| dc.description.abstract | Abstract
High-speed and high-brightness vertical-cavity surface emitting lasers (VCSELs) are utilized in numerous applications nowadays such as light source in development of lidar for use in autonomous cars, robots, and unmanned aerial vehicles, optical interconnect (OI) markets, 3-dimensional (3-D) sensing and optical wireless communication (OWC) channels which is one potential solution for development of the next generation of wireless communication systems for 5G, 6G and satellite communications. A high CW power (hundreds of mW), high-brightness, high-speed light source is critical in the aforementioned applications. In comparison to their counterparts, edge-Emitting Lasers (EELs), VCSELs have an advantage in terms of radiation resistance and by providing adequate heat dissipation, the output power of a VCSEL array can be increased proportionally with size of 2-D VCSEL array. To achieve high-brightness output, a VCSEL array with a high output power, narrow divergence angle and small active area is highly desirable which can be achieved by fabricating VCSEL array of single-mode (SM) VCSEL units either by using zinc (Zn)-diffusion, surface relief, photonic crystal or anti-guide (leaky) cavity structures. However, to suppress higher-order mode lasing in these VCSEL structures, additional intra cavity loss must be introduced, which generally leads to an increase in the threshold current (Ith) and a decrease in quantum efficiency of the laser. In addition, under different bias currents, the polarization states of the output from these SM or MM VCSELs are usually not stable. VCSEL array structure capable of producing highly SM and single-polarized output beams with minimum intra-cavity loss and less threshold current can be obtained using tensile strain induced by the integration of the electroplated copper substrate verified by the double-crystal x-ray measurement results. However, due to high optical power density of highly SM VCSEL arrays, it will result in spatial hole burning (SHB) effect that leads to significant lower frequency roll-off and degradation of eye-pattern quality for high-speed data transmission. Additionally, SM VCSELs typically have a reduced damping factor (γ), which causes noticeable resonances in the E-O and (RIN) frequency responses, resulting in significant deterioration of the eye pattern quality. In order to further improve the maximum optical power while maintaining high brightness and enhancing the eye pattern quality that are required for long-reach OWC applications, a novel VCSEL array structure is designed in which several independent single VCSEL cavities are connected in parallel and having criss-cross mesas connecting each VCSEL cavity. The performance of these arrays improves in terms of optical power, narrow divergence angle, lower RIN, and better eye-opening quality for high-speed data transmission. These enhanced static/dynamic performance is due to weakening of photon density in the SM output from each VCSEL unit produced by the extension of mesas as well as cavity of VCSEL. Moreover, if we further want to increase linking distance between various micro or nanosatellites in optical wireless communication (OWC) and data center market up to several kilometers with increased data transmission rate, then VCSEL light sources having high continuous wave (CW) power with wider and dampened E-O frequency response is highly desired. A novel design in both ultra-compact array layout and pad electrodes with a small pitch size (20 μm) between the light emission apertures has been demonstrated that possess high (CW) optical output power, results in weak optical coupling between neighboring VCSEL units by the non-uniform current injection from dual electrodes. Due to such such weak coupling in our array, the electrical-optical (E-O) frequency response is dampened more that substantially leads to further improvement in eye-pattern quality. Such novel array has high possibility to further improve transmission performance in the next generation OWC channel.
| en_US |