Method to determine the topological charge of an optical beam
An apparatus for determining a topological charge of one of more optical beams. For single beams, a trapezoidal optical element having a front face and an opposing rear face that is not parallel to the front face is oriented so that the optical beam is reflected in a direction other than along the optical path. The reflection of the optical beam by the trapezoidal optical element produces an interference pattern that can be captured by an optical imager and that can be decoded to determine the topological charge of the optical beam. For a plurality of superpositioned beams, an air spaced trapezoidal optical element may oriented to reflect the plurality of beams onto an optical imager to capture the interference pattern. The interference pattern may be interpreted to identify the topological charge of each of the plurality of optical beams.
1. An apparatus for determining a topological charge of an optical beam, comprising:
a pair of confocal lenses configured to planarize the wavefront of an optical beam extending along a first optical path;
a trapezoidal optical element aligned with the pair of confocal lenses and oriented to define a non-perpendicular angle of incidence for the optical beam so that the optical beam is reflected along a second optical patch that is different than the first optical path, wherein the trapezoidal optical element extends along an axis and has a right trapezoid cross-section along the axis such that trapezoidal optical element includes a front face formed by the right angles of the right trapezoid cross-section and an opposing rear face that is not parallel to the front face to define a non-perpendicular angle of incidence for the optical beam and wherein the reflection of the optical beam by the trapezoidal optical element produces an interference pattern that corresponds to the topological charge of the optical beam; and
an optical imager positioned along the second optical path to capture a digital image of the optical beam after reflection by the trapezoidal prism.
2. The apparatus of claim 1 , wherein the interference pattern includes a plurality of forked structures having at least two conjoined handles if the topological charge of the optical beam is positive.
3. The apparatus of claim 2 , wherein the interference pattern includes a plurality of forked structures having at least two conjoined tines if the topological charge of the optical beam is negative.
4. The apparatus of claim 3 , further comprising a device coupled to the optical imager and programmed to identify the topological charge of the optical beam based on the interference pattern.
5. An apparatus for decoding modal superpositions of optical beams, comprising:
a series of lenses configured to planarize the wavefront of a plurality of light beams;
a beam splitter forming a second optical path and a third optical path that is different from the second optical path;
a first optical imager aligned along the second optical path to capture digital images of the plurality of light beams;
a trapezoidal optical element positioned along the third optical path and oriented to define a non-perpendicular angle of incidence for the plurality of optical beams so that the plurality of optical beams are reflected in a direction other than along the third optical path, wherein the trapezoidal optical element is an air spaced trapezoidal optical element and wherein the reflection of the plurality of optical beams by the trapezoidal optical element produces an interference pattern; and
a second optical imager aligned with the trapezoidal optical element to capture optical images of the plurality of optical beams after reflection by the trapezoidal optical element.
6. The apparatus of claim 5 , wherein the interference pattern corresponds to the topological charge of each of the plurality of optical beams.
7. The apparatus of claim 5 , further comprising a device coupled to the first optical imager and the second optical imager that is programmed to identify the topological charge of the optical beam based on the interference pattern.