Abstract:

Optical communications, which utilize visible light, have been termed the "next generation" of communication technology because of their potential for reliable, high-speed, and secure broadband connections. Although light-emitting diodes (LEDs) are commonly used as transmitters in optical communications, they suffer from limited modulation bandwidths and low output power density. In contrast, vertical-cavity surface-emitting lasers (VCSELs) can offer a higher modulation bandwidth in the gigahertz range and a higher output power density, making them ideal transmitters. Moreover, VCSELs have circular and symmetric beam profiles with low divergence, facilitating efficient coupling with optical fibers. However, visible VCSELs still require significant progress to meet this technology's demands. This dissertation aims to provide high-quality and high-speed 650-nm red VCSEL arrays with the added potential of integrating orbital angular momentum (OAM) beams as low-cost, low-crosstalk, and compact sources and to design several novel systems to increase the data rate of optical communication channels toward terabit per second (Tb/s) aggregate rates.

To that end, we demonstrate 650-nm red VCSEL-based optical communications to achieve Gb/s links. We achieved, for the first time, the highest data rate (up to 4.7 Gbit/s) of a single 650-nm red VCSEL with the lowest energy consumption (2 pJ/bit) through plastic optical fiber communication by using direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM). Moreover, we report a novel technique to increase the data rate capacity to 1 Tb/s using a massively parallel interconnected system based on a (14×16) 650-nm red VCSEL array. A single 650-nm red VCSEL also reaches a 2 Gbit/s data rate through underwater wireless optical communication (UWOC) using non-return-to-zero on-off keying (NRZ-OOK). We further designed a novel scheme to increase the data rate of red VCSELs in highly turbid water using the wavelength-division multiplexing (WDM) technique with another 680-nm red VCSEL.

In addition, the beam of the VCSEL can be converted from a Gaussian to an OAM beam with a high purity by using 3D two-photon lithography printing of spiral phase plates (SPPs) on top of the aperture of the VCSEL. This novel technique allows design flexibility given its high resolution and fast printing. We achieved 6 Gb/s in free-space optical communication based on a 2×2 OAM red VCSEL array through the mode division multiplexing (MDM) technique.

All reported techniques are promising for using red VCSELs in optical communication applications to offer the potential for high-speed communications with high data rates and low energy consumption. Their compatibility with existing infrastructure, energy efficiency, miniaturization, spectral efficiency, and reliability make them well-suited for a wide range of applications, including data centers, telecommunications networks, and high-performance computing environments.