L. Korte

Novel surface emitting GaAs/AlGaAs laser diodes based on surface mode emission

We present a novel concept to achieve surface emission from conventional semiconductor laser diodes. This new type of laser diode is modified to allow a coupling of the laser mode to a transverse electric polarized surface mode. As a result we achieve surface emission from GaAs/AlGaAs double heterostructure laser diodes with a beam divergence of 0.2%. This novel concept has a high potential for the realization of a beam steering device.

Highly reliable 40-W cw InGaAlAs/GaAs 808-nm laser bars

The fundamental question whether aluminum-free semiconductor lasers in the 808 nm band are significantly more reliable than Al-containing lasers is still open. We have fabricated and tested high-power InGaAlAs/GaAs-lasers which show excellent reliability data at and above 40 W cw. The laser structure consists of an InGaAlAs-double-quantum well (DQW) as active layer embedded in a large optical cavity (LOC) waveguide structure. The layers were grown in a low pressure MOVPE (LP- MOVPE) reactor using high quality precursors. Asymmetrically coated bars with a width of 1 cm containing 25 groups of 200 micrometer wide emitters were mounted junction down on actively cooled heatsinks. At a heatsink temperature of 18 degrees Celsius the slope-efficiency is 1.1 - 1.2 W/A. Due to the low series-resistance of 2.2 m(Omega) and the low internal losses in the range of 1.7 cm-1 the overall efficiency at 40 W cw reaches 50%. Lifetime studies over 33 0000 h accumulated device hours show that the laser bars with a resonator length of 900 micrometer can be operated at 40 W with high reliability. The mean degradation rate is -0.11%/kh. This result emphasizes that Al-containing lasers can also have a very high reliability usually claimed for Al-free lasers. As a consequence of these encouraging results we will start further lifetime tests at 50 to 60 W.

Adjustable surface emission from AlGaAs/GaAs laser diodes based on first‐order‐grating coupled surface mode emission

Strongly improved surface emitting laser diodes based on surface mode emission are presented. A first‐order‐grating was utilized for the excitation of the surface modes. This results in an efficient quasi‐single‐beam surface emission with low divergence and a significant narrowing in the emission spectrum. A variation in the emission wavelength of up to 4 nm is achieved by adjusting the surface waveguide thickness, which demonstrates the wavelength selection mechanism of the SME technique. The decisive advantage of the SME laser diodes in comparison to DFB/DBR laser diodes is their high flexibility in fabrication, which makes them very suitable for wavelength division multiplexing applications.

Single‐mode and single‐beam emission from surface emitting laser diodes based on surface‐mode emission

Single‐mode and single‐beam emission have been achieved from surface emitting laser diodes based on the surface‐mode‐emission technique. By employing an optimized device design and a first‐order grating coupler, the laser diodes show under pulsed operation condition a single‐mode emission with a linewidth of 0.11 nm. A power up to 3.6 mW is emitted into a single, surface‐emitted beam, which has a beam divergence of 0.20°.

VCSELs for datacom applications

The use of oxide confined VCSELs in datacom applications is demonstrated. The devices exhibit low threshold currents of approximately 3 mA and low electrical series resistance of about 50 (Omega) . The emission wavelength is in the 850 nm range. Life times of the devices are several million hours under normal operating conditions. VCSEL arrays are employed in a high performance parallel optical link called PAROLITM. This optical ink provides 12 parallel channels with a total bandwidth exceeding 12 Gbit/s. The VCSELs optimized for the parallel optical link show excellent threshold current uniformity between channels of < 50 (mu) A. The array life time drops compared to a single device, but is still larger than 1 million hours.

Surface mode coupling in GaAs/AlGaAs laser diodes—A novel concept for a single laser mode emission

We demonstrate a novel concept for a mode selection mechanism in surface emitting laser diodes. This concept is based on a strong coupling process between the laser mode and a surface mode on top of the laser diode. The mode selection mechanism is the result of a strong feedback from the surface mode into the laser diode. Nearly single‐modelike emission spectra are achieved from surface emitting GaAs/AlGaAs laser diodes and qualitatively explained by a model based on ray optics. The main advantage of this type of laser diode is its simple fabrication and the possibility of adjusting the desired wavelength independent of the growth process by external technological parameters.

Five-wavelength surface emitting laser diode array based on postgrowth adjustment of emission wavelength

A five-wavelength surface emitting laser diode array based on surface mode emission is reported. The wavelength control is achieved by postgrowth adjustment of the surface structure. Wavelength spacing between laser groups is 1.1 nm in average and the wavelength reproducibility is ±0.13 nm. The total change in the emission wavelength over the array is 4.78 nm. The single array elements show single mode emission with a full width at half-maximum of 0.08 nm in average and a side mode suppression ratio up to 20 dB. This type of laser diode is of high interest for wavelength division multiplexing applications.

Novel surface-emitting GaAs/AlGaAs laser diode beam steering device based on surface mode emission

A novel surface emitting laser diode beam steering device based on the excitation and emission of surface modes is presented. This new device is a longitudinally segmented wavelength tunable GaAs/AlGaAs double heterostructure laser diode, which is modified to allow a coupling of the laser mode to a transverse electric polarized surface mode. This results in surface emission with very narrow beam divergence. A steering of the surface emitted farfield pattern is achieved by a variation of the emission wavelength: By electrically changing the emission wavelength from 877.54 nm to 879.13 nm the dominant surface emitted peak is steered by 0.4 degree(s).

Digital beam steering from surface-emitting laser diodes based on surface mode emission

We present a surface emitting GaAs/AlGaAs laser diode beam steering device based on the surface mode emission (SME) technique. The SME-laser diodes operate in a single-mode and show efficient surface emission into a single beam with a minimum beam divergence of 0.11 degree(s). We demonstrate a large digital beam steering from this device, which is achieved by mode switching. The special SME-structure supports two single-mode emission wavelengths, which are spaced by 8.38 nm. Digital switching between these two modes by a proper current pulse sequence leads to a steering of the surface emitted single-beam by 4.9 degree(s). Presently the beam steering frequency is limited to a maximum value of 0.15 MHz. An optimized device design for a continuous steering of the single, surface emitted beam is proposed.

A novel surface emitting GaAs/AlGaAs laser diode beam steering device based on surface mode emission

We present a novel surface emitting laser diode beam steering device based on the excitation and emission of surface modes. This new device is a wavelength tunable GaAs/AlGaAs laser diode, which is modified to allow a coupling of the laser mode to a transverse electric polarized surface mode. A steering of the surface emitted farfield pattern is achieved by a variation of the emission wavelength. By electrically switching the emission wavelength from 877.54 run to 879.13 nm the dominant surface emitted peak is steered by 0.4°.