Light-matter-interaction is an intriguing research hotspot that covers the linear and nonlinear control of electromagnetic waves in various optical media. Since it is an immensely broad topic, our work focuses on the extra- and intra-cavity manipulation of ultrashort optical pulses by integrated and nanophotonic systems.
For extra-cavity approaches, the temporal Talbot effect is investigated due to its ability to multiplicate the repetition rate of a pulse train while preserving its spectrum, which is not achievable inside a laser cavity. We demonstrate for the first time, the temporal Talbot effect of dark pulse trains with unconventional bright-and-dark-pulse mixing patterns by a commercial wave shaper and single-mode fibres, revealing a novel type of temporal Talbot effect. Then we consider the on-chip realization of bright and dark Talbot pulses. We show that the size of a Talbot-generating device can be significantly reduced by two-stage Mach-Zehnder interferometers on a silicon nitride photonic integrated chip (PIC). The presented PIC can switch between a pass-through and the Talbot mode by tuning the thermo-optic actuators. The proposed technology is highly scalable. It will provide new possibilities for future Talbot effect studies and for applications such as optical signal processing, encoding, and decoding in ultrafast communications.
For intra-cavity part, we study the novel behaviours of optical pulses with epsilon-near-zero (ENZ) effects in nanophotonic indium-tin-oxide. Unlike in the extensive extra-cavity studies, the rarely-investigated intra-cavity environment allows ENZ materials to interact with light accumulatively under a weaker pump fluence, while preserving the benefit of having enhanced electric field and nonlinearity. Firstly, we unveil a novel mode-lock wavelength reselection mechanism by intra-cavity ENZ components: their ENZ wavelengths are imprinted in the lasing wavelength shifts. This proposed experiment is expected to be further improved by in-situ ENZ wavelength modulation by electro- and thermo-optic tunabilities of the media. We present an attempt on the ENZ electro-optic tunability by fabricating a metal-on-oxide multilayer device. Although the device does not function as expected due to experimental constraints, we gained a deeper understanding on ENZ electro-optic tunability. As an alternative to electro-optic tunability, we investigated the reversible thermo-optic tunability under annealing threshold for the first time. It is found that the linear thermo-optic effect and the ultrafast thermo-optic nonlinearity are greatly enhanced by an order of magnitude under the ENZ conditions. These thermo-optic ENZ effects are broadband and have an ultrafast consideration threshold which was thought to be slow in conventional media. The findings of the thermo-optic ENZ effects are useful as a prerequisite reference design for future packaged electro-optic integrations. To demonstrate the potential applications of the intra-cavity ENZ effects, we realize a dual-range frequency switching operations with a high frequency conversion efficiency. These features allow programmable multiple commutative and non-commutative logic functions in a single setup. The results might provide an insight into not only the ultrafast nonlinear ENZ photonics itself, but also reveal a pathway towards novel nanophotonic on-chip optical devices of various logical and operational functions.