Simultaneous magnetic field and temperature measurement with high resolution based on cascaded microwave photonic filters.

A simultaneous magnetic field and temperature sensing scheme based on cascaded microwave photonic filters (MPFs) with high resolution is proposed and experimentally demonstrated. A polarization maintaining fiber bonded with a giant magnetostrictive material acts both as a magnetic field sensing probe and an important unit of a dispersion-induced MPF. A 500 m single mode fiber in a two-tap MPF is used to perform temperature compensation. The power fading frequency of the dispersion-induced MPF and the dip frequency of the two-tap MPF are selected to monitor the magnetic field and temperature changes. When temperature changes, both power fading frequency and dip frequency will change. While only power fading frequency shifts as magnetic field changes. Consequently, dual parameter sensing can be achieved by monitoring the characteristic microwave frequencies of the two MPFs. The temperature cross-sensitivity is well resolved in this way. In the experiment, the microwave frequency changes 5.84 MHz as external magnetic field increases by 1 mT. The corresponded theoretical resolution can reach 0.17 nT, which is only limited by the minimum resolution of vector network analyzer.

Simultaneous modulation format identification and OSNR monitoring based on optoelectronic reservoir computing.

An approach for simultaneous modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) monitoring in digital coherent optical communications is proposed based on optoelectronic reservoir computing (RC) and the signal's amplitude histograms (AHs) obtained after the adaptive post-equalization. The optoelectronic RC is implemented using a Mach-Zehnder modulator and optoelectronic delay feedback loop. We investigate the performance of the proposed model with the number of symbols, bins of AHs and the hyperparameters of optoelectronic RC. The results show that 100% MFI accuracy can be achieved simultaneously with accurate OSNR estimation for different modulation formats under study. The lowest achievable OSNR estimation mean absolute errors for the dual-polarization (DP)-quadrature phase-shift keying signal, the DP-16-ary quadrature amplitude modulation (16QAM) signal, and the DP-64QAM signal are 0.2 dB, 0.32 dB and 0.53 dB, respectively. The robustness of the proposed scheme is also evaluated when the optoelectronic RC is in presence of additive white Gaussian noises. Then, a proof of concept experiment is demonstrated to further verify our proposed method. The proposed approach offers a potential solution for next-generation intelligent optical performance monitoring in the physical layer.

Sensitivity-improved fiber optic current sensor based on an optoelectronic oscillator utilizing a dispersion induced microwave photonic filter.

An optoelectronic oscillator (OEO)-based fiber optic current sensor (FOCS) with greatly improved sensitivity is proposed and experimentally demonstrated. A microwave photonic filter (MPF) induced by the dispersion effect of a linearly chirped fiber Bragg grating (LCFBG) is used to select the frequency of the OEO oscillating signal. A two-tap MPF formed by a polarization multiplexed composite cavity is cascaded to achieve a stable single mode oscillation. When the current changes, the magneto-optic phase shift induced by Faraday effect will be introduced between the left and right circularly polarized lights transmitted in the reflective sensing unit. The magneto-optic phase shift is converted to the phase difference between the optical carrier and sidebands through a LiNbO3 Mach-Zehnder modulator. This phase difference is the decisive factor for the center frequency of the cascaded MPF as well as the oscillating frequency. Therefore, the current can be measured in the microwave frequency domain, which can improve the interrogation speed and accuracy to a large extent. The experimental results show that the oscillating frequency shifts up to 407.9 MHz as the current increases by 1 A.

Linearity improvement of analog photonic link based on a phase-coherent orthogonal light wave generator.

This Letter presents a novel, to the best of our knowledge, linearized analog photonic link (APL) based on a phase-coherent orthogonal light wave generator that consists of a polarization-dependent Mach-Zehnder modulator (MZM) and a polarization controller (PC). By adjusting the PC and bias voltage of MZM, the third-order intermodulation (IMD3) terms can be suppressed while retaining a high gain for the fundamental terms, which indicates that the spurious free dynamic range (SFDR) of the proposed APL can be much improved. To further verify the feasibility of the proposed APL, a proof-of-concept experiment is performed, and the performances are compared with conventional APL. The experimental results demonstrate that a 14 dB improvement in the fundamental to IMD3 power ratio and an SFDR of 100.2dB⋅Hz2/3 or 119.1dB⋅Hz2/3 for a noise floor of -139dBm/Hz or -163.9dBm/Hz are achieved. In addition, an orthogonal frequency division multiplexing signal with 30 MHz bandwidth centered at 2.5 GHz is delivered by our proposed APL, whose signal-to-noise ratio is increased by 10 dB, compared to conventional APL.

High sensitivity demodulation of a reflective interferometer-based optical current sensor using an optoelectronic oscillator.

A novel, to the best of our knowledge, interrogation scheme based on an optoelectronic oscillator (OEO) with high sensitivity and high speed response for a fiber optical current sensor utilizing a reflective interferometer is proposed and experimentally demonstrated. Due to the Faraday effect, a magneto-optic phase shift induced by current variation is generated between two orthogonal light waves. The polarization-dependent properties of the Mach-Zehnder modulator are used to convert the magneto-optic phase shift into the phase difference between the optical carrier and sideband, which is then mapped to the oscillating frequency shift by closing an OEO loop. A high current sensitivity of 152.5 kHz/A with a range of 0-2.5 A is obtained in the experiment.

Scale factor improvement for angular velocity measurement based on an optoelectronic oscillator.

A scheme of angular velocity measurement with an improved scale factor is proposed and experimentally demonstrated based on the joint operation of a Sagnac loop and an optoelectronic oscillator (OEO). In this scheme, the Sagnac-induced phase difference is mapped into the oscillating frequency shift of the OEO with a large scale factor by making one of the two counter-propagating signals in the Sagnac loop carrier-suppressed modulated and the other just travel through the modulator. The cascaded Sagnac loop and OEO structure can further improve the scale factor by setting a long Sagnac loop and a short OEO loop independently. A sensitivity scale factor as high as 742 kHz/(rad/s) is obtained in our experiment.