The coherent transmission technology using digital signal processing and advanced modulation formats, is bringing networks closer to the theoretical capacity limit of optical fibres, the Shannon limit. The in-phase/quadrature electro-optic modulator that encodes information on both the amplitude and the phase of light, is one of the underpinning devices for the coherent transmission technology. Ideally, such modulator should feature a low loss, low drive voltage, large bandwidth, low chirp and compact footprint. However, these requirements have been only met on separate occasions. Here, we demonstrate integrated thin-film lithium niobate in-phase/quadrature modulators that fulfil these requirements simultaneously. The presented devices exhibit greatly improved overall performance (half-wave voltage, bandwidth and optical loss) over traditional lithium niobate counterparts, and support modulation data rate up to 320 Gbit s −1. Our devices pave new routes for future highspeed, energy-efficient, and cost-effective communication networks.

We demonstrate a high-efficiency thermo-optic (TO) tunable micro-ring resonator in thin-film lithium niobate. Thermal insulation trenches around the heated micro-ring resonator and the underlying silicon substrate significantly reduce the heating power consumption and improve the tuning efficiency. Compared to conventional TO devices without thermal insulation trenches, the proposed device achieves a full free spectral range wavelength shift with a 14.9 mW heating power, corresponding to a thermal tuning efficiency of 53.7 pm/mW, a more than 20-fold improvement of tuning efficiency. The approach enables energy-efficient high-performance TO devices such as optical switches, wavelength routers, and other reconfigurable photonic devices.

Significant improvements in the lithium niobate on insulator (LNOI) platform are pushing LNOI-based laser sources to the forefront of integrated photonics. Here, we report the first, to the best of our knowledge, electrically pumped hybrid lithium niobate/III-V laser by butt coupling an InP-based optical gain chip with a LNOI photonic integrated circuit (PIC). In the PIC, a Vernier filter consisting of two LNOI microring resonators is employed to select the lasing wavelength. A wavelength tuning range of more than 36 nm is achieved in the O band. The hybrid laser has a maximum on-chip optical power of 2.5 mW and threshold current density of 2.5 k A / c m 2 . A side mode suppression ratio better than 60 dB is achieved.

Heterogeneous integration of III–V active devices on lithium niobate-on-insulator (LNOI) photonic circuits enable fully integrated transceivers. Here we present the co-integration of InP-based light-emitting diodes (LEDs) and photodetectors on an LNOI photonics platform. Both devices are realized based on the same III–V epitaxial layers stack adhesively bonded on an LNOI waveguide circuit. The light is evanescently coupled between the LNOI and III–V waveguide via a multiple-section adiabatic taper. The waveguide-coupled LEDs have a 3-dB bandwidth of 40 nm. The photodetector features a responsivity of 0.38 A/W in the 1550-nm wavelength range and a dark current of 9 nA at −0.5 V at room temperature.

Thin-film lithium niobate (TFLN) photonic integrated circuits (PICs) have emerged as a promising integrated photonics platform for the optical communication, microwave photonics, and sensing applications. In recent years, rapid progress has been made on the development of low-loss TFLN waveguides, high-speed modulators, and various passive components. However, the integration of laser sources on the TFLN photonics platform is still one of the main hurdles in the path toward fully integrated TFLN PICs. Here, we present the heterogeneous integration of InP-based semiconductor lasers on a TFLN PIC. The III–V epitaxial layer stack is adhesively bonded to a TFLN waveguide circuit. In the laser device, the light is coupled from the III–V gain section to the TFLN waveguide via a multi-section spot size converter. A waveguide-coupled output power above 1 mW is achieved for the device operating at room temperature. This heterogeneous integration approach can also be used to realize on-chip photodetectors based on the same epitaxial layer stack and the same process flow, thereby enabling large-volume, low-cost manufacturing of fully integrated III–V-on-lithium niobate systems for next-generation high-capacity communication applications.