The authors design Vertical Cavity Surface Emitting Laser (VCSEL) arrays emitting multiple wavelengths. They present optical techniques based on a fully integrated sensor as a building block for bio-sensing and bio-imaging. VCSEL device basic properties and nearly all applicable cavity design rules are introduced. VCSELs emit a circular and uniform beam, perpendicular to the top surface which can greatly reduce the complexity and cost. Other advantages include a narrow and stable emission of light spectrum and good reliability.