Vertical-cavity Surface-emitting Laser Structure Research Articles

Performance analysis of VCSEL using finite difference time domain method

Vertical Cavity Surface Emitting Laser (VCSEL) with significantly diverse structures has evolved with time for a different type of applications. A number of researchers used Finite Element Method (FEM) solver for computation of optical resonance modes in VCSEL but this method has a limitation of accuracy because it uses an approximate solution of partial differential equationsand integral equations. Furthermore, FEM is based either on eliminating the time derivatives completely or by rendering the partial differential equations into an equivalent ordinary differential equations. In this research work, we have used Finite Difference Time Domain (FDTD) method which elaborates the fine features of VCSEL and the accuracy of the VCSEL results got improved.The proposed approach is also beneficial for calculating reflectance for multiple wavelengths of light per simulation which is the major advantage over FEM. In this research paper, a new VCSEL structure is modeled and also numerically investigated by using proposed FDTD method. A complete analysis of VCSEL light emission, its electric field and Poynting vector are also evaluated at different points of light in thesecond window of optical communication. A rigorous evaluation in terms of spectrum analysis, transmission analysis and farfield projection analysis is done for wavelength ranging from 1310 nm to 1350 nm. Results show that the maximum power of 0.81 W is obtained at a wavelength of 1320 nm with maximum peak voltage of 1.4 V/m and 0.006 W/m2 Poynting vector.

Simulation and optimization of 2.6\u20132.8\xa0\u03bcm GaSb-based VCSELs

We present the simulation results of threshold operation of mid-infrared GaSb-based vertical-cavity surface-emitting lasers (VCSELs) obtained with the use of comprehensive fully self-consistent optical-electrical-thermal-recombination numerical model. The results show that by a proper design of VCSEL structure and composition of the active region it is theoretically possible to achieve room-temperature (RT) threshold operation for wavelength of 2.8 μm which is about 0.2 μm longer than those reported so far in the literature for III-V VCSELs with type-I quantum wells. Calculated values of the RT threshold current were equal to 2.5 and 4.0 mA for tunnel-junction diameters of 2 and 4 μm, respectively.

Design and analysis of an electrically pumped microcavity organic laser device

We propose a new structure of organic vertical-cavity surface-emitting laser to be pumped electrically. The microcavity structure consists of an organic light emitting diode with field-effect electron transport set in between multilayer dielectric mirrors. The threshold behavior and the dynamics of the proposed OVCSEL are analyzed numerically. We show that the device can reach the lasing threshold under electrical pump at a current density of 24 A/cm2. Also, the dynamic behavior of the device under pulsed excitation is investigated. The results show that pulse excitation reduces field quenching and triplet exciton losses; hence, output photon density can be increased.

Analysis of Threshold Currents and Transverse Modes in Nitride VCSELs With Different Resonators

This paper presents a comprehensive, self-consistent, room-temperature simulation of the operation of 414-nm nitride-based vertical-cavity surface-emitting lasers (VCSELs). We calculate the threshold currents and optical modes in a VCSEL structure based on the first continuous-wave nitride VCSEL reported to operate at room temperature, and in subsequent modifications of that structure. The effects of spectral detuning and of variations in resonator length and optical/electrical apertures are analyzed. Mechanisms of mode selection are described, and the fact that nitride VCSELs can operate on a very high-order mode is explained.

Optical properties of intermixed vertical cavity surface emitting lasers: a theoretical model

The effect of intermixing on some important optical properties of vertical cavity surface emitting lasers (VCSELs) has been successfully modeled and analyzed. A combined superposition of the error function solution to the diffusion equation for a hypothetical AlxGa1−xAs/GaAs VCSEL structure has been applied to simulate the intermixing process during growth or post-growth thermal annealing using a depth-independent and/or a depth-dependent interdiffusion coefficient. The simulations of the VCSEL reflectivity and phase shift revealed no appreciable difference between the two assumptions. It has been shown that for diffusion lengths of about 20 nm the overall VCSEL reflectivity and phase shift does not change significantly, however, the VCSEL bandwidth was shown to decrease at relatively small diffusion length. The width of the transmission “dip”, which is the VCSEL emission wavelength was also shown to increase with increasing diffusion length indicating an appreciable intermixing of the active region and hence different conduction and valence band transitions due to modifications in the quantum wells and barriers shapes and widths. The presented model may provide a simple yet versatile technique for the analysis of interdiffusion during VCSEL growth or post-growth thermal annealing for device efficiency and optimization.

