An experimental setup was built to detect orbital angular momentum (OAM) states of light beams. The helical beams with different OAM states were generated by using a spatial light modulator. A Mach-Zehnder (M-Z) interferometer was used to detect helical beams with odd or even OAM number. Sorting of coaxial helical beams was also experimentally realized.
An experimental setup was built to detect orbital angular momentum (OAM) states of light beams. The helical beams with different OAM states were generated by using a spatial light modulator. A Mach-Zehnder (M-Z) interferometer was used to detect helical beams with odd or even OAM number. Sorting of coaxial helical beams was also experimentally realized.
Orbital angular momentum (OAM) of a helical beam is of great interests in the high density optical communication due to its infinite number of eigen-states. In this paper, an experimental setup is realized to the information encoding and decoding on the OAM eigen-states. A hologram designed by the iterative method is used to generate the helical beams, and a Michelson interferometer with two Porro prisms is used for the superposition of two helical beams. The experimental results of the collinear superposition of helical beams and their OAM eigen-states detection are presented.
We report the experimental preparation of optical superpositions of high orbital angular momenta (OAM). Our method is based on the use of a spatial light modulator to modify the standard Laguerre-Gaussian beams to bear excessive phase helices. We demonstrate the surprising performance of a traditional Mach-Zehnder interferometer with one inserted Dove prism to identify these superposed twisted lights, where the high OAM numbers as well as their possible superpositions can be inferred directly from the interfered bright multiring lattices. The possibility of the present scheme working at the photon-count level is also shown using an electron multiplier CCD camera. Our results hold promise in high-dimensional quantum-information applications when high quanta are beneficial.
Orbital angular momentum (OAM) of light is a promising degree of freedom for quantum communication and quantum computation. However, efficient methods to transform and measure OAM modes are still not available readily. Here, we propose a method for full quantum state tomography for arbitrary OAM states of light. The key component in our scheme is the helicity sorter, a device that can sort OAM modes of a light beam based on their Helicity. We present two setups to implement the Helicity sorted, one requires O(N) number of optical elements for 2N OAM modes, and the other uses spatial light modulators and is independent of the number of OAM modes. Ours is the first method to provide the efficient and scalable full quantum state tomography of the OAM modes and can be extremely important for quantum communication and quantum computation.
Light carrying orbital angular momentum (OAM) has many applications ranging from optical manipulation, imaging and remote sensing, and optical communications, and can be used to perform fundamental studies in quantum mechanics and quantum information. Moreover, single photons with high-order OAM allow for increasing the amount of information carried per photon in quantum communication. This thesis describes the study of methods for the preparation and detection of OAM of light in high mode order by utilizing beam shaping techniques using spatial light modulators (SLMs). The quality of the generated high-order OAM mode is limited by optical aberrations which are induced by optical elements in realistic systems and propagation through realistic channels. In order to create and characterize the OAM modes with high quality, we investigate methods for aberration detection and correction using SLMs. These beam shaping techniques for the correction of optical aberrations allow us to generate and detect light carrying OAM with mode order ranging from l = 0 to l = 8 with good quality, and to generate high-quality superpositions of OAM modes with high mode order or in high dimensions. Furthermore, we observe low crosstalk and good levels of mode discrimination between different OAM modes of light. Our experimental setup can be applied in future studies to investigate and test different protocols in quantum information with high dimensional systems, such as high dimensional quantum state tomography.
Detection of photons in orbital angular momentum (OAM) superposition states is crucial to verification of OAM entanglement. In the past this has been realized by laterally shifting a hologram designed to remove a charge 1 phase singularity at its center. Such a laterally shifted hologram converts a beam with an off-center singularity (similar to that created by superposing an m = 0 beam and an m = 1 beam, where in is the OAM mode number) into a Gaussian beam, which is then filtered through a single mode fiber (SMF). However, it has been shown that a photon detected by this method is not a simple superposition of a photon in the m = 0 Gaussian mode and the m = 1 mode detected with an unshifted hologram, making it necessary to apply complicated analysis. One problem is that the radial distributions of the detected m = 0 and 1 components as determined by the SMF change as the hologram is shifted. Another, possibly more serious problem is the mixing of other OAM components. To overcome this problem we propose a new scheme for the detection of OAM superposition states consisting of a hologram and a path interferometer. The hologram is designed so that the output is equally distributed between the 0th and 1st order diffraction beams. The 0th order is the input beam itself, whose m = 0 Gaussian component is filtered through an SMF. In the 1st order beam the m = 1 component is converted to m = 0 and is filtered through a second SMF. The filtered beams now have the same spatial distribution, and can be superposed by a beam splitter. By inserting attenuators and phase modulators within the interferometer, superpositions with varying amplitude ratios and relative phases can be detected without shifting the hologram.
Introduction In this chapter, we will be concerned with entangled states of light. Historically, quantum states of light, i.e., photons, have played a dominant role in the experimental study of quantum entanglement. For instance, the first Bell tests and the first realizations of quantum teleportation were performed using two-dimensional polarization-entangled twophoton states [3]. From an experimental point of view these states are readily prepared and manipulated using conventional polarization optics. Recently, however, both theoretical and experimental efforts have shifted towards entanglement in more than two modes , which is often referred to as high-dimensional entanglement. This is much richer than two-dimensional entanglement, as is, for instance, reflected in stronger violations of various measures of nonlocality which reveal the complexity of high-dimensional Hilbert spaces [4–7]. Also, from an applications perspective, it promises a larger channel capacity [8, 9] and improved security for quantum communication [10, 11]. There are several ways to implement high-dimensional two-photon entanglement. One can exploit the temporal [12], frequency [13], or spatial [14–18] degrees of freedom of the optical field. A promising way to implement high-dimensional two-photon entanglement is to use the orbital-angular-momentum (OAM) degree of freedom of light. Light beams that carry OAM have a helical wavefront that spirals around the optical axis during propagation [19]. The winding number m , which characterizes the OAM eigenmodes, can adopt any integer value between −∞ and ∞; since all coaxial OAM modes are orthogonal they can thus span a very high-dimensional Hilbert space.