Abstract
Group-III-nitride superluminescent diodes (SLDs) are emerging as light sources for white lighting and visible light communications (VLC) owing to their droop-free, low speckle noise, and large modulation bandwidth properties. In this paper, we discuss the development of GaN-based visible SLDs, and analyze their electro-optical properties by studying the optical power-bandwidth products and injection current densities. The significant progress in blue SLDs and their applications for white light VLC is highlighted. A blue SLD, with an optical power of >100 mW and large PBP of 536 mW·nm, is utilized to generate white light, resulting in a high color rendering index (CRI) of 88.2. In a modulation experiment designed for an SLD-based VLC system, an on-off keying scheme exhibits a 1.2 Gbps data rate, with a bit error rate of 1.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , which satisfies the forward error correction criteria. A high data rate of 3.4 Gbps is achieved using the same SLD transmitter, by applying the 16-quadrature-amplitude-modulation (16-QAM) discrete multitone modulation scheme for high-speed white light communication. The results reported here unequivocally point to the significant performance and versatility that GaN-based SLDs could offer for beyond-5G implementation, where white lighting and high spectral efficiency VLC systems can be simultaneously implemented.
Highlights
T HE development of group-III-nitride optoelectronic devices is essential for many important applications, suchManuscript received February 1, 2019; revised April 1, 2019; accepted April 29, 2019
Because enhancing the power-bandwidth product (PBP) of SLD devices is of prime importance, here we evaluate the PBPs from SLDs with different designs and configurations
Of all the reported devices we reviewed, the highest PBP is 931.7 mW·nm, calculated based on an optical power of 121 mW and a peak full-width at half-maximum (FWHM) of 7.7 nm at 9.5 kA/cm2, from a 446-nm-emitting SLD grown on a semipolar GaN substrate with a passive absorber design operating in CW mode reported in 2017 [54]
Summary
T HE development of group-III-nitride optoelectronic devices is essential for many important applications, such. GaN-based LDs have been employed in SSL-VLC systems, owing to their large modulation bandwidth, and Gbps data rates have been reported using on-off keying (OOK) [29], and orthogonal frequency division multiplexing (OFDM) modulation techniques [30]. Such systems find unique applications in underwater wireless optical communication [31], [32]. We recently demonstrated the utilization of a GaN-based SLD as an alternative light source for SSL-VLC systems [25], which offers high output power and “efficiency-droop”-free characteristics as a compact optical transmitter. A data rate beyond Gbps is achieved based on OOK modulation scheme, and a record data rate of 3.4 Gbps is demonstrated using the spectral-efficient quadrature- amplitude-modulation (QAM) discrete-multitone (DMT) technique
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