In this paper, we designed hexagonal ring resonator using localized surface plasmon resonance (LSPR) phenomenon to enhance the sensitivity which is a significant factor in bio-chemical sensors. We used a hexagonal ring resonator structure to eliminate the bending loss which is one of the prime factors affects sensitivity. The sensing area of the hexagonal ring resonator with LSPR is deposited metal nanoparticle on cladding which makes difference with general sensing region of the hexagonal ring resonator. In this sensing region, the wavelength of light should be longer than the size of the nanoparticle because the metal nanoparticle reacts the light in specific condition. The sensitivity of the resonator can be improved with using this phenomenon. We used finite difference time domain (FDTD) methods for theoretical analysis. Also, we optimized the structure to reduce LSPR loss and enhance the sensitivity by adjusting type, size, thickness of the metal nanoparticle. As a simulation result, we verified that sensitivity of hexagonal ring resonator with LSPR can be 2.5 times higher than without LSPR.
We analyzed regular polygonal ring resonators based on multi-mode waveguide using finite-difference time-domain simulation. It consists of the regular polygonal ring waveguide, total internal reflection mirror, and MMI coupler. In general, multi-mode waveguide-based resonator is difficult to use as sensors because of poor output characteristics. By using the low reflectance of the higher-order mode compared to the fundamental mode in the TIR mirror, we designed a regular polygonal ring resonator that can be used as sensors even when a multi-mode waveguide is used instead of a single-mode waveguide. In fabrication, the multi-mode waveguide has a wider line width than the single-mode waveguide, which reduces the process cost and enables mass production. The width and height of the multi-mode waveguide are designed to be 2.5 μm and 2 μm, respectively using SU-8 polymer. The regular hexagon ring resonator shows the highest Q-factor of 1.03×10<sup>4</sup> among the various regular polygonal ring resonators.
We propose a rectangular resonator sensor structure with butterfly MMI coupler using SOI. It consists of the rectangular resonator, total internal reflection (TIR) mirror, and the butterfly MMI coupler. The rectangular resonator is expected to be used as bio and chemical sensors because of the advantages of using MMI coupler and the absence of bending loss unlike ring resonators. The butterfly MMI coupler can miniaturize the device compared to conventional MMI by using a linear butterfly shape instead of a square in the MMI part. The width, height, and slab height of the rib type waveguide are designed to be 1.5 μm, 1.5 μm, and 0.9 μm, respectively. This structure is designed as a single mode. When designing a TIR mirror, we considered the Goos-Hänchen shift and critical angle. We designed 3:1 MMI coupler because rectangular resonator has no bending loss. The width of MMI is designed to be 4.5 μm and we optimize the length of the butterfly MMI coupler using finite-difference time-domain (FDTD) method for higher Q-factor. It has the equal performance with conventional MMI even though the length is reduced by 1/3. As a result of the simulation, Qfactor of rectangular resonator can be obtained as 7381.
In this paper, we propose temperature sensing method by using optical beating. When temperature changes, a peak wavelength of the sensing laser varies slightly. However, with limitation of the optical spectrum analyzer’s (OSA) spectral resolution (sub-nm), it is hard to measure the exact quantity of the wavelength variation. Therefore, we used electrical spectrum analyzer (ESA) and two lasers to obtain the wavelength shift. We used DFB-LD (distributed feedback laser diode) and TLS (tunable laser source) to get beating signal. Each of laser has 1550 nm of wavelength, -20 dBm of intensity and 10<sup>8</sup> of Q factor. We varied temperature by 0.1 °C from 17.4 °C to 18.4 °C using TEC (temperature controller). We observed 0.01 nm/°C of wavelength change through OSA and 9.5 GHz/°C of beating frequency change through ESA. With this result, we verified that we can measure relative temperature change with having ultra-fine resolution of 9.5×10<sup>-7</sup> °C theoretically for the ESA resolution bandwidth of 1 kHz. This detecting ability can be applied to highly sensitive temperature sensor.