Africa has a long history in optics, but decades of turmoil have seen optical science in Africa advance only slowly, punching far below its weight. But a younger generation of scientists hold promise for the brighter future, addressing continental issues with photonics. In this Feature Issue on Optics in Africa we capture some of the exciting optical research from across the continent in 51 research reports, covering both fundamental and applied topics. The issue is supplemented by invited review articles that offer authoritative perspectives on the historical development of key research fields, from early advances in lasers to present-day progress in photonic materials. To encourage the exploration of new research directions, the issue has several tutorial articles that lower the entry barrier for emerging researchers, while highlighting the scope of research on the continent and its international context.
© 2020 Optical Society of America
Africa is often credited as being the birthplace of humankind, and thus it is likely that they were the first to gaze at the stars. Africa was also home to early civilizations who made inroads into what is today known as optics: the first reference to optical magnification as well as evidence for lens design appear in ancient Egyptian writings, while the Egyptian-Roman, Hero of Alexandria, made important contributions to the early theories of reflection as well as among the first experiments in optics. Unfortunately, the turmoil of colonialization and decades of misspent opportunity during fledgling democracy has seen African optical science dither: today Africa produces only a tiny fraction of the world’s research outputs, dominated by North African countries and South Africa. Yet pockets of excellence remain, and there is optimism for a brighter future, turning continental challenges into opportunities: a green-fields approach to a modern internet infrastructure devoid of legacy issues, optical solutions for large scale agriculture, harnessing the sun with optical materials for clean energy, and optics for vision to address eye care, to name but a few, all fueled by emerging researchers in a continent with the largest youth numbers on the planet.
In this Feature Issue on Optics in Africa we have assembled reviews, tutorials, and research articles from across the African continent, with contributions from South Africa, Botswana, Egypt, Tunisia, Cameroon, Algeria, Zimbabwe, Morocco, Ethiopia, Kenya, and Ghana. The issue includes five authoritative reviews, putting the developments of these fields in Africa into perspective. These include the developments and present state of the art in luminescence studies in Africa, capturing the work of many groups with an interest in photonic materials , an overview of plasmonic modeling techniques , the importance of optical communication over free space  and optical fiber  in the African context, and Africa’s history in laser development, a first-hand account from one of its pioneers . The three tutorials, always useful to young emerging researchers and students alike, cover topical fields such as quantum cryptography with spatial modes of light , how to unravel light by modal decomposition , and how to use modern tools such as digital micro-mirror devices (DMDs) for fast and cheap solutions to Stokes polarimetry , all three falling in the topical field of structured light and its applications.
The bulk of the Feature Issue covers the recent research by groups across the continent in just over fifty research articles. In physical optics and diffraction we see advances in our understanding of the classes of non-diffracting light [9–11], how to arbitrarily structure light through lossless beam shaping , the generation of Airy beams using acousto-optical tools , and temporal pulse shaping by birefringence . Optical fiber and free-space communications is a topic highly relevant to Africa given the importance of bridging the digital divide. In this issue, we find exciting reports on stable time-frequency standards over fiber [15,16], the value-add of photonics to 5G implementations [17,18], amplification in multi-core fiber for space division multiplexing over long distance , visible light communication systems , and the effects of turbulence on modulation schemes for effective free-space communication . Beyond communication, the research reported here in fiber optics on the continent includes theoretical studies such as chirp dispersion management  and fiber lasers . The laser theme covers not only fiber lasers  but also amplification in the mid-infrared , as well as applications of high-power lasers in cutting and welding .
Spectroscopy has always been a core research activity in Africa, with this Feature Issue capturing the diversity of studies [26–32], including pump-probe studies  and nonlinear microscopy  with ultrafast pulses, to more conventional techniques such as FTIR but applied to African heritage, studying ancient bone artifacts .
By far the largest experimental optical community in Africa is that of photonic materials. In this Issue we get a glimpse into recent progress, highlighting development in techniques such as Brillouin scattering [33,34] applied to various materials, and the use of femtosecond lasers to excite nonlinear responses from materials [35–37]. A large drive is in nano-photonic materials [38–41], particularly for light emitting and/or light controlling systems, as also covered in our invited review .
