RGB laser generation from fiber MOPAs coupled to external enhancement cavities

Abstract

Red (631 nm), green (532 nm), and blue (448 nm) continuous-wave (CW) lasers have been developed by Evans & Sutherland (E&S). These multi-watt RGB lasers are used as light sources in E&S' laser projector (ESLP), which delivers ultrahigh-resolution content (8192 × 4096 pixels) to large-surface-area venues (e.g., planetariums, simulators, visualization centers, etc.). Efficient visible wavelength generation is obtained by coupling single-frequency nearinfrared (NIR) beams into free-space enhancement cavities containing critically phase-matched lithium triborate (LBO) crystals. The NIR energy is produced by a master-oscillator-power-amplifier (MOPA) system which is fiber-based, thus yielding Gaussian beams which are near-ideal for efficient fundamental-to-harmonic conversion. Both polarizationmaintaining (PM) fibers and non-PM fibers have been employed with non-PM fiber systems requiring polarization sensing and control. Green laser light is produced by a second-harmonic generation (SHG) process with a 1064 nm fundamental. Red laser light is produced by a sum-frequency mixing (SFM) process with 1064 nm and 1550 nm as fundamentals. Blue laser light is produced by an SFM process with 1064 nm and 775 nm as fundamentals, where 775 nm is first produced by an SHG process with a 1550 nm fundamental. All resulting visible lasers are single-axialfrequency with FWHM bandwidths less than 400 kHz, and are spatially pure with M² values less than 1.05. At least 18 W of CW optical power has been generated at all three visible wavelengths, with available NIR amplifier power as the primary limiting factor.