Nonlinear Photonics 2014: Introduction N. Akhmediev1,* and Yaroslav Kartashov2,3 1
Optical Sciences Group, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2600, Australia 2 ICFO - Institut de Ciencies Fotoniques, and Universitat Politecnica de Catalunya, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain 3 Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow Region 142190, Russia *[email protected]
Abstract: International Conference “Nonlinear Photonics-2014” took place in Barcelona, Spain on July 27–31, 2014. It was a part of the “Advanced Photonics Congress” which is becoming a traditional notable event in the world of photonics. The current focus issue of Optics Express contains contributions from the participants of the Conference and the Congress. The articles in this focus issue by no means represent the total number of the congress contributions (around 400). However, it demonstrates wide range of topics covered at the event. The next conference of this series is to be held in 2016 in Australia, which is the home of many researchers working in the field of photonics in general and nonlinear photonics in particular. © 2015 Optical Society of America OCIS codes: (060.0060) Fiber optics and optical communications; (130.0130) Integrated optics; (140.0140) Lasers and laser optics; (160.0160) Materials; (190.0190) Nonlinear optics; (230.0230) Optical devices; (270.0270) Quantum optics; (320.0320) Ultrafast optics.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
N. Akhmediev and K. Rottwitt, “Focus issue introduction: nonlinear photonics,” Opt. Express 20(24), 27212– 27220 (2012). M. Klimczak, G. Sobon, K. Abramski, and R. Buczynski, “Spectral coherence in all-normal dispersion supercontinuum in presence of Raman scattering and direct seeding from sub-picosecond pump,” Opt. Express 22(26), 31635–31645 (2014). F. Leo, J. Safioui, B. Kuyken, G. Roelkens, and S.-P. Gorza, “Generation of coherent supercontinuum in a-Si:H waveguides: experiment and modeling based on measured dispersion profile,” Opt. Express 22(23), 28997– 29007 (2014). I. A. Sukhoivanov, S. O. Iakushev, O. V. Shulika, J. A. Andrade-Lucio, A. Diez, and M. Andrés, “Supercontinuum generation at 800 nm in all-normal dispersion photonic crystal fiber,” Opt. Express 22(24), 30234–30250 (2014). F. Li, Q. Li, J. Yuan, and P. K. A. Wai, “Highly coherent supercontinuum generation with picosecond pulses by using self-similar compression,” Opt. Express 22(22), 27339–27354 (2014). A. Al-kadry, M. El Amraoui, Y. Messaddeq, and M. Rochette, “Two octaves mid-infrared supercontinuum in As2Se3 microwires,” Opt. Express 22(25), 31131–31137 (2014). J. Ahuja, D. B. Nalawade, J. Zamora-Munt, R. Vilaseca, and C. Masoller, “Rogue waves in injected semiconductor lasers with current modulation: role of the modulation phase,” Opt. Express 22(23), 28377–28382 (2014). S. Chen, J. M. Soto-Crespo, and Ph. Grelu, “Dark three-sister rogue waves in normally dispersive optical fibers with random birefringence,” Opt. Express 22(22), 27632–27642 (2014). C. Dai, Y. Wang, and X. Zhang, “Controllable Akhmediev breather and Kuznetsov-Ma soliton trains in PTsymmetric coupled waveguides,” Opt. Express 22(24), 29862–29867 (2014). G. Weerasekara, A. Tokunaga, H. Terauchi, M. Eberhard, and A. Maruta, “Soliton’s eigenvalue based analysis on the generation mechanism of rogue wave phenomenon in optical fibers exhibiting weak third order dispersion,” Opt. Express 22(24), 30128–30134 (2014). V. L. Kalashnikov and E. Sorokin, “Dissipative Raman Solitons,” Opt. Express 22(24), 30118–30126 (2014). B. Liu, Y.-F. Liu, and X.-D. He, “Impact of phase on collision between vortex solitons in three-dimensional cubic-quintic complex Ginzburg-Landau equation,” Opt. Express 22(21), 26203–26211 (2014). S. R. Domingue and R. A. Bartels, “Three-photon excitation source at 1250 nm generated in a dual zero dispersion wavelength nonlinear fiber,” Opt. Express 22(25), 30777–30785 (2014). D. Shayovitz, H. Herrmann, W. Sohler, R. Ricken, Ch. Silberhorn, and D. M. Marom, “Real-time coherent detection of phase modulated ultra-short pulses after time-to-space conversion and spatial demultiplexing,” Opt.
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Express 22(25), 31138–31145 (2014). 15. S. O. Iakushev, O. V. Shulika, I. A. Sukhoivanov, V. I. Fesenko, M. V. Andrés, and H. Sayinc, “Formation of ultrashort triangular pulses in optical fibers,” Opt. Express 22(23), 29119–29134 (2014). 16. J. Butet and O. J. F. Martin, “Fano resonances in the nonlinear optical response of coupled plasmonic nanostructures,” Opt. Express 22(24), 29693–29707 (2014). 17. H. Fattahi, A. Schwarz, X. T. Geng, S. Keiber, D. E. Kim, F. Krausz, and N. Karpowicz, “Decoupling chaotic amplification and nonlinear phase high-energy thin-disk amplifiers for stable OPCPA pumping,” Opt. Express 22(25), 31440–31447 (2014). 18. H. H. Liu and K. K. Chow, “Dark pulse generation in fiber lasers incorporating carbon nanotubes,” Opt. Express 22(24), 29708–29713 (2014). 19. Sh. Amiranashvili, U. Bandelow, and N. Akhmediev, “Spectral properties of limiting solitons in optical fibers,” Opt. Express 22(24), 30251–30256 (2014). 20. H. Chen, S.-P. Chen, Z.-F. Jiang, and J. Hou, “Flexible rectangular wave-breaking-free pulse generation in actively mode-locked ytterbium-doped fiber laser,” Opt. Express 22(22), 26449–26456 (2014). 21. W. Q. Zhang, M. A. Lohe, T. M. Monro, P. Bettotti, L. Pavesi, and V. Afshar, “Nonlinear self-polarization flipping in silicon sub-wavelength waveguides: distortion, loss, dispersion, and noise effects,” Opt. Express 22(22), 27643–27654 (2014). 