Dynamic control of light propagation and optical switching through an RF-driven cascade-type atomic medium

We study nonlinear optical behaviors in pulse propagation through a medium consisting of four-level cascade-type cold atoms, where a radio-frequency (RF) field couples upper two-folded levels and double-dark resonances (DDRs) can arise. By numerically solving the coupled Bloch-Maxwell equations for atom and field simultaneously in space and time, we demonstrate dynamic control of light propagation and optical switching in such a four-level atomic medium. The proposed scheme may have potential applications in the design of optical switching and optical storage devices.     

Ultrafast optical switching by instantaneous laser-induced grating formation and self-diffraction in barium fluoride

Received: 13 January 1999     

Far-off resonance conditional phase-shifter using the ac Stark shift

We suggest a conditional phase-shifter that achieves a phase shift of π radians between two weak laser beams with a total energy density on the level of 1000 photons per atomic cross-section. The two laser beams interact through the simple nonlinear technique of ac Stark shifting the common ground state of a V-type system. We find that this switch can operate in the far-off resonance regime, with low absorption and high phase accumulation. Additionally, the bandwidth of this switch can be increased independently of the energy requirement.     

Optical bistability via amplitude and phase control of a microwave field

We investigate the steady-state optical bistability behavior in a three-level Λ-type atomic system closed by a microwave field under the condition that the applied fields are in resonance with corresponding atomic transitions. It is shown that the bistable hysteresis cycles can be controlled by both the amplitude and the phase of the microwave field.     

Conditional phase-shifter in refractive index enhancement scheme

We propose a conditional phase-shifter between two weak laser beams in an alkali vapor. We begin by enhancing the refractive index of a weak, far-detuned probe beam while maintaining vanishing absorption. The enhancement is a result of interfering an absorptive and an amplifying Raman resonance in a four-level atomic system. Then, a conditional switching beam ac stark shifts the narrow Raman resonances, modifying the phase accumulation experienced by the probe beam. We find that the scheme works with acceptable fidelity at the tens of photons level, and that the energy requirement can be reduced further at the expense of noise.     

Generation of nonclassical states by nonlinear optical systems

We review the main results obtained recently by our group in the field of quantum noise reduction in nonlinear optical systems. We illustrate the possibility of obtaining significant effects in degenerate parametric oscillators, intracavity second-harmonic generation, nondegenerate four-wave mixing, and one- and two-photon optical bistability.     

Passive, “self-trapped family” all-optical half adder using all-optical XOR and AND gates

The paper presents an alternative novel approach to obtain all-optical logic. We show that XOR, NOT, and AND logic could be obtained by appropriately setting parameter of all-optical passive transistor. An AND gate followed by NOT gives NAND logic (building block) that, in principle can provide complete set of passive, fiber compatible “self-trapped family” all-optical logic gates (with Boolean completeness) and may find many possibilities in the area of all-optical computing. To give one example, we propose all-optical half adder.     

Delay limit of slow light in an optical fiber

We show that coherent population oscillations effect produces a very narrow spectral hole in the absorption spectrum. The large dispersion of the refractive index associated with this hole permits us to achieve a group velocity as low as 1496.25 m/s at room temperature in an erbium-doped fiber. When the input intensity is equal to the saturation intensity, the dispersion is optimal. The optimal dispersion corresponds to the maximum fractional delay. Therefore, the input intensity can be used as a control parameter to increase the fractional delay. Our theoretical results based on population oscillation agree very well with the experimental data. In addition, we confirm that the spectral hole experiences power broadening for optical fibers of different lengths.     

A dense collection of two-level atoms embedded in a dielectric medium in a ring cavity

The hysteresis behavior of a dense collection of two-level atoms embedded in a linear dielectric medium in an optical cavity is investigated theoretically in terms of a parametric formulation method under the thin-sample approximation. The relation of the output intensity to the input intensity is obtained in an explicit formula. The numerical results show that the hysteresis behavior and the cavity transmission are different from those in vacuum because of the local-field enhancement and the local cooperative decay effect. Received: 27 June 2000 / Revised version: 11 September 2000 / Published online: 10 January 2001     

Control of the switch between optical multistability and bistability in three-level V-type atoms

We theoretically investigated a hybrid absorptive-dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.     

