Single-mode lasing in a coupled twin circular-side-octagon microcavity

We demonstrate the curvature of coupled twin circular-side-octagon microcavity(TCOM)lasers as the degree of freedom to realize manipulation of mode quality(Q)factor and lasing characteristics.Numerical simulation results indicate that mode Q factors varying from 10^(4) to 10^(8),wavelength intervals of different transverse modes,and mode numbers for four-bounce modes can be manipulated for five different deformations.Global mode distributes throughout coupled microcavity with mode Q factor around the order of 10^(4) or 10^(5).Four-bounce modes lase with injection currents applied single microcavity.By pumping both microcavities simultaneously,single-mode lasing for global modes with side mode suppression ratios(SMSRs)of 30,32,32,31,and 36 dB is achieved at the deformation of 0,0.5,1,1.5,and 2 with four-bounce modes suppressed,respectively.Moreover,the linewidths less than 11 MHz for the single mode are obtained with the deformation of 2.The results show that the lasing modes can be efficiently manipulated considering variable curvature for TCOM lasers,which can promote practical applications of microcavity lasers.

Nonlinear dynamics in a circular-sided square microcavity laser

Self-chaotic dual-mode and tri-mode microcavity lasers have been recently proposed and demonstrated for highspeed 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±4 d B.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.

Chaotic microlasers caused by internal mode interaction for random number generation

Chaotic semiconductor lasers have been widely investigated for generating unpredictable random numbers,especially for lasers with external optical feedback.Nevertheless,chaotic lasers under external feedback are hindered by external feedback loop time,which causes correlation peaks for chaotic output.Here,we demonstrate the first self-chaotic microlaser based on internal mode interaction for a dual-mode microcavity laser,and realize random number generation using the self-chaotic laser output.By adjusting mode frequency interval close to the intrinsic relaxation oscillation frequency,nonlinear dynamics including self-chaos and period-oscillations are predicted and realized numerically and experimentally due to internal mode interaction.The internal mode interaction and corresponding carrier spatial oscillations pave the way of mode engineering for nonlinear dynamics in a solitary laser.Our findings provide a novel and easy method to create controllable and robust optical chaos for high-speed random number generation.

Whispering-gallery mode hexagonal micro-/nanocavity lasers [Invited]

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 singletransverse-mode property was realized in waveguide-coupled ideal and deformed hexagonal microcavity lasers.

Widely tunable single-mode lasers based on a hybrid square/rhombus-rectangular microcavity

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.

Modulation characteristics and microwave generation for AlGaInAs/InP microring lasers under four-wave mixing

The dynamic characteristics are investigated for a microring laser with an external radius of 12μm 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.

Investigation of hybrid microring lasers adhesively bonded on silicon wafer

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∕cm^2. 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 radiusof 30 μm and a ring width of 3 μm.

Relative intensity noise in high-speed hybrid square-rectangular lasers

Relative intensity noise(RIN) and high-speed modulation characteristics are investigated for an Al Ga In As/In P 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 2 hv∕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.

Octave-spanning frequency comb generation based on a dual-mode microcavity laser

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 octavespanning 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 to11 p J 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.

Variable-curvature microresonators for dual-wavelength lasing

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 twodimensional 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 10~4 and 10~5, respectively. The dual modes in the phase space of the Poincarésurface 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.