A method of dual-broadband signal generation based on the same optoelectronic oscillator with different tuning mechanisms is proposed in this paper. The structure includes a compatible dual-passband microwave photonic filter based on stimulated Brillouin Scattering effect (SBS) and phase-shifted Bragg fiber (PS-FBG). By implementing the Fourier-domain mode-locked mechanism, the proposed optoelectronic oscillator can simultaneously generate signals in different frequency bands with adjustable center frequency and bandwidth. The effectiveness of the proposed method is verified by experiments. Oscillating signals with bandwidth of 600 MHz and center frequencies at 5 GHz and 6 GHz are generated.
A microwave photonic (MWP) pulse radar system for high-resolution target detection is proposed and experimentally demonstrated in this article. In the transmitter, a pulsed linearly-frequency-modulated (LFM) wave is generated based on optical frequency operation module (OFOM), which can generate LFM waves with ultra-flexibly tunable center frequency. In the receiver, optical-domain down-conversion is employed to convert the incoming echo to an intermediate frequency signal by a microwave photonic frequency mixer, which can free the receiver from high-speed ADC and provide an excellent wideband processing. Experimentally, a Ku-band pulsed LFM wave with a bandwidth of 840 MHz is generated and received through self-closed-loop and target detection test by the constructed system. The performance verifies that the proposed pulsed MWP radar has the potential of supporting high-resolution detection and recognition of distant targets.
A single sideband (SSB) phase-modulated link with an improved spurious-free dynamic range (SFDR) is proposed and experimentally demonstrated. By generating a single-sideband phase-modulated signal containing a specific spectrum for demodulation, the third-order intermodulation distortion (IMD3) is effectively suppressed. The theoretical analysis is presented, and the experimental results show that a carrier-to-interference ratio of 62.45 dB is achieved. The improved SFDR is 120.25 dB · Hz4/5, which is 14.47 dB higher than that of a conventional SSB phase-modulated link.
An ultra-wideband random OEO using both stimulated Brillouin effect and Rayleigh scattering effect is proposed, which can generate random oscillating microwave signals covering all frequency bands. By using stimulated Brillouin scattering effect to amplify weak reverse Rayleigh scattering, the microwave signals with random characteristics which is independent of fixed cavity length can be generated. Experimentally, the work realized the generation of ultra-wideband (DC up to 32 GHz) random microwave signals. Compared with previous methods,the proposed random OEO mechanism is realized in an easier way, which can avoid using 1450 nm laser and promote its application in electronic interference.
With the rapid development of microwave photonic technology in recent years, microwave photonic radar can generate and process signals far beyond the relative bandwidth of traditional radar, and can achieve centimeter-level resolution when imaging. However, the echo characteristics of microwave photonic radar are quite different from those of traditional radar, which degrades the performance of traditional imaging algorithms. Therefore, it is crucial to propose an imaging algorithm that is compatible with the characteristics of microwave photonic imaging radars. This paper first summarizes the development of microwave photonic imaging radar. Then analyzes the typical problems in the imaging process of microwave photonic radar, and proposes corresponding solutions to these problems. Finally the processing results of some measured data of microwave photonic imaging radar are shown.
KEYWORDS: Radar, Microwave photonics, Signal generators, Receivers, Digital signal processing, X band, Modulation, Transmitters, Optical filters, Ku band
A coherent dual-band microwave photonic (MWP) radar system is proposed and experimentally demonstrated in this paper. In the transmitter, coherent dual band linear frequency modulation (LFM) waves with the characteristics of tunable central frequency and the same large bandwidth are generated based on an improved optical frequency operation module (OFOM). In the receiver, the information of targets is obtained after the echoes at two bands are received and de-chirp processed simultaneously. Experimentally, the presented coherent dual-band MWP radar system operating in X band and Ku band with an instantaneous bandwidth of 3GHz is constructed. A target-detection experiment verifies that centimeter level resolution can be achieved by the system.
A phase-coded microwave signal generation method based on parallel Mach-Zehnder modulator (MZM) with tunable frequency multiplication factor is proposed and demonstrated. By controlling the modulation index and the optical power ratio of the parallel MZMs, phase-coded microwave signals with frequency multiplication factors of 1, 3 and 5 are obtained. The feasibility of this approach is demonstrated by theoretical analysis and simulation, in which binary phase-coded signals with carrier frequency of 1GHz, 3GHz or 5GHz are respectively generated under 1GHz radio frequency (RF) signal input.
We propose and experimentally demonstrate a pulse radar signal generation based on the Fourier domain mode-locked optoelectronic oscillator (FDML-OEO). In this method, two low-frequency control signals generated by a direct digital synthesizer (DDS) are adopted to control the tunable laser source (TLS) and the bias voltage of Mach-Zehnder modulators (MZM) respectively. The broadband pulse signals are generated by directly truncating the broadband signals on the basis of a FDML-OEO by controlling the frequency and amplitude of the bias voltage of the MZM. In the experiment, the broadband radar pulse signals with tunable duty cycle and the center frequency are demonstrated. In particular, the center frequency of signals are tuned by changing the initial phase of pulse driving signal and the triangular wave or the wavelength of TLS, which have greatly potential in improving the detection capability of the radar system.