22. K. Kim, “Enhanced optical phase conjugation in nonlinear metamaterials,” Opt. Express 22(S7), A1744–A1752 (2014). 23. S. Sun, N. Yi, W. Yao, Q. Song, and S. Xiao, “Enhanced second-harmonic generation from nonlinear optical metamagnetics,” Opt. Express 22(22), 26613–26620 (2014). 24. C. Huang, F. Ye, Z. Sun, and X. Chen, “Tunable subwavelength photonic lattices and solitons in periodically patterned grapheme monolayer,” Opt. Express 22(24), 30108–30117 (2014). 25. Y. Sun, G. Qiao, and G. Sun, “Direct generation of graphene plasmonic polaritons at THz frequencies via four wave mixing in the hybrid graphene sheets waveguides,” Opt. Express 22(23), 27880–27891 (2014). 26. J. Parravicini, M. Brambilla, L. Columbo, F. Prati, C. Rizza, G. Tissoni, A. J. Agranat, and E. DelRe, “Observation of electro-activated localized structures in broad area VCSELs,” Opt. Express 22(24), 30225– 30233 (2014). 27. M. Gaafar, Ph. Richter, H. Keskin, Ch. Möller, M. Wichmann, W. Stolz, A. Rahimi-Iman, and M. Koch, “Selfmode-locking semiconductor disk laser,” Opt. Express 22(23), 28390–28399 (2014). 28. M. D. I. Castillo, S. C. Cerda, and D. R. Martinez, “Splitting after collision of high-order bright spatial solitons in Kerr media,” Opt. Express 22(25), 30769–30776 (2014). 29. A. Ziołkowski, “Numerical method for an analysis of nonlinear light propagation in photorefractive media - time nonlocal approach,” Opt. Express 22(S7), A1907–A1925 (2014). 30. A. Alberucci, N. Kravets, A. Piccardi, O. Buchnev, M. Kaczmarek, and G. Assanto, “Nematicons in planar cells subject to the optical Freedericksz threshold,” Opt. Express 22(25), 30663–30668 (2014). 31. Z. Chen, J. Liu, S. Fu, Y. Li, and B. A. Malomed, “Discrete solitons and vortices on two-dimensional lattices of PT-symmetric coupler,” Opt. Express 22(24), 29679–29692 (2014). 32. F. Di Mei, J. Parravicini, D. Pierangeli, C. Conti, A. J. Agranat, and E. DelRe, “Anti-diffracting beams through the diffusive optical nonlinearity,” Opt. Express 22(25), 31434–31439 (2014). 33. L. Ge, M. Shen, C. Ma, T. Zang, and L. Dai, “Gap solitons in PT-symmetric optical lattices with higher-order diffraction,” Opt. Express 22(24), 29435–29444 (2014). 34. J. Qin, G.-W. Lu, T. Sakamoto, K. Akahane, N. Yamamoto, D. Wang, C. Wang, H. Wang, M. Zhang, T. Kawanishi, and Y. Ji, “Simultaneous multichannel wavelength multicasting and XOR logic gate multicasting for three DPSK signals based on four-wave mixing in quantum-dot semiconductor optical amplifier,” Opt. Express 22(24), 29413–29423 (2014). 35. T. Kodama, K. Morita, G. Cincotti, and K. Kitayama, “A low-power photonic quantization approach using OFDM subcarrier spectral shifts,” Opt. Express 22(23), 28719–28730 (2014). 36. A. Lorences-Riesgo, L. Liu, S. L. I. Olsson, R. Malik, A. Kumpera, C. Lundstrom, S. Radic, M. Karlsson, and P. A. Andrekson, “Quadrature demultiplexing using a degenerate vector parametric amplifier,” Opt. Express 22(24), 29424–29434 (2014). 37. J. Liu, F. Tan, H. Shi, and P. Wang, “High-power operation of silica-based Raman fiber amplifier at 2147 nm,” Opt. Express 22(23), 28383–28389 (2014). 38. M. Kuznetsov, O. Vershinin, V. Tyrtyshnyy, and O. Antipov, “Low-threshold mode instability in Yb3 + -doped few-mode fiber amplifiers,” Opt. Express 22(24), 29714–29725 (2014). 39. F. Vanier, Y.-A. Peter, and M. Rochette, “Cascaded Raman lasing in packaged high quality As₂S₃ microspheres,” Opt. Express 22(23), 28731–28739 (2014). 40. T. Wang, T. Yang, D. Jia, Z. Wang, and C. Ge, “Multi-wavelength lasers with suppressed spectral linewidth of 10 kHz,” Opt. Express 22(22), 26862–26871 (2014). 41. A. Billat, S. Cordette, and C.-S. Brès, “Broadly tunable source around 2050 nm based on wideband parametric conversion and thulium-holmium amplification cascade,” Opt. Express 22(22), 26635–26641 (2014). 42. S. Shahin, S. Mehravar, P. Gangopadhyay, N. Peyghambarian, R. A. Norwood, and K. Kieu, “Multiphoton microscopy as a detection tool for photobleaching of EO materials,” Opt. Express 22(25), 30955–30962 (2014). 43. P. Parra-Rivas, D. Gomila, M. A. Matias, P. Colet, and L. Gelens, “Effects of inhomogeneities and drift on the dynamics of temporal solitons in fiber cavities and microresonators,” Opt. Express 22(25), 30943–30954 (2014).
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44. O. A. Gorbunov, S. Sugavanam, and D. V. Churkin, “Revealing statistical properties of quasi-CW fibre lasers in bandwidth-limited measurements,” Opt. Express 22(23), 28071–28076 (2014). 45. B. Klus, U. A. Laudyn, M. A. Karpierz, and B. Sahraoui, “All-optical measurement of elastic constants in nematic liquid crystals,” Opt. Express 22(24), 30257–30266 (2014). 46. A. B. Ortega, M. L. Carrasco, M. M. Otero, E. R. Lara, E. V. Ramírez, and M. D. Castillo, “Analytical expressions for Z-scan with arbitrary phase change in thin nonlocal nonlinear media,” Opt. Express 22(23), 27932–27941 (2014). 47. X. Wang, H. Ren, N. An, X. Zhao, Y. Zheng, and X. Chen, “Large acceptance of non-collinear phase-matching second harmonic generation on the surface of an anomalous-like bulk dispersion medium,” Opt. Express 22(23), 28234–28239 (2014). 48. V. A. Makarov, V. M. Petnikova, and V. V. Shuvalov, “Adiabatic modulation of a cnoidal wave by a breather with orthogonal circular polarization in an isotropic gyrotropic nonlinear medium,” Opt. Express 22(22), 26607– 26612 (2014). 49. L. Yuan and Y. Y. Lu, “Bilateral symmetry breaking in nonlinear circular cylinders,” Opt. Express 22(24), 30128–30134 (2014). 50. H. Kianirad, A. Zukauskas, Th. Frisk, C. Canalias, and F. Laurell, “Contact poling of Rb: KTiOPO4 using a micro-structured silicon electrode,” Opt. Express 22(24), 30128–30134 (2014).
