Optical mode engineering and high power density per facet length (>8.4 kW/cm) in tilted wave laser diodes

Tilted Wave Lasers (TWLs) based on optically coupled thin active waveguide and thick passive waveguide offer an ultimate solution for thick–waveguide diode laser, preventing catastrophic optical mirror damage and thermal smile in laser bars, providing robust operation in external cavity modules thus enabling wavelength division multiplexing and further increase in brightness enabling direct applications of laser diodes in the mainstream material processing. We show that by proper engineering of the waveguide one can realize high performance laser diodes at different tilt angles of the vertical lobes. Two vertical lobes directed at various angles (namely, +/–27° or +/–9°) to the junction plane are experimentally realized by adjusting the compositions and the thicknesses of the active and the passive waveguide sections. The vertical far field of a TWL with the two +/–9° vertical beams allows above 95% of all the power to be concentrated within a vertical angle below 25°, the fact which is important for laser stack applications using conventional optical coupling schemes. The full width at half maximum of each beam of the value of 1.7° evidences diffraction– limited operation. The broad area (50 μm) TWL chips at the cavity length of 1.5 mm reveal a high differential efficiency ~90% and a current–source limited pulsed power >42W for as–cleaved TWL device. Thus the power per facet length in a laser bar in excess of 8.4 kW/cm can be realized. Further, an ultimate solution for the smallest tilt angle is that where the two vertical lobes merge forming a single lobe directed at the zero angle is proposed.