Airbridged high-speed AlGaAs-GaAs ridge waveguide lasers

The design of a high modulation response multiple-quantum-well ridge waveguide laser in AlGaAs-GaAs, with low parasitics is discussed. The device was fabricated on a semi-insulating substrate with a wide top contact, and airbridges have been used to connect the ridge top contact to the bonding pads on the semi-insulating substrate. The 3-dB frequency response of the laser has been measured to be 21 GHz, which is a record for unstrained quantum-well AlGaAs-GaAs lasers.     

Monolithic colliding-pulse mode-locked quantum-well lasers

Integration of the whole mode-locked laser onto a single piece of semiconductor offers a number of advantages, including total elimination of optical alignment processes, improved mechanical stability, and the generation of short optical pulses at much higher repetition frequencies. Semiconductor laser processing technologies were used to implement the colliding-pulse mode-locking (CPM) scheme, which is known to effectively shorten the pulses and increase stability, on a miniature monolithic semiconductor cavity. The principles of and recent progress in monolithic CPM quantum-well lasers are reviewed     

Design of quantum well AlGaAs-GaAs stripe lasers for minimizationof threshold current-application to ridge structures

The gain saturation effect and the various leakage currents related to a strip structure (spreading current, lateral diffusion current, optical cavity recombination current, and Auger recombination current) are considered. The minimum threshold current (3.3 mA) is obtained with a multiquantum-well (MQW) structure (5×80 Å) at a cavity length of 80 μm. At these values, the lateral leakage current (spreading and lateral diffusion currents) represents about 50% of the threshold current. It is shown that for short-cavity lasers, the MQW is preferred to the SQW (single-quantum-well) structure. However, the well number in the active layer of a ridge structure is limited by the decrease of the parallel confinement and the increase of the lateral leakage current. Finally, good agreement was obtained in comparing the calculations with experimental results for GRINSCH (graded-index separate-confinement heterojunction) SQW lasers     

Fabrication of AlGaAs-GaAs quantum-wire gain-coupled DFB lasers bya single MOCVD growth step

AlGaAs-GaAs quantum-wire (QWR) gain-coupled distributed-feedback (GC-DFB) lasers have been fabricated by a single metal-organic chemical vapor deposition growth step on 0.36-μm pitch V-groove arrays of GaAs. A record low-threshold current of 13 mA is achieved via DFB lasing from QWR gain at room temperature. The consistency of the photon energies of the lasing and the photoluminescence peaks from QWR, and about 4-nm-wide stopband with a large threshold gain difference observed in the near-threshold spectrum are presented as possible evidence for GC-DFB effects in these devices     

AlInGaAs/AlGaAs strained quantum-well ridge waveguide lasers grownby metalorganic chemical vapor deposition

AlInGaAs/AlGaAs strained quantum-well ridge waveguide diode lasers with an emission wavelength of 890 nm are presented. These devices exhibit both single spatial and longitudinal mode operation up to 30 mW of optical output power. A CW threshold current of 13 mA was obtained for a 5-μm-wide ridge waveguide having a cavity length of 500 μm. The differential quantum efficiency was 52%. The lateral and perpendicular far-field radiation patterns (FWHM) from the laser were 6° and 51°, respectively. Reliability testing on uncoated gain-guided lasers made from the same wafer showed no sudden death failures and degradation rates as low as 4.6%/kh     

Highly coherent long cavity GaAs/AlGaAs single quantum-well lasers

Measurements of the spectral properties of ridge waveguide graded index separate-confinement heterostructure single-quantum-well GaAs/AlGaAs lasers are discussed. Long cavity lasers (800 μm) exhibit remarkably pure single-longitudinal mode spectra under continuous operation in spite of the short cavity mode spacing. At an output power of 5 mW, the sidemode suppression exceeds 24 dB and the linewidth is 1.5 MHz. The linewidth-power product is 6.4 MHz-mW. Measurements of the linewidth power product as a function of cavity length L gives an L^-2 dependence in agreement with theory for lasers with small internal loss. The results are used to deduce the linewidth enhancement factor α at the gain peak wavelength ant its dependence on the excitation level. A decrease in α was observed for lasers operating at the second quantized state due to a recovery of the differential gain     

Monolithic integration of GaAs-AlGaAs quantum-well lasers with directional couplers using vertical coupling of light

A novel technique for the monolithic integration of a laser and a directional coupler in the GaAs-AlGaAs material system is demonstrated. The combination of single-step molecular beam epitaxy (MBE) on a planar substrate, vertical coupling of light between the active and passive waveguide in a p-n-p-doped structure and the use of a self-aligned fabrication process for the ridge waveguides in the active and passive sections results in a threshold current of 52 mA and an output power of up to 0.6 mW. The directional coupler is completely switched at an applied bias of 4.0 V.     

