Study of optical bistability and multistability with optical waveguide modulator

An impedance boundary method of moments (IBMOM) is proposed to accurately and efficiently compute the propagation characteristics including the number of guided modes of general graded-index dielectric slab waveguide structures. The method is based on Galerkin's procedure in the method of moments and employs the exact impedance boundary condition at the interfaces between the graded-index region and constant-index cladding. Legendre polynomials are utilized in the field expansion. Computational results are shown for waveguides with various inhomogeneous refractive index profiles. The results indicate that typically five Legendre polynomials are sufficient for accurate solutions of the dominant TE and TM modes in optical waveguides having a finite region of inhomogeneous refractive index. Diffused optical waveguides with untruncated index profiles as well as coupled dielectric waveguides can be accurately analyzed using ten Legendre polynomials.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The refractive index profile of buried graded-index planar optical waveguides fabricated by ion migration can be described by a buried secant hyperbolic function. Using such a profile, we have obtained the exact propagation characteristics for such buried optical waveguides. We have also shown that profiles which deviate slightly from the above profile can be treated as perturbations and a first-order perturbation correction gives very accurate results.

In this paper, the optical bistability (OB) and optical multistability (OM) properties of weak probe light in a defect dielectric medium doped by four-level graphene nanostructure is theoretically discussed. The double dark resonance can arise by linear polarized control laser fields which consist of linear left and right circularly polarized light. We show that by adjusting the Rabi-frequencies of control fields, frequency detuning of bichromatic electric fields, the intensity threshold and hysteric curves of OB and OM can be manipulated. Moreover, the thickness of the slab is considered as a controllable parameter which can impact the OB and OM behaviors of weak probe light in a defect slab. We find that the transition from OB to OM or vice versa can be possible by adjusting the thickness of the slab. Our results may provide some new application on Nano-scale devices in future all-optical communication and quantum information technologies.

The steady-state optical bistability (OB) and optical multistability (OM) behavior in the quasi-Λ-type atomic system driven by a probe field and a coherent coupling field inside a unidirectional ring cavity are shown, and the effects of coupling-field detuning and coupling-field intensity on the OB and OM behavior are investigated. The transition from OB to OM or vice versa is found by varying the detuning of the coherent coupling field or by adjusting the intensity of the coupling field. The influence of the atomic cooperation parameter on the OM behavior is also discussed.

: Optical transmission of analog RF signals is potentially useful in a number of applications including RF distribution systems. Such systems can be used in commercial CATV and wireless communications and in military communication and radar systems. With compatible components used at transmitters and receivers, analog fiber optic links suffer much less performance degradation than conventional coaxial cable links as the system bandwidth increases. In the first year program we studied large Optical Cavity waveguide modulator design and demonstrated a low optical insertion loss waveguide modulator at 1.34 microns wavelength (as low as 8 dB w/o AR coating). This design is based Upon the matching of the mode profile of the fiber and the modulator waveguides. The design is extended to 1.55 microns wavelength. We also demonstrated a novel scheme of bias-tracking of the electroabsorption waveguide modulator. The scheme is based upon the photocurrent generated at the modulator. Effective tracking is obtained as the polarization, wavelength (or ambient temperature), and power of the input light are varied. Experimental evidence was obtained for a combined Franz-Keldysh effect and Quantum Confined Stark Effect modulator for a large multi-octave spurious free dynamic range. Low loss planar photoelastic waveguide on both InP and GaAs substrates was achieved.

Optical bistability (OB) and optical multi-stability (OM) of a four-level Λ-type atomic system with two fold lower levels inside a unidirectional ring cavity is investigated. The effect of quantum interference arising from spontaneous emission and incoherent pumping on OB and OM is discussed. It is found that the threshold of OB and OM can be controlled by quantum interference mechanisms. In addition intensity of coupling field and the rate of an incoherent pumping field on behavior of OB and OM are then discussed.

A full-vectorial finite-element-based approach is used to find accurate modal solutions for the acoustic modes in a Ge-doped planar silica optical waveguide. To enhance accuracy of the solution, the existing structural symmetry is exploited, and rigorous analyses of the interactions between the guided acoustic and optical modes are performed. The stimulated Brillouin scattering frequency and the overlaps between the fundamental and the higher-order transverse and longitudinal acoustic modes and the fundamental quasi-TE optical mode are presented.

