Self-chaotic dual-mode and tri-mode microcavity lasers have been recently proposed and demonstrated for high-speed random number generation. Here, we report the characteristics of irregular pulse packages and self-chaos operation for a dual-mode circular-sided square microcavity laser. In addition to the mode interaction between the fundamental and first-order transverse modes, we observed irregular pulse packages due to the mode beating of near-degenerate modes for the first time to our best knowledge. Moreover, a successive route from periodic-one and periodic-three states to chaos is first experimentally illustrated by increasing injection current. The chaotic state is observed over a current range of 10 mA, and the maximum chaos effective bandwidth of 22.4 GHz is realized with a flatness of ±4dB. Chaotic characteristics are also investigated for different longitudinal modes, which indicates that the self-chaotic microlaser can provide robust parallel chaotic outputs for practical application.

Octave-spanning optical frequency comb (OFC) generation has achieved great breakthroughs and enabled significant applications in many fields, such as optical clocks and spectroscopy. Here, we demonstrate octave-spanning OFC generation with a repetition rate of tens of GHz via a four-wave mixing (FWM) effect seeded by a dual-mode microcavity laser for the first time, to our knowledge. A 120-m Brillouin nonlinear fiber loop is first utilized to generate wideband OFCs using the FWM effect. Subsequently, a time-domain optical pulse is shaped by appropriate optical filtering via fiber Bragg gratings. The high-repetition-rate pulse train is further boosted to 11 pJ through optimal optical amplification and dispersion compensation. Finally, an octave optical comb spanning from 1100 to 2200 nm is successfully realized through the self-phase modulation effect and dispersion wave generation in a commercial nonlinear optical fiber. Using dual-mode microcavity lasers with different mode intervals, we achieve frequency combs with octave bandwidths and repetition rates of 29–65 GHz, and demonstrate the dual-mode lasing microcavity laser as an ideal seeding light source for octave-spanning OFC generation.

Whispering-gallery-mode (WGM) hexagonal optical micro-/nanocavities can be utilized as high-quality (Q) resonators for realizing compact-size low-threshold lasers. In this paper, the progress in WGM hexagonal micro-/nanocavity lasers is reviewed comprehensively. High-Q WGMs in hexagonal cavities are divided into two kinds of resonances propagating along hexagonal and triangular periodic orbits, with distinct mode characteristics according to theoretical analyses and numerical simulations; however, WGMs in a wavelength-scale nanocavity cannot be well described by the ray model. Hexagonal micro-/nanocavity lasers can be constructed by both bottom-up and top-down processes, leading to a diversity of these lasers. The ZnO- or nitride-based semiconductor material generally has a wurtzite crystal structure and typically presents a natural hexagonal cross section. Bottom-up growth guarantees smooth surface faceting and hence reduces the scattering loss effectively. Laser emissions have been successfully demonstrated in hexagonal micro-/nanocavities synthesized with various materials and structures. Furthermore, slight deformation can be easily introduced and precisely controlled in top-down fabrication, which allows lasing-mode manipulation. WGM lasing with excellent single-transverse-mode property was realized in waveguide-coupled ideal and deformed hexagonal microcavity lasers.

Hybrid square/rhombus-rectangular lasers (HSRRLs) consisting of a Fabry–Perot (FP) cavity and a square/rhombus microcavity (SRM) are proposed and demonstrated for realizing single-mode lasing with a wide wavelength tuning range. The SRM is a deformed square microcavity with a vertex extended to the FP cavity to control the coupled mode field pattern in the FP cavity. Single-mode operation with a side-mode suppression ratio (SMSR) over 45.3 dB is realized, and a wide wavelength tuning range of 21 nm with SMSR >35 dB is further demonstrated by adjusting the injection currents of the SRM and the FP cavity simultaneously. Furthermore, a 3-dB modulation bandwidth of 14.1 GHz and an open-eye diagram at 35 Gb/s are demonstrated for the HSRRL.

Relative intensity noise (RIN) and high-speed modulation characteristics are investigated for an AlGaInAs/InP hybrid square-rectangular laser (HSRL) with square side length, rectangular length, and width of 15,300, and 2 μm, respectively. Single-mode operation with side-mode suppression larger than 40 dB has been realized for the HSRL over wide variation of the injection currents. In addition, the HSRL exhibits a 3 dB modulation bandwidth of 15.5 GHz, and an RIN nearly approaches standard quantum shot-noise limit 2hv/P= 164 dB/Hz at high bias currents due to the strong mode selection of the square microcavity. With the increase of the DC bias current of the Fabry–Perot section, significantly enhanced modulation bandwidth and decreased RIN are observed. Furthermore, intrinsic parameters such as resonance frequency, damping factor, and modified Schawlow–Townes linewidth are extracted from the noise spectra.

Stable dual-mode semiconductor lasers can be applied for the photonic generation of microwave and terahertz waves. In this paper, the mode characteristics of a variable curvature microresonator are investigated by a two-dimensional finite element method for realizing stable dual-mode lasing. The microresonator features a smooth boundary and the same symmetry as a square resonator. A small variable-curvature microresonator with a radius of 4 μm can support the fundamental four-bounce mode and the circular-like mode simultaneously, with quality factors up to the order of 104 and 105, respectively. The dual modes in the phase space of the Poincaré surface of sections distribute far from each other and can maintain enough stability for dual-mode lasing. Furthermore, the refractive index and waveguide can modulate the dual-mode wavelength difference and quality factors efficiently thanks to the spatially separated fields of these two modes.

Thermal characteristics are numerically investigated for the hybrid AlGaInAs/InP on silicon microring lasers with different ring radii and widths. Low threshold current and low active region temperature rise are expected for a microring laser with a narrow ring width. Based on the thermal analysis and the 3D simulation for mode characteristics, a hybrid AlGaInAs/InP on silicon microring lasers with an inner n-electrode laterally confined by the p-electrode metallic layer is fabricated using an adhesive bonding technique. A threshold current of 4 mA is achieved for a hybrid microring laser with a radius of 20 μm and a ring width of 3.5 μm at 12°C, and the corresponding threshold current density is as low as 1 kA∕cm². The influence of the location of silicon waveguide on output performance is studied experimentally for improving the output coupling efficiency. Furthermore, continuous-wave electrically injected lasing up to 55°C is realized for a hybrid microring laser with a radius of 30 μm and a ring width of 3 μm.China under grant 2012AA012202 and NSFC/RGC joint projectunder grant 61431166003. The authors thank Professor Andrew W. Poon and the Nanoelectronics FabricationFacility (NFF) of HKUST for support in the fabrication ofsilicon waveguides.

The dynamic characteristics are investigated for a microring laser with an external radius of 12 μm subject to external optical injection. Single-mode operation with a side mode suppression ratio of 33.4 dB is realized at a biasing current of 25 mA and a temperature of 290 K, and the corresponding small-signal modulation response is obtained with a resonance peak frequency of 7.5 GHz. Under the optical injection from a tunable laser, the improvements of the small-signal modulation response induced by four-wave mixing are observed for the microring laser, which shows an additional resonance peak around the frequency of the beat frequency between the lasing mode and the injecting light. Furthermore, optical generation of a microwave signal is realized by the light beating between the lasing mode and the injecting light measured by a high-speed photodetector and a spectrum analyzer.