Mid-infrared luminescence properties of Dy-doped silver halide crystals

The absorption and the kinetics of the emission in the mid-infrared (mid-IR) were investigated in AgCl(x)Br(1-x) crystals doped with Dy(3+) ions. Strong emission bands were detected at 3, 4.4, and 5.5 μm and attributed to the (6)H(13/2)→(6)H(15/2), (6)H(11/2)→(6)H(13/2), and (6)F(11/2)+(6)H(9/2)→(6)H(11/2) transitions. Various optical parameters were calculated for the Dy(3+) doped crystals, using the Judd-Ofelt approximation and the rate equations. The measured results and the calculated parameters indicate that these doped crystals could be used for the development of mid-IR solid-state lasers or mid-IR fiber lasers.     

Infrared evanescent field sensing with quantum cascade lasers and planar silver halide waveguides

We demonstrate the first midinfrared evanescent field absorption measurements with an InGaAs/AlInAs/InP distributed feedback (DFB) quantum cascade laser (QCL) light source operated at room temperature coupled to a free-standing, thin-film, planar, silver halide waveguide. Two different analytes, each matched to the emission frequency of a QCL, were investigated to verify the potential of this technique. The emission of a 1650 cm(-1) QCL overlaps with the amide absorption band of urea, which was deposited from methanol solution, forming urea crystals at the waveguide surface after solvent evaporation. Solid urea was detected down to 80.7 microg of precipitate at the waveguide surface. The emission frequency of a 974 cm(-1) QCL overlaps with the CH3-C absorption feature of acetic anhydride. Solutions of acetic anhydride in acetonitrile have been detected down to a volume of 0.01 microL (10.8 microg) of acetic anhydride solution after deposition at the planar waveguide (PWG) surface. Free-standing, thin-film, planar, silver halide waveguides were produced by press-tapering heated, cylindrical, silver halide fiber segments to create waveguides with a thickness of 300-190 microm, a width of 3 mm, and a length of 35 mm. In addition, Fourier transform infrared (FT-IR) evanescent field absorption measurements with planar silver halide waveguides and transmission absorption QCL measurements verify the obtained results.     

Transmission of IR light by light guides made of silver halide solid solutions

The possibility of transferring IR emission by light guides made of silver halide solid solutions has been experimentally studied. The energy loss in transmission of the heat radiation through a light guide in various wavelength ranges of IR light was determined. The possibility of using IR light guides for transport of thermal energy and temperature measurements by IR thermography was considered.     

Bend loss effects in diffused, buried waveguides

Bend loss effects can be a significant concern in the design and performance of diffused, buried waveguide devices. Since diffused, buried waveguides typically do not have analytical mode solutions, the bend mode must be expressed as an expansion of straight waveguide modes. For the case of buried ion-exchanged waveguides, the bend loss is affected by bend radius, the duration of the ion exchange and burial processes, as well as the size of the mask opening used to create the waveguides and applied field during burial. The bend loss effects for each of these variables are explored under typical fabrication conditions.     

Finite signals in planar waveguides

We examine the evolution in phase space of an N-point signal, produced and sensed at finite arrays transverse to a planar waveguide within the framework of the finite quantization of geometric optics. We use the Kravchuk coherent states provided by the finite oscillator model to evince the nonlinear transformations that elliptic-profile waveguides produce on phase space by means of the SO(3) Wigner function.     

Empirical relations for the propagation characteristics of diffused channel waveguides

Empirical relations for the propagation constant and the field profile parameters of integrated optical diffused channel waveguides have been developed. The field profile used is the evanescent secant-hyperbolic field, which has been shown earlier to be a very good approximation for diffused channel-waveguide modes. Least-square fitting has been used to obtain the empirical relations. The results show that the error in empirical relations for the propagation constant is within 2% for a broad range of waveguide parameters. The obtained empirical relations for the field profile and the propagation constant have been used, as an example, to calculate the coupling length of diffused channel-waveguide-based directional couplers.     

Analysis of general multi-channel planar waveguides

Using the planar waveguide concept in surface acoustic wave (SAW) technology is often advantageous when the modeling of transversely distributed phenomena is indispensable for an accurate design of SAW devices. This is especially true when complex multi-track structures such as transversely coupled resonator filters (TCRFs) are under consideration where, e.g., transverse velocity and stiffness profiles have to be incorporated in the device simulation. The interdigital transducers (IDTs) and the reflector gratings composing those devices behave as planar waveguides, supporting, in principle, all kinds of modes such as bound, semi-bound, and radiation modes. Therefore, to model these SAW propagation effects, we subdivide the SAW structures in transverse direction into several parallel waveguiding channels (N regions), and take, as the wave-describing quantity, a two-dimensional scalar potential function. By doing so, we obtain a complete set of orthonormal modes into which an arbitrary transverse excitation function can be expanded to study its propagation. The general mode spectrum includes a discrete spectrum of bound modes and continuous spectra of semi-bound and radiation modes. We calculate all types of modes by making use of the stack matrix technique. The present work, which arose from the requirement of creating an efficient mathematical tool for the simulation of TCRFs, provides the complete analysis of general SAW multi-channel structures.     

