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New Concept: the nanophotonic vertically integrated modulator technology

A breakthrough concept paving the way to higher data rates beyond 40 Gbit/s is the implementation of the novel nanophotonic concept of vertical monolithic-integration of an electro-optic reflectance modulator (EOM) and laser. This monolithic all-epitaxial approach can be realized in Vertical Cavity Surface Emitting Lasers (VCSEL) or edgeemitting lasers, reducing the cost while increasing the speed of the optical components and modules used in networks. In contrast to the conventional direct current modulation approach, the light intensity modulation is based on the electro-optic modulation of the mirror reflectivity and, thus, the light output of the laser while keeping the laser current constant.

Opposite to Mach-Zehnder electro-optic modulators (EOM) the modulator section can be directly monolithically integrated into the device and the size, the power consumption, the epitaxial wafer and processing costs are the same as for conventional lasers. The electric field changes the refractive index of certain layers of the mirror, which leads to a change in the mirror reflectivity without any significant absorption of the laser emission. Thus, no time-of-flight related speed limitations, overheating of the modulator section by carrier absorption and other parasitic effects, characteristic of electroabsorption modulators, are relevant in this case. In this indirect modulation scheme the light intensity is modulated by varying the reverse bias voltage in an ultralow differential capacitance regime, thus, requiring minimal switching power and enabling ultrahigh modulation speed. Low cost CW drivers can be used for the gain section. Such novel ultra-high speed types of lasers, both 850 nm VCSELs as well as 1.3 mm edge emitting lasers, will be demonstrated and studied in the frame of this projects.

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