Method and system for grating taps for monitoring a DWDM transmitter array integrated on a PLC platform
An integrated DWDM transmitter apparatus includes a silica-on-silicon substrate which includes a silica layer and a silicon layer. A plurality of input waveguides and a plurality of gratings are provided within the silica layer. Each of the plurality of gratings is coupled to a corresponding one of the input waveguides. An arrayed waveguide grating within the silica layer is coupled to the plurality of input waveguides, and at least an output waveguide within the silica layer are coupled to the arrayed waveguide grating. The transmitter also includes a plurality of lasers disposed in a recessed region of the silica-on-silicon substrate, and each of the lasers is optically coupled to a corresponding one of the plurality of input waveguides. The integrated transmitter also includes plurality of photodiodes, each of the plurality of photodiodes overlying a corresponding one of the plurality of grating.
1. An integrated DWDM transmitter apparatus, the apparatus comprising:
a silica-on-silicon substrate, the silica-on-silicon substrate including a silica layer and a silicon layer, the silica-on-silicon substrate having a recessed region;
a plurality of input waveguides within the silica layer;
a plurality of gratings within the silica layer, each of the plurality of gratings coupled to a corresponding one of the input waveguides;
an arrayed waveguide grating within the silica layer and coupled to the plurality of input waveguides;
at least an output waveguide within the silica layer and coupled to the arrayed waveguide grating;
a plurality of lasers mounted on a surface of the recessed region of the silica-on-silicon substrate, each of the plurality of lasers being optically coupled to a corresponding one of the plurality of input waveguides; and
a plurality of photodiodes, each of the plurality of photodiode overlying a corresponding one of the plurality of gratings.
2. The apparatus of claim 1 wherein each of the input waveguides within the silica layer comprises a core region surrounded by a cladding region, the core region being characterized by an index of refraction higher than an index of refraction of the cladding region.
3. The apparatus of claim 2 wherein each of the plurality of gratings is formed in a portion of the cladding region above the core region.
4. The apparatus of claim 2 wherein each of the plurality of gratings comprises a plurality of diffraction regions in the cladding region, the plurality of diffraction regions being characterized by a refractive index different from a refractive index of the cladding region.
5. The apparatus of claim 4 wherein the cladding region comprises undoped silica and the diffraction regions comprise doped silica.
6. The apparatus of claim 2 wherein each of the plurality of gratings comprises a plurality of grating elements in a portion of the cladding region, a pitch of the plurality of grating elements is selected to provide maximum diffracted power at 90 degrees relative to an axis of the core region while avoiding back reflection.
7. The apparatus of claim 6 wherein an input waveguide is characterized by DWDM wavelengths in a band between a first wavelength λ 1 and a second wavelength λ 2 , and a pitch of the grating elements in each of the plurality of gratings is selected from outside the ranges between L 1 =m(λ 1 /n)/2 and L 2 =m(λ 2 /n)/2, where n is a refractive index of the waveguide and m is an integer.
8. The apparatus of claim 2 wherein the core region comprises doped silica and the cladding region comprises undoped silica.
9. The apparatus of claim 1 wherein the surface of the recessed region is a silicon surface.
10. The apparatus of claim 1 wherein the surface of the recessed region is a silica surface.
11. The apparatus of claim 1 wherein the plurality of lasers are bonded to the surface of the recessed region.
12. The apparatus of claim 1 wherein the plurality of lasers are made in InP.
13. The apparatus of claim 1 wherein the plurality of lasers are InP lasers.