In-phase Evanescent Coupled Implant Defined Vertical Cavity Laser Arrays

Abstract

Arrays of vertical cavity surface emitting lasers (VCSELs) have been studied extensively for coherent coupling between lasers [1-8]. Coherent coupling allows for increased power in the far field at a single frequency, which may be used in applications such as optical logic, imaging, and beam steering. Because of the loss between evanescently coupled VCSELs, a phase-shift of 180 degrees is typically observed between neighboring lasers [1]. This creates an out-of-phase mode with an on-axis null which is undesirable for most applications. Phase-adjusted arrays [2] and anti-guided VCSELs [5, 6] can overcome this setback at the cost of a complicated fabrication process. It is also possible to achieve in-phase coupling with photonic crystal VCSELs [7]; however, the hole(s) between lasers frequently promote the out-of-phase mode. In this work, we show that proton implantation may be used to define individual elements in the coupled array. This approach adds no fabrication complexity to that of a conventional implant VCSEL. A cross-sectional sketch of this device is shown in Fig. 1, and the implant geometry is shown in Fig. 2. Because the implant provides electrical confinement without adding optical loss, the lasers tend to lock inphase. A near-field image and a far-field pattern for a 2×1 array are shown in Fig. 3, at an injection current of 4.3 mA (1.4 times threshold). In the near-field image of Fig. 3, the minor lobe located between the two major lobes of the array elements is out of phase with the major lobes.