Purity of vector vortex beams through a birefringent amplifier

Physical Review Applied

Sroor, H., Nyameko, L., Naidoo, D., Litvin, I., and Forbes, A.

VVAmp Creating high-quality vector vortex (VV) beams is possible with a myriad of techniques at low power, and while a few studies have produced such beams at high power, none have considered the impact of amplification on the vector purity. Here we employ tools to study the amplification of VV beams and, in particular, the purity of such modes. We outline a versatile toolbox for such investigations and demonstrate its use in the general case of VV beams through a birefringent gain medium. Intriguingly, we show that it is possible to enhance the purity… Download


Entanglement beating in free space through spin-orbit coupling

Light: Science & Application

Otte, E., Rosales-Guzman, C., Ndagano, B., Denz, C., and Forbes, A.

entbeat It is well known that the entanglement of a quantum state is invariant under localunitary transformations. This rule dictates, for example, that the entanglement of internal degrees of freedom of a photon remain invariant during free-space propagation. Here, we outline a scenario in which this paradigm does not hold. Using local Bell states engineered from classical vector vortex beams with non-separable degrees of freedom, so-called classically entangled states, we demonstrate that the entanglement evolves during propagation, oscillating between maximally entangled (purely vector) and product states (purely scalar). We outline… Download


Turbulence and the Hong-Ou-Mandel effect

Physical Review A

Prabhakar, S., Mabena, C., Konrad, K., and Roux, F.

detVVB The effect of a decoherence channel, such as a turbulent atmosphere, on the second order quantum interference in the Hong-Ou-Mandel (HOM) effect is investigated. The investigation includes both theoretical analyses and an experimental implementation of the process. In our experiment, entangled input states are prepared with spontaneous parametric down-conversion. The atmospheric turbulence is modelled as a single-phase screen and simulated with a spatial light modulator according to the theory of Kolmogorov. We find both theoretically and experimentally… Download


Structured Laguerre-Gaussian beams for mitigation of spherical aberration in tightly focused regimes

Journal of Optics

Haddadi, S., Bouzid, O., Fromager, M., Hasnaoui, A., Harfouche, A., Cagniot, E., Forbes, A., and Ait-Ameur, K.

detVVB Many laser applications utilise a focused laser beam having a single-lobed intensity profile in the focal plane, ideally with the highest possible on-axis intensity. Conventionally, this is achieved with the lowest-order Laguerre–Gaussian mode (LG00), the Gaussian beam, in a tight focusing configuration. However, tight focusing often involves significant spherical aberration due to the high numerical aperture of the systems involved, thus degrading the focal quality. Here, we demonstrate that a high-order radial LGp0 mode can be tailored to meet and in some instancesexceed the performance of the Gaussian. We achieve… Download


Creation and detection of vector vortex modes for classical and quantum communication

Journal of Lightwave Technology

Ndagano, B., Nape, I.,Cox M., Rosales-Guzmán C. and Forbes, A.

detVVB Vector vortex beams are structured states of light that are nonseparable in their polarisation and spatial mode, they are eigenmodes of free-space and many fiber systems, and have the capacity to be used as information carriers for both classical and quantum communication. Here, we outline recent progress in our understanding of these modes, from their creation to their characterization and detection. We then use these tools to study their propagation behavior in free-space and optical fiber and show that modal cross-talk results in a decay of vector states into separable scalar modes, with a concomitant loss of information. We present… Download


A hybrid quantum eraser scheme for characterization of free-space and fiber communication channels

Optics Communications

Nape, I., Kyeremah, C., Vallés, A., Rosales-Guzmán, C., Buah-Bassuah, P., and Forbes, A.

quanterase We demonstrate a simple projective measurement based on the quantum eraser concept that can be used to characterize the disturbances of any communication channel. Quantum erasers are commonly implemented as spatially separated path interferometric schemes. Here we exploit the advantages of redefining the which-path information in terms of spatial modes, replacing physical paths with abstract paths of orbital angular momentum (OAM). Remarkably, vector modes (natural modes of free-space and fiber) have a non-separable feature of spin–orbit coupled states, equivalent to the description of two independently marked paths. We explore… Download

Ndagano, B., Nape, I., Perez-Garcia, B., Scholes, S., Hernandez-Aranda, R.I., Konrad, T., Lavery, M.P. and Forbes, A. (2017). A deterministic detector for vector vortex states. Scientific reports, 7(1), 13882. Download

Bouzid O., Haddadi, S., Fromager, M., Cagniot, E., Ferria, K., Forber, A. and Ait-Ameur, K. (2017). Focusing anomalies with binary diffractive optical elements, Applied Optics 56, 9735.

