Symmetric Waveguide Structure Research Articles

Observation of magneto-optical effect in extremely dilute ferrofluids under weak magnetic field

We propose a novel liquid-core waveguide using water-based ferrofluids as the guiding layer in a symmetrical metal-cladding waveguide structure to investigate the magneto-optical effect of extremely dilute ferrofluids. Owing to the high sensitivity of the ultra-high-order modes, the reflection intensity can be effectively tuned even by a weak magnetic field and the modulated reflectivity exhibits no threshold behavior. Furthermore, by properly adjusting the transmission axes of the polarizer, the detected laser intensity can be magnetic-field independent because the refractive indices for ordinary and extraordinary rays vary oppositely under the external field.

The dispersion relations for surface plasmon in a nonlinear–metal–nonlinear dielectric structure

In the asymmetric and symmetric nonlinear-metal-nonlinear dielectric structures, this paper studies the analytic dispersion relation for surface plasmon in a system consisting of a thin metallic film covered on two sides media of intensity-dependent refractive indexes by applying a generalised first integral approach. Especially in the symmetric waveguide structure, two possible modes can exist: the odd mode and the even mode. The dispersion relations of the two modes are obtained. Due to the nonlinear dielectric, the squared magnitude of the electric field at the interface appears and alters the dispersion relations. Numerical results are compared to those from a certain approximate treatment.

Comparative study of asymmetric versus symmetric planar slab dielectric optical waveguides

In this paper we have studied the asymmetric versus symmetric planar waveguide in terms of their usefulness in optical fiber communication systems. We have explored the thin waveguide versus thick waveguide first. Later on usefulness of asymmetric versus symmetric waveguide is carried out to target for WDM optical network application. All kinds of optical network components are fabricated on Si substrate with the point of view of their application. Here asymmetric planar structure may be more useful compared to symmetric waveguide in terms of their non-uniform power confinement properties. However, the symmetric waveguide structure may be more useful for their high power confinement properties. It is well known that the thin symmetric waveguide supports at least one mode. However the thick waveguide may support many even as well as odd modes. We study the power confinement properties for symmetric as well as asymmetric waveguide structure. We conclude that higher order modes show the nonlinear power variations. Mode field profile for various cases is discussed as well. Comparative study between asymmetric versus symmetric waveguide has a lot of significance in optical network area. It has been shown through analysis that in asymmetric waveguide, the power flows more through film region in the case of fundamental mode. Power confinement properties for asymmetric waveguide versus symmetric waveguide have been studied.

非对称波导结构提高980 nm激光二极管电光效率的机理研究

The optical losses of asymmetric and symmetric waveguide structures were calculated theoretically for high power 980 nm diode lasers, by means of the continuity equation under strong injection and the Helmholtz equation of complex refractive index model. The epitaxial materials of the both waveguide structures were prepared by the metallorganic chemical vapor deposition growth technique, and corresponding laser devices were fabricated. The electro-optical performances of both devices were measured and analyzed by comparison. The theoretical calculations and experimental results indicates that, the asymmetric waveguide structure material does not reduce the optical loss, but decreases the series resistance of the diode, therefore, it reduces the joule heating, and enhances the conversion ef

Tunable polarization beam splitting based on a symmetrical metal-cladding waveguide structure

Electrical tuning of polarization beam splitting is demonstrated in the structure of symmetrical metal-cladding waveguide by introducing optically nonlinear material into both the coupling prism and the guiding layer. Due to the anisotropy of the coupling material, different excitation conditions for TE and TM modes are obtained, which results in polarization-dependent reflections and transmissions. And the splitting effect of the two orthogonally polarized beams can be manipulated through an electrical modulation of the guiding layer properties.

An intensity measurement refractometer based on a symmetric metal-clad waveguide structure

An optical refractometer using intensity measurement to detect minute changes in the refractive index (RI) of aqueous analyte is illustrated in this paper. In this sensor, the analyte, which is sealed by an O-ring between two metal films, serves as the guiding layer of a symmetric metal-clad waveguide. By using the free-space coupling technique, an incident laser beam is coupled into the sensor structure as the sensing probe. The reflected beam intensity is monitored to analysis the sample's RI change. Both theoretical analysis and experimental results show that, due to concentrated power in the sample layer, the sensor exhibits magnificent sensitivity improvement. Besides, it also presents polarization independence.

Athermal High-Index-Contrast Waveguide Design

We present generalized design rules for athermal performance and materials compatibility in high-index-contrast (HIC) waveguides. Thermal stability of integrated photonic devices is one critical limitation in the development of commercially viable integrated optoelectronic circuits. Thermooptically neutral designs are achieved by choosing a cladding material whose thermooptic coefficient is opposite to that of the waveguide core. We derive analytical expressions of athermal conditions for both symmetric and asymmetric channel waveguide structures. The equations apply to general HIC systems such as silicon-on-insulator and SiN-based structures.

