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.

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°.

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 frequency servo SoC with output power stabilization loop technology for miniaturized atomic clocks

A frequency servo system-on-chip(FS-SoC)featuring output power stabilization technology is introduced in this study for high-precision and miniaturized cesium(Cs)atomic clocks.The proposed power stabilization loop(PSL)technique,incorporating an off-chip power detector(PD),ensures that the output power of the FS-SoC remains stable,mitigating the impact of power fluctuations on the atomic clock's stability.Additionally,a one-pulse-per-second(1PPS)is employed to syn-chronize the clock with GPS.Fabricated using 65 nm CMOS technology,the measured phase noise of the FS-SoC stands at-69.5 dBc/Hz@100 Hz offset and-83.9 dBc/Hz@1 kHz offset,accompanied by a power dissipation of 19.7 mW.The Cs atomic clock employing the proposed FS-SoC and PSL obtains an Allan deviation of 1.7×10^(-11) with 1-s averaging time.

Wideband All-Polarization-Maintaining Yb-Doped Mode-Locked Fiber Laser Using a Nonlinear Optical Loop Mirror

We report on a wide-band and stable mode-locked all-polarization-maintaining fiber laser configuration using a nonlinear optical loop mirror. The central wavelength of the laser is 1080.14nm and the 3dB bandwidth is 20.29nm. The repetition rate of the pulse is 3.28 MHz and the pulse width is 848ps. By tuning the pump power, which is centered at 980nrn, from 300mW to 380mW, we obtain a linearly changed output power from 6row to 7.12roW. The all-polarization-mMntaining fiber configuration is fundamental to the stability of the output power.

Effects of Higher-order Dispersion on Time Delay in Femtosecond Pulse Generated from a Nonlinear Optical Loop Mirror Constructed from Dispersion Decreasing Fiber

The time delay（TD） of femtoseeond pulses is studied for the first time, which generated from the nonlinear optical loop mirror composed of dispersion decreasing fiber（DDF-NOLM）. The results show that the higher-order dispersion and high order nonlinearities such as Raman frequency shift play a key role in producing TD, and that the time delay ean be suppressed by the third-order dispersion（TOD） in DDF-NOLM. The mechanism of the time delay suppression is also discussed in detail.

Nonlinear Dynamics in Directly Modulated Semiconductor Lasers with Optical Loop Mirror Feedback

The investigation of the nonlinear dynamics of a semiconductor laser based on nonlinear optical loop mirror (NOLM) feedback using Ge doped optical fiber was carried out experimentally. Animations of compilations of the output power as a function of time series and phase plane with effects of optical feedback level, carrier current and modulation signal strength are demonstrated as a tool to give insight into the laser dynamics. Different dynamic states, including 2×, 4× multiplication and quasi-periodic and periodic frequency-locked pulsing states extended to chaotic behaviour were observed by varying the parameters of modulated frequency and optical feedback strength. The frequency-locked pulsing states were observed to exhibit a harmonic frequency-locking phenomenon and the pulsing frequency is locked to a harmonic nonlinearity in loop instead of the modulated frequency.

Generation of visible Raman operation laser by a fiber electro-optical modulator feedback loop

Phase-coherent multi-tone lasers play a critical role in atomic,molecular,and optical physics.Among them,the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase noise to retain long-term coherence.Raman operation lasers generated by directly modulated and frequency-multipled infrared lasers are compact and stable but lack feedback control to actively suppress the phase noise,which limits their performance in practical applications.In this work,we employ a fiber electro-optical modulator driven by a voltage-controlled oscillator(VCO)to modulate a monochromatic laser and employ a second-harmonic generation process to convert it to the visible domain,where the beat note of the Raman operation laser is stabilized by controlling the output frequency of VCO with a digital phase-locked loop(PLL).The low-frequency phase noise is effectively suppressed compared to the scheme without active feedback and it reaches-80 d Bc/Hz@5 k Hz with a 20 k Hz loop bandwidth.Furthermore,this compact and robust scheme effectively reduces the system's complexity and cost,which is promising for extensive application in atomic,molecular,and optical physics.

