Nonlinear Optics has continued to develop over the last few years at an extremely fast pace, with significant advances being reported in nonlinear optical metamaterials, optical signal processing, quantum optics, nonlinear optics at subwavelength scale, and biophotonics. These exciting new developments have generated significant potential for a broad spectrum of technological applications in which nonlinear-optical processes play a central role.
© 2013 Optical Society of America
Impressive progress in nanofabrication techniques has led to unprecedented control of the materials and geometrical design parameters of metallic and dielectric nanostructures. These advances have facilitated important breakthroughs in relatively new areas of nonlinear optics, namely nonlinear-optical metamaterials and nonlinear plasmonics, and have generated a renewed drive towards increased device integration at the chip scale. We have witnessed equally exciting developments in more traditional areas of nonlinear optics as well, including new techniques for spectral and temporal optical pulse shaping, wavelength mixing and nonlinear-frequency generation, multi-wavelength broadband optical sources and frequency-comb generators, ultra-compact lasers, and nonlinear-optical switching.
This year’s Focus Issue consists of contributions from the authors of papers that have been accepted for presentation at this year’s Nonlinear Optics (NLO) 2013 conference held at The Fairmont Orchid, Kohala Coast, Hawaii, USA on 21-26 July 2013.
We start this feature with an exposé by Elsa Garmire, on how nonlinear optics is relevant for our daily life . Much of the contemporary nonlinear optics research of today is devoted to optical frequency combs, and in this feature this is covered by three papers [2–4]. In  a mid-IR comb around 4300 nm is reported, with state-of-the-art power density. An analysis of the timing jitter of a Kerr-comb is reported in , and  provides a theoretical analysis of cross-phase modulation-induced comb.
Fiber optic nonlinearities [5–9] remain another important area, and nonlinearities in multimode fibers receive increasing interest. In [5,6] the modal dynamics of few-mode fibers are in focus, and in  a multimode junction is reported for mode locking. A theoretical analysis of Raman-induced quantum noise in fiber-based parametric amplifiers is given in , and  deals with the problem of carrier depletion in an active microstructured waveguide.
Nonlinear optical processes in which the interacting waves are surface plasmons are investigated in [10–12]. In  a three-wave mixing process is analyzed in which a photon and a surface plasmon are annihilated simultaneously to generate a photon, whose frequency is equal to the sum of the frequencies of the two incoming waves; the enhancement of transverse-magnetic second-harmonic generation (SHG) due to the excitation of surface plasmons is studied in ; whereas in , the enhancement of nonlinear optical effects due to the excitation of optical Tamm plasmon-polaritons in one-dimensional photonic crystal structures is reported.
A significant number of papers are devoted to harmonic generation and wavelength conversion [13–19]. In , parametric down-conversion from near-IR to mid IR (2-5 micrometers) is demonstrated. A periodically poled Lithium Niobate (PPLN) waveguide is used in , via SHG, to broadcast channels in the communication C-band around 1550 nm. A PPLN waveguide is also used in , as two tunable parametric-oscillator sources in the mid-IR range, which then are difference-frequency mixed to generate light in the 8-10 micrometer region. SHG generated from gold nanoparticles is demonstrated in , and in  by using Strontium Barium Niobate. The latter is used to obtain information of domain patterns and structures. The spectral properties of an aperiodic PPLN-based frequency doubler are investigated in . In , a high-power microchip Nd:YAG laser is used to demonstrate second and up to ninth-harmonic generation in various nonlinear media, and the first 118 nm UV generation is accomplished.
The role of optical nonlinearities in ultrafast laser sources is explored [20,21]. In , Kerr-lens modelocking of a vertical external-cavity surface-emitting laser (VECSEL) is analyzed and experimentally demonstrated, while in , the chaotic regime of chirped-pulse oscillators having significant third-order dispersion is investigated experimentally. In this second case, the chaotic regime is found to have long-term stability and is accompanied by a characteristic spectral shape and may be recognized by using special filters and by second-harmonic or two-photon absorption detectors. A new development in Raman spectroscopy is being pursued with the goal of suppressing the nonresonant background signal in coherent anti-Stokes Raman scattering (CARS) spectroscopy by the investigation of the relationship between four-wave mixing (FWM) and cascaded second-order wavelength conversion . Finally special materials are also being explored for their roles in the control of light and nonlinear-optical processes [23,24]. In , spatial light modulators are used to implement fully randomized nondiffracting beams of variable structural size, to control the modulation length (photonic grain size) as well as the depth (disorder strength) of a random potential induced within a photorefractive crystal; Anderson localization is demonstrated and analyzed in the ensuing optically induced randomized potential. In , slabs of materials with near-zero permittivity display greatly enhanced nonlinear optical processes. The field enhancement arises from the continuity of the normal component of the displacement field relative to the surface, which in turn, drastically enhances nonlinear optical processes such as second- and third-harmonic generation.
To summarize, the set of topics in this year’s Focus Issue reflect the most recent advances in the field of nonlinear optics. We believe that these current advances will stimulate future research that will further knowledge and understanding, as well as future breakthroughs in nonlinear optical phenomena.
The Topical Editors would like to thank all the authors who have contributed to this issue, and the Peer Review Manager Ms. Carmelita Washington and the staff of Optics Express for their continuous help during the preparation of this Focus Issue.
