On-chip orbital angular momentum modes generator ... - OSA Publishing

Vol. 25, No. 15 | 24 Jul 2017 | OPTICS EXPRESS 18492

On-chip orbital angular momentum modes generator and (de)multiplexer based on trench silicon waveguides SHUANG ZHENG, AND JIAN WANG* Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074, Hubei, China *[email protected]

Abstract: Based on an integrated silicon platform, we present an ultracompact structure to generate optical orbital angular momentum (OAM) modes, where only a waveguide with a specially designed trench is involved. Single-trench waveguide can support two orthogonal LP-like modes whose optical axes are rotated by around 45° with respect to the horizontal and vertical directions. By optimizing the structure parameters, OAM modes with topological charges of + 1 and −1 can be selectively generated by combining two orthogonal LP-like modes with different propagation constants. We study the structure parameters for both x- and y-polarizations over a wide wavelength range from 1.45 µm to 1.65 µm. The average mode purities are close to 90% for x- and y-polarizations. Moreover, we design an on-chip OAM modes (de)multiplexer (OAM0, OAM ± 1) for x-polarization based on trench silicon waveguides. It is shown that the mode extinction ratio can achieve approximately 20 dB from 1.52 µm to 1.58 µm. © 2017 Optical Society of America OCIS codes: (130.3120) Integrated optics devices; (230.7370) Waveguides; (050.4865) Optical vortices.

References and links 1. 2. 3.

4. 5.

6.

7. 8. 9. 10. 11.

12. 13. 14.

L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, and J. P. Woerdman, “Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes,” Phys. Rev. A 45(11), 8185–8189 (1992). M. J. Padgett, “Orbital angular momentum 25 years on,” Opt. Express 25(10), 11265–11274 (2017). J. Wang, J.-Y. Yang, I. M. Fazal, N. Ahmed, Y. Yan, H. Huang, Y. Ren, Y. Yue, S. Dolinar, M. Tur, and A. E. Willner, “Terabit free-space data transmission employing orbital angular momentum multiplexing,” Nat. Photonics 6(7), 488–496 (2012). N. Bozinovic, Y. Yue, Y. Ren, M. Tur, P. Kristensen, H. Huang, A. E. Willner, and S. Ramachandran, “Terabitscale orbital angular momentum mode division multiplexing in fibers,” Science 340(6140), 1545–1548 (2013). A. Wang, L. Zhu, S. Chen, C. Du, Q. Mo, and J. Wang, “Characterization of LDPC-coded orbital angular momentum modes transmission and multiplexing over a 50-km fiber,” Opt. Express 24(11), 11716–11726 (2016). A. E. Willner, H. Huang, Y. Yan, Y. Ren, N. Ahmed, G. Xie, C. Bao, L. Li, Y. Cao, Z. Zhao, J. Wang, M. P. J. Lavery, M. Tur, S. Ramachandran, A. F. Molisch, N. Ashrafi, and S. Ashrafi, “Optical communications using orbital angular momentum beams,” Adv. Opt. Photonics 7(1), 66–106 (2015). J. Wang, “Advances in communications using optical vortices,” Photonics Res. 4(5), B14–B28 (2016). J. Wang, “Data information transfer using complex optical fields: a review and perspective,” Chin. Opt. Lett. 15(3), 030005 (2017). M. Gecevičius, R. Drevinskas, M. Beresna, and P. G. Kazansky, “Single beam optical vortex tweezers with tunable orbital angular momentum,” Appl. Phys. Lett. 104(23), 231110 (2014). M. Chen, M. Mazilu, Y. Arita, E. M. Wright, and K. Dholakia, “Dynamics of microparticles trapped in a perfect vortex beam,” Opt. Lett. 38(22), 4919–4922 (2013). D. S. Ding, W. Zhang, Z. Y. Zhou, S. Shi, G. Y. Xiang, X. S. Wang, Y. K. Jiang, B. S. Shi, and G. C. Guo, “Quantum storage of orbital angular momentum entanglement in an atomic ensemble,” Phys. Rev. Lett. 114(5), 050502 (2015). M. W. Beijersbergen, L. Allen, H. Vanderveen, and J. P. Woerdman, “Astigmatic laser mode converters and transfer of orbital angular momentum,” Opt. Commun. 96(1), 123–132 (1993). M. W. Beijersbergen, R. P. C. Coerwinkel, M. Kristensen, and J. P. Woerdman, “Helical-wave front laser beams produced with a spiral phase plate,” Opt. Commun. 112(5), 321–327 (1994). S. Slussarenko, A. Murauski, T. Du, V. Chigrinov, L. Marrucci, and E. Santamato, “Tunable liquid crystal qplates with arbitrary topological charge,” Opt. Express 19(5), 4085–4090 (2011).

