An optically tunable optoelectronic oscillator (OEO) with a wide frequency tunable range incorporating a tunable microwave photonic filter implemented based on phase-modulation to intensity-modulation conversion using a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. The PS-FBG in conjunction with two optical phase modulators in the OEO loop form a high-Q, wideband and frequency-tunable microwave photonic bandpass filter, to achieve simultaneously single-frequency selection and frequency tuning. Since the tuning of the microwave filter is achieved by tuning the wavelength of the incident light wave, the tunability can be easily realized at a high speed. A theoretical analysis is performed, which is verified by an experiment. A microwave signal with a frequency tunable from 3 GHz to 28 GHz is generated. To the best of our knowledge, this is the widest frequency tunable range ever achieved by an OEO. The phase noise performance of the OEO is also investigated.

A Wideband Frequency Tunable Optoelectronic Oscillator Incorporating a Tunable Microwave Photonic Filter Based on Phase-Modulation to Intensity-Modulation Conversion Using a Phase-Shifted Fiber Bragg Grating

In this paper, major photonic microwave generation and modulation methods are described. Their advantages and limitations are identified and compared through the analysis of the key characteristics relevant to practical photonic microwave applications. The focus of this paper is on the photonic microwave based on the nonlinear dynamics of optically injected semiconductor lasers. Both single-beam optically injected semiconductor lasers and dual-beam optically injected semiconductor lasers are considered. In particular, the three dynamic states of stable injection locking, period-one oscillation, and period-two oscillation are considered and demonstrated for photonic microwave generation, modulation, and conversion applications. Several prospects for future research and development in this area are discussed.

Photonic Microwave Applications of the Dynamics of Semiconductor Lasers

The broad bandwidth and low loss offered by modern photonics have led to an ever-increasing interest in the design and implementation of photonically assisted systems for the genera- tion, processing, control and distribution of microwave signals, an area called microwave photonics. In this article, a tutorial on microwave photonics is presented with an emphasis on photonic true-time delay beamforming, radio-over-fiber and UWB-over- fiber distribution and photonic analog-to-digital conversion.

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A Tutorial on Microwave Photonics

Besides distinct features on RF/optical signal generation, optoelectronic oscillators (OEOs) have also been rapidly developed as emerging techniques towards sensing, measurement, and detection. In this paper, we start with the conceptual architecture and the analytical model of OEOs. Then, three operation principles behind sensing, measurement, and detection applications are categorized, including the variation on the time delay of loop, the passband reconfiguration of microwave photonic filter in loop, and the oscillation gain from injection locking, which clearly clarify the X-to-frequency mapping (X denotes target parameter or signal) for supporting practical solutions and approaches. Next, a comprehensive review to advances in OEO-based sensing, measurement, and detection applications is presented, including length change and distance measurement, refractive index estimation, load and strain sensing, temperature and acoustic sensing, optical clock recovery, and low-power RF signal detection. As a new application example, a novel approach for in-line position finding is proposed. When a long fiber Bragg grating inserted into OEO is locally heated to slightly broaden its reflection spectrum, the target position heated is mapped into the oscillating frequency shift, according to the first operation principle. A sensitivity of 254.66 kHz/cm is obtained for position finding in the experiment. Afterward, solutions for calibration and stabilization are briefly introduced, which enable us to improve the accuracy and reliability. Finally, features and future prospects on the sensing, measurement, and detection applications are discussed, such as compact and integrated OEOs.

