  Given a subgroup $H$ of a group $(G,+)$, a $(G,H,k,1)$ difference family (DF)
is a set $\mathcal F$ of $k$-subsets of $G$ such that $\{f-f':f,f'\in F, f\neq
f',F\in \mathcal F\}=G\setminus H$. Let $g\mathbb Z_{gh}$ is the subgroup of
order $h$ in $\mathbb Z_{gh}$ generated by $g$. A $(\mathbb Z_{gh},g\mathbb
Z_{gh},k,1)$-DF is called cyclic and written as a $(gh,h,k,1)$-CDF. This paper
shows that for $h\in\{2,3,6\}$, there exists a $(gh,h,4,1)$-CDF if and only if
$gh\equiv h\pmod{12}$, $g\geq 4$ and $(g,h)\not\in\{(9,3),(5,6)\}$. As a
corollary, it is shown that a 1-rotational S$(2,4,v)$ exists if and only if
$v\equiv4\pmod{12}$ and $v\neq 28$. This solves the long-standing open problem
on the existence of a 1-rotational S$(2,4,v)$. As another corollary, we
establish the existence of an optimal $(v,4,1)$-optical orthogonal code with
$\lfloor(v-1)/12\rfloor$ codewords for any positive integer $v\equiv
1,2,3,4,6\pmod{12}$ and $v\neq 25$. We also give applications of our results to
cyclic group divisible designs with block size four and optimal cyclic $3$-ary
constant-weight codes with weight four and minimum distance six.
