Fiber-optic Frequency Research Articles

A Novel GIS Partial Discharge Detection Sensor With Integrated Optical and UHF Methods

A novel gas insulated switchgear (GIS) partial discharge (PD) sensor with integrated optical fiber and ultrahigh frequency (UHF) method is developed in this paper. The integrated sensor is formed by placing an optical fiber on the surface of the UHF sensor. The novel sensor can be mounted inside the GIS and measure the PD through optical and UHF signals at the same time. The validity and sensitivity of the sensor are proved by experiments on a physical 110 kV GIS. This PD detection sensor solves the problem that the optical fiber is difficult to be mounted inside GIS and provides a novel method for PD detection in GIS.

Absolute frequency measurement of the 40Ca+ clock transition based on an optical frequency comb

We demonstrate an approach of absolute frequency measurement 40Ca+ 4S1/2-3D5/2 clock transition based on an optical frequency comb. Based on this method, the frequency of 729nm ultra-stable laser is measured by using a self-built 250 MHz Yb-doped fiber optical frequency comb and a beat frequency signal with SNR of about 10 dB has been obtained preliminarily.

Monitoring of phase jitter in fibre optic time and frequency transfer systems

Monitoring of phase jitter in fibre optic time and frequency transfer systems

Observation of the 1S0–3P0 optical clock transition in cold 199Hg atoms

We report on the observation of the highly forbidden 1S0–3P0 optical clock transition in laser-cooled 199Hg atoms. More than 95% depletion of cold 199Hg atoms is detected in the magneto-optical trap. Using the free-of-field detection method, the AC Stark shift from the cooling laser is removed from the in-field spectroscopy. At low-power clock laser pumping, the linewidth of the clock spectroscopy is approximately 450 kHz (full width at half-maximum), which corresponds to a Doppler broadening at the atom temperature of 60 μK. We determine the 1S0–3P0 transition frequency to be 1,128,575,290.819(14) MHz by referencing with a hydrogen maser and measuring with a fiber optical frequency comb. Moreover, a weak Doppler-free signal is observed.

Ultra-stability Yb-doped fiber optical frequency comb with 2 × 10-18/s stability in-loop.

We demonstrate a full control ultra-stability Yb-doped fiber optical frequency comb (OFC). The carrier-envelop offset frequency (fceo) and the repetition rate (fr) are locked with the standard phase locked loop (PLL) technique. The fceo is locked to the radio frequency (RF) synthesizer, and the Allan deviation is 1.2 × 10-17/s. The fr is locked to an ultra-stability continuous wave (CW) laser at 972 nm. The beat signal (fbeat) between the Yb-doped fiber OFC and CW laser is obtained with the signal to noise ratio (SNR) of 43 dB at 300 kHz resolution bandwidth (RBW). The time jitter of the fbeat signal is 278 as, which is integrated from 1 Hz to 10 MHz. The long-term stability is 575 μHz in 3 hours, and the corresponding Allan deviation is 2 × 10-18/s, which is the best stability result in Yb-doped fiber OFC. The linewidth is narrowed from 200 kHz to subhertz magnitude limited by the instrument resolution bandwidth.

Stabilisation of a fibre frequency synthesiser using acousto-optical and electro-optical modulators

A fibre-optic frequency synthesiser is developed that is stabilised to the optical frequency standard based on molecular iodine . The possibility of transferring stability of the optical frequency standard to other optical frequencies in the IR range and to the RF range by using synthesiser phase-locked loops (PLLs) with acousto-optical and electro-optical modulators is experimentally demonstrated. The additive instability introduced into the optical frequency comb of the synthesiser (which arises due to PLL residual random errors) is several orders less than the intrinsic instability of the reference optical frequency standard employed (i.e., is noticeably less than for and for ).

Comb mode filtering silver mirror cavity for spectroscopic distance measurement.

In this work we present a design of an external optical cavity based on Fabry-Perot etalons applied to a 100 MHz Er-doped fiber optical frequency comb working at 1560 nm to increase its repetition frequency. A Fabry-Perot cavity is constructed based on a transportable cage system with two silver mirrors in plano-concave geometry including the mode-matching lenses, fiber coupled collimation package and detection unit. The system enables full 3D angle mirror tilting and x-y off axis movement as well as distance between the mirrors. We demonstrate the increase of repetition frequency by direct measurement of the beat frequency and spectrally by using the virtually imaged phased array images.

A fiber-optic frequency transducer of variable pressure in gaseous and liquid media

Fiber-optic sensors of variable pressure are proposed and implemented on fiber lasers with microoptomechanical resonance structures generating in automodulation regimes. Possibilities of sound pressure monitoring in gaseous and liquid media are considered, and the sensitivity of these fiber-optic sensors is estimated.

