Xiu-Wen Ma

Diode-end-pumped passively mode-locked ceramic Nd:YAG Laser with a semiconductor saturable mirror

We report on a diode-pumped CW passively mode locked ceramic Nd:YAG laser with SESAM (semiconductor saturable absorber mirror), wavelength 1064nm. At a pump power of 7.6w, the pulse width was estimated to be ~8.3ps with repetition rate ~130MHz and the average output power was 1.59w. To our knowledge, this was the first demonstration that ceramic Nd:YAG was used for diode pumped CW passively mode locking.

Photonic-Molecule Single-Mode Laser

We report in this letter the fabrication of edge-alignment-coupled whispering gallery mode photonic-molecule microdisk by femtosecond laser direct writing of dye-doped resins, which results in single-mode lasing output. Under picosecond laser pumping, the excited energy is distributed at the disk periphery and the coupling happens at the overlapping edge of two disks. As a result of mode coupling through Vernier effect, single-mode lasing is achieved in two-microdisk and three-microdisk coupled lasers of various sizes. The effect in the coupled system is confirmed by numerical simulation. This letter may open up a new avenue to the 3-D integrated optoelectronics.

Spatial hole burning degradation of AlGaAs/GaAs laser diodes

The degradation of AlGaAs/GaAs laser diodes is studied in detail using laser scanning confocal microscopy, cathodoluminescence images, and x-ray diffraction (XRD) techniques. Our analysis has identified a degradation mechanism that results from the periodic distribution of the carrier density and the near-field intensity originating from periodic spatial hole burning. Based on the XRD measurements, we find that the epitaxial layer enters a polycrystalline phase during degradation due to the dark line defects, and the out-of-plane strain and in-plane compressive stress are induced by degradation.

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.

Thermal and high speed modulation characteristics for AlGaInAs/InP microdisk lasers

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.

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.

Mode coupling in hybrid square-rectangular lasers for single mode operation

Mode coupling between a square microcavity and a Fabry-Perot (FP) cavity is proposed and demonstrated for realizing single mode lasers. The modulations of the mode Q factor as simulation results are observed and single mode operation is obtained with a side mode suppression ratio of 46 dB and a single mode fiber coupling loss of 3.2 dB for an AlGaInAs/InP hybrid laser as a 300-μm-length and 1.5-μm-wide FP cavity connected to a vertex of a 10-μm-side square microcavity. Furthermore, tunable single mode operation is demonstrated with a continuous wavelength tuning range over 10 nm. The simple hybrid structure may shed light on practical applications of whispering-gallery mode microcavities in large-scale photonic integrated circuits and optical communication and interconnection.

Mode Q factor and lasing spectrum controls for deformed square resonator microlasers with circular sides

Deformed square resonators with the flat sides replaced by circular sides are proposed and demonstrated to enhance mode Q factors and adjust transverse mode intervals using the regular ray dynamic analysis and numerical simulations. Dual-transverse-mode emissions due to the ultrahigh-Q factors with different wavelength intervals are realized experimentally for AlGaInAs/InP circular-side square microlasers, and the stationary condition of the dual-mode emission is satisfied because the high-Q confined modes have totally different mode numbers. Furthermore, optical frequency combs are generated using the dual-mode lasing microlaser as a seeding light source by cascaded four-wave mixing in a highly nonlinear optical fiber.

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.

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.