Power Broad Area Diode Lasers Research Articles

Chip-carrier thermal barrier and its impact on lateral thermal lens profile and beam parameter product in high power broad area lasers

High power broad area diode lasers with high optical power density in a small focus spot are in strong commercial demand. For this purpose, the beam quality, quantified via the beam parameter product (BPP), has to be improved. Previous studies have shown that the BPP is strongly affected by current-induced heating and the associated thermal lens formed within the laser stripe. However, the chip structure and module-assembly related factors that regulate the size and the shape of the thermal lens are not well known. An experimental infrared thermographic technique is used to quantify the thermal lens profile in diode lasers operating at an emission wavelength of 910 nm, and the results are compared with finite element method simulations. The analysis indicates that the measured thermal profiles can best be explained when a thermal barrier is introduced between the chip and the carrier, which is shown to have a substantial impact on the BPP and the thermal resistance. Comparable results are observed in further measurements of samples from multiple vendors, and the barrier is only observed for junction-down (p-down) mounting, consistent with the barrier being associated with the GaAs-metal transition.

Experimental investigation of factors limiting slow axis beam quality in 9xx nm high power broad area diode lasers

GaAs-based broad-area diode lasers are needed with improved lateral beam parameter product (BPPlat) at high power. An experimental study of the factors limiting BPPlat is therefore presented, using extreme double-asymmetric (EDAS) vertical structures emitting at 910 nm. Continuous wave, pulsed and polarization-resolved measurements are presented and compared to thermal simulation. The importance of thermal and packaging-induced effects is determined by comparing junction -up and -down devices. Process factors are clarified by comparing diodes with and without index-guiding trenches. We show that in all cases studied, BPPlat is limited by a non-thermal BPP ground-level and a thermal BPP, which depends linearly on self-heating. Measurements as a function of pulse width confirm that self-heating rather than bias-level dominates. Diodes without trenches show low BPP ground-level, and a thermal BPP which depends strongly on mounting, due to changes in the temperature profile. The additional lateral guiding in diodes with trenches strongly increases the BPP ground-level, but optically isolates the stripe from the device edges, suppressing the influence of the thermal profile, leading to a BPP-slope that is low and independent of mounting. Trenches are also shown to initiate strain fields that cause parasitic TM-polarized emission with large BPPlat, whose influence on total BPPlat remains small, provided the overall polarization purity is >95%.

Suppression of Higher-Order Lateral Modes in Broad-Area Diode Lasers by Resonant Anti-Guiding

For a maximum fiber-coupled power, high power broad-area diode lasers must operate with a small lateral far-field divergence at high continuous wave (CW) powers. However, these structures are laterally multi-moded, with a low beam quality and wide emission angles. We present a new approach to suppress higher-order lateral modes based on an anti-guiding layer with a high refractive index inserted at the edges of the active stripe. Simulations of planar waveguides containing germanium layers reveal that strong mode-coupling effects occur. These are found to vary as a function of the thickness of the inserted layer. By embedding the germanium layer in the outer region of a ridge-waveguide, the mode coupling effects result in a reduction of the modal gain of higher-order lateral modes. The lateral far-field divergence of fabricated 90- μm stripe lasers emitting at 980 nm and containing such an anti-guiding layer is narrowed by 3° at a CW output power of 10 W.

The concept and the realization of the high-power laser diodes with multi-stripe-gain distribution

