Zongyang Xia

Distribution of high-stability 100.04 GHz millimeter wave signal over 60 km optical fiber with fast phase-error-correcting capability

We demonstrate a phase-stabilized remote distribution of 100.04 GHz millimeter wave signal over 60 km optical fiber. The phase error of the remote millimeter wave signal induced by fiber transmission delay variations is detected by dual-heterodyne phase error transfer and corrected with a feedback system based on a fast response acousto-optic frequency shifter. The phase noise within the bandwidth of 300 Hz is effectively suppressed; thus, the fast transmission delay variations can be compensated. The residual phase noise of the remote 100.04 GHz signal reaches -56  dBc/Hz at 1 Hz frequency offset from the carrier, and long-term stability of 1.6×10(-16) at 1000 s averaging time is achieved. The fast phase-noise-correcting capability is evaluated by vibrating part of the transmission fiber link.

Compensation of phase error in optical frequency-domain reflectometry using delay-matched sampling

Abstract. We proposed and experimentally demonstrated a delay-match sampling method to measure and compensate the laser phase error in optical frequency-domain reflectometry system. By using the error signal extracted from a simple auxiliary Mach-Zehnder interferometer with only a 10-ns delay, the laser phase error is effectively compensated. Considerable improvement is achieved in spatial resolution from 200 m to 7 cm at a measurement distance over 10 times the round-trip laser coherence length.

Photonic generation of low phase noise arbitrary chirped microwave waveforms with large time-bandwidth product.

We present a photonic approach for generating low phase noise, arbitrary chirped microwave waveforms based on heterodyne beating between high order correlated comb lines extracted from frequency-agile optical frequency comb. Using the dual heterodyne phase transfer scheme, extrinsic phase noises induced by the separate optical paths are efficiently suppressed by 42-dB at 1-Hz offset frequency. Linearly chirped microwave waveforms are achieved within 30-ms temporal duration, contributing to a large time-bandwidth product. The linearity measurement leads to less than 90 kHz RMS frequency error during the entire chirp duration, exhibiting excellent linearity for the microwave and sub-THz waveforms. The capability of generating arbitrary waveforms up to sub-THz band with flexible temporal duration, long repetition period, broad bandwidth, and large time-bandwidth product is investigated and discussed.

Coherent Comb Generation With Continuous Sweep of Repetition Rate Over One-Octave

We proposed and demonstrated a coherent optical frequency comb generation with broadband continuous sweep of repetition rate based on cascaded phase and intensity modulators. Broadband phase matching between electrical drive signals applied on the cascaded phase and intensity modulators is achieved by compensating propagation delay skew between optical signal path and electrical signal path. Therefore, phase mismatch induced flatness deterioration is effectively suppressed. A flat-top 19-line optical frequency comb with repetition rate continuously sweeping over one-octave from 8.5 to 19 GHz is obtained, where the overall power deviation is .

Fourier transform-limited optical frequency-modulated continuous-wave interferometry over several tens of laser coherence lengths.

We report on a versatile optical frequency-modulated continuous-wave interferometry technique that exploits wideband phase locking for generating highly coherent linear laser frequency chirps. This technique is based on an ultra-short delay-unbalanced interferometer, which leads to a large bandwidth, short lock time, and robust operation even in the absence of any isolation from environmental perturbations. In combination with a digital delay-matched phase error compensation, this permits the achievement of a range window about 60 times larger than the intrinsic laser coherence length with a 1.25 mm Fourier transform-limited spatial resolution. The demonstrated configuration can be easily applied to virtually any semiconductor laser.

Efficient dynamic coherence transfer relying on offset locking using optical phase-locked loop

We design and experimentally demonstrate a highly efficient coherence transfer based on composite optical phaselocked loop comprising multiple feedback servo loops. The heterodyne offset-locking is achieved by conducting an acousto-optic frequency shifter in combination with the current tuning and the temperature controlling of the semiconductor laser. The adaptation of the composite optical phase-locked loop enables the tight coherence transfer from a frequency comb to a semiconductor laser in a fully dynamic manner.

Photonic generation of linearly chirped millimeter wave based on comb-spacing tunable optical frequency comb

Abstract. We demonstrated a photonic approach to generate a phase-continuous frequency-linear-chirped millimeter-wave (mm-wave) signal with high linearity based on continuous-wave phase modulated optical frequency comb and cascaded interleavers. Through linearly sweeping the frequency of the radio frequency (RF) driving signal, high-order frequency-linear-chirped optical comb lines are generated and then extracted by the cascaded interleavers. By beating the filtered high-order comb lines, center frequency and chirp range multiplied linear-chirp microwave signals are generated. Frequency doubled and quadrupled linear-chirp mm-wave signals of range 48.6 to 52.6 GHz and 97.2 to 105.2 GHz at chirp rates of 133.33 and 266.67  GHz/s are demonstrated with the ±1st and ±2nd optical comb lines, respectively, while the RF driving signal is of chirp range 24.3 to 26.3 GHz and chirp time 30 ms.

Photonic Radio-Frequency Phase Detector based on Radio-Frequency to Intermediate-Frequency Phase Mapping

A photonic radio-frequency phase detector based on radio-frequency (RF) to intermediate-frequency mapping is demonstrated, and the theoretical principle of the design is explained.