A deformed square microcavity laser, based on internal mode interactions, exhibits spontaneous chaotic behavior without external disturbances. Unlike traditional methods that rely on photodetectors for photoelectric conversion, we propose and demonstrate a novel approach to directly extract chaotic signals from the laser's P-electrode. This scheme successfully extracts the chaotic electrical signal with a 4.4GHz bandwidth. Our approach offers advantages in cost-effectiveness and simplicity. It holds promise for applications such as high-speed physical random number generation and radar detection.
Deformed square microcavities composed of two partly overlapped square microcavities are proposed and investigated theoretically and experimentally. Single-mode lasing with the maximum side-mode suppression ratio (SMSR) of 39 dB and 52 dB are obtained for the deformed square microcavity lasers, connected an output waveguide to the jointed region and a vertex of the square microcavities, with a side length of 10 μm, respectively. Furthermore, higher output power is obtained for the deformed square microcavity laser with a vertex output waveguide than that with an output waveguide to the jointed region.
We numerically demonstrate the enhancement of chaos bandwidth using a dual-mode microsquare laser under optical feedback. The bandwidth and flatness of the chaotic power spectrum are investigated under different optical feedback rates, mode-frequency intervals and mode intensity differences. Enough feedback strengths, suitable mode-frequency intervals and small mode intensity differences are responsible for wide-band and flat chaotic power spectrum. The results indicate that we can enhance laser chaos by using a laser device with dual-mode lasing.
We report nonlinear dynamics in directly connected twin circular-sided square microcavity semiconductor lasers with mutual optical injection. Rich nonlinear dynamics including injection locking, four-wave fixing, and multi-period oscillation states are observed experimentally by adjusting the mode frequency offset between two circular-side square microcavities. Internal optical injection or mode coupling can be realized directly in the connected twin circular-sided square microcavity lasers, which effectively relaxes device processing techniques of the integrated microcavities for photonic integration.
A numerical scheme for calculating phase noise is proposed for hybrid square-rectangular semiconductor lasers. By establishing a two-section single-mode rate equation model driven by Langevin noise sources and considering the nonlinear gain effect, we numerically studied the phase noise characteristics and linewidth of the hybrid-cavity laser. The time-varying spectra of carrier density, photon density and phase are simulated and the frequency spectra of phase noise are presented with the help of the fast Fourier transform. With the increase of the bias current, the frequency noise has an obvious downward trend and a narrower linewidth is obtained. The linewidth of the hybrid square-rectangular laser is calculated according to the phase noise at low frequency. The simulated linewidth of the hybrid-cavity semiconductor laser is 0.36 MHz at the linewidth enhancement factor of 3 when the square microcavity bias current is 20 mA and the FP cavity bias current is 100 mA.
Whispering-gallery mode (WGM) microcavities with the merits of small mode volumes and high quality (Q) factors have attracted great research interests as potential low-power-consumption light sources for photonic integration. We propose and demonstrate deformed square microcavity lasers with the flat sidewalls replaced by circular arcs as converge mirrors to control the WGMs inside the laser cavity. The ray dynamic analysis results indicate that the circular-sides can confine the light rays with stable islands, although full chaotic dynamics are observed under certain deformation. With the numerical simulation of the circular-side square microcavities, ultrahigh-Q modes are obtained owing to the elimination of the scattering losses from the vertices, and a reduction of mode Q factors due to the chaotic ray dynamics is also observed. Different transverse modes have distinct light trajectories, which results in a difference of the effective roundtrip length and a controllable transverse mode interval. Low threshold lasing is achieved experimentally due to the high Q factors of the WGMs. The lasing spectra can be engineered by designing the cavity geometry for the waveguidecoupled circular-side square microcavity lasers. The robust structure and ultrahigh-Q of the waveguide-coupled microlasers provide a potential solution for the compact light sources in photonic integrated circuits.
