A temperature-insensitive magnetic field sensor with high interrogation performance and large measurement range based on an optoelectronic oscillator (OEO) merging a Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. In the OEO loop, a finite impulse response (FIR)-microwave photonic filter (MPF) and an infinite impulse response-MPF are cascaded to select the oscillating frequency and further suppress the side mode. The center frequency of the FIR-MPF, which is composed of a non-coherent broadband optical source, a MZI, a dispersion compensating fiber (DCF), and a photodetector, is determined by dispersion of DCF and the free spectral range (FSR) of the MZI jointly. In one arm of the MZI, a section of optical fiber is bonded with a giant magnetostrictive material (GMM) to achieve the magnetic field sensing, where the GMM is acted as a magnetic field-strain transducer. When the magnetic field varies, the FSR of the MZI will be changed, resulting in an oscillating frequency shift of the OEO. Therefore, a high interrogation performance magnetic field measurement can be achieved by simply monitoring frequency change of microwave signal generated by OEO in the microwave domain. Moreover, by placing a section of unprocessed fiber with appropriate length in the other arm of the MZI, the temperature cross-talk for the magnetic field can be alleviated greatly. In the experiment, the magnetic field sensitivity of 1.33 MHz/mT with a large range of 20.9 mT to 58 mT is obtained and the measurement error induced by temperature is as low as 0.09 mT.

The active mode-locking (AML) technique has been widely used in erbium-doped fiber lasers to generate picosecond pulse trains. Here we propose a novel active mode-locking dual-loop optoelectronic oscillator (AML-DL-OEO), which can generate microwave frequency comb (MFC) signals with adjustable comb spacings. Based on this scheme, the order of harmonic mode-locking is dramatically decreased for a certain AML driving frequency compared with a single-loop AML-OEO. Thus, the supermode noise caused by harmonic mode-locking can be efficiently suppressed. In addition, the sidemodes are well suppressed by the dual-loop architecture. An experiment is performed. MFC signals with different comb spacings are generated under fundamental or harmonic mode-locking states. AML-DL-OEO systems with different length differences between two loops are implemented to evaluate supermode noise suppression capability. The performance of the generated MFC signals is recorded and analyzed.

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.

Fundamental and harmonic mode-locking in the dissipative soliton resonance (DSR) regime is experimentally investigated in a net-normal-dispersion Er/Yb co-doped fiber laser based on the semiconductor saturable mirror (SESAM), where an equivalent narrow-band spectral filter is used for triggering multi-pulsing. By monotonically increasing the pump power with the fixed polarization controller (PC), the fundamental mode-locking operation of DSR pulses can be transformed into the harmonic mode-locking (HML) under the specific conditions. The main reason is the peak-power-clamping effect induced by the combined effects of the spectral filtering and saturable absorption of the SESAM at higher pump levels, which is applied to achieve the HML in the DSR regime for the first time. The DSR pulse broadens linearly with the pump power in a certain range, no matter whether it is in the fundamental mode-locking or HML state. By incorporating the dispersion compensation fiber (DCF) with different lengths, the pulse characteristics are discussed and compared in detail. The enhanced nonlinearity caused by increasing DCF length can lead to higher orders of HML pulses and even the generation of noise-like pulses (NLPs) with a long-enough DCF.

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.

A switchable, widely wavelength-tunable noise-like pulse (NLP) and Q-switched Er-doped fiber (EDF) laser with a linear cavity structure is proposed and experimentally demonstrated in this work. The net-normal-dispersion mode-locked NLP operation based on a semiconductor saturable mirror (SESAM) is realized in a 57 nm continuous tuning range from 1528 to 1585 nm by using a tunable filter (TF). When the pump power is 500 mW, the NLPs produce a maximum average output power of about 16 mW with a 3-dB spectral bandwidth of about 17 nm at the central wavelength of 1555 nm, while the average peak power is about 58.8 W. The measured characteristics of the output NLPs at 1555 nm are consistent with the numerical results under the condition of Δβ_{2, net} = 0.095 ps², and E_sat = 0.77 nJ. In addition, stable Q-switched pulses with a 67 nm wavelength tuning range from 1518 to 1585 nm are obtained by adjusting the central wavelength of the filter. The maximum pulse energy reaches 231.4 nJ at the center wavelength of 1555 nm, corresponding to a peak power of about 278.8 mW. The proposed wavelength-tunable fiber laser is simple and versatile, demonstrating significant potential for numerous practical applications.