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TU Berlin

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Small-Signal Analysis

Small-Signal Response
Lupe

Both, the oxide aperture size and the shape of the driving electrode, have a major impact on the spectral emission characteristics of high-speed oxide-confined VCSELs. Moreover, in devices with a circular shaped injection electrode, the number of lasing modes is directly related to driving current level and the aperture diameter confining this current. For VCSELs with an aperture diameter below 3 µm, single-mode emission is supported. However, increasing the oxide aperture diameter, and operating the device at higher driving currents, the number excited higher order transverse modes increase.

Despite the fact that multi-mode oxide VCSELs emit at multi-wavelengths, the dynamic behavior is still modelled using single-mode rat equations.  This is probably based on the assumption, which indicates that the modulation response of “highly” index guided VCSELs shows typical single-mode transfer function characteristics. However, anomalies in the modulation response data are experimentally observed and regularly reported. More recently, an attempt was made to extract more figures of merit from such data. But, taking into consideration the multi-mode emission behavior and effects such as  spatial hole burnning (SHB), shifts some promising approaches to the foreground.  The main concept of these approaches is based on the interaction of the different lasing modes through their carrier reservoirs, resulting from the competition for the shared carrier density in the active region. This causes the splitting of the common reservoir into multiple carrier reservoirs. Thus, distinct carrier reservoirs are established, each serving its spatially separated mode. The different modes also partially overlapping.    

In order to get better understanding of the nature behind the discrepancies in the measured small-signal response mentioned above, we derive an advanced fitting model and show under which conditions it is compulsory to be deployed for the extraction of reliable figures of merit.

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Betreuer: Wissam Hamad

Ansprechpartner: Prof. Werner Hofmann

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