Surface and edge electroluminescence study of as-grown VCSEL structures

We present a simple quick evaluation method on vertical-cavity-surface-emitting laser (VCSEL) structures, which is designed for atomic clock working at high temperature (>350K), to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) gain peak. The surface and edge electroluminescence (EL) measurements were performed non-destructively on pieces of as-grown VCSEL structures by employing soldered indium (In) contacts. The surface EL spectra determine the CM position, while the edge EL spectra are used to identify the wavelength of ground-state emission from the QW in the active region (QW gain peak). The room temperature EL measurements from a cleaved edge of the VCSEL structures indicate that the QW gain peak is at ∼780.5nm, while the CM measured in the VCSEL surface emission EL peak (sample B) is at ∼793nm. When the sample is heated up, the amount of CM shift with temperature can be fitted with ΔλCM=T×0.068 nm/K, also corroborated by temperature dependence surface reflectivity measurement, and the gain peak can be fitted withλQWpeak=780.5nm + T×0.26 nm/K. The CM and QW gain peak of sample B will be brought into alignment at ∼365K by fitting curve and this was confirmed by measurement. In summary, the surface and edge EL measurements using soldered In as electrodes can be very useful for post growth non-destructive characterization of VCSELs at different temperature.

The influence of quaternary electron blocking layer on the performance characteristics of intracavity-contacted oxide-confined InGaN-based vertical cavity surface emitting lasers

The effect of electron blocking layer (EBL) on the performance characteristics of InGaN-based vertical cavity surface emitting lasers (VCSELs) was numerically investigated using an integrated system engineering technical computer aided design (ISE TCAD) simulation program. Simulation results indicated that the performance characteristics of InGaN quantum well VCSEL were improved by the ternary [Formula: see text] EBL. Better performance was also obtained when [Formula: see text] EBL was replaced by a polarization-matched [Formula: see text] EBL having the same energy bandgap. The quaternary EBL enhances the output power and differential quantum efficiency (DQE) as well as reduces the threshold current compared with the ternary EBL. Enhancement in the value of the optical intensity was also observed in the VCSEL structure with quaternary EBL. Furthermore, the effect of Al composition of AlInGaN EBL on the performance of InGaN-based VCSEL structure that uses the quaternary AlInGaN EBL was studied. In mole fraction was 0.115, Al mole fraction changed from 0.260 to 0.290 by step 0.005, and optimum performance was achieved in 0.275 Al mole fraction of AlInGaN EBL.

Very High Bit-Rate Distance Product Using High-Power Single-Mode 850-nm VCSEL With Discrete Multitone Modulation Formats Through OM4 Multimode Fiber

In order to investigate the tradeoff between optical spectral width and modulation speed of 850-nm Zn-diffusion vertical-cavity surface-emitting laser (VCSEL) and its influence on the performance of discrete multitone (DMT) modulation, two kinds of high-speed VCSEL structures with different cavity lengths (λ/2 and 3λ/2) are studied. By shortening the cavity length to λ/2, allocating the oxide layer in the standing-wave peak, and performing a Zn-diffusion aperture in our VCSEL structure, stable dual mode in the output optical spectra across the full range of bias currents with good high-speed performance (∼16-GHz bandwidth) can be achieved. Compared with its multimode reference, it shows far less roll-off with regard to the maximum data rate versus transmission distance over OM4 multimode fibers under forward error correction (FEC) threshold (BER $ ). On the other hand, for the 3λ/2 VCSEL structure, by using the same Zn-diffusion conditions as those of dual-mode counterpart, highly single-mode operation (side-mode suppression ratio> 35 dB) with high available power can be achieved over the full range of bias currents. Although such device shows a smaller 3-dB electrical-to-optical bandwidth (12 versus 16 GHz) than that of the dual-mode one, it exhibits a superior transmission performance by use of DMT modulation format. A record high bit-rate distance product (107.6 Gb/s·km) at nearly 50-Gb/s transmission under FEC threshold (BER $ ) through 2.2-km OM4 fibers has been successfully demonstrated by the use of single-mode VCSEL with optimized structures. In addition, error-free (BER $ ) transmission at 20.3 Gb/s with bit-rate distance product of 44.66 Gb/s·km has also been demonstrated.

Improved carrier injection in GaN-based VCSEL via AlGaN/GaN multiple quantum barrier electron blocking layer.

