Abstract
We propose and demonstrate a compact and cost-effective photonic approach to generate arbitrarily phase-modulated microwave signals using a conventional dual-drive Mach-Zehnder modulator (DDMZM). One arm (arm1) of the DDMZM is driven by a sinusoidal microwave signal whose power is optimized to suppress the optical carrier, while the other arm (arm2) of the DDMZM is driven by a coding signal. In this way, the phase-modulated optical carrier from the arm2 and the sidebands from the arm1 are combined together at the output of the DDMZM. Binary phase-coded microwave pulses which are free from the baseband frequency components can be generated when the coding signal is a three-level signal. In this case, the precise π phase shift of the microwave signal is independent of the amplitude of the coding signal. Moreover, arbitrarily phase-modulated microwave signals can be generated when an optical bandpass filter is attached after the DDMZM to achieve optical single-sideband modulation. The proposed approach is theoretically analyzed and experimentally verified. The binary phase-coded microwave pulses, quaternary phase-coded microwave signal, and linearly frequency-chirped microwave signal are experimentally generated. The simulated and the experimental results agree very well with each other.
Highlights
In modern radars, pulse compression is widely used to increase the range resolution
The other arm of the dual-drive Mach-Zehnder modulator (DDMZM) is driven by a coding signal
The schematic diagram of the proposed phase-modulated microwave signal generator is shown in Fig. 1(a), which consists of a laser diode (LD), a DDMZM, a tunable optical bandpass filter (OBPF) and a PD
Summary
Pulse compression is widely used to increase the range resolution. This technique permits the transmission of long phase-modulated microwave signals, leading to an efficient use of the average power capability of the radars and avoiding the generation of high peak power microwave pulses [1]. The two optical carriers can be separated into two orthogonal polarization states using a polarization maintaining fiber [10], a polarization modulator (PolM) [11], or a polarization beam combiner [12] In this way, arbitrarily phasemodulated microwave signals can be generated. The precise π phase shift of the microwave signal is determined by the amplitude of the coding signal and an electrical bandpass filter is required to remove the baseband frequency components [15]. The electrical bandpass filter [8] is no longer required In this case, the precise π phase shift is independent of the amplitude of the coding signal which is totally different from [15]. Binary phase-coded microwave pulses, quaternary phase-coded, and linearly frequency-chirped microwave signals are experimentally generated, which fit well with the simulated results
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