Heng Long

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.

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.

Mode Characteristics of Unidirectional Emission AlGaInAs/InP Square Resonator Microlasers

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.

Nonlinear Dynamics for Semiconductor Microdisk Laser Subject to Optical Injection

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.

Dual-transverse-mode microsquare lasers with tunable wavelength interval

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.

Narrow-linewidth microwave generation using AlGaInAs/InP microdisk lasers subject to optical injection and optoelectronic feedback

Narrow-linewidth and low phase noise photonic microwave generation under sideband-injection locking are demonstrated using an 8-μm-radius AlGaInAs/InP microdisk laser subject to optical injection and optoelectronic feedback. Microdisk laser subject to external optical injection at the period-one state provides the microwave subcarrier seed signal, and the optoelectronic feedback serves as direct current modulation to stabilize and lock the generated microwave signal without using the electrical filter. High-quality photonic microwave signals are realized with the 3-dB linewidth of less than 1 kHz and the frequency tunable range from 8.8 to 17 GHz. Single sideband phase noise of -101 dBc/Hz is obtained at a frequency offset of 10 kHz for the generated 14.7 GHz signal. Furthermore, the dependences of photonic microwave signal on the optical injection and optoelectronic feedback parameters are investigated.

High-Speed Direct-Modulated Unidirectional Emission Square Microlasers

High-speed modulation characteristics are investigated for a 20-μm-side-length AlGaInAs/InP square resonator microlaser with a 1.5-μm-wide midpoint output waveguide. Single-mode operation with a maximum output power of 0.34 mW and a side mode suppression ration of 42 dB are realized for the microlaser at a temperature of 288 K. A 3-dB bandwidth of 14.9 GHz is obtained, and the eye diagrams at 15 and 20 Gb/s are demonstrated for the microlaser with a bias current of 30 mA. Furthermore, the bit error rate of 2 × 10-8 is obtained at 8 Gb/s for a square microlaser with a 3-dB bandwidth of 10 GHz. In addition, different output patterns are observed for different lasing modes, which agree with the finite-difference time-domain simulation results.

Microwave Generation Directly From Microsquare Laser Subject to Optical Injection

Microwave generation based on the nonlinear dynamics of a microsquare laser subject to optical injection is proposed and demonstrated experimentally. The nonlinear dynamics are illustrated and analyzed based on the lasing spectra under the optical injection with different detuning frequencies. The microwave signal related to the oscillation of carrier density is directly measured from the electrode of the microsquare laser. The generated microwave power versus the microwave frequency is in agreement with small signal modulation response curve. The results provide a possible approach to the on-chip integrated photonic microwave source.

Investigation of High Efficiency Unidirectional Emission From Metal Coated Nanocylinder Cavities

We investigate the mode properties for metal coated nanocylinder cavities by three-dimensional finite difference time domain technique, for realizing high efficiency and unidirectional emission from the nanocavities. In a nanocavity confined by a metal layer, the metal layer provides mode confinement because it reduces the radiation loss greatly, but it also introduces a great metal dissipation loss. The compromise of the metal dissipation loss and the efficient output coupling is investigated for realizing high-output efficiency nanolasers, especially accounting the destructive interference of leakage waves. The different characteristics of the vertical radiation losses are investigated for TE and TM confined modes. Furthermore, the nanocavities connected with a thin output waveguide are proposed and numerically simulated for realizing the unidirectional emission metallic confined nanolasers.

High-Q modes in defected microcircular resonator confined by metal layer for unidirectional emission

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.