11.6-GHz 0.18-μm monolithic CMOS phase-locked loop

A design of a ll. 6-GHz phase-locked loop （PLL） fabricated in 49-GHz 0. 18-μm CMOS （complementary metal-oxide-semiconductor transistor） technology is described. An analog multiplier phase detector （PD）, a one-pole passive low pass filter and a three-stage ring oscillator with variable negativeresistance loads build up the monolithic phase-locked loop. The measured rms jitter of output signal via onwafer testing is 2. 2 ps under the stimulation of 2^31 - 1 bit-long pseudo random bit sequence （PRBS） at the bit rate of 11.6 GHz. And the tracking range is 250 MHz. The phase noise in the locked condition is measured to be - 107 dBc/Hz at 10 MHz offset, and that of the ring VCO at the central frequency is -99 dBc/Hz at 10 MHz offset. The circuit area of the proposed PLL is only 0. 47mm×0.72mm and the direct current （DC） power dissipation is 164 mW under a 1.8-V supply.

Electrical crosstalk-coupling measurement and analysis for digital closed loop fibre optic gyro

The phase modulation and the closed-loop controller can generate electrical crosstalk-coupling in digital closed- loop fibre optic gyro. Four electrical cross-coupling paths are verified by the open-loop testing approach. It is found the variation of ramp amplitude will lead to the alternation of gyro bias. The amplitude and the phase parameters of the electrical crosstalk signal are measured by lock-in amplifier, and the variation of gyro bias is confirmed to be caused by the alternation of phase according to the amplitude of the ramp. A digital closed-loop fibre optic gyro electrical crosstalk-coupling model is built by approximating the electrical cross-coupling paths as a proportion and integration segment. The results of simulation and experiment show that the modulation signal electrical crosstalk-coupling can cause the dead zone of the gyro when a small angular velocity is inputted, and it could also lead to a periodic vibration of the bias error of the gyro when a large angular velocity is inputted.

CMOS analog and mixed-signal phase-locked loops: An overview

CMOS analog and mixed-signal phase-locked loops(PLL)are widely used in varies of the system-on-chips(SoC)as the clock generator or frequency synthesizer.This paper presents an overview of the AMS-PLL,including:1)a brief introduction of the basics of the charge-pump based PLL,which is the most widely used AMS-PLL architecture due to its simplicity and robustness;2)a summary of the design issues of the basic CPPLL architecture;3)a systematic introduction of the techniques for the performance enhancement of the CPPLL;4)a brief overview of ultra-low-jitter AMS-PLL architectures which can achieve lower jitter(<100 fs)with lower power consumption compared with the CPPLL,including the injection-locked PLL(ILPLL),subsampling(SSPLL)and sampling PLL(SPLL);5)a discussion about the consideration of the AMS-PLL architecture selection,which could help designers meet their performance requirements.

An improved arctangent algorithm based on phase-locked loop for heterodyne detection system

We present an ameliorated arctangent algorithm based on phase-locked loop for digital Doppler signal processing,utilized within the heterodyne detection system. We define the error gain factor given by the approximation of Taylor expansion by means of a comparison of the measured values and true values. Exact expressions are derived for the amplitude error of two in-phase & quadrature signals and the frequency error of the acousto-optic modulator. Numerical simulation results and experimental results make it clear that the dynamic instability of the intermediate frequency signals leads to cumulative errors, which will spiral upward. An improved arctangent algorithm for the heterodyne detection is proposed to eliminate the cumulative errors and harmonic components. Depending on the narrow-band filter, our experiments were performed to realize the detectable displacement of 20 nm at a detection distance of 20 m. The aim of this paper is the demonstration of the optimized arctangent algorithm as a powerful approach to the demodulation algorithm, which will advance the signal-to-noise ratio and measurement accuracy of the heterodyne detection system.

Design of radiation hard phase-locked loop at 2.5 GHz using SOS-CMOS

A radiation hard phase-locked loop （PLL） is designed at 2.5 GHz using silicon on sapphire complementary metal-oxide-semiconductor process. Radiation hardness is achieved through improving circuit design without sacrificing real estate. Stability is guaranteed by a fully self-bias architecture. The lock time of PLL is minimized by maximizing the loop bandwidth. Frequency tuning range of voltage controlled oscillator is significantly enhanced by a novel load configuration. In addition, multiple bias stages, asynchronous frequency divider, and silicon on sapphire process jointly make the proposed PLL more radiation hard. Layout of this PLL is simulated by Cadence Spectre RF under both single event effect and total induced dose effect. Simulation results demonstrate excellent stability, lock time 〈 600 ns, frequency tuning range [1.57 GHz, 3.46 GHz], and jitter 〈 12 ps. Through comparison with PLLs in literatures, the PLL is especially superior in terms of lock time and frequency tuning range performances.

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.

