Characteristics Of VCSELs Research Articles

Scaling Characteristics of Multijunction VCSELs

Scaling Characteristics of Multijunction VCSELs

49‐2: Invited Paper: Blue and Green VCSEL for Full‐Color Display

VCSELs have recently received increasing attention from engineers and scientists. The progress of the research on GaN‐based VCSELs that allowed blue and green emissions are often one of the main topics discussed in this field. Combining these lasers with existing red VCSELs realized a full‐color light source with superior characteristics of VCSELs, such as small power consumption, circular beam profiles, and arraying ability. These features should be suitable for displays, for example, AR displays. In this report, a brief review of the recent progress regarding these VCSELs and their future applications is provided.

Studying the light current characteristics of VCSEL by changing oxide confinement aperture

GaAs-based VCSELs with oxide-confined (OC) are performed by using fine selective radial “oxidation of AlAs-rich (AlGaAs) layers” from outside to the device axis leaving the central part unaffected. Such oxide apertures produced inside the cavities enhance the radial confinements related to current spreading and to a field that is optical altogether. A Modern design with a single fundamental mode is proposed to reduce threshold current operation to the extent of higher output by using the two OC VCSELs. Both of the oxide apertures were added to the node position of the resonator standing wave. Then, the diameters of together apertures can be adjusted independently giving VCSEL design an extra degree of freedom that allows optimization. It found that when both apertures had a radius of 4.2 µm, the low threshold current operation at a higher extent output is achieved with a single fundamental mode.

Vertical cavity surface emitting laser of 1.55 μm spectral range, manufactured by molecular beam epitaxy and wafer fusion technique

The heterostructure design for 1.55 μm range VCSELs is proposed and realized. The wafer fusion technique was used to form the final heterostructure. The growth of AlGaAs/GaAs distributed Bragg reflectors (DBRs) on GaAs substrate and the optical cavity with an active region on InP substrate as well as a tunnel junction (TJ) regrowth was performed by molecular beam epitaxy (MBE). A key feature of the proposed design is the use of n++-InGaAs/p++-InGaAs/p++-InAlGaAs TJ, which allows, due to the effective removal of oxide from the InGaAs surface, to use MBE for re-growth of the TJ surface relief. Despite of the presence in heterostructure a narrow-gap InGaAs layers, a noticeable increase in internal optical loss in lasers can be avoided due to the short-wavelength shift of the edge of interband light absorption in ++-InGaAs layers (Burshtein-Moss effect). Fabricated VCSELs demonstrate single-mode operation with a threshold current less than 2 mA and a slope efficiency of ~ 0.46 W/A, which are comparable with characteristics of VCSELs with n++/p++-InAlGaAs TJ with a similar level of mirror losses.

Whispering Gallery Modes and Spontaneous Emission in Compact VCSEL Structures

The radiation power from active area into the planar waveguide has been studied theoretically in order to model VCSEL characteristics. Exact and simple quantitative connection between modal gain and spontaneous emission into planar waveguide has been established. The possibility of the in-plane lasing in the conventional VCSEL with gain area laterally limited by gain aperture has been examined and condition required for this has been found.

Design and Analysis of Static Characteristics of VCSEL at 1160 nm for Optical Interconnects

Abstract VCSEL can be used as the transmitter for optical interconnect applications especially for short reach communication. In this research paper, we proposed a VCSEL structure design which can generate the wavelength of 1160 nm. The VCSEL structure is proposed with the aim of small aperture diameter because for optical interconnects applications the size should reduce. Two distributed Bragg reflectors (DBR), i. e. top DBR and bottom DBR are used to confine the active cavity area and InGaAsP/InP material is used for the formation of active cavity region. Then, the performance of the proposed VCSEL is evaluated at various oxide aperture diameters in the range 2–7 µm for anode voltage, anode current and total power emitted is also calculated to achieve optimized performance.

Performance Analysis of Modulation Response of a Designed 1550 nm Oxide Confined Vertical Cavity Surface Emitting Laser

This paper aims to present the impact of using oxidized layer and the effect of oxide aperture size on VCSEL’s modulation performance. After the introduction of oxidized layer, the characteristics of VCSEL have improved immensely, especially in modulation performance. The peak material gain of Al0.06Ga0.24In0.70As/InP MQW VCSEL found from the MATLAB simulation tools has been utilized for investigating the modulation characteristics of the laser model. The optical output power of 27.23 dBm is found at 2.5 mA of current injection. Later, by varying the injection current up to 2.5 mA a maximum frequency of resonance of 10.75 GHz and the equivalent -3dB cut off frequency of 11.85 GHz are achieved. It is seen that with the reduction of oxide aperture size and increase of injection current, the frequency of resonance in addition to the -3dB cut off frequency of the laser increases. The use of oxidized layer and impact of aperture size effect on VCSEL’s -3dB cut off frequency.

