An adaptive delay calibration method for optical beamforming networks (OBFN) based on wideband sweep and windowed FFT spectrum analysis is proposed and demonstrated by simulation. With the FFT spectrum analysis of the wideband sweep signal, the delay difference between different channels in OBFN can be obtained continuously, and can be canceled adaptively by controlling variable optical delay lines(VODL), resulting in fast and high precision calibration for an OBFN. Furthermore, assisted by pilot carriers with multiple frequencies, the phase unwrapping can be achieved, and phase difference beyond 2π can be compensated. In order to demonstrate such method, a 16-arrayoptical beamforming simulation system is presented in this paper. Simulation results show that delay calibration range reaches467.1ps with the frequency range of 6-18 GHz. The delay calibration accuracy is increased by 50 times from5ps to 0.1ps. In addition, the number of simultaneous beamformer achieves to be 3, which covers the airspace from-30° to +30°.
A temporal convolution system for the short-time Fourier transformation (STFT) of an electrical signal based on a bidirectional chirped fiber Bragg grating (CFBG) is proposed and experimentally demonstrated. In this system, the electrical signal to be analyzed is applied to an electro-optical modulator to simultaneously modulate the temporal waveform and the spectrum of a time-stretched optical pulse, which is generated by a mode-locked laser and dispersed by a CFBG. The modulated optical signal is filtered to be several parts, added with separate time delays and sent to the other port of the same CFBG. Thus the optical signal is temporally recompressed and the spectrum of the electrical signal is able to be mapped into the time domain. The bidirectional CFBG realizes exactly complementary dispersion value for the optical pulse propagating in two opposite directions, which guarantees an optimal frequency resolution of the STFT system. An STFT experiment for a microwave signal with four different frequencies at 5 GHz, 10 GHz, 15 GHz and 20 GHz has been demonstrated.
KEYWORDS: Extremely high frequency, Photonics, Radar, Signal generators, Signal detection, Radar signal processing, Signal processing, Wireless communications
Multifunctional integration of electronic equipment is a main development trend in the future, wherein the integrated signal generation enables a key part. Therefore, it is of great significance to develop the generation of anti-jamming joint radar-communication (JRC) signal. Here, a photonics-assisted generation scheme of millimeter-wave (MMW) anti-jamming JRC signal is proposed. A large-bandwidth MMW dual-band agile JRC signal is generated based on a photonic MMW up-conversion and frequency permutation techniques. Meanwhile, thanks to the dual-band photonic radar de-chirping combined with coherent fusion method and low-cost communication self-coherent reception, the high resolution radar detection and communication with large amount of information are realized simultaneously. In the photonics-assisted JRC simulation system in W-band, a dual-band agile stepped-linear frequency modulation JRC signal covering 81-93 GHz is generated. Moreover, through a dual-band coherent fusion processing, the dual-band signals occupying with only a bandwidth of 2 GHz are successfully fused into an equivalent ultra-wideband signal with a bandwidth of 12 GHz, enabling a radar ranging with a resolution of 1.26 cm. Using a low-cost self-coherent reception, an anti-jamming wireless communication with factorial 10 is demonstrated, which can achieve up to 21.8 bits quantity of information.
A multi-beam optical beamforming network with low loss is proposed based on the integrated arrayed waveguide grating (AWG). By using the diffraction effect of AWG, the optical multiple beamforming architecture is reduced significantly since the true time delays for different wavelength can be realized simply by employing only one module. The 3 channels of 88 AWG for dense wavelength division multiplexing (WDM) with low loss is fabricated successfully, and then the integrated optical multiple beamformer for eight-element is demonstrated. Experimental results show that the insertion loss for each beamformer is reduced to 5.64 dB. Furthermore, the number of simultaneous beamformer achieves to be 4, which could cover the airspace from -36° to 18°.
KEYWORDS: Microwave photonics, Computer simulations, Computing systems, Data modeling, Digital signal processing, Microwave radiation, Radar signal processing, Antennas, Parallel computing
Due to the difficulty in simulation for massive array microwave photonics systems, a distributed cross-domain parallel simulation method is proposed in this paper. Firstly, the link parallel computation across system structural domains is achieved based on the independent transmission between channels for each array element in the microwave photonics system. Secondly, the data parallel computing across time domains is achieved by utilizing the relative independence between the pre and post processing times. Furthermore, assisting by a static load balancing strategy to allocate computational resources, these two approaches are effectively combined to achieve high efficient simulation of the microwave photonics system, which addresses the issue of long simulation time caused by large amounts of data and models. For a microwave photonics system with a 64-array and more than 400 models, this technique reduces the simulation time from 39 hours to 23 minutes, resulting in a simulation efficiency improvement of two orders of magnitude. This advancement holds the potential to significantly shorten the development cycle of microwave photonics engineering prototypes.
In this paper, a dispersion-assisted multi-functional scheme with compact structure and high cost-effectiveness based on microwave photonics is proposed. By virtue of the amplitude regulation mechanism of intermediate frequency signal induced by fiber dispersion, combined with the optical high-precision time delay matching, the image interference and the self-interference can be eliminated simultaneously. It avoids applying electrical tuning devices with lower precision and electrical couplers with limited bandwidth or extra optical filters which is beneficial to improve the system performance and compactness. It is also compatible with optical fiber transmission, which can be combined with radio over fiber technology to bring out the advantages of high spectrum utilization, distributed configuration and low loss transmission of in-band full-duplex radio over fiber systems.