In this report, the improved lasing performance of the III-nitride based vertical-cavity surface-emitting laser (VCSEL) has been demonstrated by replacing the bulk AlGaN electron blocking layer (EBL) in the conventional VCSEL structure with an AlGaN/GaN multiple quantum barrier (MQB) EBL. The output power can be enhanced up to three times from 0.3 mW to 0.9 mW. In addition, the threshold current density of the fabricated device with the MQB-EBL was reduced from 12 kA/cm2 (9.5 mA) to 10.6 kA/cm2 (8.5 mA) compared with the use of the bulk AlGaN EBL. Theoretical calculation results suggest that the improved carrier injection efficiency can be mainly attributed to the partial release of the strain and the effect of quantum interference by using the MQB structure, hence increasing the effective barrier height of the conduction band.

Monolithic Subwavelength High-Index-Contrast Grating VCSEL

In this letter, we propose and numerically investigate a new vertical-cavity surface-emitting laser (VCSEL) structure consisting of a nearly lambda-thick active optical cavity sandwiched between two planar monolithic subwavelength high-index-contrast gratings (MHCGs) etched directly into the semiconductor layers surrounding the optical cavity. The structure allows the reduction of the vertical thickness of the subsequent MHCG VCSEL to roughly 0.6 $\mu \text{m}$ for emission at 980 nm. Compared with a conventional all-semiconductor VCSEL with distributed Bragg reflector mirrors, the MHCG VCSEL has a shorter effective cavity length and thus a shorter roundtrip cavity time. Our proposed design enables the fabrication of VCSELs with lattice-matched mirror layers in all common semiconductor optoelectronic material systems, or alternatively VCSELs with hybrid HCGs.

Numerical investigation of side emission from large-area vertical-cavity surface-emitting lasers.

For large-area ion-implanted vertical-cavity surface-emitting lasers (VCSELs), side emission from the edges of a chip disturbs the laser emission of a VCSEL mode, and suppression of it is fundamental. In this paper, we present results of a numerical investigation of the side emission from large-area VCSELs. We have modeled a VCSEL structure by an infinitely broad layer structure with mirror loss at the edge surfaces. Estimated threshold gains indicate that laser emission occurs either in a VCSEL mode or in an edge-emitting Fabry-Perot (EEFP) mode. Calculated emitter length dependence of the threshold gain of these modes shows good agreement with experimental results, and the side emission is verified to be the laser emission of the EEFP mode. We have also discussed the way to suppress the side emission and confirmed that our recent achievement of over 200 W quasi-continuous-wave output from an ion-implanted VCSEL array is due to antireflection coatings of the edges and introduction of optical losses in ex-emitter regions.

Upconversion Lasers: Stable and Low‐Threshold Optical Gain in CdSe/CdS Quantum Dots: An All‐Colloidal Frequency Up‐Converted Laser (Adv. Mater. 17/2015)

An all-colloidal vertical-cavity surface-emitting laser (VCSEL) is reported by C. Dang, H. Sun, H. V. Demir and co-workers on page 2741, which offers high performance and stability while being fully solution processed. This all-colloidal laser is based on a stacked architecture of dielectric mirrors, based on metal oxide nanoparticles sandwiching semiconductor nanocrystals as the optical gain medium, forming an all-solution-processed VCSEL structure. Here, using tailored core-shell quantum dots that have suppressed non-radiative Auger recombination enables the achievement of sub-mJ cm−2 frequency up-converted lasing thresholds, which make these all-colloidal devices highly promising for optoelectronic and biomedical applications.

Electrically tunable organic vertical-cavity surface-emitting laser

An electrically tunable organic vertical-cavity surface-emitting laser (VCSEL) is demonstrated and characterized. A lasing wavelength tunability of Δλ = 10 nm with 6 V actuation is shown for a red laser emission tuned between λ = 637 nm and λ = 628 nm. Wavelength tuning of the VCSEL structure is enabled by electrostatic deflection of a reflective flexible membrane that is suspended over an air gap and a dielectric mirror, forming a 3λ lasing cavity. The lasing gain medium consists of an evaporated organic thin film coated on a reflective membrane, which is then additively placed over a patterned substrate containing the dielectric mirror to fabricate an array of air-gap-VCSEL structures, each 100 μm in diameter. Beyond the electrostatic actuation of these tunable lasers, the VCSEL array geometry also has the potential to be used as pressure sensors with an all-optical remote excitation and readout and a pressure sensitivity of 64 Pa/nm in the demonstrated configuration.

