Optoelectronic oscillator (OEO) has received growing attentions from researchers in the field of demodulations for optical sensors because of its excellent performance of combining optics and electronics in signal processing. In this article, we present a wideband-tunable OEO for angular velocity measurement. The OEO consists of two cascaded microwave photonic filters (MPFs), namely, a dispersion-induced MPF for mainly determining the OEO's oscillating frequency and a two-tap MPF for the fine selection of the oscillating frequency. With proper control of polarization of the optical signal, the angular velocity is first mapped into the central frequency shift of the dispersion-induced MPF, which will then cause an oscillating frequency shift of the OEO. This approach ensures a large-scale factor for the angular velocity measurement due to the fact that a small phase change in the optical domain causes a large frequency shift in the electrical domain. An experiment is conducted to validate the scheme. The experimental results show that the oscillating frequency shift can reach nearly 700 MHz when the system rotates at about 1 rad/s by using a 560-m Sagnac loop. In addition, the measurement range can be achieved to 5.24 rad/s with a 2.5-GHz oscillating frequency tuning range and the maximum measurement error is 0.06 rad/s.

A novel photonics-assisted method for tunable microwave frequency comb (MFC) generation based on an actively mode-locked optoelectronic oscillator (AML-OEO) is proposed and experimentally demonstrated in this letter. Two key factors for the proposed system, periodic gain modulation and widely tunable center frequency, are implemented by an externally introduced intensity-modulated optical signal and a microwave photonic filter (MPF) based on the phase-shifted fiber Bragg grating (PS-FBG) respectively. Unlike a conventional OEO with only one dominant oscillation mode, an AML-OEO operates in a stable multimode oscillation state and thus can generate MFC signal. Through simply adjusting the center frequency of the PS-FBG-based MPF, the center frequency of the generated MFC changes accordingly. In the proof-of-principle experiment, two sets of MFC signals with center frequency tuning from 3.5 GHz to 6.5 GHz and frequency intervals of 1.02 MHz and 340.46 kHz are generated.

Mode selection is crucial for a stable single-mode oscillation of an optoelectronic oscillator (OEO). In this paper a parity-time (PT)-symmetric frequency-tunable OEO is proposed and experimentally demonstrated, to realize precise frequency tuning without using any narrowband filter. The proposed PT-symmetric OEO is implemented based on two identical optoelectronic hybrid loops mainly consisting of a shared dual-parallel Mach-Zehnder modulator (DPMZM) and a photodetector. The PT-symmetry condition can be achieved by enabling antisymmetric gain/loss in the two loops through manipulating the bias voltages of the two child-MZMs of DPMZM, and continuous frequency tunability is realized by adjusting the bias voltage of the parent-MZM. A theoretical model is developed for the proposed PT-symmetric OEO to analyze the dynamics of the PT-supermodes as the gain/loss coefficient changing. Furthermore, an experiment is performed. Without high-Q filter, stable single-mode oscillation of the PT-broken supermode at 4.2 GHz with side-mode suppression ratios of 60 and 50 dB is demonstrated in the OEO with 6 and 2000 m fiber loop lengths, respectively. The frequency tuning ranges are 1.4 MHz and 1.5 kHz for two OEOs with different fiber loop lengths.

A novel high-speed and high-sensitivity refractive index (RI) and temperature sensing based on an optoelectronic oscillator (OEO) is proposed and demonstrated. A novel Fabry-Perot fiber Bragg grating (FP-FBG), incorporated in the OEO to implement a microwave photonic filter, has a narrow notch in the reflection spectrum and combines a gap with two FBGs in a silica V-sharp slot. A microwave signal is generated by the OEO whose oscillating frequency is determined by the center frequency of the FP-FBG notch. The RI or the temperature change can be measured by monitoring the frequency shift of the microwave signal using an electrical spectrum analyzer or a digital signal processor. An experiment is performed to verify the proposal. The sensing sensitivities of the RI and temperature as high as 413.8 MHz/0.001RIU and 2516 MHz/°C are demonstrated respectively.

Recently, optoelectronic oscillators (OEOs) have shown good behavior in microwave signal generation. In this letter, we propose a rational harmonic mode-locking OEO (RHML-OEO) to generate microwave frequency combs (MFCs) with tunable comb intervals. By embedding an extra Mach–Zehnder modulator (MZM) into the OEO cavity, the intensity of the oscillating mode can be modulated by the signal applied on the MZM, and sidebands having fixed phase differences are produced in addition to the oscillating mode. A main feature of the RHML-OEO is that there is a frequency detuning between the modulation signal and longitudinal mode spacing of the OEO. Consequently, MFCs with large comb intervals can be generated even with a low-frequency modulation signal. In our experiment, third-order, fifth-order, and tenth-order RHML-OEOs are realized to generate MFCs with different frequency intervals of 1.128, 1.88, and 3.76 MHz when the modulation frequencies are 564, 940 kHz, and 1.253 MHz, respectively.

A microwave photonics deceptive RF regeneration method with multi-characteristic regulatory is proposed for radar jamming. In this scheme, Doppler frequency shift (DFS) is implemented by a Serrodyne structure based on the modulation of a sawtooth wave signal. This structure can effectively fulfill a small frequency shift of the original carrier through carrier-suppressed single sideband modulation without any filter, which makes a small frequency shift possible for a wideband radio frequency signal. The phase shifting of the RF signal is achieved by adjusting the bias voltage of the modulator. The RF modulation pulse signal is stored in an optical loop. Two semiconductor optical amplifiers and an Erbium-doped optical fiber amplifier are combined to control the delay time and ensure the fidelity. The experimental results show that the DFS from 100 Hz to 5 MHz can be realized and its minimum frequency step is 50 Hz. The phase shift covers from −180° to 180°. Furthermore, the RF signal can be delayed more than 100 μs with a small signal-to-noise degradation (<7.32 dB). This method supplies flexibility of multi-parameter adjustment, and has broad potential applications in modern radar interference.