Michael C. Riedl

Single-mode VCSELs

We compare various approaches aiming at large-area high-power single-mode oxidized VCSELs. Stable and reproducible single-mode emission with SMSR (side-mode suppression ratio) greater than 30dB and output powers well above 5mW are reported for the long monolithic cavity and self-aligned shallow surface etching approaches, both of which are suitable for commercial production. Additionally, Photonic Crystal Surface-Emitting Lasers (PCSELs) are introduced, which enable advanced mode control by novel transverse optical guiding techniques.

Large-Area Single-Mode Selectively Oxidized VCSELs: Approaches and Experimental

We present the investigation of several methods to increase the active diameter of single transverse mode oxide confined VCSELs in both the 850 and 980 nm wavelength regimes. Among the concepts considered are mode intensity specific shallow surface etched reliefs, monolithically increased cavity lengths, current confinement matching the fundamental mode intensity distribution and saturable absorbers. All approaches are introduced in theoretical considerations and corresponding measurement results are presented. Additionally, numerical simulations are performed to gain an increased understanding of some of the mode selection mechanisms. The considered concepts are evaluated in terms of decrease of the series resistance (for impedance matching/driving reasons) and device lifetime (as derived from maximum current densities). The results obtained are also compared to other approaches found in literature (e.g. metal apertures, photocurrent feedback, Fabry-Perot etalon, half-symmetric cavity). Conventional devices with optimized thin oxide aperture location have shown single-mode output powers above 4 mW with an active diameter of 3.5 micrometer. A record high single-transverse mode output power of 5 mW at a series resistance of 98 (Omega) is obtained for a 7 micrometer aperture device by increasing the cavity length monolithically by 4 micrometer.

Monolithic polarization control of multimode VCSELs by a dielectric surface grating

Based on design guidelines from a three-dimensional, fully vectorial model, we have fabricated vertical-cavity surface-emitting lasers (VCSELs) with a monolithically integrated dielectric surface grating for polarization control. For VCSELs with emission wavelengths of 850 and 980 nm we have achieved orthogonal polarization suppression ratios (OPSRs) above 15 dB for all modes up to thermal rollover, which very well agrees with theory. It is shown both theoretically and experimentally that the grating has no influence on the emission far-field. The surface grating has also been combined with a surface relief to stabilize the polarization and to increase the fundamental mode output power at the same time.

Design of Highly Efficient High-Power Optically Pumped Semiconductor Disk Lasers

In this paper, we present a carefully elaborated layer design for semiconductor disk lasers. Experimental results of devices mounted on simple copper heat spreaders reveal a conversion efficiency of 54% at 13.2 W for 970-nm wavelength laser emission and a differential quantum efficiency of 73%.

Polarization-controlled monolithic oxide-confined VCSELs

We report on advances in the fabrication and performance of monolithic 850 nm, linearly polarized vertical-cavity surface-emitting lasers (VCSELs) incorporating a semiconductor surface grating at the outcoupling facet. Depending on the grating parameters, the light is polarized either parallel or perpendicular to the grating grooves. Deep-etched gratings enable complete polarization pinning even in directions that are 45 degrees off the preferred crystal axes. On the other hand, such devices can show strong side-lobes in the far-field which may limit the available output power for some applications. Shallow-etched VCSELs with almost undistorted far-fields deliver output powers as high as 29 mW with about 12 dB orthogonal polarization suppression ratio. A combination of surface relief and grating is used to increase the transverse single-mode output power while maintaining polarization stability.

Improved VCSEL structures for 10 gigabit-Ethernet and next generation optical-integrated PC-boards

We have investigated direct optical interconnection between processor ICs on chip-to-chip level using VCSELs and 2-D 17 cm long, 120 /spl mu/m diameter step-index polymer optical fiber (POF) bundles. Their bandwidth-length-product of 2 GHz/spl middot/m makes them well suited for low-cost high-speed parallel optical interconnects on a board level. We have demonstrated 10 Gbit/s PRBS NRZ data transmission over four channels of a POF array.

760-nm high-performance VCSEL growth and characterization

High-performance vertical-cavity surface-emitting lasers (VCSELs) with an emission wavelength of approximately 764 nm are demonstrated. This wavelength is very attractive for oxygen sensing. Low threshold currents, high optical output power, single-mode operation, and stable polarization are obtained. Using the surface relief technique and in particular the grating relief technique, we have increased the single-mode output power to more than 2.5mW averaged over a large device quantity. The laser structure was grown by molecular beam epitaxy (MBE) on GaAs (100)-oriented substrates. The devices are entirely based on the AlGaAs mixed compound semiconductor material system. The growth process, the investigations of the epitaxial material together with the device fabrication and characterization are discussed in detail.