Optoelectronic Oscillators (OEOs) to Sensing, Measurement, and Detection

An optically tunable optoelectronic oscillator (OEO) implemented by employing a two-port optical phase modulator without using any electronic microwave filters is proposed and experimentally demonstrated The key device in the system is the two-port phase modulator, which functions, in conjunction with a dispersive element in the loop, to form a high-Q microwave filter to perform microwave frequency selection The central frequency of the microwave filter is a function of the optical wavelength and the chromatic dispersion of the dispersive element, therefore, the oscillation frequency can be simply tuned by tuning the wavelength of the laser source or the chromatic dispersion of the dispersive element A theoretical analysis is provided, which is verified by experiments The phase noise performance and the frequency tunability are both experimentally investigated

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An Optically Tunable Optoelectronic Oscillator

A dual loop optoelectronic oscillator (OEO) is able to effectively suppress the sidemodes in each single loop. In this paper, a dual-loop OEO scheme is reported. By utilizing a polarization-beam splitter and a polarization-beam combiner, the two loops are directly joined in the optical domain without adding any active electrical device. The laser's phase-to-intensity noise is discussed. We present free-running experimental results, which show a phase noise of -109 dBc/Hz at 10kHz away from the carrier (12 GHz) and a Q value of 1010 with a sidemode suppression ratio of 60 dB, which is improved by 30-50dB in the experimental comparison. Meanwhile, the experimental comparison indicates that no significant noise is introduced by this configuration

An Optical Domain Combined Dual-Loop Optoelectronic Oscillator

The functional corticomuscular coupling (FCMC) is defined as the interaction, coherence and time synchronism between cerebral cortex and muscle tissue, which could be revealed by the synchronization analyses of electroencephalogram (EEG) and electromyogram (EMG) firing in a target muscle. The FCMC analysis is an effective method to describe the information transfer and interaction in neuromuscular pathways. Forthermore, the multiscaled coherence analyses of EEG and EMG signals recorded simultaneously could describe the multiple spatial and temporal functional connection characteristics of FCMC, which could be helpful for understanding the multiple spatial and temporal coupling mechanism of neuromuscular system. In this paper, based on the adaptively decomposing signal into frequency band characteristis of variational mode decomposition (VMD) and the quantitatively detecting the directed exchange of information between two systems of transfer entropy (TE), a new methodvariational mode decomposition-transfer entropy (VMD-TE) is proposed. The VMD-TE method could quantitatively analyze the nonlinear functional connection characteristic on multiple time-frequency scales between EEG over brain scalp and surface EMG signals from flexor digitorum surerficialis, which are recorded simultaneously during grip task with steady-state force output.In this paper, application of VMD-TE method consists of two steps. Firstly, the EEG and EMG signals are adaptively decomposed into multi intrinsic mode functions based on variational mode decomposition method, respectively, to describe the information on different time-frequency scales. Then the transfer entropies between the different timefrequency scales of EEG and EMG are calculated to describe the nonlinear corticomuscular coupling characteristic in different pathways (EEGEMG and EMGEEG), to show the functional coupling strength (namely VMD-TE values). finally, the maximum VMD-TE values between the different time-frequency scales of EEG and EMG signals among the eight subjects are selected, to describe the discrepancies of FCMC interaction strength between all time-frequency scales. The results show that functional corticomuscular coupling is significant in both descending (EEGEMG) and ascending (EMGEEG) directions in the beta-band (15-35 Hz) in the static force output stage. Meanwhile, the interaction strength between EEG signal and the gamma band (50-72 Hz) of EMG signal in descending direction is higher than in ascending direction. Our study confirms that the beta oscillations of EEG travel bidirectionally between sensorimotor

Functional coupling analyses of electroencephalogram and electromyogram based on variational mode decomposition-transfer entropy

The mathematical expression of DOP with DGD for pseudo random m sequence code using Gauss pulses was derived.Then the relationship was theoretically analyzed and simplified.The result shows that the relationship between DOP and DGD is independent of chirp and fiber dispersion and can be determined by the FWHM of the optical spectrum.Experiments with 10Gbit/s RZ seven stages′ m sequence was given,theoretical calculation and experimental results were compared.The comparison shows that they match closely.

Zhang Li-Tai

Papers

An Optical Domain Combined Dual-Loop Optoelectronic Oscillator

Functional coupling analyses of electroencephalogram and electromyogram based on variational mode decomposition-transfer entropy

Analysis of DOP-DGD for Sequence of Gaussian Pulses