This paper is focused on a 940 nm edge type of semiconductor laser, which is made from 940 nm InGaAs double-quantum-well epitaxial wafer, produced by Metal Organic Chemical Vapor Deposition (MOCVD). In the absence of coating, the efficiency at the room temperature is 0.89 W/A, and the averaged threshold current is 0.307 A. The present study investigates the impact of temperature on the P-I curve, V-I curve and the centre wavelength, the temperature ranging from 286.15-333.15 K. It shows that the threshold current increases from 0.28 A to 0.41 A with the increasing temperature. The increase rate is 0.0027 A/K. With the temperature ranging from 286.15-333.15 K, the characteristic temperature is calculated to be 120 K. At driven current of 2 A, the output power decreases from 1.47 W to 1.27 W at a rate of 0.00425 W/K. At a constant voltage, the output current initially increases with the temperature within a certain range, beyond which the impact of the temperature is minimum. The ideal factor obtained from V-I curve by curve fitting is 1.076. The series resistance is 0.609 Ω. The centre wavelength shifts to a longer wavelength with the increasing temperature at a rate of 0.275288 nm/K.
A 852 nm ridge waveguide edge emitting laser has important applications. But lateral mode instability leads to its poor beam quality because of its ridge structure. Such a structure gives rise to two guidance mechanisms (gain-guide and index-guide), whose change leads to kink effect. So, the control of the single fundamental lateral mode is more difficult. There is no well-informed study in these aspects for ridge waveguide edge emitting lasers. In this paper we study how to improve the beam quality for achieving a stable fundamental lateral mode output experimentally. We are to investigate the influence of lateral mode characteristics of the laser with different ridge depth-to-width ratios in detail by waveguide theory and equivalent refractive index method. Depth and width of the ridge are two key parameters influencing lateral mode. The depth can control lateral guidance mechanism, and the width can control lateral mode order. We find that the ratio must be in a limited range to ensure the single fundamental lateral mode steady. Through theoretical analysis of waveguide theory and equivalent refractive index method, we obtain a limited range of depth-to-width ratio. Then we conduct an experimental comparison, where we adjust the ridge depth, with the width fixed, to control the ratio. Meanwhile we improve the fabrication technology to ensure the accuracy of the structure. We design and fabricate an asymmetric waveguide ridge waveguide edge emitting laser with isolation grooves, whose active region is the core of asymmetric waveguide epitaxy structure. The key structural parameters are 5 m in ridge width, 500 nm in ridge depth, 2 m in isolation grooves depth, 10 m in width, 30 m in spacing between the grooves, and 1 mm in cavity length. Isolation grooves are very useful for improving the performance of the laser: threshold decreased by 50%, output power raised by 44%, and slop efficiency increased by 17%. And the equally crucial role of grooves is to avoid being damaged at packaging process to maintain laser structure. Finally we achieve a stable single fundamental lateral mode output and an accurate tuning wavelength at 852 nm of ridge waveguide edge emitting laser without cavity surface coated at working current 150 mA, working temperature 30 ℃ (working conditions can be changed in a small range). The slope efficiency is on average 0.7 mW/mA (its maximum value is 0.89 mW/mA), and the full wave at half maximum is less than 1 nm. Although we improve the performance of ridge waveguide edge emitting laser and beam quality for stable output, there is still a need to further study the stable output over a wide range. The results in this paper will provide a useful reference for realizing the stable output ridge waveguide edge emitting lasers and the ultra-narrow line-width lasers.
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