InGaAs quantum well diode lasers with regrown Al containing layers for application to current confinement structures

Remarkable progress made in performance characteristics and reliability of high-speed (> 10 GHz) 850-nm multi-mode (MM) oxide-confined vertical cavity surface emitting lasers (VCSELs) during the last decade has led them to find applications in space satellite systems. The main advantage of deploying high-speed VCSELs in space satellites over directly modulated 850-nm edge emitting lasers is the absence of COMD (catastrophic optical mirror damage). In recent years, leading VCSEL manufacturers introduced higher speed (~ 20 GHz or 25 Gbps) VCSELs with encouraging characteristics. However, little has been reported on reliability and failure modes of these state-of-the-art VCSELs although it is crucial to understand failure modes and degradation mechanisms in these VCSELs through physics of failure investigation and subsequently develop VCSELs that exceed lifetime requirements for space satellite systems. For the present study, we performed short-term and long-term accelerated life-tests on 25 Gbps oxide-confined MM VCSELs to study reliability of these devices. Our goal is to extract credible reliability model parameters (thermal activation energy and current exponent factor) from these life-tests to determine suitability of these lasers for future space satellite systems. We also performed failure mode analysis on VCSELs at different stages of degradation using various techniques. We employed nondestructive techniques including optical beam induced current (OBIC) and electron beam induced current (EBIC) techniques as well as destructive techniques including focused ion beam (FIB) and high-resolution TEM techniques. Our detailed reliability and failure mode analysis results are reported along with our understanding on the physical origin of degradation in high-speed VCSELs with strained InGaAs quantum wells.

A novel multi-oxide layer structure for vertical cavity surface emitting laser (VCSEL) structures is proposed to achieve higher single mode output power. The structure has four oxide layers with different aperture sizes and thicknesses. The oxide layer thicknesses are optimized simultaneously to reach the highest single mode output power. A heuristic method is proposed for plotting the influence of these variable changes on the operation of optical output power. A comprehensive optical-electrical thermal-gain self-consistent VCSEL model is used to simulate the continuous-wave operation of the multi-layer oxide VCSELs. A comparison between optimized VCSELs with different structures is presented. The results show that by using multi-oxide layers with different thicknesses, higher single-mode optical output power could be achieved in comparison with multi-oxide layer structures with the same thicknesses.

We present the fabrication process and experimental results of 850-nm oxide-confined vertical cavity surface emitting lasers (VCSELs) fabricated by using dielectric-free approach. The threshold current of 0.4 mA, which corresponds to the threshold current density of 0.5 kA/cm2, differential resistance of 76 Ω, and maximum output power of more than 5 mW are achieved for the dielectric-free VCSEL with a square oxide aperture size of 9 μm at room temperature (RT). L–I–V characteristics of the dielectric-free VCSEL are compared with those of conventional VCSEL with the similar aperture size, which indicates the way to realize low-cost, low-power consumption VCSELs with extremely simple process. Preliminary study of the temperature-dependent L–I characteristics and modulation response of the dielectric-free VCSEL are also presented.

We demonstrate 1.55-/spl mu/m buried-heterostructure (BH) vertical-cavity surface-emitting lasers (VCSELs) on a GaAs substrate. Thin-film wafer-fusion technology enables InP-based BH VCSELs to be fabricated on GaAs/AlAs distributed Bragg reflectors. Detailed investigations of the device resistance are also described. As a result of introducing BH and obtaining low device resistance, the threshold current density under CW operation shows the independence of mesa size due to a strong index guide and small noneffective current. A 5-/spl mu/m VCSEL exhibits a record threshold current of 380 /spl mu/A at 20/spl deg/C. This VCSEL also operates with single transverse mode up to the maximum optical output power.

The influence of using multiple oxide layers with different positions and aperture sizes on vertical-cavity surface-emitting laser (VCSEL) performance is analyzed to show their effects on the optical output power, single-mode operation, and threshold current. The number of oxide layers, their positions, and aperture sizes are optimized to emit the maximum optical output power and transversally single-mode operation. A comprehensive 3-D optical-electrical thermal-gain self-consistent VCSEL model is used to simulate the continuous-wave operation of the multilayer oxide VCSELs. A comparison between optimized VCSELs possessing for different numbers of oxide layers is proposed. The results show that by using multilayer oxides, high-power single-mode VCSELs could be achieved.

