Analysis of the modulation behaviour of red VCSELs

摘要

This talk focuses on the high frequency characteristics of red VCSELs. After a short description of important fabrication issues the modulation behaviour of GaInP surface emitting lasers is discussed on the basis of the laser rate equations. The influence of the geometric dimensions of the laser structure and of the operating conditions is investigated From the S-parameter analysis a modulation coefficient of 3 GHz/(mA)~(1/2) for VCSELs with a 7 μm aperture and a differential gain of 1.15-10~(-16) cm~2 are deduced. A more detailed analysis reveals, that the modulation behaviour of red VCSELs nearly solely depends on their photon density inside the quantum wells as expected from the rate equations. These results imply that for a certain range of geometries diffusion and diffraction have a second order influence on the high frequency characteristics of red VCSELs. The K-factor analysis indicates very short carrier transfer and relaxation times around 5 ps and a maximum frequency of 25 GHz. Large signal modulation issues such as the properties of the eye diagram are also addressed. From the device characteristics it is concluded that the GaInP-VCSEL is suitable for data communication applications. Low cost fabrication makes the red VCSEL an attractive candidate for both automotive and high-speed data communication.