\documentclass{standalone}
\pagestyle{empty}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
\clip (-2,-.1) rectangle (2,2);

\draw [red] (0,0)--(1,2);
\begin{scope}
\clip (0,0)--(1,2)--(2,2)--(2,0);
\foreach \j in {0,.5,...,5} \draw [very thin, cyan] (\j,0)--(\j-1, 2);
\end{scope}

\draw[thick]  (-2,0)--(2,0);
\begin{scope}
\clip (0,0)--(1,2)--(-2,2)--(-2,0);
\foreach \j in {0,-.5,...,-5} \draw [very thin,cyan] (\j,0)--(\j+3, 2);
\end{scope}
\node at (1.45,.5) {$u=u_+$};
\node at (-1.25,.5) {$u=u_-$};
\end{tikzpicture}
\end{document}