Shlomo Ruschin

Sol‐gel glass waveguides prepared at low temperature

Planar waveguides of TiO2‐organically modified silanes deposited on glass substrates were prepared by the sol‐gel method, either in a pure form or doped by red perylimide laser dye, and their optical properties characterized. The refractive index increases and film thickness decreases as TiO2 contents rise. Waveguiding in the pure film and the trapped luminescence in the doped films were measured. Typically three guided modes were observed.

Light amplification in a dye‐doped glass planar waveguide

Glass waveguiding films were prepared from titania and modified silica using the sol‐gel method and doped by the laser dye rhodamine B. The guided and amplified fluorescence (pumped by a double frequency Nd‐YAG laser) was coupled out either by static grating written on the film or by a prism. The gain of the emitted superradiance was determined from the amplified spontaneous emission intensity dependence on the pumped strip length. A maximum net gain of 54 dB/cm was measured.

Linear electro‐optic effect in sputtered polycrystalline LiNbO3 films

Light guiding and modulation was demonstrated in sputtered LiNbO3 films deposited on glass substrates. We report on films’ exceptionally low attenuation (<2 dB/cm) and the highest electro‐optical coefficient reported so far for this kind of film (1.34×10−12 m/V).

Evanescent Bessel beams

Bessel beams of the evanescent kind are presented and analyzed. They rapidly decay with propagation but retain their original transversal shape. A physical method of generation is proposed in the form of propagation of an ordinary (nonevanescent) Bessel beam across an interface between two different dielectric media. Transmission and reflection coefficients are calculated for this type of beam. The analysis is vectorial and is fully consistent with Maxwell’s equations. Apodized beams of Gauss–Bessel and Circ–Bessel types are propagated by numerical simulation and are shown also to retain a narrow central lobe. Beams of these types have evident advantages in near-field applications, microscopy, and high-density data storage with subwavelength resolution.

Coupling effects in symmetrical three-guide structures

A directional coupler consisting of three parallel waveguides is analyzed. The radiation is coupled between the two external guides, while the center-guide refraction index controls the coupling. By means of a coupled-mode analysis, a cross-and-bar diagram is drawn for the device, and regions are located in it for near-complete energy transfer between the guides. A rigorous mode analysis is presented for a three-guide layered structure, and the radiation-transfer process is numerically simulated for single-mode as well as for highly multimode guides. Although the analysis is carried out only for slab waveguides, the results are applicable for channel guides as well when the method of effective index approximation is utilized.

Modified Bessel nondiffracting beams

Solutions of the scalar-wave equation that are based on modified Bessel functions are introduced. These functions are radially nonoscillating, unbound, and nondiffractive. Their propagation constant is larger than that of vacuum, meaning that there is an inverse Guoy effect or a phase velocity smaller than c. The beams are physically realized by apodization of the modified Bessel profiles by means of suitable window functions. When Gaussian apodization functions are used, axial decay is slower than in the Gaussian case and the case of ordinary Bessel counterparts. Super-Gaussian and circular apodization are also examined. In the latter case a persistent narrow axial lobe that also has a nondecaying character is encountered.

Periodically segmented waveguides in Ti:LiNbO 3

Periodically segmented waveguides with periods of few tens of micrometers and nonconnected segments are studied experimentally in Ti:LiNbO(3). The near-field patterns were found to expand with decreasing duty cycle but to be independent of the segmentation period. The measured segmentation losses vary between 0.5 and 2.5 dB/cm, depending on the period and the duty cycle. These results agree with a simple numerical model, based on two loss mechanisms: waveguide segmentation and surface relief related to Ti indiffusion.

Monolithic rare-earth doped sol-gel tapered rib waveguide laser

We report the design, fabrication, and characterization of a monolithic tapered rib waveguide laser made of Nd doped silica hafnia sol-gel. The laser has a 604nm thick guiding layer. CW pumping was coupled in via a grating which also coupled out the lasing signal output, while reflection gratings supported the feedback. A lasing threshold of 20mW and an output power of 2.45mW were measured in a 3cm long device.

Ray model for transmission of metallic-dielectric hollow bent cylindrical waveguides.

The problem of transmitting CO(2) laser radiation through metallic or metallic with inner dielectric coating (metallic-dielectric) bent hollow cylindrical waveguides is investigated using a ray model. Computer calculations of transmission as a function of the geometrical dimensions of the waveguide are performed. The coupling of laser radiation at the entrance of the waveguide is also taken into account. The theoretical calculated transmission is compared with previously published experimental data and good agreement is obtained for a large range of curvatures. The devised ray model contributes to a better understanding of the role of the dielectric layer in the metallic-dielectric waveguide, increasing the transmission of the radiation. The calculation of the transmission as a function of the radius of the cross section of the waveguide shows that, for a best metallic-dielectric waveguide, an optimal cross-sectional diameter appears where the transmitted energy is maximum. The method presented will be of value as a tool in the design of hollow cylindrical waveguides.

Stimulated Raman scattering in methane-experimental optimization and numerical model

The stimulated Raman effect in methane was investigated both theoretically and experimentally. An experimental setup was used to optimize the Raman conversion of a 1.06-/spl mu/ laser source into a wavelength of 1.54 /spl mu/m in pressurized methane. Efficient conversion (up to 45% efficiency) is accomplished when using a full-resonator configuration for the Stokes wavelength. A numerical model is introduced, describing the Raman conversion process in the backward and the forward directions. Half-resonator and full-resonator configurations are studied. The results of the numerical model are in agreement with the experimental results. >