We investigate dispersion effects in dynamically-tuned, coupled-resonator delay lines. Provided that the system is tuned to a zero-bandwidth state, a signal can be delayed indefinitely without dispersion. We present a theoretical analysis of such a light-stopping system and verify the results using numerical simulations of
an example system.
We describe how a quantum non-demolition device based on electromagnetically-induced transparency in solidstate atom-like systems could be realized. Such a resource, requiring only weak optical nonlinearities, could potentially enable photonic quantum information processing (QIP) that is much more efficient than QIP based on linear optics alone. As an example, we show how a parity gate could be constructed. A particularly interesting physical system for constructing devices is the nitrogen-vacancy defect in diamond, but the excited-state structure for this system is unclear in the existing literature. We include some of our latest spectroscopic results that indicate that the optical transitions are generally not spin-preserving, even at zero magnetic field, which allows the realization of a Λ-type system.
We discuss a new integrated approach to realizing optical quantum interference effects such as electromagnetically induced transparency (EIT), slow light, and highly efficient nonlinear processes on a semiconductor chip. An ensemble of alkali atoms represents one of the canonical systems that exhibit slow light and related phenomena. At the same time, it would be desirable to build slow-light and related devices on a semiconductor platform in order to move to practical applications. We review progress towards combining the large magnitude of quantum interference effects in alkali vapors with the convenience of integrated optics in the form of hollow-core antiresonant reflecting optical waveguides (ARROWs). We discuss the benefits and challenges of this integrated approach with special emphasis on nonlinear optics. We present strategies to optimize the optical waveguides and discuss the current status of building rubidium-filled optical waveguides on a chip. Recent results on optimization of waveguide loss and transfer of rubidium atoms through hollow microchannels on a chip are presented.
Recently artificial inhomogeneous broadening was proposed to expand the bandwidth of slow light. The point is to independently slow down all harmonic components of the input pulse via inhomogeneous broadening. An input pulse or sequence of pulses can be split into independent spectral channels by a dispersive element such as a prism or grating. These sub-pulses are then slowed by bandwidth-matched slow-light array elements, and then recombined with another dispersive element to produce the output pulse. The proof of principle experiment was done with a photorefractive crystal Ce:BaTiO3 where the crystal function as both dispersive elements and slow lights devices.
We present a theoretical analysis of light pulse delay in resonant photonic bandgap structures made from Bragg-spaced semiconductor quantum wells. Quantum well Bragg structures offer the possibility for parametric manipulation of the polariton band structure. This, in turn, may be used for stopping, storing, and releasing of light pulses. Based on a theoretical model utilizing a time-dependent transfer matrix approach to the solution of Maxwell's equations, we study light pulse propagation, light pulse trapping and releasing, and light pulse deformation in these structures. We discuss the photonic band structure concepts relevant to our light delay scheme and present numerical simulation results of pulse delay through presently existing quantum well Bragg structures.
Liouville-space (reduced-density-operator) descriptions are developed for resonant and coherent electromagnetic interactions of quantized electronic systems, taking into account environmental decoherence and relaxation phenomena. Applications of interest include electromagnetically-induced transparency and related pump-probe optical phenomena in many-electron atomic systems (in electron-ion beam interactions, gases, and high-temperature plasmas) and
semiconductor materials (bulk crystals and nanostructures). Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. The standard Born (lowest-order perturbationtheory) and Markov (short-memory-time) approximations are systematically introduced within the framework of the general non-perturbative and non-Markovian formulations. A preliminary semiclassical description of the entire electromagnetic interaction is introduced. Compact Liouville-space operator expressions are derived for the linear and the general (n'th order) non-linear electromagnetic-response tensors occurring in a perturbation-theory treatment of the semiclassical electromagnetic interaction. These expressions can be evaluated for coherent initial electronic excitations and for the full tetradic-matrix form of the Liouville-space self-energy operator representing the environmental interactions in the Markov approximation. Intense-field electromagnetic interactions are treated by means of an alternative, non-perturbative method, which is based on a Liouville-space Floquet-Fourier representation of the reduced density operator. Electron-electron quantum correlations are treated by the introduction of a cluster decomposition of the reduced density operator and a coupled hierarchy of reduced-density-operator equations.