Fiber-optic radio frequency transfer based on passive phase noise compensation with frequency dividing and filtering.

In this Letter, a passive phase noise compensation-based fiber-optic frequency transfer scheme with frequency dividing and filtering is proposed. The probe signal is divided at the remote site and effectively discriminated from the backscattering noises by electrical bandpass filtering at the local site. By combining the bidirectional transmission with the same wavelength on a single fiber, the scheme can reach the maximum bidirectional propagation symmetry and effectively suppress the effect of backscattering at the same time. The proposed scheme is experimentally demonstrated and compared with the scheme with backscattering. The relative frequency stabilities of 3.9×10(-14)/s and 1.2×10(-16)/10(4) s are reached for 40 km transfer, which obviously outperform the scheme with backscattering, especially in terms of short-term stability, and are closed to the floor of the back-to-back experimental system.

Tunable cw UV laser with

We present a solid-state laser system that generates over 200 mW of continuous-wave, narrowband light, tunable from 316.3 nm - 317.7 nm and 318.0 nm - 319.3 nm. The laser is based on commercially available fiber amplifiers and optical frequency doubling technology, along with sum frequency generation in a periodically poled stoichiometric lithium tantalate crystal. The laser frequency is stabilized to an atomic-referenced high finesse optical transfer cavity. Using a GPS-referenced optical frequency comb we measure a long term frequency instability of < 35 kHz for timescales between 10(-3) s and 10(3) s. As an application we perform spectroscopy of Sr Rydberg states from n = 37 - 81, demonstrating mode-hop-free scans of 24 GHz. In a cold atomic sample we measure Doppler-limited linewidths of 350 kHz.

Power enhancement of burst-mode ultraviolet pulses using a doubly resonant optical cavity.

We report a doubly resonant enhancement cavity (DREC) that can realize a simultaneous enhancement of two incoming laser beams at different wavelengths and different temporal structures. The double-resonance condition is theoretically analyzed, and different DREC locking methods are experimentally investigated. Simultaneous locking of a Fabry-Perot cavity to both an infrared (1064 nm) and its frequency-tripled ultraviolet (355 nm) pulses has been demonstrated by controlling the frequency difference between the two beams with a fiber-optic frequency shifter. The DREC technique enables novel applications of optical cavities to power enhancement of burst-mode lasers with arbitrary macropulse width and repetition rate.

First Evaluation and Frequency Measurement of the Strontium Optical Lattice Clock at NIM**Supported by the National Natural Science Foundation of China under Grant Nos 91336212 and 91436104.

An optical lattice clock based on 87Sr is built at National Institute of Metrology (NIM) of China. The systematic frequency shifts of the clock are evaluated with a total uncertainty of 2.3×10−16. To measure its absolute frequency with respect to NIM's cesium fountain clock NIM5, the frequency of a flywheel H-maser of NIM5 is transferred to the Sr laboratory through a 50-km-long fiber. A fiber optical frequency comb, phase-locked to the reference frequency of this H-maser, is used for the optical frequency measurement. The absolute frequency of this Sr clock is measured to be 429228004229873.7(1.4)Hz.

Offset-free broadband Yb:fiber optical frequency comb for optical clocks.

We demonstrate a passively offset-frequency stabilized optical frequency comb centered at 1060 nm. The offset-free comb was achieved through difference frequency generation (DFG) between two portions of a supercontinuum based on a Yb:fiber laser. As the DFG comb had only one degree of freedom, repetition frequency, full stabilization was achieved via locking one of the modes to an ultra-stable continuous wave (CW) laser. The DFG comb provided sufficient average power to enable further amplification, using Yb-doped fiber amplifier, and spectral broadening. The spectrum spanned from 690 nm to 1300 nm and the average power was of several hundred mW, which could be ideal for the comparison of optical clocks, such as optical lattice clocks operated with Sr (698 nm) and Hg (1063 nm) reference atoms.

Strontium optical lattice clocks for practical realization of the metre and secondary representation of the second

We present a system of two independent strontium optical lattice standards probed with a single shared ultranarrow laser. The absolute frequency of the clocks can be verified by the use of Er:fiber optical frequency comb with the GPS-disciplined Rb frequency standard. We report hertz-level spectroscopy of the clock line and measurements of frequency stability of the two strontium optical lattice clocks.

Precise method of estimation of semiconductor laser phase-noise-to-intensity-noise conversion in dispersive fiber

In this paper a new method is presented for the estimation of an intensity noise induced by an interaction of a laser phase noise with a chromatic dispersion of an optical fiber. The idea is based on performing a reference measurement of the phase-to-intensity converted noise using a standard dispersion compensating module, and further scaling of obtained data to estimate the noise for different values of dispersion. The experimental validation of this method for various lasers and various lengths of dispersive fiber is presented, and a noise optimization of a real link is briefly described. Proposed method is efficient laboratory tool allowing evaluation of the influence of the phase noise of particular laser on transmitted signals in all cases where it is important, e.g. in fiber optic bidirectional time and frequency transfer.

