Switching Of Light Beams Research Articles

Double symmetry breaking of solitons in one-dimensional virtual photonic crystals

We demonstrate that spatial solitons undergo two consecutive spontaneous symmetry breakings (SSBs), with the increase of the total power, in nonlinear photonic crystals (PhCs) built as arrays of alternating linear and nonlinear stripes, in the case when the maxima of the effective refractive index coincide with the minima of the self-focusing coefficient and vice versa (i.e., the corresponding linear and nonlinear periodic potentials are in competition). This setting may be induced, as a virtual PhC, by means of the electromagnetically induced-transparency (EIT) technique, in a uniform optical medium. It may also be realized as a Bose-Einstein condensate (BEC) subject to the action of the combined periodic optical potential and periodically modulated Feshbach resonance. The first SSB happens at the center of a linear stripe, pushing a broad low-power soliton into an adjacent nonlinear stripe and gradually suppressing side peaks in the soliton's shape. Then the soliton restores its symmetry, being pinned to the midpoint of the nonlinear stripe. The second SSB occurs at higher powers, pushing the narrow soliton off the center of the nonlinear channel, while the soliton keeps its internal symmetry. The results are obtained by means of numerical and analytical methods. They may be employed to control switching of light beams by means of the varying power.

On Bright and Dark Breathers in Lattices with Saturable Nonlinearity

In the past two decades the special attention is devoted to the strongly localized modes [1] which are promising candidates for guiding, steering, and switching of light beams in the nonlinear optical lattices. The effect of energy localization through discreteness and nonlinearity is universal and relevant for many non-optical systems, such as DNA-promoter dynamics [2], discrete breathers in a Josephson ladder [3], localized modes in the anharmonic crystals [4], or localization of matter waves in the Bose–Einstein condensates using optically-induced periodic potentials [5]. Bright discrete solitons have been studied in detail in photonic lattices exhibiting cubic, quadratic, saturable, and nonlocal nonlinearity [1, 6–9]. Because of various experimental difficulties and demand for higher input power dark solitons are investigated discernible rarely when compared to their bright analog [10, 11]. Very recently, stable propagation of on-site and inter-site dark solitons were experimentally observed in the self-defocusing lithium niobate waveguide arrays with saturable nonlinearity at microwatt power level [12, 13]. In this paper the comparative study of the moving localized bright and dark modes in lattices with saturable nonlinearity [14] is presented. This study is based on the grand canonical free energy concept [15] and analysis of the eigenvalue spectra of the localized configurations.

Electrically controlled switching of light beams in the plane of liquid crystal layer

A simple experimental method and a set-up to control light beams in the plane of liquid crystal (LC) cell is developed. The main idea of the method is the reflection and the refraction of light beams propagating in a plane of LC layer from the boundary, which separates the regions of a liquid crystal cell with different director orientations and refractive indices. This boundary can be produced by electric field applied to the LC layer with a planar homogeneous orientation. The disclination lines that separate the extremely sharp changes of LC orientation can be also used for this purpose. The possibility of discrete deflection of light beam from the initial direction is shown. A computer simulation confirmed that the proposed experimental geometry was most suitable to control intensity of extraordinary rays propagating in the plane of liquid crystal layer.

Ultrafast directional switching in photonic-crystal branched waveguides using electro-optical control

We propose and investigate ultrafast switching of light beams between different ports of a multibranch waveguide in photonic crystals. The branched waveguide is made of chains of coupled defects with degenerate states providing guided modes. Introduced at the corner of branches is a control cell made of an electro-optical active material. Depending on the symmetry of the refractive index changes, light propagation can be directed to specified direction. Dynamic changes of refractive index then provide ultrafast switching of light beams into a desired branch.

Permanent magnet-based guided-wave magnetooptic Bragg cell modules

Compact magnetostatic forward volume wave-based guided-wave magnetooptic (MO) Bragg cell modules have been realized by utilizing a pair of small samarium-cobalt permanent magnets together with a pair of current-carrying coils. A highly uniform DC magnetic field, has been obtained in the air gap where yttrium iron garnet-gadolinium gallium garnet (YIG-GdGG) waveguide samples are inserted. A tunable DC magnetic field as large as 2446 Oe corresponding to a tunable carrier frequency band of 6.85 GHz has been achieved. The resulting MO Bragg cell modules, at the optical wavelength of 1.303 mu m, with carrier frequencies ranging from 2.0 to 12.0 GHz have provided performance characteristics comparable to those obtained by using a bulk electromagnet. Compact MO Bragg cell modules have potential applications, such as scanning, switching of light beams, and real-time processing of wide-band microwave signals without requiring frequency down-conversion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical TIR switches using PLZT thin-film waveguides on sapphire

Light beam switching in a four-port channel waveguide has been achieved using electrooptic modulation of epitaxially grown PLZT thin film on sapphire. The switches exhibited a low drive voltage of 4.7 V with a switching speed of higher than 1 GHz.

Optical channel waveguide switch and coupler using total internal reflection

Light beam switching and coupling in a four-port channel waveguide-horn structure has been accomplished using electrooptic modulation of the critical angle of a refractive index interface in a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</tex> -cut LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> substrate. The resulting double-pole double-throw switch/coupler is potentially capable of simultaneously providing a combination of desirable characteristics.

A Method for Measuring High Reflectivity

Reflectivity measurement of highly reflective mirrors was made easily and efficiently, using a He–Ne laser, ordinary lenses and mirrors, and a silicon solar cell. The power of the incident and the reflected light beams are precisely compared by use of light beam switching by a rotating mirror and electronic sampling and integration. As the method utilized a single reflection at a point on the test mirror, it enables point-by-point measurement and is not influenced by the mirror curvature. The accuracy of the measurement was ±0.03%, and the nonlinearity of the photo-sensor and the electronics used in the measurement was assumed small enough compared to 2%.

Light beam switching and modulation using a built-in dielectric channel in LiNbO_3 planar waveguide

The results of light beam switching and modulation experiments utilizing electrooptic control of the refractive index of a built-in dielectric channel in a Y-cut LiNbO(3) planar waveguide are reported. The resulting device is capable of simultaneously providing a combination of desirable characteristies.

Light beam switching and modulation using a built-in dielectric channel in LiNbO3planar waveguide

The results of light beam switching and modulation experiments utilizing electrooptic control of the refractive index of a built-in dielectric channel in a Y-cut LiNbO3 planar waveguide are reported. The resulting device is capable of simultaneously providing a combination of desirable characteristics.