Gigahertz frequency hopping in an optical phase-locked loop for Raman lasers

Raman lasers are essential in atomic physics,and the development of portable devices has posed requirements for time-division multiplexing of Raman lasers.We demonstrate an innovative gigahertz frequency hopping approach of a slave Raman laser within an optical phase-locked loop(OPLL),which finds practical application in an atomic gravimeter,where the OPLL frequently switches between near-resonance lasers and significantly detuned Raman lasers.The method merges the advantages of rapid and extensive frequency hopping with the OPLL’s inherent low phase noise,and exhibits a versatile range of applications in compact laser systems,promising advancements in portable instruments.

Dynamic Free-Spectral-Range Measurement for Fiber Resonator Based on Digital-Heterodyne Optical Phase-Locked Loop

We propose a novel scheme, based on digital-heterodyne optical phase-locked loop with whole-fiber circuit, to dynamically measure the free-spectral-range of a fiber resonator. The optical phase-locked loop is established with a differential frequency-modulation module consists of a pair of acousto-optic modulators. The resonance-tracking loop is derived with the Pound-Drever-Hall technique for locking the heterodyne frequency of the OPLL on the frequency difference between adjacent resonance modes. A stable locking accuracy of about 7 × 10?9 and a dynamic locking accuracy of about 5 × 10?8 are achieved with the FSR of 8.155 MHz, indicating a bias stability of the resonator fiber optic gyro of about 0.1?/h with 10 Hz bandwidth. In addition, the thermal drift coefficient of the FSR is measured as 0.1 Hz/?C. This shows remarkable potential for realizing advanced optical measurement systems, such as the resonant fiber optic gyro, and so on.

A sapphire fibre thermal probe based on fast Fourier transform and phase-lock loop

A sapphire fibre thermal probe with Cr^3＋ ion-doped end is developed by using the laser heated pedestal growth method. The fluorescence thermal probe offers advantages of compact structure, high performance and ability to withstand high temperature in a detection range from room temperature to 450℃. Based on the fast Fourier transform （FFT）, the fluorescence lifetime is obtained from the tangent function of phase angle of the non-zeroth terms in the FFT result. This method has advantages such as quick calculation, high accuracy and immunity to the background noise. This FFT method is compared with other traditional fitting methods, indicating that the standard deviation of the FFT method is about half of that of the Prony method and about 1/6 of that of the log-fit method. And the FFT method is immune to the background noise involved in a signal. So, the FFT method is an excellent way of processing signals. In addition, a phase-lock amplifier can effectively suppress the noise.

Optical Generation of mm-Wave Signal Through Optoelectronic Phase-Locked Loop

In this paper, we propose a scheme for the generation of low phase noise tunable mm-wave signal by bearing two lightwaves in a photodiode. These two lightwaves are made phase coherent by an optoelectronic phase locked loop. Calculated mm-wave power at a frequency of 60 GHz is found to be -4 dBm.

Digital-analog hybrid optical phase-lock loop for optical quadrature phase-shift keying

We analyze a feasible high-sensitivity homodyne coherent optical receiver for demodulating optical quadrature phase-shift keying(QPSK). A fourth-power phase-lock loop based on a digital look-up table is used. Considering the non-negligible loop delay, we optimize the loop natural frequency. Without error correction coding, a sensitivity of -37 dBm/-35 dBm is achieved, while the bit error rate is below 10-9 at 2.5 Gbaud/5 Gbaud rate.For the QPSK communication system, the bit rate is twice the baud rate. The loop natural frequency is 0.647 Mrad/s, and the minimized steady-state phase-error standard deviation is 3.83°.

2.5Gb/s Monolithic IC of Clock Recovery,Data Decision,and 1∶4 Demultiplexer

A high integrated monolithic IC, with functions of clock recovery, data decision, and 1 ： 4 demultiplexer,is implemented in 0.25μm CMOS process for 2.5Gb/s fiber-optic communications. The recovered and frequency divided 625MHz clock has a phase noise of -106.26dBc/Hz at 100kHz offset in response to a 2.5Gb/s PRBS input data （2^31-1）. The 2.5Gb/s PRBS data are demultiplexed to four 625Mb/s data. The 0.97mm× 0.97mm IC consumes 550mW under a single 3.3V power supply （not including output buffers）.

