Raster multiplexing in photonic circuits

A circuit comprising:

• a number (N) of source circuits, each source circuit having an output path to propagate a photon, wherein N is greater than 1;
• a downstream circuit having a number (R) of input paths to receive photons, wherein R is at least 2;
• and
• a raster multiplexer circuit having:
• a number N of multiplexer input paths, each multiplexer input path coupled to an output path of one of the source circuits;
• a plurality of multiplexer output paths including a raster group of multiplexer output paths, wherein the raster group of multiplexer output paths includes R multiplexer output paths, each multiplexer output path in the raster group of multiplexer output paths being coupled to one of the input paths of the downstream circuit;
• an optical switching network coupled between the multiplexer input paths and the multiplexer output paths, the optical switching network comprising a plurality of active optical switches arranged to selectably couple a photon from any one of the multiplexer input paths to any one of the multiplexer output paths;
• and
• control logic coupled to the optical switching network and configured to:
• receive, for each of a plurality of time bins, an input signal indicative of whether the output path of each source circuit is propagating a photon;
• select, based on the input signal, one of the multiplexer input paths as an active multiplexer input path for the time bin;
• select one of the multiplexer output paths as an active multiplexer output path for the time bin, wherein multiplexer output paths in the raster group are selected according to a fixed order such that each multiplexer output path in the raster group of multiplexer output paths is selected as the active multiplexer output path once during a raster period consisting of R consecutive time bins;
• and
• generate control signals to set a state of the optical active switches such that a photon from the active multiplexer input path is coupled to the active multiplexer output path.

A circuit comprising:

• a number (N) of source circuits, each source circuit having an output path to propagate a photon, wherein N is at least 2;
• a number (R) of downstream circuits, each downstream circuit having a number (M) of input paths to receive photons, wherein R is at least 2 and M is at least 2;
• and
• a set of M raster multiplexer circuits, each raster multiplexer circuit having:
• a set of N multiplexer input paths, each multiplexer input path coupled to an output path of one of the N source circuits;
• a plurality of multiplexer output paths including a raster group of multiplexer output paths, wherein the raster group of multiplexer output paths includes R multiplexer output paths, each multiplexer output path in the raster group of multiplexer output paths being coupled to one of the input paths of a different one of the R downstream circuits;
• and
• an optical switching network coupled between the multiplexer input paths and the multiplexer output paths, the optical switching network comprising a plurality of active optical switches arranged to selectably couple a photon from any one of the multiplexer input paths to any one of the multiplexer output paths;
• and
• control logic coupled to the raster multiplexer circuits and configured to:
• receive, for each of a plurality of time bins, an input signal indicative of whether the output path of each source circuit is propagating a photon;
• select, for each of the raster multiplexer circuits, one of the multiplexer input paths as an active multiplexer input path for the time bin, the selection being based at least in part on the input signal;
• select, for each of the raster multiplexer circuits, one of the multiplexer output paths as an active multiplexer output path for the time bin, wherein, for each raster multiplexer circuit, multiplexer output paths in the raster group are selected according to a fixed order such that each multiplexer output path in the raster group of multiplexer output paths is selected as the active multiplexer output path once during a raster period consisting of R consecutive time bins and wherein all M of the multiplexer output paths that couple to a same one of the R downstream circuits are selected as the active multiplexer output paths for a same time bin;
• and
• generate control signals to set a state of the active switches in the optical switching network of each of the R raster multiplexer circuits such that, in each of the R raster multiplexer circuits, a photon from the active multiplexer input path is coupled to the active multiplexer output path.

A method comprising:

• receiving, for each time bin in a series of time bins, a plurality of input signals indicating whether photons are present on each of a plurality of input paths of an optical circuit;
• selecting, for each time bin in the series of time bins, an active input path for the optical circuit based at least in part on the input signals;
• selecting, for each time bin in the series of time bins, an active output path for the optical circuit from a plurality of output paths that includes a raster group of a number (R) of output paths, wherein R is at least 2, wherein output paths in the raster group are selected according to a fixed order such that each output path in the raster group of output paths is selected as the active output path once during a raster period consisting of R consecutive time bins;
• and
• controlling, for each time bin in the series of time bins, a plurality of active switches in the optical circuit to couple a photon from the active input path to the active output path.