Microwave photonic filter with multiple independently tunable passbands based on a broadband optical source

High resolution and large measurement range voltage sensing based on an optoelectronic oscillator utilizing an unbalanced Mach-Zehnder interferometer

A voltage sensor with high resolution and large measurement range based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The key component in the cavity to select the oscillating signal is a finite impulse response (FIR)-microwave photonic filter (MPF) which consists of a sinusoidal broadband optical signal, an unbalanced Mach-Zehnder interferometer (MZI), a section of dispersion compensating fiber, and a photodetector. The center frequency of the FIR-MPF is mainly determined by the free spectral range (FSR) of the FIR-MPF. In the lower arm of the MZI, a cylindrical piezoelectric ceramic (PZT) wrapped with a section of optical fiber acts as voltage sensing head. Due to the inverse piezoelectric effect of PZT, the variation of the voltage will cause radial deformation of the cylindrical PZT and then lead to the change of the FSR of the MZI, determining the shift of center frequency of FIR-MPF as well as the frequency of the oscillating signal of the OEO. Thus, by monitoring the shift of the oscillation frequency of the OEO using an electric spectrum analyzer or a digital signal processor, a high-speed interrogation and high-resolution voltage measurement can be realized. Additionally, in the proposed scheme, an infinite impulse response (IIR)-MPF consisting of a fiber ring resonator is cascaded with the FIR-MPF to ensure the single-mode oscillation of the OEO. The experimental results show that a total range of 1700 V voltage sensing from - 200 V to 1500 V is accomplished with the voltage sensitivity of 0.25 GHz/100 V and the resolution of 0.3 V. By adjusting the proportion of the length of single mode fiber between two branches of MZI, the impact of temperature can be greatly reduced. The proposed sensor offers advantages such as a large measurement range, high resolution, high-speed interrogation, and stability to temperature disturbances, making it highly suitable for sensing applications in smart grids.

Tunable multiple-passband microwave photonic filter based on external optical injected Fabry-Pérot laser

This paper proposes a tunable multiple-passband microwave photonic filter (MPF) that is incorporated with an injection-locked Fabry-Pérot (FP) laser. In the proposed MPF, multiple passbands can be easily generated based on the frequency-selection effects of the laser structure in the case of multiple light waves injection. The novelty here is that the obtained multiple-passband MPF can achieve either a dual-passband or a single-passband by using merely one experimental scheme. Moreover, since the laser injection ratio of the proposed scheme is high, the central frequency of each passband has a large tunable range. More tunable passbands can be generated by employing more external wavelengths. By fine-detuning the injection parameters, the frequency tuning range of 17 GHz and the out-of-band rejection ratio of 24.1 dB are achieved for the dual-passband MPF, and the out-of-band rejection ratio of 22 dB and the 3-dB bandwidth of 360 MHz are achieved for the single-passband MPF. In addition, the attained peak power and bandwidth of the proposed MPF are investigated with respect to the injection parameters, including detuning frequency, injection ratio and bias current of FP laser. The stability and dynamic range of the MPF are also evaluated through experiments.

Microwave photonic multiband filter with independently tunable passband spectral properties

Multiband RF filters with independently controllable passbands are an essential component in dynamic multiband RF communications. Unfortunately, even a fixed multiband RF filter without the capability to adjust the passband properties individually is very difficult to achieve using either RF electronics or microwave photonic technologies. In microwave photonic approaches, the critical limitation is the close relationship between passbands-the tuning of one passband leads to a change in another, hindering the ability to independently control each passband. In this Letter, a programmable microwave photonic multiband filter with full control of amplitude, frequency, bandwidth, group delay slope, and the spectral shape of each passband has been experimentally demonstrated. A multiband filter design algorithm has also been developed that considers each RF passband as an individual, then uses inverse Fourier transform and filter design rule to determine the corresponding optical parameters and combines a series of shaped cosine functions to achieve the desired RF properties.