Optical isolator based on volume Bragg gratings
View Patent ↗An optical isolator may include one or more rotated volume Bragg gratings (r-VBGs) within a volume of a material having an input face, where each of the r-VBGs reflects along a reflection path portions of input light propagating along an incidence vector through the input face that satisfies a Bragg condition for one or more selected wavelengths and has a polarization orthogonal to a diffraction plane formed by the associated grating vector and the incidence vector, and where each of the r-VBGs transmits remaining portions of the input light as transmitted light along a transmission path. The isolator may also include one or more polarization-controlling optics located along the transmission path configured to modify a polarization of return light propagating back along the transmission path towards the one or more r-VBGs, where the one or more r-VBGs reflect portions of the return light that satisfy the Bragg condition.
1 . An optical isolator comprising:
one or more rotated volume Bragg gratings (r-VBGs) within a volume of a material having an input face, wherein each of the r-VBGs is formed as planes of refractive index variation with periodicity along a grating vector at a non-zero angle relative to a normal vector of the input face, wherein each of the r-VBGs reflects along a common reflection path portions of input light propagating along an incidence vector through the input face that satisfies a Bragg condition for one or more selected wavelengths and has a polarization orthogonal to a diffraction plane formed by the associated grating vector and the incidence vector, wherein each of the r-VBGs transmits remaining portions of the input light as transmitted light along a transmission path; and
one or more polarization-controlling optics located along the common reflection path of the one or more r-VBGs configured to rotate a polarization of retroreflected light propagating back along the common reflection path towards the one or more r-VBGs by 90 degrees, wherein the one or more r-VBGs transmit the retroreflected light.
2 . The optical isolator of claim 1 , wherein the one or more r-VBGs comprise a single r-VBG.
3 . The optical isolator of claim 1 , wherein the one or more r-VBGs comprise:
a first r-VBG; and
a second r-VBG, wherein the grating vectors of the first and second r-VBGs are oriented along a common direction, wherein the refractive index variations of the first and second r-VBGs have different distributions along the respective grating vectors, wherein the one or more selected wavelengths reflected by the first r-VBG are different than the one or more selected wavelengths reflected by the second r-VBG.
4 . The optical isolator of claim 3 , wherein the refractive index variations of the first and second r-VBGs have uniform periods along the respective grating vectors.
5 . The optical isolator of claim 3 , wherein the refractive index variations of the first and second r-VBGs are chirped along the respective grating vectors.
6 . The optical isolator of claim 1 , wherein the one or more polarization-controlling optics comprise:
a quarter waveplate.
7 . The optical isolator of claim 1 , wherein the material comprises:
at least one of a glass, a crystal, a polymer, or a sol-gel.
8 . The optical isolator of claim 1 , wherein the r-VBG is apodized.