Geum-Yoon Oh

The characterization of GH shifts of surface plasmon resonance in a waveguide using the FDTD method

We have explicated the Goos-Hänchen (GH) shift in a mum-order Kretchmann-Raether configuration embedded in an optical waveguide structure by using the finite-difference time-domain method. For optical waveguide-type surface plasmon resonance (SPR) devices, the precise derivation of the GH shift has become critical. Artmanns equation, which is accurate enough for bulk optics, is difficult to apply to waveguide-type SPR devices. This is because Artmanns equation, based on the differentiation of the phase shift, is inaccurate at the critical and resonance angles where drastic phase changes occur. In this study, we accurately identified both the positive and the negative GH shifts around the incidence angle of resonance. In a waveguide-type Kretchmann-Raether configuration with an Au thin film of 50 nm, positive and negative lateral shifts of -0.75 and + 1.0 microm are obtained on the SPR with the incident angles of 44.4 degrees and 47.5 degrees, respectively, at a wavelength of 632.8 nm.

Compact polarizing beam splitter based on a metal-insulator-metal inserted into multimode interference coupler

We propose and analyze a compact polarizing beam splitter (PBS) based on a metal-insulator-metal (MIM) structure inserted into a multimode interference coupler (MMI). Owing to the MIM structure, the TE polarized state is reflected by the cut-off condition while the TM polarized state is transmitted by the surface plasmon polariton, and the two polarized states can thus be separated. In this paper, the dependence of the reflected TE and transmitted TM field intensities on the MIM length and the gap thickness has been studied systematically. The proposed PBS structure, with a total size of 4 × 0.7 × 44 µm(3) is designed with MIM length, gap thickness, and metal thickness of 0.6 µm, 0.5 µm, and 0.05 µm, respectively. In the designed PBS, the transmittance for the TM polarized light, reflectance for the TE polarized light, extinction ratio, and insertion losses of the TE and TM modes are obtained using a 3D finite-difference time-domain method to be 0.9, 0.88, 12.55 dB, and 1.1 dB and 0.9 dB, respectively. The designed PBS has a much shorter length, 44 µm, compared to previous PBS devices.

Extremely small multimode-interference coupled triangular resonator with sharp angle of incidence

Novel triangular ring resonators combining extremely small multimode-interference (MMI) coupler, low loss total internal reflection (TIR) mirrors, and semiconductor optical amplifiers are reported for the first time. The MMI length of 90 microm is among the shortest reported. The incidence angle of the TIR mirror inside the resonator is 22 degrees. A free-spectral range of approximately 2 nm is observed near 1550 nm along with an on-off ratio of 17 dB. The triangular resonators with a sharp angle are very attractive components due to their promise of compact size and high levels of integration. Therefore, large numbers of resonators can be integrated on a chip to increase functionality in future optical wavelength division multiplexing system.

Design of ultra-sensitive biosensor applying surface plasmon resonance to a triangular resonator.

We propose an ultra-sensitive integrated photonic sensor structure using an InP-based triangular resonator, in which a surface plasmon resonance (SPR) gold film is applied on a total internal reflection mirror. We have analyzed and optimized the triangular resonator sensor structure with an extremely small SPR mirror sensing area of 3.3 × 0.35 μm2. Due to the large phase shift in the SPR mirror, a significantly enhanced sensitivity of 930 nm/RIU (refractive index unit) and the maximum peak shift of half free spectral range have been obtained at the SPR angle of 24.125° with Au thickness of 33.4 nm for the change of the refractive index Δn = 1x10(-3). This value is larger than the previous largest value in micro resonator-type biosensors. Moreover, the proposed triangular resonator sensor can be easily made in a micro structure with optical source integration.

