Folded AWG architecture

1. Apparatus comprising:

a first arrayed waveguide grating having a first waveguide array and a region of vertical-only confinement that is shared for both input and output beams of the first waveguide array, the input and output beams to and from the first waveguide array crossing each other within the region of vertical-only confinement; and

a second arrayed waveguide grating having a second waveguide array, input and output beams to and from the second waveguide array crossing each other and further crossing at least one of the input and output beams to and from the first waveguide array within the region of vertical-only confinement.

2. Apparatus comprising a first waveguide grating having:

a first input set of at least one optical waveguide disposed and oriented to deliver input optical energy into a region of vertical-only confinement;

a first waveguide array having an input end disposed and oriented to receive optical energy from the first input set of at least one optical waveguide after passage across the region of vertical-only confinement, the first waveguide array further having an output end disposed and oriented to deliver optical energy into the region of vertical-only confinement; and

a first output set of at least one optical waveguide disposed and oriented to receive optical energy from the output end of the first waveguide array after passage across the region of vertical-only confinement,

wherein at least one of the first input and first output sets of optical waveguides includes more than one waveguide,

and wherein the optical energy passing across the region of vertical-only confinement from the first input set of at least one optical waveguide to the input end of the first waveguide array crosses the optical energy passing across the region of vertical-only confinement from the output end of the first waveguide array to the first output set of at least one optical waveguide,

the apparatus further comprising a second arrayed waveguide grating having:

a second input set of at least one optical waveguide disposed and oriented to deliver input optical energy into the region of vertical-only confinement;

a second waveguide array having an input end disposed and oriented to receive optical energy from the second input set of at least one optical waveguide after passage across the region of vertical-only confinement, the second waveguide array further having an output end disposed and oriented to deliver optical energy into the region of vertical-only confinement; and

a second output set of at least one optical waveguide disposed and oriented to receive optical energy from the output end of the second waveguide array after passage across the region of vertical-only confinement,

wherein at least one of the second input and output sets of optical waveguides includes more than one waveguide,

and wherein the optical energy passing across the region of vertical-only confinement from the second input set of at least one optical waveguide to the input end of the second waveguide array crosses the optical energy passing across the region of vertical-only confinement from the output end of the second waveguide array to the second output set of at least one optical waveguide, and further crosses at least one of the group consisting of (a) the optical energy passing across the region of vertical-only confinement from the first input set of at least one optical waveguide to the input end of the first waveguide array, and (b) the optical energy passing across the region of vertical-only confinement from the output end of the first waveguide array to the first output set of at least one optical waveguide.

3. Apparatus according to claim 1 , wherein the second waveguide array is nested with the first waveguide array.

4. Apparatus according to claim 2 , wherein the second waveguide array is nested with the first waveguide array.