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Optical pulses in silicon nanowires


Self-similar pulse generation and compression


Pulse propagation in PhC waveguides


Zero-n metamaterials



Theoretical Modeling of Optical Pulse Dynamics in Silicon Photonic Nanowires
The distinctive features of silicon photonic nanowires are that they have extremely large third-order susceptibility and strongly enhanced dispersive properties. As a result, the relatively low threshold powers for nonlinear optical effects in these wires make them potential candidates for functional on-chip nonlinear optical devices of just a few millimeters in length; conversely, the absence of nonlinear optical impairment is important for the use of silicon wires in on-chip interconnects. In addition, the characteristic length scales of linear and nonlinear optical effects in Si wires are markedly different from those in commonly used optical guiding systems, such as optical fibers or photonic crystal fibers, and therefore guiding structures based on silicon wires represent ideal optical media for investigating new and intriguing physical phenomena. In this context, we are actively involved in several projects aimed to developed rigorous, comprehensive theoretical models and software tools that describe the propagation of optical pulses in silicon-based deep sub-wavelength waveguides. In particular, we seek to develop models that account for linear optical effects, such as material and waveguide dispersion, free-carrier absorption, and free-carrier induced dispersion, nonlinear effects, such as self- and cross-phase modulation, two-photon absorption, spontaneous and stimulated Raman scattering, and the frequency dispersion of the effective optical nonlinearity of the waveguide, as well as the mutual interaction between the optical field and the free-carriers. This work is an ongoing collaboration with Prof. Richard Osgood's group from Columbia University's Department of Electrical Engineering.

Relevant publications:
  • X. Chen, N. C. Panoiu, and R. M. Osgood, Jr., Theory of Raman-mediated pulsed amplification in silicon-wire waveguides, IEEE J. Quantum Electron. 42, 160 (2006). [pdf]
  • J. I. Dadap, N. C. Panoiu, X. Chen, I-W. Hsieh, X. Liu, C.-Y. Chou, E. Dulkeith, S. J. McNab, F. Xia, W. M. J. Green, L. Sekaric, Y. A. Vlasov, and R. M. Osgood, Jr., Nonlinear-optical phase modification in dispersion-engineered Si photonic wires, Opt. Express 16, 1280 (2008). [pdf]
  • N. C. Panoiu, X. Liu, and R. M. Osgood, Jr., Self-steepening of ultrashort pulses in silicon photonic nanowires, Opt. Lett. 34, 947 (2009) (also featured in the Virtual Journal of Nanoscale Science and Technology 19 (17), April 27, 2009 and the Virtual Journal of Ultrafast Science 8 (5), May, 2009). [pdf]
  • R. M. Osgood, Jr., N. C. Panoiu, J. I. Dadap, X. Liu, X. Chen, I-W. Hsieh, E. Dulkeith, W. M. J. Green, and Y. A. Vlasov, Engineering nonlinearities in nanoscale optical systems: physics and applications in dispersion-engineered silicon nanophotonic wires, Adv. Opt. Photon. 1, 162 (2009). [pdf]
  • J. B. Driscoll, R. R. Grote, X. Liu, J. I. Dadap, N. C. Panoiu, and R. M. Osgood, Jr., Directionally anisotropic Si nanowires: on-chip nonlinear grating devices in uniform waveguides, Opt. Lett. 36, 1416 (2011). [pdf]


Generation of Optical Similaritons and Optical Pulse Compression in Silicon Photonic Nanowires
Due to their strongly enhanced frequency dispersion and optical nonlinearity, silicon photonic nanowires represent an ideal test bed for exploring new physical regimes of optical pulse dynamics in nonlinear media. In particular, these photonic nanodevices provide an effective chip-scale aproach for optical pulse generation as well as temporal and spectral reshaping of optical pulses. In this context, in collaboration with Prof. Richard Osgood's group from Columbia University's Department of Electrical Engineering, we have recently demonstrated that by tapering photonic nanowire waveguides made of silicon one can generate parabolic self-similar optical pulses both at telecom and mid-IR wavelengths. Our computational study is based on a rigorous theoretical model, which fully describes the influence of linear and nonlinear optical effects on pulse propagation in silicon photonic wire waveguides with arbitrarily varying transverse size. Numerical simulations demonstrate that in the normal dispersion regime Gaussian pulses evolve naturally into parabolic pulses, upon their propagation in millimeter-long tapered silicon photonic wire waveguides, the efficiency of this pulse reshaping process being strongly dependent on the spectral and pulse parameter regime in which the device operates. In addition, we have demonstrated that one could achieve temporal compression of ultra-short optical pulses by more than three times in millimetre-long adiabatically tapered silicon photonic nanowire waveguides when the optical pulses propagate in the soliton regime.