Because of the lack of experimental facilities at many African institutes, it is not surprising that theoretical optical research has flourished. In this Feature Issue we have reports on theoretical nonlinear optics [42–47], quantum optics [42,48–50], and topics as diverse as rogue waves in waveguide arrays , optomechanics , metamaterials , and fundamental light–matter interactions .
At the other end of the spectrum, applications of photonics still lag behind the fundamental science, but here we see initial reports on exciting developments in sensors for measuring small phase variations , photonic crystals for gas sensing , “intelligent” imaging by incorporating machine learning to monitor health , and fiber optical sensors for detecting water impurities  and in geological mapping .
The timing of this Feature Issue coincides with the worldwide movement of #blacklivesmatter, raising awareness of diversity and mutual respect. The optical community too has a role to play in this arena. In this Feature Issue, we hear from mostly young African scientists, who show us that optical research in Africa is alive and well, with a healthy diversity in topic as well as across pure and applied research. But challenges remain: how to increase critical mass in research on the continent, and to accelerate the conversion of good science into technologies that change African lives for the better? To this end, advocacy for, and promotion of, African photonics will be of paramount importance, an area in which the OSA could play an important role through initiatives along the vein of this Feature Issue.
1. S. G. Menon and H. C. Swart, “Luminescence in Africa: a brief overview [Invited],” J. Opt. Soc. Am. B 37, A18–A35 (2020). [CrossRef]
2. A. Said, K. S. R. Atia, and S. S. A. Obayya, “On modeling of plasmonic devices: overview,” J. Opt. Soc. Am. B 37, A163–A174 (2020). [CrossRef]
3. A. Trichili, M. A. Cox, B. S. Ooi, and M.-S. Alouini, “Roadmap to free space optics,” J. Opt. Soc. Am. B 37, A184–A201 (2020). [CrossRef]
4. T. C. Kofané, C. B. Tabi, A. B. Moubissi, and C. Tchawoua, “From African ‘tam-tam’ to nonlinear optics [Invited],” J. Opt. Soc. Am. B 37, A346–A355 (2020). [CrossRef]
5. H. von Bergmann, “Laser research on the African continent,” J. Opt. Soc. Am. B 37, A83–A95 (2020). [CrossRef]
6. E. Otte, I. Nape, C. Rosales-Guzmán, C. Denz, A. Forbes, and B. Ndagano, “High-dimensional cryptography with spatial modes of light: tutorial,” J. Opt. Soc. Am. B 37, A309–A323 (2020). [CrossRef]
7. J. Pinnell, I. Nape, B. Sephton, M. A. Cox, V. Rodríguez-Fajardo, and A. Forbes, “Modal analysis of structured light with spatial light modulators: a practical tutorial,” J. Opt. Soc. Am. A 37, C146–C160 (2020). [CrossRef]
8. K. Singh, N. Tabebordbar, A. Forbes, and A. Dudley, “Digital Stokes polarimetry and its application to structured light: tutorial,” J. Opt. Soc. Am. A 37, C33–C44 (2020). [CrossRef]
9. A. Bencheikh and A. Forbes, “The non-diffracting nature of truncated Hermite–Gaussian beams,” J. Opt. Soc. Am. A 37, C1–C6 (2020). [CrossRef]
10. A. Bencheikh, S. Chabou, O. C. Boumeddine, H. Bekkis, A. Benstiti, L. Beddiaf, and W. Moussaoui, “Cosine beam: diffraction-free propagation and self-healing,” J. Opt. Soc. Am. A 37, C7–C14 (2020). [CrossRef]
11. A. Bencheikh, S. Chabou, and O. C. Boumeddine, “Far-field modeling of obstructed Laguerre–Gauss beams,” J. Opt. Soc. Am. A 37, C20–C26 (2020). [CrossRef]
