As a new pulse compression signal, the phase-coded linearly frequency modulated (LFM) signal is proposed to faciliate multi-purpose radars. Here, we propose and demonstrate a phase-coded LFM signal generator, whose center frequency and bandwidth can be both adjusted. The phase-coded LFM signal generator is realized by feeding a phase-modulated optical signal into an optoelectronic oscillator (OEO). When the Fourier domain mode-locking is achieved, a phasecoded LFM signal is successfully generated. The center frequency and bandwidth of the generated microwave signal can be adjusted by changing the wavelength of the tunable laser source (TLS) and the peak-to-peak voltage of the driving signal, respectively. Experiment results show that a phase-coded LFM microwave signal with a center frequency of 9.5 GHz and a bandwidth of 5 GHz is successfully generated, whose TBWP is 5.6×105. To demonstrate the flexibility of the proposed scheme, the center frequency and bandwidth of the generated phase-coded LFM signal are adjusted to 12.4 and 2.6 GHz, respectively. The signal generator can be used in pulse compression radar in the future.
KEYWORDS: Optoelectronics, Microwave radiation, Oscillators, Waveguides, Frequency response, Silicon, Signal attenuation, Photonics, Signal generators, Solids
Parity‐time (PT) symmetry breaking offers mode selection capability for facilitating single‐mode oscillation in the optoelectronic oscillator (OEO) loop. However, most OEO implementations depend on discrete devices, which impedes proliferation due to size, weight, power consumption, and cost. In this work, we propose and experimentally demonstrate an on-chip tunable PT‐symmetric OEO. A tunable microwave photonic filter, a PT‐symmetric mode‐selective architecture, and two photodetectors are integrated on a silicon‐on‐insulator chip. By exploiting an on‐chip Mach–Zehnder interferometer to match the gain and loss of two mutually coupled optoelectronic loops, single‐mode oscillation can be obtained. In the experiment, the oscillation frequency of the on-chip tunable PT‐symmetric OEO can be tuned from 0 to 20 GHz. To emulate the integrated case, the OEO loop length is minimized, and no extra-long fiber is used in the experiment. When the oscillation frequency is 13.67 GHz, the single‐sideband phase noise at 10-kHz offset frequency is −80.96 dBc / Hz and the side mode suppression ratio is 46 dB. The proposed on-chip tunable PT‐symmetric OEO significantly reduces the footprint of the system and enhances mode selection.
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