An approach to microwave frequency measurement with a high resolution and a broad bandwidth is proposed based on three parallel low-speed photonic analog-to-digital converters (ADCs) architecture. Through simultaneously bandpass sampling the input microwave signal with the three photonic ADCs, the input frequency can be calculated from the Fourier frequencies of the photonic ADCs using the proposed frequency recovery algorithm. Theoretical analysis and simulation results indicate that the proposed method is applicable for both single-tone and multi-tone microwave signals. By employing three ~1 GS/s@8 bits photonic ADCs, 0-100 GHz frequency measurement with an error of ± 0.5 MHz and a spur-free dynamic range of 94 dB-Hz^2/3 over the full band has been numerically demonstrated. Additionally, a proof-of-concept experiment is carried out to demonstrate the effectiveness of the proposed method, where a frequency measurement range of 0-20 GHz with a measurement error of ± 8 kHz is realized by utilizing three photonic ADCs with sampling rates of 27.690 MS/s, 27.710 MS/s, and 27.730 MS/s. Larger frequency measurement range can be achieved by using an optical modulator with a larger bandwidth.

A Fourier domain mode locking (FDML) optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) is proposed to generate complementary linearly chirped microwave waveform (LCMW) pairs with flexibly-reconfigurable frequency sweep range and excellent frequency sweep linearity. The FDML OEO involves an SBS-based dual-passband microwave photonic filter with its two passbands linearly and fast scanning in the opposite direction at an identical frequency sweep rate, which is realized by using a single laser source to obtain a fast frequency sweep probe light and a two-tone pump light through electro-optic modulation. A proof-of-concept experiment is carried out to demonstrate the proposed scheme. In the experiment, frequency-sweep-range-reconfigurable complementary LCMW pairs with period of 20.5 's are generated in the range of 5 GHz to 18 GHz, where the maximum time-bandwidth product and chirp rate are 82000 and ±0.195 GHz/μs, respectively. Most importantly, the frequency sweep linearity is measured to be 1.76%, which is much better than the results obtained in the existing FDML OEOs.

We demonstrate a stable and finely tunable optoelectronic oscillator (OEO) based on stimulated Brillouin scattering. In the proposed scheme, the optical carrier in the OEO loop and the Brillouin pump light is generated by a single laser source, which guarantees the frequency stability of the output microwave signal from the OEO. Frequency tuning is achieved by varying the pump frequency via an electro-optic frequency shifter composed of a dual-parallel Mach–Zehnder modulator (DPMZM) and an electrical 90° hybrid. Through subtly varying the frequency of the low-frequency microwave signal applied to the DPMZM, a finely tunable high-frequency microwave signal can be obtained from the OEO. In the proof-of-concept experiment, the output frequency of the OEO is tuned from 10.645 GHz to 12.645 GHz with a tuning resolution of 10 MHz. The stable performance of the OEO is also achieved, where the maximum frequency and power drifts at 11.145 GHz are measured to be 6.25 kHz (i.e., ∼ 0.6 p p m ) and 0.77 dB in a measurement time duration of 1000 s, respectively. Through using broadband devices in the OEO architecture, the proposed scheme can generate stable and finely tunable microwave signals up to 40 GHz or even higher.

An approach to generating periodic spiking and spiking cluster in a broadband nonlinear opto-electronic oscillator (OEO) is proposed and demonstrated. Through injecting a long-duration square-wave pulse train with a repetition frequency equal to an integral multiple of the free spectral range into the OEO with a high net gain, controllable spiking and spiking cluster oscillation can be achieved when the dual-drive Mach-Zehnder modulator (DDMZM) in the OEO is biased far away from its quadrature point. The proposed scheme is verified by both numerical simulation and experiment. The results indicate that, when the DDMZM in the OEO cavity is biased near its minimum transmission point, positive spiking train with nanosecond-level pulse width is excited by the rising edge of the injected square-wave pulse train. Through further enhancing the injection strength, uniformly-spaced positive spiking fills the high-level voltage duration of each injected square-wave pulse. Hence, spiking cluster oscillation is achieved. Benefiting from its controllability, this approach can be applied in ultra-wideband (UWB) communications, electronic countermeasures, spiking coding and high-speed neuromorphic computing.

An approach to characterizing the microwave performance of an electro-optic Mach-Zehnder modulator (MZM) is proposed based on photonic down-conversion sampling. Through low-speed sampling, the magnitude response of the MZM at the input microwave frequency is transferred to the duplicate component in the first Nyquist frequency range, and can be measured via low-frequency detection and spectrum analysis. A proof-of-concept experiment is carried out to demonstrate the feasibility of the proposed method, where magnitude-frequency response and half-wave voltage versus frequency of a commercial MZM in the frequency range of 0-40 GHz have been accurately measured under a sampling rate of 96.9 MS/s. Both simulation and experimental results indicate that the proposed method can be implemented without any extra calibration.

A broadband linearization scheme for time-stretch analog-to-digital converters (TS-ADCs) is proposed based on an asymmetrical dual-parallel Mach-Zehnder modulator and a balanced detector. The theoretical and simulation results indicate that, compared with the differential and arcsine operation method generally employed in TS-ADCs, the proposed scheme has a superior performance on enhancing the spur-free dynamic range and suppressing the even-order distortions and the third-order spurs even under a large modulation depth. Additionally, the proposed scheme realizes online linearization. Therefore, it has the potential to enhance the dynamic range of a broadband TS-ADC in real time.