Design of the Bimodal Grating Sensor with a Built-In Mode Demultiplexer

Andrei Tsarev

doi:10.3390/s23094327

Design of the Bimodal Grating Sensor with a Built-In Mode Demultiplexer

Sensors (Basel). 2023 Apr 27;23(9):4327. doi: 10.3390/s23094327.

Author

Andrei Tsarev^{1

2}

Affiliations

¹ Laboratory of Optical Materials and Structures, Rzhanov Institute of Semiconductor Physics, SB RAS, 630090 Novosibirsk, Russia.
² Physics Department, Novosibirsk State University, 630090 Novosibirsk, Russia.

Abstract

This new sensor design provides good volume sensitivity (around 1600 nm/RIU) via collinear diffraction by the asymmetric grating placed in the waveguide vicinity. It provides the mode transformation between the fundamental TE₀ and the first TE₁ modes of the silicon wire (0.22 μm by a 0.580 μm cross-section) in the water environment. In order to provide the wavelength interrogation with a better extinction ratio for the measuring signal, the grating design is incorporated with the mode filter/demultiplexer. It selects, by the compact directional coupler (maximum 4 μm wide and 14 μm long), only the first guided mode (close to the cutoff) and transmits it with small excess loss (about -0.5 dB) to the fundamental TE₀ mode of the neighboring single mode silicon wire, having variable curvature and width ranging from 0.26 μm to 0.45 μm. At the same time, the parasitic crosstalk of the input TE₀ mode is below -42 dB, and that provides the option of simple and accurate wavelength sensor interrogation. The environment index is measured by the spectral peak position of the transmitted TE₀ mode power in the output single mode silicon wire waveguide of the directional coupler. This type of optical sensor is of high sensitivity (iLOD~ 2.1 × 10^-4 RIU for taking into account the water absorption at 1550 nm) and could be manufactured by modern technology and a single-step etching process.

Keywords: bimodal grating optical sensor; mode demultiplexer; numerical modeling; silicon waveguide.

Grants and funding

This research received no external funding. It was accomplished under the program of the basic research of the Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk, Russia.