Ridge-waveguide Laser Structure Research Articles

Vertically Coupled Partially Tapered Ridge Waveguide Semiconductor FP Laser With Improved Divergence Angles

In this work, we present a semiconductor FP laser design with significantly reduced divergence angles particularly in the vertical direction. The laser has a pair of vertically stacked, propagation constant unmatched twin waveguides that is coupled by a tapered ridge at the output end. As such, the laser has a significantly extended mode profile at the output section while the light propagation in the main section is not affected. Our simulation result shows that the divergence angles can be reduced to 13° $ \times $ 14° (horizontal $ \times $ vertical), as opposed to typical values of 20° $ \times $ 29° in conventional ridge waveguide laser structures without a sport size convertor integrated. This design does not need any regrowth, with no appreciable penalty brought to other laser characteristics either.

Investigation Into the Integration of a Resonant Tunnelling Diode and an Optical Communications Laser: Model and Experiment

A resonant tunnelling diode has been monolithically integrated with an optical communications laser [the resonant tunnelling diode (RTD-LD)] to form a simple optoelectronic integrated circuit (OEIC) that is a novel bistable device suitable for an optical communications system. The RTD-LD was based on a ridge-waveguide laser structure and was fabricated from an InAlGaAs-InP epi-wafer grown by molecular beam epitaxy; it emitted at around 1500 nm. Voltage controlled optical-electrical switching and bistability were observed during the characterisation of the RTD-LD - useful features for a fibre-optic communications laser. Optical and electrical simulations of the RTD-LD were carried out using the circuit simulation tool PSPICE. In addition, a discrete component version of the RTD-LD was constructed which exhibited optical power oscillations, and along with the results of the simulations, gave insight into the operating principles of the monolithically integrated RTD-LD.

Multi-active region laser diode with a narrow beam divergence angle

A novel large optical cavity laser diode, which consists of multi-active regions cascaded together through tunnel junctions, is proposed. After growing the epi-layers with LP-MOCVD system on GaAs substrate, the ridge waveguide laser structure is fabricated, and it shows a transverse divergence angle as low as 14.4°.

Elimination of mode grouping in InGaAsP∕InP ridge waveguide laser using quantum-well intermixing

In this letter, we report the observation of the longitudinal mode grouping effect in the InGaAsP∕InP multiquantum-well ridge waveguide laser. Two mode groups were observed and showed different behaviors with the changing of the injection current. The higher order lateral modes and the current spreading in the ridge waveguide structure is proposed to be responsible for this mode grouping phenomena. A one-step quantum-well intermixing process using the SiO2 electrical isolation layer itself was introduced and proved to be effective in improving the lateral electrical and optical confinement in a ridge waveguide laser structure as well as eliminating the mode grouping.

Optimization of p-dopant profiles for GaInAsP MQW laser structures in MOMBE

For industrial device fabrication gaseous dopant sources are preferred in metalorganic growth technologies. Both in metalorganic vapor phase epitaxy (MOVPE) and metalorganic molecular beam epitaxy (MOMBE/CBE) diethylzinc is used. For doping of InP based ridge waveguide laser structures the critical parts are the active region with GaInAsP confinement layers, MQW layers and the p-type region with InP spacer layer, GaInAsP etch stop layer and InP cladding layer. Growing Zn doped InP in between GaInAsP layers leads to a significant Zn diffusion into the adjacent GaInAsP layers. This effect is much more pronounced in MOMBE than in MOVPE. It is demonstrated how this effect is reduced by insertion of additional intermediate layers with appropriate dopant concentration, and by compensating Si co-doping in the spacer and adjacent layers taking advantage of the Fermi level effect. Applying these techniques, reduced threshold current densities and improved high temperature performance can be obtained. The results are discussed by models of dopant diffusion in MOMBE in comparison to MOVPE.

Optical Properties of Diffused AlGaAs/GaAs Multiple Quantum Wells and their Applications in high Power Laser

ABSTRACTWe will present results for an Al0.24Ga0.76As/GaAs diffused multiple quantum well with five periods of 100/100 Å thick well/barrier layers grown in between Al0.24Ga0.76As guiding layers and cladded on top by a 1 μm thick p-Al0.44Ga0.56As layer and on the bottom by an n-Al0.44Ga0.56As layer of equal thickness, on a n+-GaAs buffer layer and n+-GaAs substrate. Vacancy enhanced QW diffusion is employed where a 2000 Å thick layer of SiO2 is deposited on top of the diffused multiple quantum well structure. Photoluminescence measurement and photovoltage measurement at room temperature show that after rapid thermal annealing for 30 sec at 1000 °C to 1040 °C, a bandgap shift of 30 nm is obtained for the exciton edge. Further, this technique is applied to a ridge waveguide laser structure to make two windows for high power output up to 36 mW. This device shows that the diffusion process may have practical applications.