Design and fabrication of a InGaN vertical-cavity surface-emitting laser with a composition-graded electron-blocking layer

In this study, the design and fabrication of a InGaN vertical-cavity surface-emitting laser (VCSEL) with a composition-graded electron blocking layer (GEBL) are revealed experimentally and theoretically. It has been demonstrated that laser output performance is improved by using a GEBL when compared to the typical VCSEL structure of a rectangular EBL. The output power obtained at 20 kA cm−2 is enhanced by a factor of 3.8 by the successful reduction of threshold current density from 12.6 to 9.2 kA cm−2 and the enlarged slope efficiency. Numerical simulation results also suggest that the improved laser output performances are due mainly to the reduction of electron leakage current and the enhanced hole injection efficiency in the multiple-quantum-well (MQW) active region.

OPTICAL GAIN AND ENERGY BAND STRUCTURE OF PHOTONIC CRYSTAL VCSELs WITH HIGH-INDEX-CONTRAST SUBWAVELENGTH GRATINGS

Photonic crystal vertical-cavity surface-emitting laser structure with incorporation of high-index-contrast subwavelength gratings is fabricated and the three quantum well active region of the structure is investigated with 8 band k.p model. The dispersion of energy sub-bands and wave functions in the conduction bands and valence bands indicate that effective overlapping and interactions between electrons and holes can be realized in the quantum wells and that the maximum spontaneous emission rate and optical gain occurs at the expected wavelength, which is confirmed by the measured photoluminescence spectrum.

Characterization of 2.3 μm GaInAsSb-based vertical-cavity surface-emitting laser structures using photo-modulated reflectance

We report angle dependent and temperature dependent (9 K–300 K) photo-modulated reflectance (PR) studies on vertical-cavity surface-emitting laser (VCSEL) structures, designed for 2.3 μm mid-infrared gas sensing applications. Changing the temperature allows us to tune the energies of the quantum well (QW) transitions relative to the VCSEL cavity mode (CM) energy. These studies show that this VCSEL structure has a QW-CM offset of 21 meV at room temperature. Consequently the QW ground-state transition comes into resonance with the CM at 220 ± 2 K. The results from these PR studies are closely compared with those obtained in a separate study of actual operating devices and show how the PR technique may be useful for device optimisation without the necessity of having first to process the wafers into working devices.

Polarization axis fluctuations in a single mode VCSEL laser at 780nm

We present a transmission method to determine the polarization axis fluctuations for VCSEL (Vertical Cavity Surface Emitting Laser). The research is focused mainly on commercial lasers operatingat 780 nm, designed forlaser spectroscopy. The angle fluctuation of the laser linear axis polarization iselaborated to be less than 150 mrad. Measurement errors of this method are studied and calculated. The measurement uncertainty is ?1,4 mrad andthis is equivalent to ? 5? of arc.Changes of the linear polarization axis depending on the laser current and temperaturearepresented. Full Text: PDF References T. Ohtoshi et al., "Dependence of optical gain on crystal orientation in surface?emitting lasers with strained quantum wells", Appl. Phys. Lett.63, 1886 (1994). CrossRef K. Tateno et al., "Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition", Appl. Phys. Lett.70, 3395 (1997). CrossRef O. Tadanaga et al., "An 850-nm InAlGaAs strained quantum-well vertical-cavity surface-emitting laser grown on GaAs (311)B substrate with high-polarization stability", IEEE Photon. Tech. Lett.12, 942 (2000) CrossRef K. Choquette, R. Leibenguth, "Control of vertical-cavity laser polarization with anisotropic transverse cavity geometries", IEEE Photon. Tech. Lett. 6, 40 (1994) CrossRef B. Weigl et al., "High-performance oxide-confined GaAs VCSELs", IEEE J. Sel. Top.Quantum Electron. 3, 409 (1997) CrossRef P. Dowd et al., "Complete polarisation control of GaAs gain-guided top-surface emitting vertical cavity lasers", Electron. Lett. 33, 1315 (1997) CrossRef M. Grabherr et al., "Volume production of polarization controlled single-mode VCSELs", Proc. SPIE,6908, 690803 (2008) CrossRef R. Roy et al., "First-Passage-Time Distributions under the Influence of Quantum Fluctuations in a Laser", Phys. Rev. Lett.45, 1486 (1980) CrossRef J. Martin-Regalado et al., "Polarization switching in vertical-cavity surface emitting lasers observed at constant active region temperature", Appl. Phys. Lett. 70, 3350 (1997) CrossRef M. B. Willemsen et al., "Polarization Switching of a Vertical-Cavity Semiconductor Laser as a Kramers Hopping Problem", Phys. Rev. Lett. 82, 4815 (1999) CrossRef M. B. Willemsen et al., "Anatomy of a Polarization Switch of a Vertical-Cavity Semiconductor Laser", Phys. Rev. Lett. 84, 4337 (2000) CrossRef T. Mukaihara et al., "Excess intensity noise originated from polarization fluctuation in vertical-cavity surface-emitting lasers", IEEE Photon. Technol. Lett. 7, 1113 (1995) CrossRef

