Polarization filter for autofocus pixel structures having symmetric apertures
Image sensors and devices for phase-detection auto focus processes are provided. A symmetric polarization filter includes a first polarizer defining a first plurality of apertures and a second polarizer adjacent with the first polarizer defining a second plurality of apertures. The first plurality of apertures can be mirror symmetrical with the second plurality of apertures about a lateral axis of the symmetric polarization filter between the first polarizer and the second polarizer. The lateral axis can be defined as an axis of symmetry of the symmetric polarization filter in plane with the first polarizer and the second polarizer.
1 . A symmetric polarization filter, comprising:
a first polarizer defining a first plurality of apertures; and
a second polarizer, adjacent with the first polarizer, defining a second plurality of apertures,
wherein the first plurality of apertures is mirror symmetrical with the second plurality of apertures about a lateral axis of the symmetric polarization filter between the first polarizer and the second polarizer, wherein the lateral axis is defined as an axis of symmetry of the symmetric polarization filter, wherein the axis of symmetry is:
in plane with the first polarizer and the second polarizer, and configured through a center point of the entire symmetric polarization filter,
wherein the center point is configured at an equal distance from opposite edges of the symmetric polarization filter,
and wherein the lateral axis is the axis of symmetry common to the mirror symmetry between the pluralities of apertures of the laterally adjacent polarizers across the axis of symmetry of the symmetric polarization filter for all polarizers of the filter.
2 . The symmetric polarization filter of claim 1 , wherein:
the first polarizer is characterized by a first extinction ratio;
the second polarizer is characterized by a second extinction ratio; and
the first extinction ratio and the second extinction ratio are substantially equal.
3 . The symmetric polarization filter of claim 1 , wherein:
the first polarizer is disposed overlying a first photodiode of an image sensor;
the second polarizer is disposed overlying a second photodiode of the image sensor;
the first plurality of apertures overly a first portion of the first photodiode;
the second plurality of apertures overly a second portion of the second photodiode; and
the first portion and the second portion are substantially equal in area.
4 . The symmetric polarization filter of claim 1 , wherein a first aperture of the first plurality of apertures overlies a first center of the first polarizer.
5 . The symmetric polarization filter of claim 1 , wherein two apertures of the first plurality of apertures are offset by a spacing and are substantially aligned along a nonzero polarization angle relative to a vertical axis of the symmetric polarization filter, the vertical axis being orthogonal to the lateral axis.
6 . The symmetric polarization filter of claim 5 , wherein the polarization angle is about 22.5 degrees relative to a positive clockwise rotation of the vertical axis.
7 . The symmetric polarization filter of claim 5 , further comprising:
a third polarizer, laterally adjacent with the first polarizer, and defining a third plurality of apertures offset by the spacing and substantially aligned at an angular orientation different from the polarization angle.
8 . The symmetric polarization filter of claim 7 , wherein the angular orientation comprises a rotated polarization angle of about 45 degrees or about-45 degrees relative to the polarization angle.
9 . The symmetric polarization filter of claim 7 , further comprising:
a fourth polarizer, diagonally adjacent to the first polarizer, vertically adjacent to the third polarizer, and laterally adjacent to the second polarizer, defining a fourth plurality of apertures separated by the spacing and mirror-symmetrical about the lateral axis with the third plurality of apertures of the third polarizer.
10 . An imaging system, comprising:
an image sensor including a plurality of photodiodes arranged as a photodiode array, the plurality of photodiodes disposed on a substrate to form a plurality of polarization pixels, including:
a symmetric polarization filter, comprising:
a first polarizer defining a first plurality of apertures; and
a second polarizer, adjacent with the first polarizer, defining a second plurality of apertures,
wherein the first plurality of apertures is mirror symmetrical with the second plurality of apertures about a lateral axis of the symmetric polarization filter between the first polarizer and the second polarizer, wherein the lateral axis is defined as an axis of symmetry of the symmetric polarization filter, wherein the axis of symmetry is:
in plane with the first polarizer and the second polarizer, and configured through a center point of the entire symmetric polarization filter,
wherein the center point is configured at an equal distance from opposite edges of the symmetric polarization filter,
and wherein the lateral axis is the axis of symmetry common to the mirror symmetry between the pluralities of apertures of the laterally adjacent polarizers across the axis of symmetry of the symmetric polarization filter for all polarizers of the filter.
