A coherently driven Kerr optical cavity is able to convert a continuous-wave laser to a sequence of ultrashort soliton pulses, enabling the generation of broadband and mode-locked frequency combs. Kerr cavity solitons are balanced through an energy exchange with the driving pump field. Improving the energy conversion efficiency from the pump to the soliton is of great significance for practical applications, but remains an outstanding challenge due to a limited temporal overlap between the soliton and the pump. Here, we report the discovery of temporal Kerr solitons in mutually coupled cavities instead of a traditional single cavity. We propose a strategy for breaking the limitation of pump-to-soliton energy conversion, and connect the underlying mechanism to impedance matching in radiofrequency electronic circuits. With macro optical fiber ring cavities which share the same physical model as miniature optical microresonators, we demonstrate nearly one-order improvement of the efficiency. Our findings pave the way towards super-efficient soliton microcombs based on optical microresonators with ultra-high quality factors. Dissipative solitons are localized particle-like structures which are double balanced by gain and loss, and nonlinearity and dispersion (or diffraction) [1], [2]. The study of dissipative solitons spreads in a large variety of different areas, has led to many exciting scientific findings and useful applications. Dissipative temporal solitons in coherently driven Kerr optical cavities have attracted great interest in recent years. The study arose in two different scenarios. One focused in the time domain, i.e., exciting and maintaining solitons to form optical buffers [3]; the other focused in the frequency domain, i.e., optical frequency comb generation with miniature microresonators [4]. The experimental demonstration of temporal cavity solitons was first performed in macro fiber ring cavities [3], and then repeated in optical microresonators [5], [6]. The researches from frequency and time domains then merged to a clear subject of cavity solitons [7], [8]. The discovery of microresonator solitons truly brings cavity solitons to a hot active research area because it enables integrated coherent frequency comb sources which may revolutionize many applications [9]- [17].Following the historical trend, the researches of cavity solitons nowadays have been performed on mainly two platforms. One is macro fiber ring cavities [3], [18]- [21]; the other is miniature optical microcavities [5], [8], [22]-[26]. In comparison, fiber cavities are more convenient for precise frequency detuning control and can be easily investigated in real time due to their much slower time scale; microresonators are particularly useful as compact frequency comb generators for practical applications. Previous studies have shown that both platforms share the similar physical model and useful technical hints may be learned from each other.

Microwave phased array antennas (PAAs) are very attractive to defense applications and high-speed wireless communications for their abilities of fast beam scanning and complex beam pattern control. However, traditional PAAs based on phase shifters suffer from the beam-squint problem and have limited bandwidths. True-time-delay (TTD) beamforming based on lowloss photonic delay lines can solve this problem. But it is still quite challenging to build large-scale photonic TTD beamformers due to their high hardware complexity. In this paper, we demonstrate a photonic TTD beamforming network based on a miniature microresonator frequency comb (microcomb) source and dispersive time delay. A method incorporating optical phase modulation and programmable spectral shaping is proposed for positive and negative apodization weighting to achieve arbitrary microwave beam pattern control. The experimentally demonstrated TTD beamforming network can support a PAA with 21 elements. The microwave frequency range is 8 ∼ 20 GHz; and the beam scanning range is ±60.2 • . Detailed measurements of the microwave amplitudes and phases are performed. The beamforming performances of Gaussian, rectangular beams and beam notch steering are evaluated through simulations by assuming a uniform radiating antenna array. The scheme can potentially support larger PAAs with hundreds of elements by increasing the number of comb lines with broadband microcomb generation.

We have designed and tested a laser-diode-pumped monolithic Nd:YAG oscillator. The electrical-to-optical slope efficiency was 6.5%. The frequency jitter was less than 10 kHz over a 0.3-sec period, the best frequency stability reported for a Nd:YAG laser to date.

We demonstrate a novel microwave photonic filter based on a non-coherent broadband optical source and the variable optical carrier time shift (VOCTS) method. Optical slicing which is essential conventionally is not employed in our scheme. Nevertheless, equivalent "electrical slicing" is performed by VOCTS, generating a passband free from the carrier-suppression effect. The baseband response is eliminated by using carrier-suppression or phase modulation. Single bandpass is also achieved due to the continuous-time sinusoidal impulse response. Detailed theoretical analyses are presented and agree with the experiments quite well.

A carrier phase-shifted (CPS) double sideband (DSB) modulation technique in radio-over-fiber (RoF) system is proposed and experimentally demonstrated. By tuning the biases in a single-drive dual parallel Mach-Zehnder modulator (SD-DPMZM), the optical carrier in the DSB spectrum acquires additional phase shift. The transmittance response of a dispersive RoF link is thus being controlled and shifted in the frequency domain. Experiments successfully turned the maximum transmission frequency to 10 GHz and 15 GHz for both 25 and 39 km fiber links. This is also a highly linear scheme, of which a spurious-free dynamic range (SFDR) of 111.3 dB·Hz^2/3 is experimentally obtained.