Method of fabricating anisotropic optical interference filter
In a method of manufacturing a one-dimensionally varying optical filter, a substrate is coated to form a stack of layers of two or more different types. The coating may, for example, employ sputtering, electron-beam evaporation, or thermal evaporation. During the coating, the time-averaged deposition rate is varied along an optical gradient direction by generating reciprocation between a shadow mask and the substrate in a reciprocation direction that is transverse to the optical gradient direction. In some approaches, the shadow mask is periodic with a mask period defined along the direction of reciprocation, and the generated reciprocation has a stroke equal to or greater than the mask period along the direction of reciprocation. The substrate and the shadow mask may also be rotated together as a unit during the coating. Also disclosed are one-dimensionally varying optical filters, such as linear variable filters, made by such methods.
1. A shadow mask comprising:
an elongated body extending in a longitudinal direction, wherein the longitudinal direction is mutually parallel with a direction of reciprocation of the shadow mask during use in a variable filter deposition system; and
a plurality of openings disposed in the elongated body along the direction of reciprocation, wherein each opening of the plurality of openings is a rectangular opening having a width oriented in the direction of reciprocation and a length oriented in a direction transverse to the direction of reciprocation with the length oriented at an angle of 90° relative to the direction of reciprocation, wherein each rectangular opening has a first end and a second end that together define the length, and wherein each rectangular opening extends lengthwise in a direction perpendicular to the direction of reciprocation;
wherein the plurality of openings are positioned in the elongated body such that the shadow mask is periodic with mask periods defined along the direction of reciprocation, wherein each mask period of the mask periods consists of a pattern of at least three rectangular openings of successively longer length, wherein the at least three rectangular openings of successively longer length are positioned in the elongated body such that:
each first end of the at least three rectangular openings in each mask period of the mask periods is arranged in one common plane that extends parallel with the direction of reciprocation, and each second end of the at least three rectangular openings is disposed in a different plane from other second ends in the same mask period, wherein each different plane extends parallel to the direction of reciprocation, and
wherein the shadow mask is configured to form a one-dimensionally varying optical filter.
2. The shadow mask of claim 1 , wherein the width of each rectangular opening is of equal size.
3. The shadow mask of claim 1 , wherein each mask period of the mask periods consists of a pattern of four rectangular openings of successively longer length.
4. The shadow mask of claim 1 , wherein the rectangular opening having the longest length extends lengthwise over a majority of the elongated body in a direction transverse to the longitudinal direction of the elongated body.
5. The shadow mask of claim 1 , wherein each mask period of the mask periods that consists of the pattern of at least three rectangular openings of successively longer length is configured to form the one-dimensionally varying optical filter having a thickness-versus-position profile that is either non-increasing or non-decreasing over each mask period of the mask periods such that the thickness-versus-position profile is monotonic.
6. A shadow mask comprising:
an elongated body extending in a longitudinal direction, wherein the longitudinal direction is mutually parallel with a direction of reciprocation of the shadow mask during use in a variable filter deposition system; and
a plurality of openings disposed in the elongated body along the direction of reciprocation, wherein each opening of the plurality of openings has a width oriented in the direction of reciprocation and a length oriented in a direction transverse to the direction of reciprocation with the length oriented at an angle of 90° relative to the direction of reciprocation, wherein each opening has a first end and a second end that together define the length, wherein the length comprises a first length and a second length, the first length extending between the first end of the opening and the second length, the second length extending between the first length and the second end of the opening, and wherein the opening extends lengthwise in a direction perpendicular to the direction of reciprocation,
wherein the shadow mask is periodic with mask periods defined along the direction of reciprocation,
wherein each mask period of the mask periods comprises a pattern of one or more openings, wherein;
the width of each opening varies non-linearly over the first length of the opening such that the width gets smaller over the first length moving from the first end towards the second length in the direction transverse to the direction of reciprocation, each opening having a non-linear right hand edge over the first length, and
the width of each opening is constant over the second length moving from the first length towards the second end in the direction transverse to the direction of reciprocation, and
wherein the shadow mask is configured to form a one-dimensionally varying optical filter.
7. The shadow mask of claim 6 , wherein the non-linear variation in the width of each opening over the first length of the opening is configured to form the one-dimensionally varying optical filter having a thickness-versus-position profile that is monotonic.
8. The shadow mask of claim 6 , wherein the first length is greater than the second length.
9. The shadow mask of claim 6 , wherein the non-linear variation in the width of each opening over the first length of the opening is configured to form the one-dimensionally varying optical filter having a thickness-versus-position profile that is non-linear.