Mabena, C. and Roux, F. (2017). High-dimensional quantum channel estimation using classical light, Phys. Rev. A. 96, 053860. Download

Ndagano, B., Mphuthi, N., Milione, G. and Forbes, A. (2017). Comparing mode-crosstalk and mode-dependent loss of laterally displaced orbital angular momentum and Hermite–Gaussian modes for free-space optical communication. Optics letters, 42(20), 4175-4178. Download

Rosales-Guzmán, C., Bhebhe, N. and Forbes, A. (2017). Simultaneous generation of multiple vector beams on a single SLM. Optics express, 25(21), 25697-25706. Download

Zhang, Y., Agnew, M., Roger, T., Roux, F.S., Konrad, T., Faccio, D., Leach, J. and Forbes, A. (2017). Simultaneous entanglement swapping of multiple orbital angular momentum states of light. Nature Communications, 8(1), 632. Download

Vetter, C., Dudley, A., Szameit, A. and Forbes, A. (2017). Real and virtual propagation dynamics of angular accelerating white light beams. Optics express, 25(17), 20530-20540. Download

Rosales-Guzmán, C. and Forbes, A. (2017). How to shape light with spatial light modulators. SPIE.SPOTLIGHT Download

Forbes, A. and Botha, L., (2017). Laser Isotope Separation. Laser Beam Shaping Applications (2nd ed.), Ch. 7, eds. F.M. Dickey and T. Lizotte. CRC Taylor & Francis Group (New York) Download

Rosales-Guzmán, C., Bhebhe, N., Mahonisi, N. and Forbes, A. (2017). Multiplexing 200 modes on a single digital hologram. Journal of Optics, 19 113501 Download

Nape, I., Kyeremah, C., Vallés, A., Rosales-Guzmán, C., Buah-Bassuah, P.K. and Forbes, A., (2017). Hybrid quantum erasure scheme for channel disturbance characterization. Optics Communications 408, 53-57 Download

Roux F.S. (2017). Biphoton states in correlated turbulence, Phys. Rev. A.Download

Nape, I., Ndagano, B. and Forbes, A., (2017). Erasing the orbital angular momentum information of a photon. Physical Review A, 95 (5), 053859 Download

Ismail, Y., Joshi, S., Forbes, A. and Petruccione, F., (2017). Instrumentation limitation on a polarization-based entangled photon source. JOSA B, 34(6), 1084-1089 Download

McLaren, M. and Forbes, A., (2017). Digital spiral-slit for bi-photon imaging. Journal of Optics, 19(4), 044006 Download

Webster, J., Rosales-Guzmán, C. and Forbes, A., (2017). Radially dependent angular acceleration of twisted light. Optics letters, 42(4), 675-678. Download

Ndagano, B., Perez-Garcia, B., Roux, F.S., McLaren, M., Rosales-Guzman, C., Zhang, Y., Mouane, O., Hernandez-Aranda, R.I., Konrad, T. and Forbes, A., (2017). Characterizing quantum channels with non-separable states of classical light. Nature Physics, 13(4), 397 Download

Forbes, A., (2017). Controlling light’s helicity at the source: orbital angular momentum states from lasers. Phil. Trans. R. Soc. A, 375(2087), 20150436 Download

Sephton, B., Dudley, A. and Forbes, A. (2017). Quantum Walks. Quest, 13(4), 15-18. Download

Forbes, A. (2017). Blurring the classical quantum divide. Optics and photonics news, 17(12), 36. Download

Rubinsztein-Dunlop, H., Forbes, A., Berry, M., Dennis, M., Andrews, D., Mansuripur, M., Denz, C., Alpmann, C., Banzer, P., Bauer, T. and Karimi, E., (2016). Roadmap on structured light. Journal of Optics, 19(1), 013001. Download

Roux, F. S. (2016). Topological charge conservation in stochastic optical fields. Journal of Optics, 18(5), 054005. download

Roux, F. S. (2016). Non-Markovian evolution of photonic quantum states in atmospheric turbulence. Journal of Optics, 18(5), 055203. download

Zhang, Y., Prabhakar, S., Rosales-Guzmán, C., Roux, F. S., Karimi, E., & Forbes, A. (2016). Hong-Ou-Mandel interference of entangled Hermite-Gauss modes. Physical Review A, 94(3), 033855. download

