I am drawing an optical experiment that involves making a path take a detour.

Looped path

This is possible with PSTricks, but I haven't found a way to achieve this with TikZ.

What I currently have:

  • The beam splitter and mirror are positioned with relative node positioning.
  • The lasers are connected simply by defining paths from nodes.

So far I've tried the loop library (can only loop back to the node itself, like a state diagram), setting bends (will not turn one whole turn, just bend slightly), using a coil decoration, (best so far, but ugly and won't look good in the paper).

Does anybody have a pointer to a library that could do this for me?

Edit: I have taken the accepted answer and done a few tweaks. Note that the end angles are set to vertical.



\tikzstyle{beamsplitter} = [
    fill opacity=0.3,

\tikzstyle{left-hand-mirror} = [
        mark=between positions 0.015 and 0.98 step 0.1072 with {\draw (0,0)--(60:3pt);}

\tikzstyle{laser} = [
    line cap=round,

\tikzstyle{laserarrow} = [
    line cap=round,
    decoration={markings,mark=at position 0.55 with{\arrow[rotate=-20,maroon]{latex'}}},
    mark options={color=maroon}


\begin{tikzpicture}[use Hobby shortcut]
    \node (source) {};  

    \node[right=1cm of source] (splitter) {}; 

    \node[above=1 cm of splitter] (mirror) {};
    \node[right=5mm of splitter] (combiner) {};
    \node[right=5mm of mirror] (end) {};

    \path[laser] (source.east) -- (splitter.center);

    \path[laser] (mirror.center) -- (end.center) {};

    \path[laser] (splitter.center) -- (combiner.center);

% Create a node to the left of the midway between the splitter and mirror
    \path (splitter) -- (mirror.center) node[midway,left]
    (midway) {};

% Create a node to the left of the above node
    \node [left = 5mm of midway] (midway-left) {};

% Create the loop
    \draw [laserarrow]
    ([out angle=90, in angle=-90]splitter.center) .. (midway) .. (midway-left) 
    .. (midway) .. (mirror.center);

    \path[left-hand-mirror] (mirror.south west) --
    (mirror.north east) ;

    \draw[beamsplitter] (splitter.north west) rectangle (splitter.south east);
    \draw (splitter.north east) -- (splitter.south west);


and this creates the following output:

Final result

I still need to fix that arrow positioning, but I'm getting there.

  • 1
    Welcome to TeX.SX! We normally don't put greetings in questions so I removed yours. Commented Feb 19, 2014 at 13:10
  • 1
    Search for hobby in this site.
    – user11232
    Commented Feb 19, 2014 at 13:16
  • Harish, thanks for the suggestion for the hobby package. It might be a good answer for my question, however it refuses to work on MiKTeX 2.9 even though I am using the latest package version. Not even an MWE compiles. Should I ask a separate question about this? The error message in question is "Undefined Control Sequence" withouth telling me which control sequence is undefined. Commented Feb 19, 2014 at 13:51
  • I intended this as a comment but do not have the prerequisite reputation to make comments. Did any one answering this consider controls ? If not was there a reason, other then it's a bit fiddly. \tikz draw (0,0) .. controls (3,1) and (-2,1).. (1,0);
    – Carel
    Commented Aug 3, 2015 at 8:51

1 Answer 1


A possible solution:


\begin{tikzpicture}[use Hobby shortcut]
%\draw[help lines] (-1,-1) grid (4,3);

\draw[thick,maroon] (0,0) -- (2.75,0);

\begin{pgfonlayer}{foreground}% to avoid:
% http://tex.stackexchange.com/q/156613/13304
\node[thick,inner sep=5pt,fill,draw,fill opacity=0.2](n) at (2,0){};
  shorten <=\pgflinewidth, 
  shorten >=\pgflinewidth
 (n.south west)--(n.north east);

 decoration={markings,mark= at position 0.44 with 
 (2,0) .. (1.75,1) .. (1.6,1.25) .. (1,1) .. 

\draw[thick] (2,2)--($(2,2)!0.25!(1,1)$)coordinate(a)
(2,2)--($(2,2)!0.25!(3,3)$) coordinate(b);

 decoration={markings,mark=between positions 0 and 1 step 4pt
  with {\draw[thick] (0,0)--(70:3pt);}}


The result:

enter image description here

  • Interesting! However, I seem to be having trouble with the hobby package on my Windows computer as per my above comment. Please allow me to look into this issue before I can accept your answer. Commented Feb 19, 2014 at 14:03
  • 1
    @JonathanFors: sure, no problem at all. Please check your hobby version: mine is 1.4 from 2014-01-21. Also notice that hobby is implemented in LaTeX3, hence you should have an updated version of expl3, xparse and pml3array. Commented Feb 19, 2014 at 14:07
  • I am still not able to compile the document. I have submitted a separate question here: tex.stackexchange.com/questions/161282/… Commented Feb 19, 2014 at 14:47
  • It now works, and your solution was spot on. Commented Feb 19, 2014 at 15:37
  • 1
    By the way, pml3array ("Poor Man's LaTeX3 Array") is one of the files installed by the hobby package. Commented Feb 19, 2014 at 21:47

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