def beam_splitter(ax, p0, size=2.54, alpha=0, format=None, **kwds):
    r"""Draw a beam splitter."""
    if format is None: format = 'k-'
    a = size/2
    x0 = [a, -a, -a, a, a, -a]
    y0 = [a, a, -a, -a, a, -a]

    cur_list = [(x0, y0)]
    cur_list = rotate_and_traslate(cur_list, alpha, p0)

    for curi in cur_list: ax.plot(curi[0], curi[1], format, **kwds)
r"""Draw a beam splitter.