Dylan F. Williams
= Dylan F. Williams
{c}
\b[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.<Frequency response metrology for high-speed optical receivers by Paul D. Hale and others>[Byline and pp. 1–2, equations 1–3 and Figure 1]{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> as
$$
H_{\rm measured}(f)=H_{\rm receiver}(f)H_{\rm connection}(f).
$$
For 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:
$$
20\log_{10}(1/2)=10\log_{10}(1/4)\simeq-6.02.
$$
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.