#300621 Journal © 2017

https://doi.org/10.1364/OE.25.018492 Received 22 Jun 2017; accepted 16 Jul 2017; published 21 Jul 2017


15. A. Forbes, A. Dudley, and M. McLaren, “Creation and detection of optical modes with spatial light modulators,” Adv. Opt. Photonics 8(2), 200–227 (2016). 16. N. Yu, P. Genevet, M. A. Kats, F. Aieta, J. P. Tetienne, F. Capasso, and Z. Gaburro, “Light propagation with phase discontinuities: generalized laws of reflection and refraction,” Science 334(6054), 333–337 (2011). 17. P. Genevet, N. Yu, F. Aieta, J. Lin, M. Kats, R. Blanchard, M. Scully, Z. Gaburro, and F. Capasso, “Ultra-thin plasmonic optical vortex plate based on phase discontinuities,” Appl. Phys. Lett. 100(1), 013101 (2012). 18. L. Huang, X. Chen, H. Mühlenbernd, G. Li, B. Bai, Q. Tan, G. Jin, T. Zentgraf, and S. Zhang, “Dispersionless phase discontinuities for controlling light propagation,” Nano Lett. 12(11), 5750–5755 (2012). 19. X. Zhang, Z. Tian, W. Yue, J. Gu, S. Zhang, J. Han, and W. Zhang, “Broadband terahertz wave deflection based on C-shape complex metamaterials with phase discontinuities,” Adv. Mater. 25(33), 4567–4572 (2013). 20. Z. Zhao, J. Wang, S. Li, and A. E. Willner, “Metamaterials-based broadband generation of orbital angular momentum carrying vector beams,” Opt. Lett. 38(6), 932–934 (2013). 21. Y. Yang, W. Wang, P. Moitra, I. I. Kravchenko, D. P. Briggs, and J. Valentine, “Dielectric meta-reflectarray for broadband linear polarization conversion and optical vortex generation,” Nano Lett. 14(3), 1394–1399 (2014). 22. B. Guan, R. P. Scott, C. Qin, N. K. Fontaine, T. Su, C. Ferrari, M. Cappuzzo, F. Klemens, B. Keller, M. Earnshaw, and S. J. Yoo, “Free-space coherent optical communication with orbital angular, momentum multiplexing/demultiplexing using a hybrid 3D photonic integrated circuit,” Opt. Express 22(1), 145–156 (2014). 23. E. Karimi, S. A. Schulz, I. De Leon, H. Qassim, J. Upham, and R. W. Boyd, “Generating optical orbital angular momentum at visible wavelengths using a plasmonic metasurface,” Light Sci. Appl. 3(5), e167 (2014). 24. J. Du and J. Wang, “Design of on-chip N-fold orbital angular momentum multicasting using V-shaped antenna array,” Sci. Rep. 5(1), 9662 (2015). 25. X. Cai, J. Wang, M. J. Strain, B. Johnson-Morris, J. Zhu, M. Sorel, J. L. O’Brien, M. G. Thompson, and S. Yu, “Integrated compact optical vortex beam emitters,” Science 338(6105), 363–366 (2012). 26. D. Zhang, X. Feng, K. Cui, F. Liu, and Y. Huang, “Generating in-plane optical orbital angular momentum beams with silicon waveguides,” IEEE Photonics J. 5(2), 2201206 (2013). 27. Z. Ma, H. Chen, K. Wu, Y. Zhang, Y. Chen, and S. Yu, “Self-imaging of orbital angular momentum (OAM) modes in rectangular multimode interference waveguides,” Opt. Express 23(4), 5014–5026 (2015). 28. Z. Wang and D. Dai, “Ultrasmall Si-nanowire-based polarization rotator,” J. Opt. Soc. Am. B 25(5), 747–753 (2008). 29. D. M. H. Leung, B. M. A. Rahman, and K. T. V. Grattan, “Numerical analysis of asymmetric silicon nanowire waveguide as compact polarization rotator,” IEEE Photonics J. 3(3), 381–389 (2011). 30. A. V. Velasco, M. L. Calvo, P. Cheben, A. Ortega-Monux, J. H. Schmid, C. A. Ramos, I. M. Fernandez, J. Lapointe, M. Vachon, S. Janz, and D. X. Xu, “Ultracompact polarization converter with a dual subwavelength trench built in a silicon-on-insulator waveguide,” Opt. Lett. 37(3), 365–367 (2012). 31. S.-H. Kim, R. Takei, Y. Shoji, and T. Mizumoto, “Single-trench waveguide TE-TM mode converter,” Opt. Express 17(14), 11267–11273 (2009). 32. J. Wang, D. Zhao, J. Xu, X. Xue, and X. Zhang, “High-order mode rotator on the SOI integrated platform,” IEEE Photonics J. 8(2), 1–8 (2016). 33. K. Saitoh, T. Uematsu, N. Hanzawa, Y. Ishizaka, K. Masumoto, T. Sakamoto, T. Matsui, K. Tsujikawa, and F. Yamamoto, “PLC-based LP11 mode rotator for mode-division multiplexing,” Opt. Express 22(16), 19117–19130 (2014). 34. D. Martens, A. Z. Subramanian, S. Pathak, M. Vanslembrouck, P. Bienstman, W. Bogaerts, and R. G. Baets, “Compact silicon nitride arrayed waveguide gratings for very near-infrared wavelengths,” IEEE Photonics Technol. Lett. 27(2), 137–140 (2015). 35. W. Jin and K. S. Chiang, “Mode converters based on cascaded long-period waveguide gratings,” Opt. Lett. 41(13), 3130–3133 (2016). 36. A. Liu, C. L. Zou, X. Ren, Q. Wang, and G. C. Guo, “On-chip generation and control of the vortex beam,” Appl. Phys. Lett. 108(18), 181103 (2016). 37. Y. Ding, J. Xu, F. Da Ros, B. Huang, H. Ou, and C. Peucheret, “On-chip two-mode division multiplexing using tapered directional coupler-based mode multiplexer and demultiplexer,” Opt. Express 21(8), 10376–10382 (2013). 38. L. F. Frellsen, Y. Ding, O. Sigmund, and L. H. Frandsen, “Topology optimized mode multiplexing in silicon-oninsulator photonic wire waveguides,” Opt. Express 24(15), 16866–16873 (2016). 39. D. Chen, X. Xiao, L. Wang, Y. Yu, W. Liu, and Q. Yang, “Low-loss and fabrication tolerant silicon mode-order converters based on novel compact tapers,” Opt. Express 23(9), 11152–11159 (2015).