Lasing mode control and direct modulation characteristics have been investigated for waveguide-coupled unidirectional-emission square microcavity lasers. A quasi-analytical model is introduced to analyze the mode field distributions and quality (Q) factors for the confined modes inside the square optical microcavities with directly coupled waveguide, where high-Q whispering-gallery-like (WG-like) modes are induced by the mode coupling between doubly-degenerate modes. AlGaInAs/InP waveguide-coupled unidirectional-emission square microcavity lasers are fabricated by using standard planar technology, and electrically-injected lasing is realized at room temperature. The lasing modes are controlled by properly designing the lasing cavity, output waveguide and injection pattern. Dual-transverse-mode lasing with a tunable wavelength interval from 0.25 to 0.39 nm is realized by using a spatially selective current injection to modulate the refractive index, as the mode field distributions of different transverse are spatially separated. The wavelength interval can be further increased to a few nanometers by reducing the cavity size and replacing the flat sidewalls with circular arcs. The field distributions of WG-like modes distribute uniformly in square microcavity, which avoid the burning-induced carrier diffusion in high-speed direct modulation. A small-signal modulation 3dB bandwidth exceeding 16 GHz, and an open eye diagram at 25 Gb/s are demonstrated for the high-speed direct modulated square microcavity laser.
The characteristics of integrated lasers consisting of a Fabry-Pérot (FP) cavity with one side connected to a whisperinggallery mode (WGM) microcavity are reported, in which the WGM microcavity acts as a resonant reflector for the FP cavity with its reflectivity capable of being modulated. The mode coupling between the WGM and FP mode would clamp the lasing mode around the wavelength of the WGM and suppress additional side modes. Single mode lasing with the side mode suppression ratio higher than 40 dB is realized for an integrated laser with the FP cavity directly connecting to one vertex of a square microcavity. The wavelength tunability is further demonstrated by varying the bias currents into the square cavity and the FP cavity regions. In addition to the lasing characteristics of single mode operation, we also report the high speed modulation characteristics of the integrated laser.
Due to the merits of small size and low power consumption, microdisk lasers have been widely investigated as a potential light source for photonic integrated circuits. We investigate the dynamic and mode characteristics for a directional-emission microdisk laser subject to optical injection. At the free-running state, single-mode operation at 1540.16 nm with side-mode suppression ratio of 35 dB is realized for an 8-μm-radius microdisk laser connected with a 2-μm-width output waveguide at 7 mA. Under the injection locking state with the injection optical power of 2 mW, the 3-dB bandwidth of the small signal modulation response is enhanced from 3.4 to 13.7 GHz for the microdisk laser biased at 7 mA. Furthermore, the nonlinear states including four-wave mixing, period-one, and period-two oscillations are also observed and discussed for the microdisk laser subject to the optical injection with different wavelength detuning and optical power.
The dynamic characteristics are investigated for an 8-μm-radius directional-emission microdisk laser subject to optical injection. Single mode operation with lasing mode wavelength of 1540.1 nm and the side mode suppression ratio of 35 dB is realized for the microdisk laser at the biasing current of 10 mA and the temperature of 288 K. Under the optical injection from a tunable laser, optical injection locking and the enhancement of the 3dB bandwidth of small signal modulation response from 3.4 to 13.7 GHz are observed for the microdisk laser biased at 7 mA with an injected optical power of 0.5 mW. By varying the wavelength detuning between the injection light and the lasing mode, we demonstrate the nonlinear states of four-wave mixing, period-one and period-two oscillations from the lasing spectra. Multiple peaks are observed for the period-one and period-two oscillation states.
High-speed modulation characteristics are investigated for microdisk lasers theoretically and experimentally. In rate equation analysis, the microdisk resonator is radially divided into two regions under uniform carrier density approximation in each region. The injection current profile, carrier spatial hole burning, and diffusion are accounted for in the evaluation of small-signal modulation curves and the simulation of large-signal responses. The numerical results indicate that a wide mode field pattern in radial direction has merit for high-speed modulation, which is expected for coupled modes in the microdisk lasers connected with an output waveguide. For a 15-μm-radius microdisk laser connected with a 2-μm-wide output waveguide, the measured small-signal response curves with a low-frequency roll-off are well in agreement with the simulated result at a 2-μm radial width for the mode intensity distribution. The resonant frequencies of 7.2, 5.9, and 3.9 GHz are obtained at the temperatures of 287, 298, and 312 K from the small-signal response curves, and clear eye diagrams at 12.5 Gb/s with an extinction ratio of 6.1 dB are observed for the microdisk laser at the biasing current of 38 mA and 287 K.
