Ultralow phase noise microwave generation with an Er:fiber-based optical frequency divider

We present an optical frequency divider based on a 200 MHz repetition rate Er:fiber mode-locked laser that, when locked to a stable optical frequency reference, generates microwave signals with absolute phase noise that is equal to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz carrier, the phase noise is below -100 dBc/Hz, limited by the optical reference. For offset frequencies >10 kHz, the phase noise is shot noise limited at -145 dBc/Hz. An analysis of the contribution of the residual noise from the Er:fiber optical frequency divider is also presented.     

Monolithic CEO-stabilization scheme-based frequency comb from an octave-spanning laser

We demonstrate a carrier-envelope phase-stabilized octave-spanning oscillator based on the monolithic scheme. A wide output spectrum extending from 480 nm to 1050 nm was generated directly from an all-chirped mirror Ti:sapphire laser. After several improvements, the carrier-envelope offset(CEO) beat frequency accessed nearly 60 d B under a resolution of 100 k Hz. Using a feedback system with 50-k Hz bandwidth, we compressed the residual phase noise to 55 mrad(integrated from 1 Hz to 1 MHz) for the stabilized CEO, corresponding to 23-as timing jitter at the central wavelength of790 nm. This is, to the best of our knowledge, the smallest timing jitter achieved among the existing octave-spanning laser based frequency combs.     

Monolithic 0–f Scheme-Based Frequency Comb Directly Driven by a High-Power Ti:Sapphire Oscillator

A monolithic O-f scheme-based femtosecond optical frequency comb directly driven by a high-power Ti:sapphire laser oscillator is demonstrated.The spectrum covering from 650 nm to 950 nm is generated from the Ti:sapphire oscillator with a repetition rate of 170 MHz.The average output power up to 630 mW is delivered under the pump power of 4.5 W.A 44-dB signal-to-noise ratio(SNR) of the carrier-envelope phase offset(CEO) beat note is achieved under the resolution of 100 kHz and is long-term stabilized to a reference source at 20 MHz.The integrated phase noise(IPN) in the range from 1 Hz to 1 MHz is calculated to be 138 mrad,corresponding to the timing jitter of 63 as at the central wavelength of 790 nm.     

Subfemtosecond synchronization of microwave oscillators with mode-locked Er-fiber lasers

We synchronize an 8.06 GHz microwave signal from a voltage-controlled oscillator with an optical pulse train from a 77.5 MHz mode-locked Er-fiber laser using a fiber-based optical-microwave phase detector. The residual phase noise between the optical pulse train and the synchronized microwave signal is -133 dBc/Hz (-154 dBc/Hz) at 1 Hz (5 kHz) offset frequency, which results in 838 as integrated rms timing jitter [1 Hz-1 MHz]. The long-term residual phase drift is 847 as (rms) measured over 2 h, which reaches 4×10(-19) fractional frequency instability at 1800 s averaging time. This method has a potential to provide both subfemtosecond-level short-term phase noise and long-term phase stability in microwave extraction from mode-locked fiber lasers.     

Ultra-stable microwave generation with a diode-pumped solid-state laser in the 1.5-μm range

We demonstrate the first ultra-stable microwave generation based on a 1.5-μm diode-pumped solid-state laser (DPSSL) frequency comb. Our system relies on optical-to-microwave frequency division from a planar-waveguide external cavity laser referenced to an ultra-stable Fabry–Perot cavity. The evaluation of the microwave signal at ~10 GHz uses the transportable ultra-low-instability signal source ULISS^®, which employs a cryo-cooled sapphire oscillator. With the DPSSL comb, we measured ?125 dBc/Hz phase noise at 1 kHz offset frequency, likely limited by the photo-detection shot-noise or by the noise floor of the reference cryo-cooled sapphire oscillator. For comparison, we also generated low-noise microwave using a commercial Er:fiber comb stabilized in similar conditions and observed >20 dB lower phase noise in the microwave generated from the DPSSL comb. Our results confirm the high potential of the DPSSL technology for low-noise comb applications.     

Wideband and high frequency stabilization of an injection-locked Nd:YAG laser to a high-finesse Fabry Perot cavity

High frequency stabilization of a 2.2-W injection-locked laser-diode-pumped Nd:YAG laser to a high-finesse optical cavity has been realized by frequency control of the master laser. With the help of an external electro-optical modulator, the feedback bandwidth was extended to 1 MHz and the frequency noise relative to the reference cavity was suppressed to 3 x 10(-4) Hz/Hz(1/2) below 1 kHz. This feedback laser system is an ideal laser source for gravitational wave detectors, which require both ultralow frequency noise and high output power.     