Optical bistability (OB) and optical multistability (OM) behavior in molecular magnets is theoretically studied. It is demonstrated that the OB of the system can be controlled via adjusting the magnetic field intensity. In addition, it is shown that the frequency detuning of probe and coupling fields, as well as the cooperation parameter, has remarkable effects on the OB behavior of the system. Also, we find that OB can be converted to OM through the magnitude of control-field detuning. Our results can be used as a guideline for optimizing and controlling the switching process in the crystal of molecular magnets.

For the first time detailed interactions between optical and acoustic modes in a silicon slot waveguide are presented. A new computer code has been developed by using a full-vectorial formulation to study the acoustic modes in optical waveguides. The results have shown that the acoustic modes in an optical slot waveguide are not purely longitudinal or transverse but fully hybrid in nature. The model allows the effects of Stimulated Brillouin Scattering and the associated frequency shift due to the interaction of these hybrid acoustic modes with the fully hybrid optical mode also to be presented.

We discuss the optical bistability and multistability properties of incident light on a unidirectional ring cavity consisting of a hybrid semiconductor quantum dot-metal nanoparticle system driven by coupling and incoherent pumping fields. We consider the quantum dot system as a three-level V-type configuration which is placed near the metallic nanoparticle. We realize that the threshold of optical bistability and optical multistability can be controlled by tuning the center-to-center distance between quantum dots and metallic nanoparticles. Moreover, the effect of incoherent pumping field on optical bistability and optical multistability has been discussed for different distances between quantum dots and metallic nanoparticles.

A search-and-track algorithm is proposed for controlling the number of guided modes of planar optical waveguides with arbitrary refractive index profiles. The algorithm starts with an initial guess point in the parameter space that supports a specific number of guided modes. Then, it searches for, and tracks, the boundaries of this space or another space supporting different number of modes. It does so by monitoring the sign of a unified cutoff dispersion function. The algorithm is applied to both symmetric and asymmetric silicon-based parabolic-index waveguides. It shows that unlike asymmetric waveguides, the single-mode condition of symmetric waveguides is controlled by TM-, as opposed to TE-, polarization. This abnormal polarization control is strongest for high index contrast waveguides of sub-micrometer core sizes. The results are verified by full-vectorial beam propagation method.

: The purpose of this project was to examine several different quantum well waveguide modulator designs with the goal of developing a quantum well waveguide optical modulator suitable for integration into III-V opto-electronic integrated circuits

In this letter, a comprehensive investigation has been conducted on the optical bistability (OB) and optical multistability (OM) phenomena manifested by transmitted light in a ring cavity consisting of a hybrid system of metal nanoparticle (MNP) and semiconductor quantum dot (SQD). Our study has been primarily devoted to examining the influence of the distance between SQD and MNP, as well as the susceptibilities of the SQD, the MNP, and the hybrid nanostructure as a whole, on the OB and OM traits of the transmitted light. Our discoveries demonstrate that a transition from OB to OM, or vice versa, can be accomplished for a definite distance between MNP and QD. It is our contention that our proposed model may have potential applications in the domain of quantum information processes based on SQD-MNP hybrid systems.

In combination with the transfer matrix method and the concept of an equivalent attenuated coefficient, a first-order perturbation theory is proposed to study the leaky modes in planar optical waveguides. Simplified analytical expressions of the perturbed propagation constants are presented in a more explicit and general manner compared to the existing theory.

We proposed a new model for controlling the optical bistability (OB) and optical multistability (OM) in a defect slab doped with four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al0.3 Ga0.7As barriers. The effects of biexciton energy renormalization, exciton spin relaxation, and thickness of the slab on the OB and OM properties of the defect slab were theoretically investigated. We found that the transition from OB to OM or vice versa is possible by adjusting the controllable parameters in a lab. Moreover, the transmission, reflection, and absorption properties of the weak probe light through the slab were also discussed in detail.