Ronald Reindert Drenten

Blue‐green injection lasers containing pseudomorphic Zn1−xMgxSySe1−y cladding layers and operating up to 394 K

We describe the performance of blue‐green injection lasers containing Zn1−xMgxSySe1−y cladding layers. The devices have yielded the lowest reported threshold current densities (500 A/cm2) and the highest reported pulsed output powers (500 mW) at room temperature. Lasing has been observed at temperatures as high as 394 K. The room temperature and 85 K lasing wavelengths are 516 and 496 nm, respectively. The use of Zn1−xMgxSySe1−y, instead of ZnSzSe1−z, cladding layers provides a clear improvement in optical confinement, demonstrated by the widening of the far‐field pattern in the direction perpendicular to the layers. The lasers are separate‐confinement heterostructures with a ZnS0.06Se0.94 waveguiding region and a single Cd0.2Zn0.8Se strained quantum well. The entire structure is pseudomorphic with the GaAs substrate.

Improvement in lasing characteristics of II–VI blue-green lasers using quaternary and ternary alloys to produce pseudomorphic heterostructures

Abstract Pseudomorphic heterostructures with increased electrical and optical confinement were used to improve II–VI blue-green laser operating characteristics. These lasers employ Zn 1− x Mg x S y Se 1− y alloys for the cladding layers, ZnS y Se 1− y for the waveguiding layers and Zn 1− z Cd z Se quantum wells for the active layer. The defect density through the active layer in such a heterostructure was found to range from ≤ 4 × 10 6 to 6 × 10 8 cm -2 . The density found in the active layer is directly related to the growth of the quaternary alloy which is often accompanied by a high density of stacking faults and threading dislocations. By comparing lasers with varying defect densities a direct correlation between the threshold current density and the structural quality has been observed. The lasers with the lowest defect density have threshold current densities of 400 A/cm 2 (without facet coating) which are the lowest reported for II–VI devices and comparable to state-of-the-art III–V devices.

Thermal characteristics of blue‐green II‐VI semiconductor lasers

Threshold current densities and wavelengths of gain maximum and longitudinal modes have been determined as a function of temperature for various laser structures. The onset of intrapulse heating has been studied and interpreted. In Zn0.92Mg0.08S0.12Se0.88/ZnS0.06Se0.94 /Zn0.8Cd0.2Se lasers, thermal resistances have been measured, using substrate‐up and substrate‐down mounting. From these, continuous‐wave lasing regimes have been determined.

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.

II–VI Semiconductor blue-green laser device characteristics

Abstract Threshold current densities and lasing wavelengths of both ZnSSe/ZnSe/ ZnCdSe and ZnMgSSe/ZnSSe/ZnCdSe lasers under short-pulse (100 ns) operation have been measured as a function of temperature. In the second structure, improved electrical confinement and a lower defect density leads to a better T0 and a higher maximum lasing temperature. In these lasers a room-temperature pulsed threshold current density of 400 A/cm2 has been obtained. Using ZnSe/ZnTe graded electrical contacts, a laser operating voltage of 6.5 V has been realized. Thermal resistances have been measured in ZnMgSSe/ZnSSe/ZnCdSe lasers. A value of 31 K W has been obtained in a 20 μm stripe laser of 600 μm length, mounted substrate-up. Both substrate-up and substrate-down mounted lasers meet the thermal continuous-wave lasing condition at room temperature. The relationship between stacking fault density and laser performance has been measured. Defect densities higher than 107 cm−2 significantly increase the lasing threshold. Characteristics of narrow-stripe gain-guided lasers have been measured. Clear changes are seen between short-pulse (100 ns) and longer pulse (800 ns) operation. A simple model that represents thermal index-guiding is used to explain the behavior. The antiguiding parameter is found to be about −1.1.

Visible Y‐junction diode laser with mixed coupling

An experimental study and theoretical analysis of a phase‐locked, visible, λ=670 nm, 2‐3 Y‐junction semiconductor laser array are presented. In a ridgetype 2‐3 Y‐junction, AlInGaP/InGaP array, both in‐phase and anti‐phase array modes are observed to lase simultaneously. The experimental results are discussed in the framework of a model based on the beam propagation method. The influence of the presence of both interferometric and evanescent coupling on the array modes is analyzed.

Semiconductor laser far-field shaping by means of an angle-selective facet coating.

An optical short-wave pass filter, applied as a coating on a semiconductor laser facet, is observed to decrease the far-field width perpendicular to the active layer. The resulting far field has a higher coupling efficiency to circular optics. Combination of this coating with a highly reflective coating on the rear facet gives an improvement of the available external differential efficiency and maintains the threshold current of the uncoated laser. The experimental results obtained can be explained in the framework of a simple model.

Power saturation in 2-1 Y-junction diode lasers

An experimental and theoretical study of 2-1 Y-junction semiconductor lasers is presented. In a V-channeled substrate inner stripe laser (VSIS)-type antireflection coated 2-1 Y-junction array lasing at a wavelength of 780 nm, stable in-phase operation is observed up to a CW output power of 100 mW. In uncoated devices, saturation effects occur which limit stable in-phase operation to low-power output. The experimental results are discussed in the framework of a model based on the beam propagation method. >

Device processing of II-VI semiconductor lasers

ZnMgSSe/ZnSSe/ZnCdSe laser structures were grown on n-type GaAs substrates by Molecular Beam Epitaxy (MBE). We have mounted lasers substrate up and substrate down and measured the thermal resistance. We have also fabricated index-guided and gain-guided laser devices enabling a direct comparison of their optical and electrical performance. Thermal measurements were made on gain-guided devices soldered substrate-up and substrate-down onto a copper heat sink. For devices with contact stripe width of 20 X 600 micrometers 2, the thermal resistance is 48 Kelvin/Watt for substrate down mounting and 31 Kelvin/Watt for substrate-up mounting. CW lasing has been obtained for both mounting configurations. To allow for a direct comparison, 10 micrometers wide gain- guided structures were fabricated using an oxide as an insulating layer beside the contact stripe. The laser threshold voltage was 15 volts for this case. Both 2.5 micrometers and 10 micrometers width index-guided lasers were fabricated using reactive ion etching. The structure is a mesa etched to a depth to produce a real lateral refractive index step of approximately 3 X 10-3. No facet coatings were used. When operated with 100 nsec pulses, the gain-guided devices have an external differential efficiency of .25 Watts/Amp and a strongly astigmatic beam. The 10 micrometers width index-guided devices show a clear reduction in astigmatism and an improvement of external differential efficiency to .33 Watts/Amp. The threshold current density and voltage remain the same.

Blue-Green Injection Lasers Operating at Temperatures up to 394K

Recent results on blue-green injection lasers containing ZnprMl5rSySer_y cladding layers are presented. The lasers are separate-confinement heterosuucnues with a ZnSs.06Ses.94 waveguiding rcgion and a single %.zh.sSe strained quantum well. The devices have yielded threshold curent densities as low as 500 Ncrr2 e20 Ncr2 with facet coating) and pulsed output poweru as high as 500 mW per facet at room temperarure. The lasers have operated at temperatures as high as 394K. CW operation, for a few seconds, was observed at 77K. Emission spectroscopy measurements of the thermal properties are also presented.