High contrast gratings (HCGs) are diffraction gratings whose period is less than the wavelength of light, made of a material with a high refractive index. Monolithic HCGs (MHCGs) are made of the same material as the cladding. They can be made of almost any material used in optoelectronics. We show experimentally and via simulations that shaping the cross-section of the MHCG stripes enables very broad high reflection spectrum.
We design and process more than 100 different 980 nm MHCG mirror designs, to determine optimal parameters for the use of the MHCGs as mirrors for VCSELs. We present measured power reflectance spectra and compare the results to our with numerical simulations. We discuss the impact of the actual processed geometric shape of the MHCG stripes on the measured power reflectance of the MHCGs..
980 nm VCSELs with different numbers of top dielectric DBR periods added to a 5.5-period top semiconductor DBR and with various oxide aperture diameters are investigated to determine the impact of the added dielectric DBR’s impact on the static and dynamic properties of the VCSELs. For VCSELs with the same oxide aperture diameter we observe smaller small-signal modulation bandwidth and lower D-factor for the VCSELs with more pairs of dielectric DBRs. For the VCSELs with 4 μm oxide aperture diameters with 8 and 12 periods of added top dielectric DBRs we measured bandwidths of 29 and 26 GHz, respectively.
We demonstrate the operation of two optically pumped high-power membrane external-cavity surface-emitting lasers (MECSELs) that emit in 1600–1800 nm spectral region. The region of the MECSEL consisted of eight strained InGaAs quantum wells (QWs) that are enclosed by InGaAlAs barriers. The heterostructures were deposited on InP substrates by molecular beam epitaxy. In order to efficiently dissipate heat, the developed MECSEL technology requires etching-off the epitaxial substrate and bonding two diamond heat spreaders on both sides of membrane. Maximum output powers of 1.6 W at 1640 nm and 2.1 W at 1760 nm were achieved. The mount temperatures were -6°C in both cases. The introduction of a birefringent filter into the resonator of the 1760 nm emitting laser produced a 133-nm wavelength tuning range, from 1695 nm to 1828 nm.
Using a Vertical Cavity Surface Emitting Laser (VECSEL) “as-grown” heterostructure we set-up a laser emitting at 488
nm with the output power approaching 20mW. The short wavelength emission was due to the conversion of the 976nm
emission by a second harmonic generation process in a type-I lithum triborate (LBO). The V-type external cavity
permitted efficient focusing of the laser beam on both the VECSEL heterostructure and the non linear crystal. A small
diameter focused spot on the gain mirror is required when “as-grown” heterostructures are used. No birefringent filter
was used in the resonator. In the case of our heterostructure we observed that the light was spontaneously polarized
along the one of the crystallographic direction. The polarization ratio was 1000:1. The VECSEL heterostructure was of
the resonant type strongly enhancing a single wavelength emission. The wavelength fine tuning was performed by
heatsink temperature adjustment. The heterostructure was grown by molecular beam epitaxy. It consisted of 12 InGaAs
quantum wells enclosed by GaAs barriers and a AlAs/GaAs DBR.