Modelling and analysis of polarization noise in vertical cavity surface emitting LASERs

Previous researches have provided mathematical models of vertical cavity surface emitting LASER’s (VCSEL’s) that evaluated the effect of spontaneous noise on the Laser’s performance but completely neglected the effect of polarization noise. Also the results presented were in terms of RIN variation with respect to frequency. In this paper,a model is proposed to analyse the effect of spontaneous and polarization noise on VCSEL’s output power. Spontaneous noise is included by augmenting feedback in photon rate equations. Polarization noise is incorporated in the dynamics with the help of self-stabilizing and gain recovering coefficients. Characteristics of VCSEL’s output power are studied under continuous wave (CW) and sinusoidal modulation. VCSEL dynamics are simulated for both the cases with and without noise , firstly without noise and then with the effect of noise. The output light’s power curves depict the effect of spontaneous and polarization noise in VCSEL. For high frequency modulation, the outputs have fluctuations throughout the simulation time but noise amplifies these fluctuations, affecting the performance of LASER. For CW modulation, the output light shows exponential behaviour with respect to bias.

Temperature dependent polarization switch of 850-nm VCSELs with different apertures

Temperature greatly affects the polarization properties of VCSELs. In this paper, these polarization properties of top-emitting 850-nm VCSELs are simulated by numerical calculation and then they are verified by experimental measurement. For a 4-μm aperture VCSEL, polarization switch current reduces from 1.4 mA to 0.4 mA as the temperature increases from 273 K to 323 K, which is caused by the change of the reflectivity of DBR and differential gain for LP01 transverse-mode. For VCSELs with 8-μm aperture, the first polarization switch current reduces from 2.1 mA to 0.8 mA as temperature increases from 273 K to 313 K. However, the second polarization switch current increases from 3.8 mA to 6.3 mA for the same increase in temperature because of the competition and polarization selection among several higher-order transverse modes. When the device aperture is further increased to 12 μ mo r 16μm, there are several high-order transverse modes emitting even at small injection current, resulting in a serious competition and selection among themselves. This is why the polarization characteristics of VCSELs with 12 μm or larger aperture are irregular and different from those of smaller aperture devices. Our research results provide useful guidelines for the application of VCSELs operating at different ambient temperatures.

Effect of doping on the polarization characteristics of spin-injected quantum dot VCSEL

The polarization characteristics of doped spin-injected quantum dot vertical cavity surface emitting laser (QD-VCSEL) have been studied using multi-population spin-flip coupled rate equation model. The stability conditions of spin-injected VCSEL are also investigated for different device parameters. Our analysis reveals that QD-VCSEL emitting at high lasing energies, close to the first excited state energy, demonstrates high output ellipticity and high ellipticity gain compared to QD-VCSEL emitting at the ground state energy. Also, we find that increasing the p-type doping concentration of the quantum dots increases the output ellipticity gain of the device and significantly alters the stability conditions of the VCSEL. Large instability is observed when the VCSEL is emitting near \(\sim \!\!70\hbox {meV}\) above the ground state energy and when the quantum dots are doped with \(\sim \!\!4\times 10^{10}\,\hbox {cm}^{-2}\) of p-type concentration. Moreover, we find that QD-VCSEL exhibits good stability when its emission energy is approximately 10–20 meV higher than the ground state energy and when the dots are doped with more than \(4\times 10^{10}\,\hbox {cm}^{-2}\) of p-type concentration.

Continuous Wave Threshold Characteristics of Coupled-Cavity VCSELs: Experiment and Model

We carry out a detailed characterization of continuous wave threshold behavior of coupled-cavity vertical-cavity surface-emitting lasers with various radii of the ion-implantation and oxide apertures. We obtain modal threshold current maps and wavelength at threshold and identify three groups of lasers with qualitatively different behavior, i.e. 1) lasing only on the short, 2) on both short and long and 3) only on the long wavelength fundamental mode. All lasers show profound impact of the current induced self-heating. In order to elucidate this impact, we improve the existing rate equation model by considering nonuniform longitudinal temperature distribution and adding the gain and refractive index temperature dependencies. We are able to reproduce the experimentally observed switchings between different longitudinal modes, as well as all the three different types of modal behavior.

