MOVPE-grown GaInNAs VCSELs at 1.3 /spl mu/m with conventional mirror design approach

1.3 /spl mu/m oxide confined GaInNAs VCSELs designed using the same design philosophy used for standard 850 nm VCSELs is presented. The VCSELs have doped mirrors, with graded and highly doped interfaces, and are fabricated using production-friendly procedures. Multimode VCSELs (11 /spl mu/m oxide aperture) with an emission wavelength of 1287 nm have a threshold current of 3 mA and produce 1 mW of output power at 20/spl deg/C. The maximum operating temperature is 95/spl deg/C. Emission at 1303 nm with 1 mW of output power and a threshold current of 7 mA has been observed from VCSELs with a larger detuning between the gain peak and the cavity resonance.     

Failure mode analysis of oxide VCSELs in high humidity and high temperature

High-speed fiber-optic transceiver modules using parallel optics require that oxide-confined vertical-cavity surface-emitting lasers (VCSELs) be moisture resistant in a non-hermetic package. We have found that the conventional storage 85/85 (85/spl deg/C/85% relative humidity) test does not adequately characterize oxide VCSELs moisture resistance. We have identified three failure modes in the oxide VCSELs under operating conditions in high humidity. In this paper, we discuss the failure mechanisms including dislocation growth, semiconductor cracks, and aperture surface degradation, all associated with operation under high relative humidity. Understanding of these failure modes has led to more appropriate qualification standards and environmentally robust oxide VCSELs.     

Low threshold current 1.3-/spl mu/m GaInNAs VCSELs grown by MOVPE

The structure of the conventional contact 1.3-/spl mu/m GaInNAs-GaAs vertical-cavity surface-emitting lasers (VCSELs) was optimized and low threshold current 1.3-/spl mu/m GaInNAs VCSELs grown by metal-organic vapor-phase epitaxy were reported. The idea is to optimize the active region, the doping profiles, and the pairs of p-distributed Bragg reflectors, and the detuning between the emission wavelength and the photoluminescence gain peak wavelength. The continuous-wave 1.0-mA threshold current was achieved for the single-mode VCSEL. For the multiple-mode VCSELs, the below 2-mA threshold currents at 5/spl deg/C-85/spl deg/C , the 1.13-mA threshold current at 55/spl deg/C, and 1.52-mA threshold current at 85/spl deg/C are the best results for 1.3-/spl mu/m GaInNAs VCSELs.     

High-performance 1.3 /spl mu/m InGaAs vertical cavity surface emitting lasers

A report is presented on high-performance InGaAs/GaAs double quantum well vertical cavity surface emitting lasers (VCSELs) with record long emission wavelengths up to 1300 nm. Due to a large gain-cavity detuning these VCSELs show excellent temperature performance with very stable threshold current and output power characteristics. For 1.27 /spl mu/m singlemode devices the threshold current is found to decrease from 2 to 1 mA between 10 and 90/spl deg/C, while the peak output power only drops from 1 to 0.6 mW. Large-area 1300 nm VCSELs show multimode output power close to 3 mW.     

Silicon oxide-planarized single-mode 850-nm VCSELs with TO package for 10 Gb/s data transmission

In this letter, we report on an alternative method to fabricate a high-efficiency planar-type oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs). The planarized process of VCSELs was to use the silicon oxide as the buried layer. As a result, these devices with an oxidized aperture of 3 /spl mu/m in diameter exhibit a single-transverse mode behavior throughout the operation current range. In addition, the static characteristics of VCSELs at 300 K include a threshold current of 0.52mA corresponding to a threshold voltage of 2.2 V, a maximum single transverse-mode light output power of 1.13 mW at 4.5 mA, and an external differential quantum efficiency of 35%. On the other hand, this TO-packaged planar-type 850-nm VCSEL for back-to-back test shows a wide open along with symmetric eye diagram and could also pass the 10 Gb/s mask as operating at 10.3 Gb/s and 4 mA. Furthermore, the VCSEL can still keep the eye diagram open and symmetric after the 66-m multi-mode fiber transmission and has a power penalty of 6.6 dB because of fiber dispersion for 10.3 Gb/s data rate at a bit error rate of 10/sup -11/. These results confirm the excellent high-speed performance of SiO/sub x/-planarized VCSELs as compared to the polyimide-planarized VCSELs.     