An electro-optic polymer modulator based on the free-space coupling technique

An electro-optic (EO) polymer modulator employing a symmetrical metal-cladding waveguide structure is presented. Based on the free-space coupling technique, the energy of incident light on the metal-cladding is coupled directly from free space into the waveguide without using a prism, grating and other coupling components. An externally applied voltage modulates the reflected light intensity by changing the energy coupling efficiency of the incident light into the waveguide through the refractive index of the EO polymer. The fabricated modulator achieves an 8.2% modulation depth with 10 Vp−p driving voltage at 1 MHz. The device also provides the benefits of simple fabrication and compact size owing to the use of the free-space coupling technique.

Analyzing multilayer optical waveguide with all nonlinear layers

We propose a general method for analyzing a multilayer optical waveguide with all nonlinear layers. This general method can be degenerated into some special cases, such as symmetric or asymmetric nonlinear optical waveguide structures, the intensity-dependent refractive index with self-focusing nonlinear medium, hollow waveguides, and multilayer systems. Based on this general method, the analysis and calculation of complicated multilayer optical planar waveguides can be achieved easily. The analytical and numerical results show excellent agreement.

The dynamics of amplified spontaneous emission in CdSe∕ZnSe quantum dots

We have used the variable stripe technique and pump-probe spectroscopy to investigate both gain and the dynamics of amplified spontaneous emission from CdSe quantum dot structures. We have found modal gain coefficients of 75 and 32cm−1 for asymmetric and symmetric waveguide structures, respectively. Amplified spontaneous emission decay times of 150 and 300ps and carrier capture times of 15 and 40ps were measured for the structures with high and low material gains respectively. The difference in the capture times are related to the fact that for the symmetric waveguide, carriers diffuse into the active region from the uppermost ZnMgSSe cladding layer, yielding a longer rise time for the pump-probe signals for this sample.

Free-carrier absorption and active layer heating in large optical cavity high-power diode lasers

An analytical theory is developed for the thermal properties of a large optical cavity semiconductor laser high above threshold. The performance of symmetric and asymmetric waveguide structures is analyzed and compared. Narrow asymmetric waveguides are predicted to be advantageous from the thermal point of view.

Influence of spinel substrate and over-layer for enhanced SAW and AO properties with KNbO3 thin film.

Surface acoustic wave (SAW) propagation characteristics have been studied using modeling calculations for a potassium niobate (KNbO3) thin film-layered structure with (001) and (110) orientation on a single crystal spinel (MgAl2O4) substrate, and a spinel buffer layer on silicon. Variation in the electromechanical coupling and acoustic attenuation has been compared. A significantly high value of coupling factor (k2max = 23%) is obtained for the (001)KNbO3/spinel structure by introducing an optimum thickness of spinel over-layer for potential wide bandwidth SAW device applications. The dispersion characteristics with the (110) KNbO3 orientation indicate an initial peak in the coupling coefficient value (k2max = 8.8%) at a relatively low KNbO3 film thickness that appears attractive for fabricating devices with thinner films. The KNbO3 film with (001) orientation is found attractive for efficient acousto-optic (AO) device application with the formation of a symmetric waveguide structure (spinel(0.5 microm)/KNbO3(1.0 microm)/spinel). A high value of k2 = 23.5% with 50% diffraction efficiency has been obtained for the spinel(0.5 microm)/KNbO3(1.0 microm)/spinel structure at 1 GHz SAW frequency and 633 nm optical wavelength at a very low input drive power of 15.4 mW.

The index changes of waveguides fabricated by light irradiation in LiNbO3:Fe c rystals

The refractive index changes of waveguides fabricated by light irradiation in LiNbO3:Fe crystals were investigated by using ordinary and extraordinary laser beams at wavelengths of 632.8nm and 532nm. The experimental results show that the waveguide fabricated by ordinary light is better than that by extraordinary lig ht, as the ordinary light causes much less light-induced scattering. The illuminated time must be strictly controlled when the region with a positive index change, formed by a single thin laser beam, is used as waveguide structure. This is beacuse the waveguide properties may be influenced by the strong noise grati ng and the shift of the waveguide region after the LiNbO3:Fe crystal was irrad iated for a long time. For avoiding the influence of the noise grating, the symm etric waveguide structure with high quality can be fabricated by sheet beam illu mination employing the sandwich method at a relatively low exposure intensity. M oreover, waveguides with different index distributions and different dimensions can be fabricated by changing the width of the irradiating beam and the distance between twice irradiations.

