Seok-Hwan Jeong

Low-loss, flat-topped and spectrally uniform silicon-nanowire-based 5th-order CROW fabricated by ArF-immersion lithography process on a 300-mm SOI wafer

We report superior spectral characteristics of silicon-nanowire-based 5th-order coupled resonator optical waveguides (CROW) fabricated by 193-nm ArF-immersion lithography process on a 300-mm silicon-on-insulator wafer. We theoretically analyze spectral characteristics, considering random phase errors caused by micro fabrication process. It will be experimentally demonstrated that the fabricated devices exhibit a low excess loss of 0.4 ± 0.2 dB, a high out-of-band rejection ratio of >40dB, and a wide flatband width of ~2 nm. Furthermore, we evaluate manufacturing tolerances for intra-dies and inter-dies, comparing with the cases for 248-nm KrF-dry lithography process. It will be shown that the 193-nm ArF-immersion lithography process can provide much less excess phase errors of Si-nanowire waveguides, thus enabling to give better filter spectral characteristics. Finally, spectral superiorities will be reconfirmed by measuring 25 Gbps modulated signals launched into the fabricated device. Clear eye diagrams are observed when the wavelengths of modulated signals are stayed within almost passband of the 5th-order CROW.

Polarization-independent all-optical switching in a nonlinear GaInAsP-InP highmesa waveguide with a vertically etched Bragg reflector

We have theoretically designed and experimentally demonstrated polarization-independent all-optical switching in a nonlinear GaInAsP-InP highmesa distributed feedback (DFB) waveguide. The device, which is composed of a highmesa waveguide stripe and a vertically etched Bragg reflector, can be simply fabricated using one-step electron beam lithography and a reactive ion etching process. The device is suitable for integration with other photonic devices such as semiconductor optical amplifiers and wavelength converters. The structural birefringence of the device has a dependence on the waveguide parameters such as the refractive index and thickness of core and cladding. The structural birefringence was successfully eliminated by adjusting the width of the highmesa waveguide. The nonlinear vertical-groove DFB highmesa waveguide is attractive for a polarization-independent all-optical switch from the viewpoint of a large grating coupling coefficient, as compared with a grating-loaded DFB highmesa waveguide. The polarization dependence of the grating coupling coefficient has also been investigated experimentally. It is possible to obtain the polarization-independent grating coupling coefficient by adjusting the grating depth in the vertical-groove DFB highmesa waveguide, together with structural zero-birefringence of the device. Polarization-independent all-optical thresholding and bistable switching operations have been successfully demonstrated in the nonlinear vertical-groove DFB highmesa waveguide.

GaInAsP-InP distributed feedback waveguides for all-optical switching

All-optical switching characteristics of waveguide devices having a nonlinear distributed feedback structure are reported theoretically and experimentally. These devices were composed of a strip-loaded GaInAsP-InP waveguide and a Bragg reflector, which were suitable for optical integrated circuit. In the experiments, all-optical and gate operation and set-reset operation for two output ports were successfully demonstrated.

1 × 4 Channel Si-Nanowire Microring-Assisted Multiple Delayline-Based Optical MUX/DeMUX

We proposed theoretically analyzed and experimentally demonstrated novel 1 × 4 channel flatband optical multiplexer/demultiplexer (MUX/DeMUX) that is based on Si-nanowire microring-assisted multiple delaylines. The proposed optical MUX/DeMUX scheme, which includes all-pass microring-type phase controllers and a Banyan-type 4 × 4 coupler, exhibits superior spectral flatness to any Si-nanowire optical DeMUXs that have previously been experimentally demonstrated.

Resonant Characteristics in a Two-Dimensional Photonic Crystal Ring Resonator with a Triangular Lattice of Air Holes

We fabricated and characterized a GaAs-based two-dimensional photonic-crystal ring resonator consisting of a directional coupler and bent waveguides. We experimentally demonstrated the periodic transmittance variation based on ring resonance and clarified the dependence of the ring-resonant response on the coupling characteristics of the photonic-crystal directional coupler.

Analysis and demonstration of single-passband response and tuning characteristics in a chirped ladder interferometric filter for a widely tunable laser diode

We have designed and demonstrated a chirped ladder-type tunable filter and discussed its potential application for a tunable diode laser. A ladder interferometric filter normally has a periodic passband, which makes it impossible to stabilize laser oscillation frequency. To overcome this drawback, we have designed, fabricated, and characterized a novel chirped tunable ladder filter. We have successfully demonstrated a single-passband response in the fabricated device. Furthermore, a tuning operation of more than 30 nm was achieved by introducing a current injection structure and optimizing electrode lengths at each single-stage ladder interferometer.

Dependence of Threshold Switching Power on the Control-Light Wavelength in a Nonlinear Distributed-Feedback GaInAsP Waveguide.

We demonstrate all-optical bistable switching by using orthogonally and parallelly polarized control light in a nonlinear distributed feedback GaInAsP waveguide. When the control light that is orthogonally polarized to the signal light is within its stopband, it is possible to extract the signal without using any external devices. Also, we investigate theoretically and experimentally the dependence of threshold switching power on the wavelength and polarization of control light.

Process control and monitoring in device fabrication for optical interconnection using silicon photonics technology

Precise dimension control technology for the fabrication of silicon photonics devices was established. The dimension control technology is based on the devices fabrication using 40-nm-node CMOS technology and in-line process monitoring by optical wafer-level probing system. As the results of process optimization in waveguide formation, superior dimension control in 440-nm-wide / 220-nm-thick waveguides was achieved, in which waveguide width deviation of 1.0 nm and height deviation of0.3 nm were respectively obtained for a single 300-mmφ wafer. In the characterization of 5th-order coupled resonator optical waveguides (CROWs), remarkably small deviation of resonant frequency 0.7 nm in a single wafer was confirmed, which values agreed with the theoretical estimation from the fabrication error. As for the optical wafer-level probing system, quite small deviation less than 0.2 dB in I/O coupling loss between optical devices under test and fiber probe was confirmed. It was successfully shown that the combination of the precise process control and the in-line optical process control monitor is sufficient to the reproducible device fabrication for wide-bandwidth optical interconnection.

Demonstration of all-optical AND gate operation in a GaInAsP waveguide

In the present paper an all-optical AND gate operation in a nonlinear DFB waveguide monolithically integrated with a Y-coupler is reported. It is concluded that the device does exhibit optical AND gate operation due to the intensity-dependent nonlinearity.

Silicon-Wire Waveguide Based External Cavity Laser for Milliwatt-Order Output Power and Temperature Control Free Operation with Silicon Ring Modulator

We report a novel hybrid laser based on a silicon-wire external cavity filter. We characterize the hybrid silicon laser from the viewpoint of high output extraction efficiency and temperature control free operation with a silicon microring resonator. First, it is experimentally verified that output extraction efficiency of the laser is significantly improved by locating an optical coupler within the laser cavity. As a result, we show mW-order output power and wall-plug efficiency of ~0.9%. In addition, we demonstrate that the operating window of the silicon microring modulator is adaptable to the oscillation wavelength of the hybrid silicon laser in regard to temperature change of a silicon substrate from 25 to 55 °C.