11 . The imaging system of claim 10 , wherein:
the first polarizer is characterized by a first extinction ratio;
the second polarizer is characterized by a second extinction ratio; and
the first extinction ratio and the second extinction ratio are substantially equal in area.
12 . The imaging system of claim 10 , wherein:
the first polarizer is disposed overlying a first photodiode of the plurality of photodiodes;
the second polarizer is disposed overlying a second photodiode of the plurality of photodiodes;
the first plurality of apertures overly a first portion of the first photodiode;
the second plurality of apertures overly a second portion of the second photodiode; and
the first portion and the second portion are substantially equal.
13 . The imaging system of claim 10 , wherein a first aperture of the first plurality of apertures overlies a first center of the first polarizer and wherein a second aperture of the second plurality of apertures overlies a second center of the second polarizer.
14 . The imaging system of claim 10 , further comprising:
a controller coupled with the image sensor and logic that when executed by the controller causes the imaging system to perform operations including:
reading out an electrical signal generated in response to incident light, the electrical signal generated by the plurality of photodiodes.
15 . The imaging system of claim 14 , further comprising additional logic that when executed by the controller causes the imaging system to perform further operations including:
determining a focus state for the imaging system based at least in part on the electrical signal as part of phase-detection auto focus (PDAF).
16 . The imaging system of claim 10 , wherein two apertures of the first plurality of apertures are offset by a spacing and are substantially aligned along a nonzero polarization angle relative to a vertical axis of the symmetric polarization filter orthogonal to the lateral axis.
17 . The imaging system of claim 16 , wherein the polarization angle is about 22.5 degrees relative to a positive clockwise rotation of the vertical axis.
18 . The imaging system of claim 16 , further comprising:
a third polarizer, laterally adjacent with the first polarizer, and defining a third plurality of apertures offset by the spacing and substantially aligned at an angular orientation different from the polarization angle.
19 . The imaging system of claim 18 , wherein the angular orientation comprises a rotated polarization angle of about 45 degrees or about-45 degrees relative to the polarization angle.
20 . The imaging system of claim 18 , further comprising:
a fourth polarizer diagonally adjacent to the first polarizer, vertically adjacent to the third polarizer, and laterally adjacent to the second polarizer, defining a fourth plurality of apertures separated by the spacing and mirror-symmetrical about the lateral axis with the third plurality of apertures of the third polarizer.
21 . An image sensor, comprising a plurality of image pixels, each image pixel comprising a plurality of subpixels and one or more groups of polarization pixels, wherein:
the plurality of subpixels comprising at least one blue subpixel, at least one green subpixel, and at least one red subpixel,
each subpixel of the plurality of subpixels being laterally or diagonally adjacent to one group of the one or more groups of polarization pixels, and
each group of the one or more groups of polarization pixels comprises:
a first polarization pixel and a second polarization pixel, and
a symmetric polarization filter, comprising:
a first polarizer defining a first plurality of apertures, the first polarizer being disposed over the first polarization pixel; and
a second polarizer, laterally adjacent with the first polarizer, defining a second plurality of apertures, the second polarizer being disposed over the second polarization pixel,
wherein the first plurality of apertures is mirror symmetrical with the second plurality of apertures about a lateral axis of the symmetric polarization filter between the first polarizer and the second polarizer, wherein the lateral axis is defined as an axis of symmetry of the symmetric polarization filter, wherein the axis of symmetry is in plane with the first polarizer and the second polarizer and is configured through a center point of the entire symmetric polarization filter, wherein the center point is configured at an equal distance from opposite edges of the symmetric polarization filter,
and wherein the lateral axis is the axis of symmetry common to the mirror symmetry between the pluralities of apertures of the laterally adjacent polarizers across the axis of symmetry of the symmetric polarization filter for all polarizers of the filter.