Studies on acousto-optical interaction in epitaxial thin film heterostructures

Thin film epitaxial heterostructures consisting of and /Si have been studied theoretically with interdigital transducer (IDT) electrodes at various locations. The thickness of each individual layer has been optimized for achieving an efficient SAW performance with a high electromechanical coupling coefficient. The structural feasibility and practical implications of various device configurations for an acousto-optical device are discussed. The introduction of a thin non-piezoelectric over-layer onto a piezoelectric film is found to enhance the electromechanical coupling coefficient . In a symmetrical /IDT/ waveguide structure the maximum value of is found to increase from 2.438 to 9.23% for a variation in the thickness of the over-layer in the range 0-0.12. Symmetrical and asymmetrical waveguide structures formed with and thin films in combination have been examined and a symmetrical waveguide structure (/IDT//Si) is found to exhibit a high acousto-optical figure of merit and % for a device operating with the fundamental mode at wavelength m.

Coupled waveguides for Raman studies of thin liquid films

The propagation of light in a symmetrical optical waveguide structure comprising two identical ion-exchanged or sol-gel waveguides with a thin water film between them has been analysed using numerical modelling. The results show that in the case of ion-exchanged waveguides there is an increase of times in the field intensity at the surface of the waveguides for liquid film thickness of the order of a few tens of nanometres and times in the case of sol-gel waveguides. In the case of sol-gel waveguides the fraction of light power propagating in the liquid film is of the order of 10% of the total power propagating in the waveguide structure even at small separations of the waveguides. Thus improved sensitivity of signal detection for Raman and fluorescence waveguide spectroscopy can be realized with the proposed waveguide structure with high spatial resolution.

Optical phase conjugation and waveguide coupling by cascading transverse second-harmonic and difference-frequency generation in a vertical cavity

We propose a novel scheme for implementing optical phase conjugation (OPC) by cascading transverse second-harmonic and difference-frequency generation in a vertical cavity. We propose to achieve phase conjugation in the pump and input-output two-waveguide structure. For a symmetric waveguide structure, the structure can be used as an optical phase conjugate mirror. For a realistic structure based on III–V semiconductor materials, a pump power per unit waveguide of 0.74 W μm-1 is required to reach a conversion efficiency of ∼9.4%. Combined with another phase-conjugate mirror, the reflectivity of the proposed phase-conjugate mirror can be efficiently modulated by control of the pump power. For an asymmetric waveguide structure, a gain is predicted. In addition, by cascading second-harmonic generation (SHG) and parametric oscillation, we propose to use the same structure as a waveguide coupler. There is a threshold to achieve coupling.

Thermal pump saturation in CW optically pumped far infrared lasers

Vibrational-translationally relaxing far infrared (FIR) laser gases are heated by relaxation from the first vibrational state containing the lasing levels to the ground state. This reduces the molecule density, thus leading to a lower effective pump absorption compared with a cold gas. This phenomenon is investigated theoretically by solving the appropriate heat diffusion equation, considering both the traditional circular symmetric waveguide structure and the sandwich (or parallel slab) structure. The most important results are discussed and compared with previously reported experiments. A method is given for an estimation of the effective pump absorption and the excess temperature.

A highly dispersive wavelength division demultiplexer in InGaAlAs-InP for 1.5 mu m operation

A novel integrated optical wavelength division demultiplexer in InGaAlAs-InP is described. It uses interference between the fundamental (zeroth) and second-order modes in a symmetric waveguide structure. Experimental results show that this device is twice as dispersive as two-mode interference (TMI) devices based on interference between the fundamental and antisymmetric modes. Channel spacings between 15 mu m and 40 nm were obtained with channel isolation in excess of +or-10 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of device length and background doping on the relative magnitudes of phase and amplitude modulation in GaAs/AIGaAs PIN multiple quantum well waveguide optical modulators: erratum

This erratum Letter points out an error in the caption of Fig. 4 of this paper.

Effect of device length and background doping on the relative magnitudes of phase and amplitude modulation in GaAs/AlGaAs PIN multiple quantum well waveguide optical modulators

In this paper we present a model for the behavior of a PIN waveguide optical modulator utilizing the quantum confined Stark effect. The model uses experimental data to determine the electric field dependence of absorption coefficient and refractive index changes in 100-A GaAs/100-A Al(0.3)Ga(0.7)As quantum wells, and then uses these data to model a symmetric waveguide structure with a core full of quantum wells. We have determined general design rules for the background doping and length of low chirp amplitude modulators and phase modulators with low amplitude modulation. The chief results are that the doping should be high for an amplitude modulator and low for a phase modulator, and in both cases the device should be kept short.