Liang Feng

Demonstration of a large-scale optical exceptional point structure

We report a large-size (4-inch) optical exceptional point structure at visible frequencies by designing a multilayer structure of absorbing and non-absorbing dielectrics. The optical exceptional point was implemented as indicated by the realized unidirectional reflectionless light transport at a wafer scale. The associated abrupt phase transition is theoretically and experimentally confirmed when crossing over the exceptional point in wavelengths. The large scale demonstration of phase transition around exceptional points will open new possibilities in important applications in free space optical devices.

One-way invisible cloak using parity-time symmetric transformation optics

We propose a one-way invisible cloak using transformation optics of parity-time (PT) symmetric optical materials. At the spontaneous PT-symmetry breaking point, light is scattered only for incidence along one direction since the phase-matching condition is unidirectionally satisfied, making the cloak one-way invisible. Moreover, optical scattering from the one-way cloak can be further engineered to realize more interesting effects, for example, creating a unidirectional optical illusion of the concealed object.

Adiabatic elimination-based coupling control in densely packed subwavelength waveguides

The ability to control light propagation in photonic integrated circuits is at the foundation of modern light-based communication. However, the inherent crosstalk in densely packed waveguides and the lack of robust control of the coupling are a major roadblock toward ultra-high density photonic integrated circuits. As a result, the diffraction limit is often considered as the lower bound for ultra-dense silicon photonics circuits. Here we experimentally demonstrate an active control of the coupling between two closely packed waveguides via the interaction with a decoupled waveguide. This control scheme is analogous to the adiabatic elimination, a well-known procedure in atomic physics. This approach offers an attractive solution for ultra-dense integrated nanophotonics for light-based communications and integrated quantum computing.

Parity-time optical metamaterial devices

The interplay between gain and loss in optical metamaterials can lead to novel device functionalities. Here we demonstrate a single-mode laser with unique cavity mode manipulation capability based on thresholdless parity-time symmetry breaking.

Parity-time optical metamaterials

Exploration of the interplay between gain and loss in optical materials can lead to novel device functionalities. Here we demonstrated a single-mode laser based on parity-time symmetry breaking.

Single mode parity-time laser

The concept of parity-time (PT) symmetry exploits the interplay between the material loss and gain to attain novel optical phenomena such as exceptional point and unidirectional light propagation. Here we experimentally demonstrate a PT symmetry breaking laser that allows unique control of the resonant modes. In contrast to conventional ring cavity lasers with multiple competing modes, our on-chip InGaAsP/InP based PT microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation at the specific whispering gallery mode order.

Parity-Time Symmetry Breaking Laser

Exploration of the interplay between gain and loss in optical metamaterials can lead to novel device functionalities. Here we demonstrate a single-mode laser with unique cavity mode manipulation capability based on thresholdless parity-time symmetry breaking.

Sub-wavelength critical coupling for densely integrated nano-photonics

We experimentally demonstrate a novel approach for densely packed coupled waveguides, based on adiabatic elimination scheme, allowing control of the inherent coupling between waveguides. At the nano-scale, zero coupling between the waveguides can be achieved.