Highly Strained 1.22-μ m InGaAs Lasers Grown by MOVPE

In this work, the highly strained In_0.39Ga_0.61As-GaAs lasers grown by metal-organic vapor phase epitaxy were studied. The InGaAs lasers could emit at 1.22 mum under continuous-wave conditions, whereas the threshold current density (J_th) and transparency current density (J_tr) were 140 and 37.2 A/cm², respectively. To the best of our knowledge, the Jtr was the lowest among the reported InGaAs lasers longer than 1.2 mum. The characteristic temperature (T_o) was 146.2 K indicating the good temperature stability. These excellent laser characteristics could be attributed to the optimized growth conditions.     

Analysis of the Double Laser Emission Occurring in 1.55-μm InAs–InP (113)B Quantum-Dot Lasers

In this paper, a theoretical model based on rate equations is used to investigate static and dynamic behaviors of InAs-InP (113)B quantum-dot (QD) lasers emitting at 1.55 mum. More particularly, it is shown that two modelling approaches are required to explain the origin of the double laser emission occurring in QD lasers grown on both, GaAs and InP substrates. Numerical results are compared to experimental ones by using either a cascade or a direct relaxation channel model. The comparison demonstrates that when a direct relaxation channel is taken into account, the numerical results match very well the experimental ones and lead to a qualitative understanding of InAs-InP (113)B QD lasers. Numerical calculations for the turn-on delay are also presented. A relaxation oscillation frequency as high as 10 GHz is predicted which is very promising for the realization of directly modulated QD lasers for high-speed transmissions.     

InP(001)衬底上的InAs量子线

在分子束外延生长的InAs/In0.52Al0.48As/InP异质结体系中,形成InAs量子线.这些InAs量子线在生长和结构方面有一些独到的特性,并介绍了本实验室在研究InAs量子线的生长和结构方面所做的工作.     

InAs Wires on InP (001)

在分子束外延生长的InAs/In0.52Al0.48As/InP异质结体系中,形成InAs量子线.这些InAs量子线在生长和结构方面有一些独到的特性,并介绍了本实验室在研究InAs量子线的生长和结构方面所做的工作.     

Passively Mode-Locked High-Power (210 mW) Semiconductor Lasers at 1.55-μm Wavelength

We report on the generation of stable passively mode-locked pulses at 1.55-mum wavelength from high-power electrically pumped, large transverse mode semiconductor diode lasers. Optical pulses as short as 5.8 ps were measured directly from the laser. This is the shortest pulsewidth reported (without external compression) from a monolithic mode-locked slab coupled optical waveguide laser. The highest average power measured in mode-locked operation was 212 mW albeit the pulsewidths were larger. It was also found that length of the laser changes the power-current efficiency with the largest recorded efficiency of 165 mW/A.     

Dynamics and Temperature-Dependence of 1.3-μm GaInNAs Double Quantum-Well Lasers

We have measured the small-signal modulation response of 1.3-mum ridge waveguide GaInNAs double quantum-well lasers over a wide range of temperatures (25 degC-110 degC) and analyzed the temperature dependence of the modulation bandwidth and the various bandwidth limiting effects. The lasers have low threshold currents and high differential efficiencies with small temperature dependencies. A short-cavity (350 mum) laser has a modulation bandwidth as high as 17 GHz at room temperature, reducing to 4 GHz at 110 degC, while a laser with a longer cavity (580 mum) maintains a bandwidth of 8.6 GHz at 110 degC. We find that at all ambient temperatures the maximum bandwidth is limited by thermal effects as the temperature increases with current due to self-heating. The reduction and subsequent saturation of the resonance frequency with increasing current is due to a reduction of the differential gain and an increase of the threshold current with increasing temperature. We find large values for the differential gain and the gain compression factor. The differential gain decreases linearly with temperature while there is only a weak temperature dependence of the gain compression. At the highest temperature we also find evidence for transport effects that increase the damping rate and reduce the intrinsic bandwidth     

InAs–InP (1.55- μm Region) Quantum-Dot Microring Lasers

In this letter, we demonstrate electrically pumped continuous-wave lasing at room temperature in microring lasers, which employ a quantum-dot gain medium. Lasing occurs in the important 1.55-mum telecom wavelength range. The 2-mum-wide ring waveguides are made from InGaAsP-InP (100) material suitable for active-passive photonic integrated circuits. Lasing in rings down to 22 mum in diameter is found, with a threshold current of 12.5 mA.     

Room-Temperature Operation of Buffer-Free GaSb–AlGaSb Quantum-Well Diode Lasers Grown on a GaAs Platform Emitting at 1.65 μm

Buffer-free growth of GaSb on GaAs using interfacial misfit (IMF) layers may significantly improve the performance of antimonide-based emitters operating between 1.6 and 3 mum by integrating III-As and III-Sb materials. Using the IMF, we are able to demonstrate a GaSb-AlGaSb quantum-well laser grown on a GaAs substrate and emitting at 1.65 mum, the longest known operating wavelength for this type of device. The device operates in the pulsed mode at room temperature and shows 15-mW peak power at -10degC and shows high characteristic temperature (T_o) for an Sb-based active region. Further improvements to IMF formation can lead to high-performance lasers operating up to 3 mum.     

