The supermode structure of phase-locked diode laser arrays with variable channel spacing

The supermode structure of index-guided, phase-locked arrays of diode lasers with nonuniform laser spacing is investigated theoretically. It is shown that in a variable spacing array, the super-mode field patterns can be significantly different from those of a uniform array. However, in a variable-spacing array with
N
elements, supermodes ν and
N + 1 - \nu(\nu = 1, 2, ..., N)
have similar near-field intensity patterns and modal gains, as in the case of uniform arrays. As a result, the discrimination between the fundamental (0° phase shift) and the highest order (180° phase shift) supermodes is small and depends sensitively on the amount of gain in the interchannel regions, as for uniform arrays. This may explain the inefficient supermode discrimination and the wide beams exhibited by variable-spacing diode laser arrays, in contrast to the strong discrimination and the narrow beams obtained with chirped (variable channel width) arrays structures.