Determination of active-region leakage currents in ridge-waveguidestrained-layer quantum-well lasers by varying the ridge width

This paper is concerned with the investigation of lateral current spreading in InGaAsP strained-layer, ridge-waveguide multiple-quantum-well (MQW) semiconductor lasers consisting of nine quantum wells (QWs) and having ridge widths varying from 1.5 to 5 μm. By using a simple analytical model, it is possible to demonstrate that as much as 60% of the injected current escapes out of the active region of a 1.5-μm laser at threshold. For the first time, such an analysis is extended into the above-threshold regime to examine the effects of lateral current spreading on the external differential efficiency     

Modal analysis of IncGaAsP-InP,GaAs/AlGaAs-GaAs,and InGaAsP/AlGaAs-GaAs MIS heterostructure lasers

The transverse modal behavior of Metal-Insulator (Oxide)-Semiconductor (MIS) heterostructure injection lasers is analyzed. MIS structures have been proposed by Jain and Marciniec as an alternate approach to p-n heterojunctions to obtain minority carrier injection and subsequent lasing action. In the modal analysis the MIS structure is treated as an asymmetrical three-layer slab waveguide with appropriate boundary conditions. Numerical computations of electric field strength, intensity and confinement factor P are presented for various GaAs and InP based MIS structures. A comparison of the output characteristics of a GaAs MIS laser with a conventional GaAs p-n double heterostructure laser is also reported.     

分析半导体激光器端面单层减反射膜的有效性

图解辅以计算研究了镀制减反射膜的半导体激光器镀膜面的有效反射。由于减反膜自身反射率曲线的波长依赖性和谱线宽度的有限性,故一般情况下镀膜面的实际反射率比减反膜自身的最低反射率高。针对这种情况,我们进一步讨论了如何通过选择最低反射率所处的波长来提高减反射膜的有效性。     

A single regrowth integration platform for photonic circuits incorporating tunable SGDBR lasers and quantum-well EAMs

A monolithic integration platform is demonstrated for high functionality photonic circuits that include quantum-well electroabsorption modulators, semiconductor optical amplifiers, and widely tunable lasers. The platform is based on the selective removal of a set of active quantum wells located above an optical waveguide layer. The waveguide layer contains a second set of quantum wells to be used in modulator regions. Fabrication requires only a single blanket InP regrowth.     

CW operation of monolithic arrays of surface-emitting AlGaAs diodelasers with dry-etched vertical facets and parabolic deflecting mirrors

A monolithic two-dimensional array of surface-emitting AlGaAs diode lasers with dry-etched vertical facets and parabolic deflecting mirrors was mounted junction-side up on a W/Cu microchannel heatsink and evaluated under continuous-wave (CW) operating conditions. Both the facets and parabolic deflecting mirrors were etched using chlorine ion-beam-assisted etching. Threshold current densities of different sections of the array were consistently around 240 A/cm², and measured CW differential quantum efficiencies were in the 46-48% range. CW power densities as high as 148 W/cm² were achieved with an average temperature rise of less than 25°C in this junction-side-up configuration     

High speed quantum-well lasers and carrier transport effects

Carrier transport can significantly affect the high-speed properties of quantum-well lasers. The authors have developed a model and derived analytical expressions for the modulation response, resonance frequency, damping rate, and K factor to include these effects. They show theoretically and experimentally that carrier transport can lead to significant low-frequency parasitic-like rolloff that reduces the modulation response by as much as a factor of six in quantum-well lasers. They also show that, in addition, it leads to a reduction in the effective differential gain and thus the resonance frequency, while the nonlinear gain compression factor remains largely unaffected by it. The authors present the temperature dependence data for the K factor as further evidence for the effects of carrier transport     

Gain and intervalence band absorption in quantum-well lasers

The linear gain and the intervalence band absorption are analyzed for quantum-well lasers. First, we analyze the electronic dipole moment in quantum-well structures. The dipole moment for the TE mode in quantum-well structures is found to be about 1.5 times larger at the subband edges than that of conventional double heterostructures. Also obtained is the difference of the dipole moment between TE and TM modes, which results in the gain difference between these modes. Then we derive the linear gain taking into account the intraband relaxation. As an example, we applied this analysis to GaInAs/InP quantum-well lasers. It is shown that the effects of the intraband relaxation are 1) shift of the gain peak toward shorter wavelength with increasing injected carrier density even in quantum-well structures, 2) increase of the gain-spectrum width due to the softening of the profile, and 3) reduction in the maximum gain by 30-40 percent. The intervalence band absorption analyzed for quantum-well lasers is nearly in the same order as that for conventional structures. However, its effect on the threshold is smaller because the gain is larger for quantum wells than conventional ones. The characteristic temperature T0of the threshold current of GaInAs/InP multiquantum-well lasers is calculated to be about 90 K at 300 K for well width and well number of 100 Å and 10, respectively.     

