Wei Yu Wang

Triangular Microwave Waveforms Generation Based on an Optoelectronic Oscillator

We demonstrate a novel scheme to generate full-duty-cycle triangular microwave waveforms using an optoelectronic oscillator (OEO). The OEO produces high-quality local oscillator signal. Thus, an external microwave source, which is usually involved in orthodox approaches obviates the need. A polarization modulator is involved in both the OEO loop and a microwave photonic filter (MPF) structure. To generate a triangular waveform, the undesired electrical harmonics are suppressed by the MPF. The proposed method is theoretically analyzed and experimentally verified. Triangular waveforms at fundamental tone of 4.6 GHz and frequency doubling tone of 9.2 GHz are generated, which fit well with the stimulated ones. The root mean square errors between the generated and the simulated triangular waveforms are 6.6e-5 and 1.61e-3 for triangular pulses at 4.6 and 9.2 GHz, respectively.

Widely tunable single bandpass microwave photonic filter based on Brillouin-assisted optical carrier recovery

A widely tunable single bandpass microwave photonic filter (MPF) based on Brillouin-assisted optical carrier recovery in a highly nonlinear fiber (HNLF) with only one optical filter is proposed and experimentally demonstrated. The fundamental principle lies in the fact that the suppressed optical carrier of the phase modulated optical signal could be recovered by the stimulated Brillouin scattering (SBS) amplification effect. When phase modulated optical signals go through an optical filter with a bandpass response, the optical carrier and the upper sidebands suffer from the suppression of the optical filter because they fall in the stopband of that. In our system, the optical carrier could be recovered by the SBS operation around 38 dB. The MPF is achieved by one-to-one mapping from the optical domain to the electrical domain only when one of phase modulated sidebands lies in the bandpass of the optical filter. It shows an excellent selectivity with a 3-dB bandwidth of 170 MHz over a tuning frequency range of 9.5-32.5 GHz. The out-of-band suppression of the MPF is more than 20 dB. Moreover, the MPF shows an excellent shape factor with 10-dB bandwidth of only 520 MHz. The frequency response of the MPF could be widely tuned by changing the frequency difference between the frequency of the optical carrier and the center frequency of the bandpass of the optical filter. A proof-of-concept experiment is carried out to verify the proposed approach.

Photonic generation of triangular pulses based on nonlinear polarization rotation in a highly nonlinear fiber

We propose a novel method to generate triangular pulses based on the nonlinear polarization rotation (NPR) effect in a highly nonlinear fiber. A continuous wave probe beam is polarization-rotated by an intensity-modulated control beam via the NPR effect. A polarization-division-multiplexing emulator is exploited to split the probe beam into two orthogonally polarized states with imbalanced time delay. After detection by a photodetector, a 90° microwave phase shifter is used to compensate the phases of the fundamental and the third-order harmonic components in order to generate triangular pulses. Triangular pulses at 5 and 6 GHz with full duty cycles are experimentally generated. The root mean square errors between the generated and the simulated waveforms are 3.6e-4 and 1e-4 for triangular pulses at 5 and 6 GHz, respectively.

Optical Vector Network Analyzer With Improved Accuracy Based on Brillouin-Assisted Optical Carrier Processing

We propose a new method to improve the accuracy of an optical vector network analyzer (OVNA) based on stimulated Brillouin scattering (SBS) in a dispersion-shifted fiber (DSF). Generally, the measurement error of the OVNA mainly derives from the beat signals between adjacent optical sidebands. In this paper, the measurement error is significantly suppressed using a two-step measurement process. For the first measurement, both the transmission response of an optical device-under-test (ODUT) and the measurement error are recorded. For the second measurement, only the measurement error is obtained by suppressing the optical carrier using SBS in the DSF. The accurate transmission response of the ODUT is subsequently extracted by subtracting the error from the first measurement. The proposed method is theoretically investigated and experimentally demonstrated. The experimental results show that the accuracy of the OVNA is significantly improved.

Triangular Microwave Waveform Generation Based on Stimulated Brillouin Scattering

We proposed a new approach to generate full-duty-cycle triangular waveforms using a sinusoidal radio-frequency (RF) signal based on stimulated Brillouin scattering. In order to generate a triangular waveform, the even-order harmonics of the RF signal has to be removed. In our scheme, we use both the pump and Stokes waves to manipulate the amplitudes and phases of the optical components. In this way, the amplitudes and phases of the fundamental RF tone and its harmonics can be controlled. The proposed method is theoretically analyzed and experimentally verified. For a proof-of-concept demonstration, triangular waveforms at 8.5, 10.5, and 12.5 GHz are generated. The measured results agree well with the simulated ones.

Microwave Photonic Filter with Co mplex Coefficient Based on Optical Carri er Phase Shift Utilizing two Stimulated Brillouin Scattering Pumps

A microwave photonic filter (MPF) with complex coefficient based on the frequency transparent magnitude response by independent control of the frequency and power of two stimulated Brillouin scattering (SBS) pumps is proposed and experimentally demonstrated. The motivation of this paper lies in the fact that the operation bandwidth of the previous SBS-based complex coefficient MPFs is unavoidably limited by the Brillouin frequency shift. In our scheme, the complex coefficients are obtained by a broadband microwave photonic phase shifter based on the two SBS pumps. The two SBS pump signals are located at the same side of the optical carrier. In principle, the working bandwidth of the proposed MPF is infinite. One pump is used to introduce a controllable phase shift on the optical carrier, whereas the other pump is used to retain the power of the optical carrier invariant. By simply changing the phase shift of a complex coefficient, the frequency response of the two-tap complex coefficient MPF is continuously tuned over the full free spectral range (FSR), keeping shape and FSR invariant.

Photonic Generation of Microwave Pulse Using a Phase-Modulator-Based Sagnac Interferometer and Wavelength-to-Time Mapping

We report a new photonic microwave pulse generator using a phase-modulator-based Sagnac interferometer (PM-SI) and wavelength-to-time mapping in a dispersive element. The key significance of the proposed scheme is that the phase of the generated microwave pulse can be continuously tuned by adjusting the bias voltage applied to the PM. Thanks to the wide bandwidth of the PM, high-speed phase modulation of the microwave pulse can be realized. Moreover, the PM-SI is polarization independent, which means that the PM-SI is insensitive to the state of polarization of the input optical signal, ensuring a stable operation of the system. The proposed scheme is theoretically analyzed and experimentally verified.

Frequency-quadrupling microwave signal generation based on Brillouin-assisted optical notch filter

A novel technique to generate frequency quadrupling microwave signal is proposed and experimentally demonstrated based on a Brillouin-assisted optical notch filter (BAOF). The intensity modulated optical signal is firstly working at the maximum transmission point to suppress the first order sidebands. Microwave signals at the frequency corresponding to four times of the fundamental tone are successfully generated.

Photonic Generation of Pulsed Microwave Signal Based on Phase Shifted Lyot Optical Filter

We propose and experimentally verify an approach to generate pulsed microwave signal with continuously tunable phase and discrete tuning in microwave frequency based on phase shifted Lyot optical filter in conjunction with wavelength-to-time mapping technology. The Lyot optical filter with the discretely tunable spectral spacing is realized by changing the state of polarization of the bidirectionally propagated optical signals. The frequency response of the filter is continuously tuned over a full free-spectral range (FSR) keeping its shape and FSR unchanged by simple adjusting the bias voltage of the phase modulator. The proposed approach could also obtain pulsed microwave frequency multiplication with a discretely tunable multiplication factor by simply cascading multiple Lyot optical filters in the form of series. The proposed scheme is theoretically analyzed and experimentally demonstrated.