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Studies on infrared RW lasers

Collaborator: U. Bandelow , R. Hünlich , H. Gajewski  

Cooperation with: F. Fidorra, Ch. Radüge (MergeOptics GmbH, Berlin), J. Kreissl (Heinrich-Hertz-Institut für Nachrichtentechnik (HHI) Berlin GmbH)

Supported by: MergeOptics GmbH

Description: Investigations on InP-based 1.55 $\mu m$-emitting Ridge Waveguide semiconductor lasers  with strained Multi Quantum Well active region by MergeOptics GmbH have been performed for improving their performance. The simulations have been based on the device simulator     WIAS-TeSCA, which allows for a selfconsistent treatment of the optical, electrical, and thermal behavior of semiconductor  devices (see Fig.1).

 

Fig. 1:  Simulated hole injection current density and power distribution (left) and temperature distribution (right) in a part of the transverse cross-section of a RW-MQW laser

Among others, simulation results have been compared with measurements, which have been performed at HHI Berlin ([2]). Simulated device characteristics showed a good agreement with experimental findings, cf. the power-current characteristics in Fig.2. Besides the behavior in the non-thermal regime (below 100 mA in Fig.2) also the impact of the internal heating (Fig.1, right) at higher injection currents is displayed properly by the simulations.

Based on this fact, further simulations have been used to predict properties with relevance for applications of possible future devices with changed geometry.

 

Fig. 2:  Power-current characteristics, measured for a set of devices (boxes) and simulated with WIAS-TeSCA (solid line)

Using the optical field distribution at the facet of the laser, which has been obtained as one of the outputs of     WIAS-TeSCA, also the farfield  distribution has been calculated in a postprocessing procedure ([1]). Again, such farfield distributions have been compared with experimental data which have been obtained from measurements at HHI. Some typical farfield intensity patterns are displayed within Fig.3.

 

Fig. 3:   Farfield intensity pattern, left: horizontal direction (parallel to the quantum wells), right: vertical direction (perpendicular to the quantum wells). Solid lines: experiment, dashed lines: simulation.

Basic farfield characteristics, as FWHM-parameters and basic diffraction effects could be reproduced by the simulations in good agreement with the measurements, see Fig.3. However, some details, especially of the vertical farfield intensity pattern (Fig.3, right) are very difficult to be resolved by the model implemented so far. For the investigation of such effects future work would be required.

References:

1.  S.L. CHUANG, Physics of Optoelectronic Devices, Wiley & Sons, New York, 1995.
2.  HEINRICH-HERTZ-INSTITUT FÜR NACHRICHTENTECHNIK BERLIN GMBH, Annual Report, http://www.hhi.de , 2000.

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