For $m \geq 1$, define a **link** to be a zero-one word $w=d_0d_1 \ldots d_k$, where $d_0=0$ and $k=2^m-1$ , such that the words

$$ w_0=0^{m-1}d_0, w_1=w_0d_1, w_2=w_1d_2, \ldots, w_k = w_{k-1}d_k $$

include as subwords every zero-one word of length $m$. How many links are there, and how can they be produced? If the answer is known, all I need is a reference. Otherwise, the question extends naturally to links of words on the alphabet from $0$ to $n>1$.

**Example:** For $m = 3$ two links are $01011100$ and $01110100$. The first link codes the following words:
$$w_0 = 000, w_01, w_010, w_0101, w_01011, w_010111, w_0101110, w_01011100, w_010111000, $$
in which all $8$ zero-one words of length $3$ occur as the final $3$ letters of the words. (The final word, $w_010111000$, is shown as the first word in a second link in an infinite chain.)