Vertical-cavity surface-emitting lasers integrated onto siliconsubstrates by PdGe contacts

Vertical-cavity surface-emitting lasers (VCSELs) have been integrated onto an aluminium coated silicon substrate. The InGaAs top-emitting VCSELs were grown by molecular beam epitaxy and individual lasers were defined by high energy proton implantation. The substrate was removed by a new substrate removal process and the lasers were bonded to an aluminised silicon substrate using a Pd/Ge/InSn contact. Threshold currents below 5.5 mA and output powers of ~1 mW were obtained for 40 μm VCSELs bonded to Si     

Vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

Molecular beam epitaxy-grown 0.98-/spl mu/m vertical-cavity surface-emitting lasers (VCSELs) with a three-stack submonolayer (SML) InGaAs quantum-dot (QD) active region and fully doped Al/sub x/Ga/sub 1-x/As-GaAs DBRs was studied. Large-aperture VCSELs demonstrated internal optical losses less than 0.1% per one pass. Single-mode operation throughout the whole current range was observed for SML QD VCSELs with the tapered oxide apertures diameter less than 2 /spl mu/m. Devices with 3-/spl mu/m tapered-aperture showed high single-mode output power of 4 mW and external quantum efficiency of 68% at room temperature.     

Analysis of bit-error rate of vertical-cavity surface-emitting lasers modulated at high speed

A theoretical study of single and multimode vertical-cavity surface-emitting lasers (VCSELs) subject to pseudorandom modulation of the current at a rate of 10 Gb/s is performed. Eye diagrams, probability density functions of the power at the decision time, averaged turn-on delay, and timing jitter are analyzed for different values of the on- and off-state currents. Bit sequences where errors occur are identified. Extensive simulations have been performed to obtain the bit-error rate (BER) for the back-to-back configuration. We find that the BER performance of single-mode VCSELs is better than the one obtained with multimode VCSELs when the off-state current is smaller than the threshold current. The same result is obtained when the off-state current is larger than the threshold value, providing that the on-state current is large enough. However, BER in single-mode VCSELs is greater than in multimode VCSELs when the off-state current is equal to the threshold current. BER performance is also better for multimode VCSELs when the off-state current is larger than the threshold value, if the on-state current is small enough.     

Electrically-pumped vertical-cavity lasers with Al/sub x/O/sub y/-GaAs reflectors

We have fabricated the first electrically-pumped vertical-cavity surface-emitting lasers (VCSELs) which use oxide-based distributed Bragg reflectors (DBRs) on both sides of the gain region. They require a third the epitaxial growth time of VCSELs with semiconductor DBRs. We obtain threshold currents as low as 160 /spl mu/A in VCSELs with an active area of 8 /spl mu/m/spl times/8 /spl mu/m using a two quantum well InGaAs-GaAs active region. By etching away mirror pairs from the top reflector, quantum efficiencies as high as 61% are attained, while still maintaining a low threshold current of 290 /spl mu/A.     

Temperature Analysis of Threshold Current in Infrared Vertical-Cavity Surface-Emitting Lasers

The temperature dependence of threshold current$I_ th$in vertical-cavity surface-emitting lasers (VCSELs) can be approximated by the equation$I_ th (T) = alpha + beta (T-T_min)^2$, where$T_min$is the temperature of lowest$I_ th, alpha$and$beta$are parameters, and temperature is$T$. We compare the temperature dependence of threshold current in VCSELs with GaAs, InGaAs, and strain compensated InGaAs–GaAsP quantum wells. From our analysis we find the coefficient$beta$is related to the gain properties of the quantum well, and is shown to serve as a benchmark for the VCSEL temperature sensitivity. The incorporation of strain-compensated high-barrier GaAsP layers in the active region of 980-nm VCSELs is demonstrated to reduce the threshold dependence on temperature.     

"Anti" up the aperture [antiguided VCSEL structures]

Coupled vertical cavity surface-emitting laser (VCSEL) arrays are an attractive means to increase the coherent output power of VCSELs. Single-mode VCSELs, with output powers greater than 10 mW, would be useful as telecommunication transmitters /spl lambda/=1.3-1.55 /spl mu/m) or sources for optical interconnects. Commercially available single-mode VCSELs, even at shorter wavelengths /spl lambda/=0.85 /spl mu/m), are generally limited to a few milliwatts of output power. The conventional VCSEL structure incorporates a built-in positive-index waveguide, designed to support a single fundamental mode. Promising results in the 3-5 mW range (/spl lambda/=0.85 /spl mu/m) have been obtained from wet-oxidized, positive-index-guided VCSELs with small emission apertures (less than 3.5 /spl mu/m-dia). The small aperture size leads to a high electrical resistance and high current density, which can impact device reliability. By contrast, antiguided VCSEL structures have shown promise for achieving larger aperture single-mode operation. To obtain high single-mode powers with a larger emitting aperture, the use of a negative-index guide (antiguide) is beneficial. This paper discusses antiguided structures and some of their advantages when incorporated in 2-D VCSEL array structures.     

