Author:       2014-10-11

OAM beams have been widely used in a variety of interesting applications, such as generation of Pancharatnam–Berry phase, optical microscopy, micromanipulation, quantum information, free-space and fiber optical communication. One key operation of an optical system that makes use of OAM beams is the capability of distinguishing different OAM states. There are several existing methods to detect optical vortices, such as interference with a plane wave, self-homodyne detection, Cartesian to log-polar coordinate transformation, diffraction patterns of various apertures or slits. For the first time, Sztul and Alfano revealed the interference characteristics of OAM beams with Young’s double-slit geometry and pointed out the twist fringes were closely related to the TC of  OAM beams. However, no detailed analysis of this measuring method was presented. Besides, the polarization of light was not distinguishable with the structure of double-slit interference.

Several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang, Prof. Jianji Dong, and Dr. Hailong Zhou, etc. have put forward a double-slit interference device based on two metal subwavelength slit arrays to measure the orbital angular momentum (OAM) and the polarization of beams simultaneously. The subwavelength slit serves as a localized spatial polarizer and each slit array can be regarded as a wide diffraction-slit. When an OAM beam normally incidents upon the two slit arrays, the interference fringes twist, and the displacement depends on the topological charge of OAM beams. A detailed theoretical analysis of this measurement model is presented. This model does not need additional reference light and is a linear model.

This work has been on-line published in Optics Letters on 23 May 2014. Relative work was partially supported by the National Basic Research Program of China (GrantNo. 2011CB301704), the Program for New Century Excellent Talents in Ministry ofEducation of China (Grand No. NCET-11-0168), a Foundation for Author of NationalExcellent Doctoral Dissertation of China (Grand No. 201139), and the National NaturalScience Foundation of China (Grand No. 11174096).