1. General information The conference “Nonlinear Photonics” celebrated its 25th anniversary in Barcelona in July 2014. The first one of this series has been organised by George Stegeman and Roger Stolen in Houston in 1989 under the name “Nonlinear guided waves”. The complete list of previous conferences can be found in [1]. Traditionally, the conference was preceded by the satellite workshop on the hot subjects of modern nonlinear optics held on July 25–26, 2014. It was kindly hosted by ICFO (The Institute of Photonics Sciences) due to generosity of its founding and acting director Lluis Torner. This year the major topics were reflected in the title of the workshop: “Rogue waves, dissipative solitons, plasmonics, supercontinuum and special fibres”. Not surprisingly, the scope of the workshop was wider than that. Leading scientists in nonlinear optics were invited to take part in this event. The venue of the conference (Fira Centre, Barcelona) contributed to the success of the conference. The choice of Barcelona as the place for the conference also provided its success. The city is a popular destination for tourists from all over the world. It is one of the major European cultural centres. Its location on the Mediterranean attracts many holiday makers. The presence of the ICFO in Barcelona makes it one of the major centres on photonics in Europe. The conference was co-located with three other conferences with the common name “Advanced Photonics.” The other three conferences included “Bragg Gratings, Photosensitivity and Poling in Glass Waveguides (BGPP),” “Optical Sensors (SENSORS)” and “Specialty Optical Fibers & Applications (SOF)”. The set of articles presented in this focus issue provides a general impression about the research areas considered at the conference, although, of course, not the whole range of topics presented at the conference is covered here. We received a total of 68 submissions with 49 papers accepted and published. Only high quality submissions have been chosen for publication. The former General Chairs of the conference (N. Akhmediev, K. Rottwitt and J. M. Dudley) express the wish that traditions will be continued with the organisation of future events. The next conference “Nonlinear Photonics” is to be held in Australia in 2016. General Chairs of the conference are Yaroslav Kartashov and Alex Gaeta. Program Chairs are: GianLuka Oppo, Stefan Wabnitz and Andrey Sukhorukov. 2. Short description of the papers presented in this focus issue Below, we present the short description of each article categorised according to the content. Classification cannot be perfect as the articles may belong to two or more areas of research. Nevertheless, the sectioning may simplify searching of a particular paper that is of interest for
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 486
a reader. We also note that the subheadings here are different from the standard ones used in the table of content. This offers an alternative way of searching for the work of interest. 2.1. Supercontinuum generation The authors of [2] studied intensity stability and wavelength correlations of near-infrared supercontinuum generation in all-normal flattened dispersion, all-solid soft glass photonic crystal fiber. They used dispersive Fourier transformation method to measure shot-to-shot resolved spectra with pumping by a sub-picosecond, fiber-based chirped pulse amplification system. The results suggest a convenient way of stabilizing of shot-to-shot coherence. The authors of [3] experimentally demonstrated the generation of a supercontinuum (SC) in a − Si: H photonic wire waveguide at telecommunication wavelengths using femtosecond input pulse with energy lower than 5 pJ. A direct comparison of SC generation shows the higher performances of a − Si: H over c − Si waveguides for broadband low power SC generation at telecommunication wavelengths. The authors of [4] numerically studied the supercontinuum generation and pulse compression in a special all-normal dispersion photonic crystal fiber with a flat-top dispersion curve, pumped by the Ti:Sapphire laser at 800 nm. The influence of realistic fibre fabrication errors on the SC generation and pulse compression are investigated. For generating the supercontinuum, the authors of [5] propose to first self-similarly compress a high power picosecond pump pulse by injecting it into a fiber with variable increasing nonlinearity. The compressed pulse is then injected into a dispersion-shifted fibre for SC generation. In this scheme, the noise level of the compressed pulse can be reduced. The authors of [6] report mid-infrared supercontinuum generation in As2Se3 chalcogenide microwires with the added advantage of using low energy pulses. The generated SC cover two octaves of bandwidth from 1.1 μm to 4.4 μm at −30 dB. This may exceed the supercontinuum bandwidth reported earlier in As2Se3 microwires by a factor of 3.5. 2.2. Rogue waves The authors of [7] performed a numerical analysis of rogue waves statistics in semiconductor lasers with continuous-wave optical injection. They show that, when rogue waves are not suppressed by the current modulation, their probability of occurrence strongly depends on the phase of the modulation. The authors of [8] study, analytically, dark rogue wave solutions in normal dispersion birefringent optical fibers. They obtained exact rational solutions of the coupled nonlinear Schrödinger equations in the form of vector dark “three-sister” rogue waves. The authors of [9] derived the PT-symmetric and PT-antisymmetric Akhmediev breather (AB) and Kuznetsov-Ma (KM) soliton train solutions in the frame of (2+1)-dimensional coupled nonlinear Schrödinger equations with variable-coefficients. This is done for PTsymmetric coupled waveguides with gain and loss. They investigated the controllable behaviours of AB and KM soliton trains in a diffraction decreasing medium with exponential profile. The authors of [10] numerically analysed rogue waves in an optical fibre taking into account the third order dispersion. They show that the rogue waves are formed due to the collision of quasi-solitons in a fibre with anomalous dispersion. 2.3. Dissipative solitons Based of numerical study of the generalised complex Ginzburg-Landau equation, the authors of [11] found a new type of dissipative solitons named “dissipative Raman solitons”. They demonstrated that the increase of the group-delay dispersion can suppress the multi-pulsing instability and leads to the formation of the dissipative Raman soliton. They also showed that in practice, a spectral filter can extend the stability regions of high-energy pulses.
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 487
An analysis of collision outcomes between stable dissipative vortices of the threedimensional cubic-quintic complex Ginzburg-Landau equation is presented in [12]. The considered scenarios include merger of the vortices into a single one, creation of an extra vortex and quasi-elastic interaction. 2.4. Pulse amplification and generation In [13], the authors generated 1250 nm pulses in dual zero dispersion photonic crystal fiber. The durations and energies make these pulses useful for producing light at 1250 nm for multiphoton microscopy. The authors of [14] demonstrated real-time demultiplexing to the spatial domain and single- shot coherent detection of a phase modulated ultrashort pulse train by time-to-space conversion. They showed that time-to-space conversion can be a valuable tool in ultrahigh bit rate OTDM optical communications. In [15], it is shown, theoretically, that short (1-2 m) conventional single mode fiber can be used for triangular pulse formation in the steady-state regime without pre-chirping when femtosecond pulses are used for pumping. The pulse parameters found in this work can serve as a guide for experiments and implementation of all-fiber schemes in optical signal processing. Using a surface integral equation method, the authors of [16] studied the second order non- linear optical response of plasmonic metamolecules supporting Fano resonances. They showed that the typical lineshape of Fano resonances is also clearly observable in the nonlinear regime. The results can be useful for the design of efficient nonlinear plasmonic metamolecules with controlled nonlinear radiation. The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers are described in [17]. It is shown that reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and providing a reproducible spectral phase. The authors of [18] demonstrated generation of dark pulses by an erbium-doped fibre ring laser with net anomalous dispersion. A side-polished fibre coated with carbon nanotube layer is embedded into the laser to enhance the birefringence and nonlinearity of the laser cavity. The dual-wavelength domain-wall dark pulses were obtained at a relatively low pump threshold of 50.6 mW. The authors of [19] studied the shortest possible optical soliton and explicitly calculated its spectrum using the so-called short pulse equation. The latter applies to ultra-short solitons in transparent materials like fused silica thus being relevant for optical fibers. The authors of [20] demonstrated nanosecond range rectangular wave-breaking-free pulse generation in an actively mode locked Yb-doped fiber laser. The approach is based on a combined action of active periodic cavity loss modulation and nonlinear polarization rotation effect. The laser presents flexible tunabilities in pulse width, pulse energy and pulse shape. The authors of [21] numerically investigated nonlinear self-polarization flipping in a silicon waveguide. They identified specific silicon waveguide geometries that enhance this effect. In optimized waveguides, the nonlinear self-polarization flipping can be observed with few tens of watts peak power pulses with widths as short as 60 ps and laser noise level as large as 7%. 