Square microcavities with high quality factor whispering-gallery-like modes have a series of novel optical properties and can be employed as compact-size laser resonators. In this paper, the mode ...characteristics of square optical microcavities and the lasing properties of directional-emission square semiconductor microlasers are reviewed for the realization of potential light sources in the photonic integrated circuits and optical interconnects. A quasi-analytical model is introduced to describe the confined modes in square microcavities, and high quality factor whispering-gallery-like modes are predicted by the mode-coupling theory and confirmed by the numerical simulation. An output waveguide directly coupled to the position with weak mode field is used to achieve directional emission and control the lasing mode. Electrically-pumped InP-based directional-emission square microlasers are realized at room temperature, and the lasing spectra agree well with the mode analysis. Different kinds of square microcavity lasers, including dual-mode laser with a tunable interval, single-mode laser with a wide tunable wavelength range, and high-speed direct-modulated laser are also demonstrated experimentally.
In this work, we investigate an alternative directly modulated laser solution with applications to multiwavelength 25 Gb/s systems. The presented solution is based on a hybrid ...square/rhombus-rectangular laser (HSRRL), which consists of a Fabry–Pérot (FP) cavity and a square/rhombus microcavity (SRM). This structure is implemented and demonstrates single-mode lasing over a wide wavelength tuning range (30.8 nm). Single-mode operation is achieved with a side-mode suppression ratio (SMSR) greater than 30 dB and a linewidth of 10 MHz. Furthermore, with an electrical 3 dB bandwidth of 10 GHz. It is possible to directly modulate at 25 Gb/s with promising performance. These devices are simple and they are expected to meet the cost and power requirements of current networks.
We demonstrate silicon nitride mode-division multiplexing (MDM) and wavelength-division multiplexing (WDM) using asymmetrical directional couplers and microring resonators. Our experiments reveal ...three-mode multiplexing and demultiplexing. We demonstrate 30Gb/s open eye diagrams with an extinction ratio of ~9 dB for each of the three modes. We observe the worst-case modal crosstalk of ~-10 dB. Our analysis of the measured transmission spectra suggests three contributions to the observed crosstalks, with the dominant cause being a compromised input-coupling at the directional couplers in the multiplexer.
Mode characteristics of three-dimensional (3-D) microsquare resonators are investigated by finite-difference time-domain (FDTD) simulation for the transverse electric (TE)-like and the transverse ...magnetic (TM)-like modes. For a pillar microsquare with a side length of 2 mum in air, we have Q-factors about 5 times 10 3 for TM-like modes at the wavelength of 1550 nm, which are one order larger than those of TE-like modes, as vertical refractive index distribution is 3.17/3.4/3.17 and the corresponding center layer thickness is 0.2 mum. The mode field patterns show that TM-like modes have much weaker vertical radiation coupling loss than TE-like modes. TM-like modes can have high Q-factors in a microsquare with weak vertical field confinement.
Square microcavity lasers with a cut-corner are proposed and demonstrated for realizing unidirectional emission single-mode lasers. The mode characteristics of the square resonator with a cut-corner ...are investigated by 2-D finite-element method simulation. Far field patterns with single petal and double petals are obtained numerically for symmetric and antisymmetric modes, respectively. Square microcavity lasers with a cut-corner are fabricated using planar photolithography and inductively coupled-plasma etching techniques. A continuous wave single-mode operation with a side mode suppression ratio of 31 dB is achieved at an injection current of 25 mA for a 20 μm-side-length square microcavity laser with a cut-corner width of 10 μm. The far field patterns agreement with the simulated symmetric and anti-symmetric modes are observed at different injected currents.
Optical frequency comb (OFC) generation based on four-wave mixing in highly nonlinear fiber (HNLF) is investigated using dual-transverse-mode square microlaser as a seed source. Dual-mode lasing ...microlasers with wavelength intervals from 1.11 to 0.36 nm are realized and applied for OFC generation at different square side lengths. For an 18- μm-side-length microlaser, a frequency comb with 50 nm bandwidth and 102 GHz line spacing is achieved using two stages of erbium-doped fiber amplifier and HNLF. A phase-locked comb with a pulse width of 1 ps is also verified using frequency resolved optical gating analyses. In addition, the comb linewidths are nearly linearly increased with the comb order, which is in agreement with the linewidth behavior determined by 1/ f noise. The results indicate that 1/f noise deteriorates the laser linewidth greatly.
The lasing characteristics are investigated for an InAlGaAs/InP wavelength-scale square cavity laser with a height of 800 nm and a side length of 2.2 μm. The laser is coated by aluminum/silica on the ...bottom and sidewalls and bonded on a silicon wafer. Single-mode lasing at 1556.5 nm with a sidemode suppression ratio of 21 dB is observed under optical pulse pumping for the square cavity laser at room temperature. The lasing mode profile captured by an infrared camera and the spectrum agree well with the simulated results of the three-dimensional finite-difference time-domain technique. In addition, a spontaneous emission factor of 1.5 × 10 -2 is measured by fitting the output power versus input pump power curve with the dynamical results of rate equations.
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.
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.
AlGaInAs-InP microcylinder lasers with an output waveguide surrounded by benzocyclobutene are fabricated, using standard photolithography and inductively coupled-plasma etching technique. ...Room-temperature continuous-wave (CW) operation is realized for a microlaser with a radius of 20 μm and a 2-μm-wide output waveguide. Single-mode operation with side-mode suppression ratio around 25 dB is achieved, and the wavelength shifts from 1563.5 to 1567.3 nm with the injection current increases from 50 to 100 mA. The characteristic temperature of the threshold current is 58 K, obtained by fitting the output power versus the injection current with analytical relations. The practical laser temperature is expected to be about 391 K at the CW injection current of 130 mA.
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