Complex electromagnetic environment in the future battlefield requires spectrum sensing equipment to have broadband and high-resolution measurement capabilities. This paper proposes a microwave photonic frequency measurement method based on optical spectrum operation and stimulated Brillouin scattering. The use of optical spectrum operation is to realize generating pump light in a large range, so as to realize the excitation of stimulated Brillouin scattering in a wide spectrum range, and further the stimulated Brillouin scattering is employed to realize high-resolution frequency sensing. The principle of this method is given and the feasibility of the method is verified experimentally. Experiment results show the measurement capability of the proposed method covers a frequency range of 0.03–40 GHz with a resolution of 25 MHz. The proposed method can effectively support high-resolution frequency sensing in complex electromagnetic environments.
A simple single sideband (SSB) analog optical link with enhancement spurious free dynamic range (SFDR) is proposed. By coupling the independent optical carrier and +1st, +2nd order phase-modulated optical sidebands to be demodulation, the suppression of IMD3 is achieved. An theoretical model is established and the simulation results show that the carrier-to-interference ratio (CIR) presents a 32dB improvement and the corresponding improved SFDR is 123.5 dB·HZ2/3 , which is 18.6 dB larger than that of conventional single sideband phase-modulated link. In particular, the proposed SSB link can avoid the periodic power attenuation caused by dispersion, presenting great potential usage in modern radar system.
Detecting targets with long distance and high resolution is the goal of radar techniques. Traditional electrical radar which has a long working distance always work at low frequency and thus has a limited bandwidth. We demonstrate a microwave photonic radar system which can realize larger bandwidth at low-frequency band based on optical-domain frequency operation. P-band and C-band radio-frequency (RF) signals with 700-MHz and 4-GHz bandwidths, respectively are generated, while the latter is adopted to detect space-separated corner reflectors to demonstrate the effectiveness of the proposed system.
A photonic approach to generate triangular frequency modulated microwave waveform (TFMMW) using frequency-scanning (FS) laser and dual-output dual-parallel Mach-Zehnder modulator (DO-DPMZM) is proposed and demonstrated. In the scheme, a DO-DPMZM followed by a time delayer and a polarization beam combiner is utilized to generate orthogonally polarized -1rst-order sideband and +1rst-order sideband with time delay. After that, a TFMMW with large time-bandwidth product (TBWP) can be generated by photoelectric balanced detection. In the simulation experiments, Ka band TFMMW with TBWP of 9830.4 is generated and its ambiguity function is investigated
An optical length measuring method exploiting microwave interrogated cascaded fiber Mach-Zehnder interferometer (MZI) is proposed. The frequency response of the filter with respect to the fiber length change of MZI is studied and an length measuring sensitivity of 2.580 GHz/mm is obtained. The proposed sensing configuration is with high sensitivity, easy to implement and shows the capability for other parameters measurement such as temperature, strain, and vibration.
An approach for photonic generation dual-chirp microwave waveform (DCMW) with frequency and bandwidth multiplication without filtering is proposed and demonstrated. A continuous-wave (CW) optical signal is sent to a polarization division multiplexing modulator. In the modulator, one part of the CW optical signal is modulated by the radio-frequency (RF) driving signals to generate ±2 nd-order single-frequency sidebands, while another one is modulated by the baseband chirped signals to generate ±2 nd-order chirped sidebands. After that, a frequency-doubled and bandwidth-quadrupled DCMW can be generated by photoelectric balanced detection. In the simulation experiments, by using a RF driving signal at 5GHz and a baseband single-chirp signal with bandwidth of 0.5GHz as the input electrical signals, a DCMW with central frequency of 10GHz and bandwidth of 2GHz is generated.
Generation of phase-coded chirped microwave waveforms by an improved frequency-sweeping optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In the proposed system, an upgraded frequency-sweeping OEO has function to generate not only a linearly chirped microwave waveform (LCMW) but also to output an optical sideband and the latter is then modulated in phase by a binary phase-coded electrical signal. By beating the phase modulated signal and a portion of the frequency-sweeping laser light at a high-speed photodetector, a phase-coded chirped microwave waveform is generated. In order to realize large time-bandwidth product (TBWP), the key significance of the improved frequency-sweeping OEO is that a near-zero-dispersion single-mode-fiber (SMF) introduced into the loop which can not only avoid the limitation of high frequency oscillation caused by dispersion, but also construct long OEO delay loop to realize large time duration. Finally, phase-coded chirped microwave waveform with a bandwidth of 6 GHz and a TBWP of 130,392 is experimentally demonstrated.