2.5. Metamaterials Optical phase conjugation by degenerate four-wave mixing in nonlinear metamaterials is studied theoretically in [22] by solving the coupled wave equations. It is found that the efficiency of phase conjugation can be significantly enhanced due to the enhancement of electromagnetic fields in various metamaterial structures. A numerical simulation of second-harmonic generation (SHG) in a nonlinear magnetic metamaterial is presented in [23]. The convertion efficiency of SHG can be significantly
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 488
enhanced by almost four orders of magnitude by inserting a nonlinear material into the high local field area of magnetic metamaterial consisting of periodic arrays of paired thin silver strips. 2.6. Graphene in optics The authors of [24] studied linear and nonlinear mode properties in a periodically patterned graphene sheet. They found graphene lattice solitons at the deep-subwavelength scales in two dimensions due to the combination of graphene self-focusing nonlinearity and the graphene plasmonic confinement effects. The authors of [25] proposed a compact waveguide incorporating a high-index nano-ridge sandwiched between graphene sheets for direct generation of graphene plasmonic polaritons via four wave mixing. The proposed waveguide supports graphene plasmonic polariton modes at the THz frequencies and photonic modes at the infrared wavelengths. The proposed waveguide may have a great potential as an integrated chip-scale graphene plasmonic polariton source. 2.7. Vertical-cavity surface-emitting lasers The electro-activation of a localized optical structure in a coherently driven broad-area vertical-cavity surface-emitting laser (VCSEL) operated below threshold has been observed experimentally in [26]. Control is achieved by electro-optically steering a writing beam through a pre-programmable switch based on a photorefractive funnel waveguide. The authors of [27] highlight recent achievements in the area of vertical-external-cavity surface-emitting lasers (VECSELs). They provide an evidence of mode-locking in a saturable absorber-free device. A beam-profile measurement reveals the excellent beam quality of the device. 2.8. Photorefractive media, liquid crystals, spatial and gap solitons Numerical studies of (1 + 1)-dimensional higher order bright spatial solitons in a Kerr nonlinear media in [28] showed that after the collision, the higher order solitons split into the first order solitons. Their number corresponds to the order of the original soliton. Various collision scenarios of higher order solitons are considered. Nonlinear light propagation in nonlocal photorefractive media is analyzed in [29] using numerical methods. Two algorithms are presented, and compared in terms of physical results and computing times. The tests were carried out for a one-carrier model that describes most of photorefractive media, and for a model with bipolar transport and hot electron effect, used in descriptions of semiconductor materials. The authors of [30] investigated theoretically and experimentally self-trapping of light beams in nematic liquid crystals. They studied the role of the optical Fréedericksz transition in the nonlinear propagation of finite-size optical beams. In particular, they predicted and observed a bistable behaviour accompanied by hysteresis as power changed up and down. In [31], the authors introduced a 2D network built of PT-symmetric dimers with on-site cubic nonlinearity. The gain and loss elements of the dimers are linked by parallel squareshaped lattices. The system supports PT-symmetric and antisymmetric solitons and on-sitecentered solitary vortices. Stability regions of these discrete solitons in the parameter space are identified through the computation of stability eigenvalues and verified by numerical simulations. The authors of [32] observed anti-diffracting beams supported by the peak-intensity independent diffusive nonlinearity. The beams are shown to be able to shrink below their diffraction-limited size in photorefractive lithium-enriched potassium-tantalate-niobate (KTN:Li). The authors of [33] studied the existence and stability of gap solitons in the semi-infinite gap of a parity-time (PT)-symmetric optical lattice with a higher-order diffraction. They
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 489
showed that the Bloch bands and band gaps of PT-symmetric optical lattice depend crucially on the coupling constant of the fourth-order diffraction. Fundamental solitons are found to be linearly stable with arbitrary positive value of the coupling constant. 2.9. Optical information processing In [34], the authors experimentally demonstrated simultaneous multichannel wavelength multi- casting and exclusive-OR logic gate multicasting for three 10 Gbps non-return-to-zero differential phase-shift-keying signals in quantum-dot semiconductor optical amplifier by exploiting the four-wave mixing process. All the new generated channels are with a power penalty less than 1.2 dB at a BER of 10−9. The authors of [35] proposed and demonstrated an energy-efficient photonic analog-todigital converter based on spectral shifts of orthogonal frequency division multiplexing subcarriers and optical quantisation using a new frequency-packed arrayed waveguide grating device. They showed the feasibility of a 2, 3 and 4-bit optical quantisation scheme. The authors of [36] consider quadrature demultiplexing of a quadrature phase-shift keying signal into two cross-polarized binary phase-shift keying signals with negligible penalty at bit error rate equal to 10−9. A stable quadrature decomposition phase-locked loop scheme is proposed that is based on detecting the envelope of one of the signals after demultiplexing. 2.10. Lasers, amplifiers and other light sources The authors of [37] demonstrated a 2147 nm silica-based Raman fiber amplifier with output power of 14.3 W directly pumped with a 1963 nm CW thulium-doped all-fiber masteroscillator power-amplifier. The conversion efficiency is 38.5% from 1963 nm to 2147 nm in the HNLF. The authors of [38] observed the spatio-temporal instability of the fundamental mode in Y b3+ doped few-mode PM fibre amplifiers with a core diameter of 8.5 μm. The instability in the experiment and in theory is caused by the nonlinear power transformation of the LP01 fundamental mode into higher-order modes. Cascaded Raman lasing has been observed in high-Q As2S3 microspheres in [39]. Cascaded stimulated Raman scattering emission is obtained up to the 5-th order for a pump wavelength of 1557 nm and up to the 3-rd order for a pump wavelength of 1880 nm. High-Q As2S3 microspheres are used in a self-frequency locking laser setup without an external laser source. In [40], a method to suppress the linewidths of the multi-wavelength light source from 6 MHz to 10 kHz using an all-optical approach is proposed and demonstrated. More than 8 wavelengths over 10 nm are suppressed simultaneously using the approach of this work. Each wavelength of the multi-wavelength operates in single longitudinal mode. In [41], the authors report the design of a short-wave infrared continuous-wave light source with 20 mW average output power, and with a wavelength that can be selected in the 2000–2100 nm range. The operating principle is based on the simultaneous broadband parametric conversion of two seeds in a highly nonlinear silica fiber. 2.11. Optical measurements and frequency combs The authors of [42] used the multi-photon microscopy operating at 1550 nm as a rapid characterisation tool for studying the photostability of three well-known electro-optical materials. The technique is rapid, accurate, and can be used to study the photostability of a broad range of materials. The authors of [43] studied the effect of inhomogeneities and drift on temporal solitons and Kerr frequency combs in fibre cavities and microresonators. The theory is based on the Lugiato-Lefever equation with periodic boundary conditions. The work can be relevant for all applications relying on stable frequency combs.
