Showing papers by "Mika Valden published in 2015"

Thermal Management in Long-Wavelength Flip-Chip Semiconductor Disk Lasers

Abstract: We address the thermal management of flip-chip semiconductor disk lasers (SDLs) emitting at wavelengths 1.3–1.6 μm. The emphasis of the study is on fabricating thin SDL structures with high thermal conductance. An essential part of this task is to use GaAs-based materials in the distributed Bragg reflector (DBR), because they can provide a combination of high thermal conductivity and high refractive index contrast. Furthermore, the reflectivity of the GaAs-based DBR should preferably be enhanced using a thin dielectric layer and a highly reflecting metal layer. Such a configuration enables very thin mirror structures with a reduced number of DBR layer pairs without compromising the reflectivity. The concept is demonstrated experimentally with a 1.32-μm flip-chip SDL, where the GaAs-based DBR is finished with a thin Al2O3 layer and a highly reflective Al layer. In addition, the design principles, thermal management, and the development issues related to semiconductor–dielectric–metal mirrors in 1.3–1.6-μm flip-chip SDLs are discussed.

Towards high power flip-chip long-wavelength semiconductor disk lasers

Abstract: Optically pumped semiconductor disk lasers (SDLs) are presented with emphasis on wafer bonding InP-based active regions with GaAs-based distributed Bragg reflectors (DBRs) and reducing the number of required layer pairs in the DBR. The wafer bonding is performed at a relatively low temperature of 200 °C utilizing transparent intermediate bonding layers. The reflectivity of the semiconductor DBR section is enhanced by finishing the DBR with a thin low refractive index layer and a highly reflecting metal layer. Su ch a design enables considerab ly thinner mirror structures than the conventional design, where the semiconductor DBR is finished with mere metal layers. In addition, a 90 nm thick Al 2 O 3 layer is shown to produce negligible increase in the thermal resistance of the SDL. Furthermore, a flip-chip SDL with a GaAs/AlAs-Al 2 O 3 -Al mirror is demonstrated with watt-level output power at the wavelength of 1.32  m. The properties and future improvement issues for flip-chip SDLs emitting at 1.3–1.6  m are also discussed. Keywords: Semiconductor disk laser (SDL), vertical-external-cavity surface-emitt ing laser (VECSEL), wafer bonding, flip-chip, distributed Bragg reflector (DBR), diel ectric mirror, metal mirror, semiconductor mirror.