12. S. Scholes, V. Rodríguez-Fajardo, and A. Forbes, “Lossless reshaping of structured light,” J. Opt. Soc. Am. A 37, C80–C85 (2020). [CrossRef]
13. A. Benstiti, K. Ferria, and A. Bencheikh, “Generation of a variety of Airy beams using a dynamic diffractive optical phase element,” J. Opt Soc. Am B 37, A45–A53 (2020). [CrossRef]
14. A. Halassi, Y. Driouche, R. Hamdi, and B.-E. Benkelfat, “Generalized temporal synthesis method for a birefringent laser pulse shaper,” J. Opt. Soc. Am. A 37, C15–C19 (2020). [CrossRef]
15. S. Wassin, K. Leburu, G. Isoe, and T. Gibbon, “Development of ultrastable fiber-optic time and frequency reference networks in Africa,” J. Opt. Soc. Am. A 37, C57–C66 (2020). [CrossRef]
16. D. M. Osiemo, D. W. Waswa, K. M. Muguro, G. M. Isoe, T. B. Gibbon, and A. W. R. Leitch, “Frequency stability characterization: DFB laser and Raman pump performance on a distributed clock signal over 24.69 km fiber,” J. Opt. Soc. Am. A 37, C95–C102 (2020). [CrossRef]
17. K. Nfanyana, S. Wassin, R. Karembera, J. Jena, and T. Gibbon, “All-photonic 20-MHz clock for latency monitoring in a 5G network at 10 Gbps over optical fiber,” J. Opt. Soc. Am. B 37, A202–A206 (2020). [CrossRef]
18. R. Karembera, S. Wassin, G. Isoe, K. Nfanyana, and T. Gibbon, “All-optical flexible 5G signal generation and transmission for spectrum resource optimization,” J. Opt. Soc. Am. B 37, A324–A330 (2020). [CrossRef]
19. A. Nassiri, A. Boulezhar, and H. I. Saba, “Numerical model of an Er3+/Yb3+ co-doped seven-core fiber amplifier for a space division multiplexing system,” J. Opt. Soc. Am. A 37, C50–C56 (2020). [CrossRef]
20. E. Shawky, M. El-Shimy, A. Mokhtar, E. A. El-Badawy, and H. M. H. Shalaby, “Improving the visible light communication localization system using Kalman filtering with averaging,” J. Opt. Soc. Am. B 37, A130–A138 (2020). [CrossRef]
21. S. S. Abdelhak, A. E. Morra, F. E. A. El-Samie, and A. E. Elfiqi, “Performance analysis of different intensity modulation techniques over atmospheric turbulent free-space optical channels,” J. Opt. Soc. Am. A 37, C138–C145 (2020). [CrossRef]
22. C. Heuteu, L. Mandeng Mandeng, and C. Tchawoua, “Chirp-dispersion management inducing regeneration of truncated Airy pulses in fiber optics links,” J. Opt. Soc. Am. B 37, A121–A129 (2020). [CrossRef]
23. D. J. F. Jubgang, A. M. Dikandé, and A. Sunda-Meya, “Continuous-wave stability and multipulse structures in a universal complex Ginzburg–Landau model for passively mode-locked lasers with a saturable absorber,” J. Opt. Soc. Am. B 37, A175–A183 (2020). [CrossRef]
24. W. Koen, C. Jacobs, M. J. D. Esser, and H. J. Strauss, “Optically pumped HBr master oscillator power amplifier operating in the mid-infrared region,” J. Opt. Soc. Am. B 37, A154–A162 (2020). [CrossRef]
25. T. Tamsaout, E. H. Amara, and A. Bouabdallah, “Numerical approach for hydrodynamic behavior in the kerf with a quasi-complete model of the laser cutting process,” J. Opt. Soc. Am. A 37, C86–C94 (2020). [CrossRef]
26. L. C. Ugwuoke, T. Mančal, and T. P. J. Krüger, “Optical properties of a nanoegg–nanorod heterodimer: a quasi-static analysis,” J. Opt. Soc. Am. B 37, A293–A303 (2020). [CrossRef]
27. R. Viljoen, P. Neethling, D. Spangenberg, A. Heidt, H.-M. Frey, T. Feurer, and E. Rohwer, “Implementation of temporal ptychography algorithm, i2PIE, for improved single-beam coherent anti-Stokes Raman scattering measurements,” J. Opt. Soc. Am. B 37, A259–A265 (2020). [CrossRef]
