Fang Ou

Enhanced radiation-loss-based radial-waveguide-coupled electrically pumped microresonator lasers with single-directional output

A novel enhanced radiation-loss (ERL)-based radial waveguide coupling mechanism for microresonator lasers is experimentally demonstrated for the first time, to the best of our knowledge, resulting in single-directional output from the lasers. A 20 microm diameter InGaAsP/InP electrically pumped microresonator laser in the form of a microcylinder resonator integrated with a transparent ERL radial output coupler is designed and fabricated. Measurement shows a low 1.5 mA lasing threshold and a relatively high output power of >0.4 mW.

Electro-optic modulator with exceptional power-size performance enabled by transparent conducting electrodes.

An EO phase modulator having transparent conducting oxide electrodes and an inverted rib waveguide structure is demonstrated. This new modulator geometry employs an EO polymer having an in-device r33 = 60pm/V. The measured half-wave voltage Vpi of these devices ranges from 5.3V to 11.2V for 3.8 and 1.5 mm long devices, respectively. The lowest VpiL figure-of-merit corresponds to 0.6V-cm (7.2mW-cm(2) of power length product) in a dual-drive configuration. The trade-off between Vpi, insertion loss and modulation bandwidth is systematically analyzed. An optimized high-speed structure is proposed, with numerical simulation showing that this new structure and an in-device r33 = 150pm/V, can achieve Vpi = 0.5V in a 5mm long active length with dual drive operation. The insertion loss is targeted at 6dB, and a 3dB optical modulation bandwidth can reach > 40GHz.

Ohmic Contact of Cadmium Oxide, a Transparent Conducting Oxide, to n-type Indium Phosphide

Good ohmic contact to n-type indium phosphide (n-InP) with cadmium oxide (CdO), a transparent conducting oxide (TCO), has been achieved. Hydrogen plasma surface pretreatment of the n-InP substrate, prior to the pulsed laser deposition (PLD) of the CdO film, is key to achieving ohmic contact. On substrates pretreated with a hydrogen plasma, contact resistances as low as (6.8 ± 2.8) × 10(-6) Ω cm(2) are obtained.

Modeling and Design of High-Speed Ultralow Voltage GaAs Electro-optic Modulators Enabled by Transparent Conducting Materials

We present a comprehensive modeling study of a high-speed gallium arsenide electro-optic modulator with ultralow switching voltages and large modulation bandwidths enabled by transparent conducting (TC) electrodes. The driving voltage, optical insertion loss, and modulation bandwidth of the TC-enabled modulator are systematically analyzed. Optimized designs for both a top-down and a side conduction geometry using Ta2O5 as both buffer and side cladding layers are presented. The results predict half-wave voltages from 0.5 down to 0.2 V, optical insertion losses of 6-10 dB, and optical 3 dB modulation bandwidths from 25-50 GHz for a top-down conduction geometry and 15-30 GHz for a side conduction geometry, assuming that proper impedance transforming parts and terminations are used. The use of benzocyclobutane as side cladding layers in the top-down conduction geometry to realize direct impedance matching was also explored. The corresponding modulation bandwidths are 13 GHz for 0.5 V case and 6 GHz for 0.2 V case, mainly limited by RF-optical wave velocity mismatch.

Ohmic contact of indium oxide as transparent electrode to n-type indium phosphide

Ohmic contacts of n-type indium phosphide (n-InP) with indium oxide (In2O3), a transparent conducting oxide (TCO), have been achieved. Hydrogen plasma surface pretreatment of the n-InP substrates (H2-cleaned n-InP) prior to the deposition of In2O3 films, is the key to achieve Ohmic contact. Oxygen flow rate during the In2O3 film deposition, which equivalently determines its doping level, is the main tuning parameter for In2O3 thin films growth. Rapid thermal annealing process (RTP) at different temperatures was found to have little effects on the Ohmic contact type.

Near-field nanoimaging by nanoscale photodetector array

We report a demonstration of near-field nanoimaging using nanoscale photodetector (NPD) array. The NPD array has detector pixels with subwavelength dimension and is capable of pixel addressing. An active-media finite-difference time-domain simulation of the NPD array shows an imaging resolution of 150 nm for 1.55 microm light. Additionally, we demonstrate the realization and characterization of the NPD array. The smallest NPD array obtained has 100-nm-wide pixels with 100 nm spacing. A responsivity of 0.28 A/W at 1.31 microm and 3.3 V bias is registered for a 2x2 NPD array pixel. The corresponding photocurrent is 735 nA with a dark current of 0.483 nA. Using near-field photocurrent microscopy, an imaging resolution of 390 nm has been demonstrated.

Ohmic contacts of ZnO/SnO2 equal-cosubstituted In2O3 films to n-InP and p-GaAs

ZnO/SnO2 equal-cosubstituted In2O3 (ZITO) films were deposited by ion beam assisted deposition onto n-InP and p-GaAs substrates. Rapid contact annealing processes (RCP) at different temperatures were done to study the thermal stability of their interfacial contact properties between ZITO films and the semiconductor substrates. Oxygen flow rate during deposition is the main tuning parameter for ZITO films growth. Highest conductivity for ZITO film deposited at the oxygen flow rate of 0 sccm (ZITO-0) was got at 525.2 S cm−1; lowest optical loss at wavelength of 1550 nm for ZITO film prepared at the oxygen flow rate of 7 sccm (ZITO-7) was obtained at 592.7 cm−1. Ohmic contacts have been achieved between ZITO films and n-InP pretreated both by hydrogen plasma and by oxygen plasma (H2-cleaned n-InP and O2-cleaned n-InP). The contact between ZITO-0 film and H2-cleaned n-InP substrate shows good thermal stability in RCP, the specific contact resistivity of 1.84 × 10−4 Ω cm2 for as-deposited ZITO-0 film contact to H2-cleaned n-InP and 1.24 × 10−4 Ω cm2 for the one annealed at 450 °C. While, RCP at proper temperature (360 °C and 400 °C) is the key to achieve ohmic contact between ZITO-0 film to H2-cleaned p-GaAs substrate.

Transparent conductive oxides for effective low-refractive-index Ohmic contact to nanophotonic devices demonstrated with Fabry-Perot lasers

We show the possibility of using transparent conductive oxide (TCO) for the current injection into nanophotonic devices. An InP based coplanar electrode Fabry-Perot micro-laser utilizing indium oxide (In2O3) as the n-type cladding electrode is demonstrated.

Ultra-compact angular reflector based InGaAsP/InP micro-lasers

We demonstrate a linear cavity micro-laser design utilizing the ultra-compact angular reflector as end mirrors. Laser fabricated on InGaAsP/InP quantum well wafer has a threshold of 22.4mA and can give mW output power.

Compact GaAs electro-optic (EO) modulator with ultra low switching voltage and large bandwidth enabled by transparent conducting (TC) bridge electrodes

We propose a compact GaAs EO modulator structure with ultra low switching voltage (∼ 0.5V) and large modulation bandwidth (f<inf>3dBo</inf> ≈ 50GHz), enabled by transparent conducting (TC) material as bridge electrodes.