Abstract: The possibility of phase locking high-order lateral modes of broad-stripe laser diode array (LDA) with a short external cavity is analyzed theoretically. The far field pattern of multi-lateral modes, which comprises a main lobe and side lobes, is observed for a LDA positioned in a short external cavity. From the experimental records, structures composed of peaks and valleys, symbolizing phase locking, can be observed within the side lobes. Moreover, the modulation depth of this structure is considerably larger than that in the main lobe. From these results, it can be concluded that the phase-locking between high-order lateral modes of emitters of the LDA is realized when the external cavity is short enough.