Enhanced optical nonlinearity and fiber-optical frequency comb controlled by a single atom in a whispering-gallery-mode microtoroid resonator

Based on a single atom coupled to a fiber-coupled, chip-based microresonator [B. Dayan et al., Science 319, 1062 (2008)], we put forward a scheme to generate optical frequency combs at driving laser powers as low as a few nanowatts. Using state-of-the-art experimental parameters, we investigate in detail the influences of different atomic positions and taper-resonator coupling regimes on optical-frequency-comb generation. In addition to numerical simulations demonstrating this effect, a physical explanation of the underlying mechanism is presented. We find that the combination of the atom and the resonator can induce a large third-order nonlinearity which is significantly stronger than Kerr nonlinearity in Kerr frequency combs. Such enhanced nonlinearity can be used to generate optical frequency combs if driven with two continuous-wave control and probe lasers and significantly reduce the threshold of nonlinear optical processes. The comb spacing can be well tuned by changing the frequency beating between the driving control and probe lasers. The proposed method is versatile and can be adopted to different types of resonators, such as microdisks, microspheres, microtoroids or microrings.

Digitally enhanced optical fiber frequency reference

We use digitally enhanced heterodyne interferometry to measure the stability of optical fiber laser frequency references. Suppression of laser frequency noise by over four orders of magnitude is achieved using post processing time delay interferometry, allowing us to measure the mechanical stability for frequencies as low as 100 μHz. The performance of the digitally enhanced heterodyne interferometer platform used here is not practically limited by the dynamic range or bandwidth issues that can occur in feedback stabilization systems. This allows longer measurement times, better frequency discrimination, a reduction in spatially uncorrelated noise sources and an increase in interferometer sensitivity. An optical fiber frequency reference with the stability reported here, over a signal band of 20 mHz-1 Hz, has potential for use in demanding environments, such as space-based interferometry missions and optical flywheel applications.

高Q光纤环谐振腔陀螺角速度传感研究

The transmission spectrum and demodulation curve of the fiber ring resonator were simulated.As can be seen,the lowest value of transmission spectrum was corresponding to the modulation resonance point,the linear zone of demodulation curve was the dynamic range of gyroscope,the midpoint of the linear region was corresponds to the resonance point and it could be used as the maximum of scale factor.In order to achieve the high accuracy and steady frequency locked of the resonance point,resonant gyroscope angular velocity measurement scheme was designed,which used proportional integral circuit to lock the resonant frequency and sine wave to scan the piezoelectric transducer of narrow linewidth laser(linewidth is less than 1kHz),so that the length of laser resonant cavity was changed to adapt the changes of the fiber ring resonator which real-time tracked and locked with the external environment.Through the method of linewidth,calculated quickly that the quality value of fiber ring resonator was 107.The real-time output of the fiber ring cavity in resonant and non-resonant points frequency locked were compared and analyzed,the continuous rotation in the two kinds condition was obtained by rotation test.The detection sensitivity of fiber optic gyro system in the theory was calculated finally.The results show that the output level of the gyro value in the resonant point is 3times than the non-resonant point,which proves the importance of the resonator fiber optic gyroscope resonant frequency locking.

Widely time-dispersion-tuned fiber optical oscillator and frequency comb based on multiple nonlinear processes

An all-fiber optical oscillator based on three nonlinear processes, namely stimulated Raman scattering and broad-band and narrow-band optical parametric amplification, is presented and experimentally characterized. The wavelength tuning is achieved by means of the time-dispersion technique and spans over 160 nm. Through the same technique a fast tunable optical frequency comb has been realized exploiting cascaded four-wave mixing.

Fiber-optic sensors based on fluctuation oscillations of waveguide micro-optomechanical resonance structures

The characteristics of fiber-optic oscillation frequency sensors of deformation and temperature that employ the thermal fluctuation resonant oscillations in the SMS(M) fiber structures (sensitive elements that represent oscillation systems with distributed parameters based on series-connected single- and multimode step-index fibers) are developed and studied. The measurements of the fluctuation oscillations are based on the amplitude-phase modulation of the optical wave in the multimode oscillating section due to variations in the path-length difference and tunneling of interfering beams. Accuracies of temperature and relative deformation measurements of ±2°C and ±10−5, respectively, are demonstrated. The estimation of the ultimate measurement sensitivity of the resonance frequency is based on the approximate calculation of the Allan variance that shows a possibility of the above sensors with temperature and deformation threshold sensitivities of 0.001°C and 10−8, respectively.