The effects of carrier dependant nonlinear gain on quantum well VCSEL characteristics

In this paper, we present a numerical opto-electro-thermal model for studying vertical cavity surface emitting lasers operation. The model is applied to an index-guided structure with an oxide aperture and multiple quantum-wells in active layer. The interdependent process of carrier transport, heat generation and optical field are solved self-consistently using finite difference time domain in cylindrical system. The gain of quantum wells (QWs) is calculated based on the solution of Schrodinger equation considering heavy hole-light hole band-mixing effect. The calculated maximum gain versus injected carriers is fitted by a 3th order polynomial function and used in opto-electro-thermal model. The inclusion of QW maximum gain calculation for constant wavelength in the model allows us to study threshold current value and higher order transverse modes as well as their dependencies on variation of gain and refractive index induced by carrier and heat more accurately than linear gain approximation. The results show a lower threshold current compared with linear gain approximation. For injection current above the threshold, we consider the spatial hole burning, thermal lensing and self focusing effects.

Polarization Characteristics of Quantum-Dot Vertical-Cavity Surface-Emitting Laser With Light Injection

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This investigation explores experimentally the optical characteristics of long-wavelength quantum-dot vertical-cavity surface-emitting lasers (QD VCSELs). The InAs QD VCSEL, fabricated on a GaAs substrate, is grown by molecular beam epitaxy with fully doped distributed Bragg reflectors. The optical characteristics of QD VCSEL without and with light injection are studied in detail. The QD VCSEL has the potential to be used in all-optical signal processing systems. </para>

Influence of fused interface on the optical and thermal characteristics of vertical cavity lasers

From the effective absorption coefficient of bonded interface and the relationship of interface to reflectivity at cavity mode for double bonded vertical cavity laser, it can be seen that bonded interfaces should be positioned at the null of standing wave distribution, and the thickness of interface should be less than 20 nm. Using the finite elements method, the temperature contour map of laser can be calculated. Results showed that the influence of thin interface to thermal characteristics of VCSELs is slight, while thick interface will lead to temperature increase of active region. SEM images demonstrate that hydrophobic bonding is suitable for the fabrication of the device, while hydrophilic bonding interface is unfavorable to optical and thermal properties of devices with interface thickness larger than 40 nm.

Towards Dynamic Surface-Emitting Fiber Lasers

The surface-emitting fiber laser combines characteristics of fiber lasers and VCSELs that could be translated into new and exciting applications in medicine, security and smart fabrics.

Theoretical Studies of Polarization Bistability in Birefringent ARROW VCSELs

The polarization bistable characteristics of birefringent antiresonant reflection optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) under external optical injection is studied and juxtaposed theoretically with an equivalent index-guided device. The simulation results show that ARROW VCSELs exhibit bistable behaviour and have wider hytheresis loops. The wider hytheresis loop in ARROW VCSEL is attributed to the difference in the lateral profiles of the two polarization modes, resulting in the accentuation of the optical gain difference between the two polarizations. This is because the introduction of a birefringent ARROW has an equivalent effect of creating an anisotropic geometrical cavity in the laser structure. Our theoretical studies also show that the polarization bistability characteristics of ARROW VCSELS are not sensitive to small values of birefringence and can be easily tailored by varying the cladding thicknesses, an option that is not available to index-guided VCSELs

Theoretical analysis of polarization bistability in vertical cavity surface emitting semiconductor lasers

The polarization bistability of vertical cavity surface emitting lasers under external optical injection is analyzed theoretically. It is found that on the condition where the optical gain is blue-shifted relative to the cavity mode, the bistable characteristics of VCSEL's can be improved significantly: (1) low optical power of the external injection light is required, (2) the influence of self-heating effects is minimized, and (3) wide bistable hysteresis loop width can be maintained. Furthermore, it is also shown that the reflectivity of Bragg reflectors should also be optimized to improve the performance of VCSEL's as bistable switches.

Influence of ordering on the polarization characteristics of GaInP vertical-cavity surface-emitting lasers

We investigate the polarization characteristics of GaInP vertical-cavity surface-emitting lasers (VCSEL's) as a function of substrate misorientation and quantum-well strain. All the structures investigated show dominant polarization along the [110] direction. The polarization selectivity is found to be essentially independent of QW strain but increases significantly as the substrate misorientation is reduced from 10/spl deg/ to 3/spl deg/. These results provide clear experimental evidence that the major contribution to the polarization characteristics of GaInP VCSEL's is a consequence of ordering-induced gain anisotropy.

Influence of external optical feedback on threshold and spectral characteristics of vertical-cavity surface-emitting lasers

We report a study of the effects of external optical feedback on the threshold and spectral characteristics of VCSELs with feedback levels in the range from /spl minus/25 dB to 0 dB. A large threshold current reduction and multi-extended-cavity-mode operation have been observed. The experimental results are in good agreement with the theoretical calculations based on a compound cavity laser model. >