利用共振无源腔分析和抑制飞秒脉冲激光噪声的理论和实验研究

理论分析了共振无源腔对飞秒脉冲激光的强度和相位噪声的转化模型,分析表明,通过测量无源腔透射场或者反射场相对于输入场强度噪声的变化,可以间接得到输入场飞秒脉冲激光的相位噪声.在此基础上设计了精细度约为1500、自由光谱区为75 MHz的八镜环形共振无源腔,并测量了钛宝石锁模激光经过该共振无源腔后透射场和反射场强度噪声的变化.实验观察到,飞秒脉冲激光经过无源腔透射后,强度噪声特性得到较好改善,在探测频率2 MHz附近达到散粒噪声极限.同时,结合共振无源腔对激光强度和相位噪声的转化模型,间接给出了钛宝石锁模激光的相位噪声及无源腔对相位噪声的有效抑制作用.     

Optical phase locking of two extended-cavity diode lasers with ultra-low phase noise for atom interferometry

We present a phase coherent laser system with ultra-low phase noise with a frequency difference of 6.9 GHz. The laser system consists of two extended-cavity diode lasers that are optically phase-locked with electrical feedback to the injection current of a slave laser. The bandwidth of the optical phase-locking loop is extended up to 8 MHz. We achieve the residual phase noise of two phase-locked lasers of below ?120 dBrad²/Hz in the offset frequency range of 100 Hz–350 kHz and a flat phase noise of ?127 dBrad²/Hz from 700 Hz to 20 kHz. These results are, to the best of our knowledge, the lowest phase noise level ever reported with two extended-cavity diode lasers.     

A chirp-compensated, injection-seeded alexandrite laser

A Q-switched alexandrite laser suitable for high-resolution spectroscopy is described which produces pulses of 35 mJ energy in a 10 MHz bandwidth, with a high-purity TEM₀₀ mode. The laser can be synchronised to external event to within 100 ns. The output pulse length is 120 ns and the repetition rate 25 Hz. The laser is injection-seeded by a Ti:sapphire laser operating around 730 nm. To preserve single-mode seeding under external triggering conditions, and to obtain small time-jitter, active cavity length control was used. In order to achieve the 10 MHz output bandwidth, intra-cavity electro-optic modulators were used to compensate for the frequency chirp. The refractive index of alexandrite was found to vary linearly with inversion density with a constant of proportionality equal to 1.6᎒^-24 cm³. In pulsed operation at 730 nm, the index change due to this effect is only partially compensated by changes due to ground state phonon relaxation.     

Compact, thermal-noise-limited optical cavity for diode laser stabilization at 1x10(-15)

We demonstrate phase and frequency stabilization of a diode laser at the thermal noise limit of a passive optical cavity. The system is compact and exploits a cavity design that reduces vibration sensitivity. The subhertz laser is characterized by comparison with a second independent system with similar fractional frequency stability (1x10(-15) at 1 s). The laser is further characterized by resolving a 2 Hz wide, ultranarrow optical clock transition in ultracold strontium.     

Low noise, continuous-wave single-frequency 1.5-μm laser generated by a singly resonant optical parametric oscillator

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 1.06 μm. 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 ±1.5% 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.     

Noise characterization of an all-solid-state mirror-dispersion-controlled 10-fs Ti:sapphire laser

We characterized the phase and amplitude noise of a mirror-dispersion-controlled 10-fs Ti:sapphire laser pumped by a frequency-doubled cw diode-pumped Nd:YVO₄ laser and compared with these of the Ti:sapphire laser pumped by an Ar-ion laser. The rms timing jitters and rms amplitude noise for the all-solid-state and Ar-ion laser pumped Ti:sapphire lasers are calculated to be 0.31 ps rms and 0.71 ps rms and 0.15% rms and 0.32% rms, in the frequency range from 20 kHz to 400 kHz, respectively. The phase and amplitude noise characteristics of the Ti:sapphire laser were greatly improved by using the diode-pumped solid state laser as a pump source.     

基于光学-微波同步的低噪声微波产生方法

低噪声微波在冷原子光钟、光子雷达、大科学装置远程同步等领域具有重要的应用价值.本文介绍了一种基于光学-微波相位探测技术的低噪声微波产生方案,利用光纤环路光学-微波鉴相器,将超稳激光的频率稳定度相干传递至介质振荡器.实验采用梳齿相位参考至超稳激光的窄线宽掺铒光纤飞秒光学频率梳,结合光纤环路光学-微波鉴相器和精密锁相装置,将7 GHz介质振荡器同步至光频梳重复频率的高次谐波,同步后的光脉冲序列与微波信号的剩余相位噪声为–100 d Bc/Hz@1 Hz,定时抖动为8.6 fs [1 Hz—1.5 MHz];通过搭建两套低噪声微波产生系统,测得7 GHz微波的剩余相位噪声为–90 d Bc/Hz@1 Hz,对应的频率稳定度为4.8×10^–15@1 s.该研究结果对基于光学相干分频的低噪声微波产生提供了一种新思路.     

