  We propose a device consisting of $m$ Mach-Zehnder interferometers and
realizing sorting of first $2^m$ temporal Hermite-Gauss modes of light passing
though it by adjusting the accumulated temporal Gouy phase acquired by every
mode. This mode-order-dependent phase shift is achieved by a fractional Fourier
transform realized by a time lens in one of interferometer's arms. We consider
application of such a sorter with just two interferometers to sorting the
Schmidt modes of a photon pair generated in spontaneous parametric
downconversion and find the theoretical lower bond on the cross-talk
probability of 5.5%.
