REPORTS which consists of a right-hand circularly polar- indicated by the chirality of the pattern. Thus, the sisting of three identical emitters(R=7.5 um, q ized(RHCP) beam with topological charge of nine resonances correspond to 1=0, +1, #2, #3, 72)coupled to the same access waveguide(Fig 4, 7+ I and a left-hand circularly polarized (LHCp) and +4. Similar results for the device with r= A and B). Simultaneous emission of identical beam with 1-1. This indicates a new scheme of 3.9 um are given in the supplementary materials vortices has been verified, as shown in Fig 4, C measuring the value of/: When the radiated beam (16). Moreover, the spiral patterns rotate when and D. The spiral patterns rotate synchronously interferes with a copropagating circularly polar- the phase of the reference beam is changed con- when the phase of the reference beam is changed ized reference beam, spiral interference pattems tinuously(movies SI and S2). These results show (movie S3). should be produced, with the number of arms unambiguously that the wavefront of the radiated Our OAM emitters based on complementary qual to either 1-1 or 1+1, depending on the beams is helical with /=p-g Beams with larger metal oxide semiconductor compatible silicon andedness of the reference beam SoP OAM quantum numbers I can be generated from PICs produce optical vortex beams with distinc- The measured interference patterns(Fig 3, B the device. However, the observable /is limited tive and variable OAM values from a very simple nd C) have spiral arms equal to /-1(RHCP)or by the tuning range of the tunable laser. and small device, with no need for any fine ad 1+1(LHCP)as predicted in the aforementioned To demonstrate the potential of photonic in- justment of optical phase. While we have al- heme, and the sign of the topological charge is tegration, we fabricated OAM emitter arrays con- ready achieved useful emission efficiency of up to 13%, efficiency can be maximized by engineer ing the coupling ratio between the resonator and the access waveguide to the critical coupling point Mode splitting (23), at which all of the input power enters the R=7.5m resonator. As demonstrated by the integrated ar- rays, integration of a large number of devices can 7 be realized with the use of standard integrated cir- s2 uit technology to form complicated formations on silicon wafers Such scalable integration could open up truly large-scale integrated applications opportunities For example, it is possible to build oaM quan- communications channels between two chi ining the same integrated OAMPIC吕 as the oam transmitter and the other as DAM receiver(according to the principle of rec- 9 iprocity, the device emitting a specific vortex 圆國回國回國同包 electively receive the same beam). g been shown that OAM multiplex- d use of PICs(14), our device enables rapid switch- Fig. 3. (A) Radiation spectrum for a device with R= 7.5 um measured by scanning input laser wave ong oam states, as semiconductor tun- ngth Thel=0 wavelength is-1525 nm The doublets in the spectrum result from the mode splitting able lasers can already switch wavelengths in E strongest cross-coupling occurs at the wavelength with/=0 due to Bragg reflection, which is therefore been shown to tune at frequencies up to 40 GHzg associated with the largest split. (B and C) Interference patterns with LHCP and RHCP reference beams. (25). Therefore, our device provides an approach for an integrated oAM switch or modulator. An- lation of particles(26). By selectively lighting s groups of integrated emitter arrays, controllable and reconfigurable drivers can be configured for microfluidic and nanoparticle manipulation ma hines, such as lab-on-a-chip, optical tweezers, R I C Spreeuw, A45,8185(1992 2. S. Furhapter, A Jesacher, 5. Bernet, M. Ritsch-Marte pt. Lett.30.1953(2005) Fig. 4. (A)llustration of an array 3. D. G. Grier. Nature 424. 81 insisting of three identical emitters. 4. G. Gibson et al., Opt. Express The three-dimensional emission pa tern is calculated with the use of a Communication Conference, OSA Technical Dige dipole-emissionbased semianalyt ical model (16).(B)Micrograph of a fabricated array. (C)Near-field intensity patterns emitted from the array. The difference in their brightness 313(2001).1, G. Weihs, A. Zeilinger, Nature 412 is attributed to slight differences in their resonance peaks due to fabrication variations. (D)Example of an 7. G. Molina-lerriza, J. P. Torres, L. Torner, Nat. Phys. 3, interference pattern between the emitted beams from the array and the copropagating RHCP Gaussian 305(2007 beam. All beams have four arms and, therefore, the same OAM order 1=-3 The uneven brightness is due. ot et 7 221 01992),.r >min, A g winte, tensen, side vortices are somewhat deformed due to lens aberration causing phase-front distortion 1. P. Woerdman, Opt. Commun. 