Optical-fiber pulse rate multiplier for ultralow phase-noise signal generation

In this Letter we report on an all optical-fiber approach to the synthesis of ultralow-noise microwave signals by photodetection of femtosecond laser pulses. We use a cascade of Mach-Zehnder fiber interferometers to realize stable and efficient repetition rate multiplication. This technique increases the signal level of the photodetected microwave signal by close to 18 dB. That in turn allows us to demonstrate a residual phase-noise level of -118 dBc/Hz at 1 Hz and -160 dBc/Hz at 10 MHz from a 12 GHz signal. The residual noise floor of the fiber multiplier and photodetection system alone is around -164 dBc/Hz at the same offset frequency, which is very close to the fundamental shot-noise floor.     

Generation of 10fs Ti:sapphire laser at repetition rate of 525MHz and measurement of carrier-envelope phase frequency

This paper presents a Kerr-lens mode-locked Ti:sapphire laser at the repetition rate of 525 MHz, stable laser pulse as short as 10 fs with average output power of 480 mW is obtained. By injecting the pulse into photonics crystal fibre, octave-spanning spectrum covered from 500 to 1050 nm is generated, carrier-envelope phase frequency with signal-to-noise ratio of 31dB is measured, which paves the way for the generation of a compact frequency comb.     

飞秒钛宝石光学频率梳的精密锁定

经相位锁定后的飞秒钛宝石光学频率梳已经广泛用于绝对光频的测量，这是光频标领域一个革命性的突破.在自建的90MHz飞秒钛宝石激光器的基础上首先采用光子晶体光纤将其光谱展宽到一个光倍频程，接着利用锁相环技术分别将重复频率和载波包络频移同时高精度地锁定到一台稳定度为6×10^－14的Cs钟上，进而得到了稳定度相同的飞秒光学频率梳.     

Environmentally-stable all-normal-dispersion picosecond Yb-doped fiber laser with an achromatic quarter-wave-plate

We present an environmentally-stable picosecond Yb-doped fiber laser by employing an achromatic quarter-wave-plate (AQWP) as a pulse stabilizer in the all-normal-dispersion and polarization-maintaining linear laser cavity. It is shown that the AQWP plays a critical role to control both the polarization state and spectral filtering of the proposed mode-locked laser. The demonstrated laser generates 2-ps-long pulses with pulse energies of 1 nJ at a repetition rate of 117 MHz and parabolic spectral width of 26 nm. The fundamental RF carrier frequency exhibits Allan deviation of 3.8 × 10⁻⁸ at 1-s averaging time and phase noise of −95 dBc/Hz at 10-Hz offset frequency.     

Direct frequency comb generation from an octave-spanning, prismless Ti:sapphire laser

We describe a self-referenced optical frequency comb generator based on an octave-spanning, prismless Ti:sapphire laser. Dispersion compensation is provided by novel double-chirped mirror pairs and BaF2 wedges. Current versions operate at 80 and 150 MHz. The compact prismless design allows system scaling to a gigahertz repetition rate. Its carrier-envelope beat note is intrinsically stable with a signal-to-noise ratio of 30 dB in a 100-kHz bandwidth. The octave is reached at 25 dB below the average power level. The in-loop accumulated phase error is 1.4 rad (20 mHz to 1 MHz). The technique has the advantages of simplicity and stability compared with previous designs.     

Short- and long-term frequency stabilization of a He-Ne laser using a Fabry-Perot cavity locked to the lamb dip

We have developed a frequency-stabilization system for the He-Ne laser using an external Fabry-Perot cavity which is locked to the Lamb dip of the laser. The cavity serves as a frequency discriminator for high-frequency noise suppression, while the length of the Fabry-Perot cavity is controlled, reffered to the Lamb dip, in order to eliminate low-frequency fluctuations. The frequency noise of a laser stabilized with the cavity suspended in a vacuum tank can be suppressed to about 1 $$0.1Hz/\sqrt {Hz} $$ at around 100 Hz by an FM-sideband locking method. The oscillation frequency is fixed to the Lamb dip at low frequency by controlling the cavity length thermally. The frequency fluctuation around the Lamb dip was estimated to be ～ 2.3 MHz.     

Carrier-envelope phase-controlled quantum interference of injected photocurrents in semiconductors

We demonstrate quantum interference control of injected photocurrents in a semiconductor using the phase stabilized pulse train from a mode-locked Ti:sapphire laser. Measurement of the comb offset frequency via this technique results in a signal-to-noise ratio of 40 dB (10 Hz resolution bandwidth), enabling solid-state detection of carrier-envelope phase shifts of a Ti:sapphire oscillator.