Optical out-coupler unit for out-coupling light from a waveguide
An optical out-coupler unit for out-coupling light from a waveguide, comprising a substrate having a planar top surface, a waveguide arranged on the top surface of the substrate and having a facet, a reflective surface, wherein the reflective surface is arranged spaced apart from the facet and opposing the facet, wherein the reflective surface is inclined with respect to a normal to the top surface of the substrate by more than 45°. The optical out-coupler may be part of a photonic integrated chip (PIC).
1. An optical out-coupler unit for out-coupling light from a waveguide, comprising:
a substrate having a planar top surface;
a silicon rib waveguide arranged on the top surface of the substrate and having a facet, the rib waveguide comprising a base section and a ridge protruding from the base section;
a silicon support layer, a first portion of the support layer being spaced apart from the facet and opposing the facet, a second portion of the support layer adjacent to the first portion of the support layer having a side surface and a top surface, and the top surface of the second portion of the support layer and a top surface of the base section having a same height from the substrate;
a reflection layer defining a reflective surface, the reflection layer being on the support layer and extending from the side surface onto the top surface of the second portion of the support layer, the reflection layer and the support layer being different in material, and the reflection layer having a thickness of 250 nm or more;
a filler portion between the facet and the reflective surface, the filler portion being directly on the reflection layer and comprising a material having a first refractive index, and the reflection layer having a second refractive index less than the first refractive index such that a light beam coming from the waveguide and impinging on the reflection layer is reflected by total internal reflection;
a cladding on the base section and on a side of the ridge of the rib waveguide, the cladding and the reflection layer being the same in material, a thickness of the reflection layer on the top surface of the second portion of the support layer and a thickness of the cladding being the same, and a top surface of the ridge of the rib waveguide, a top surface of the cladding, a top surface of the filler portion, and a top surface of the reflection layer on the second portion of the support layer together forming a continuous flat surface; and
an anti-reflection coating comprising a first top layer arranged on a portion of the continuous flat surface formed by at least part of the top surface of the filler portion, at least part of the top surface of the ridge, at least part of the top surface of the cladding, and at least part of the top surface of the reflection layer, the first top layer having a refractive index less than a refractive index of the filler portion,
wherein the reflective surface is arranged spaced apart from the facet and opposing the facet,
wherein the reflective surface is inclined with respect to a normal to the top surface of the substrate by 46° to 51°,
wherein the reflective surface is aligned on the substrate, in a plan view parallel to the top surface of the substrate, at approximately 90° to a direction of light emitted from the facet.
2. The optical out-coupler unit of claim 1 , wherein the filler portion comprises amorphous silicon and/or the reflection layer comprises silicon oxide (SiO2).
3. The optical out-coupler unit of claim 1 , wherein the first top layer comprises silicon nitride (SiN).
4. The optical out-coupler unit of claim 1 , wherein the first top layer has a thickness of λ/4, λ being a wavelength in a wavelength range of electromagnetic radiation passing through the first top layer.
5. The optical out-coupler unit of claim 4 , wherein the thickness of the first top layer is between 100 nm and 300 nm.
6. The optical out-coupler unit of claim 1 , wherein the anti-reflection coating further comprises a second top layer arranged on the first top layer.
7. The optical out-coupler unit of claim 6 , wherein the second top layer comprises a material having a refractive index that is smaller than the refractive index of a material of the first top layer.
8. The optical out-coupler unit of claim 6 , wherein the first top layer and/or the second top layer have a thickness of λ/4, λ being a wavelength in a wavelength range of electromagnetic radiation passing through the first top layer and the second top layer.
9. The optical out-coupler unit of claim 6 , wherein the first top layer comprises silicon nitride (SiN) and has a thickness between 100 nm and 200 nm, and/or the second top layer comprises silicon oxide (SiO2) and has a thickness between 100 nm and 200 nm.
10. The optical out-coupler unit of claim 1 , wherein the waveguide includes a T-bar providing the facet.