The slow axis far-field widening (far-field blooming) is one of the factors, which decrease the quality of the emitted beam of high-power laser diodes. This effect is connected with rising number of maintained lateral optical modes in the laser waveguide. In this paper the design of the gain distribution by the steering of current flow is presented as a way to restrict the far-field blooming. The numerical and experimental results are presented. The almost constant slow-axis width of the optical field distribution in the far-field is obtained up to four times above the threshold current. Full Text: PDF References J. Piprek, "Inverse Thermal Lens Effects on the Far-Field Blooming of Broad Area Laser Diodes", IEEE Photon. Technol. Lett., 25, 958 (2013) CrossRef J. Piprek, "Self-consistent far-field blooming analysis for high-power Fabry-Perot laser diodes", Proc. SPIE 8619, 861910 (2013) CrossRef P. Crump, S. Boeldicke, C. M. Schultz, H. Ekhteraei, H. Wenzel and G. Erbert, "Experimental and theoretical analysis of the dominant lateral waveguiding mechanism in 975 nm high power broad area diode lasers", Semicond. Sci. Technol., 27, 045001 (2012) CrossRef Y. Twu, K. L. Chen, A. Dienes, S. Wang and J. R. Whinnery, "High-performance index-guided phase-locked semiconductor laser arrays", Electron. Lett., 21, 324 (1985) CrossRef M. V. Maximov, Y. M. Shernyakov, I. I. Novikov, L. Ya. Karachinsky, N. Yu. Gordeev, U. Ben-Ami, D. Bortman-Abriv, A. Sharon, V. A. Shchukin, N. N. Ledentsov, T. Kettler, K. Posilovic, D. Bimberg, "High-Power Low-Beam Divergence Edge-Emitting Semiconductor Lasers with 1- and 2-D Photonic Bandgap Crystal Waveguide", IEEE J. Sel. Topics Quantum Electron., 14, 1113 (2008) CrossRef G. Sobczak, E. Dąbrowska, M. Teodorczyk, J. Kalbarczyk and A. Maląg, "Characterization of the optical beam emitted by high-power phase-locked arrays of diode lasers (P = 1 W CW)", Proc. SPIE 8902, 890217 (2013) CrossRef G. Sobczak, A. Maląg, "Optimization of phase-locked arrays geometry for high brightness laser systems", Opto-Electronics Review, 20, 134 (2012) CrossRef G. Sobczak, E. Dąbrowska, M. Teodorczyk, J. Kalbarczyk and A. Maląg, "Improving the beam quality of high-power laser diodes by introducing lateral periodicity into waveguides", Proc. SPIE 8702, 87020B (2013) CrossRef M. Spreemann, B. Eppich, F. Schnieder, H. Wenzel and G. Erbert, "Modal Behavior, Spatial Coherence, and Beam Quality of a High-Power Gain-Guided Laser Array", IEEE J. Quantum Electron., 46, 1619 (2010) CrossRef A. Maląg, E. Dąbrowska, M. Teodorczyk, G. Sobczak, A. Kozłowska and J. Kalbarczyk, "Asymmetric Heterostructure With Reduced Distance From Active Region to Heatsink for 810-nm Range High-Power Laser Diodes", IEEE J. Quantum Electron., 48, 465 (2012) CrossRef A. Kozłowska, A. Maląg, "Far-field emission characteristics of high-power laser diodes", Proc. SPIE 5120, 183 (2003) CrossRef W. Sun, R. Pathak, G. Campbell, H. Eppich, J. H. Jacob, A. Chin and J. Fryer, "Higher brightness laser diodes with smaller slow axis divergence", Proc. SPIE 8605, 86050D-1 (2013) CrossRef

Experimental and theoretical analysis of the dominant lateral waveguiding mechanism in 975 nm high power broad area diode lasers

For maximum fibre-coupled power, high power broad area diode lasers must operate with small lateral far field angles at high continuous wave (CW) powers. However, these structures are laterally multi-moded, with low beam quality and wide emission angles. In order to experimentally determine the origin of the low beam quality, spectrally resolved near and far field measurements were performed for a diode laser with 50 µm stripe width. Within the range measured (CW optical output powers to 1.5 W) the laser is shown to operate in just six stable lateral modes, with spatially periodic profiles. Comparisons of the measured profiles with the results of two-dimensional modal simulation demonstrate that current-induced thermal lensing dominates the lateral waveguiding, in spite of the presence of both strong built-in index guiding and gain guiding. No evidence is seen for filamentation. Building on the diagnosis, proposals are presented for improvements to beam quality.