Discussion of the relaxation oscillation frequency in Ga(Al)As quantum well laser structures

The dependence of the relaxation oscillation frequency on the main laser device parameters as the number of quantum wells, well width, threshold modal gain and optical confinement is systematically investigated in GaAs/GaAlAs multiquantum well laser structures. The theoretical results are well confirmed by detailed measurements on ridge waveguide laser structures.

High-performance uncooled 1.3-μm Al/sub x/Ga/sub y/In/sub 1-x-y/As/InP strained-layer quantum-well lasers for subscriber loop applications

Design considerations for fabricating highly efficient uncooled semiconductor lasers are discussed. The parameters investigated include the temperature characteristics of threshold current, quantum efficiency, and modulation speed. To prevent carrier overflow under high-temperature operation, the electron confinement energy is increased by using the Al/sub x/Ga/sub y/In/sub 1-x-y/As/InP material system instead of the conventional Ga/sub x/In/sub 1-x/As/sub y/P/sub 1-y//InP material system. To reduce the transparency current and the carrier-density-dependent loss due to the intervalence-band absorption, strained-layer quantum wells are chosen as the active layer. Experimentally, 1.3-/spl mu/m compressive-strained five-quantum-well lasers and tensile-strained three-quantum-well lasers were fabricated using a 3-/spl mu/m wide ridge-waveguide laser structure. For both types of lasers, the intrinsic material parameters are found to be similar in magnitude and in temperature dependence if they are normalized to each well. Specifically, the compressive-strained five-quantum-well lasers show excellent extrinsic temperature characteristics, such as small drop of 0.3 dB in differential quantum efficiency when the heat sink temperature changes from 25 to 100/spl deg/C, and a large small-signal modulation bandwidth of 8.6 GHz at 85/spl deg/C. The maximum 3 dB modulation bandwidth was measured to be 19.6 GHz for compressive-strained lasers and 17 GHz for tensile-strained-lasers by an optical modulation technique. The strong carrier confinement also results in a small k-factor (0.25 ns) which indicates the potential for high-speed modulation up to 35 GHz. In spite of the aluminum-containing active layer, no catastrophic optical damage was observed at room temperature up to 218 mW for compressive-strained five-quantum-well lasers and 103 mW for tensile-strained three-quantum-well lasers. For operating the compressive-strained five-quantum-well lasers at 85/spl deg/C with more than 5 mW output power, a mean-time-to-failure (MTTF) of 9.4 years is projected from a preliminary life test. These lasers are highly attractive for uncooled, potentially low-cost applications in the subscriber loop.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evaluation of electroluminescence current and voltage dependence in ridge waveguide laser structures

The d.c. integral electroluminescence power ( P) of ridge waveguide laser structures has been modeled in terms of injection level (current I) and applied voltage ( U), considering possible current spreading effects. The analytical model allows a quick PC-assisted analysis of experimental P- I, P- U and I- U characteristics. From the above an estimation of the diffusion saturation current ( I s) in a laser diode chip (despite masking by nonradiative currents) together with the lateral conductance and the minority carrier lifetime ( τ nr) in combination with the equilibrium majority carrier concentration ( n 0) can be obtained.

The AlGaAs/GaAs ridge waveguide laser array

Abstract The single transverse mode AlGaAs/GaAs laser array with pulsed peak power up to 100 mW has been fabricated successfully. The ridge waveguide laser structure was chosen since it needs only one step liquid phase epitaxy which greatly improves the yield. The ridge waveguide was formed by etching the top p‐type cladding layer through a 4 μm to 5 μm mask down to the neighborhood of the active layer to form a lateral refraction index difference. It is found that when the spacing between ridge is 5 μm, individual lasers are not coupled, and the far field pattern displays a diverged single lobe with a half width of 18° similar to that of a single laser. When an end broad area region is inserted, however, the laser array starts to couple and forms a narrow two‐lobe beam with a half width of 5°. The near‐field pattern can be used to analyze the coupling condition.

Optimum design of 155-μm double heterostructures and ridge-waveguide lasers

The dependence of threshold current density and lateral-index difference for transverse guiding in a 1.55-microm InGaAsP/InP ridge-waveguide laser on the number of cladding layers, their thicknesses, and their compositions is presented. It is found that two cladding layers of intermediate band-gap InGaAsP (lambda(g) = 1.2-1.3 microm) are desirable to reduce the threshold current density and to reduce its sensitivity to layer-thickness variations. The use of active- and cladding-layer thicknesses between 0.1 and 0.15 microm minimizes the threshold current density and its sensitivity to layer-thickness variations. This regime of layer thicknesses results in relatively strong lateral-index guiding (Deltan(eff) approximately 0.06) in the 1.55-microm ridge-waveguide laser structure.