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 490
In [44], the authors developed a model of bandwidth-limited measurements. They predict universal laws for intensity probability density function and intensity auto-correlation function of ideal completely stochastic source of Gaussian statistics. The variables are limited measurement bandwidth and measurement noise level. The experimental results are in good agreement with model predictions. The authors of [45] present a new all-optical method to measure elastic constants connected with twist and bend deformations. The method is based on the optical Fréedericksz threshold effect induced by the linearly polarized electro-magnetic wave. The results of experimental measurements are in good agreement with the values obtained by other methods based on an electro-optical effect. 2.12. Nonlinear wave propagation Analytical expressions for normalized transmittance of a thin material with simultaneous nonlocal nonlinear change in refraction and absorption are reported in [46]. Experimental results confirm the analytic predictions. The authors of [47] investigated non-collinear phase-matching second harmonic wave, which is generated at the inner surface of a z-cut 5%/mol MgO: LiNbO3 crystal. The ranges of angle, temperature and wavelength in this configuration are measured to be ≈ 0.51°, ≈ 4.1°C and ≈ 6nm, respectively. An approximate analytical solution of the non-integrable problem of steady-state adiabatic interaction of a cnoidal wave with a breather is obtained in [48]. It is shown that the interaction results in a strong amplitude and frequency modulation of the information signal. The authors of [49] analysed the scattering of plane waves by one or two circular cylinders with Kerr nonlinearity. They found solutions that break a reflection symmetry in the lateral direction perpendicular to the incident wave vector. 2.13. Fabrication of optical gratings The authors of [50] presented a new method for fabrication of periodically poled Rb: KTiOPO4 RKTP samples using an array of silicon electrodes. They showed that using this technique high quality quasi-phase matching gratings can be reproducibly fabricated. Acknowledgments N. A. acknowledges the support of the Australian Research Council (Discovery Project number DP140100265) and support from the Volkswagen Stiftung.
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 491
Optical Sciences Group, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2600, Australia 2 ICFO - Institut de Ciencies Fotoniques, and Universitat Politecnica de Catalunya, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain 3 Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow Region 142190, Russia *[email protected]
Abstract: International Conference “Nonlinear Photonics-2014” took place in Barcelona, Spain on July 27–31, 2014. It was a part of the “Advanced Photonics Congress” which is becoming a traditional notable event in the world of photonics. The current focus issue of Optics Express contains contributions from the participants of the Conference and the Congress. The articles in this focus issue by no means represent the total number of the congress contributions (around 400). However, it demonstrates wide range of topics covered at the event. The next conference of this series is to be held in 2016 in Australia, which is the home of many researchers working in the field of photonics in general and nonlinear photonics in particular. © 2015 Optical Society of America OCIS codes: (060.0060) Fiber optics and optical communications; (130.0130) Integrated optics; (140.0140) Lasers and laser optics; (160.0160) Materials; (190.0190) Nonlinear optics; (230.0230) Optical devices; (270.0270) Quantum optics; (320.0320) Ultrafast optics.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
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Hou, “Flexible rectangular wave-breaking-free pulse generation in actively mode-locked ytterbium-doped fiber laser,” Opt. Express 22(22), 26449–26456 (2014). 21. W. Q. Zhang, M. A. Lohe, T. M. Monro, P. Bettotti, L. Pavesi, and V. Afshar, “Nonlinear self-polarization flipping in silicon sub-wavelength waveguides: distortion, loss, dispersion, and noise effects,” Opt. Express 22(22), 27643–27654 (2014). 22. K. Kim, “Enhanced optical phase conjugation in nonlinear metamaterials,” Opt. Express 22(S7), A1744–A1752 (2014). 23. S. Sun, N. Yi, W. Yao, Q. Song, and S. Xiao, “Enhanced second-harmonic generation from nonlinear optical metamagnetics,” Opt. Express 22(22), 26613–26620 (2014). 24. C. Huang, F. Ye, Z. Sun, and X. Chen, “Tunable subwavelength photonic lattices and solitons in periodically patterned grapheme monolayer,” Opt. Express 22(24), 30108–30117 (2014). 25. Y. Sun, G. Qiao, and G. Sun, “Direct generation of graphene plasmonic polaritons at THz frequencies via four wave mixing in the hybrid graphene sheets waveguides,” Opt. Express 22(23), 27880–27891 (2014). 26. J. Parravicini, M. Brambilla, L. Columbo, F. Prati, C. Rizza, G. Tissoni, A. J. Agranat, and E. DelRe, “Observation of electro-activated localized structures in broad area VCSELs,” Opt. Express 22(24), 30225– 30233 (2014). 27. M. Gaafar, Ph. Richter, H. Keskin, Ch. Möller, M. Wichmann, W. Stolz, A. Rahimi-Iman, and M. Koch, “Selfmode-locking semiconductor disk laser,” Opt. Express 22(23), 28390–28399 (2014). 28. M. D. I. Castillo, S. C. Cerda, and D. R. Martinez, “Splitting after collision of high-order bright spatial solitons in Kerr media,” Opt. Express 22(25), 30769–30776 (2014). 29. A. Ziołkowski, “Numerical method for an analysis of nonlinear light propagation in photorefractive media - time nonlocal approach,” Opt. Express 22(S7), A1907–A1925 (2014). 30. A. Alberucci, N. Kravets, A. Piccardi, O. Buchnev, M. Kaczmarek, and G. Assanto, “Nematicons in planar cells subject to the optical Freedericksz threshold,” Opt. Express 22(25), 30663–30668 (2014). 31. Z. Chen, J. Liu, S. Fu, Y. Li, and B. A. Malomed, “Discrete solitons and vortices on two-dimensional lattices of PT-symmetric coupler,” Opt. Express 22(24), 29679–29692 (2014). 32. F. Di Mei, J. Parravicini, D. Pierangeli, C. Conti, A. J. Agranat, and E. DelRe, “Anti-diffracting beams through the diffusive optical nonlinearity,” Opt. Express 22(25), 31434–31439 (2014). 33. L. Ge, M. Shen, C. Ma, T. Zang, and L. Dai, “Gap solitons in PT-symmetric optical lattices with higher-order diffraction,” Opt. Express 22(24), 29435–29444 (2014). 34. J. Qin, G.-W. Lu, T. Sakamoto, K. Akahane, N. Yamamoto, D. Wang, C. Wang, H. Wang, M. Zhang, T. Kawanishi, and Y. Ji, “Simultaneous multichannel wavelength multicasting and XOR logic gate multicasting for three DPSK signals based on four-wave mixing in quantum-dot semiconductor optical amplifier,” Opt. Express 22(24), 29413–29423 (2014). 35. T. Kodama, K. Morita, G. Cincotti, and K. Kitayama, “A low-power photonic quantization approach using OFDM subcarrier spectral shifts,” Opt. Express 22(23), 28719–28730 (2014). 36. A. Lorences-Riesgo, L. Liu, S. L. I. Olsson, R. Malik, A. Kumpera, C. Lundstrom, S. Radic, M. Karlsson, and P. A. Andrekson, “Quadrature demultiplexing using a degenerate vector parametric amplifier,” Opt. Express 22(24), 29424–29434 (2014). 37. J. Liu, F. Tan, H. Shi, and P. Wang, “High-power operation of silica-based Raman fiber amplifier at 2147 nm,” Opt. Express 22(23), 28383–28389 (2014). 38. M. Kuznetsov, O. Vershinin, V. Tyrtyshnyy, and O. Antipov, “Low-threshold mode instability in Yb3 + -doped few-mode fiber amplifiers,” Opt. Express 22(24), 29714–29725 (2014). 39. F. Vanier, Y.-A. Peter, and M. Rochette, “Cascaded Raman lasing in packaged high quality As₂S₃ microspheres,” Opt. Express 22(23), 28731–28739 (2014). 40. T. Wang, T. Yang, D. Jia, Z. Wang, and C. Ge, “Multi-wavelength lasers with suppressed spectral linewidth of 10 kHz,” Opt. Express 22(22), 26862–26871 (2014). 41. A. Billat, S. Cordette, and C.-S. Brès, “Broadly tunable source around 2050 nm based on wideband parametric conversion and thulium-holmium amplification cascade,” Opt. Express 22(22), 26635–26641 (2014). 42. S. Shahin, S. Mehravar, P. Gangopadhyay, N. Peyghambarian, R. A. Norwood, and K. Kieu, “Multiphoton microscopy as a detection tool for photobleaching of EO materials,” Opt. Express 22(25), 30955–30962 (2014). 43. P. Parra-Rivas, D. Gomila, M. A. Matias, P. Colet, and L. Gelens, “Effects of inhomogeneities and drift on the dynamics of temporal solitons in fiber cavities and microresonators,” Opt. Express 22(25), 30943–30954 (2014).