A 5.12-GHz LC-based phase-locked loop for silicon pixel readouts of high-energy physics

There is an urgent need for high-quality and high-frequency clock generators for high-energy physics experiments.The transmission data rate exceeds 10 Gbps for a single channel in future readout electronics of silicon pixel detectors.Others,such as time measurement detectors,require a high time resolution based on the time-to-digital readout architecture.A phase-locked loop(PLL)is an essential and broadly used circuit in these applications.This study presents an application-specific integrated circuit of a low-jitter,low-power LC-tank that is PLL fabricated using 55-nm CMOS technology.It includes a 3rd-order frequency synthesis loop with a programmable bandwidth,a divide-by-2 pre-scaler,standard low-voltage differential signaling interfaces,and a current mode logic(CML)driver for clock transmissions.All the d-flip-flop dividers and phase-frequency detectors are protected from single-event upsets using the triple modular redundancy technique.The proposed VCO uses low-pass filters to suppress the noise from bias circuits.The tested LC-PLL covers a frequency locking range between 4.74 GHz and 5.92 GHz with two sub-bands.The jitter measurements of the frequency-halved clock(2.56 GHz)are less than 460 fs and 0.8 ps for the random and deterministic jitters,respectively,and a total of 7.5 ps peak-to-peak with a bit error rate of 10^(-12).The random and total jitter values for frequencies of 426 MHz and 20 MHz are less than 1.8 ps and 65 ps,respectively.The LC-PLL consumed 27 mW for the core and 73.8 mW in total.The measured results nearly coincided with the simulations and validated the analyses and tests.

A LOW POWER TIME-TO-DIGITAL CONVERTER FOR ALL-DIGITAL PHASE-LOCKED LOOP

Time-to-Digital Converter (TDC) is a key block used as the phase/frequency detector in an All-Digital Phase-Locked Loop (ADPLL). Usually, it occupies a large proportion of ADPLL's total power consumption up to about 30% to 40%. In this paper, the detailed power consumption of different components in the TDC is analyzed. A Power Management Block (PMB) is presented for the TDC to reduce its power consumption. A 24-bits TDC core with the proposed PMB is implemented in HJTC 0.18 μm CMOS technology. Simulation results show that up to 84% power reduction is achieved using our proposed technique.

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.

Phase-Locked Loop Based Cancellation of ECG Power Line Interference

Power line(PL)interference is one significant artifact in electrocardiography(ECG)that needs to be reduced to ensure accurate recording of cardiac signals.Because PL interference is non-stationary and has varying frequency,phase,and amplitude in ECG measurement,adaptive techniques are often necessary to track and cancel the interference.In this paper we present a phase-locked loop(PLL)-based adaptive filter to cancel PL interference.The PLL obtains the reference signal that is fed into the adaptive filter to remove the PL interference at the central frequency of 50 Hz.It is found that the technique can effectively cancel PL interference in real ECG signals and,when compared with some existing techniques such as least mean squares(LMS)adaptive filter,the new technique produces better results in terms of signal-to-interference ratio(SIR).

All polarization-maintaining Er:fiber-based optical frequency comb for frequency comparison of optical clocks

We demonstrate an optical frequency comb(OFC)based on a turnkey mode-locked laser with a figure-9-shape structure and polarization-maintaining fibers,for the comparison of frequency among optical clocks with wavelengths of 698 nm,729 nm,1068 nm,and 1156 nm.We adopt a multi-branch approach in order to produce high power OFC signals at these specific wavelengths,enabling the signal-to-noise ratio of the beatnotes between the OFC and the clock lasers to exceed30 d B at a resolution bandwidth of 300 k Hz.This approach makes the supercontinuum spectra much easier to be generated than a single branch OFC.However,more out-of-loop fibers degrade the long-term frequency instability due to thermal drift.To minimize the thermal drift effect,we set the fiber lengths of different branches to be similar,and we stabilize the temperature as well.The out-of-loop frequency instability of the OFC due to the incoherence of the multi-branch is about5.5×10^(19) for 4000 s,while the in-loop frequency instability of fceo and that of fbeat are 7.5×10^(18) for 1 s and 8.5×10^(18) for 1 s,respectively.The turnkey OFC meets the requirement for the comparison of frequency between the best optical clocks.

Design of 622 Mb/s Clock-recovery Monolithic IC for Optical Communication System

A monolithic clock-recovery circuit used in 622 Mb/s optical communication system is designed,which is based on the phase-locked loop theory,and uses bipolar transistor model.It overcomes the shortcoming of clock recovery method based on filter,and implements monolithic clock-recovery IC.The designed circuits include phase detector,voltage-controlled oscillator and loop filter.Among them,the voltage-control oscillator is a modified two-stage ring oscillator,which provides quadrature clock signals and presents wide voltage-controlled range and high voltage-controlling sensitivity.