Mitsubishi Electric has developed new high power laser diodes emitting high-intensity red light with a wavelength of 638nm. The new devices dubbed ML5xx71 and ML5xx54 series are suited to application in pico projectors. These laser diodes provide an output power of up to 300mW or 110mW respectively, in the fundamental mode at continuous wave operation.
Even though high-power red laser diodes emitting at 660nm have become a kind of a commodity for recordable DVD players, this wavelength is not the best-suited for compact projectors equipped with RGB laser light sources, because red light at this wavelength appears relatively dark to the human eye; moving to a shorter wavelength increases the perceived brightness of the light source even at the same output intensity. The new 638nm laser diode appears to be much brighter than 660nm or even commonly used 645nm laser diodes at the same output power.
During the design of the ML5xx54 series Mitsubishi used its expertise originally developed for 660nm lasers, which are almost standard in DVD recorders. The results are so-called ridge-type lasers offering high brightness and single mode characteristics. In order to compensate the typical deviations occurring at higher power levels Mitsubishi Electric developed its specific low-loss waveguide structure offering a kink-free operation even at an output power of 140mW combined with an excellent beam quality even at temperatures of up to 60ºC.