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44. O. A. Gorbunov, S. Sugavanam, and D. V. Churkin, “Revealing statistical properties of quasi-CW fibre lasers in bandwidth-limited measurements,” Opt. Express 22(23), 28071–28076 (2014). 45. B. Klus, U. A. Laudyn, M. A. Karpierz, and B. Sahraoui, “All-optical measurement of elastic constants in nematic liquid crystals,” Opt. Express 22(24), 30257–30266 (2014). 46. A. B. Ortega, M. L. Carrasco, M. M. Otero, E. R. Lara, E. V. Ramírez, and M. D. Castillo, “Analytical expressions for Z-scan with arbitrary phase change in thin nonlocal nonlinear media,” Opt. Express 22(23), 27932–27941 (2014). 47. X. Wang, H. Ren, N. An, X. Zhao, Y. Zheng, and X. Chen, “Large acceptance of non-collinear phase-matching second harmonic generation on the surface of an anomalous-like bulk dispersion medium,” Opt. Express 22(23), 28234–28239 (2014). 48. V. A. Makarov, V. M. Petnikova, and V. V. Shuvalov, “Adiabatic modulation of a cnoidal wave by a breather with orthogonal circular polarization in an isotropic gyrotropic nonlinear medium,” Opt. Express 22(22), 26607– 26612 (2014). 49. L. Yuan and Y. Y. Lu, “Bilateral symmetry breaking in nonlinear circular cylinders,” Opt. Express 22(24), 30128–30134 (2014). 50. H. Kianirad, A. Zukauskas, Th. Frisk, C. Canalias, and F. Laurell, “Contact poling of Rb: KTiOPO4 using a micro-structured silicon electrode,” Opt. Express 22(24), 30128–30134 (2014).
1. General information The conference “Nonlinear Photonics” celebrated its 25th anniversary in Barcelona in July 2014. The first one of this series has been organised by George Stegeman and Roger Stolen in Houston in 1989 under the name “Nonlinear guided waves”. The complete list of previous conferences can be found in [1]. Traditionally, the conference was preceded by the satellite workshop on the hot subjects of modern nonlinear optics held on July 25–26, 2014. It was kindly hosted by ICFO (The Institute of Photonics Sciences) due to generosity of its founding and acting director Lluis Torner. This year the major topics were reflected in the title of the workshop: “Rogue waves, dissipative solitons, plasmonics, supercontinuum and special fibres”. Not surprisingly, the scope of the workshop was wider than that. Leading scientists in nonlinear optics were invited to take part in this event. The venue of the conference (Fira Centre, Barcelona) contributed to the success of the conference. The choice of Barcelona as the place for the conference also provided its success. The city is a popular destination for tourists from all over the world. It is one of the major European cultural centres. Its location on the Mediterranean attracts many holiday makers. The presence of the ICFO in Barcelona makes it one of the major centres on photonics in Europe. The conference was co-located with three other conferences with the common name “Advanced Photonics.” The other three conferences included “Bragg Gratings, Photosensitivity and Poling in Glass Waveguides (BGPP),” “Optical Sensors (SENSORS)” and “Specialty Optical Fibers & Applications (SOF)”. The set of articles presented in this focus issue provides a general impression about the research areas considered at the conference, although, of course, not the whole range of topics presented at the conference is covered here. We received a total of 68 submissions with 49 papers accepted and published. Only high quality submissions have been chosen for publication. The former General Chairs of the conference (N. Akhmediev, K. Rottwitt and J. M. Dudley) express the wish that traditions will be continued with the organisation of future events. The next conference “Nonlinear Photonics” is to be held in Australia in 2016. General Chairs of the conference are Yaroslav Kartashov and Alex Gaeta. Program Chairs are: GianLuka Oppo, Stefan Wabnitz and Andrey Sukhorukov. 2. Short description of the papers presented in this focus issue Below, we present the short description of each article categorised according to the content. Classification cannot be perfect as the articles may belong to two or more areas of research. Nevertheless, the sectioning may simplify searching of a particular paper that is of interest for
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 486
a reader. We also note that the subheadings here are different from the standard ones used in the table of content. This offers an alternative way of searching for the work of interest. 2.1. Supercontinuum generation The authors of [2] studied intensity stability and wavelength correlations of near-infrared supercontinuum generation in all-normal flattened dispersion, all-solid soft glass photonic crystal fiber. They used dispersive Fourier transformation method to measure shot-to-shot resolved spectra with pumping by a sub-picosecond, fiber-based chirped pulse amplification system. The results suggest a convenient way of stabilizing of shot-to-shot coherence. The authors of [3] experimentally demonstrated the generation of a supercontinuum (SC) in a − Si: H photonic wire waveguide at telecommunication wavelengths using femtosecond input pulse with energy lower than 5 pJ. A direct comparison of SC generation shows the higher performances of a − Si: H over c − Si waveguides for broadband low power SC generation at telecommunication wavelengths. The authors of [4] numerically studied the supercontinuum generation and pulse compression in a special all-normal dispersion photonic crystal fiber with a flat-top dispersion curve, pumped by the Ti:Sapphire laser at 800 nm. The influence of realistic fibre fabrication errors on the SC generation and pulse compression are investigated. For generating the supercontinuum, the authors of [5] propose to first self-similarly compress a high power picosecond pump pulse by injecting it into a fiber with variable increasing nonlinearity. The compressed pulse is then injected into a dispersion-shifted fibre for SC generation. In this scheme, the noise level of the compressed pulse can be reduced. The authors of [6] report mid-infrared supercontinuum generation in As2Se3 chalcogenide microwires with the added advantage of using low energy pulses. The generated SC cover two octaves of bandwidth from 1.1 μm to 4.4 μm at −30 dB. This may exceed the supercontinuum bandwidth reported earlier in As2Se3 microwires by a factor of 3.5. 