Incoherent optical switching of semiconductor resonator solitons

We demonstrate experimentally the bistable nature of the bright resonator solitons in a semiconductor microresonator with mixed absorptive/defocusing nonlinearity and show that they can be written and erased by incoherent local optical injection. Received: 22 February 2001 / Published online: 27 April 2001     

Guiding and high-harmonic generation of sub-10-fs pulses in hollow-core fibers at 1015 W/cm2

15 W/cm². The high resistance of fused silica to damage in the sub-10-fs regime allows stable reproducible operation without degradation of the capillary waveguide. In preliminary experiments, we demonstrate kHz-repetition-rate guided-wave high-harmonic generation in helium down to the 10-nm range. The reported experiments open up the way to realizing high-field interactions with plane-wave excitation at intensity levels in excess of 10¹⁵ W/cm² under well-controlled conditions. Received: 28 May 1998     

Coherent control of optical bistability in tunnel-coupled double quantum wells

We analyze optical bistability (OB) behavior based on intersubband transitions in an asymmetric coupled-quantum well (CQW) driven coherently by a probe laser field and a control laser field by means of a unidirectional ring cavity. We demonstrate that OB can be controlled by tuning the energy splitting between two tunnel-coupled electronic levels, the intensity of the control field, and the frequency detuning of the probe and control fields. The influence of the electronic cooperation parameter on the OB behavior is also discussed. This investigation may be used for optimizing and controlling the optical switching process in the CQW solid-state system, which is much more practical than that in atomic system because of its flexible design and the controllable interference strength.     

Control of the optical multistability in a three-level ladder-type quantum well system

We theoretically investigated a hybrid absorptive-dispersive optical multistability (OM) behavior in a three-level ladder-type quantum well system inside a unidirectional ring cavity. We find that the frequency detuning of the control field and the electronic cooperation parameter as well as the total decay rates can affect the optical multistability behavior dramatically, which can be used to manipulate efficiently the threshold intensity and the hysteresis loop. The effect of the intensity of the control field on the OM is also studied. Our study is much more practical than its atomic counterpart due to its flexible design and the wide adjustable parameters. Thus it may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.     

Optical broadband analog-digital conversion on the base of microring resonator

We propose the fast method of analog-digital conversion of optical signals by the use of waveguide ring resonators of micron size. The results of calculation are presented which allow optimization of the parameters of such optical analog-digital converter (ADC) for specific applications. Conversion operating speed of the ADC proposed is limited by the time of steady output signal establishing. For microresonator of 10 μm radius this time is about 10 ps. Analysis of the proposed optical method of analog-digital conversion shows that such optical ADC is capable to operate with the conversion frequency above 10⁹ counts/s in a broad spectral range. Optical loss in resonator reduces its switching time. However, the switching contrast also decreases. To keep the switching contrast constant it is necessary to increase discretization step of the analog signal power.     

Phase-sensitive multimodal optical parametric amplifier for beam angle amplification

The single-mode phase-sensitive parametric amplifier has been proposed as an approximation to an ideal quantum phase amplifier. We demonstrate numerically that a real, multimode parametric amplifier operated in the spatial domain, and realized by the use of three-wave mixing in nonlinear media, behaves similar to a single-mode quantum phase amplifier, but exhibits smaller phase gain. Constraints for operation in this regime are found to be consistent with small departures of phase from the ideal deamplification condition.     

Dynamics of refractive-index changes and two-beam coupling in resonant media

The dynamics of light-induced change in the refractive index of a resonant medium are examined. For illumination with weak fields, the two relevant relaxation times are T ₁, the population lifetime and T ₂, the dipole-dephasing time. The response time of the index change is determined by the slower relaxation time of the medium which is usually the time T ₁ taken by the excited system to relax back to its thermal equilibrium value. Illumination with two beams of the same frequency that intersect within the medium leads to the formation of a volume grating in the medium that is spatially local. Hence there is no exchange of energy between the beams that write the grating, each beam merely reducing the absorption experienced by the other beam. Illumination with a moving, spatially periodic intensity pattern leads to gain for one beam and additional absorption for the other beam as they propagate through the medium. A complete set of coupled equations describing the intensities and phases of the beams undergoing non-degenerate two-wave mixing in the resonant media is derived using third-order perturbation theory, and the solutions are studied numerically. In particular, the two-beam coupling constant for intensity is shown to depend on the frequency difference between the two beams and on the pressure-induced collisional relaxations in the system.     

Characterization of nonlinear optical parameters of polymethine dyes

We investigated nonlinear refraction, nonlinear absorption, and saturable absorption of polymethine dyes by the Z-scan technique (λ=1064 nm). The analysis of simultaneous appearance of several nonlinear optical processes in dye solutions excited by picosecond pulses was carried out. The saturable absorption was analyzed taking into account various models. Nonlinear refractive indices, nonlinear absorption coefficients, and saturation intensities of various polymethine dyes were measured. Received: 27 December 2002 / Revised version: 6 March 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +81-471/363-366, E-mail: r_ganeev@issp.u-tokyo.ac.jp RID="**" ID="**"Present address: The Institute for Solid State Physics, The Tokyo University, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan     

Cross-phase modulation in one-dimensional photonic crystals: applications to all-optical devices

We present a numerical study of a finite photonic band gap structure with a χ⁽³⁾ nonlinearity that couples two input pump beams at frequencies ω₁ and ω₂. We show that in this configuration a variety of all-optical devices can be obtained: an optical transistor, a double switch, and a dynamical switch.