numerical optimization of fiber Bragg grating frequency response to maximize the achievable capacity of a spectral-amplitude-coded optical code-division multiple-access (SAC-OCDMA) system. The optimal encoders are realized, and we experimentally demonstrate an incoherent SAC-OCDMA system with seven simultaneous users. We report a bit error rate (BER) of 2.7times10^-8 at 622 Mb/s for a fully loaded network (seven users) using a 9.6-nm optical band. We achieve error-free transmission (BER<1times10^-9) for up to five simultaneous users     

1047-nm master oscillator power amplifier free-space opticalcommunications laser transmitter

We report on the performance of a 1047-nm laser diode master oscillator (MO) diode pumped Nd:YLF power amplifier (PA) laser transmitter in a 50-Mbps quaternary pulse position modulation (Q-PPM) free-space optical direct detection communications experiment. The transmitter produced greater than 1 W of 1047-nm average optical power. At optical transmitter powers up to 0.2 W, we achieved nearly the same communications performance (~210 photons/b at 10^-6 bit-error rate) using the 1047-nm MOPA transmitter as with the 50 mW laser diode alone. We relied on an external-cavity grating feedback scheme for the 1047-nm laser diode MO to achieve this communications performance     

High performance single frequency fiber grating-basederbium/ytterbium-codoped fiber lasers

The device characteristics of Er³⁺,Yb³⁺ single frequency fiber lasers are reported. A 5-cm long 1550-nm distributed feedback fiber laser with 4 mW output power is shown to have excellent specifications in terms of optical linewidth, signal-to-noise ratio (SNR), relative intensity noise, side-mode suppression and polarization purity. For higher power applications, a 1.5 cm single frequency Er³⁺,Yb³⁺ grating-based fiber laser with 60 mW output power and a net efficiency of 12% is demonstrated     

Frequency Uncertainty for Optically Referenced Femtosecond Laser Frequency Combs

We present measurements and analysis of the currently known relative frequency uncertainty of femtosecond laser frequency combs (FLFCs) based on Kerr-lens mode-locked Ti:sapphire lasers. Broadband frequency combs generated directly from the laser oscillator, as well as octave-spanning combs generated with nonlinear optical fiber are compared. The relative frequency uncertainty introduced by an optically referenced FLFC is measured for both its optical and microwave outputs. We find that the relative frequency uncertainty of the optical and microwave outputs of the FLFC can be as low as 8times10^-20 and 1.7times10^-18, with a confidence level of 95%, respectively. Photo-detection of the optical pulse train introduces a small amount of excess noise, which degrades the stability and subsequent relative frequency uncertainty limit of the microwave output to 2.6times10^-17     

Generation of frequency-tunable light and frequency reference gridsusing diode lasers for one-petahertz optical frequency sweep generator

Generation of frequency-tunable light and frequency reference grids in a wide frequency span for a diode laser based optical frequency sweep generator has been performed. Frequency tuning and noise characteristics in nonlinear frequency conversions have been discussed. By using AlGaAs, InGaAsP lasers and their frequency conversions in the type II angle phase-matching KTP crystal, highly coherent frequency-tunable outputs have been obtained from 600 THz (0.5 μm) to 170 THz (1.7 μm). Use of the DFB lasers ensures the continuous tuning with a frequency range as wide as 1 THz. Atomic potassium and molecular iodine absorption resonances have been employed as frequency references for stabilizing the frequencies of lasers and the generated light with the frequency stability of 10^-9-10^-10. Optical frequency comb generation has been realized at the 0.8 μm wavelength with a two-sided sidebands span of 4 THz. We have also proposed and demonstrated specific frequency-tunable systems based on sum and difference-generations of diode lasers     

Femtosecond excitonic optoelectronics

The authors discuss a novel approach to femtosecond optoelectronics which uses the excitonic response to electric fields as a detector and the excitonic nonlinear response to optical fields as a generator. The sensitivity of the quantum-well exciton to applied electric fields is used to measure electrical transients with femtosecond time resolution. The authors examine several mechanisms for femtosecond electrical pulse generation, including exciton ionization and two-photon absorption, and present measurements of the propagation properties of coplanar striplines on ultrathin semiconductor substrates in the 1-100-THz frequency range. The generation and detection of an electrical pulse with a 180-fs risetime propagating on a coplanar stripline on GaAs/AlGaAs quantum wells are demonstrated     

Atomic ion frequency standards

The history and status of trapped-ion frequency standards are reviewed. In a trapped-ion frequency standard, the frequency of an oscillator is servoed to a resonance which corresponds to a transition between two energy levels of an atomic ion. The ions are suspended in space by a combination of electric and magnetic fields. In a conventional rubidium cell, the atoms are surrounded by a buffer gas having a pressure of about 10³ Pa (approximately 10 torr). In an ion trap, the ions are held either in a vacuum or in a low-pressure buffer gas (less than 10^-3 Pa). In an atomic beam, the atoms also move through a vacuum, without collisions. However, the time available for interaction with the electromagnetic field is limited to their flight time through the apparatus, usually about 10 ms or less. Trapped ions can be observed for much longer periods. Consequently clocks based on ions trapped in electromagnetic fields portend orders-of-magnitude improvement in the development of new frequency standards. Prospects for future standards are discussed     

A monolithically integrated 1-Gb/s optical receiver in 1-μm CMOStechnology

Results of a monolithically integrated Si optical receiver for applications in optical data transmission and in optical interconnects with wavelengths of 638 and 850 nm are presented. The optoelectronic integrated circuit (OEIC) implementing a vertical p-type-intrinsic-n-type photodiode achieves a data rate of 1 Gb/s for 638 nm with a sensitivity of -15.4 dBm at a bit-error rate of 10^-9 . The sensitivity of this OEIC in a 1.0-μm CMOS technology is improved by at least a factor of four compared to that of published submicrometer OEICs. A 25-THz.Ω effective transimpedance bandwidth product of the implemented amplifier is achieved     

基于超高Q值氟化镁晶体微腔的克尔光频梳产生研究

克尔光频梳具有等距分布的梳状光谱结构,在精密测量、光钟、相干光通信、微波和光学任意波产生、光谱学及天文光谱仪校准等方面有着重要的应用。首先,微腔光频梳与其他光频梳系统相比,具有集成性高、体积小、功耗低的优势,大大扩展了光频梳的应用;其次,通过超精密加工方法制备了品质因子Q值达到了4.8×107的氟化镁微腔,并且得到了干净规律、排列规则的谐振谱,自由频率范围为9.73 GHz,为产生低重复频率光频梳提供了条件;最后,根据实验结果结合Lugiato-Lefever方程分析了氟化镁微腔光频梳的产生过程,研究了泵浦功率对光频梳的影响,通过调整失谐参数得到了孤子态光频梳。并且通过色散调控优化了微腔的光场模式,为产生具有超光滑光谱的孤子光频梳创造了先决条件,提升了光频梳性能。