2.2. Rogue waves The authors of [7] performed a numerical analysis of rogue waves statistics in semiconductor lasers with continuous-wave optical injection. They show that, when rogue waves are not suppressed by the current modulation, their probability of occurrence strongly depends on the phase of the modulation. The authors of [8] study, analytically, dark rogue wave solutions in normal dispersion birefringent optical fibers. They obtained exact rational solutions of the coupled nonlinear Schrödinger equations in the form of vector dark “three-sister” rogue waves. The authors of [9] derived the PT-symmetric and PT-antisymmetric Akhmediev breather (AB) and Kuznetsov-Ma (KM) soliton train solutions in the frame of (2+1)-dimensional coupled nonlinear Schrödinger equations with variable-coefficients. This is done for PTsymmetric coupled waveguides with gain and loss. They investigated the controllable behaviours of AB and KM soliton trains in a diffraction decreasing medium with exponential profile. The authors of [10] numerically analysed rogue waves in an optical fibre taking into account the third order dispersion. They show that the rogue waves are formed due to the collision of quasi-solitons in a fibre with anomalous dispersion. 2.3. Dissipative solitons Based of numerical study of the generalised complex Ginzburg-Landau equation, the authors of [11] found a new type of dissipative solitons named “dissipative Raman solitons”. They demonstrated that the increase of the group-delay dispersion can suppress the multi-pulsing instability and leads to the formation of the dissipative Raman soliton. They also showed that in practice, a spectral filter can extend the stability regions of high-energy pulses.
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 487
An analysis of collision outcomes between stable dissipative vortices of the threedimensional cubic-quintic complex Ginzburg-Landau equation is presented in [12]. The considered scenarios include merger of the vortices into a single one, creation of an extra vortex and quasi-elastic interaction. 2.4. Pulse amplification and generation In [13], the authors generated 1250 nm pulses in dual zero dispersion photonic crystal fiber. The durations and energies make these pulses useful for producing light at 1250 nm for multiphoton microscopy. The authors of [14] demonstrated real-time demultiplexing to the spatial domain and single- shot coherent detection of a phase modulated ultrashort pulse train by time-to-space conversion. They showed that time-to-space conversion can be a valuable tool in ultrahigh bit rate OTDM optical communications. In [15], it is shown, theoretically, that short (1-2 m) conventional single mode fiber can be used for triangular pulse formation in the steady-state regime without pre-chirping when femtosecond pulses are used for pumping. The pulse parameters found in this work can serve as a guide for experiments and implementation of all-fiber schemes in optical signal processing. Using a surface integral equation method, the authors of [16] studied the second order non- linear optical response of plasmonic metamolecules supporting Fano resonances. They showed that the typical lineshape of Fano resonances is also clearly observable in the nonlinear regime. The results can be useful for the design of efficient nonlinear plasmonic metamolecules with controlled nonlinear radiation. The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers are described in [17]. It is shown that reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and providing a reproducible spectral phase. The authors of [18] demonstrated generation of dark pulses by an erbium-doped fibre ring laser with net anomalous dispersion. A side-polished fibre coated with carbon nanotube layer is embedded into the laser to enhance the birefringence and nonlinearity of the laser cavity. The dual-wavelength domain-wall dark pulses were obtained at a relatively low pump threshold of 50.6 mW. The authors of [19] studied the shortest possible optical soliton and explicitly calculated its spectrum using the so-called short pulse equation. The latter applies to ultra-short solitons in transparent materials like fused silica thus being relevant for optical fibers. The authors of [20] demonstrated nanosecond range rectangular wave-breaking-free pulse generation in an actively mode locked Yb-doped fiber laser. The approach is based on a combined action of active periodic cavity loss modulation and nonlinear polarization rotation effect. The laser presents flexible tunabilities in pulse width, pulse energy and pulse shape. The authors of [21] numerically investigated nonlinear self-polarization flipping in a silicon waveguide. They identified specific silicon waveguide geometries that enhance this effect. In optimized waveguides, the nonlinear self-polarization flipping can be observed with few tens of watts peak power pulses with widths as short as 60 ps and laser noise level as large as 7%. 2.5. Metamaterials Optical phase conjugation by degenerate four-wave mixing in nonlinear metamaterials is studied theoretically in [22] by solving the coupled wave equations. It is found that the efficiency of phase conjugation can be significantly enhanced due to the enhancement of electromagnetic fields in various metamaterial structures. A numerical simulation of second-harmonic generation (SHG) in a nonlinear magnetic metamaterial is presented in [23]. The convertion efficiency of SHG can be significantly
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 488
enhanced by almost four orders of magnitude by inserting a nonlinear material into the high local field area of magnetic metamaterial consisting of periodic arrays of paired thin silver strips. 2.6. Graphene in optics The authors of [24] studied linear and nonlinear mode properties in a periodically patterned graphene sheet. They found graphene lattice solitons at the deep-subwavelength scales in two dimensions due to the combination of graphene self-focusing nonlinearity and the graphene plasmonic confinement effects. The authors of [25] proposed a compact waveguide incorporating a high-index nano-ridge sandwiched between graphene sheets for direct generation of graphene plasmonic polaritons via four wave mixing. The proposed waveguide supports graphene plasmonic polariton modes at the THz frequencies and photonic modes at the infrared wavelengths. The proposed waveguide may have a great potential as an integrated chip-scale graphene plasmonic polariton source. 2.7. Vertical-cavity surface-emitting lasers The electro-activation of a localized optical structure in a coherently driven broad-area vertical-cavity surface-emitting laser (VCSEL) operated below threshold has been observed experimentally in [26]. Control is achieved by electro-optically steering a writing beam through a pre-programmable switch based on a photorefractive funnel waveguide. The authors of [27] highlight recent achievements in the area of vertical-external-cavity surface-emitting lasers (VECSELs). They provide an evidence of mode-locking in a saturable absorber-free device. A beam-profile measurement reveals the excellent beam quality of the device. 