Hexagonal Transverse Coupled Cavity VCSEL Redefining the High-Speed Lasers

In recent years vertical-cavity surface-emitting lasers (VCSELs) have been deployed aside semiconductor diode lasers as the sources in cost-effective fiber links and data center networks  due to their distinct features, such as high reliability, low cost and high yield, low power consumption and easy packaging; low threshold and operating currents, high temperature stability and straightforward fabrication of dense arrays. For data-transmission applications, a high modulation bandwidth is desired. The 3-dB bandwidth of the VCSEL, is limited by thermal effects, parasitic resistance, capacitance, and nonlinear gain effects such as the relaxation oscillations. Thus, with an opportune design of the active region and RC-parasitic, which shunts the modulation current outside the active region at high frequencies, a high modulation bandwidth can be achieved. Optical feedback has proven to increase the modulation bandwidth of VCSELs, due to an induced photon-photon resonance (PPR) effect. Dr. Dalir has successfully demonstrated modulation bandwidth enhancement of the VCSEL via adding a single transverse-coupled-cavity (TCC) to a primary VCSEL cavity. The underlying principle is to control the slow-light delay in the TCC via an induced slow-light feedback. However, strong PPR effects incur relatively large kinks in the light-versus-current (L-I) characteristics. The kinks indicate that because of the supply current being increased, the laser behavior turns from stable to unstable. Interestingly, multiple TCCs (MTCCs) are advantageous to avoid the kinks in the stable region of L-I curve. This is the common issue in standard coupled cavities (twin cavities) as well as optical injection. Recently, Dr. Dalir (PI of this proposal) together with Broadcom corp. have demonstrated a micro-cavity laser adiabatically coupled with MTCC forming a hexagonal lattice, this enables to have a slow-light feedback from each TCC directly into the center (modulated) cavity. With an aim to achieve high power, single-mode operation, the Vernier effect in the hexagonal VCSEL can be utilized in a larger aperture design. Dr. Dalir has shown an operation speed up-to 45 GHz, and side-mode suppression (SMSR) of > 30 dB with signal-to-noise ratio (SNR) of > 45 dB. Here, a VCSEL laterally integrated with multiple transverse coupled cavities with a 3-dB modulation bandwidth of 100 GHz or (170 Gbps) is proposed. Please note that a 45 GHz is already demonstrated by the PI of this proposal.Finally, we will fully optimize the lattice design to extend the stability along larger output suitable for temperature change from -40 ~ 150 ºC.