28. P. O.-W. Adueming, M. J. Eghan, B. Anderson, S. Kyei, J. Opoku-Ansah, C. L. Yeboah Amuah, C. Darko Takyi, and P. K. Buah-Bassuah, “Laser-induced autofluorescence assisted by multivariate techniques discriminates a cataractous lens from healthy lens tissues of Sprague–Dawley rats,” J. Opt. Soc. Am. A 37, C27–C32 (2020). [CrossRef]
29. C. L. Yeboah Amuah, M. J. Eghan, B. Anderson, P. O.-W. Adueming, J. Opoku-Ansah, and P. K. Buah-Bassuah, “Laser-induced fluorescence combined with multivariate techniques identifies the geographical origin of antimalarial herbal plants,” J. Opt. Soc. Am. A 37, C103–C110 (2020). [CrossRef]
30. A. A. Adeniyi, P.-F. X. von Stein, G. W. Bosman, C. M. Steenkamp, T. Chiweshe, K. G. von Eschwege, and J. Conradie, “Probing ultrafast reaction mechanisms of photo-excited dithizone through transient absorption spectroscopy and computational CASSCF studies,” J. Opt. Soc. Am. B 37, A356–A366 (2020). [CrossRef]
31. G. Dwapanyin, D. Spangenberg, A. Heidt, T. Feurer, G. Bosman, P. Neethling, and E. Rohwer, “Generalized spectral phase-only time-domain ptychographic phase reconstruction applied in nonlinear microscopy,” J. Opt. Soc. Am. B 37, A285–A292 (2020). [CrossRef]
32. A. El-Hussein, I. Yousef, and M. A. Kasem, “Exploiting FTIR microspectroscopy and chemometric analysis in the discrimination between Egyptian ancient bones: a case study,” J. Opt. Soc. Am. B 37, A110–A120 (2020). [CrossRef]
33. J. Kuria, D. Wamwangi, D. Comins, A. Every, and D. Billing, “Surface Brillouin scattering study of tantalum nitride (TaN) thin films,” J. Opt. Soc. Am. A 37, C125–C131 (2020). [CrossRef]
34. K. Singh, D. Wamwangi, B. Mathe, D. Billing, and M. Madhuku, “Minimum lattice thermal conductivity of In3SbTe2 by surface Brillouin scattering,” J. Opt. Soc. Am. A 37, C132–C137 (2020). [CrossRef]
35. A. Shehata, W. Z. Tawfik, and T. Mohamed, “Cobalt enhanced nonlinear optical properties and optical limiting of zinc oxide irradiated by femtosecond laser pulses,” J. Opt. Soc. Am. B 37, A1–A8 (2020). [CrossRef]
36. M. Ali, A. Shehata, M. Ashour, W. Z. Tawfik, R. Schuch, and T. Mohamed, “Measuring the nonlinear optical properties of indium tin oxide thin film using femtosecond laser pulses,” J. Opt. Soc. Am. B 37, A139–A146 (2020). [CrossRef]
37. W. I. Ndebeka, P. H. Neethling, E. G. Rohwer, C. M. Steenkamp, and H. Stafast, “Counter-intuitive strength of electric field induced second harmonic (EFISH) signals at the rear side of thin silicon membranes,” J. Opt. Soc. Am. B 37, A228–A236 (2020). [CrossRef]
38. M. K. Musembi, F. B. Dejene, I. Ahemen, and K. G. Tshabalala, “Influence of Ho3+ doping on the structural and optical characteristics of ZnO–ZrO2 nanocomposites synthesized by the solution combustion method,” J. Opt. Soc. Am. B 37, A266–A276 (2020). [CrossRef]
39. M. Maaza and C. N. R. Rao, “Anderson localization of IR light in 1D nanosystems,” J. Opt. Soc. Am. A 37, C111–C117 (2020). [CrossRef]
40. H. E. A. Mohamed, K. Hkiri, M. Khenfouch, S. Dhlamini, M. Henini, and M. Maaza, “Optical properties of biosynthesized nanoscaled Eu2O3 for red luminescence applications,” J. Opt. Soc. Am. A 37, C73–C79 (2020). [CrossRef]
41. N. Numan, B. Mabakachaba, A. Simo, Z. Nuru, and M. Maaza, “VO2-based active tunable emittance thermochromic flexible coatings,” J. Opt. Soc. Am. A 37, C45–C49 (2020). [CrossRef]
42. H. Jabri and H. Eleuch, “Nonlinear dynamics in a dipolariton cavity with a squeezed vacuum,” J. Opt. Soc. Am. B 37, A9–A17 (2020). [CrossRef]
