Broadband star coupler

An echelle grating, comprising:

• a first interface;
• a second interface;
• a plurality of output waveguides, at the first interface;
• one or more input waveguides, at the second interface;
• and
• a free propagation region connecting the plurality of output waveguides and the one or more input waveguides,
• a first waveguide, of the plurality of output waveguides, having a first width,
• a second waveguide, of the plurality of output waveguides, having a second width,
• the first width being at least 5% greater than the second width,
• the echelle grating being configured:
• when light is received at a first wavelength in only a third waveguide, of the one or more input waveguides, to direct the light at the first wavelength to the first waveguide;
• and
• when light is received at a second wavelength in only the third waveguide, to direct the light at the second wavelength to the second waveguide, and
• a ratio of the first width to the second width being within 10% of a ratio of the first wavelength to the second wavelength
• the first width being selected such that a first field pattern, at a grating of the echelle grating, corresponding to a fundamental mode of the first waveguide, includes, within a range of angles subtended by the grating of the echelle grating, at least 99% of the power of the first field pattern.