Increasing the luminance of a red emitting laser light source by spectral beam combining

Summary form only given. Current diode laser based projections systems suffer from low output power and hence poor visibility, especially of the red laser sources. An additional constraint for flying-spot projection is that the light source should feature an almost diffraction limited beam and a low speckle contrast. This can be achieved with tapered lasers (TPL) [1], but the output power is limited to about 1 W. One possible way to further increase the luminance is spectral beam combining of multiple emitters. We developed high power TPL with internal distributed-Bragg-reflector (DBR) gratings in the red spectral range near 635 nm [2]. The variable period length (Λ1 - Λ10) of the DBR allowed the processing of a bar of ten diode lasers with increasing, successive wavelengths (λ1 - λ10). Figure 1 shows on the left the light-current-voltage characteristics of such a DBR-TPL-BAR as a function of temperature. The right side shows the spectrum at about 1.6 W (I = 12 A, T = -20°C) showing the emission of all ten individual lasers. The cooling was required due to the combination of the low T0 value of about 30 K and the mutual heating of the laser chips on the bar.