High performance selectively oxidized VCSELs and arrays forparallel high-speed optical interconnects

High-bandwidth single-mode selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays operate at 980 nm or 850 nm emission wavelength for substrate or epitaxial side emission. Coplanar feeding lines and polyimide passivation are used to reduce electrical parasitics in top-emitting GaAs and bottom-emitting InGaAs VCSELs. To enhance fundamental single-mode emission for larger devices of reduced series resistance a surface relief transverse mode filter is employed. Fabricated VCSELs are applied in various interconnect schemes. InGaAs quantum-well based VCSELs at 935 nm emission wavelength are investigated for use in perfluorinated graded-index plastic-optical fiber (GI-POF) links. We obtain a 7 Gb/s pseudo random bit sequence (PRBS) nonreturn-to-zero (NRZ) data transmission over 80 m long 155 μm diameter GI-POF. We investigate data transmission over standard 1300 nm, 9 μm core diameter single-mode fiber with selectively oxidized single-mode GaAs and InGaAs VCSELs. We achieve biased 3 Gb/s and bias-free 1 Gb/s pseudo-random data transmission over 4.3 km at 830 nm emission wavelength where a simple fiber mode filter is used to suppress intermodal dispersion caused by the second order fiber mode. For the first time, we demonstrate 12.5 Gb/s data rate transmission of PRBS signals over 100 m graded-index multimode fiber or 1 km single-mode fiber using high performance single-mode GaAs VCSELs of 12.3 GHz modulation bandwidth emitting at λ=850 nm     

650-nm vertical-cavity surface-emitting lasers: laser properties and reliability investigations

650-nm AlGaInP-AlGaAs-based oxide-confined VCSELs are investigated in dependence on the current aperture size. VCSELs with small aperture (a=5 /spl mu/m) have a maximum continuous-wave (CW) output power of about 1 mW at room temperature. They reach higher operating temperatures (T/sub max/=55/spl deg/C), have narrower beam profiles, less transverse modes, and a higher side mode suppression compared to large aperture VCSELs (a>13 /spl mu/m). The latter devices emit a CW-output power P=3 mW at 20/spl deg/C. Reliability tests of 655-nm devices show at 20/spl deg/C an output power of P/spl ap/0.4 mW over more than 1000 h and at 40/spl deg/C P/spl ap/0.1 mW over 500 h.     

1.3-/spl mu/m Vertical-cavity surface-emitting lasers with double-bonded GaAs-AlAs Bragg mirrors

We demonstrate, for the first time, double-bonded AlGaInAs strain-compensated quantum-well 1.3-/spl mu/m vertical-cavity surface-emitting lasers (VCSELs). GaAs-AlAs Bragg mirrors were wafer-bonded on both sides of a cavity containing the AlGaInAs strain-compensated multiple-quantum-well active layers sandwiched by two InP layers. The lasers have operated under pulsed conditions at room temperature. A record low pulsed threshold current density of 4.2 kA/cm/sup 2/ and a highest maximum light output power greater than 4.6 mW have been achieved. The maximum threshold current characteristic temperature T/sub 0/ of 132 K is the best for any long wavelength VCSELs. The laser operated in a single-longitudinal mode, with a side-mode suppression ratio of more than 40 dB, which is the best results for 1.3-/spl mu/m VCSELs.     

Performance analysis of 10-/spl mu/m-thick VCSEL array in fully embedded board level guided-wave optoelectronic interconnects

We introduce a simple and effective heat sink structure for thin-film vertical cavity surface emitting lasers (VCSELs) in fully embedded board level guided-wave interconnects. A 50% quantum efficiency increase is experimentally confirmed for the 10-/spl mu/m thin-film VCSELs. The thermal resistance of a 1 /spl times/ 12 embedded thin-film VCSEL array in printed circuit board (PCB) is further analyzed. The experimental results show an excellent match with the simulated results. The 10-/spl mu/m-thick VCSEL had the lowest thermal resistance and the highest differential efficiency compared to 250-, 200-, 150-, and 100-/spl mu/m-thick VCSELs. A substrate removed VCSEL can be used in fully embedded board level optical interconnects without special cooling techniques.     

