A Laterally Integrated VCSEL–Electro-Absorption Modulator Enabled by Resonance Detuning and Slow-Light Coupling

Directly modulated VCSEL transmitters are widely deployed in short-reach optical interconnects, yet further scaling of per-lane symbol rates in AI/HPC datacenter fabrics demands modulation beyond the practical limits of direct current modulation. We demonstrate a laterally integrated VCSEL–electro-absorption modulator (EAM) transmitter enabled by resonance-detuned coupling on an oxide-confined half-VCSEL platform. A localized 20 nm surface etch produces >5 nm resonance detuning, confirmed by measured spectra and supported by transfer-matrix and mode-matching simulations, which indicate strong slow-light-assisted lateral coupling into the modulator. Experimentally, the measured spectra confirm an 5 nm resonance separation. Static characterization shows a coupling ratio of 63% extracted from near-field profiles and an extinction ratio of 4 dB (based on modulator-side power) under a −2 V modulator bias, with an apparent 1 mW absorption at a 6 mA VCSEL drive current. Dynamic measurements demonstrate a small-signal 3-dB bandwidth of approximately 23 GHz and clear NRZ eye openings at 25 Gb/s and 30 Gb/s. These results validate resonance-detuned lateral integration as a compact and manufacturable approach to VCSEL-based externally modulated transmitters for next-generation short-reach interconnects.