The heterogeneous integration of photonic integrated circuits (PICs) with a diverse range of optoelectronic materials has emerged as a transformative approach, propelling photonic chips toward larger scales, superior performance, and advanced integration levels. Notably, two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), and hexagonal boron nitride (hBN), exhibit remarkable device performance and integration capabilities, offering promising potential for large-scale implementation in PICs. In this paper, we first present a comprehensive review of recent progress, systematically categorizing the integration of photonic circuits with 2D materials based on their types while also emphasizing their unique advantages. Then, we discuss the integration approaches of 2D materials with PICs. We also summarize the technical challenges in the heterogeneous integration of 2D materials in photonics and envision their immense potential for future applications in PICs.

We demonstrate high-quality (intrinsic Q factor ∼2.8 × 10⁶) racetrack microresonators fabricated on lithium niobate thin film with a free spectral range (FSR) of ∼86 pm. By integrating microelectrodes alongside the two straight arms of the racetrack resonator, the resonance wavelength around 1550 nm can be red shifted by 92 pm when the electric voltage is raised from -100 V to 100 V. The microresonators with the tuning range spanning over a full FSR are fabricated using photolithography assisted chemo-mechanical etching.

Spatio-temporal coupling characteristics of ultrafast laser pulses are quantitatively tailored. An asymmetric microstructure is induced in the focal volume when the laser scans perpendicularly to the direction of the spatial chirp in fused silica. The tilted direction reverses when adding a Dove prism into the light path. The sign of the pulse front tilt can be turned from positive to negative by changing the group delay dispersion by steps. We reveal that the tilted direction of a microstructure depends on spatial chirp, and the interplay between spatio-temporal chirp leads to the change of tilted angles.

We report on an experimental investigation on the dynamic decoherence process of molecular rotational wavepackets during femtosecond laser filamentation based on time-dependent mean wavelength shifts of a weak probe pulse. Details of periodic revival structures of transient alignment can be readily obtained from the measured shifted spectra due to the periodic modulation of the molecular refractive index. Using the method, we measured decoherence lifetimes of molecular rotational wavepackets in N2 and O2 under different experimental conditions. Our results indicate that decoherence lifetimes of molecular rotational wavepackets are primarily determined by the relative population of rotational states in the wave packet and intermolecular collisions, rather than the focusing intensity.

We experimentally investigate the generation of above-threshold harmonics completely from argon atoms on an excited state using mid-infrared femtosecond laser pulses. The highly nonlinear dependences of the observed signal on the pulse energy and polarization of the probe laser pulses indicate its nonperturbative characteristic.

We experimentally demonstrate N2+ lasing actions at the wavelengths of 353.3, 353.8, and 354.9 nm using a circularly polarized femtosecond laser. The three laser lines correspond to the B2Σu+(v′=5,4,3)→X2Σg+(v=4,3,2) transitions, respectively. Particularly, we reveal the pressure-dependent gain dynamics of these lasing actions from highly excited vibrational states with a pump–probe scheme. Our experimental results confirm that electron collisional excitation plays an important role in the establishment of a population inversion of N2+ lasing at these wavelengths.