High speed modulation characteristics are investigated for microcircular lasers connected with an output waveguide theoretically and experimentally. The injection current profile and carrier spatial hole-burning and diffusion are accounted in the rate equation model by radially dividing the microcircular resonator into two regions under the approximation of uniform carrier densities. The numerical results indicate that wide mode field pattern in radial direction has merit for high speed modulation, which is expected for coupled modes in circular microlasers connected with an output waveguide. Small signal response curves and large signal modulation responses are investigated for a 15-μmradius microlaser connected with a 2 μm wide output waveguide. The highest resonance frequencies of 7.2, 5.9 and 3.9 GHz are obtained at the temperatures of 287, 298 and 312 K from the small signal response curves, and clear eye diagrams at 12.5Gbit/s with an extinction ratio of 6.1 dB are observed for the microlaser at biasing current of 38 mA and the temperature of 287 K.
Three-dimensional circular resonators connected with an output waveguide were simulated by the three-dimensional finite-difference time-domain (FDTD) technique. For the microcircular resonator with vertical waveguiding consisted of active layer confined by upper and lower cladding layers with the refractive indices of 3.4 and 3.17, the mode Q factors are greatly influenced by the thickness of the upper cladding layer. The numerical results of the near field and the farfield patterns indicate that the vertical waveguide with semiconductor materials does not provide enough optical confinement for the confined modes in the resonator. Furthermore, the lasing spectra and far-field patterns are measured for a circular microlaser with a radius of 15 μm and a 2-μm-width output waveguide. Single mode operation with the side mode suppression ratio up to 33 dB is realized at room temperature, and multiple peaks are observed in the vertical far-field pattern due to the vertical radiation of the mode field.
Unidirectional-emission microlasers are greatly demanded for photonic integrated circuits and optical interconnection. In
this paper, the mode characteristics of circular and coupled-circular microresonators with a bus waveguide are
numerically simulated by finite-difference time-domain technique. For a circular microresonator connected with a bus
waveguide, coupled-mode between two whispering-gallery modes can have high mode Q factor for realizing
unidirectional-emission lasing. In addition, symmetry and antisymmetry coupled modes are analyzed for the coupledcircular
microresonator with a middle bus waveguide. Furthermore, the output characteristics of a coupled-circular
microlaser, which is fabricated by standard photolithography and inductively-coupled-plasma (ICP) etching techniques,
are reported. Single mode operation is realized for the coupled-circular microlaser with a radius of 20 μm and a 2-μmwidth
bus waveguide.
Wavelength-scale defected circular microresonators with laterally confined metal layer are designed for directional
emission from high Q confined modes by boundary element method (BEM), which is firstly applied to the multilayer
structures. The influence of metal layer thickness on the mode filed patterns and Q factors are simulated. The results
indicate that the thickness of the metal layer has a great effect on far-field emission patterns and the mode Q factors.
Multiple-port directional emission microlasers are potential light sources and optical signal processing units in photonic
integrated circuits. Connecting bus waveguides to a microresonator is a simple method to realize directional emission
microlasers. In this paper, we investigate square and circular resonator microlasers connected with multiple bus
waveguides. The mode characteristics of the microresonators connected with multiple bus waveguides are simulated by
finite-difference time-domain technique, and the numerical results of mode Q factors and output coupling efficiencies
show that high efficiency directional emission microresonator lasers can be realized. Furthermore, the microcylinder
laser connected with a bus waveguide fabricated by planar technology processes is reported, and the lasing spectra of
square microlasers with four vertices connected to bus waveguides are analyzed.
Square microresonators with circular corners and a center air hole are simulated by the finite-difference time-domain
(FDTD) technology and Padé approximation method. The results show that the deformed square resonators can increase
mode Q factor at certain conditions. Furthermore, the hole in the square resonator can not only enhance the Q factor and
the output coupling efficiency, but also have the ability to select the lasing mode.
Microcavity lasers with whispering-gallery modes (WGMs) are potential light sources for photonic integrated circuits.
However, the direction emission and output power are greatly limited for microdisks with the WGMs confined by total
internal reflection. Deformed microdisk with chaos mode light rays or evanescently coupled waveguide were used to
realize directional emission microlasers. Different from the microdisk with traveling wave WGMs, confined modes in
triangle and square microcavities are standing wave WGMs. So the confined modes can still have high Q-factors if an
output waveguide is directly connected to triangle and square microcavities at the position with weak mode field
distribution. Based on theoretical analysis and numerical simulation of the mode characteristics, we fabricate directional
emission triangle and square InGaAsP/InP microcavity lasers with an output waveguide directly connected to the
resonators by standard photolithography and inductively coupled plasma etching technique. Continuous-wave (CW)
electrically injected InGaAsP triangle and square microlasers are realized at room temperature for the triangle
microlasers with side length from 10 to 30 μm and the square microlaser with the side length of 20 μm.
