10.1117/2.1200812.1319 Miniature green lasers provide the missing color David Brown, Jerry Kuper, and Sten Tornegard A new diode-pumped solid-state laser offers the technology to complete the triad of red, green, and blue sources needed to produce full-color images. The communication and information revolution is driving a need for compact portable high-information-content display sources. Several companies commercially introduced pico- and microprojectors and other portable laser-display technologies in 2008. 1 Our newly developed miniature green laser provides the missing color and enabling technology to complete the triad of red, green, and blue (RGB) light sources required to produce full-color images. While diode lasers can deliver red and blue, direct green-diode light sources are not currently available com- mercially nor will they likely be for years. Green semiconduc- tor diode-doubled lasers have been incorporated into commer- cial full-color devices. 2, 3 The design—which employs a near- monochromatic laser source—provides a wider color gamut and more lifelike color-rendition display compared to conventional backlit-LCD and phosphor-based technologies such as plasma displays. 4, 5 RGB LEDs have thus far been employed in DLP 6 (Digital Light Processing)-driven microprojector displays. LED sources produce a broader spectrum than semiconductor-based full- color laser devices, comparable to the filtered-light sources used in LCDs. They are also less efficiently matched to the display en- gine because of their highly uncollimated and unpolarized emis- sion properties. This limits LED-illuminated microprojector dis- play performance. Diode-pumped solid-state (DPSS) lasers have been genera- ting scalable green-laser emission for over 20 years. Neodymium vanadate (Nd:YVO 4 ) has been shown an efficient laser crys- tal when pumped with 808nm diodes. The harmonic material potassium-titanyl phosphate (KTP) has been produced for over 30 years and has excellent nonlinear optical properties. We have incorporated this technology into efficient miniature packages which are well suited for microprojector-display applications. 7 Figure 1. Schematic diagram of the optical components for three miniature green-laser designs. Nd:YVO 4 /KTP: Neodymium vanadate/potassium-titanyl phosphate. DFB: Distributed feedback. MgO: Magnesium oxide. PPLN: Periodically poled lithium niobate. The major optical components for three commercially availa- ble miniature green-laser sources are shown in Figure 1. The DPSS laser employs an electrically pumped 808nm diode to pro- vide the optical excitation. Its laser output is produced in a monolithic crystal that contains the Nd:YVO 4 in direct contact with the KTP harmonic crystal. The ends of the crystal assembly have mirror coatings to resonate the 1064nm radiation and emit harmonically produced 532nm emission only in the direction shown. The semiconductor-diode laser employs a 1064nm diode that can be either electrically or optically pumped. Its emission is imaged into the waveguide harmonic crystal. The 532nm emis- sion from the semiconductor-diode design is created in a single pass through the periodically poled harmonic crystal. Two different harmonic-conversion processes are employed in these miniature laser sources. The fundamental properties of the harmonic crystals are summarized in Table 1. Their values repre- Continued on next page