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Monolithic Photodiode Array with Impedance Match
High-bit-rate optical fiber networks and photonic microwave applications currently rely on photodiodes to serve as optical-to-electrical (O/E) converters. In such high performance, high-speed applications the O/E converters must exhibit high 3db bandwidth as well as a large saturation photocurrent.
Traditionally, these performance constraints have necessitated the design of a photodiode with small carrier transit times and low capacitance. However, this traditional design leaves the photodiode with the undesirable attributes of a smaller depletion layer and thin layer thickness. The reduction in absorptive area in the photodiode results in higher photocurrent densities which exacerbate space-charge effects, as compared to the performance of large-area devices.
The present invention relates to a compact, monolithically integrated high-power, high-bandwidth O/E converter exhibiting impedance matching to the external load.
In contrast to other technologies, this converter’s design does not utilize an optical waveguide. This allows both greater freedom in the choice of photodiode layer as well as impedance matching without any trade-off regarding phase or velocity match. As an alternative to a waveguide, the present invention employs multiple photodiodes illuminated vertically through free space. Optical power can be uniformly distributed to the photodiodes, each of which achieves high quantum efficiency without polarization-dependent loss, resulting in uniform photocurrent distribution within the array.
This design also allows for externally controlled phase matching, obtained according to the desired frequency characteristics of the photodiode array. The design further allows for multi-path absorption to be exploited. Additionally, broadband impedance-matching can be achieved through the physical design parameters of the array.
Campbell, Beling, and Pan
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