References and links
1. E. Garmire, “Nonlinear optics in daily life,” Opt. Express 21(25), 30532–30544 (2013). [CrossRef]
2. I. Galli, F. Cappelli, P. Cancio, G. Giusfredi, D. Mazzotti, S. Bartalini, and P. De Natale, “High-coherence mid-infrared frequency comb,” Opt. Express 21(23), 28877–28885 (2013). [CrossRef]
3. A. B. Matsko and L. Maleki, “On timing jitter of mode locked Kerr frequency combs,” Opt. Express 21(23), 28862–28876 (2013). [CrossRef]
4. R. Maram and J. Azaña, “Spectral self-imaging of time-periodic coherent frequency combs by parabolic cross-phase modulation,” Opt. Express 21(23), 28824–28835 (2013). [CrossRef]
5. J. Carpenter, C. Xiong, M. J. Collins, J. Li, T. F. Krauss, B. J. Eggleton, A. S. Clark, and J. Schröder, “Mode multiplexed single-photon and classical channels in a few-mode fiber,” Opt. Express 21(23), 28794–28800 (2013). [CrossRef]
6. L. Rishøj, P. Kristensen, S. Ramachandran, and K. Rottwitt, “Experimental demonstration of intermodal nonlinear effects between full vectorial modes in a few moded fiber,” Opt. Express 21(23), 28836–28841 (2013). [CrossRef]
7. E. Nazemosadat and A. Mafi, “Nonlinear switching in multicore versus multimode waveguide junctions for mode-locked laser applications,” Opt. Express. in press.
8. S. M. M. Friis, K. Rottwitt, and C. J. McKinstrie, “Raman and loss induced quantum noise in depleted fiber optical parametric amplifiers,” Opt. Express 21(24), 29320–29331 (2013). [CrossRef]
9. Y. Chen and J. Mørk, “Theory of carrier depletion and light amplification in active slow light photonic crystal waveguides,” Opt. Express 21(24), 29392–29400 (2013). [CrossRef]
10. J. Heckmann, M.-E. Kleemann, N. B. Grosse, and U. Woggon, “The dual annihilation of a surface plasmon and a photon by virtue of a three-wave mixing interaction,” Opt. Express 21(23), 28856–28861 (2013). [CrossRef]
11. W. Zheng, A. T. Hanbicki, B. T. Jonker, and G. Lüpke, “Surface plasmon-enhanced transverse magnetic second-harmonic generation,” Opt. Express 21(23), 28842–28848 (2013). [CrossRef]
12. K. J. Lee, J. W. Wu, and K. Kim, “Enhanced nonlinear optical effects due to the excitation of optical Tamm plasmon polaritons in one-dimensional photonic crystal structures,” Opt. Express 21(23), 28817–28823 (2013). [CrossRef]
13. H. Suchowski, P. R. Krogen, S.-W. Huang, F. X. Kärtner, and J. Moses, “Octave-spanning coherent mid-IR generation via adiabatic difference frequency conversion,” Opt. Express 21(23), 28892–28901 (2013). [CrossRef]
14. M. Ahlawat, A. Bostani, A. Tehranchi, and R. Kashyap, “Tunable single-to-dual channel wavelength conversion in an ultra-wideband SC-PPLN,” Opt. Express 21(23), 28809–28816 (2013). [CrossRef]
15. V. Kemlin, D. Jegouso, J. Debray, E. Boursier, P. Segonds, B. Boulanger, H. Ishizuki, T. Taira, G. Mennerat, J.-M. Melkonian, and A. Godard, “Dual-wavelength source from 5%MgO:PPLN cylinders for the characterization of nonlinear infrared crystals,” Opt. Express 21(23), 28886–28891 (2013). [CrossRef]
16. J. Butet, A. Lovera, and O. J. F. Martin, “Detecting the trapping of small metal nanoparticles in the gap of nanoantennas with optical second harmonic generation,” Opt. Express 21(23), 28710–28718 (2013). [CrossRef]
17. M. Ayoub, M. Paßlick, K. Koynov, J. Imbrock, and C. Denz, “Effect of the domain shape on noncollinear second-harmonic emission in disordered quadratic media,” Opt. Express. in press.
18. A. Bostani, M. Ahlawat, A. Tehranchi, R. Morandotti, and R. Kashyap, “Tailoring and tuning of the broadband spectrum of a step-chirped grating based frequency doubler using tightly-focused Gaussian beams,” Opt. Express 21(24), 29847–29853 (2013). [CrossRef]
19. R. Bhandari, N. Tsuji, T. Suzuki, M. Nishifuji, and T. Taira, “Efficient second to ninth harmonic generation using megawatt peak power microchip laser,” Opt. Express 21(23), 28849–28855 (2013). [CrossRef]
20. A. R. Albrecht, Y. Wang, M. Ghasemkhani, D. V. Seletskiy, J. G. Cederberg, and M. Sheik-Bahae, “Exploring ultrafast negative Kerr effect for mode-locking vertical external-cavity surface-emitting lasers,” Opt. Express 21(23), 28801–28808 (2013). [CrossRef]
21. E. Sorokin, N. Tolstik, V. L. Kalashnikov, and I. T. Sorokina, “Chaotic chirped-pulse oscillators,” Opt. Express 21(24), 29567–29577 (2013). [CrossRef]
22. G. I. Petrov, M. Zhi, and V. Yakolev, “Coherent anti-stokes Raman spectroscopy utilizing phase mismatched cascaded quardratic optical interactions in nonlinear crystals,” Opt. Express. in press.
23. M. Boguslawski, S. Brake, J. Armijo, F. Diebel, P. Rose, and C. Denz, “Analysis of transverse Andersen localization in refractive index structures with customized random potential,” Opt. Express in press.
24. M. A. Vincenti, D. de Ceglia, and M. Scalora, “Nonlinear dynamics in low permittivity media: the impact of losses,” Opt. Express 21(24), 29949–29954 (2013). [CrossRef]