Encoder with an alignment target

A method of determining the position of a first element with respect to a second element, said method comprising:

• providing an alignment target on said first element and said second element, the alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element;
• moving at least one of said first element and said second element with respect to the other;
• illuminating said alignment target with at least one light beam having at least one polarization state;
• detecting the radiation from said alignment target after interacting with said periodic pattern on said first element and said periodic pattern on said second element, wherein detecting the radiation from said alignment target comprises detecting the intensities at least at two polarization states of the light from said alignment target;
• and
• using said detected radiation to determine the position of said first element with respect to said second element, wherein using said detected radiation comprises comparing said intensities of said two polarization states to determine the position of said first element with respect to said second element.

A method of determining the position of a first element with respect to a second element, said method comprising:

• providing an alignment target on said first element and said second element, the alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element;
• moving at least one of said first element and said second element with respect to the other;
• illuminating said alignment target with incident radiation;
• detecting the radiation from said alignment target after interacting with said periodic pattern on said first element and said periodic pattern on said second element;
• illuminating said alignment target a second time after said first element and said second element are moved by a known distance to a new position;
• detecting the radiation from said alignment target from the second illumination;
• and
• using the detected radiation from the new position and the detected radiation from the previous detection to determine the position of said first element with respect to said second element.

A method of determining the position of a first element with respect to a second element, said method comprising:

• providing an alignment target on said first element and said second element, the alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target has a first location with the periodic pattern on the first element offset from the periodic pattern on the second element by a first amount and having a second location with the periodic pattern on the first element offset from the periodic pattern on the second element by a second amount;
• moving at least one of said first element and said second element with respect to other;
• illuminating said first and second locations on said alignment target with incident radiation;
• detecting the radiation from said first and second locations after interacting with said alignment target;
• comparing the detected radiation from said first and second locations;
• detecting when the comparison of the detected radiation is at an approximate minimum;
• and
• counting the minima produced by said comparison to determine the position of said first element with respect to said second element.

A method of determining the position of a first element with respect to a second element, said method comprising:

• providing an alignment target on said first element and said second element, the alignment target has a first periodic pattern on said first element and a second periodic pattern on said second element;
• moving at least one of said first element and said second element with respect to other;
• illuminating said first periodic pattern and said second periodic pattern of said alignment target with light having at least two polarization states;
• detecting the intensities of the polarization states of said light after interacting with said alignment target;
• and
• comparing said intensities of said polarization states;
• detecting when the comparison of the intensities is at an approximate minimum;
• and
• counting the minima produced by said comparison to determine the position of said first element with respect to said second element.

An apparatus for determining the position of a first element with respect to a second element, said apparatus comprising:

• an alignment target on said first element and said second element, the alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target has a first location with the periodic pattern on the first element offset from the periodic pattern on the second element by a first amount and having a second location with the periodic pattern on the first element offset from the periodic pattern on the second element by a second amount;
• at least one light source for producing light to be incident on said first location and said second location of said alignment target;
• a first light detector for detecting light that interacts with said first location;
• a second light detector for detecting light that interacts with said second location;
• a comparator to calculate the difference between the detected light from said first and second locations, wherein said comparator produces an output signal that has a minimum when said periodic pattern on said first element and said periodic pattern on said second element are aligned;
• and
• a counter for counting the number of minima produced by said comparator to determine the position of said first element with respect to said second element.

An apparatus for determining the position of a first element with respect to a second element, said apparatus comprising:

• an alignment target on said first element and said second element, the alignment target has a first periodic pattern on said first element and a second periodic pattern on said second element;
• at least one light source for producing light to be incident on said alignment target, said light have a plurality of polarization states;
• a light detector for detecting the intensities of the polarization states after the light interacts with said alignment target;
• a comparator to calculate the difference between the intensities of said polarization states;
• and
• a counter for counting the number of minima produced by said comparator to determine the position of said first element with respect to said second element.