G.A. Acket

Kink power in weakly index guided semiconductor lasers

A periodic dependence of kink power on laser length is observed and explained. Weakly index guided high power stripe lasers in the AlGaAs, InGaAlP, and InGaAs–AlGaAs material systems are studied and oscillation periods of 100–350 μm are found. Relative kink power differences exceeding a factor of 4 are observed. Facet coatings lead to differences in the oscillation amplitude but not in the oscillation period. The observations indicate that phase‐locked fundamental and first‐order modes exist at certain preferred laser lengths. This general model fully explains the oscillatory behavior of the kink power and the correlated changes in lateral far field distributions at the front and rear mirrors. It is concluded that the optimum diffraction limited power output can be obtained by choosing the proper laser length.

Polarization stabilization in vertical-cavity surface-emitting lasers through asymmetric current injection

We present experimental evidence that asymmetric current injection in intracavity contacted vertical-cavity surface-emitting lasers (VCSELs) stabilizes the polarization of the emitted light. Anisotropies in the gain and loss mechanisms introduced by asymmetric current injection are considered to explain this effect. The design scheme opens perspectives to obtain actual polarization control in VCSELs.

Strained layer GaAs1−yPy‐AlGaAs and InxGa1−xAs‐AlGaAs quantum well diode lasers

Separate confinement strained layer single quantum well diode lasers on GaAs substrates have been fabricated by low‐pressure organometallic vapor phase epitaxy. Laser diode structures with a 90 A quantum well under compressive strain, composed of InxGa1−xAs with x=0.00–0.17, as well as tensile strain, composed of GaAs1−yPy with y=0.00–0.29, have been studied. The emission wavelength ranges from λ=746 nm for y=0.29 up to λ=962 nm for x=0.17. The strain dependence of the threshold current for broad area devices is studied both experimentally and theoretically as a function of temperature. Regions of optimal laser performance, one for compressive and one for tensile strain, are identified.

Low-loss low-confinement GaAs-AlGaAs DQW laser diode with optical trap layer for high-power operation

A low-confinement asymmetric GaAs-AlGaAs double-quantum-well molecular-beam-epitaxy grown laser diode structure with optical trap layer is characterized, The value of the internal absorption coefficient is as low as 1.4 cm/sup -1/, while keeping the series resistance at values comparable cm with symmetrical quantum-well gradient index structures in the same material system. Uncoated devices show COD values of 35 mW//spl mu/m. If coated, this should scale to about 90 mW//spl mu/m. The threshold current density is about 1000 A/cm/sup 2/ for 2-mm-long devices and a considerable part of it is probably due to recombination in the optical trap layer. Fundamental mode operation is limited to 120-180 mW for 6.5-/spl mu/m-wide ridge waveguide uncoated devices and to 200-300 mW for 13.5-/spl mu/m-wide ones, because of thermal waveguiding effects. These values are measured under pulsed conditions, 10 /spl mu/s/l ms.

Stress-induced effects by the anodic oxide in ridge waveguide laser diodes

This paper studies, both theoretically and experimentally, stress-induced effects on the lateral far-field behavior for ridge-type semiconductor laser diodes where anodic oxide is used for the definition of the stripe width. These effects consist of antiguiding under the stripe region, and of two positive waveguiding features near the stripe edges. For low-threshold devices, these effects may be more important than thermal effects, depending on the stress in the oxide. They put a lower limit on the built-in index guiding to be introduced by lateral etch outside the ridge region in order to maintain fundamental mode operation for wider stripes. The magnitude of these effects may be as large as /spl Delta/n/sub ef/=1/spl times/10/sup -3/. An analytical mathematical model is deduced for computing stresses and strains for a certain ridge-shaped interface which bounds the elastic medium.

Diffraction-limited circular single spot from phased array lasers

Anamorphic prism optics makes it possible to obtain a diffraction-limited (lambda/8) circular single spot from index guided phased array lasers. It served not only for beam shaping but also for astigmatism correction and spatial filtering. The optical path analysis based on the interferometric fringe scanning phase measurements both in the near and far fields indicates that the phased array lasers can be applied to such diffraction-limited precise optical systems as optical disk recording, laser beam printing, or second harmonics generation.

The effect of active layer thickness on lateral waveguiding in narrow-stripe gain-guided AlGaAs DH laser diodes

It has been found that the thickness of the active layer has an important influence on the width of the far-field distribution parallel to the active layer of narrow-stripe AlGaAs lasers. Furthermore, for very thin active layers, thermal effects may show up as a result of internal temperature gradients. The influence of the laser output power has also been investigated. It is found that the far field distribution becomes narrower at higher output. All these effects can be quantitatively described as being due to an effective reduction of the anti-guiding parallel to the plane of the active layer.

Controlled Anodic Oxidation for High Precision Etch Depth in AlGaAs III‐V Semiconductor Structures

Controlled anodic oxidation for achieving a better control of etch depth in AlGaAs semiconductor structures is studied. The rates of material consumption and oxide thickness growth for p ++ -GaAs and p-Al 0.38 Ga 0.89 As are given for the citric acid/glycol/water electrolyte. The etch profiles for GaAs/Al 0.45 Ga 0.55 As and GaAs/Al 0.50 Ga 0.40 As layer sequences in laser diode structures are presented. The underetch is rather high and depends on oxidation conditions (constant voltage or constant current). The profile obtained is very rough for constant voltage oxidation and much better when using constant current conditions. The latter also improves the uniformity of oxide growth. The etch rate of the anodic oxide in diluted HCl is much larger for GaAs than for AlGaAs.

Asymmetric current injection for polarization stabilization in vertical-cavity surface-emitting lasers

Intra-cavity contacted In/sub 0.17/Ga/sub 0.83/As/AlAs VCSELs with asymmetrical and symmetric contacts were fabricated and characterized. The square devices with asymmetric current injection emit light polarized perpendicular to the direction of the current injection, despite the fact that these VCSELs have higher order transverse modes. The asymmetric current injection scheme seems thus to be able to stabilize the polarization. We expect that smaller devices working in single mode operation will further enhance the polarization contrast.

Variation of kink power with cavity length in weakly index guided semiconductor lasers

A periodic dependence of kink power on laser length is observed and explained. Weakly-index guided high power stripe lasers in the AlGaAs, InGaAlP and InGaAlAs material systems are studied and periods of 100 to 350 /spl mu/m are found. The observations indicate that phase locked fundamental and first order modes exist at certain laser lengths. This new model fully explains the oscillatory behaviour of the kink power and the correlated changes in lateral far field distributions at the front and rear mirror facets.