A blue laser diode is a type of semiconductor laser diode that emits radiation with a wavelength ranging between 360 nm and 480 nm, which is visible as blue to the human eye. Blue laser diodes are primarily based on either gallium nitride (GaN) or indium gallium nitride (InGaN) semiconductor materials. Based on the number of transmission modes, blue laser diodes are classified into single-mode blue laser diodes and multi￾mode blue laser diodes. Totally there are three transmission modes in such diodes, which are lateral, transverse, and longitudinal. When the structure of a diode is designed such that one mode can fit in the waveguide, it is termed a single-mode blue laser diode, and when it can fit more than one mode, it is known as a multi-mode blue laser diode.