The electro-optical efficiency of semiconductor vertical-cavity surface-emitting lasers (VCSELs) strongly depends on the efficient carrier injection into the quantum wells (QWs) in the laser active region. However, carrier injection degrades with increasing temperature which limits the VCSEL performance particularly in high power applications where self heating imposes high temperatures in operation. By simulation we investigate the transport of charge carriers in 808 nm AlGaAs multi-quantum-well active layers with special attention to the temperature dependence of carrier injection into the QWs. Experimental reference data was extracted from oxide-confined, top-emitting VCSELs. The transport simulations follow a drift-diffusion-model complemented by a customized, energy-resolved, semi-classical carrier capture theory. QW gain was calculated in the screened Hartree-Fock approximation with band structures from 8x8 k.p-theory. Using the gain data and by setting losses and the optical confinement factor according to experimental reference results, the appropriate threshold condition and threshold carrier densities in the QWs for a VCSEL are established in simulation for all transport considerations. With the combination of gain and transport model, we can explain experimental reference data for the injection efficiency and threshold current density. Our simulations show that the decreasing injection efficiency with temperature is not solely due to increased thermionic escape of carriers from the QWs. Carrier injection is also hampered by state filling in the QWs initiated from higher threshold carrier densities with temperature. Consequently, VCSEL properties not directly related to the active layer design like optical out-coupling or internal losses link the temperature dependent carrier injection to VCSEL mirror design.

While maintaining a stable polarization state is crucial for many optical applications, intentional polarization instability/bistability is also important for certain photonics applications, such as Ising computers or optical neural networks, where polarization bit encoding has been proposed. Vertical-cavity surface-emitting lasers (VCSELs), with their compact footprints and low power consumption, are ideal light sources for such applications. However, while methods of achieving polarization stability are well-known, the engineering of VCSELs with controllable yet easily switchable (unstable) polarization states remains challenging. In this study, we introduce a method of tailoring oxide apertures to compensate for inherent gain anisotropy and yield the desired instability. By fabricating and analyzing the polarization behavior of hundreds of VCSELs with diverse oxide aperture shapes and sizes, we identify clear trends linking aperture designs to polarization tendencies. Firstly, theoretical analysis is applied to investigate the impact of aperture design on the polarization state of multi-mode VCSELs. Subsequently, VCSELs with bespoke aperture designs are fabricated and tested, which then show predictable polarization state and switching. Under varying current injection, VCSELs reveal diverse polarization switching behaviors. The large-scale fabrication and testing conducted in this study provide recommendations for engineers seeking specific polarization behavior, presenting a promising approach to encode information into VCSEL polarization states for computational tasks.

Mode control of vertical cavity surface emitting lasers (VCSEL) is important for many applications ranging from optical interconnects to optical communications. Recently we have reported a novel buried heterostructure (BH) VCSEL lasing in a stable fundamental transverse mode [1] with the use of a passive antiguide region inside of the cavity. In the presence of a guiding boundary along the laser cavity, an analysis of mode structure cannot be based on an integral equation approach [2], but it is necessary to implement round-trip beam-propagation method. This paper is devoted to a detailed analysis of mode structure and modal losses of cavities with different antiguide and guiding regions.

A single-mode vertical-cavity surface-emitting laser (VCSEL) array at 850 nm with excellent performance in terms of high output power, single-lobe far-field, and narrow divergence angle has been demonstrated. By use of the Zn-diffusion process with proper sizes of oxide current-confined and Zn-diffusion optical apertures, each unit of VCSEL in the demonstrated array is highly single-mode (side-mode suppression ratio 30 dB) with a narrow far-field divergence angle (~5°) and an extremely high maximum single-mode output power (~7.1 mW). Due to the excellent single-mode performance of each VCSEL unit, the 10 × 10 array exhibits a single-lobe and nearly circular symmetric far-field pattern, very narrow divergence angle (~4°), and output power as high as around 187.4 mW. Furthermore, its bias-dependent output optical spectra measured in different positions of array shows very high similarity. This result indicates that the excellent uniformity of single-mode performance of each VCSEL unit in the array. The far-field pattern simulation results indicate that although the coherence in our array is low, its output beam quality is as high as that of a single-mode unit VCSEL, which exhibits a near diffraction limited M square factor (M 2 ≈ 2).

