  We report a theoretical design analysis of domain-engineered periodically
poled lithium niobate (PPLN) for wavelength conversion of near-infrared sources
to generate coherent light in the visible spectral range. Our analysis on the
spectral outputs show that with a proper design of the quasi phase matching
(QPM) periods, tunable, multiple nonlinear optical processes can be
simultaneously phase matched in a single segmented crystal. We show that a
three-segment single PPLN crystal has potential to generate violet (432 nm),
blue (490 nm) and orange (600 nm) wavelengths by simultaneous sum frequency and
second harmonic generation processes. Such a design scheme has promising
potential for a compact, robust and tunable multi-colored visible light source
which can find various applications such as in biomedicine, high-density
optical data storage and laser based color displays.
