Duanni Huang

Electrically Driven and Thermally Tunable Integrated Optical Isolators for Silicon Photonics

Optical isolators are required to block undesired reflections in many photonic integrated circuits (PICs), but the performance of on-chip isolators using the magneto-optic effect has been limited due to high loss of such materials. Moreover, they require precise positioning of a permanent magnet close to the chip, increasing footprint and impeding packaging. In this paper, we propose an optical isolator on the silicon-on-insulator platform with record performance and without the use of any external permanent magnets. A metallic microstrip above the bonded silicon microring (MR) is used to generate the magnetic field required for the nonreciprocal behavior. Simultaneously, the microstrip can be used to provide 0.6 nm of thermal tuning while preserving over 20 dB of isolation. We measure 32 dB of isolation near 1555 nm with only 2.3 dB excess loss in a 35 μm radius MR. The tunability, compactness, and lack of permanent magnets suggest this device is a major step towards integration in PICs.

Compact Tb doped fiber optic current sensor with high sensitivity.

A highly sensitive fiber optic current sensor using terbium doped fiber is presented. The Verdet constant of the terbium doped fiber at 1300nm is found to be 19.5μrad/A using both a polarimetric and interferometric type sensor. Measurements on a Sagnac-loop sensor using 10cm of terbium doped fiber placed inside a solenoid show over 40dB of open loop dynamic range as well as a minimum detectable current of 0.1mA. Extrapolations of our measurements show that in a practical setup with Tb fiber wrapped around a current carrying wire, the optimal configuration is a 0.5m piece of Tb fiber with a noise limit of 22mA/√Hz. This sensor is promising for current sensing applications that require high sensitivity and small size, weight, and power.

Full vectorial mode solver for design and optimization of magneto-optic devices

In this work, we present a curl-curl formulation for computing the electromagnetic modes that propagate in a waveguide, fully or partially made with magneto-optic material. Such medium is characterized by a nonreciprocal permittivity tensor, which is responsible for a different propagation constant for the forward and backward traveling modes. By exploiting this property, an optical integrated isolator can be effectively designed and optimized. Finally, a detailed analysis based on the proposed finite element mode solver is performed to investigate the fabrication tolerance of the nonreciprocal waveguide.

Integrated compact optical current sensors with high sensitivity

We demonstrate a Sagnac based fiber optic current sensor using only 10cm of terbium doped fiber with a high Verdet constant of 15.5 rad/Tm at a wavelength of 1300nm. Measurements of the fiber inside a solenoid show over 40dB of open loop dynamic range as well as a minimum detectable current of 0.1mA. In order to decrease size while increasing sensitivity even further, we consider integrated magneto-optic waveguides as the sensing element. Using silicon waveguides alongside magneto-optic material such as cerium doped yttrium iron garnet (Ce:YiG), we model the Verdet constant to be as high as 10,000 rad/Tm. This improvement by three orders of magnitude shows potential for magnetooptic waveguides to be used in ultra-high sensitivity optical magnetometers and current sensors. Finally, we propose a fully integrated optical current sensor using heterogeneous integration for silicon photonics.