 Dylan F. Williams

Dylan F. Williams is a metrology researcher identified with NIST in a 2001 paper coauthored with Paul D. Hale and Tracy S. Clement. Their work connects measurement calibration of an optical receiver with corrections for electrical loss and electrical impedance mismatch.^[ref]

Why does the electrical connection matter when the original signal is light? A photodiode produces a photocurrent, but the measured signal also passes through cables, connectors and an electrical load. A simple original model writes the measured transfer function asFor this scalar model, if the connection has amplitude gain $0.8$ and the measured amplitude gain is $0.4$ at one frequency, the inferred receiver amplitude gain is $0.4/0.8=0.5$. Treating $0.4$ as the receiver result would incorrectly include the connection's attenuation. A real mismatched connection requires a fuller model than this product.

The distinction between amplitude and power also matters. At the same real electrical impedance, an amplitude ratio $1/2$ corresponds to a power ratio $1/4$. Both give the same change in decibels when the appropriate definitions are used:Using $10{\log }_{10}$ on the amplitude ratio would instead give about $-3.01$ and describe a different quantity. These are illustrative calculations, rather than measurements attributed to Williams; the documented contribution is his coauthorship of the shared receiver-metrology work.