Let $C_{s,t}$ be the complete bipartite geometric graph, with $s$ and $t$ vertices on two distinct parallel lines respectively, and all $st$ straight-line edges drawn between them.
In this paper, we show that every complete bipartite simple topological graph, with parts of size $2(k-1)^4 + 1$ and $2^{k^{5k}}$, contains a topological subgraph weakly isomorphic to $C_{k,k}$.
As a corollary, every $n$-vertex simple topological graph not containing a plane path of length $k$ has at most $O_k(n^{2 - 8/k^4})$ edges.
When $k = 3$, we obtain a stronger bound by showing that every $n$-vertex simple topological graph not containing a plane path of length $3$ has at most $O(n^{4/3})$ edges.
We also prove that $x$-monotone simple topological graphs not containing a plane path of length $3$ have at most a linear number of edges.
Joint work with Andrew Suk, Gábor Tardos and Ji Zeng.