Graphene is a promising material for its exceptional electrical and mechanical properties. Starting with the initial demonstration of isolating a single graphene sheet from graphite, much progress has been made in realizing graphene based devices for diverse applications. Here, we introduce an experiment in which the electrical properties of graphene are modified by coating different-sequence single-stranded deoxyribonucleic acid (ssDNA) molecules. We fabricated a graphene-field effect transistor (FET) by transferring CVD graphene on copper foil onto a Si/SiO2 wafer. A passivation layer opened up windows on the surface of the graphene to enable interaction with liquid buffers. ssDNA molecules with different base sequences were coated onto the active graphene channels. We observed a variation in the Dirac voltage of the ssDNA-coated graphene FETs according to the ssDNA base sequences. Electrical control of the graphene FET is obtained via gating effect of the deposited ssDNAs. We conduct a systematic study of this ssDNAinduced gating effect with different base sequences, concentrations, and lengths of molecules, leading to extraction of characteristic parameters of the graphene FET accordingly.
The lasing characteristics of three-guide coupled ring lasers using the self-aligned total internal reflection
(TIR) mirrors were investigated numerically and experimentally. The rectangular laser cavity consists of four low loss
TIR mirrors and an output coupler made out of passive three coupled waveguides. Two different lasers having active
section lengths of 250 and 350 μm and total cavity lengths of 580 and 780 μm are fabricated. For both devices lasing
thresholds of 38 mA is obtained at room temperature and under CW operation. Lasing is predominantly single mode
with the side mode suppression ratio better than 20 dB.
We investigate the properties of a multimode-interference (MMI) coupled micro ring cavity resonator with
total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA). The TIR mirrors were fabricated
by the self-aligned process with a loss of 0.7 dB per mirror. The length and width of an MMI are 142 &mgr;m and 10 &mgr;m,
respectively. The resulting free spectral range (FSR) of the resonator was approximately 1.698 nm near 1571 nm and
the extinction ratio was about 17 dB. These devices might be useful as optical switching and add-drop filters in a
photonic integrated circuit or as small and fast resonator devices.
A modulation efficiency enhancement scheme for an InGaAsP waveguide-coupled micro-ring cavity resonator utilizing the self-aligned total internal reflector mirrors was proposed and investigated numerically and experimentally. Unlike the conventional electroabsorption modulators, the micro-ring cavity resonator was found to exhibit a singular modulation characteristics depending on the coupling coefficient between the micro-ring cavity and the input/output waveguide, which can be exploited to enhance the optical modulation efficiency as well as the extinction ratio.
The external feedback effect on the relative intensity noise characteristics of 405 nm InAlGaN laser diode has been analyzed taking into account the spontaneous emission noise and the high frequency modulation of the injection current. A Langevin diffusion model was exploited to characterize its relative intensity noise. The spontaneous emission noise components were quantitatively evaluated from the optical gain properties of the InAlGaN multiple quantum well active regions by using the multiband Hamiltonian for the strained wurtzite crystals. The extracted parameters were applied to the rate equations taking into account the external feedback and external current modulation effects. The simulation results were investigated to optimize the relative intensity noise characteristics.
In this paper, we propose a new technique to suppress the non- linearity of multiple quantum well (MQW) electro-absorption (EA) modulator, mainly due to an exponential-like transmission characteristics of EA modulator and non-linearity of quantum confined stark effect (QCSE), by intermixing MQW absorption region. Optical properties and its dependence on applied bias voltages of intermixed InGaAs/InGaAsP MQW absorption region, such as transition energy and gain (or absorption) spectrum have been calculated by solving Luttinger-Kohn Hamiltonian. It has been shown that the transfer function of a MQW-EA modulator can be tailored by introducing differently intermixed regions along the waveguide direction. It has been also shown that proposed technique can suppress IMD2 (2nd order intermodulation distortion) by 39.6 dB and enhance spurious free dynamic range (SFDR) by a 3.6 dB by choosing proper combination of interdiffusion lengths and waveguide lengths.