We discuss how Very Large Scale Integration (VLSI) fabrication techniques can be used to build scalable solid-state quantum computers in diamond with either room temperature operation, or low temperature operation with photonic control. For this discussion we consider nitrogen-vacancy (NV) color centers where the qubits are electron and/or nuclear spins. To achieve scalability the NV centers are placed in well-defined locations using ion implantation, and are
controlled using optical and/or microwave excitation as well as localized static electric and/or magnetic fields.
A novel means of realizing optical logic with passive silicon-on-insulator (SOI) waveguide elements is proposed and modeled. Using what we call interference logic (IL), information is encoded and manipulated in the complex domain by properly setting the amplitude and phase of information inputs through specially designed waveguide structures, with the resulting wave interference used to compute the desired function output. We demonstrate that any arbitrary Boolean logic function can be realized in any physical system in which interference occurs. In this work, optical interference logic utilizing constructive and destructive interference of 1.55 micron light waves in multi-mode interference (MMI) couplers fabricated with SOI rib waveguides is described. Defining a vector representation of the complex information, a numerical function minimization algorithm is employed to compute the optimum input vector manipulations needed to realize a given operation's truth table. As such, with the definition of an output amplitude detection threshold separating "0" and "1" results, logic operations can be performed. A digital 2 x 1 multiplexer (MUX) is implemented in a single 4 x 1 MMI coupler where 1 of the 4 inputs serves as a reference input beam. With an input spacing of 40 micron, the 2 x 1 multiplexer has an overall dimension of 160 micron x 2.25 cm. Simple varied-dimension waveguide elements are used to adjust input wave amplitude and phase. To confirm and optimize the designs, device operation is simulated using 2D beam propagation method (BPM).
Analysis of a spectral hole burning memory design implementing high oscillator strength absorbers is reported. While retaining excellent area bit density, potential I/O bandwidth is significantly enhanced while required optical power and energy decrease. Model parameter values that derive from materials recently fabricated and characterized by collaborators indicate excellent data storage system performance.
Spectral Storage using optical holeburning has the potential of providing ultrahigh densities approaching terabits per
square inch. The progress on multilayer spectral storage in Eu-doped sulfides has been presented. It is shown that
atomic scale tailoring of these structures is possible in order to design several different europium optical centers. In
the spectrum of these centers, ultrahigh density storage can be achieved with the simultaneous optimization of other
performance parameters. Results are also presented for tailoring the barrier and the capping layers.
We have demonstrated our newly considered self-organizing network nodes which realize optical concurrent communications. Using optical devices such as light emitting diode (LED) and photo diode (PD), we have experimentally composed the non-linear characteristics required for the practical adaptive nodes. We also have accomplished to incorporate some functions which realize the optical concurrent communications into our opto-electronic hybrid circuits. Therefore, without any problem of cross talking or miss formation of the propagation routes, a number of potential communicator pairs may have concurrent access to this self-organizing network formed by interconnecting our nodes. We confirmed the performance of our present nodes experimentally as well as numerically. As a consequence, our present optical nodes have been proved to be practical for the optical peer-to-peer self-organizing network in which concurrent communications are allowed.
By using cross gain modulation in semiconductor optical amplifiers, basic logics for all-optical computing
and signal processing are successfully demonstrated at 10Gbps. These functions will bring up the increased
speed and capacity of telecommunication systems, basic or complex optical computing, and many other optical
signal processing systems.
A quantitative description of optical refrigeration in rare-earth doped solids in the presence of impurities is presented. The model includes the competition of radiative processes with energy migration, energy transfer to transition-metal ions, and multiphonon relaxation. The cooling efficiency is sensitive to the presence of both 3d metal ions with absorption in the near infrared and high-frequency vibrational impurities such as OH. A case study of ZBLAN:Yb3+ identifies Cu2+, Fe2+, Co2+, and OH as the most problematic species and establishes a 1-10 ppm upper limit for each of these impurities for a practical ZBLAN:Yb3+ optical cryocooler operating at
100-150 K to become feasible. The model results form the basis for an advanced strategy for the synthesis of high-purity ZBLAN:Yb3+ that exploits the potential of available purification techniques in an aqueous intermediate step. Such
high-performance ZBLAN:Yb3+ is expected to enable optical cryocoolers with ~1% overall efficiency at 120 K and find use in a wide range of applications that require highly reliable, noise-free, and vibration-free cooling of electronic and opto-electronic components.