Calculated threshold currents of nitride- and phosphide-based quantum-well lasers

We have calculated the room temperature gain-current characteristics for a 360 nm wavelength, 80 /spl Aring/ GaN-Al/sub 0.14/Ga/sub 0.86/N and a red-emitting, 80 /spl Aring/ Ga/sub 0.51/In/sub 0.49/P-(Al/sub 0.44/Ga/sub 0.56/)/sub 0.51/In/sub 0.49/P quantum well laser structures, including many body effects. Although the carrier density and spontaneous current are much higher (by a factor of 4 and 3, respectively) in the nitride structures for a given local gain, the higher confinement factor at short wavelengths means the intrinsic threshold current of these devices is predicted to be approximately twice that of red lasers with the same optical loss.     

Temperature dependence of electrical and optical modulationresponses of quantum-well lasers

We present theory and experiment for high-speed optical injection in the absorption region of a quantum-well laser and compare the results with those of electrical injection including the carrier transport effect. We show that the main difference between the two responses is the low-frequency roll-off. By using both injection methods, we obtain more accurate and consistent measurements of many important dynamic laser parameters, including the differential gain, carrier lifetime, K factor, and gain compression factor. Temperature-dependent data of the test laser are presented which show that the most dominant effect is the linear degradation of differential gain and injection efficiency with increasing temperature. While the K-factor is insensitive to temperature variation for multiple-quantum-well lasers, we find that the carrier capture time and nonlinear gain suppression coefficient decreases as temperature increases     

Carrier DC and AC capture and escape times in quantum-well lasers

A theoretical model is proposed to study the carrier DC and AC capture and escape times in the small signal modulation response of quantum-well lasers. We derive the DC and AC capture and escape times by calculating the carrier net capture current. Our numerical results indicate that the AC capture and escape times are smaller than the DC capture and escape times. In some cases, they may be even smaller by one order of magnitude. We also find that the AC capture/escape time ratio is larger than the DC capture/escape time ratio by a factor of two. Therefore, conventional theoretical models that do not distinguish the differences between the DC and AC capture and escape times may overestimate the resonant frequency and underestimate the damping rate in the modulation response of quantum-well lasers, i.e., the AC capture and escape times limit the modulation bandwidth of quantum-well lasers more severely than that predicted by the DC capture and escape times     

Fabrication of dry-etched mirrors in GaAs-based and InP-based lasers using chemically assisted ion-beam etching at low temperatures

We have fabricated dry-etched mirrors in high-speed InGaAs/GaAs/AlGaAs pseudomorphic multiple quantum well ridge-waveguide lasers at 60°C and in InGaAs/InP bulk lasers at 5°C using enhanced chemically assisted ion-beam etching (CAIBE) technique. The technique allows the etching of laser structures with good surface morphology and excellent anisotropy without cold traps in the etching system. Characteristics of the dry-etched facet lasers match those of cleaved devices. The low sample temperatures for etching allowed the use of standard photoresists as etch masks.     

Optical gain and gain suppression of quantum-well lasers withvalence band mixing

The effects of valence band mixing on the nonlinear gains of quantum-well lasers are studied theoretically for the first time. The analysis is based on the multiband effective-mass theory and the density matrix formalism with intraband relaxation taken into account. The gain and the gain-suppression coefficient of a quantum-well laser are calculated from the complex optical susceptibility obtained by the density matrix formulation with the theoretical dipole moments obtained from the multiband effective-mass theory. The calculated gain spectrum shows that there are differences (both in peak amplitude and spectral shape) between this model with valence band mixing and the conventional parabolic band model. The shape of the gain spectrum calculated by the new model becomes more symmetric due to intraband relaxation together with nonparabolic energy dispersions. Optical intensity in the GaAs active region is estimated by solving rate equations for the stationary states with nonlinear gain suppression     

High-power single-mode operation in DFB and FP lasers usingdiffused quantum-well structure

Distributed feedback (DFB) and Fabry-Perot (FP) semiconductor lasers with step and periodic interdiffusion quantum-well structures are proposed for high-power single-longitudinal-mode operation. It is shown that the phase-adjustment region formed by the diffusion step (i.e., step change in optical gain and refractive index) counteracts the influence of spatial hole burning, especially for DFB lasers with large coupling-length products biased at high injection current. Furthermore, it is found that with careful design of the diffusion grating (i.e., grating period and amount of diffusion extent) of FP lasers, side-mode suppression ratio can be enhanced and threshold current density can be minimized to a satisfied level