Passband flattening of a phasar

A phasar, comprising:

• a first input channel being single mode within a band of transmission wavelengths;
• an optical splitter having an input port coupled to said first fiber and having two output ports receiving approximately equal energies of a signal received on said input port;
• a first and a second waveguide coupled to said two output ports and having optical lengths differing by a selected optical length difference;
• a multi-mode waveguide being multi-moded across said band of transmission wavelengths, having a input side coupled to said first and second waveguides with a lateral separation therebetween and having a length approximately equal to a multiple plus one-half of a beat length of said band of transmission wavelengths, and having an output side;
• a first free space region coupled on a first side thereof to said output side of said multi-mode waveguide;
• an array of waveguides coupled to a second side of said first free space regions having predetermined differences of lengths thereof;
• a second free space region coupled on a first side thereof to said array of waveguides;
• and
• at least one output waveguide coupled to a second side of said second free space region.

A phasar, comprising:

• a first input channel being single mode within a band of transmission wavelengths;
• an optical splitter having a input port coupled to said first fiber and having two output ports receiving approximately equal energies of a signal received on said input port;
• a first and a second waveguide coupled to said two output ports and having optical lengths differing by a predetermined optical length difference;
• a multi-mode waveguide being multi-moded across said band of transmission wavelengths, having a input side coupled to said first and second waveguides with a lateral separation therebetween;
• a first free space region coupled on a first side thereof to said output side of said multi-mode waveguide;
• an array of waveguides coupled to a second side of said first free space regions having predetermined differences of lengths thereof;
• a second free space region coupled on a first side thereof to said array of waveguides;
• and
• at least one output waveguide coupled to a second side of said second free space region;
• wherein said separation produces a lateral dispersion within said multi-mode waveguide adjacent to said first free space region substantially equal to a lateral dispersion produced by said first and second free space regions and said arrayed waveguide.

A wavelength-division multiplexing (WDM) communication system comprising multiple single-mode optical channels carrying a multiplicity of optical signals having respective optical carrier wavelengths, said system including a wavelength routing phasar comprising;

• a first free space region;
• a second free space region;
• a plurality of arrayed optical waveguides coupled to first sides of said first and second free space regions having optical lengths having predetermined optical length differences therebetween;
• a Mach-Zehnder interferometer having an optical splitter including a port on one side thereof connected to one of said single-mode optical channels and two ports on a second side thereof;
• and
• a multi-mode waveguide, which is multi-mode at all of said optical carrier wavelengths, coupled on a first longitudinal end to said two ports from said Mach-Zehnder interferometer and coupled on a second longitudinal end to one of said first and second free space regions.