Photonic technology can be applied for processing wideband signals in RF system, which can overcome some difficulty in traditional RF and digital signal processing systems. RF signal power can determine the ability of RF photonic system. When input RF signal power arrives to a great extent, the photonic system can provide some new frequency terms because of nonlinear effects. In this paper, nonlinear characteristics of RF photonic processing system are investigated, and results in theory and experiment are demonstrated.
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.
As an important method of signal receiving and processing, acousto-optic receiver can intercept wideband signal in RF domain. A large number of narrow channels for measuring RF signal can be realized by acousto-optic Bragg diffraction. The weak signal detection with high sensitivity can be implemented using time integrating photodetector array. In this paper, the principle and characteristics of time integrating acousto-optic receiver are investigated. The acousto-optic receiver with 1GHz bandwidth is demonstrated in experiment.
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.
An optical channelized receiver (OCR) with a novel structure based on two coherent optical frequency combs (OFCs) and a Fabry-Perot (FP) filter has been proposed. Input wideband signals are multicasted in all optical channels by modulating one OFC. Then, different sub-frequency bands in all optical channels are filtered out by the FP filter. Finally, the sub-frequency bands are directly converted to intermediate frequency (IF) via coherent optical heterodyne with the LO provided by another OFC. Experiment results shows that the OCR works in X band with 8 channels, and the bandwidth of each channel is 500MHz, which means the instantaneous bandwidth of the OCR is 4GHz. The max power fluctuation between different channels is 4dB, which can be improved by adding proper attenuators to certain channels. The spurious free dynamic range (SFDR) of all channels is above 44dB under noise bandwidth of 1MHz, which equals to 84 dB·Hz2/3.
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°.
RF photonic link can provide significant benefits in transmitting and distributing RF signals to many separating stations by optical fiber. However, phase noise of transmitted RF signal in electrical-optical-electrical conversions is generally deteriorated by related optical noise. In this paper, a theoretical model about phase noise of RF photonic link is built, and the expressions and characteristics about phase noise are investigated. In the RF photonic link, phase noise is investigated for 100MHz RF signal. The experimental results can agree with the theoretical analysis.
Laser plasma produced with high-intensity picosecond laser pulse like proton source for radiography was investigated. It was found that maximum particle output and best possible spatial uniformity of proton beam took place for two-layer target when the front layer was the high-Z film. It was shown that the ion radiography of the convenient objects with using the two-layer targets allow to get the projecting pictues with high spatial resolution that was about one micron. The explanation of such high spatial resolution is in laminar motion of ion flow. Threshold spatial sensitivity of proton radiography is estimated.
Ytterbium-doped silica fibers exhibit very broad absorption and emission bands, from 800nm to 1064nm for absorption and 970nm to 1200nm for emission. Therefore wide band lasers can be obtained using a wide variety of pump lasers. In this paper, the characteristics of high-doped Yb3+ fiber are analyzed and verified by experiment and a highly-doped Yb3+ fiber ring laser with short cavity has been presented. Comparing with normal Yb3+doped fiber, the relationship between the important characteristics of the Yb3+doped fiber laser such as threshold power, output power and laser parameters such as pump power, fiber length, output couple ratio is analyzed. Numerical results are coincident with the experiment phenomenon very well. A 1053 nm pulse has been achieved in our fiber laser. The output power is 6mW as pump power is 110mW and the slope efficiency is 17%. The Yb3+ fiber laser we produced can be used as a stable source in obtaining ultrafast pulse, fiber sense and optical communications.
Theory and experimental results on the self-starting passive mode-locked Yb fiber ring laser generating short pulse are reported. The relations between the laser cavity parameters and mode-locked pulse characters are discussed. 980nm LD pumped laser is used as the pump source and high concentration Yb3+-doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained, with center wavelength of 1046nm, 3dB bandwidth of 6.01nm and 20dB bandwidth of 16nm. The mode-locked threshold power is 150mW and output power is 26mW with 50MHz repetition rate.