A microwave photonic image rejection mixer (IRM) with large operation bandwidth and high image rejection ratio (IRR) is proposed and demonstrated based on a single dual-drive Mach-Zehnder modulator (DDMZM) and a wavelength division multiplexer (WDM). In the proposed scheme, the two radio-frequency (RF) ports of the DDMZM is driven by a RF signal and a local oscillator (LO) signal, respectively. Two intermediate-frequency (IF) signals are generated by beating the upper sideband and the lower sideband of the DDMZM, respectively. Then, the two IF signals are injected into an electrical 90° hybrid coupler (HC) to realize image rejection. In the experiment, a stable IRR above 60 dB in the RF signal frequency range of 10 GHz to 40 GHz and with a 1- GHz fixed IF signal frequency is achieved. When the IF signal frequency is changed from 1 GHz to 6 GHz and the LO signal is with a fixed frequency of 29 GHz, the IRR can also large than 60 dB.
Microwave photonics offers a promising solution to the increasing demand for high-frequency and broadband signals in battlefield communications. We propose a method for receiving broadband microwave signals with image-reject processing. The approach involves two main processes: signal reception and image-reject processing. In signal reception, the input broadband signal with a frequency span from DC to 40 GHz is multicast to three-tone signal optical carriers using a Mach-Zehnder modulator (MZM) biased at its minimum transmission bias point (MITB). Then, by using a three-tone local oscillator (LO) optical carriers to align with the corresponding modulation sidebands of the signal optical carriers, the input signal at any center frequency and with a bandwidth of 10 GHz can be demodulated after one capture. Hence, the full bandwidth of 40 GHz can be received by capturing the signal four times. In image-reject processing, the modulation sidebands of the signal carriers and the corresponding LO carriers are injected into an optical coherent receiver to achieve IQ demodulation. The generated in-phase (I) and quadrature (Q) signals are digitized and processed to suppress image interference. A numerical simulation is carried out to validate the proposed scheme. The simulation result indicates that the proposed scheme is capable of receiving broadband signals with a bandwidth of 40 GHz and its instantaneous bandwidth is equal to 10 GHz. Besides, the sensitivity and the dynamic range of the proposed system are equal to -85 dBm and 109.9 dB·Hz2/3, respectively. The proposed scheme is promising for enhancing the receive bandwidth and the sensitivity in electromagnetic spectrum sensing applications.
An approach to generating pulse trains with user-defined pulse positions in a phase-modulated optical frequency-shifting loop (OFSL) is proposed and experimentally demonstrated. In this method, the OFSL operates in the integer Talbot state, i.e., the repetition frequency of the driving waveform is equal to the free spectral range (FSR) of the OFSL. The phase of the optical field in the OFSL is manipulated by using an electro-optic phase modulator (PM) in each round trip. Then, pulses will be generated in the positions that the additional phase introduced by the PM is equal to an integer multiple of 2π in each round trip. Hence, the positions of the generated pulses can be controlled by designing the driving waveform. In the experiment, we firstly demonstrate the ability of the proposed scheme to control the pulse positions by applying four types of signals, namely, a linearly chirped waveform, a dual-chirp waveform, a quadratically chirped waveform, and a sinusoidal frequency-modulated waveform, to the PM. In addition, the proposed scheme can also be used to generate pulse trains with coded pulse positions. To verify this ability, two groups of coding sequences, i.e., “0101101110” and “1010010001,” are used to encode the pulse positions in a round-trip time of the OFSL. The proposed scheme can generate pulse trains with user-defined pulse positions, which can be used as a pseudo-random sampling source in compressed sensing (CS) systems.
KEYWORDS: Analog electronics, Signal processing, Signal to noise ratio, Signal attenuation, Modulation, Microwave radiation, Digital photography, Calibration, Nonlinear optics, Interference (communication), Microwave photonics
A linearization scheme in the digital domain for photonic sampling analog-to-digital converter (PS-ADC) is proposed and experimentally demonstrated, where a single-output Mach-Zehnder modulator (MZM) is used for photonic sampling instead of a dual-output MZM (DOMZM) in the traditional schemes. After frequency response calibration of the sampled signal in the digital domain, the optimal direct current (DC) component and the coefficient of sine function are found, and arcsine algorithm is performed to implement the linearization of PS-ADC. The theoretical results indicate that, compared with the differential and arcsine operation method generally employed in PS-ADC, the proposed scheme is facile to implement and decreases the system overhead. The feasibility of the scheme is verified by simulation and experiment. In the proof-of-concept experiment, for a single-tone microwave signal at 100 MHz with a modulation index of 0.45π, the second-order harmonic is suppressed below the noise floor, the third-order harmonic suppression ratio is enhanced by 17.14 dB, and the significant improvement in SINAD is equal to 7.91 dB.
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