Generation Of Full-Vector Beams With A Wollaston Prism

Polarization, amplitude and phase are important characteristics of light. Re-cently the studies of polarization have attracted much more interests. Vector beams are beams whose polarization states change with the space location. Com-pared with traditional beams whose polarization states keep identical, vector beams have lots of unique properties. These properties make vector beams useful in surface plasmon excitation, focol field regulation and optical trapping etc.Poincare sphere is a very powerful tool for describing the polarization char-acteristics. Any point on Poincare sphere corresponds to one polarization state. If you want to get a totol control of polarization, it is required that the vector beams you generate can cover the whole Poincare sphere. To simutanously control the amplitude, phase and polarization states to generate’full-vector beams’, four degrees of freedom are needed.There are lots of ways to generate vector beams. Our lab proposed a combi-nation method that was based on the 4-f system and spatial light modulator. By developing the modulation manner of the trasmission function from one dimension to two dimensions, we are able to get a complete control of amlitude, phase and polarization. This method needs loading an obliquity factor on the transmission function. Hence a Ronchi grating is required to combine the beams.As a diffracting optical element. Ronchi grating have many orders besides the ±1st order that we need, leading to a large energy loss. The Wollaston prism is a polarized beam splitter based on briefingence. If used in an inverse way, it can combine beams. The combination process does not have other orders that are not used, so it is more efficient for the beam combinationWhen the two planes of incidence are parallel to each other, it is easy to imagine the combination process. In the 4-f system we use to generate full-vector beams, we choose two beams that lacate the x and y axis respectively. In this condition the planes of incidence are not parellel. This paper studies the split angle of the Wollaston prism when the incident angle is small. The characteristics of the Wollaston prism when rotating along the axis are also discussed. With these analysises, the combining way of beams that are not parallel is determined. The experiment results are given to show the ability of the Wollaston prism to generate full-vector beams. In the 4f system, the energy efficiency is increased from 3% to 7% after replacing the Ronchi grating with the Wollaston prism.