Zhang, Y., Prabhakar, S., Roux, F. S., Forbes, A., & Konrad, T. (2016). Experimentally observed decay of high-dimensional entanglement through turbulence. Physical Review A, 94(3), 032310. download

Sephton, B., Dudley, A., & Forbes, A. (2016). Revealing the radial modes in vortex beams. Applied optics, 55(28), 7830-7835. download

Cox, M. A., Rosales-Guzmán, C., Lavery, M. P., Versfeld, D. J., & Forbes, A. (2016). On the resilience of scalar and vector vortex modes in turbulence. Optics express, 24(16), 18105-18113. download

Perez-Garcia, B., Yepiz, A., Hernandez-Aranda, R. I., Forbes, A., & Swartzlander, G. A. (2016). Digital generation of partially coherent vortex beams. Optics Letters, 41(15), 3471-3474. download

Ndagano, B., Sroor, H., McLaren, M., Rosales-Guzmán, C., & Forbes, A. (2016). Beam quality measure for vector beams. Optics Letters, 41(15), 3407-3410. download

Trichili, A., Salem, A. B., Dudley, A., Zghal, M., & Forbes, A. (2016). Encoding information using Laguerre Gaussian modes over free space turbulence media. Optics Letters, 41(13), 3086-3089. download

Gossman, D., Perez-Garcia, B., Hernandez-Aranda, R. I., & Forbes, A. (2016). Optical interference with digital holograms. American Journal of Physics, 84(7), 508-516. download

Trichili, A., Rosales-Guzmán, C., Dudley, A., Ndagano, B., Salem, A. B., Zghal, M., & Forbes, A. (2016). Optical communication beyond orbital angular momentum. Scientific reports, 6. download

Forbes, A., Dudley, A., & McLaren, M. (2016). Creation and detection of optical modes with spatial light modulators. Advances in Optics and Photonics, 8(2), 200-227. download

Perez-Garcia, B., McLaren, M., Goyal, S. K., Hernandez-Aranda, R. I., Forbes, A., & Konrad, T. (2016). Quantum computation with classical light: Implementation of the Deutsch–Jozsa algorithm. Physics Letters A, 380(22), 1925-1931. download

Naidoo, D., Roux, F. S., Dudley, A., Litvin, I., Piccirillo, B., Marrucci, L., & Forbes, A. (2016). Controlled generation of higher-order Poincaré sphere beams from a laser. Nature Photonics, 10(5), 327-332. download

Goyal, S. K., Roux, F. S., Konrad, T., & Forbes, A. (2016). The effect of turbulence on entanglement-based free-space quantum key distribution with photonic orbital angular momentum. Journal of Optics, 18(6), 064002. download

Naidoo, D., Harfouche, A., Fromager, M., Ait-Ameur, K., & Forbes, A. (2016). Emission of a propagation invariant flat-top beam from a microchip laser. Journal of Luminescence, 170, 750-754. download

Zhang, Y., Roux, F. S., Konrad, T., Agnew, M., Leach, J., & Forbes, A. (2016). Engineering two-photon high-dimensional states through quantum interference. Science advances, 2(2), e1501165. download

Brüning, R., Ndagano, B., McLaren, M., Schröter, S., Kobelke, J., Duparré, M., & Forbes, A. (2016). Data transmission with twisted light through a free-space to fiber optical communication link. Journal of Optics, 18(3), 03LT01. download

Dudley, A., Majola, N., Chetty, N., & Forbes, A. (2016). Implementing digital holograms to create and measure complex-plane optical fields. American Journal of Physics, 84(2), 106-112. download


Naidoo, D., Fromager, M., Ait-Ameur, K., & Forbes, A. (2015). Radially polarized cylindrical vector beams from a monolithic microchip laser. Optical Engineering, 54(11), 111304-111304. download

Brüning, R., Flamm, D., Ngcobo, S. S., Forbes, A., & Duparré, M. (2015, February). Rapid measurement of the fiber’s transmission matrix. In SPIE OPTO (pp. 93890N-93890N). International Society for Optics and Photonics. download

Goyal, S. K., Roux, F. S., Forbes, A., & Konrad, T. (2015). Implementation of multidimensional quantum walks using linear optics and classical light.Physical Review A, 92(4), 040302. download

Brüning, R., Zhang, Y., McLaren, M., Duparré, M., & Forbes, A. (2015). Overlap relation between free-space Laguerre Gaussian modes and step-index fiber modes. JOSA A, 32(9), 1678-1682. download