A compact nonlinear equivalent circuit model and parameter extraction method for packaged high-speed VCSELs

A compact nonlinear circuit model for the input of packaged high-speed vertical-cavity surface-emitting lasers (VCSELs) is presented in this paper. The model includes the thermal effects as well as the parasitics, due to the various levels of the packaging hierarchy, to ensure a realistic representation of the input of the VCSELs. The values of the model parameters are extracted from dc current-light-voltage characteristics and S/sub 11/ vector measurements using a two-step parameter extraction procedure. Extraction of the model parameters and comparison between measured and simulated results have been performed for two different commercially available VCSELs operating at 2.5 Gb/s. The achieved agreement between the measured and simulated results is very satisfactory for the dc as well for the S/sub 11/ curves in the frequency range from 3 MHz to 3 GHz.     

Dynamic coherence measurements of index- and gain-guided VCSELs

Coherence properties of several different types of VCSELs are examined with constant and modulated injection current with a bandwidth typical of that used in telecommunications. Large signal modulation of index-guided single transverse-mode VCSELs is found to reduce the coherence length by more than a factor of ten relative to the direct current configuration. Multiple transverse-mode index-guided VCSELs have similar coherence lengths when operated dc and modulated, and shorter than that of the single transverse-mode VCSELs. Gain-guided multiple transverse-mode VCSELs also have shorter coherence lengths than single transverse-mode VCSELs and under modulation can have coherence lengths as low as 0.5 cm.     

Low-cost, multi-GHz electrical packaging for serial optoelectroniclinks utilizing vertical cavity surface emitting lasers

Recent advances in semiconductor laser technology, specifically the emergence of vertical cavity surface emitting lasers (VCSELs), have created room for substantial improvements in the performance of low-cost, fiber-optic links. However, traditional electronic packaging of the VCSELs and detectors severely limits the performance of these new devices. In two previous papers from this laboratory [1996, 1997], traditional laser packages were described, modeled, measured and evaluated. Further, a new improved conceptual package, referred to as the optical package for advanced lasers (OPAL), was presented, as were a set of design guidelines for a new generation of packages for VCSELs and detectors. This paper, describing a continuation of the previous work, discusses the design, modeling, fabrication, and demonstration of OPALs in a laboratory environment. Measured results recorded from VCSELs packaged in OPALs operating to 5 Gbit/s data rates are presented     

High-speed digital modulation characteristics of oxide-confined vertical-cavity surface-emitting lasers-numerical simulations consistent with experimental results

The vertical-cavity surface-emitting laser (VCSEL) is a preferred light source for short-distance high-speed fiber-optic communication links. We simulate the digital modulation behavior of typical oxide-confined VCSELs under realistic working conditions with a comprehensive model that includes the detailed geometry when calculating the optical fields and that accurately accounts for the dynamic effects of carrier density and temperature on the modal distributions. The intrinsic output characteristics of single- and multimode VCSELs were studied as functions of bias and modulation depth under a 2/sup 7/-1 pseudorandom bit sequence current modulation at 2 and 10 Gb/s. The data were used to create numerical eye diagrams that show, e.g., the significant impact of the bit pattern history and the noise on the timing jitter in both single- and multimode VCSELs. For the single-mode VCSEL, the choice of the bias current and modulation depth was less critical due to its higher damping of the relaxation oscillations. The simulated VCSELs were fabricated and experimentally evaluated. The measured eye diagrams showed the same characteristic features as those in the simulations.     

Performance and Reliability of 12.5-Gb/s Oxide-Free 850-nm Mesa VCSELs

Oxide-free mesa vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm have been designed for short reach datacom applications at data rates up to 12.5 Gb/s. The top distributed Bragg reflector is etched away creating a mesa that provides both current and photon confinement. The devices exhibit low threshold current and a donut-shaped far-field profile that is suited for transmission on both legacy and laser-optimized multimode fibers. Open eye diagrams with high margin are observed in on-wafer testing of 8-10 mum VCSELs at 10.3125 Gb/s over 5degC-95degC. Accelerated aging tests indicate a long device lifetime, with the time for a cumulative failure of 1% estimated to be 15 million h at 40degC for 12-mum VCSELs.