Novel S-Bend Resonator Based on a Multi-Mode Waveguide with Mode Discrimination for a Refractive Index Sensor

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.

Thermal Reflow Effect in Multi-Mode Waveguide of S-Bend Resonator With Mode Discrimination

“…As shown in Fig. 1, the S-bend resonator consists of a MMI coupler and bending structure based on the MMW [14]. Different from the SMW-based resonator, higher-order modes may be present in the waveguide of the S-bend resonator.…”

“…The S-bend resonator uses mode discrimination in a multi-bending structure to eliminate higher-order modes of light. Mode discrimination is a phenomenon in which higher-order modes are removed based on the differences in the effective refractive index and losses between the fundamental mode and higherorder modes [14]. In this study, we considered an MMW-based S-bend resonator based on an SU-8 polymer, which can be fabricated through a photolithography process at a low cost.…”

“…However, it is difficult to use this resonator as a sensor, given that the modal dispersion causes multiple peaks in the output transmission spectrum. An S-bend resonator can be used to solve this problem by removing multiple peaks through the mode discrimination technique, which was presented in a previous study [14].…”

Racetrack Ring Resonator Integrated with Multimode Interferometer Structure Based on Low-Cost Silica–Titania Platform for Refractive Index Sensing Application

“…The proposed device demonstrated a spectrum with an FSR and ER of ~335 pm and ~11.6 dB, respectively, achieving a high Q factor of 2.3 × 10 4 [27]. In [28], the researchers put forward and designed an innovative S-bend resonator as a RI sensor, utilizing a multi-mode WG. The S-bend resonator was composed of a ridge WG, an MMI coupler, and multiple bend structures.…”

“…The S-bend resonator was composed of a ridge WG, an MMI coupler, and multiple bend structures. The researchers achieved inspiring results, with a Q-factor of 2.3 × 10 3 and a sensitivity of ~52 nm/RIU [28].…”