The sensitivity of photoconductor receivers for long-wavelength optical communications

Abstract

We calculate the sensitivity of In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</inf> As photoconductor receivers for use in moderate to high bit-rate lightwave transmission applications. It is found that the noise of photoconductive receivers is dominated at all bit rates <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B &lt; 4</tex> Gbit/s by Johnson noise in the conductive channel. Nevertheless, the total noise current decreases approximately linearly with photoconductive gain, and therefore the sensitivity of photoconductive receivers can be comparable to high-sensitivity p-i-n photodiode receivers. The sensitivity of practical photoconductive receivers compares most favorably with p-i-n receivers in the bit-rate range of 500-2 Gbit/s. However, receivers employing high-speed In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</inf> Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</inf> As/InP avalanche photodiodes are expected to be more sensitive than photoconductive receivers over the entire bit-rate range considered. In this analysis, we consider the effects of slow photoconductor response on receiver sensitivity, and find that the limited gain-bandwidth product of practical photoconductors increases the complexity of the receiver circuit by necessitating equalization, resulting in a decrease in receiver sensitivity and dynamic range.