Systematic Study of the Effects of Modulation p-Doping on 1.3-μm Quantum-Dot Lasers

The effects of modulation p-doping on 1.3-mum InGaAs-InAs quantum-dot (QD) lasers are systematically investigated using a series of wafers with doping levels from 0 to 18 acceptors per QD. Various characterization techniques for both laser diodes and surface-emitting light-emitting diode structures are employed. We report: 1) how the level of modulation p-doping alters the length dependant laser characteristics (in turn providing insight on various key parameters); 2) the effect of modulation p-doping on the temperature dependence of a number of factors and its role in obtaining an infinite T₀; 3) how increasing concentrations of modulation p-doping affects the saturated gain, differential gain, and gain profile of the lasers; and finally, 4) the effect modulation p-doping has on the small signal modulation properties of 1.3-mum QD lasers. In each of these areas, the role of modulation p-doping is established and critically discussed.     

Room-temperature operation of InAs quantum-dash lasers on InP (001)

The first self-assembled InAs quantum dash lasers grown by molecular beam epitaxy on InP (001) substrates are reported. Pulsed room-temperature operation demonstrates wavelengths from 1.60 to 1.66 μm for one-, three-, and five-stack designs, a threshold current density as low as 410 A/cm² for single-stack uncoated lasers, and a distinctly quantum-wire-like dependence of the threshold current on the laser cavity orientation. The maximal modal gains for lasing in the ground-state with the cavity perpendicular to the dash direction are determined to be 15 cm^-1 for single-stack and 22 cm^-1 for five-stack lasers     

1.3-μm GaInAsN Vertical-Cavity Surface-Emitting Lasers by Oxide-Planarized and Surface-Relief Processes for Single-Mode Operation

In this letter, we investigate and characterize the 1.3-mum single-mode vertical-cavity surface-emitting lasers (VCSELs) with two GaInAsN strained multiple quantum wells as the active region. Surface relief technique and a thick silicon oxide were used for the spatial mode filtering and the planarization processing, respectively. The VCSELs with a 5-mum-diameter surface-relief aperture and a 12-mum-diameter oxide-confined aperture at room temperature exhibit a threshold current of 3 mA, a slope efficiency of 0.14 mW/mA, a maximum operation temperature of 90 degC, and a single-mode behavior. These VCSELs show a maximum light output power of 1 mW for the single fundamental mode with a transverse-mode suppression of more than 30 dB and also show a clear eye-opening feature operated at 2.488 Gb/s and 12.6 mA     

Direct Modulation Properties of 1.55- μm InGaAsP/InP Microring Lasers

The modulation properties of 1.55-mum InGaAsP/InP microring lasers are investigated using a multimode rate equation model. A detailed study, with respect to Q-factor and extinction ratio calculations, is carried out as a function of different microring's key design and operating parameters. The modulator's performance study shows the possibility for a successful operation at a bit rate of 2.4 Gb/s for radii between 30 and 50 mum and proper values for the bus waveguide reflectivity.     

Room-temperature continuous-wave operation of InAs quantum-wire laser on InP(001) substrate

A self-assembled quantum-wire laser structure was grown by solid-source molecular beam epitaxy in an InAlGaAs-InAlAs matrix on InP(001) substrate. Ridge-waveguide lasers were fabricated and demonstrated to operate at a heatsink temperature up to 330 K in continuous-wave (CW) mode. The emission wavelength of the lasers with 5 mm-long cavity was 1.713 /spl mu/m at room temperature in CW mode. The temperature stability of the devices was analysed and the characteristic temperature was found to be 47 K in the range of 220-320 K.     

Self‐Assembled InAs Quantum Dots on InP(001) for Long‐Wavelength Laser Applications

Self‐assembled InAs quantum dots (QDs) embedded in an InAlGaAs matrix were grown on an InP (001) using a solid‐source molecular beam epitaxy and investigated using transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. TEM images indicated that the QD formation was strongly dependent on the growth behaviors of group III elements during the deposition of InAlGaAs barriers. We achieved a lasing operation of around 1.5 µm at room temperature from uncoated QD lasers based on the InAlGaAs‐InAlAs material system on the InP (001). The lasing wavelengths of the ridge‐waveguide QD lasers were also dependent upon the cavity lengths due mainly to the gain required for the lasing operation.     

Carrier Dynamics of Quantum-Dot, Quantum-Dash, and Quantum-Well Semiconductor Optical Amplifiers Operating at 1.55 μm

We assess the influence of the degree of quantum confinement on the carrier recovery times in semiconductor optical amplifiers (SOAs) through an experimental comparative study of three amplifiers, one InAs-InGaAsP-InP quantum dot (0-D), one InAs-InAlGaAs-InP quantum dash (1-D), and one InGaAsP-In-GaAsP-InP quantum well (2-D), all of which operate near 1.55-mum wavelengths. The short-lived (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the three devices are characterized via heterodyne pump-probe measurements. The quantum-dot device is found to have the shortest long-lived gain recovery (~80 ps) as well as gain and phase changes indicative of a smaller linewidth enhancement factor, making it the most promising for high-bit-rate applications. The quantum-dot amplifier is also found to have reduced ultrafast transients, due to a lower carrier density in the dots. The quantum-dot gain saturation characteristics and temporal dynamics also provide insight into the nature of the dot energy-level occupancy and the interactions of the dot states with the wetting layer.     