McLaren, M., Konrad, T., & Forbes, A. (2015). Measuring the nonseparability of vector vortex beams. Physical Review A, 92(2), 023833. download

Litvin, I. A., Mhlanga, T., & Forbes, A. (2015). Digital generation of shape-invariant Bessel-like beams. Optics express, 23(6), 7312-7319. download

Schulze, C., Roux, F. S., Dudley, A., Rop, R., Duparré, M., & Forbes, A. (2015). Accelerated rotation with orbital angular momentum modes. Physical Review A, 91(4), 043821. download

Ndagano, B., Bruning, R., McLaren, M., Duparre, M., & Forbes, A. (2015) Fiber propagation of vector modes. Optics Express, 23(13), 17330-17336. download

Perez-Garcia, B., Francis, J., McLaren, M., Hernandez-Aranda, R. I., Forbes, A., & Konrad, T. (2015). Quantum computation with classical light: The Deutsch Algorithm. Physics Letters A, 379(28), 1675-1680. download

Litvin, I. A., Mhlanga, T., & Forbes, A. (2015). Digital generation of shape-invariant Bessel-like beams. Optics express, 23(6), 7312-7319. download

McLaren, M. G., Roux, F. S., & Forbes, A. (2015). Realising high-dimensional quantum entanglement with orbital angular momentum. South African Journal of Science, 111(1-2), 01-09. download

Burger, L., Litvin, I., Ngcobo, S., & Forbes, A. (2015). Implementation of a spatial light modulator for intracavity beam shaping. Journal of Optics, 17(1), 015604. download

Milione, G., Dudley, A., Nguyen, T. A., Chakraborty, O., Karimi, E., Forbes, A., & Alfano, R. R. (2015). Measuring the self-healing of the spatially inhomogeneous states of polarization of vector Bessel beams. Journal of Optics, 17(3), 035617. download


Aspden, R.S. et al., 2014. Experimental demonstration of Klyshko’s advanced-wave picture using a coincidence-count based, camera-enabled imaging system. Journal of Modern Optics, 61(March), pp.1–5. doi: 10.1080/09500340.2014.899645 download

Ismail, Y. et al., 2014. Characterization of a Polarisation Based Entangled Photon Source. The African Review of Physics, 9, pp.217–

Litvin, I. a et al., 2014. Doughnut laser beam as an incoherent superposition of two petal beams. Optics letters, 39(3), pp.704–7. doi: 10.1364/OL.39.000704. download

Schulze, C. et al., 2014. Measurement of the orbital angular momentum density of Bessel beams by projection into a Laguerre-Gaussian basis. Applied optics, 53(August), pp.5924 – 5933. doi: 10.1364/AO.53.005924. download

Spangenberg, D.-M. et al., 2014. White light wavefront control with a spatial light modulator. Optics Express, 22(11), p.13870. doi: 10.1364/

Trichili, A., Mhlanga, T. & Ismail, Y., 2014. Detection of Bessel beams with digital axicons. Optics Express, 22(14), pp.17553 – 17560. doi: 10.1364/


Boubaha, B. et al., 2013. Spatial properties of coaxial superposition of two coherent Gaussian beams. Applied optics, 52(23), pp.5766–72. doi: 10.1364/AO.52.005766. download

Chaibi, A., Mafusire, C. & Forbes, A., 2013. Propagation of orbital angular momentum carrying beams through a perturbing medium. Journal of Optics, 15(10), p.105706. doi: 10.1088/2040-8978/15/10/105706. download

Giovannini, D. et al., 2013. Characterization of high-dimensional entangled systems via mutually unbiased measurements. Physical Review Letters, 110(14), pp.1–5. doi: 10.1103/

Goyal, S.K. et al., 2013. Implementing quantum walks using orbital angular momentum of classical light. Physical Review Letters, 110(26), pp.1–5. doi: 10.1103/PhysRevLett.110.263602. download

Litvin, I. a, Burger, L. & Forbes, A., 2013. Angular self-reconstruction of petal-like beams. Optics letters, 38(17), pp.3363–5. doi: 10.1364/OL.38.003363. download

Schulze, C. et al., 2013a. Measurement of the orbital angular momentum density of light by modal decomposition. New Journal of Physics, 15(July), p.073025. doi: 10.1088/1367-2630/15/7/073025 download

