Abstract
In this paper, a multi-mode waveguide-based optical resonator is proposed for an integrated optical refractive index sensor. Conventional optical resonators have been studied for single-mode waveguide-based resonators to enhance the performance, but mass production is limited owing to the high fabrication costs of nano-scale structures. To overcome this problem, we designed an S-bend resonator based on a micro-scale multi-mode waveguide. In general, multi-mode waveguides cannot be utilized as optical resonators, because of a performance degradation resulting from modal dispersion and an output transmission with multi-peaks. Therefore, we exploited the mode discrimination phenomenon using the bending loss, and the resulting S-bend resonator yielded an output transmission without multi-peaks. This phenomenon is utilized to remove higher-order modes efficiently using the difference in the effective refractive index between the higher-order and fundamental modes. As a result, the resonator achieved a Q-factor and sensitivity of 2.3 103 and 52 nm/RIU, respectively, using the variational finite-difference time-domain method. These results show that the multi-mode waveguide-based S-bend resonator with a wide line width can be utilized as a refractive index sensor.
Highlights
Integrated optical devices for refractive index (RI) sensors have been widely studied for applications such as bio-chemical analysis and temperature monitoring
Single-mode waveguides have generally been utilized in ring resonators, as they have the advantages of a low propagation loss, small size, and low modal dispersion [12,13]
Higher-order modes and analyzed the bending loss according to the radius of the semi-circle for the we focused on the difference in the effective refractive index between the fundamental mode and mode discrimination phenomenon
Summary
Integrated optical devices for refractive index (RI) sensors have been widely studied for applications such as bio-chemical analysis and temperature monitoring Structures such as ring resonators, microdisk resonators, Mach—Zehnder interferometers, Fabry—Perot interferometers, and fiber coupler have been developed for use as refractive index sensors [1,2,3,4,5,6,7]. These are based on measurements of the resonance wavelength peak shift through external refractive index changes when a reaction occurs in the sensing region, such as a bio-chemical reaction of the target or a temperature change. A relatively high-cost fabrication process must be employed, and mass production is difficult as single-mode waveguides typically have widths of several hundred nanometers
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