Biomedical subjects

Shanhui Fan

Publications and source records attributed to Shanhui Fan.

29 records · Page 2Linked to original sources

PubMed2004

Time reversal of light with linear optics and modulators.

We introduce a new physical process that can perform a complete time-reversal operation on any electromagnetic pulse. The process uses only small refractive index modulations of linear optical elements. No nonlinear multiphoton effects such as four-wave mixing are required. The introduced process can be implemented on chip with standard semiconductor materials. Furthermore, the same process can be used to compress or expand the spectrum of electromagnetic waves while completely preserving the coherent information. We exhibit the time-reversal process by first-principles simulations of microcavity complexes in photonic crystals.

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PubMed2004

Method for sensitivity analysis of photonic crystal devices.

We present a new method for sensitivity analysis of photonic crystal devices. The algorithm is based on a finite-difference frequency-domain model and uses the adjoint variable method and perturbation theory techniques. We show that our method is highly efficient and accurate and can be applied to calculation of the sensitivity of transmission parameters of resonant nanophotonic devices.

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PubMed2004

Designing for beam propagation in periodic and nonperiodic photonic nanostructures: extended Hamiltonian method.

We use Hamiltonian optics to design and analyze beam propagation in two-dimensional (2D) periodic structures with slowly varying nonuniformities. We extend a conventional Hamiltonian method, adding equations for calculating the width of a beam propagating in such structures, and quantify the range of validity of the extended Hamiltonian equations. For calculating the beam width, the equations are more than 10(3) times faster than finite difference time domain (FDTD) simulations. We perform FDTD simulations of beam propagation in large 2D periodic structures with slowly varying nonuniformities to validate our method. Beam path and beam width calculated using the extended Hamiltonian method show good agreement with FDTD simulations. By contrasting the method with ray tracing of the bundle of rays, we highlight and explain the limitations of the extended Hamiltonian method. Finally, we use a frequency demultiplexing device optimization example to demonstrate the potential applications of the method.

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PubMed2004

One-mode model for patterned metal layers inside integrated color pixels.

Optimized design of the optical filters inside integrated color pixels (ICPs) for complementary metal-oxide semiconductor image sensors requires analytical models. ICP optical filters consist of subwavelength patterned metal layers. We show that a one-mode model, in which subwavelength gaps in the metal layer are described in terms of single-mode waveguides, suffices to predict the salient features of measured ICP wavelength selectivity. The Airy-like transmittance formula, derived for transverse-electric polarization, predicts an angle-independent cutoff wavelength, which is in good agreement with predictions made with a two-dimensional finite-difference time-domain method.

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PubMed2004

Stopping light all optically.

We show that light pulses can be stopped and stored coherently, with an all-optical adiabatic and reversible pulse bandwidth compression process. Such a process overcomes the fundamental bandwidth-delay constraint in optics and can generate arbitrarily small group velocities for any light pulse with a given bandwidth, without any coherent or resonant light-matter interactions. We exhibit this process in optical resonators, where the bandwidth compression is accomplished only by small refractive-index modulations performed at moderate speeds.

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PubMed2003

Compact all-pass filters in photonic crystals as the building block for high-capacity optical delay lines.

Optical all-pass filters, which generate strong on-resonance optical delay while maintaining a unity transmission coefficient throughout the entire resonant bandwidth, are of great importance for constructing delay lines in optical buffer applications. We provide an analysis of optical delay lines based upon cascading multiple stages of all-pass filter structures. We show that the maximum capacity of such delay lines is determined primarily by the dimensions of each stage. Motivated by this analysis, we describe compact optical all-pass filters in two-dimensional photonic crystals. The accidental degeneracy of the cavity modes introduces a strong group delay and dispersion while maintaining total transmission.

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PubMed2003

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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PubMed2003

Mechanically switchable photonic crystal filter with either all-pass transmission or flat-top reflection characteristics.

We theoretically introduce a new type of optical all-pass filter based on guided resonance in coupled photonic crystal slabs. The filter exhibits near-complete transmission for both on- and off-resonant frequencies and yet generates large resonant group delay. We further show that such a filter can be mechanically switched into a flat-top band rejection filter.

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PubMed2003

Field expulsion and reconfiguration in polaritonic photonic crystals.

We uncover a rich set of optical phenomena stemming from the incorporation of polar materials exhibiting transverse phonon polariton excitations into a photonic crystal structure. We identify in the frequency spectrum two regimes in which the dielectric response of the polaritonic medium can induce extreme localization of the electromagnetic energy. Our analysis of the effect of polarization and the interaction between the polariton and photonic band gaps on the Bloch states leads to a pair of mechanisms for sensitive frequency-controlled relocation and/or reconfiguration of the fields.

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PubMed2003

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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PubMed2003

Temporal coupled-mode theory for the Fano resonance in optical resonators.

We present a theory of the Fano resonance for optical resonators, based on a temporal coupled-mode formalism. This theory is applicable to the general scheme of a single optical resonance coupled with multiple input and output ports. We show that the coupling constants in such a theory are strongly constrained by energy-conservation and time-reversal symmetry considerations. In particular, for a two-port symmetric structure, Fano-resonant line shape can be derived by using only these symmetry considerations. We validate the analysis by comparing the theoretical predictions with three-dimensional finite-difference time-domain simulations of guided resonance in photonic crystal slabs. Such a theory may prove to be useful for response-function synthesis in filter and sensor applications.

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