Directional emission semiconductor microcavity lasers integrated with semiconductor planar technique are potential light
sources for photonic integrated circuits. In this article, we investigate mode characteristics for equilateral triangle and
square microcavities for realizing directional emission microcavity lasers. The analytical mode field distributions and
mode wavelengths are presented for two-dimensional (2D) triangle and square resonators, and directional emission are
simulated by finite-difference time-domain (FDTD) technique. The numerical results of mode Q-factors and output
coupling efficiencies for the triangle and square resonators show that high efficiency directional emission microcavity
lasers can be realized by directly connected an output waveguide to the resonators, because the mode field patterns are
standing distributions in the triangle and square resonator. Laser output spectra of fabricated InGaAsP/InP triangle lasers
are compared with the analytical results.
The measurement and analysis of the microwave frequency response of semiconductor optical amplifiers (SOAs) are
proposed in this paper. The response is measured using a vector network analyzer. Then with the direct-subtracting
method, which is based on the definition of scattering parameters of optoelectronic devices, the responses of both the
optical signal source and the photodetector are eliminated, and the response of only the SOA is extracted. Some
characteristics of the responses can be observed: the responses are quasi-highpass; the gain increases with the bias
current; and the response becomes more gradient while the bias current is increasing. The multisectional model of an
SOA is then used to analyze the response theoretically. By deducing from the carrier rate equation of one section under
the steady state and the small-signal state, the expression of the frequency response is obtained. Then by iterating the
expression, the response of the whole SOA is simulated. The simulated results are in good agreement with the measured
on the three main characteristics, which are also explained by the deduced results. This proves the validity of the
theoretical analysis.
KEYWORDS: Quantum dots, Chemical species, 3D modeling, Systems modeling, Optoelectronics, Finite element methods, Scanning tunneling microscopy, Telecommunications, Optical communications, Luminescence
In this paper, we calculated the strain distribution of low dimension structure using the elastic continuum model in the first part we focused on the lens-shaped quantum dot, and discussed the strain distribution of the quantum dot with and without capping layer. In another section, we gave a detail analysis about the strain distribution for quantum wire and quantum dot intergrowth structure, and there are two situations: the first, a little bigger quantum dot grown within a single quantum wire, the second, Y shaped quantum wires where quantum dot grown in the cross section of the wires, and the angle of the Y shaped wires lessen than 12 degree. All the low-dimension structures discussed have been observed in the laboratory. For the lens-shaped quantum dot with and without capping layer, the results showed that in both circumstances, the strain distribution would become more uniform in the quantum dot if the transverse size becomes larger. Compared with the open quantum dot (without capping layer), the capping layered quantum dot has a more sufficient strain relaxation, and even excessive strain relaxation is observed in the simulation. This phenomenon can be used to qualitative explain the quantum dot cave in and cavern out in the sequential capping layer growth interruption observed in laboratory. It is very promising for the quantum wire and quantum dot intergrowth structure. The phenomena of photoluminescence spectrum not changing with the variation of temperature have been observed recently in the intergrowth structure. For convenience, we used a simplified model to calculate such a structure, which we adopted rectangle quantum wire and rectangle quantum dot. The growth is along the [001] direction, and the wire is along the [110] direction. The results showed that the strain in quantum dot is greatly enhanced in the intergrowth structure compared with the single quantum dot system. There are strain-focusing region around the interface of quantum dot and quantum wire.
Modes in equilateral triangle resonator (ETR) are analyzed and classified according to the irreducible representations of the point group C3v. Both the analytical method based on the far field emission and the numerical method by FDTD technique are used to calculate the quality factors (Q-factors) of the doubly degenerate states in ETR. Results obtained from the two methods are in reasonable agreement. Considering the different symmetry properties of the doubly degenerate eigenstates, we also discuss the ETR joined with an output waveguide at one of the vertices by FDTD technique and the Pade approximation. The variation of Q-factors versus width of output waveguide is analyzed. The numerical results show that doubly degenerate eigenstates of TM0.36 and TM0.38 whose wavelengths are around 1.5μm in the resonator with side-length of 5μm have the Q-factors larger than 1000 when the width of the output waveguide is smaller than 0.4μm. When the width of the output waveguide is set to 0.3μm, the symmetrical states that are more efficiently coupled to output waveguide have Q-factors about 8000, which are over 3 times larger than those of asymmetric state.
