Jin-Long Xiao

Numerical Analysis of Gain Saturation, Noise Figure, and Carrier Distribution for Quantum-Dot Semiconductor-Optical Amplifiers

The gain saturation behaviors and noise figure are numerically analyzed for quantum-dot semiconductor optical amplifiers (QD-SOAs). The carrier and photon distributions in the longitudinal direction as well as the photon energy dependent facet reflectivity are accounted in the rate equations, which are solved with output amplified spontaneous emission spectrum as iterative variables. The longitudinal distributions of the occupation probabilities and spectral-hole burning are presented for electrons in the excited and ground states of quantum dots. The saturation output power 19.7 dBm and device gain 20.6 dB are obtained for a QD-SOA with the cavity length of 6 mm at the bias current of 500 mA. The influences of the electron intradot relaxation time and the QD capture time on the gain spectrum are simulated with the relaxation time of 1, 30, and 60 ps and capture time of 1, 5, and 10 ps. The noise figure as low as 3.5 dB is expected due to the strong polarization sensitive spontaneous emission. The characteristics of gain saturation and noise figure versus input signal power for QD-SOAs are similar to that of semiconductor linear optical amplifiers with gain clamping by vertical laser fields.

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.

Influences of carrier diffusion and radial mode field pattern on high speed characteristics for microring lasers

High-speed directly modulated microlasers are potential light sources for on-chip optical interconnection and photonic integrated circuits. In this Letter, dynamic characteristics are studied for microring lasers by rate equation analysis considering radial carrier hole burning and diffusion and experimentally. The coupled modes with a wide radial field pattern and the injection current focused in the edge area of microring resonator can greatly improve the high speed response curve due to the less carrier hole burning. The small-signal response curves of a microring laser connected with an output waveguide exhibit a larger 3 dB bandwidth and smaller roll-off at low frequency than that of the microdisk laser with the same radius of 15 μm, which accords with the simulation results.

Single Transverse Whispering-Gallery Mode AlGaInAs/InP Hexagonal Resonator Microlasers

AlGaInAs/InP hexagonal resonator microlasers with an output waveguide connected to one vertex of the hexagon are fabricated using standard photolithography and inductively coupled plasma (ICP) etching process. Room-temperature continuous-wave electrically injected operation with a threshold current of 18 mA is realized for a hexagon laser with an edge length of 16 μm and an output waveguide width of 2 μm. Single-mode operation is achieved with a side mode suppression ratio of 21 and 33 dB at the injection current of 30 and 60 mA, respectively. The peak wavelength intervals of the laser spectrum agree very well with the longitudinal mode intervals of the whispering-gallery modes, which indicates single transverse mode operation. The mode Q factor of 6.53 × 103 is measured for the lasing mode at 1547 nm at the threshold current, which is in the same magnitude as the Q factor obtained by finite-difference time-domain (FDTD) simulation. The numerical simulations also indicate that the hexagonal resonator with an output waveguide is suitable to realize single transverse mode operation.

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

Mode characteristics of AlGaInAs/InP square resonator microlasers laterally confined by a bisbenzocyclobutene layer, with an output waveguide connected to one vertex or the midpoint of one side, are investigated numerically and experimentally. Numerical simulation results indicate that the square resonator with the midpoint output waveguide has a better single-mode property, but a lower mode Q-factor than that with the vertex output waveguide. For a 20-μm-side-length square microlaser with a 1.5-μm-wide vertex output waveguide, lasing spectra with multiple transverse modes are observed with the mode wavelength intervals agreeing with the 2-D-finite difference time domain simulation results. In contrast, single-mode operation with a side-mode suppression ratio of 42 dB is obtained for a 20-μm-side-length square microlaser with a 1.5-μm-wide midpoint output waveguide. The results indicate that output waveguide can result in a mode selection in addition to realizing unidirectional emission.

InGaAsP–InP Square Microlasers With a Vertex Output Waveguide

Hybrid AlGaInAs/InP microring lasers with sloped sidewalls coupled to a silicon waveguide are investigated numerically and experimentally. The mode field distribution deviations for the microring resonator with the sloped sidewalls at different tilting angles are simulated by a 3-D finite-difference time-domain technique. Obvious enhancements of output coupling to the silicon waveguide and the active region optical confinement factor can be expected as the microresonator has a trapezoidal shape. A hybrid microring laser with a radius of 19 μm and a width of 2 μm is fabricated with the laser wafer bonded on a silicon-on-insulator wafer using the divinylsiloxane-benzocyclobutene (DVS-BCB) adhesive bonding technique. Continuous-wave electrically injected operation is realized at a tilting angle of -6° with the threshold currents of 7.8 and 9 mA at 12 °C and 22 °C. In addition, for a hybrid microring laser with a radius of 29 μm and a ring width of 2.5 μm, continuous-wave electrical operation up to 50 °C is achieved.