Photonic generation approach of linearly chirped microwave waveform(LCMW) with tunable frequency and bandwidth multiplication factor(FBMF) based on parallel Mach-Zehnder modulator(MZM) is proposed. Theoretical analysis show that LCMW with FBMF of 4, 8 and 12 can be obtained by properly adjusting the amplitude of linearly chirped microwave drive signal and direct current(DC) drive signal. The scheme greatly reduce the frequency and bandwidth of electrical linearly chirped microwave drive signal. Due to no filter is employed, so the generation LCMW has a large frequency and bandwidth tunable range. Furthermore, the feasibility of the approach is demonstrated by the simulation based on OptiSystem platform.
KEYWORDS: Modulators, Microwave photonics, Modulation, Intermodulation, Phase shift keying, Radio optics, Single mode fibers, Signal attenuation, Phase modulation, Local area networks
A novel phase modulator-based microwave photonics link (MPL) with improved spurious-free dynamic range (SFDR) is proposed, in which a parallel optical sideband processing path is used to generate the opposite third-order intermodulation distortion (IMD3) for destructive combination. By controlling the magnitude of the generated IMD3 term via attenuator in one path, the suppression of IMD3 term was achieved. A theoretical analysis is presented and the simulation experiment results indicate that the SFDR is up to 128.582 dB•HZ2/3, which has an improvement of 23.66 dB compared with the nonlinearized link.
A Ka-band microwave photonic imaging radar demonstrator with 10.02 GHz-bandwidth is proposed and experimentally demonstrated. Continuous linear frequency waveform is optically generated in the transmitter and processed in the receiver. The range resolution of the demonstrator is tested to be 1.68 cm. Out-field tests while demonstrator works at inverse synthetic aperture radar (ISAR) and synthetic aperture radar (SAR) mode are carried out to image different targets.
Optical visualization of Alzheimer’s disease (AD) pathological changes is crucial to facilitate exploration of disease mechanism and treatment. We developed cryo-micro-optical sectioning tomography (cryo-MOST) to acquire brainwide map of senile plaques. Using intrinsic fluorescence emission intensified under ultra-low temperature, we accomplished senile plaque visualization at a micron-level resolution. A whole-brain coronal distribution of senile plaque in a transgenic mouse was successfully acquired without any exogenous dye. We believe cryo-MOST would be a potential tool for understanding neurodegenerative disease mechanism and evaluating drug efficacy.
The redox metabolism is variable and complicated with the progress of tumor development. Whether the tumor redox state will affect the exogenous gene expression or not, are still not clear now . To investigate the relationship between tumor endogenous redox state and the exogenous gene expression level, a far red fluorescent protein fRFP was used to monitor tumor cells proliferation and as an exogenous protein expression in tumors. NADH (nicotinamide adenine dinucleotide) and Fp (flavin protein) are two important coenzymes in the mitochondria respiratory chain, which can be as a standard representation for redox metabolism state. Three tumor subcutaneous models (melanoma, human pancreatic carcinoma and nasopharyngeal carcinoma) were used to observe their redox state and protein expression by our home-made redox scanner. The results showed that the distribution of fRFP fluorescent protein expression in the inner tumor regions are heterogeneous, and the fluorescent intensity of fRFP and the fluorescent intensity of NADH have high correlation. In addition, we also found the linear coefficient in three tumors are different, the value of coefficient is (R2 = 0.966 and R2 = 0.943) in melanoma, (R2 = 0.701 and R2 = 0.942) in human pancreatic carcinoma, and (R2 = 0.994) in nasopharyngeal carcinoma, respectively. From these results, we consider that the exogenous protein expression of fRFP in tumor had some relationship with the tumor redox state of NADH.
Cryo-imaging techniques have been widely used to measure the metabolic state of tissues by capturing reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) autofluorescence. However, NADH and FAD fluorescence is sensitive to changes in temperature, which may result in unreliable redox ratio calculations. Here, the relationship between the measured redox ratio and sample surface temperature was analyzed using a standard phantom solution and biological tissues. The results indicated that a temperature <−100°C was a suitable cryo-imaging temperature window in which redox ratio measuring was immune to temperature fluctuations. These results may serve as a reference for designing and optimizing redox cryo-imaging experiments for quantitatively mapping the metabolic state of biological samples.
KillerRed is a unique red fluorescent protein exhibiting excellent phototoxic properties. It has the ability to produce reactive oxygen species (ROS), for killing tumor cells in vitro upon laser irradiation and has the potential to act as a photosensitizer in the application of tumor therapy. Here, we investigated the effects of KillerRed-based photodynamic therapy (PDT) on tumor growth in vivo and examined the subsequent tumor metabolic states including the changes of pyridine nucleotide (PN) and flavoprotein (Fp), two important metabolic coenzymes of tumor cells. Results showed that the tumor was scabbed in response to 561 nm laser irradiation at 80 mV for 3 min, and the tumor growth had been significantly inhibited by KillerRed-based PDT treatment compared to control groups. More importantly, a home-made cryo-imaging redox scanner was used to measure intrinsic fluorescence and exogenous KillerRed fluorescence signals in tumors. The flavoprotein was remarkable elevated and the PN was seldom increased with concomitant photobleaching of KillerRed fluorescence after irradiation, suggesting that flavoprotein and PN were oxidized in the course of KillerRed-based PDT.
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