Large-area transmission modulators for 3D time-of-flight imaging

摘要

The indirect time-of-flight principle is one possibility to build a three-dimensional (3D) camera system. Available products based on this principle mostly use special CMOS sensors for demodulation of the optical signal at the receiver. This special CMOS chip can be replaced by a standard image sensor in combination with a quantum well electroabsorption modulator. In this case, the modulator heavily influences the 3D camera performance. Especially the characteristics of large-area devices are of major interest. Transmission electroaborption modulators with sizes in the square millimeter range have been fabricated for operating wavelengths of 850 and 940 nm. While the 850 nm devices were realized as non-resonant structures, for 940 nm devices a resonant design was developed to overcome the limitation in the number of quantum wells. Investigations of the static and dynamic behavior show extinction ratios up to 2.5 dB and corner frequencies up to 30 MHz. A single-point distance measurement setup demonstrates the high potential of the devices for the 3D application.