Analysis of 6-nm AlGaAs SQW low-confinement laser structures for very high-power operation

Abstract

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract-This paper reports experimental results on single quantum-well separate confinement heterostructures (SQW SCH) with low-confinement factor, designed for very high-power operation. The maximum power output for AR/HR coated 3-mm-long devices, measured in very short pulsed conditions (100 ns/1 kHz), from 10-m-wide stripes was as high as 6.4 W before catastrophical optical degradation. If scaled to continuous-wave (CW) conditions, this value would be 800-1100 mW, which would mean a factor of 2-2.7 times more than reported for the best devices with normal design for threshold minimization. The absorption coefficient for the symmetrical structure is as low as 1.1 cm 01 , in spite of the low trapping efficiency of carriers in the quantum well (QW). The maximum differential efficiency is 40% (both faces, uncoated devices) for symmetrical structure and 33% for the asymmetrical one (all measurements in pulsed conditions). Threshold current densities were 800 A/cm 2 for 5-mm-long devices in the symmetrical case and 2200 A/cm 2 in the asymmetrical one. The effects of inefficient carrier trapping in the QW on the threshold current densities and differential efficiency are discussed.

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

“…The target of our design is around 500 A/cm . Still, it is a considerable improvement if we compare with values larger than 2500 A/cm reported in [3] using a different asymmetric design.…”

“…Unlike the approach used in [3], that is a 1-m large optical waveguide, we use here an 0.17-m-thick Al Ga As "optical trap" on the n-side of the active region, as shown in Fig. 1.…”

“…Thus, the series resistance and free-carrier losses are minimized. As described in [3]- [5], the achievement of structures with absorption coefficient values around 1 cm is an important requirement for low-confinement laser diodes, in order to operate at the same material gain as usual GRIN devices with a reasonable differential efficiency. The confinement factor is per QW and the corresponding spotsize is 1.07 m, larger than around 0.55 m for symmetric structures with increased spot size [1], [2].…”

“…OR QUANTUM-WELL (QW) semiconductor laser structures, optimization for high-power operation at current densities of 2000-3000 A/cm can be realized with lower values of the confinement factor in the active region, if the threshold current density is below about 500 A/cm [3]- [5]. The optimum value of the confinement factor should be about three times smaller than in usual gradient index (GRIN) symmetrical structures.…”

Theory of direct and indirect effect of two-photon absorption on nonlinear optical losses in high power semiconductor lasers

“…The second low-loss laser waveguide design type, proposed and realised more recently by a number of authors, e.g. [2], [10] [11] [12], builds partly on the earlier ideas of [13] and involves a substantially asymmetric waveguide with a refractive index step between the n-cladding and the OCL substantially smaller than that between the OCL and the p-cladding. Depending on the OCL thickness and the exact value of the refractive index steps, such a waveguide can be broad (in the sense that most of the optical power of the mode is localized in the OCL) or narrow (in the sense that most of the mode resides in the n-cladding [14]), but in either case the overlap with the pcladding is kept low, ensuring low cladding-related optical loss.…”