\documentclass{article}
\usepackage[all]{xy}
\usepackage{amsmath,xcolor}
\newcommand{\lambdabar}{{\mkern0.75mu\mathchar '26\mkern -9.75mu\lambda}}
\begin{document}
\noindent
\pagestyle{empty}
\huge
\[
	\xymatrix@C=0.5em@R+1em{
	& \underset{_{\substack{\text{linear}\\\text{wavenumber}}}}{\tilde{\nu}}
	\ar^-{_{\color{gray}x \cdot \tau}}[rr]
	\ar^>>>>>>>>>>>>>>>>>>>>{\color{gray}\frac{1}{x}}@{<.>}[dd]
	\ar_-{_{\color{gray}x \cdot v_p}}[dl]
	&
	& \underset{_{\substack{\text{angular}\\\text{wavenumber}}}}{k}
	\ar^-{_{\color{gray}x \cdot v_p}}[dl]
	\ar^-{\color{gray}\frac{1}{x}}@{<->}[dd]
	\\
	\underset{_{\substack{\text{linear}\\\text{frequency}}}}{f}
	\ar^{_{\color{gray}\qquad\;\; x \cdot \tau}}[rr]
	&
	& \underset{_{\substack{\text{angular}\\\text{frequency}}}}{\omega}
	\ar^>>>>>>>>>>>>>>>>>>>>{\color{gray}\frac{1}{x}}@{<->}[dd]
	\\
	& \underset{_{\substack{\text{linear}\\\text{wavelength}}}}{\lambda}
	\ar^-{_{\qquad\quad\color{gray}x/\tau}}@{.>}[rr]
	\ar^>>>>>>>>>>>>>>>{_{\color{gray}x / v_p}}@{.>}[dl]
	&
	& \underset{_{\substack{\text{angular}\\\text{wavelength}}}}{\lambdabar}
	\ar^-{_{\color{gray}x / v_p}}[dl]
	\\
	\underset{_{\substack{\text{linear}\\\text{period}}}}{T}
	\ar^-{\color{gray}\frac{1}{x}}@{<->}[uu]
	\ar^-{_{\color{gray}x / \tau}}[rr]
	&
	& \underset{_{\substack{\text{angular}\\\text{period}}}}{?}
	}
\]

\vspace{1em}
\Large

$v_p =$ wave speed (phase velocity)

$\tau = 2\pi$
\end{document}