112, 321(1994) www.sciencemag.orgScieNceVol33819OctobeR2012 365which consists of a right-hand circularly polar￾ized (RHCP) beam with topological charge of l + 1 and a left-hand circularly polarized (LHCP) beam with l – 1. This indicates a new scheme of measuring the value of l: When the radiated beam interferes with a copropagating circularly polar￾ized reference beam, spiral interference patterns should be produced, with the number of arms equal to either l – 1 or l + 1, depending on the handedness of the reference beam SOP. The measured interference patterns (Fig. 3, B and C) have spiral arms equal to l – 1 (RHCP) or l + 1 (LHCP) as predicted in the aforementioned scheme, and the sign of the topological charge is indicated by the chirality of the pattern. Thus, the nine resonances correspond to l = 0, T1, T2, T3, and T4. Similar results for the device with R = 3.9 mm are given in the supplementary materials (16). Moreover, the spiral patterns rotate when the phase of the reference beam is changed con￾tinuously (movies S1 and S2). These results show unambiguously that the wavefront of the radiated beams is helical with l = p – q. Beams with larger OAM quantum numbers l can be generated from the device. However, the observable l is limited by the tuning range of the tunable laser. To demonstrate the potential of photonic in￾tegration, we fabricated OAM emitter arrays con￾sisting of three identical emitters (R = 7.5 mm, q = 72) coupled to the same access waveguide (Fig. 4, A and B). Simultaneous emission of identical vortices has been verified, as shown in Fig. 4, C and D. The spiral patterns rotate synchronously when the phase of the reference beam is changed (movie S3). Our OAM emitters based on complementary metal oxide semiconductor compatible silicon PICs produce optical vortex beams with distinc￾tive and variable OAM values from a very simple and small device, with no need for any fine ad￾justment of optical phase. While we have al￾ready achieved useful emission efficiency of up to 13%, efficiency can be maximized by engineer￾ing the coupling ratio between the resonator and the access waveguide to the critical coupling point (23), at which all of the input power enters the resonator. As demonstrated by the integrated ar￾rays, integration of a large number of devices can be realized with the use of standard integrated cir￾cuit technology to form complicated formations on silicon wafers. Such scalable integration could open up truly large-scale integrated applications opportunities. For example, it is possible to build OAM quan￾tum communications channels between two chips, each containing the same integrated OAM PICs— one as the OAM transmitter and the other as the OAM receiver (according to the principle of rec￾iprocity, the device emitting a specific vortex beam will selectively receive the same beam). Though it has been shown that OAM multiplex￾ing and demultiplexing can be achieved with the use of PICs (14), our device enables rapid switch￾ing among OAM states, as semiconductor tun￾able lasers can already switch wavelengths in nanoseconds (24), and silicon microrings have been shown to tune at frequencies up to 40 GHz (25). Therefore, our device provides an approach for an integrated OAM switch or modulator. An￾other application area could be micromanipu￾lation of particles (26). By selectively lighting groups of integrated emitter arrays, controllable and reconfigurable drivers can be configured for microfluidic and nanoparticle manipulation ma￾chines, such as lab-on-a-chip, optical tweezers, and optical spanners. References and Notes 1. L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, J. P. Woerdman, Phys. Rev. A 45, 8185 (1992). 2. S. Fürhapter, A. Jesacher, S. Bernet, M. Ritsch-Marte, Opt. Lett. 30, 1953 (2005). 3. D. G. Grier, Nature 424, 810 (2003). 4. G. Gibson et al., Opt. Express 12, 5448 (2004). 5. N. K. Fontaine, C. R. Doerr, L. Buhl, in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington, DC, 2012), paper OTu1l.2. 6. A. Mair, A. Vaziri, G. Weihs, A. Zeilinger, Nature 412, 313 (2001). 7. G. Molina-Terriza, J. P. Torres, L. Torner, Nat. Phys. 3, 305 (2007). 8. N. R. Heckenberg, R. McDuff, C. P. Smith, A. G. White, Opt. Lett. 17, 221 (1992). 9. M. W. Beijersbergen, R. P. C. Coerwinkel, M. Kristensen, J. P. Woerdman, Opt. Commun. 112, 321 (1994). Fig. 4. (A) Illustration of an array consisting of three identical emitters. The three-dimensional emission pat￾tern is calculated with the use of a dipole-emission–based semianalyt￾ical model (16). (B) Micrograph of a fabricated array. (C) Near-field intensity patterns emitted from the array. The difference in their brightness is attributed to slight differences in their resonance peaks due to fabrication variations. (D) Example of an interference pattern between the emitted beams from the array and the copropagating RHCP Gaussian beam. All beams have four arms and, therefore, the same OAM order l = –3. The uneven brightness is due to the Gaussian distribution of the reference beam, which is only coaxial with the middle vortex. The two side vortices are somewhat deformed due to lens aberration causing phase-front distortion. Fig. 3. (A) Radiation spectrum for a device with R = 7.5 mm measured by scanning input laser wave￾length. The l = 0 wavelength is ~1525 nm. The doublets in the spectrum result from the mode splitting caused by cross-coupling between the otherwise degenerate clockwise and counterclockwise WGMs. The strongest cross-coupling occurs at the wavelength with l = 0 due to Bragg reflection, which is therefore associated with the largest split. (B and C) Interference patterns with LHCP and RHCP reference beams. Each pattern in (B) has l + 1 spiral arms, whereas each pattern in (C) has l – 1 spiral arms. www.sciencemag.org SCIENCE VOL 338 19 OCTOBER 2012 365 REPORTS on October 23, 2012 www.sciencemag.org Downloaded from