Current solutions are limited by trade-offs between channel spacing, crosstalk, insertion loss, and device footprint. Abstract Wavelength division multiplexing or WDM allows the combining of a number of independent information-carrying wavelengths onto the same fiber, because of the wide spectral region in which optical signals can be transmitted efficiently. By transmitting multiple optical signals simultaneously on a single fiber, it significantly increases communication capacity. This collection encompasses a variety of research papers, conference proceedings, and technical articles that explore both foundational. ptical multiplexing techniques, wavelength division multiplexing (WDM).