We present a four-stage nonlinear optical process for producing red, green and blue color lasers. For the purpose of producing the 633, 532, and 450 nm wavelengths, we adopt a 1064-nm pumped optical parametric oscillator (OPO) with a bow-tie ring-cavity configuration, oscillating at its signal wavelength, 1562 nm. In order to obtain the red (633 nm) and blue (450 nm) colors, two sum frequency generation (SFG) sections are installed in the same OPO cavity, respectively. To produce the green (532 nm) color, a single-pass second harmonic generation (SHG) section is placed after the OPO cavity. The quasi-phase-matching periods of the OPO, the two SFG (for red and blue colors), and the SHG MgO:PPLN sections are 30.45, 11.8, 14.1, and 6.8 □m, respectively. The phase matching temperatures of the OPO, SFG and SHG MgO:PPLN crystals are 95, 93, 78, and 82oC, respectively. The total cavity length is 49.5 cm. Based upon our cavity design, the calculated mode sizes at the OPO MgO:PPLN and the SFG MgO:PPLN crystals are both ~ 80 □m. In this dissertation, we demonstrate a fiber laser pumped OPO for red, green, and blue laser generations. The pump threshold of the 633-nm generation can be as low as 3.4 W. The average power of the 633-nm generation is around 5 W at 25-W pump power, and the corresponding conversion efficiency is 20 %. The conversion efficiency of the 532 nm green-color laser is 5.7 % pumped by the residual 8-W energy of 1064 nm laser outside the OPO cavity. The average power of the 532 nm is around 460 mW. Although we have also demonstrated blue laser generation from the OPO, the PPLN crystal for red-color generation was broken and the experiment was terminated abruptly. We show in this dissertation a photograph of the blue laser as an evidence of the success of the blue-laser generation.