In-phase coherent coupling of tapered lasers in an external Talbot cavity

Abstract

ABSTRACT Tapered lasers offer both high-power, together with good beam quality. They contain a ri dge waveguide, which acts as a modal filter, and a tapered section of increasing width, which provides high power. Our lasers are based on Al-free active region and the material structure, which was grown by Metallorganic Chemical Vapor Deposition, has very low internal losses of 0.5 cm -1 , a very low transparency current density of 86 A/cm 2 , a high internal quantum efficiency of 86%, and a high characteristic temperature T 0 of 171 K. Based on these good results, we have realised fully index-guided single emitters (IG1) with a narrow output width of a few tens of microns, a narrow taper angle of less than 1°, which deliver a maximum power of 1 W CW, together with a good beam quality parameter M 2VV =3 at O =915nm. In order to obtain higher power, we have realized an arra y of N=6 fully index-guided tapered diode lasers. They deliver a maximum output power of 4W CW. The emitters of the free-running array are not optically coupled to each other, as a consequence, the array has a highly beam quality parameter M² which is at least equal to N times the single emitter one. In order to improve beam quality of diode arrays, several approaches have been investigated to combine them coherently such as evanescent coupling [1], intracavity spatial filtering [2, 3, 4], or a combining technique using a binary phase grating [5] and also the Talbot effect. For the Talbot effect, both monolithic [6] as well as external Talbot cavity [7] configurations have been demonstrated. The Talbot effect refers to a diffraction phenomenon and consists of a reproduction of the field of an illuminated periodic object at certain distances away from the object plane. These distances are multiples of the Talbot distance Z