Low-loss waveguide with undercut
An apparatus comprising a substrate; a waveguide above the substrate; and an undercut into the substrate, the undercut beneath at least a portion of the waveguide, wherein a magnitude of a maximum length of the undercut is lower than a magnitude of a maximum depth of the undercut.
1 . An apparatus comprising:
a substrate;
a waveguide above the substrate;
an undercut into the substrate, the undercut beneath at least a portion of the waveguide, wherein a magnitude of a maximum length of the undercut is higher than a magnitude of a maximum depth of the undercut, wherein the magnitude of the maximum depth of the undercut is less than 5 microns; and
an oxide layer on top of the substrate, wherein the oxide layer surrounds the waveguide.
2 . The apparatus of claim 1 , wherein the waveguide comprises silicon nitride (Si 3 N 4 ).
3 . The apparatus of claim 1 , the waveguide comprising a core material and a cladding material, wherein the cladding material is an electrically insulating material that surrounds at least a portion of the core material.
4 . The apparatus of claim 1 , further comprising a second waveguide to transfer light to the waveguide, wherein the second waveguide is on a slab comprising silicon, the slab formed above the substrate, the second waveguide and the slab surrounded by the oxide layer.
5 . The apparatus of claim 1 , wherein the undercut comprises a material other than air, the material having a lower refractive index than the substrate.
6 . The apparatus of claim 1 , further comprising a plurality of metal-oxide semiconductor field-effect transistors formed over the oxide layer.
7 . The apparatus of claim 1 , wherein the oxide layer seals off an air gap of the undercut.
8 . The apparatus of claim 1 , wherein the magnitude of the maximum length of the undercut is more than five times the magnitude of the maximum depth of the undercut.
9 . The apparatus of claim 1 , further comprising a second waveguide above the substrate, wherein the oxide layer is in contact with the second waveguide.
10 . The apparatus of claim 9 , wherein the second waveguide has a higher effective index than the waveguide.
11 . The apparatus of claim 1 , wherein the waveguide has a lower effective index than a refractive index of the substrate.
12 . The apparatus of claim 1 , wherein the oxide layer on top of the substrate and surrounding the waveguide comprises silicon dioxide.
13 . A system comprising:
a semiconductor die comprising:
a substrate comprising silicon;
a waveguide above the substrate;
an undercut into the substrate, the undercut beneath at least a portion of the waveguide, wherein a magnitude of a maximum length of the undercut is higher than a magnitude of a maximum depth of the undercut;
an oxide layer comprising silicon dioxide, the oxide layer on top of the substrate, wherein the oxide layer surrounds the waveguide; and
a second waveguide above the substrate, wherein the oxide layer is in contact with the second waveguide.
14 . The system of claim 13 , wherein the semiconductor die comprises an optical transceiver comprising an optical transmitter comprising a plurality of integrated lasers and an optical receiver comprising a demultiplexer comprising the waveguide.
15 . The system of claim 13 , wherein the system further comprises a processor.
16 . The system of claim 15 , wherein the system further comprises a second semiconductor die coupled to the semiconductor die, the second semiconductor die comprising the processor.
17 . The system of claim 15 , further comprising a battery communicatively coupled to the processor, a display communicatively coupled to the processor, or a network interface communicatively coupled to the processor.
18 . A method comprising:
forming a waveguide above a substrate comprising silicon;
forming an undercut into the substrate beneath at least a portion of the waveguide, wherein a magnitude of a maximum length of the undercut is higher than a magnitude of a maximum depth of the undercut;
forming an oxide layer comprising silicon dioxide on top of the substrate, wherein the oxide layer surrounds the waveguide; and
forming a second waveguide above the substrate, wherein the oxide layer is in contact with the second waveguide.
19 . The method of claim 18 , wherein forming the undercut comprises applying an anisotropic etch to the substrate.