Jian-Dong Lin

AlGaInAs–InP Microcylinder Lasers Connected With an Output Waveguide

AlGaInAs-InP microcylinder lasers connected with an output waveguide are fabricated by planar technology. Room-temperature continuous-wave operation with a threshold current of 8 mA is realized for a microcylinder laser with the radius of 10 μm and the output waveguide width of 2 μm. The mode Q-factor of 1.2 x 104 is measured from the laser spectrum at the threshold. Coupled mode characteristics are analyzed by 2-D finite-difference time-domain simulation and the analytical solution of whispering-gallery modes. The calculated mode Q-factors of coupled modes are in the same order as the measured value.

Mode Analysis for Unidirectional Emission AlGaInAs/InP Octagonal Resonator Microlasers

We investigate mode characteristics for octagonal resonator microlasers directly connecting an output waveguide. The threshold current of 8 mA at 286 K and single-transverse-mode operation are realized for an octagonal resonator microlaser with a side length of 10.8 μm and a 2-μm-wide vertex output waveguide. The laser spectra of multiple longitudinal modes with mode wavelength intervals of 7-8 nm are observed accompanied with three weak, higher order transverse modes. Furthermore, blueshift of mode wavelength versus the injection current around the threshold current and the far-field patterns are measured and discussed. In addition, the mode characteristics of the octagonal microresonators are simulated by the two-dimensional finite-difference time-domain technique. Two sets of high-Q longitudinal modes are observed experimentally and numerically, for the octagonal resonators with the output waveguide connected to the vertex and the midpoint of one side of the resonators, respectively.

Unidirectional-Emission Single-Mode AlGaInAs-InP Microcylinder Lasers

AlGaInAs-InP microcylinder lasers with an output waveguide surrounded by benzocyclobutene are fabricated, using standard photolithography and inductively coupled-plasma etching technique. Room-temperature continuous-wave (CW) operation is realized for a microlaser with a radius of 20 μm and a 2-μm-wide output waveguide. Single-mode operation with side-mode suppression ratio around 25 dB is achieved, and the wavelength shifts from 1563.5 to 1567.3 nm with the injection current increases from 50 to 100 mA. The characteristic temperature of the threshold current is 58 K, obtained by fitting the output power versus the injection current with analytical relations. The practical laser temperature is expected to be about 391 K at the CW injection current of 130 mA.

Analysis of Mode Coupling and Threshold Gain Control for Nanocircular Resonators Confined by Isolation and Metallic Layers

Mode coupling and the control of mode Q factor and threshold gain are analyzed for nanocircular resonators confined by isolation and metallic layers based on solving eigenvalue equation for multiple-layer structure circular resonators. For nanocircular resonators only confined by a metallic layer, the metallic layer can enhance the mode confinement for transverse magnetic (TM) whispering-gallery modes (WGMs) and result in high Q TM WGMs. But transverse electric (TE) WGMs can form hybrid modes of surface plasmon polaritons and dielectric modes, with the mode Q factors limited by the metallic layer absorption. By introducing a low index isolation layer between the resonator and the metallic layer, we can greatly enhance the mode Q factors for TE WGMs. However, the mode coupling between different radial modes and the variation of the optical confinement factor in the active layer can result in the oscillation of the mode Q factor and threshold gain versus the isolation layer thickness. The optimization of the isolation layer thickness is important to enhance the mode Q factor and the optical confinement factor for realizing low threshold gain.

Influence of Mode

Dynamical characteristics of microcavity lasers are investigated by small signal analysis and large signal simulation based on single-mode rate equations, emphasized on the influence of the mode quality factor (Q factor) of the passive cavity and the internal absorption loss. The results indicate that a large 3-dB bandwidth does not always accompany a high quality eye diagram, especially for the small signal modulation with a high resonance peak. High Q factor and low internal loss are both required for high speed operation at a low biasing current. For a 2.5-μ.m-radius microcircular laser with an internal absorption loss αi = 1 cm-1 and a cavity Q factor of 7 × 104, high-quality eye diagrams are realized at a modulation rate of 10 Gb/s under a biasing current of twice the threshold current. The results show the broad prospects for the directly modulated microcavity lasers as a low-power efficient light source in on-chip optical interconnection.

Q

InGaAsP-InP square microlasers with a vertex output waveguide are fabricated by planar processes, and the etched sidewalls of the lasers are confined by insulating layer SiO2 and p-electrode Ti-Au metals. For a square microlaser with a side length of 30 μm and a 2-μm -wide output waveguide, a continuous-wave threshold current is 26 mA at room temperature and output power is 0.72 mW at 86 mA. The mode interval of 21 and 7.4 nm is observed for the microlasers with the side length of 10 and 30 μm , respectively. Finite-difference time-domain (FDTD) simulations indicate that the lasing modes have incident angles of about 45 ° at the boundaries of the resonator. In addition, square resonators surrounded by air, SiO2-Ti-Au, and SiO2-Au are compared by FDTD simulations.

Factor and Absorption Loss on Dynamical Characteristics for Semiconductor Microcavity Lasers by Rate Equation Analysis

Microcylinder resonators with multiple ports connected to waveguides are investigated by 2D finite-difference time-domain (FDTD) simulation for realizing microlasers with multiple outputs. For a 10 μm radius microcylinder with a refractive index of 3.2 and three 2 μ mw ide waveguides, confined mode at the wavelength of 1542.3 nm can have a mode Q factor of 6.7 × 10 4 and an output coupling efficiency of 0.76. AlGaInAs/InP microcylinder lasers with a radius of 10 μm and a 2 μm wide output waveguide are fabricated by planar processing techniques. Continuous-wave electrically injected operation is realized with a threshold current of 4 mA at room temperature, and the jumps of output power are observed accompanying a lasing mode transformation. (Some figures in this article are in colour only in the electronic version)

InGaAsP–InP Square Microlasers With a Vertex Output Waveguide

Optical bistability is realized in GaInAsP/InP coupled-circular resonator microlasers, which are fabricated by planar technology. For a coupled-circular resonator microlaser with the radius of 20 μm and a 2 μm-wide bus waveguide, hysteresis loops are observed for the output power coupling into an optical fiber versus the cw injection current at room temperature. The laser output spectra of the upper and lower states of the hysteresis loop indicate that the bistability is related to mode competitions. The optical bistability can be explained as the mode competition between the symmetry and antisymmetry coupled modes relative to the bus waveguide.

Investigation on multiple-port microcylinder lasers based on coupled modes

We experimentally investigate the coherence of a single mode InAlGaAs/InP cylindrical microlaser with two output waveguides. For a cylindrical microlaser with a radius of 15 μm and two 2 μm-wide output waveguides, single mode operation with a side mode suppression ratio of 30 dB is realized, and a far-field interferometric pattern similar to a Youngs interferometer is observed. The results indicate that the microlasers with two output waveguides can be used as the light source for an optical sensor by monitoring the phase change of the output emission from one port versus that of the other port.

Optical bistability in GaInAsP/InP coupled-circular resonator microlasers.

Defected circular resonators laterally confined by a metal layer with a flat side as an emitting window are numerically investigated based on the boundary element method for realizing unidirectional emission microlasers. The results indicate that Fabry-Pérot (FP) modes become high Q confined modes in the defected circular resonator with a metallic layer. The mode coupling between the FP mode and chaotic-like mode can result in high Q confined mode for unidirectional emission with a narrow far field pattern.