Multi-mode interference coupler

A multimode interference coupler comprising:

• a multimode interference (MMI) region including:
• first and second region ends separated by a region length along a longitudinal axis, and
• first and second edges between the first and second region ends defining the MMI region, which varies in width along the region length;
• wherein each of the first and second edges includes at least three critical points in slope relative to the longitudinal axis defining at least three local minima or maxima;
• at least one port optically coupled to the first region end;
• and
• at least one port optically coupled to the second region end;
• wherein the at least three local minima or maxima comprises at least two maxima and at least three minima in each of the first and second edges;
• wherein a first derivative of a slope of the first and second edges at each local minima or maxima relative to the longitudinal axis is substantially 0.

A multimode interference coupler comprising:

• a multimode interference (MMI) region including:
• first and second region ends separated by a region length along a longitudinal axis, and
• first and second edges between the first and second region ends defining the MMI region, which varies in width along the region length;
• wherein each of the first and second edges includes at least three critical points in slope relative to the longitudinal axis defining at least three local minima or maxima;
• at least one port optically coupled to the first region end;
• and
• at least one port optically coupled to the second region end;
• wherein each of the first and second edges also includes at least one transition point with a change in curvature as the width transitions from a wider width to a narrower width, wherein a second derivative of a slope of the first and second edges at the transition point equals relative to the longitudinal axis is substantially 0.

A method of manufacturing a multimode interference (MMI) coupler comprising:

• a multimode interference (MMI) region including:
• first and second region ends separated by a region length along a longitudinal axis, and
• first and second edges between the first and second region ends, defining the MMI region, which varies in width along the region length, each of the first and second edges includes at least three critical points defining at least three local minima or maxima;
• at least one port optically coupled to the first region end;
• and
• at least one port optically coupled to the second region end;
• said method comprising:
• determining the first and second edges for a predefined set of design parameters, using a computerized optimization algorithm;
• and
• fabricating the MMI coupler with the first and second edges;
• wherein each of the first and second edges also includes at least one transition point with a change in curvature as the width transitions from a wider width to a narrower width, wherein a second derivative of a slope of the first and second edges at the transition point equals relative to the longitudinal axis is substantially 0.

A method of manufacturing a multimode interference (MMI) coupler comprising:

• a multimode interference (MMI) region including:
• first and second region ends separated by a region length along a longitudinal axis, and
• first and second edges between the first and second region ends, defining the MMI region, which varies in width along the region length, each of the first and second edges includes at least three critical points defining at least three local minima or maxima;
• at least one port optically coupled to the first region end;
• and
• at least one port optically coupled to the second region end;
• said method comprising:
• determining the first and second edges for a predefined set of design parameters, using a computerized optimization algorithm;
• and
• fabricating the MMI coupler with the first and second edges;
• wherein determining the first and second edges comprises:
• a) generating a set of region widths, perpendicular to and spaced apart along the longitudinal axis, corresponding to the plurality of local minima and maxima, using the computerized optimization algorithm, thereby forming first and second interim edges;
• and
• b) smoothing the first and second interim edges to generate the first and second edges including at least two local minima and at least three local maxima in each of the first and second edges.

A method of manufacturing a multimode interference (MMI) coupler comprising:

• a multimode interference (MMI) region including:
• first and second region ends separated by a region length along a longitudinal axis, and
• first and second edges between the first and second region ends, defining the MMI region, which varies in width along the region length, each of the first and second edges includes at least three critical points defining at least three local minima or maxima;
• at least one port optically coupled to the first region end;
• and
• at least one port optically coupled to the second region end;
• said method comprising:
• determining the first and second edges for a predefined set of design parameters, using a computerized optimization algorithm;
• and
• fabricating the MMI coupler with the first and second edges;
• wherein determining the first and second edges comprises:
• i) randomly generating a set of interim region widths, perpendicular to and spaced apart along the longitudinal axis, corresponding to the plurality of local minima and maxima, within a predefined widths range approximate to a predefined initial region width, using the computerized optimization algorithm, thereby forming first and second interim edges;
• ii) smoothing the first and second interim edges;
• iii) determining output optical power at each of the ports optically coupled to the second region end relative to a predefined input optical power at one of the ports optically coupled to the first region end, by simulating the MMI coupler for the set of interim widths and the predefined set of design parameters;
• iv) calculating a figure of merit from the output optical powers and the predefined input optical power;
• v) repeating steps i) to iv) until the figure of merit exceeds a predefined performance limit for a working set of interim widths;
• and
• vi) setting the working set of interim widths as the set of region widths.