Very compact external cavity diffraction-coupled tapered laser diodes

To maintain the same beam quality as that of a single emitter and to be close to diffraction limit, we have combined a phase corrected array, emitting at $\lambda =975\mathrm{nm}$, coherently using the Talbot effect. First, to improve the beam quality of the array, a phase correcting system was added. The FWHM divergences of the array (which is approximately the same as that of the single emitter since the emitters within the array are not optically coupled to each other) were reduced from $34°$ to $0.17°$ in the fast axis and from $3.5°$ to $0.7°$ in the slow axis at $6\mathrm{A}$. Then, to be close to the diffraction limit, we have combined this corrected array coherently using the Talbot effect. We have obtained a quasi-monolobe slow axis far field profile for the in-phase mode with a central peak divergence of only $0.27°$ at $1.5\mathrm{A}$, $315\mathrm{mW}$ under cw operation, and of only $0.20°$ at $2.5\mathrm{A}$, $787\mathrm{mW}$ under pulsed operation. To our knowledge, this is the first demonstration of coherent coupling of a corrected tapered laser diode array in an external Talbot cavity.