相干光通信中基于QPSK调制的光锁相环分析

基于四相相移键控(QPSK)调制的光锁相环工作原理,通过建立环路数学模型系统分析了QPSK环路接收系统激光器线宽以及噪声对相干光通信的影响。对环路带宽进行了优化取值,分析了在最小误差方差下环路对激光线宽的要求。最后给出了不同比特光子数下,接收系统误码率与输入信噪比关系。

空间零差相干光通信的锁相技术

针对空间激光通信会受到多普勒频移和大气湍流等不利因素的影响,研究零差相干光锁相技术以提高接收系统灵敏度。通过搭建BPSK零差相干光通信系统模型,对星间激光通信链路动态性引起的光锁相环失锁边界进行了探索,给出了光锁相环失锁过程的仿真。仿真结果表明,频差范围在±50 MHz以内时,科斯塔斯光锁相环可在1μs左右锁定信号光的相位;频差超过±50 MHz时,锁定时间增加且锁定状态不稳定。

基于锁相双光梳的多通道下变频技术

为实现稳定的宽带下变频,提出一种基于锁相双光梳的多通道宽带下变频方案,实现了将0～11.3GHz内的射频信号分割为5个通道并下变频为频率低于1.2GHz的中频信号。各通道频响平坦均衡,下变频信号最大功率偏差约为1.5dB。光锁相技术保障了下变频通道划分的稳定性,且降低了系统噪声。下变频后的信号在1kHz处相位噪声优于-75dBc/Hz。

卫星相干激光通信系统与技术发展

自由空间光通信(Free Space Optical Communication,FSOC)尤其是基于相干体制的卫星激光通信,正逐渐成为突破微波通信瓶颈、建设天地一体化网络、实现高速数据传输的重要手段。总结了欧空局、德国、日本及国内卫星相干激光通信的重要进展,给出了成功验证的相干激光通信系统的激光器、传输速率、多普勒频移补偿范围等参数,重点分析了基于Costas光锁相环(Optical Phase-Locked Loop,OPLL)技术的零差相干激光通信系统,并提炼出关键技术以及未来星间相干激光通信的发展趋势,可为卫星相干激光通信的研究提供一定的参考。

基于实时数据采集和识别的平衡光学锁相环研究

文章设计一种基于实时数据采集和识别的光学平衡锁相环,该锁相环使用高速数据采集卡,配合高速数字频率解调处理单元,代替传统锁相环中的滤波器,对相位和频率误差信号进行采集和识别,数据采集卡采集相位和频率误差电压信号,高速数字频率解调处理单元通过控制软件从采集的数据中解调频率,并利用数字PID反馈控制本振激光器。此种信号解调方式降低了系统时域噪声和各次谐波对误差信号的影响。对两个窄线宽光纤激光器的锁定实验表明,环路维持锁定状态超过2 h,激光器频率稳定度达到10^(-11),相比自由运行激光器提高了3个量级,在环路处于稳定锁定状态的396 s内,两激光器拍频频率平均波动小于20 kHz。

Pump-induced carrier envelope offset frequency dynamics and stabilization of an Yb-doped fiber frequency comb

In this paper, we demonstrate a carrier envelope phase-stabilized Yb-doped fiber frequency comb seeding by a nonlinear-polarization-evolution（NPE） mode-locked laser at a repetition rate of 60 MHz with a pulse duration of 191 fs.The pump-induced carrier envelope offset frequency（ f0） nonlinear tuning is discussed and further explained by the spectrum shift of the laser pulse. Through the environmental noise suppression, the drift of the free-running f0 is reduced down to less than 3 MHz within an hour. By feedback control on the pump power with a self-made phase-lock loop（PLL）electronics the carrier envelope offset frequency is well phase-locked with a frequency jitter of 85 m Hz within an hour.

Recent advances in microwave photonics

Microwave photonics （MWP） is an interdisci- plinary field that combines two different areas of microwave engineering and photonics. It has several key features by transferring signals between the optical domain and microwave domain, which leads to the advantages of broad operation bandwidth for generation, processing and distribution of microwave signals and high resolution for optical spectrum measurement. In this paper, we comprehensively review past and current status of MWP in China by introducing the representative works from most of the active MWP research groups. Future prospective is also discussed fi＇om the national strategy to key enabling technology that we have developed.

Direct phase control method for binary phase-shift keying space coherent laser communication

An optical phase locking method based on direct phase control is proposed.The core of this method is to synchronize the carrier by directly changing the phase of the local beam.The corresponding experimental device and the supporting algorithm were configured to verify the feasibility of this method.Phase locking can be completed without cycle skipping,and the acquisition time is 530 ns.Without an optical preamplifier,a sensitivity of-34.4 d Bm is obtained,and the bit error rate is 10^(-9) for 2.5 Gbit/s binary phase-shift keying modulation.The measured standard deviation of the phase error is 5.2805°.