The effects of birefringence on performances of SOA-based interferometer devices are analyzed theoretically, the necessity of fabricating SOA whose gain and induced phase shift are both independent on polarization state is proposed. Birefringence in SOA will degrade the performances of SOA-based devices due to polarization walkoff of the two split probe light. The calculations for a SOA-based Mach-Zehnder interferometer wavelength-converter
indicate that the extinction ratio will decrease and become very sensitive to the polarization state of input light if there is birefringence in SOAs. A scheme is proposed to eliminate these effects and the possibility of making a SOA polarization insensitive in gain and induce phase shift is analyzed theoretically.
We report some investigations on vertical cavity surface emitting laser (VCSEL) arrays and VCSEL based optoelectronic smart photonic multiple chip modules (MCM), consisting of 1x16 vertical cavity surface emitting laser array and 16- channel lasers driver 0.35 )mum CMOS circuit. The hybrid integrated multiple chip modules based on VCSEL operate at more than 2GHz in-3dB frequency bandwidth.
Polarization-insensitive semiconductor optical amplifiers (SOA's) with tensile-strained multi-quantum-wells as actice regions are designed and fabricated. The 6x6 Luttinger-Kohn model and Bir-Pikus Hamiltonian are employed to calculate the valence subband structures of strained quantum wells, and then a Lorentzian line-shape function is combined to calculate the material gain spectra for TE and TM modes. The device structure for polarization insensitive SOA is designed based on the materialde gain spectra of TE and TM modes and the gain factors for multilayer slab waveguide. Based on the designed structure parameters, we grow the SOA wafer by MOCVD and get nearly magnitude of output power for TE and TM modes from the broad-area semiconductor lasers fabricated from the wafer.
The semiconductor microlasers based on the equilateral triangle resonator (ETR) can be fabricated from the edge-emitting laser wafer by dry-etching technique, and the directional emission can be obtained by connecting an output waveguide to one of the vertices of the ETR. We investigate the mode characteristics, especially the mode quality factor, for the ETR with imperfect vertices, which is inevitable in the real technique process. The numerical simulations show that the confined modes can still have a high quality factor in the ETR with imperfect vertices. We can expect that the microlasers is a suitable light source for photonic integrated circuits.
We report on optoelectronic multiple chip modules, consisting of vertical cavity surface emitting laser (VCSEL), photodetector and 1.2 micrometer CMOS electronic circuit. The hybrid integrated components operate at a date rate of 155 Mb/s, which could be used in optical interconnects for multiple computers.
We analyze the mode behaviors for semiconductor lasers with an equilateral triangle resonator by deriving the mode field distribution and the eigenvalue equation. The eigenvalue equation shows that the longitudinal model wavelength interval is equivalent to that of a Fabry-Perot cavity with the cavity length of 1.5a, where a is the side length of the equilateral triangle resonator. The transverse waveguiding is equivalent to a strip waveguide with the width of (root)3 a/2, and the number of transverse modes supported by the resonator is limited by the total reflection condition on the sides of the equilateral triangle. Semiconductor microcavity laser with an equilateral triangle resonator is suitable to realize single mode operation, and the mode wavelength can be adjusted by changing the side length.
The behaviors of lateral propagating modes in the aperture and the oxidized regions are investigated numerically for selectively oxidized vertical-cavity surface-emitting lasers (VCSELs). The results show that the lateral propagating modes in the oxidized region are greatly affected by the oxide layer due to its low index, the modes are divergence for the VCSELs with sufficient thick double oxide layers. So the coupling between the modes in the aperture and oxidized regions is very weak, and we can expect that the lateral spontaneous emission is greatly affected in this case. Ignoring the contribution of the lateral spontaneous emission, we calculate spontaneous emission factor by counting the total number of the guided modes in selectively oxidized VCSELs with double oxide layers. The results agree very well with the reported measurements and are inversely proportional to the lateral index step.
Based on the equivalent resistance and finite element method, the current distribution in active region is analyzed with current injection from ring electrode. To improve the injection efficiency and reduce the resistance of p-type DBR, we design reverse mesa structure and achieved low threshold current InGaAs vertical cavity surface emitting laser operation. In situ thickness monitoring and controlling in MBE growth is also studied.
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