  Today, the realization of large optical interferometer schemes is necessary
for many sophisticated information processing algorithms. In this work, we
propose a modular interferometer architecture possible when the number of input
channels of a transformation populated with signals is much lesser than the
total number of its channels. The underlying idea is to split the
transformation into two stages. In the first stage, the signals undergo
scattering among multiple channels of separate optical schemes, while in the
second stage, they are made to interfere with each other, thus, we call it the
mixing stage. This way, large-scale transformations that technically
challenging to fabricate even by means of the mature integrated photonics
technology, can be realized using multiple low-depth optical circuits, yet at
the expense of single interconnection between the scattering and mixing parts
of the interferometer. Although non-universal, as witnessed by the parameters
set to define the interferometer, the architecture provides a viable approach
to construction of large-scale interferometers.
