Abstract
In this paper, we introduce a disk-shaped Ge-on-Si photodetector for refractive-index difference sensing at an operating wavelength of 1550 nm. For the implementation of a small-scale sensor, a Ge layer was formed on top of a Si layer to increase the absorption coefficient at the expense of the light-detection area. Additionally, the sensor had a ring waveguide structure along the edge of the disk formed by a recess into the inner part of the disk. This increased the interaction between the dominant optical mode traveling along the edge waveguide and the refractive index of the cladding material to be sensed, and conclusively increased detection sensitivity. The simulation results show that the proposed sensor exhibited a detection sensitivity of >50 nm/RIU (Refractive Index Unit), a quality factor of approximately 3000, and a minimum detectable refractive index change of 0.95 × 10−2 RIU with a small disk radius of 3 μm. This corresponds to 1.67 times the sensitivity without a recess (>30 nm/RIU).
Highlights
Optical resonators are widely used in the environmental and industrial fields, for example, as sensing devices to measure the refractive index of gases and fluids, due to their advantage of immunity to electromagnetic interference
When the optical mode propagates through the resonator, the resonant wavelength is influenced by the refractive index of the material surrounded by the resonator
The intrinsic limit of detection (ILOD) of Type A was over 1.66 × 10 relatively because light (RIU) for
Summary
Optical resonators are widely used in the environmental and industrial fields, for example, as sensing devices to measure the refractive index of gases and fluids, due to their advantage of immunity to electromagnetic interference. As photodetector-type sensors, Si disk photodetectors [12] and Ge PIN (positive-intrinsic-negative) photodetectors [13] have been reported as label-free refractive-index sensors In this structure, the absorption coefficient of the material determines the amount of absorbed light per unit volume. It was expected that the recess structure of the Si layer forms a waveguide along the edge of the disk It generates the dominant mode along the waveguide, and increases the interaction between the refractive index of the cladding material and the propagating optical modes along the circular waveguide, enhancing the sensitivity. The resonance characteristics depend on the propagation mode, mode loss, and the interacting area between the mode and the refractive index of the cladding material These parameters are related to geometrical parameters such as disk thickness, radius, and size. All simulations were conducted with the FDTD and MODE solutions of Lumerical Inc., Vancouver, BC, Canada
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