Analysis of all optical logic gate based on photonic crystals multimode interference

In this paper, we propose an all optical logic gate based on a photonic crystals multimode interference (PC-MMI). The all optical logic gate with multifunctional performance has been designed theoretically in two-dimensional photonic crystals (PhCs) structure using multimode interference (MMI) principle. The PhCs consist of periodical air holes in silicon-on-insulator structure. The MMI using line defect waveguide is a 3×3 structure on the PhCs. By switching the optical signal to different input waveguide ports, the device can operate as NAND, NOT, NOR, and OR gates simultaneously or individually. In our optimum design, the width of MMI section is 4.8 μm and the length is 64 μm. The spacing between two line-defect waveguides is 1.2 μm. The total length of the device is 70 μm with an input length of 3.2 μm. It is 1/10 smaller size than conventional MMI optical logic device with nearby 1 mm. Therefore, switching speed is also enhanced by the reduced device size. Our proposed structure would be very useful for construction of optical circuit, optical computer, and future Si-based optical integrated circuits.

Compact polarization rotator based on slotted optical waveguide with buffer layer using surface plasmon polariton

A novel polarization rotator with asymmetric optical waveguide based on plasmonics is proposed and analyzed for the first time. The polarization rotator using skewing effects at the slotted optical waveguide (SOW) with metal film was designed by 3D-FDTD method. A metal film on the waveguide acts to rapidly rotate the optical polarization, because the plasmonic characteristics of a metal film can induce the slow group velocity through the metal-clad optical waveguide. Here, the optical waveguide with a buffer layer is proposed to reduce the propagation loss. The polarization rotator length of 6 μm is among the shortest reported in the waveguide-type polarization rotators. The polarization conversion efficiency of 98.93 % is observed near 1550 nm along with a propagation loss of -0.43 dB. The proposed structure is smaller than previous polarization rotator with asymmetric optical waveguide and is more effective to control polarizations using by plasmonic effects.

Analysis of stadium ring resonator sensor with dual photonic crystal microcavity

A novel biosensor structure based on the stadium shaped ring resonator (SRR) with dual photonic crystal microcavity (DPCM) is proposed and the resonance characteristics are analyzed for the first time. A Q-factor of the photonic crystal microcavity (PCM) can be significantly enhanced when single PCM or DPCM has the same resonance condition with the SRR. Here, the Q-factor of the SRR with DPCM is increased by three times in comparison with that of the directional coupler structure with single PCM. The bulk refractive index resolution of 3.03×10−5 is observed on the SRR with DPCM.

Analysis of a novel micro surface plasmon resonance sensor with attenuated total reflection mirror

We propose a novel micro surface plasmon resonance (SPR) sensor system based on polymer materials. The proposed SPR system consists of the incident medium with polymer waveguide and the gold thin film for sensing area. Using a polymer optical waveguide instead of a prism in SPR sensing system offers miniaturization, low cost, and potable sensing capability. The whole device performance was analyzed using the finite-difference time domain method. The optimum gold thickness in the attenuated total reflection mirror of polymer waveguide is around 50 nm and the resonance angle to generate surface plasmon wave is 66 degrees.

Integrated Refractometric Sensor Utilizing a Triangular Ring Resonator Combined With SPR

In this letter, a triangular resonator-based surface plasmon resonance (SPR) sensor that uses total internal reflection (TIR) mirrors to provide SPR excitation for the detection of refractive index (RI) change is proposed and first demonstrated using SoI substrate without any gain medium. The fabricated triangular resonator sensor with a 35-nm-thick Au film on a TIR mirror shows an output power increment of 1.2 dB and a sensitivity of 102 nm/RIU, while that nonmetallic layer on a TIR mirror shows 30 nm/RIU. The sensitivity enhancement is attributed to a phase change in the SPR resulting in a large shift of the resonance peak. This configuration provides significant advantages by increasing the sensitivity of the RI sensor even with the extremely small sensing area of the SPR mirror.

Design of high sensitive surface plasmon resonance sensor with metallic nano-structure

In this paper, we have designed and optimized the metallic nano-structures on a conventional surface plasmon resonance (SPR) sensor which induce the localized surface plasmon resonance for an improved sensitivity. Designed SPR sensor was simulated with 3D Finite-difference time-domain method. The sensitivity is maximized to 130.9 degree/RIU when the thickness of film layer TF is 30 nm while that of a conventional SPR sensor is less than 99.6 degree/RIU, and the reflectivity is minimized when TF is 25 nm. The most appropriated diameter of particles is about 35 nm for high sensitivity.