2.8. Photorefractive media, liquid crystals, spatial and gap solitons Numerical studies of (1 + 1)-dimensional higher order bright spatial solitons in a Kerr nonlinear media in [28] showed that after the collision, the higher order solitons split into the first order solitons. Their number corresponds to the order of the original soliton. Various collision scenarios of higher order solitons are considered. Nonlinear light propagation in nonlocal photorefractive media is analyzed in [29] using numerical methods. Two algorithms are presented, and compared in terms of physical results and computing times. The tests were carried out for a one-carrier model that describes most of photorefractive media, and for a model with bipolar transport and hot electron effect, used in descriptions of semiconductor materials. The authors of [30] investigated theoretically and experimentally self-trapping of light beams in nematic liquid crystals. They studied the role of the optical Fréedericksz transition in the nonlinear propagation of finite-size optical beams. In particular, they predicted and observed a bistable behaviour accompanied by hysteresis as power changed up and down. In [31], the authors introduced a 2D network built of PT-symmetric dimers with on-site cubic nonlinearity. The gain and loss elements of the dimers are linked by parallel squareshaped lattices. The system supports PT-symmetric and antisymmetric solitons and on-sitecentered solitary vortices. Stability regions of these discrete solitons in the parameter space are identified through the computation of stability eigenvalues and verified by numerical simulations. The authors of [32] observed anti-diffracting beams supported by the peak-intensity independent diffusive nonlinearity. The beams are shown to be able to shrink below their diffraction-limited size in photorefractive lithium-enriched potassium-tantalate-niobate (KTN:Li). The authors of [33] studied the existence and stability of gap solitons in the semi-infinite gap of a parity-time (PT)-symmetric optical lattice with a higher-order diffraction. They
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 489
showed that the Bloch bands and band gaps of PT-symmetric optical lattice depend crucially on the coupling constant of the fourth-order diffraction. Fundamental solitons are found to be linearly stable with arbitrary positive value of the coupling constant. 2.9. Optical information processing In [34], the authors experimentally demonstrated simultaneous multichannel wavelength multi- casting and exclusive-OR logic gate multicasting for three 10 Gbps non-return-to-zero differential phase-shift-keying signals in quantum-dot semiconductor optical amplifier by exploiting the four-wave mixing process. All the new generated channels are with a power penalty less than 1.2 dB at a BER of 10−9. The authors of [35] proposed and demonstrated an energy-efficient photonic analog-todigital converter based on spectral shifts of orthogonal frequency division multiplexing subcarriers and optical quantisation using a new frequency-packed arrayed waveguide grating device. They showed the feasibility of a 2, 3 and 4-bit optical quantisation scheme. The authors of [36] consider quadrature demultiplexing of a quadrature phase-shift keying signal into two cross-polarized binary phase-shift keying signals with negligible penalty at bit error rate equal to 10−9. A stable quadrature decomposition phase-locked loop scheme is proposed that is based on detecting the envelope of one of the signals after demultiplexing. 2.10. Lasers, amplifiers and other light sources The authors of [37] demonstrated a 2147 nm silica-based Raman fiber amplifier with output power of 14.3 W directly pumped with a 1963 nm CW thulium-doped all-fiber masteroscillator power-amplifier. The conversion efficiency is 38.5% from 1963 nm to 2147 nm in the HNLF. The authors of [38] observed the spatio-temporal instability of the fundamental mode in Y b3+ doped few-mode PM fibre amplifiers with a core diameter of 8.5 μm. The instability in the experiment and in theory is caused by the nonlinear power transformation of the LP01 fundamental mode into higher-order modes. Cascaded Raman lasing has been observed in high-Q As2S3 microspheres in [39]. Cascaded stimulated Raman scattering emission is obtained up to the 5-th order for a pump wavelength of 1557 nm and up to the 3-rd order for a pump wavelength of 1880 nm. High-Q As2S3 microspheres are used in a self-frequency locking laser setup without an external laser source. In [40], a method to suppress the linewidths of the multi-wavelength light source from 6 MHz to 10 kHz using an all-optical approach is proposed and demonstrated. More than 8 wavelengths over 10 nm are suppressed simultaneously using the approach of this work. Each wavelength of the multi-wavelength operates in single longitudinal mode. In [41], the authors report the design of a short-wave infrared continuous-wave light source with 20 mW average output power, and with a wavelength that can be selected in the 2000–2100 nm range. The operating principle is based on the simultaneous broadband parametric conversion of two seeds in a highly nonlinear silica fiber. 2.11. Optical measurements and frequency combs The authors of [42] used the multi-photon microscopy operating at 1550 nm as a rapid characterisation tool for studying the photostability of three well-known electro-optical materials. The technique is rapid, accurate, and can be used to study the photostability of a broad range of materials. The authors of [43] studied the effect of inhomogeneities and drift on temporal solitons and Kerr frequency combs in fibre cavities and microresonators. The theory is based on the Lugiato-Lefever equation with periodic boundary conditions. The work can be relevant for all applications relying on stable frequency combs.
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 490
In [44], the authors developed a model of bandwidth-limited measurements. They predict universal laws for intensity probability density function and intensity auto-correlation function of ideal completely stochastic source of Gaussian statistics. The variables are limited measurement bandwidth and measurement noise level. The experimental results are in good agreement with model predictions. The authors of [45] present a new all-optical method to measure elastic constants connected with twist and bend deformations. The method is based on the optical Fréedericksz threshold effect induced by the linearly polarized electro-magnetic wave. The results of experimental measurements are in good agreement with the values obtained by other methods based on an electro-optical effect. 2.12. Nonlinear wave propagation Analytical expressions for normalized transmittance of a thin material with simultaneous nonlocal nonlinear change in refraction and absorption are reported in [46]. Experimental results confirm the analytic predictions. The authors of [47] investigated non-collinear phase-matching second harmonic wave, which is generated at the inner surface of a z-cut 5%/mol MgO: LiNbO3 crystal. The ranges of angle, temperature and wavelength in this configuration are measured to be ≈ 0.51°, ≈ 4.1°C and ≈ 6nm, respectively. An approximate analytical solution of the non-integrable problem of steady-state adiabatic interaction of a cnoidal wave with a breather is obtained in [48]. It is shown that the interaction results in a strong amplitude and frequency modulation of the information signal. The authors of [49] analysed the scattering of plane waves by one or two circular cylinders with Kerr nonlinearity. They found solutions that break a reflection symmetry in the lateral direction perpendicular to the incident wave vector. 2.13. Fabrication of optical gratings The authors of [50] presented a new method for fabrication of periodically poled Rb: KTiOPO4 RKTP samples using an array of silicon electrodes. They showed that using this technique high quality quasi-phase matching gratings can be reproducibly fabricated. Acknowledgments N. A. acknowledges the support of the Australian Research Council (Discovery Project number DP140100265) and support from the Volkswagen Stiftung.
#232136 - $15.00 USD Received 7 Jan 2015; published 9 Jan 2015 © 2015 OSA 12 Jan 2015 | Vol. 23, No. 1 | DOI:10.1364/OE.23.000484 | OPTICS EXPRESS 491
