Ling-Xiu Zou

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.

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

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.

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

The whispering-gallery mode microlasers with the merits of small size and low power consumption are suitable for chip-based photonic integration. In this paper, the nonlinear dynamics for microdisk laser subject to optical injection is investigated for potential applications including photonic microwave generation and improved modulation characteristics. The four-wave mixing, period-one and period-two oscillations, and optical injection locking states are investigated based on the lasing spectra and generated microwave for a 10-μm-radius directional emission microdisk laser. Furthermore, direct modulation bandwidth enhancement from 5.6 to 17.6 GHz is observed for the injection-locked microdisk laser biased at 7 mA. The results reveal the necessity of further explore toward the potential applications of microdisk lasers under optical injection in photonic integrated chip.

Mode Characteristics of Unidirectional Emission AlGaInAs/InP Square Resonator Microlasers

We experimentally study the characteristics of an integrated semiconductor twin-microdisk laser under mutually optical injection through a connected optical waveguide. Based on the lasing spectra, four-wave mixing, injection locking, and period-two oscillation states are observed due to the mutually optical injection by adjusting the injected currents applied to the two microdisks. The enhanced 3 dB bandwidth is realized for the microdisk laser at the injection locking state, and photonic microwave is obtained from the electrode of the microdisk laser under the period-two oscillation state. The plentifully dynamical states similar as semiconductor lasers subject to external optical injection are realized due to strong optical interaction between the two microdisks.

Nonlinear Dynamics for Semiconductor Microdisk Laser Subject to Optical Injection

A dual-transverse-mode microsquare laser with a tunable wavelength interval is designed and realized by using a square-ring-patterned contact window. For a 30-μm-side-length microsquare laser with the square-ring width of 4 μm, the wavelength interval varies from 0.25 to 0.37 nm with the intensity ratio less than 2.5 dB as the injection current increases from 89 to 108 mA. Based on the dual-transverse-mode microsquare laser, the microwave signals with the frequencies of 30.56, 32.70, 35.12, and 39.51 GHz and the 3-dB bandwidths of 47, 53, 54, and 47 MHz are obtained at the injection currents of 90, 95, 100, and 105 mA, respectively.

Integrated semiconductor twin-microdisk laser under mutually optical injection

Thermal and high speed modulation characteristics are investigated for a unidirectional-emission microdisk laser with a radius of 7 μm surrounded by BCB-cladding layer, with a threshold current of 1.5 mA at the temperature of 287 K. The lasing spectra under different widths of pulsed current are measured to characterize the temperature rise during the pulse period, and the thermal distribution in the microdisk laser is simulated by the finite-element modeling technique. A temperature rise of 25 K is estimated for the microdisk laser biased at 20 mA. Furthermore, small signal modulation response with 3dB bandwidth up to 20 GHz is obtained for the microdisk laser at the biasing current of 18 mA, and eye-diagrams at the modulation bit rates of 20, 25, and 30 GHz are also measured at the temperature of 287 K.