Objective: To find an alternative device scheme for optical isolators. 

The nonreciprocal devices depend on magneto-optical (MO) materials, which are not CMOS compatible due to the chemical incompatibility of materials, and MO materials typically require an external magnetic bias, preventing miniaturization of optical components. 

Results: We experimentally demonstrated that optical nonreciprocal responses are due to selective valley polarization in a TMDC monolayer optically pumped by a circularly polarized light. Additionally, our numerical and analytical results showed a ring resonator integrated with optically biased TMDCs has the potential to provide a large isolation rate of> 20 dB at room temperature.

 Selective-valley polarization effect in TMDCs

Photoluminescence (PL) arising from exciton relaxation in TMDC materials is commonly employed to probe their optical characteristics. The band gap energy at the K and K' points of these TMDCs is 1~2 eV, falling within the visible to near-infrared wavelength range. The optical behavior is primarily governed by excitons, which are comprised of a pair of interacting particles—an electron in the conduction band with a negative charge and a valence hole with a positive charge. Spin-orbit coupling induces a splitting of the valence band at the K and K' points, and the conditions for exciton formation must adhere to the corresponding selection rules. Notably, excitons, being bosons with integer quantum numbers, exhibit fermionic properties due to the spins of the electrons (±1/2). Similarly, photons, acting as bosons with spin ±1, contribute to the "selective valley polarization effect" during excitations at the K and K' valleys.

Check out our work for more details: "All-optical nonreciprocity due to valley polarization pumping in transition metal dichalcogenides"

Objective:  To demonstrate the cost-effective, compact, and sensitive refractive index sensor.

The biosensors on the markets using surface plasmon resonances require significant and bulky external instrumentation such as microscopes and spectrometers, which limits their minimization.

Results: We experimentally and numerically presented the CMOS-compatible refractive index sensor, Al nano-micro hole arrays on Ge-PIN photodiodes. The device allows us to measure the photocurrent directly (no need for microscopes or spectrometers) and provides large sensitivity > 1000 nm/RIU.

Check out our work for more details: "Integrated Collinear Refractive Index Sensor with Ge PINPhotodiodes"