An individually addressable visible semiconductor laser diode array with a 20 μm pitch is demonstrated that is highly
suited for deployment in next-generation digital print systems. The array, operating at 660 nm, comprises 22 single mode
lasers fabricated on a single GaInP/AlGaInP/GaAs substrate. The laser array is flip-chip bonded onto a patterned ceramic
submount that enables the individual elements to be driven independently and is integrated into a 26-pin butterfly
package. Arrays tested CW exhibit low threshold current (<20 mA per emitter), up to 50 mW output power per channel
with a high slope efficiency (0.9 W/A) and a high characteristic temperature of over 100 K.
Single mode laser diode arrays operating at 808 nm have been designed and fabricated using several different waveguide
and quantum well combinations. In order to operate these devices at 200 mW per element a quantum well intermixing
process has been used to render their facets non-absorbing and thus they do not suffer from mirror damage related
failure. In this paper we demonstrate extremely high levels of reliability for GaAs and AlGaAs quantum well devices
with arrays of 64 elements completing over 6000 hours continuous operation without any single laser element failure and
a correspondingly low power degradation rate of <1% k/hr. In contrast we show extremely high power degradation rates
for arrays using InGaAs and InAlGaAs 808 nm quantum wells laser arrays.
In this paper we report the development of high power high brightness semiconductor laser chips using a combination of
quantum well intermixing (QWI) and novel laser designs including laterally unconfined non-absorbing mirrors
(LUNAM). We demonstrate both multi-mode and single-mode lasers with increased power and brightness and reliability
performance for the wavelengths of 980 nm, 940 nm, 830 nm and 808 nm.
Quantum well intermixing (QWI) can bring considerable benefits to the reliability and performance of high power laser diodes by intermixing the facet regions of the device to increase the band-gap and hence eliminate absorption, avoiding catastrophic optical damage (COD). The non-absorbing mirror (NAM) regions of the laser cavity can be up to ~20% of the cavity length, giving an additional benefit on cleave tolerances, to fabricate very large element arrays of high power, individually addressable, single mode lasers. As a consequence, large arrays of single mode lasers can bring additional benefits for packaging in terms of hybrization and integration into an optics system. Our QWI techniques have been applied to a range of material systems, including GaAs/AlGaAs, (Al)GaAsP/AlGaAs and InGaAs/GaAs.
The role of a robust impurity free quantum well intermixing process in fabricating high-power high-brightness AlGaInP semiconductor laser diodes is outlined. Characteristics of the process are discussed and its attributes summarized. Bandgap shifted lasers have been fabricated to demonstrate the integrity of the material after the quantum well intermixing process. Oxide stripe lasers with non-absorbing mirrors are shown to increase the catastrophic optical damage threshold of semiconductor laser devices. Finally high brightness extended cavity lasers are shown to significantly improve the beam quality, and the insignificant change in the threshold current and slight decrease of the external efficiency demonstrates that the process is low loss.
A novel technique for quantum well intermixing is demonstrated which has proven to be a reliable means for obtaining post-growth shifts in the band edge of a wide range of III-V material systems. The techniques relies upon the generation of point defects via plasma induced damage during the deposition of sputtered silica, and provides a simple and reliable process for the fabrication of both wavelength tuned lasers and monolithically integrated devices. Wavelength tuned board area oxide stripe lasers are demonstrated in InGaAs-InAlGaAs, InGaAs-InGaAsP, and GaInP- AlInP quantum well systems, and it is shown that low absorption losses are obtained after intermixing. Oxide stripe lasers with integrated slab waveguides have also enabled the production of a narrow single lobed far field pattern in both InGaAs-InAlGaAs, and GaInP-AlGaInP devices. Extended cavity ridge waveguide lasers operating at 1.5 micrometers are demonstrated with low loss waveguides, and it is shown that this loss is limited only by free carrier absorption in the waveguide cladding layers. In addition, the operation of intermixed multi-mode interference coupler lasers is demonstrated, where four GaAs-AlGaAs laser amplifiers are monolithically integrated to produce high output powers of 180 mW in a single fundamental mode. The results illustrate that the technique can routinely be used to fabricate low los optical interconnects and offers a very promising route toward photonic integration.
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