450-nm GaN laser diode enables high-speed visible light communication with 9-Gbps QAM-OFDM

TLDR

GaN blue laser diodes in TO‑38 cans have a 3‑dB analog bandwidth of only 900 MHz at 65 mA, but can be extended to 1.5 GHz for OFDM encoding after intensity optimization. The packaged GaN blue laser diode achieved 9 Gbps 64‑QAM OFDM over a 5‑m free‑space link, delivering 5.1 % EVM, 22 dB SNR and a BER of 3.6 × 10⁻³ that meets FEC, while lower‑bandwidth configurations reached 4 Gbps with BER 3.5 × 10⁻⁸ and 6 Gbps with BER 1 × 10⁻⁶.

Abstract

A TO-38-can packaged Gallium nitride (GaN) blue laser diode (LD) based free-space visible light communication (VLC) with 64-quadrature amplitude modulation (QAM) and 32-subcarrier orthogonal frequency division multiplexing (OFDM) transmission at 9 Gbps is preliminarily demonstrated over a 5-m free-space link. The 3-dB analog modulation bandwidth of the TO-38-can packaged GaN blue LD biased at 65 mA and controlled at 25°C is only 900 MHz, which can be extended to 1.5 GHz for OFDM encoding after throughput intensity optimization. When delivering the 4-Gbps 16-QAM OFDM data within 1-GHz bandwidth, the error vector magnitude (EVM), signal-to-noise ratio (SNR) and bit-error-rate (BER) of the received data are observed as 8.4%, 22.4 dB and 3.5 × 10(-8), respectively. By increasing the encoded bandwidth to 1.5 GHz, the TO-38-can packaged GaN blue LD enlarges its transmission capacity to 6 Gbps but degrades its transmitted BER to 1.7 × 10(-3). The same transmission capacity of 6 Gbps can also be achieved with a BER of 1 × 10(-6) by encoding 64-QAM OFDM data within 1-GHz bandwidth. Using the 1.5-GHz full bandwidth of the TO-38-can packaged GaN blue LD provides the 64-QAM OFDM transmission up to 9 Gbps, which successfully delivers data with an EVM of 5.1%, an SNR of 22 dB and a BER of 3.6 × 10(-3) passed the forward error correction (FEC) criterion.