Metalorganic vapor phase epitaxial growth and structural characterization of self-assembled InAs nanometer-sized Islands on InP(001)

Self-assembled InAs islands were grown by metalorganic vapor phase epitaxy on InP(001) and characterized by atomic force microscopy and transmission electron microscopy. The growth temperature (450–600°C), the InAs deposition time (3–12 s, using a growth rate of ～2.3Å/s), and the growth interruption time (8–240 s) were varied systematically in order to investigate the effect of thermodynamic and kinetic factors on the structural properties of InAs/InP and InP/InAs/InP structures. It is found that the structural properties of islands vary widely with the growth conditions, ranging from very small (4–5 nm height, ～30–60 nm in diameter) coherent islands at low temperature (450–500°C) to large (～350 nm wide) plastically relaxed islands at high temperature (600°C). For a given deposition time, the height of the coherent islands increases markedly with the growth temperature while their diameter shows only a moderate increase. The growth interruption time also affects the formation and the evolution of islands, which clearly shows that these processes are kinetically limited. Coherent islands with structural properties suitable for use in optoelectronic devices are obtained from ～2.4–4.8 monolayer thick InAs layers using a growth temperature of 500°C and a 30 s interruption time.     

Optical anisotropy and photoluminescence temperature dependence for self-assembled InAs quantum islands grown on vicinal (001) InP substrates

In this paper, we report on a detailed investigation of the effect of misorientated InP(001) substrates on the optical properties of InAs quantum islands grown by molecular beam epitaxy in the Stranski-Krastanow regime. Temperature-dependent photoluminescence and polarization of photoluminescence (PPL) are studied. PPL shows a high degree of linear polarization, near 40%, for the sample grown on the substrate with 2° off miscut angle towards [110] direction (2°F) and only 16% for the sample grown on the substrate with 2° off miscut angle towards [010] direction (2°B). This result pointing out the growth of InAs quantum wires (QWr) on 2°F substrate and of quasi-isotropic InAs quantum dots (QD) on 2°B substrate. The luminescence remains strong at 300 K as much as 36% of that at 8 K, indicating a strong spatial localization of the carriers in the InAs QIs grown on InP(001).     

40-Gb/s Direct Modulation With High Extinction Ratio Operation of 1.3-μm InGaAlAs Multiquantum Well Ridge Waveguide Distributed Feedback Lasers

Direct modulation at 40 Gb/s of a 1.3-mum InGaAlAs distributed feedback ridge waveguide laser is experimentally demonstrated. By combination of the high differential gain of an InGaAlAs multiquantum well active layer, a short cavity length of 100 mum, and a low-resistance notch-free grating, it achieves high bandwidth of 29 GHz and high-extinction ratio of 5 dB at 40-Gb/s modulation. Moreover, the laser operates at a record maximum ambient temperature of 60degC under 40-Gb/s directly modulation. It also achieves 40-Gb/s modulated transmission over 2 km with a low power penalty of 0.25 dB at 25degC .     

(113)B和(100)面InAs/GaAs量子点光致发光光谱特性研究

利用分子束外延技术在(100)和(113)B GaAs衬底上进行了有/无AlAs盖帽层量子点的生长,测量了其在4～100 K温度区间的PL光谱。通过对PL光谱的积分强度、峰值能量和半高宽进行分析进而研究载流子的热传输特性。无AlAs盖帽层的(113)B面量子点的PL光谱的热淬灭现象可以由载流子极易从量子点向浸润层逃逸来解释。然而,有AlAs盖帽层的(113)B量子点的PL热淬灭主要是由于载流子进入了量子点与势垒或者浸润层界面中的非辐射中心引起的。并且其PL的温度依存性与利用Varshni定律计算的体材料InAs的温度依存性吻合很好,表明载流子通过浸润层进行传输受到了抑制,由于AlAs引起的相分离机制(113)B量子点的浸润层已经消失或者减小了。(100)面有AlAs盖帽层的PL半高宽的温度依存性与无AlAs盖帽层的量子点大致相同,表明在相同外延条件下相分离机制在(100)面上不如(113)B面显著。     

2.5-Gb/s Hybrid Single-Mode and Multimode Fiber Transmission of 1.5-μm Wavelength VCSEL

We report, for the first time, a successful 2.5-Gb/s transmission performance of a 1.5-mum emission monolithic vertical-cavity surface-emitting laser (VCSEL) over hybrid links composed of 25-km-long conventional single-mode fibers (SMFs) and a 2.2-km-long 50-mum core multimode fibers (MMFs). This result suggests that 1.5-mum wavelength VCSELs can be effectively used for multigigabit-per-second transmission over hybrid links interconnecting SMF-based long-distance and (or) subscriber network lines with MMF-based local-area network lines in the future ubiquitous network era