Relevant publications:
  • S. Lavdas, J. B. Driscoll, H. Jiang, R. R. Grote, R. M. Osgood, Jr, and N. C. Panoiu, Generation of parabolic similaritons in tapered silicon photonic wires: comparison of pulse dynamics at telecom and mid-infrared wavelengths, Opt. Lett. 38, 3953 (2013). [pdf]
  • S. Lavdas, J. B. Driscoll, R. R. Grote, R. M. Osgood, Jr, and N. C. Panoiu, Analysis of optical pulse compression in tapered silicon photonic wires, Optics Express 22, 6296 (2014). [pdf]


Optical Pulse Propagation in Photonic Crystal Slab Waveguides
An effective approach to enhance both the frequency dispersion and the optical nonlinearity of subwavelength silicon based waveguiding nanodevices is to pattern them at subwavelength scale. This provides an efficient design tool for engineering the optical properties of photonic waveguiding nanodevices and, equally important, it allows one to design nonlinear photonic structures in which optical pulses propagate in the slow-light regime. Guided by these ideas, recently we have developed a comprehensive theoretical description of the propagation of optical pulses in one-dimensional waveguides consisting of a line defect in a photonic crystal slab waveguide made of silicon. We have incorporated in our analysis linear optical effects, such as group-velocity dispersion and optical losses, as well as nonlinear effects induced by the Kerr nonlinearity of the photonic crystal. We have also included in our model the free-carrier dispersion and free-carrier induced optical losses, and thus studied the influence of free-carriers generated through two-photon absorption on the optical pulse dynamics. Our analysis has revealed that important quantities, such as the pulse group-velocity, waveguide dispersion coefficients, or the waveguide nonlinear coefficient are strongly affected by the periodic nature of the guiding structure. Equally important, we have demonstrated that both linear and nonlinear effects are stronger in the case of slow-light modes, with the nonlinear effects being enhanced more as compared to the linear ones. This work represents an ongoing collaboration with Prof. Chee Wei Wong's group from the Fu Foundation School of Engineering and Applied Science at Columbia University.

Relevant publications:
  • N. C. Panoiu, J. F. McMillan, and C. W. Wong, Theoretical Analysis of Pulse Dynamics in Silicon Photonic Crystal Wire Waveguides, IEEE J. Sel. Top. Quantum Electron. 16, 257 (2010). [pdf]
  • J. B. Driscoll, N. Ophir, R. R. Grote, J. I. Dadap, N. C. Panoiu, K. Bergman, and R. M. Osgood, Jr, Width-modulation of Si photonic wires for quasi-phase-matching of four-wave-mixing: experimental and theoretical demonstration, Opt. Express 20, 9227 (2012). [pdf]


Photonic Metamaterials with Zero Index of Refraction
One of the most remarkable properties of metamaterials is that, unlike naturally occurring materials, their physical properties can be easily engineered or tuned by simply modifying the structure and/or materials properties of their building blocks. One such example of a metamaterial with unusual electromagnetic properties is an optical medium whose index of refraction is equal to zero. These metamaterials have unique optical properties, including a new type of surface states and gap solitons, unusual transmission and emission properties, complete photonic bandgaps, a phase-invariant propagating electromagnetic field (a temporally "frozen" electromagnetic field that is spatially inhomogeneous), and an omnidirectional bandgap that is insensitive to wave polarization, incidence angle, structure periodicity, and structural disorder. Recently, we have demonstrated theoretically that under certain circumstances a photonic super-lattice consisting of alternating layers of homogeneous media with positive index of refraction and photonic crystal layers with negative index of refraction emulates the properties of an optical medium with zero index of refraction. In a collaborative project with Prof. Chee Wei Wong's group from the Fu Foundation School of Engineering and Applied Science at Columbia University, these ideas  have recently been experimentally validated. In adition, chip-scale photonic devices based on these zero-n metamaterials, including optical filters and interferometers, have been demonstrated.

Relevant publications:
  • N. C. Panoiu, R. M. Osgood, Jr., S. Zhang, and S. R. J. Brueck, Zero–n  band-gap in photonic crystal superlattices, J. Opt. Soc. Am. B 23, 506 (2006). [pdf]
  • S. Kocaman, R. Chatterjee, N. C. Panoiu, M. B. Yu, R. M. Osgood, Jr., D. L. Kwong, and C. W. Wong, Observations of Zero-order Bandgaps in Negative Refraction Photonic Crystal Superlattices at the Near-Infrared, Phys. Rev. Lett. 102, 203905 (2009) (also featured in the Virtual Journal of Nanoscale Science and Technology 19 (23), June 8, 2009). [pdf]
  • S. Kocaman, M. S. Aras, P. C. Hsieh, J. F. McMillan, C. G. Biris, N. C. Panoiu, M. B. Yu, D. L. Kwong, A. Stein, and C. W. Wong, Zero phase delay in negative-index photonic crystal superlattices, Nature Photonics 5, 499 (2011). [pdf]
  • S. Kocaman, M. S. Aras, N. C. Panoiu, Ming Lu, and C. W. Wong, On-chip optical filters with designable characteristics based on an interferometer with embedded silicon photonic structures, Opt. Lett. 37, 665 (2012). [pdf]
  • C. W. Wong, S. Kocaman, M. S. Aras, P. C. Hsieh, J. F. McMillan, C. G. Biris, N. C. Panoiu, M. B. Yu, D. L. Kwong, and A. Stein, Negative Index Photonic Crystals Superlattices and Zero Phase Delay Lines, in Photonic Crystals – Innovative Systems, Lasers and Waveguides, Ed. A. Massaro (InTech, 2012). [pdf]