Very compact external cavity diffraction-coupled tapered laser diodes

Abstract

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 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 degrees to 0.17 degrees in the fast axis and from 3.5 degrees to 0.7 degrees in the slow axis at 6 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 degrees at 1.5 A, 315 mW under cw operation, and of only 0.20 degrees at 2.5 A, 787 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.

Reformatting linear beam arrays to hexagonal beam arrays using custom refractive micro-optics

“…Individual beams were circularised and redistributed into hexagon arrays to maximise fill factor and improve overall beam quality. We believe, however, that our technique is especially suitable for the next generation of high-power high-brightness tapered emitter arrays [3]; and more generally, for broad-area emitter arrays and linear fiber array for brightness enhancement and tailored near-and farfield profiles which are required in numerous illumination and direct-use applications.…”

“…Recently, utilising custom laser-machined refractive surfaces (or phase-plates), single-axis [2,3] and dual-axis corrections [4] of diode bars and stacks have been demonstrated. Here, using a matched pair of laser-cut refractive phase-plates, a linear array of elliptical single-mode beams is reformatted into various aperture-filling close-packed hexagonal arrays with circular near-and far-field patterns, whilst conserving the already-good beam quality per emitter.…”

Beam conditioning of high power diode lasers

“…For example, compensation of device-specific fast-axis wavefront errors can be combined with slow-axis collimation, to provide a single-element "Comp-SAC" [2]. Including fixed compensation for typical smile-induced fast-axis pointing errors in a SAC provides a "Smile-SAC", which optimizes brightness in both fast and slow axes.…”

In-phase synchronization of array laser using intra-Talbot-cavity second harmonic generation

“…Because Talbot cavity does not need any electrical feedback system, we think it is significantly useful in development of compact, low-cost, and literallyscalable high intensity laser modules. Indeed, Talbot cavity has been studied for laser-diode (LD) arrays [3][4][5][6] and waveguide solid-state lasers [7].…”