Shiguang Wang

Optical ultra-wide-band pulse bipolar and shape modulation based on a symmetric PM-IM conversion architecture

A simple and feasible technique for ultra-wide-band (UWB) pulse bipolar modulation (PBM) and pulse shape modulation (PSM) in the optical domain is proposed and demonstrated. The PBM and PSM are performed using a symmetric phase modulation to intensity modulation conversion architecture, including a couple of phase modulators and an optical bandpass filter (OBPF). Two optical carriers, which are separately phase modulated by two appropriate electrical pulse patterns, are at the long- and short-wavelength linear slopes of the OBPF spectrum, respectively. The high-speed PBM and PSM without limit of chip length, polarity, and shape are implemented in simulation and are also verified by experiment.

Photonic generation of various modulation formats in high speed UWB over fiber system

We firstly propose one system configuration for generating three kinds of modulation formats used in high-speed ultra-wide-band (UWB) over fiber application. 2Gbps UWB signal transmission over 20km single mode fiber without any compensation is experimentally demonstrated.

Investigation of the nonlinear CPT spectrum of 87Rb and its application for large dynamic magnetic measurement

The coherent population trapping (CPT) phenomenon has found widespread application in quantum precision measurements. Various designs based on the narrow resonant spectrum corresponding to the linear Zeeman effect have been demonstrated to achieve high performance. In this article, the nonlinear Zeeman split of the CPT spectrum of 87Rb in the lin ∥ lin setup is investigated. We observe re-split phenomenon for both magnetic sensitive and magnetic insensitive CPT resonant lines at a large magnetic field. The re-split in the magnetic sensitive lines raises a practical problem to magnetometers worked in the lin ∥ lin setup while the other one shows a good potential for applications in large magnetic field. We propose a design based on the nonlinear split of the magnetic insensitive lines and test its performance. It provides a much larger measurement range compared to the linear one, offering an option for atomic magnetometers where a large dynamic range is preferred.

Progress Towards a Microwave Atomic Clock Based on the Laser-Cooled Cadmium Ions

In the past decades, many groups in the world were engaged in building the microwave or optical frequency standards based on different trapped ions and achieved great improvements. A project aimed at a microwave atomic clock based on the laser-cooled 113Cd+ ions has been carried out since 2010 in our laboratory. The cadmium ion clock, a transportable clock with excellent frequency stability, is suitable in the comparison between the clocks located in different places, for example, to compare the time systems at different stations of BeiDou Navigation Satellite System, or to examine the general relativity. A linear quadruple ion trap and the technique of laser cooling are applied in this clock. Meanwhile, the cadmium clock can be designed to be transportable which requires only one laser to accomplish the laser cooling, optical pump and optical detection. In this paper, we will report the detailed progress of this clock.

Ultrawideband pulse generation and bipolar coding based on optical cross-polarization modulation in highly nonlinear photonic crystal fiber

A novel optical method for ultrawideband (UWB) monocycle pulse generation and bipolar coding is proposed and experimentally demonstrated. The proposed scheme is based on the cross-polarization modulation effect in highly nonlinear photonic crystal fiber (HNPCF). The monocycle pulse with a time duration of 84 ps is generated, and four groups of bipolar codes are obtained.

Note: An atomic self-sustaining magnetic gradiometer with a 1/τ uncertainty property based on Larmor precession

We demonstrate an atomic magnetic gradiometer based on self-sustaining Larmor precession. By coherent optical pumping, we measure the phase of the Larmor precession directly and observe that the gradiometer shows a 1/τ improvement in magnetic field gradient uncertainty over time τ. Since the measurement gives frequency signals, the gradiometer can be easily implemented by mixing and filtering the different frequency signals from two adjacent magnetometers. A gradient sensitivity of 186 fT/Hz/cm-1) is realized, which is close to the shot-noise limit. In a noisy environment, the gradiometer can still maintain its 1/τ behavior by suppressing 90% of the common-mode noise. This method should be widely applicable to the measurement of magnetic field gradients owing to its simplicity and outstanding performance.

Progress on Novel Atomic Magnetometer and Gyroscope Based on Self-sustaining of Electron Spins

The gyroscope based on atomic technology has the potential to provide the end user a high-performance device in a small package with low-power. Generally, the atomic gyroscope detects the rotation or angular rate of the object by measuring the Larmor precession frequency of spins. However, the precision is limited by the shorter coherence time caused by relaxation effects, and since the nuclear spin precession is often used in detection for atomic gyroscope, longer polarization time limits its application environment. Presented in this paper is a self-sustaining gyroscope based on electron spins. By non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the Larmor precession can persist indefinitely, and the system can quickly regain polarization to environmental variations. Magnetic field measurement has been accomplished by using the self-sustaining technology. The precision of the magnetometer increases with time following a much faster \( \tau^{{{ - }1}} \) rule rather than the traditional \( \tau^{{{ - }1/2}} \) rule. The mean sensitivity is close to the shot noise in 300 ms, and the magnetometer has a quick response to sudden magnetic change. The self-sustaining technology can hopefully improve the measurement precision and the response time of the atomic gyroscope.

A stabilized laser continuously tunable over a range of 1.5 GHz

We demonstrate a method to stabilize laser frequency which can be continuously tuned over a range of 1.5 GHz. It is based on saturated absorption spectroscopy (SAS) generated by an external-cavity diode laser (ECDL) which is modulated by an electro-optic amplitude modulator (EO-AM). The spectra consist of not only the original peaks corresponding to resonant and crossover lines of 133Cs D2 line, but also signals introduced by sidebands from an EO-AM. Thus, the laser frequency can be locked to any point within the range of the spectra. Furthermore, the tuning range of the laser can be doubled compared to the coverage of common SAS by fixing the frequency of the pumping laser. The best stability of the locked laser induced by the EO-AM is 1.27 × 10-11 over an integrating time of 125 s. This method may be applied for more precise and flexible manipulation of atoms and molecules.

Note: A novel design of a microwave feed for a microwave frequency standard with a linear ion trap

Linear ion traps are important tools in many applications, particularly in mass spectrum analyzers and frequency standards. Here a novel design of a microwave feed integrated into one electrode of a linear quadrupole ion trap is demonstrated for the application of a microwave frequency standard based on cadmium ions. The mechanical structure of the microwave feed is compact and easy to build. The ion trap integrated with this microwave feed is successfully applied to measure the hyperfine splitting of the ground state of (113)Cd(+), thus demonstrating the practicality and reliability of the microwave feed.

High-Resolution Frequency Measurement of the Ground-State Hyperfine Splitting of 113 Cd + Ions

Time-keeping clock is one of the most important parts in COMPASS global navigation satellite system (GNSS) of China and the synchronization of these time-keeping clocks is the basis of GNSS. Recently, we have engaged in developing a transportable atomic clock based on 113Cd+ ions, which is potentially applied in the comparison of atomic clocks in different locations, including the time-keeping clocks at the ground stations of the COMPASS system. To operate a high precision microwave atomic clock, one has to measure its clock transition frequency precisely at zero external magnetic field. In this paper, the progress of the precision measurement of the ground-state hyperfine splitting of laser-cooled 113Cd+ ions is reported. In the previous experiment, the hyperfine splitting was measured to be 15,199,862,854.96(12) Hz, using Ramsey’s separated oscillation fields technique. Recently, by upgrading the ion trap apparatus, the control time sequence, and the magnetic field stabilization, we obtained a preliminary improved result of 15,199,862,855.013 Hz. This value is nearly one order of magnitude more accurate than the results obtained before.