Phase-locking dynamics of a 2D VCSEL hexagonal array with an integrated Talbot cavity

Abstract

In this paper, phase-locking dynamics of 2D VCSEL hexagonal array with an integrated Talbot cavity are numerically investigated based on rate equations aiming at achieving high brightness output. The processes of wavelength synchronization and phase locking under different fill factors ff and fractional Talbot cavity lengths L were addressed comprehensively. Different supermodes of phase-locked VCSEL array were then analyzed from both near-field and far-field pattern, and proved to be well matched with the results of coupled-mode theory. With appropriate configuration the Talbot-VCSEL system can operate in a full in-phase mode eventually, which is beneficial for determining the parameter interval corresponding to the most expected single narrow-lobe far-field pattern. Furthermore, the simulation results also indicate that, considering the parametric interactions the distribution of optical feedback from the fractional Talbot cavity should be consistent as much as possible to facilitate the realization of phase-locked state. Our study could provide a theoretical support to obtain the full in-phase coupled VCSEL array with high performance.

Single-mode single-polarization multijunction VCSELs

“…In other words, as long as the device operates in the single-mode regime, it appears that the devices are polarized along the [110] axis. However, as VCSEL becomes multi-mode, the dominant polarization direction starts to switch from [110] to [1][2][3][4][5][6][7][8][9][10] direction. It can be deduced that the fundamental mode is mostly polarized along the [110] direction, while the higher order transverse modes are polarized orthogonally.…”

“…Firstly, it can be observed that the VCSELs are polarized along the minor axis of the elliptical relief feature. For VCSEL with 4µm×5µm relief geometry, the VCSEL is initially polarized towards [1][2][3][4][5][6][7][8][9][10], and it switches abruptly toward [110] at 2.3mA, all while the device remains reliably single-mode at all bias currents. This polarization switching behavior can be explained by considering the effect of the mode filter geometry in dictating the dominant polarization direction toward [1][2][3][4][5][6][7][8][9][10].…”

“…For VCSEL with 4µm×5µm relief geometry, the VCSEL is initially polarized towards [1][2][3][4][5][6][7][8][9][10], and it switches abruptly toward [110] at 2.3mA, all while the device remains reliably single-mode at all bias currents. This polarization switching behavior can be explained by considering the effect of the mode filter geometry in dictating the dominant polarization direction toward [1][2][3][4][5][6][7][8][9][10]. It was previously observed that the VCSELs with circular relief feature tend to be inherently polarized toward [110].…”

“…The shape and size of the relief feature is defined using conventional UV lithography techniques. It should be mentioned that the non-circular relief features are defined in the shape of an ellipse, where it is oriented along the crystal axes of [1][2][3][4][5][6][7][8][9][10] and [110]. Figure 1.b shows an SEM image from the top surface of a VCSEL, in which a shallow-etched surface relief feature with both elliptical and circular geometries is shown.…”

“…In addition to these, VCSELs are being adopted in high-power applications, such as long-distance sensing, especially for automotive LiDAR applications [5]. VCSELs offer notable advantages over traditional edge-emitting laser diodes (EELs), such as emission of circular beam, eliminating the need for additional optics to control the beam shape, emission wavelength stability especially over temperature, easier integration in 2-D arrays, and overall lower cost of the module in which the VCSEL is used at [6]. On the other hand, the complex epitaxial structure of VCSELs, which is fundamentally composed of a cavity, which includes the active light emitting region, placed in between the top and bottom highly reflective mirrors make makes growth and fabrication of such devices challenging.…”