Electronically demodulating indirect time-of-flight (iTOF) image sensors can be replaced by a combination of a transmission electroabsorption modulator (T-EAM) and a common image sensor. In this case the demodulation is done by the modulator in the optical domain. In this work a three-dimensional (3D) imaging system utilizing this combination is built and its performance using two identical modulators with different size is compared. Measurement results show the strong influence of the modulation bandwidths of the T-EAM, leading to depth inaccuracies of 1 and 4 cm at a distance of 1 m for modulators with bandwidths of 75 and 23 MHz, respectively. In addition, simulation results matching the measured values are presented.
Using an optical transmission electroabsorption modulator (T-EAM) in combination with a common image sensor and a high-power illumination source allows to build a three-dimensional (3D) imaging system based on the indirect time-of-ight (iTOF) principle. In contrast to most available iTOF systems that use specialized image sensors, in this case the EAM is doing the required demodulation at the receiver in the optical domain. A first 3D imaging setup was built and investigations on the performance of the system are reported. A high-power laser source was characterized in order to design and fabricate matched large-area T-EAMs. The fabricated modulators show extinction ratios of about 6 dB and bandwidths of up to 37MHz at 1mm2 size. 3D images taken with the prototype camera consisting of the T-EAM, the laser source, and a Raspberry Pi camera show promising results with a depth inaccuracy below 5 cm at a distance of 1 m.
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 850nm devices were realized as non-resonant structures, for 940nm 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.
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