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

• Published in: ACS photonics Vol. 3; no. 2; pp. 262 - 268
• Main Authors: Shen, Chao, Ng, Tien Khee, Leonard, John T, Pourhashemi, Arash, Oubei, Hassan M, Alias, Mohd S, Nakamura, Shuji, DenBaars, Steven P, Speck, James S, Alyamani, Ahmed Y, Eldesouki, Munir M, Ooi, Boon S
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.02.2016
• Subjects: nitride semiconductor; laser diode; solid-state lighting; visible light communication; electroabsorption modulator
• ISSN: 2330-4022; 2330-4022
• DOI: 10.1021/acsphotonics.5b00599

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 (202̅1̅) 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.