Microwave radomes exhibiting bandpass behavior are highly desirable for antenna systems. However, most of these radomes are not frequency switchable owing to their fixed structures. Here, a switchable metasurface based on complementary diamond-ring-shaped resonators is proposed for radomes. The microwave properties of the metasurface are investigated via simulations and experiments at X-band. By adjusting the rotation angle θ from 0° to 90°, the bandpass frequency is switched from 11.0 to 9.4 GHz. Two passbands appear for 0° <; θ <; 90°. In addition, the bandwidth can also be tuned by adjusting the rotation angle. This approach paves the way for designing switchable microwave radomes.

An optoelectronic oscillator (OEO) is an optoelectronic hybrid oscillator which utilizes ultra-low-loss fiber as an electro-magnetic energy storage element, overcoming the limits of traditional microwave oscillators in phase noise performance. Due to their ability to generate ultra-low phase noise microwave signal, optoelectronic oscillators have attracted considerable attentions and are becoming one of the most promising and powerful microwave signal sources. In this paper, we briefly introduce the operation principle and discuss current research on frequency stability and spurious suppression of optoelectronic oscillators.

To improve the frequency-drift compensation range for the stabilized optoelectronic oscillator, a novel stabilization scheme based on the frequency conversion pair has been proposed and experimentally demonstrated. The cavity length is adjusted by controlling the phase shift of oscillation signal at relative low frequency via frequency division and frequency multiplication. In the proof-of-concept experiment, a 10 GHz signal has been successfully generated with the phase noise about -123 dBc/Hz at 10 kHz offset frequency assisted by the external triggering. The optoelectronic resonant cavity is tuned at 5 GHz via divide-by-2 prescaler and frequency doubler, and the frequency compensation range can be enlarged more than 3 times compared with conventional phase-locked-loop based stabilization method. Finally, the stability of the locked optoelectronic oscillator is improved from 4.1×10-7 to 1.1×10-10 at 1000s averaging time.

A triple band frequency generator based on the optoelectronic oscillator (OEO) with low phase noise has been proposed and experimentally demonstrated. In this novel scheme, the phase-coherent triple band frequency in C, Ku and K bands can be achieved simultaneously by biasing the first modulator in the oscillation loop at the minimum transmission point (MITP) and the second modulator near the MITP with a small deviation. In the proof-of-concept experiment, the triple band frequency signals at 5.36, 16.08 and 21.44 GHz are generated with the phase noise of −123.32, −113.68 and −111.19 dBc/Hz at 10 kHz offset frequency, respectively. The proposed scheme provides a novel strategy for phase-coherent multi-band frequency and low phase noise signals generation, which can be potentially used in the multi-function and multi-band frequency electrical systems.

We experimentally demonstrate that multiple microcombs can coexist in monochromatically pumped Si₃N₄ microresonators. By pumping around the mode crossing using a CW laser with mixed polarization, three types of coherent microcombs are generated simultaneously: (i) TE-polarized soliton microcomb; (ii) TM-polarized Turing rolls microcomb; and (iii) cross-phase-modulation-induced TM-polarized microcomb. It is proved that the type-(iii) microcomb shares the same comb line spacing with the type-(i) microcomb although the free spectral ranges of TE and TM modes are different. In addition, a 22.95-GHz signal is extracted from a ∼100-GHz microresonator by heterodyning the TE and TM comb lines, and phase noise analysis reveals their coherence characteristics.

An optical vector network analysis (OVNA) based on double sidebands (DSB) modulation and the Pound Drever Hall (PDH) technique is proposed and demonstrated. The frequency responses measurement of the high Q optical device with high stability are achieved by transmitting the DSB modulation signals through the device. The high stability can be realized by using the PDH feedback loop. Compared with the conventional DSB-based OVNA, the proposed scheme with only one step measurement avoids the complex post-processing. Moreover, the long-term measurement with high stability can also be realized. A proof-of-concept experiment is carried out, which achieves the magnitude and phase responses of the Fabry-Perot interferometer, and there is no frequency response shift even though the test time is up to 90 minutes. The proposed method is simple and stable, which can be potentially applied in characterization and fabrication of high Q optical devices.