Doo Gun Kim

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.

Optical properties of selectively oxidized vertical cavity laser with depleted optical thyristor structure

The authors show that the optical properties of selectively oxidized vertical cavity lasers with a depleted optical thyristor structure have a low threshold current and high sensitivity to input optical light. The oxidized thyristor laser clearly shows a nonlinear s-shaped current-voltage and lasing characteristics. A switching voltage of 5.24V, a holding voltage of 1.50V, and a very low threshold current of 0.65mA are measured, making these devices attractive for optical processing applications.

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.

Optical AND/OR gates based on monolithically integrated vertical cavity laser with depleted optical thyristor structure

Latching optical switches and optical logic gates with AND and OR functionality are demonstrated for the first time by the monolithic integration of a vertical cavity lasers with depleted optical thyristor structure. The thyristors have a low threshold current of 0.65 mA and a high on/off contrast ratio of more than 50 dB. By simply changing a reference switching voltage, this single device operates as two logic functions, optical logic AND and OR. The thyristor laser fabricated by using the oxidation process and has achieved high optical output power efficiency and a high sensitivity to the optical input light.

Multimode-interference-coupled ring resonators based on total-internal-reflection mirrors

We investigate the properties of a multimode-interference (MMI) coupled ring cavity resonator with total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA) in an InGaAsP material system. The TIR mirrors were fabricated by the self-aligned process with a loss of about 1.4 dB per mirror. The resulting free spectral range (FSR) was approximately 0.8 nm (97 GHz) near 1569 nm. The on–off ratio and the full width at half maximum (FWHM) were 8 dB and 0.152 nm, respectively, corresponding to a finesse of 5.2 and a Q factor of 10,322. Hence, such resonators can be directly integrated with other devices making possible the fabrication of compact and highly functional photonic integrated circuits.

AlGaAs/GaAs NpnP Depleted Optical Thyristor Using Bottom Mirror Layers

A novel fully depleted optical thyristor (DOT) using quarter wavelength reflector stacks (QWRS) is proposed. QWRS are employed as bottom mirrors to enhance the emission efficiency as well as optical sensitivity. To analyze their switching characteristics, s-shapes nonlinear current–voltage curves were simulated and the reverse full-depletion voltages (Vnegs) of DOTs were obtained as a function of semiconductor parameters using a finite difference method associated with a current-oriented method. The fabricated DOTs show sufficient nonlinear s-shaped current–voltage (I–V) characteristics, and switching voltage changes with and without bottom mirrors are 1.82 V and 1.52 V, respectively. Compared to a conventional DOT, this device with the bottom mirror shows about 20% and 20–50% enhancement in switching voltage changes and spontaneous emission efficiency, respectively.

Lasing characteristics of InGaAs∕InGaAsP multiple-quantum-well waveguide-type depleted optical thyristor with vertical window

This study demonstrates the lasing characteristics of InGaAs∕InGaAsP multiple-quantum-well waveguide-type depleted optical thyristor using the vertical window. The measured switching voltage and current are 3.36V and 10μA, respectively. The lasing threshold current is 131mA at 25°C. The output peak wavelength is 1570nm at a bias current of 1.22 Ith and there is no input signal. The vertically injected depleted optical thyristor shows very good isolation between input and output signals.

Waveguide-type PnpN optical thyristor operating at 1.55 μm

Waveguide-type PnpN depleted optical thyristors operating at 1.55 /spl mu/m are proposed and fabricated for the first time. In the optical thyristors, we employ InGaAs-InP multiple quantum-well (MQW) and InGaAsP bulk layers for the active n- and p-layers. The thyristors show sufficient nonlinear s-shape I-V characteristics and spontaneous emission along the waveguide. Very low switching voltages of 2.1 and 2.0 (V) for bulk and MQW thyristors with L=300 /spl mu/m and 350 /spl mu/m respectively are measured.