For the true time delay (TTD) of optical fiber changes with temperature, integrated optical chips are proposed to improve the delay consistency among channels. A 5-bit TTD chip is proposed in this paper. By using cascaded switches and optical waveguides, the chip is switchable and wavelength independent. A beamforming system operating at 6GHz is established for demonstration. 7 beam directions covering ±15° is obtained with proper mainside lobe ratio.
The simultaneous distance and velocity measurement system based on a bidirectional chirped fiber Bragg grating (CFBG) is proposed. By using the bidirectional CFBG, a dual-chirp optical signal with large bandwidth is generated. After the dechirp processing in the optical domain, both the distance and velocity information can be obtained simultaneously. A simulation is carried out. A dual-chirp optical signal with a bandwidth of 0.208 THz is generated. The simultaneous distance and velocity measurement is achieved, with the ranging resolution of 0.9 mm and the velocity resolution of 0.058 km/s, respectively.
Frequency diverse array requires frequency offset between adjacent antenna elements. By using two coherent optical frequency combs, a series of microwave signals with stepped discrete frequencies are developed simultaneously. The proposed system is simplified for large arrays.
Broadband, free beam squinting and large scanning angle are essential for many applications. In views of these requirements, a tunable optical beam-forming for millimeter wave is proposed and demonstrated experimentally based on dispersive prism and variable optical delay line (VODL). Experiments are implemented with 1×4 antenna array operating at Ka band. Two beams are produced simultaneously for amplitude comparison direction finding. By tuning the relative delay of four VODLs, the beams can sweep across -30°~30°.
A wide-band microwave frequency shifter with high precision has been proposed and constructed based on paralleled PM and DP-MZM. PM is used to control the optical carrier phase that is driven by a sawtooth wave with a center frequency, while DP-MZM is used to generate a single-sideband suppressed carrier modulation. Results show that the frequency shift of kHz~GHz can be realized with the microwave carrier suppression of better than 50dB.
Comparing with the conventional double-sideband (DSB) modulation in communication system, single-sideband (SSB) modulation only demands half bandwidth of DSB in transmission. Two common ways are employed to implement SSB modulation by using optical filter (OF) or electrical 90° phase shift, respectively. However, the bandwidth of above methods is limited by characteristics of current OF and electrical phase shift. To overcome this problem, an ultra-wideband microwave photonic link based on SSB modulation is proposed and demonstrated. The radio frequency (RF) signal modulates a single-drive dual-parallel Mach-Zehnder modulator, and the SSB modulation is realized by combining an electrical 90° hybrid coupler and an optical bandpass filter. The experimental results indicate that the system can achieve SSB modulation for RF signal from 2 to 40 GHz. The proposed microwave photonic link provides an ultra-wideband approach based on SSB modulation for radio-over-fiber system.
A microwave photonic frequency downconverter is proposed and experimentally demonstrated based on an integrated polarization division multiplexing dual-parallel Mach-Zehnder (PDM-DPMZM) modulator. The radio frequency (RF) and the local oscillator (LO) signals are feed to the modulator through two electrical 90° hybrid couplers, respectively. The carrier suppress single sideband (CS-SSB) modulation can be achieved by adjusting the DC biases of the modulator. Then an intermediate frequency (IF) signal can be obtained by beating. The microwave photonic frequency downconversion link based on PDM-DPMZM is built. The result shows that both optical carrier sideband suppression ratio and sideband suppression ratio are over 20dB, and the spurious-free dynamic range achieves 98.0 dB·Hz2/3. No extra mixing spurs interferes the interested IF signal owing to the CS-SSB modulation. Besides, the proposed method has good isolation between the RF signal and LO signal.
A photonic microwave down-conversion approach is proposed and experimentally demonstrated based on a Mach-Zehnder modulator paralleled with a phase modulator. The incident radio frequency signal and the local oscillator signal are feed to the MZM and PM, respectively, and these two modulated optical signals interfere in the coupler. The useless higher-order sidebands are removed by a tunable optical band-pass filter. The principle of microwave frequency down-conversion is analyzed theoretically, the MZM and PM paralleled frequency down-conversion system is built. Then the performance of system is tested, and the experimental results show that the spurious-free dynamic range achieves 104.8 dB:Hz2/3. Compared to the conventional MZM-MZM cascaded system, the SFDR has been improved by 16 dB. The MZM and PM paralleled frequency down-conversion system can balance the intensity of the two coherent beams easily, and only single DC bias is needed. The proposed method possesses simple structure and high dynamic range.
In order to enhance conversion efficiency and spurious free dynamic range of microwave photonic link, we present a microwave photonic down-conversion system based on an integrated dual-parallel Mach Zehnder modulator (DPMZM) and microwave photonic filter. The principle of frequency down conversion is analyzed. We demonstrate the conversion efficiency of system through theoretical derivation and simulation. The performance of the microwave photonic link is tested experimentally. It is found that the spurious free dynamic range of the proposed method is up to 102.5dB/Hz2/3 and the conversion efficiency is up to -22.01dB. The integrated dual-parallel Mach-Zehnder modulator link can serve as a good alternative to improve the conversion efficiency and spurious free dynamic range.
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