43. S. Subramaniyan, O. T. Lekeufack, R. Radha, and T. C. Kofane, “Interplay of three-body and higher-order interactions on the modulational instability of Bose–Einstein condensate,” J. Opt. Soc. Am. B 37, A54–A61 (2020). [CrossRef]
44. J. S. Deumi Kamaha, J. H. Talla Mbé, and P. Woafo, “Routes to chaos and characterization of limit-cycle oscillations in wideband time-delayed optoelectronic oscillators with nonlinear filters,” J. Opt. Soc. Am. B 37, A75–A82 (2020). [CrossRef]
45. J. H. Talla Mbé and Y. K. Chembo, “Coexistence of bright and dark cavity solitons in microresonators with zero, normal, and anomalous group-velocity dispersion: a switching wave approach,” J. Opt. Soc. Am. B 37, A69–A74 (2020). [CrossRef]
46. K. K. Ndebele, C. B. Tabi, and T. C. Kofané, “Modulational instability in nonlinear doped optical fiber induced by the cubic–quintic–septic complex Ginzburg–Landau equation with higher-order dispersions,” J. Opt. Soc. Am. B 37, A214–A227 (2020). [CrossRef]
47. D. K. Choge, D. W. Waswa, K. M. Muguro, and W.-G. Liang, “Design of simultaneous multicolor coherent light generation in a single MgO:PPLN bulk crystal,” J. Opt. Soc. Am. B 37, A304–A308 (2020). [CrossRef]
48. D. A. M. Abo-Kahla, “Long-lived quantum coherence and nonlinear properties of a two-dimensional semiconductor quantum well,” J. Opt. Soc. Am. B 37, A96–A109 (2020). [CrossRef]
49. O. El Bir and M. El Baz, “Quantum correlations under the effect of a thermal environment in a triangular optomechanical cavity,” J. Opt. Soc. Am. B 37, A237–A244 (2020). [CrossRef]
50. T. G. Tesfahannes, “Generation of the bipartite entanglement and correlations in an optomechanical array,” J. Opt. Soc. Am. B 37, A245–A252 (2020). [CrossRef]
51. C. D. Pelwan, A. Quandt, and R. Warmbier, “Onset times of long-lived rogue waves in an optical waveguide array,” J. Opt. Soc. Am. A 37, C67–C72 (2020). [CrossRef]
52. P. Djorwe, J. Y. Effa, and S. G. Nana Engo, “Multistability, staircases, and optical high-order sideband combs in optomechanics,” J. Opt. Soc. Am. B 37, A36–A44 (2020). [CrossRef]
53. M. A. Njifon, C. B. Tabi, and T. C. Kofané, “Few-cycle optical pulses in negative index materials with dispersive permittivity and permeability,” J. Opt. Soc. Am B 37, A331–A345 (2020). [CrossRef]
54. A. Quandt and R. Warmbier, “Theory and numerical aspects of fundamental light–matter interactions,” J. Opt. Soc. Am. B 37, A207–A213 (2020). [CrossRef]
55. H. H. Wahba, W. A. Ramadan, and A. S. El-Tawargy, “Employment of Fizeau fringe disintegration to magnify small phase variations,” J. Opt. Soc. Am. B 37, A62–A68 (2020). [CrossRef]
56. L. Kassa-Baghdouche, “High-sensitivity spectroscopic gas sensor using optimized H1 photonic crystal microcavities,” J. Opt. Soc. Am. B 37, A277–A284 (2020). [CrossRef]
57. A. I. Siam, N. A. El-Bahnasawy, G. M. El Banby, A. A. Elazm, and F. E. A. El-Samie, “Efficient video-based breathing pattern and respiration rate monitoring for remote health monitoring,” J. Opt. Soc. Am. A 37, C118–C124 (2020). [CrossRef]
58. K. Azil, K. Ferria, and S. Bouzid, “Cladless optical fiber sensor based on evanescent wave absorption for monitoring methylene blue induced water pollution,” J. Opt. Soc. Am. B 37, A253–A258 (2020). [CrossRef]
59. J. Jena, S. Wassin, L. Bezuidenhout, M. Doucouré, and T. Gibbon, “Polarization-based optical fiber acoustic sensor for geological applications,” J Opt. Soc. Am. B 37, A147–A153 (2020). [CrossRef]