High-Modulation-Efficiency, Integrated Waveguide Modulator?Laser Diode at 448 nm

To date, solid-state lighting (SSL), visible light communication (VLC), and optical clock generation functionalities in the blue-green color regime have been demonstrated based on discrete devices, including light-emitting diodes, laser diodes, and transverse-transmission modulators. This work presents the first integrated waveguide modulator?laser diode (IWM-LD) at 448 nm, offering the advantages of small footprint, high speed, and low power consumption. A high modulation efficiency of 2.68 dB/V, deriving from a large extinction ratio of 9.4 dB and a low operating voltage range of 3.5 V, was measured. The electroabsorption characteristics revealed that the modulation effect, as observed from the red-shifting of the absorption edge, resulted from the external-field-induced quantum-confined Stark effect. A comparative analysis of the photocurrent versus wavelength spectra in semipolar- and polar-plane InGaN/GaN quantum wells (QWs) confirmed that the IWM?LD based on semipolar (202?1?) QWs was able to operate in a manner similar to other III?V materials typically used in optical telecommunications, due to the reduced piezoelectric field. Utilizing the integrated modulator, a ?3 dB bandwidth of ?1 GHz was measured, and a data rate of 1 Gbit/s was demonstrated using on?off keying modulation. Our experimental investigation highlighted the advantage of implementing the IWM?LD on the same semipolar QW epitaxy in enabling a high-efficiency platform for SSL?VLC dual functionalities.