Comment on "Explanation of the inverse Doppler effect observed in nonlinear transmission lines".
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Biomedical subjects
Marin Soljacić
Publications and source records attributed to Marin Soljacić.
Achieving centimetre-scale supercollimation in a large-area two-dimensional photonic crystal.
Diffraction, a fundamental process in wave physics, leads to spreading of the optical beams as they propagate. However, new photonic crystal (PhC) meta-materials can be nano-engineered to generate extreme anisotropy, resulting in apparent propagation of light without diffraction. This surprising phenomenon, called supercollimation, effectively freezes the spatial width of a light beam inside a PhC, observed over a few isotropic diffraction-lengths. However, using such experiments to predict the behaviour for longer propagation lengths is difficult, as a tiny error in a measured width can extrapolate to order unity uncertainty in the width at distances over hundreds of diffraction-lengths. Here, supercollimation is demonstrated in a macroscopic PhC system over centimetre-scale distances, retaining spatial width confinement without the need for waveguides or nonlinearities. Through quantitative studies of the beam evolution in a two-dimensional PhC, we find that supercollimation possesses unexpected but inherent robustness with respect to short-scale disorder such as fabrication roughness, enabling supercollimation over 600 isotropic diffraction-lengths. The effects of disorder are identified through experiments and understood through rigorous simulations. In addition, a supercollimation steering capability is proposed.
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Coherent optical photons from shock waves in crystals.
We predict that coherent electromagnetic radiation in the 1-100 THz frequency range can be generated in crystalline materials when subject to a shock wave or soliton-like propagating excitation. To our knowledge, this phenomenon represents a fundamentally new form of coherent optical radiation source that is distinct from lasers and free-electron lasers. The radiation is generated by the synchronized motion of large numbers of atoms when a shock wave propagates through a crystal. General analytical theory and NaCl molecular dynamics simulations demonstrate coherence lengths on the order of mm (around 20 THz) and potentially greater. The emission frequencies are determined by the shock speed and the lattice constants of the crystal and can potentially be used to determine atomic-scale properties of the shocked material.
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Surface-plasmon-assisted guiding of broadband slow and subwavelength light in air.
A class of axially uniform waveguides is introduced, employing a new mechanism to guide light inside a low-index dielectric material without the use of photonic band gap, and simultaneously exhibiting subwavelength modal size and very slow group velocity over an unusually large frequency bandwidth. Their basis is the presence of plasmonic modes on the interfaces between dielectric regions and the flat unpatterned surface of a bulk metallic substrate. These novel waveguides allow for easy broadband coupling and exhibit absorption losses limited only by the intrinsic loss of the metal.
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Enhancement of microcavity lifetimes using highly dispersive materials.
We show analytically and numerically that highly dispersive media can be used to drastically increase lifetimes of high- Q microresonators. In such a resonator, lifetime is limited either by undesired coupling to radiation, or by intrinsic absorption of the constituent materials. The presence of dispersion weakens coupling to the undesired radiation modes and also effectively reduces the material absorption.
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Cutoff solitons in axially uniform systems.
The optical response of axially uniform nonlinear photonic bandgap fibers is studied theoretically. We observe gap-soliton-like generation and associated bistability, similar to what is typically found in periodically modulated nonlinear structures. This response stems from the nature of the guided-mode dispersion relations, which involve a frequency cutoff at zero wave vector. In such systems, solutions with zero group velocities and minimal coupling to radiation modes come in naturally. We term such solitons "cutoff solitons"; they provide an interesting alternative to gap solitons in periodically index-modulated fibers for in-fiber all-optical signal processing.
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Superprism effect based on phase velocities.
The superprism effect has been studied in the past by use of the anomalous group velocities of optical waves in photonic crystals. We suggest the possibility of realizing agile beam steering based on purely phase-velocity effects. We present designs of photonic crystal prisms that might make experimental observation of this effect possible.
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Enhancement of nonlinear effects using photonic crystals.
The quest for all-optical signal processing is generally deemed to be impractical because optical nonlinearities are usually weak. The emerging field of nonlinear photonic crystals seems destined to change this view dramatically. Theoretical considerations show that all-optical devices using photonic crystal designs promise to be smaller than the wavelength of light, and to operate with bandwidths that are very difficult to achieve electronically. When created in commonly used materials, these devices could operate at powers of only a few milliwatts. Moreover, if these designs are combined with materials and systems that support electromagnetically induced transparency, operation at single-photon power levels could be feasible.
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All-optical transistor action with bistable switching in a photonic crystal cross-waveguide geometry.