In this article, the effect of residual stress on active region misalignment of laser light sources for vertical cavity surface emitting laser (VCSEL) modulus has been studied. The post-weld-shift variation of active region introduced from the residual stress distribution variation for different VCSEL solder joints, i.e. tin-silver (Sn/3.5Ag) and tin-lead (Sn/37Pb) solder joints, are simulated by employing the thermal-elastic-plastic finite element model of MARC package. The ball grid solidification in reflow process and the creep deformation in the acceleration aging were simulated and analyze. The time and temperature dependent material properties of solders are employed. Numerical results indicate that the post-weld-shift introduced from residual stress in the solidification process are significant, and are also the key reasons to reduce the coupling efficiency in VCSEL packaging. The non-sequential components models in commercial Zemax optical package were used to estimate the optical coupling power loss between the active region and the fiber tip in VSCEL modulus. The results show that the proposed post-weld-shift model is feasible to analyze and to improve the solder joint design in the VCSEL packaging.

Using a Vertical Cavity Surface Emitting Laser (VECSEL ) ³as -grown ´ heterostructure we set -up a laser emitt ing at 488 nm with the output power approaching 20mW. The short wavelength emission was due to the conversion of the 976nm emission by a second harmonic generation process in a type -I lithum triborate (LBO). The V -type external cavity permitted efficient f ocusing of the laser beam on both the VECSEL heterostructure and the non linear crystal. A small diameter focus ed spot on the gain mirror is required when ³as -grown ´ heterostructures are used. N o birefringent filter was used in the resonator . In the case o f our heterostructure we observed that the light was spontaneously polarized along the one of the crystallographic direction. The polarization ratio was 1000:1. The VECSEL heterostructure was of the resonant type strongly enhancing a single wavelength emis sion. The wavelength fine tuning was performed by heatsink temperature adjustment. The heterostructure was grown by molecular beam epitaxy . It consisted of 12 InGaAs quantum wells enclosed by GaAs barriers and a AlAs/GaAs DBR. Keywords: MBE, VECSEL, SHG, 4 88nm

The design of an electrically pumped InGaAs quantum well based vertical cavity surface emitting laser (VCSEL) on InP substrate is presented. Such optically pumped VCSELs have already been demonstrated. To design electrically pumped VCSEL, three simulations steps are needed: optical simulation gives access to the standing-wave electric field distribution, to design the active region and the Bragg mirrors. Thermal simulation is helpful to design metallic contacts while the energy band diagram is obtained by electrical simulation to design the buried tunnel junction useful for carrier injection. All these simulations are compared to experiment.

Oxide-confined top-emitting vertical-cavity surface-emitting-laser (VCSEL) 8 × 8 arrays were designed and fabricated with ultralow thresholds. The arrays were flip-chip bonded onto sapphire substrates and mounted in pin-grid-array packages as optical transmitter arrays. By using the offset-contact bonding process, we were able to obtain very high yield for hybridized devices without damaging the VCSEL mesas. Room-temperature lasing thresholds below 70 μA were found from some of these packaged VCSELs with measured oxide apertures 2.6 μm in diameter. The emission spectrum at an injection current of 70 μA showed a full-width at half-maximum linewidth of less than 2.5 A. Polarization properties were also confirmed from the output of the device. The superior performance was attributed to the optimized size and placement of the confinement aperture and the precise alignment of the gain profile of the active region to the mode of the resonant cavity.

Surface selective growth of GaInAsP heterostructures by metalorganic MBE

A detailed threshold analysis of room-temperature pulsed operation of GaN/AlGaN/AlN vertical-cavity surface-emitting lasers (VCSELs) is carried out. The model takes advantage of the latest results concerning gain in active regions, material absorption in the cladding layers, as well as cavity diffraction and scattering losses. The simulation showed that although VCSELs with single (S) or multiple (M) quantum-well (QW) active regions exhibit lower threshold currents, they are much more sensitive to any increase in optical losses than their bulk counterparts. In particular, decreasing the active region radius of gain-guided QW VCSELs below 5 μm (which increases diffraction losses) or increasing dislocation densities (which, in turn, raises scattering losses) gives an enormous rise to their threshold currents. Therefore small-size GaN VCSELs should have an index-guided structure. In the case of MQW VCSELs, the optimal number of quantum wells strongly depends on the reflectivities of resonator mirrors. According to our study, MQW GaN lasers usually require noticeably lower threshold currents compared to SQW lasers. The optimal number of QW active layers is lower in laser structures exhibiting lower optical losses. Although the best result occurred for an active region thickness of 4 nm, threshold currents for the various sizes differ insignificantly.