PhD defence by Xingyu Huang
Moiré-Engineered On-chip Light Sources for Silicon Photonics
Abstract
Silicon chips already steer light with extraordinary precision, but they still rely on bulky offchip lasers to generate that light. The core obstacle is silicon itself: its atomic structure makes it an inefficient emitter. My PhD research shows how to place the laser back on the chip by combining silicon photonics with “moiré superlattices” formed from two atom-thin semiconductors, molybdenum disulfide (MoS2) and tungsten diselenide (WSe2).
When these two layers are stacked with a near-zero twist angle, their overlapping lattices create a moiré pattern that reshapes the electronic landscape. This twist unlocks bright interlayer excitons—tiny electron–hole pairs that emit light up to four times more intensely than comparable single-layer materials. Crucially, the emitted wavelength sits in the optical-fiber O-band (1260–1360 nm), exactly where today’s internet traffic travels.
To turn this phenomenon into a practical device, I integrated the moiré layers with a silicon asymmetric nanobeam cavity. The cavity funnels the light directly into on-chip waveguides while boosting its intensity and spectral purity. The resulting source reaches high quality factors (above 6000), maintains a single clean spectral peak even at low pump power, and remains stable in ordinary laboratory air for at least nine months. Interferometry confirms excellent coherence, with a visibility near unity and a coherence length of ~3.8 mm.
Key innovations:
- Twist-angle engineering to create a moiré superlattice that emits efficiently at telecom wavelengths.
- A high-Q nanobeam cavity that couples this light emission into silicon waveguides with minimal loss.
- Long-term, room-temperature stability with a coherence length of ~3.8 mm—well suited for practical application.
Prospective applications
This platform paves the way for fully integrated optical interconnects in data centres, high-bandwidth on-chip communication for artificial-intelligence processors, and compact sources for quantum photonic circuits. By overcoming silicon’s emission bottleneck with scalable two-dimensional materials, the work moves us closer to photonic chips that generate, route, and detect light entirely on a single piece of silicon.
Supervisors
- Principal supervisor: Associate Professor Sanshui Xiao, DTU Electro, Denmark
- Co-supervisor: Professor Martijn Wubs, DTU Electro, DenmarkCo-supervisor: Professor Zhipei Sun, Aalto University, Finland
Evaluation Board
- Senior Researcher Minhao Pu, DTU Electro, Denmark
- Professor Uriel Levy, Hebrew University of Jerusalem, Israel
- Senior Researcher Antti Moilanen, University of Eastern Finland, Finland
Master of the Ceremony
- Associate Professor Andrei Laurynenka, DTU Electro, Denmark
Contact
Sanshui Xiao Associate Professor saxi@dtu.dk