We demonstrate all-optical switching action in a nonlinear photonic crystal cross-waveguide geometry with instantaneous Kerr nonlinearity, in which the transmission of a signal can be reversibly switched on and off by a control input. Our geometry accomplishes both spatial and spectral separation between the signal and the control in the nonlinear regime. The device occupies a small footprint of a few micrometers squared and requires only a few milliwatts of power at a 10-Gbit/s switching rate by use of Kerr nonlinearity in AlGaAs below half the electronic bandgap. We also show that the switching dynamics, as revealed by both coupled-mode theory and finite-difference time domain simulations, exhibits collective behavior that can be exploited to generate high-contrast logic levels and all-optical memory.
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Reversed Doppler effect in photonic crystals.
Nonrelativistic reversed Doppler shifts have never been observed in nature and have only been speculated to occur in pathological systems with simultaneously negative effective permittivity and permeability. This Letter presents a different, new physical phenomenon that leads to a nonrelativistic reversed Doppler shift in light. It arises when light is reflected from a moving shock wave propagating through a photonic crystal. In addition to reflection of a single frequency, multiple discrete reflected frequencies or a 10 GHz periodic modulation can also be observed when a single carrier frequency of wavelength 1 microm is incident.
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Cavity pattern formation with incoherent light.
We study the propagation dynamics of an incoherent light beam circulating in a passive cavity containing noninstantaneous nonlinear media. It is shown that patterns form in this cavity in spite of spatial incoherence of the light. We show that the pattern formation process is always associated with two consecutive thresholds. The first (instability) threshold is unaffected by the cavity boundary conditions, whereas the second threshold is induced by the feedback through the interplay of nonlinear gain and cavity loss.
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White-light solitons.
Optical spatial solitons made from incoherent white light were experimentally observed in 1997 by Mitchell and Segev [Nature (London) 387, 880 (1997)]. We present what is believed to be the first theory describing these solitons and find the characteristic features of their spatiotemporal coherence properties and their temporal power spectrum.
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Collisions of two solitons in an arbitrary number of coupled nonlinear Schrödinger equations.
We show that pairwise soliton collisions in N>2 intensity-coupled nonlinear Schrödinger equations can be reduced to pairwise soliton collisions in two coupled equations. The reduction applies to a wide class of systems, including the N-component Manakov system. This greatly simplifies the analysis of such systems and has important implications for the application of soliton collisions to all-optical computing.
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Color of shock waves in photonic crystals.
Unexpected and stunning new physical phenomena result when light interacts with a shock wave or shocklike dielectric modulation propagating through a photonic crystal. These new phenomena include the capture of light at the shock wave front and reemission at a tunable pulse rate and carrier frequency across the band gap, and bandwidth narrowing as opposed to the ubiquitous bandwidth broadening. To our knowledge, these effects do not occur in any other physical system and are all realizable under experimentally accessible conditions. Furthermore, their generality make them amenable to observation in a variety of time-dependent photonic crystal systems, which has significant technological implications.
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Analysis of mode structure in hollow dielectric waveguide fibers.
In this paper, we analyze the electromagnetic mode structure of an OmniGuide fiber-a hollow dielectric waveguide in which light is confined by a large index-contrast omnidirectional dielectric mirror. In particular, we find that the modes in an OmniGuide fiber are similar to those in a hollow metallic waveguide in their symmetries, cutoff frequencies, and dispersion relations. We show that the differences can be predicted by a model based on a single parameter-the phase shift upon reflection from the dielectric mirror. The analogy to the metal waveguide extends to the transmission properties, resulting in the identification of the TE01 mode as the lowest-loss mode of the OmniGuide fiber.
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Nonlinear photonic crystal microdevices for optical integration.
A four-port nonlinear photonic crystal system is discussed that exhibits optical bistability with negligible backscattering to the inputs, making it particularly suitable for integration with other active devices on the same chip. Devices based on this system can be made to be small [O(lambda3)] in volume, have a nearly instantaneous response, and consume only a few milliwatts of power. Among many possible applications, we focus on an all-optical transistor and integrated optical isolation.
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Optical bistability in axially modulated OmniGuide fibers.
We demonstrate the feasibility of optical bistability in an axially modulated nonlinear OmniGuide fiber through analytical theory and detailed numerical experiments. At 1.55-microm carrier wavelength, the in-fiber devices that we propose can operate with only a few tens of milliwatts of power, can have a nearly instantaneous response and recovery time, and can be shorter than 100 microm.
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Optimal bistable switching in nonlinear photonic crystals.
We present an analytical model and numerical experiments to describe optimal bistable switching in a nonlinear photonic crystal system. It is proved that only three parameters are needed to characterize a bistable switch: the resonant frequency omega(res), the quality factor Q, and parameter kappa that measures nonlinear "feedback strength." A photonic crystal enables the device to operate in single-mode fashion, as if it were effectively one dimensional. This provides optimal control over the input and output and facilitates further large-scale optical integration.
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