Schulze, C. et al., 2013b. Reconstruction of laser beam wavefronts based on mode analysis. Applied optics, 52(21), pp.5312–7. doi: 10.1364/


Dudley, A. & Forbes, A., 2012. From stationary annular rings to rotating Bessel beams. Journal of the Optical Society of America A, 29(4), p.567. doi: 10.1364/

Flamm, D. et al., 2012. Mode analysis with a spatial light modulator as a correlation filter. Optics Letters, 37(13), p.2478. doi: 10.1364/OL.37.002478. download

Ismail, Y. et al., 2012. Shape invariant higher-order Bessel-like beams carrying orbital angular momentum. Journal of Optics, 14(8), p.085703. doi: 10.1088/2040-8978/14/8/085703. download

Litvin, I. a. et al., 2012. Azimuthal decomposition with digital holograms. Optics Express, 20(10), p.10996. doi: 10.1364/OE.20.010996. download

Naidoo, D. et al., 2012. Observing mode propagation inside a laser cavity. New Journal of Physics, 14(May), p.053021. doi: 10.1088/1367-2630/14/5/053021. download

Schulze, C., Flamm, D., et al., 2012. Beam-quality measurements using a spatial light modulator. Optics Letters, 37(22), pp.4687–9. doi: 10.1364/OL.37.002478.Decomp_Schulze2012 (1)

Schulze, C., Ngcobo, S., et al., 2012. Modal decomposition without a priori scale information. Optics Express, 20(25), pp.27866–73. doi: 10.1364/

Schulze, C., Naidoo, D., et al., 2012. Wavefront reconstruction by modal decomposition. Optics Express, 20(18), p.19714. doi: 10.1364/OE.20.019714.Decomposition_Schulze2012


Agnew, M. et al., 2011. Tomography of the quantum state of photons entangled in high dimensions. Physical Review A – Atomic, Molecular, and Optical Physics, 84(6), p.062101. doi: 10.1103/PhysRevA.84.062101.

Godin, T. et al., 2011. Transverse correlation vanishing due to phase aberrations. Optics Communications, 284(19), pp.4601–4606. doi: 10.1016/j.optcom.2011.05.062.

Lavery, M.P.J. et al., 2011. Robust interferometer for the routing of light beams carrying orbital angular momentum. New Journal of Physics, 13(September), p.093014. doi: 10.1088/1367-2630/13/9/093014.

Litvin, I. a., Dudley, A. & Forbes, A., 2011. Poynting vector and orbital angular momentum density of superpositions of Bessel beams. Optics Express, 19(18), p.16760. doi: 10.1364/OE.19.016760.

McLaren, M., Sidderas-Haddad, E. & Forbes, A., 2011. Accurate measurement of microscopic forces and torques using optical tweezers. South African Journal of Science, 107(9-10), pp.1–8. doi: 10.4102/sajs.v107i9/10.579.

Naidoo, D. et al., 2011. Transverse mode selection in a monolithic microchip laser. Optics Communications, 284(23), pp.5475–5479. doi: 10.1016/j.optcom.2011.08.017.

2010 & older

Bernhardi, E.H. et al., 2008. Estimation of thermal fracture limits in quasi-continuous-wave end-pumped lasers through a time-dependent analytical model. Optics Express, 16(15), pp.11115–11123. doi: 10.1364/OE.16.011115.

Burger, L. & Forbes, A., 2008. Kaleidoscope modes in large aperture Porro prism resonators. Optics Express, 16(17), pp.12707–12714. doi: 10.1364/OE.16.012707.

Litvin, I. A. & Forbes, A., 2009. Gaussian mode selection with intracavity diffractive optics. Optics Letters, 34(19), pp.2991–2993. doi: 10.1364/OL.34.002991.

Litvin, I. A. & Forbes, A., 2008. Bessel-Gauss resonator with internal amplitude filter. Optics Communications, 281(9), pp.2385–2392. doi: 10.1016/j.optcom.2007.12.052.

Litvin, I.A. & Forbes, A., 2009. Intra – cavity flat – top beam generation. Optics Express, 17(18), pp.15891–15903. doi: 10.1364/OE.17.015891.

Mafusire, C. et al., 2008. Optical aberrations in a spinning pipe gas lens. Optics Express, 16(13), pp.9850–9856. doi: 10.1364/OE.16.009850.

Vasilyeu, R. et al., 2009. Generating superpositions of higher-order Bessel beams. Optics Express, 17(26), pp.23389–23395. doi: 10.1364/OE.17.023389.