1. Introduction Angular momentum can be divided into spin angular momentum (SAM) and orbital angular momentum (OAM) in paraxial beams, which are related to circular polarization and spatial distribution, respectively. In recent years, light beams carrying OAM (i.e. OAM modes), also referred to as vortex beams, have attracted more and more attention owing to their distinct characteristics such as the phase singularity at the beam center and the resultant doughnut


shape intensity profiles [1, 2]. OAM modes with different topological charge values l , are theoretically unbounded and orthogonal to each other. Similar to other mode bases in free space or fiber, OAM modes are another mode basis with which to represent spatial modes. Different mode bases including OAM modes can be employed in mode-division multiplexing (MDM), which is a subset of space-division multiplexing (SDM). Very recently, OAM modes have shown great potential for MDM both in free space and fiber-based optical communications [3–8]. Vortex beams or OAM modes also provide unique opportunities for manipulation of micro-/nano-particles as they assert torque in addition to forces related to optical intensity gradient, giving rise to orbital and spin movements beyond trapping. Remarkably, for diverse applications of vortex beams in optical communications [3–8], optical tweezers [9], optical trapping [10] and quantum information technology [11], the successful generation of OAM modes is of great importance. Driven by their distinctive properties and miscellaneous applications, there have been many attempts to generate and manipulate OAM beams. Such attempts include cylindrical lens mode converters, spiral phase plates, q-plates, and spatial light modulators (SLM) [12– 15]. Recently, integrated approaches based on fibers or silicon devices are developed due to their outstanding features of small footprint, high speed, low-cost, and adaptation for various applications [16–25]. In 2011, a nanoscale V-shaped antenna meta-surface structure was proposed to generate single OAM beam by adjusting the wavefront parameters of scattered fields [16]. From then on, varieties of optical antenna, including metallic and dielectric metasurface arrays, have been used to generate OAM beams [17–24]. In [25], Cai et al. proposed and demonstrated an OAM beam emitter based on a silicon microring with azimuthally distributed second-order gratings. The operation principle of microring grating is based on the scattering fields, which are generated out-plane and propagated in free space. In addition, it also attracts much attention to fully explore and employ the unique feature of OAM beams in the region of guided optics [26, 27]. However, the generation of OAM beams in-plane on a silicon chip is still challenging and relevant works have not yet been reported much, as the conventional optical waveguide cannot support OAM modes. In this paper, we present a scheme to generate OAM modes on silicon-on-insulator (SOI) chip by using a single-trench silicon waveguide. Trench structures have been previously employed to enable polarization rotator and mode converter [28–33]. A trench silicon waveguide can support two orthogonal LP-like modes whose optical axes are rotated by around 45° with respect to the horizontal and vertical directions. By combining two eigenmodes with different phase differences, one can selectively convert an input LP-like mode to OAM ± 1 modes at the output terminal of the single-trench waveguide. The proposed trench structure for x- and y-polarizations are optimized, and high mode purity can be achieved over a wide wavelength range from 1.45 µm to 1.65 µm. As one typical example of applications, an on-chip OAM modes (de)multiplexer (OAM0, OAM ± 1) for x-polarization is designed based on the tailored trench structure. Such an on-chip OAM modes (de)multiplexer has a footprint of