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.
A very low CW threshold current of l.65 mA at room temperature was obtained for an uncoated burie-dheterostructure strained layer multiquantum well InGaAs-GaAs laser fabricated using hybrid molecular beam epitaxy and liquid phase epitaxy crystal growth technique. External differential quantum efficiency as high as 446% (0.53 mW/mA) and output power of more than 30mW per facet were achieved in the same laser.
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 10 4 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.
Optical frequency comb (OFC) and picosecond pulse generation are demonstrated experimentally based on a directly modulated AlGaInAs/InP square microcavity laser. With the merit of a high electro-optics modulation response of the microcavity laser, power-efficient OFCs with good flatness are produced. Ten 8-GHz-spaced optical tones with power fluctuation less than 3 dB are obtained based on the laser modulated by a sinusoidal signal. Moreover, the comb line number is enhanced to 20 by eliminating the nonlinear dynamics through optical injection locking. Owing to the high coherence of the OFC originating from the directly modulated microcavity laser, a 6.8 ps transform-limited pulse is obtained through dispersion compensation. The optical pulse is further compressed to 1.3 ps through the self-phase modulation effect in high nonlinear fiber.
A coherent optical frequency comb (OFC) with suppressed linewidth is demonstrated based on the spectral broadening of a directly modulated semiconductor microcavity laser with self-injection locking. Due to the high electro-optical response, the directly modulated microcavity laser provides a 10-GHz-spaced seeding OFC with 9 comb teeth in a 10 dB flatness window. Besides, an optical feedback fiber loop with two sub-loops is introduced to reduce the linewidth of the microlaser and suppress the undesired longitudinal modes. Self-injection locking is realized at the feedback power of 72 µW, and the laser linewidth is narrowed from 10 MHz to 14.5 kHz. Moreover, spectral broadening and pulse compression are used to broaden the optical spectrum and compress the pulse width, which results in an OFC with 36 comb lines in a 10 dB power deviation and a 1.8 ps optical pulse. Owing to the high coherence of the directly modulated OFC, all comb lines feature narrow linewidths in the range of 14.5∼18.2 kHz.
All-optical flip-flop has been demonstrated experimentally based on our optical bistable hybrid square-rectangular lasers. In this paper, dual-mode rate equations are utilized for studying the optical bistability in the two-section hybrid-coupled semiconductor laser. A phenomenological gain spectrum model is constructed for considering the mode competition in gain section and saturable absorption effect in the absorptive section in a wide wavelength range. The mechanisms of the optical bistability are verified in the aspect of the distribution of carriers and photons in the two-section hybrid-coupled cavity. In addition, we find that with the adjustment of the device parameters, both of the width and biasing current for achieving the bistability can be tuned for a wide range. Furthermore, a dynamic response of all-optical flip-flop is simulated, using a pair of set/reset optical triggering pulses, in order to figure out the laws for faster transition time with lower power consumption.
Single mode operations are realized for hexagonal and circular microlasers connected with an output waveguide. Output waveguide cause direction emission and mode selection and avoid output power jump caused by the transverse mode competition.
Lasing characteristics are investigated for coupled-cavity Fabry-Pérot lasers for realizing single-mode emission. Side-mode suppression ratios are improved by tuning the bias voltage of the integrated polygon microcavity due to a modulation of equivalent reflectivity.
Self-pulsing and dual-mode lasing in a square microcavity semiconductor laser are studied experimentally. Self-sustained pulses originating from undamped relaxation oscillation induced by a two-mode interaction are obtained, as the injection current is slightly above the laser threshold. A repetition frequency of 4.4 GHz and a pulse width of 30-40 ps are obtained at a current of 8 mA. The laser switches to continuous-wave operation when the injection current is higher than a certain value, and dual-mode lasing with 30.7 GHz at 16 mA and 10.7 GHz at 27 mA are observed in the lasing spectra. Furthermore, the relative intensity noise spectra are presented to reveal the relationship between the lasing states and the dynamics induced by relaxation oscillation and mode beating.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)