In this work, fundamental ultrafast transient responses are studied for optical wireless communication (OWC) detectors. It is shown that material impulse responses, associated with transient photoconductivity, and geometrical input responses, associated with transient optical power, must be considered in tandem when OWC photodetection is pursued with broad spectral and directional characteristics. An OWC detector, composed of GaAs photoconductive gaps in a corner-cube geometry, is fabricated and analyzed. The GaAs material response times are investigated experimentally and found to range from approximately 3 ps to 200 fs for 390 nm (violet) to 780 nm (red) photoexcitation. The geometrical response times are investigated theoretically and found to range from approximately 2 to 20 ps for device dimensions from 1 to 10 mm. The overall response times manifest themselves in two distinct dimensional regimes, with differing levels of wavelength and dimension dependence. The relevance of these findings is discussed for future ultrafast OWC detectors.

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