Polarization axis fluctuations in a single mode VCSEL laser at 780nm

We present a transmission method to determine the polarization axis fluctuations for VCSEL (Vertical Cavity Surface Emitting Laser). The research is focused mainly on commercial lasers operatingat 780 nm, designed forlaser spectroscopy. The angle fluctuation of the laser linear axis polarization iselaborated to be less than 150 mrad. Measurement errors of this method are studied and calculated. The measurement uncertainty is ?1,4 mrad andthis is equivalent to ? 5? of arc.Changes of the linear polarization axis depending on the laser current and temperaturearepresented. Full Text: PDF References T. Ohtoshi et al., "Dependence of optical gain on crystal orientation in surface?emitting lasers with strained quantum wells", Appl. Phys. Lett.63, 1886 (1994). CrossRef K. Tateno et al., "Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition", Appl. Phys. Lett.70, 3395 (1997). CrossRef O. Tadanaga et al., "An 850-nm InAlGaAs strained quantum-well vertical-cavity surface-emitting laser grown on GaAs (311)B substrate with high-polarization stability", IEEE Photon. Tech. Lett.12, 942 (2000) CrossRef K. Choquette, R. Leibenguth, "Control of vertical-cavity laser polarization with anisotropic transverse cavity geometries", IEEE Photon. Tech. Lett. 6, 40 (1994) CrossRef B. Weigl et al., "High-performance oxide-confined GaAs VCSELs", IEEE J. Sel. Top.Quantum Electron. 3, 409 (1997) CrossRef P. Dowd et al., "Complete polarisation control of GaAs gain-guided top-surface emitting vertical cavity lasers", Electron. Lett. 33, 1315 (1997) CrossRef M. Grabherr et al., "Volume production of polarization controlled single-mode VCSELs", Proc. SPIE,6908, 690803 (2008) CrossRef R. Roy et al., "First-Passage-Time Distributions under the Influence of Quantum Fluctuations in a Laser", Phys. Rev. Lett.45, 1486 (1980) CrossRef J. Martín-Regalado et al., "Polarization switching in vertical-cavity surface emitting lasers observed at constant active region temperature", Appl. Phys. Lett. 70, 3350 (1997) CrossRef M. B. Willemsen et al., "Polarization Switching of a Vertical-Cavity Semiconductor Laser as a Kramers Hopping Problem", Phys. Rev. Lett. 82, 4815 (1999) CrossRef M. B. Willemsen et al., "Anatomy of a Polarization Switch of a Vertical-Cavity Semiconductor Laser", Phys. Rev. Lett. 84, 4337 (2000) CrossRef T. Mukaihara et al., "Excess intensity noise originated from polarization fluctuation in vertical-cavity surface-emitting lasers", IEEE Photon. Technol. Lett. 7, 1113 (1995) CrossRef

Oxide confinement and high contrast grating mirrors for Mid-infrared VCSELs

A new mid-infrared (MIR) Vertical Cavity Surface Emitting Laser (VCSEL) structure is proposed. We have integrated to the VCSEL structure both an oxide aperture for lateral confinement, and a sub-wavelength high-contrast-grating top mirror. Upon the GaSb-based half-VCSEL, we have grown a metamorphic AlGaAs heterostructure to enable thermal oxidation and grating mirror fabrication steps. A methodology based on optimization and anti-optimization methods has been used to design the optical grating, with improved parameter tolerances regarding processing errors. Finally, we show the complete fabrication of an electrically-pumped MIR monolithic VCSEL structure implementing both oxide confinement and a subwavelength grating top mirror.

Two-step growth of metamorphic GaAs/AlGaAs mirror on an InP substrate by MOCVD

This paper describes a high-reflectivity metamorphic undoped GaAs/Al0.98Ga0.02As distributed Bragg reflector grown on an InP substrate by metalorganic chemical vapor deposition (MOCVD). Optimal two-step growth conditions at low and high growth temperatures can provide a smooth surface morphology, leading to a high reflectivity (>99.5%) with little optical scattering loss. We also show that a large mismatched interface does not create dislocations in the active layer at a slow cooling rate after the growth sequence. These results indicate that metamorphic GaAs/Al0.98Ga0.02As directly grown on an InP substrate by MOCVD is promising for application to InP-based vertical cavity surface-emitting laser structures.