We present the possibilities of atomic tailoring of electronic and vibrational properties of rare earth based materials in order to achieve compact high efficiency laser refrigerators operating at cryogenic temperatures
Using an optical cavity, we demonstrate enhanced pump light absorption for laser cooling of solids. A Fabry-Perot cavity containing Yb:ZBLAN glass shows enhancement of resonant absorption by a factor of 11 compared to the double-pass configuration. This corresponds to 85% absorption of the incident laser power.
We investigate both theoretically and experimentally the electro- magnetically induced transparency (EIT) phenomenon of atomic 87Rb at the room temperature with a static magnetic field lifting the degeneracy of all three involved hyperfine levels. Two collinearly propagating and linearly polarized laser fields (a probe field and a coupling field) are used to couple one hyperfine level (the upper level) of the 5P1/2 state to two hyperfine levels (the lower levels) of the 5S1/2 state, respectively. In the case of zero magnetic fields, we observed a deep EIT window with the contrast of about 66%. Here, the EIT window width is limited by both the spontaneous decay rate of the upper level and the coupling field intensity. When a magnetic field parallel to both laser beams is applied, the EIT window is split into three much narrower sub-windows with contrasts of about 32%. If the magnetic field is perpendicular to the laser beams, however, the EIT window is split into four much narrower sub-windows whose contrasts are 32% or 16%. This is because the decomposition of the linearly polarized optical fields strongly depends on the orientation of the used magnetic field. The underlying physics is that, in the limit of a weak probe field, an ideal degenerate three-level system can be split into three or four sets of independent three-level systems by a magnetic field due to the lifting of magnetic sublevels of the involved hyperfine levels. In this paper the absorption spectra corresponding to different magnetic field directions are clearly shown and compared. And a straightforward but effective theoretical method for analyzing the experimental results is put forward. Our theoretical calculations are in good agreement with the experimental results.
We theoretically study propagation of light in a vertically coupled whispering gallery mode resonator (WGMR) waveguide consisting of a chain of disc WGMRs etched on the surface of a cylinder made of an optically transparent material. The waveguide is capable of reducing the group velocity of light by as much as a factor of a billion, is much more efficient than usual coupled resonator optical waveguides, and compete with slow light atomic systems. We discuss practical as well as fundamental advantages and disadvantages of the resonator and atomic delay lines.
We propose a scheme that provides all optically controlled steering of light beam. The system is based on steep dispersion of coherently driven medium. Using eikonal equation, we study the steering angle, the spread of optical beam, and the limits set by residual absorption of medium under conditions of electromagnetically induced transparency (EIT). Implementation of another scheme for ultra-short pulses is also discussed.
Slow-light components will degrade the data bits in an optical communication system due to narrow-band amplitude and phase responses. A bit-pattern dependence is produced in the output data stream. These effects are observed in simulation as well as in an experiment based on slow light induced by stimulated Brillouin scattering (SBS) in an optical fiber. We define figure of merit involving pulse delay and data degradation to optimize slow-light components. It is demonstrated experimentally and numerically that the pattern dependence can be reduced by detuning the slow-light devices.
The physics of slow-light propagation in atomic Lambda systems is described by the theory of integrable systems, which allows the existence of solitons. Slow-light solitons are stable polarization structures that propagate through the atomic medium at a controllable speed. They represent generalizations of the experimentally demonstrated slow-light pulses in atomic media where one light polarization dominates the other, the probe, and controls its group velocity. In the general case, the overall intensity controls the speed of the entire polarization structure. For zero detuning between light and atoms, even more general shape-preserving pulses exist. Quantum fluctuations of slow-light pulses can be stored in atomic media. In the case of solitons, these are fluctuations of the soliton parameters.