Metal phosphate planar waveguides for biosensors

Hard, impermeable, glassy, metal phosphate films have been fabricated inexpensively by the use of a spin-coating and low-temperature-curing technique. Films that are suitable for use as monomode waveguides in biosensors have been identified through an examination of the optical and chemical properties of films containing Fe, Al, Ga, In, Cr, or V. The refractive index is controlled over the range 1.49-1.78 by varying the film composition. The film thickness is controlled over the range 50-1200 nm by varying the spin speed and the deposition temperature. Films can be patterned by photolithography or by embossing. Input coupling through an embossed grating of 833-nm pitch is demonstrated.     

Long-period gratings in planar optical waveguides

We present a theoretical analysis of light propagation in a four-layer planar waveguide that consists of a long-period grating (LPG) having a period of the order of 100 microm. By means of the coupled-mode theory, we show that such a structure is capable of coupling light from the fundamental guided mode to the cladding modes at specific wavelengths (resonance wavelengths) and thus results in sharp rejection bands in the transmission spectrum of the waveguide. Our numerical results show that the resonance wavelengths as well as the transmission spectrum can be significantly changed with the waveguide and grating parameters. A waveguide-based LPG should provide a useful approach to the design of a wide range of integrated-optic devices, including wavelength-tunable filters, switches, and environmental sensors.     

Photonic bandgap structures in planar waveguides

If a one-dimensional (1D) or two-dimensional (2D) photonic bandgap (PBG) structure is incorporated into a planar optical waveguide, the refractive-index nonuniformity in the direction perpendicular to the waveguide plane responsible for waveguiding may affect its behavior detrimentally. Such influence is demonstrated in the paper by numerical modeling of a deeply etched first-order waveguide Bragg grating. On the basis of physical considerations, a simple condition for the design of 1D and 2D waveguide PBG structures free of this degradation is formulated; it is, in fact the separability condition for the wave equation. Its positive effect is verified by numerical modeling of a modified waveguide Bragg grating that fulfills the separability condition.     

High-cycle fatigue of silver halide infrared fibers

The transmission of CO(2) laser radiation by silver halide infrared fibers was measured during cyclic bending of the fibers. High-cycle fatigue of the fibers was investigated. The fibers were found to transmit without significant deterioration after more than 10(7) cycles. The fatigue-stress limit, based on 10(7) bending cycles, was estimated to be approximately 75 MPa.     

Near-field characterization of thin planar optical waveguides

Abstract

A detailed near-field analysis of planar waveguides supporting two modes has been carried out. Theoretical calculations for both step- and gradedindex profiles, have shown the near-field features produced by interference of the two mode wavefunctions, which depend on their phase difference and intensity ratio. Theoretical results have been experimentally confirmed by performing an independent control of the two last magnitudes during the measurements. Fitting the calculated near-field intensity distribution to the measured one, the index profile of the waveguide has been reconstructed. The profile parameters differ by less than 5% from those obtained with the m-line method. Theoretical and experimental single mode analysis, also included for comparison, result in less accurate parameters showing index jump deviations, with respect to the m-line method, of the order of 10%.     

Ray analysis of parabolic-index segmented planar waveguides

A ray analysis of periodically segmented waveguides with parabolic-index variation in the high-index region is presented. We carried out the analysis using ray transfer matrices, which is convenient to implement and which can be extended to study different types of graded-index segmented waveguide. Results of this ray tracing approach clearly illustrate the waveguiding properties and the existence of stable and unstable regions of operation in segmented waveguides. We also illustrate the tapering action exhibited by segmented waveguides in which the duty cycle varies along the length of the waveguide. This analysis, although restricted to multimode structures, provides a clear visualization of the waveguiding properties in terms of ray propagation in segmented waveguides.     

Analysis of planar waveguides using wentzel-kramers-brillouin-type methods

Abstract

A presentation of four different schemes of semiclassical or Wentzel-Kramers-Brillouin-type approximations to planar waveguides is given. Attention is paid to a recent proposal for mapping a general symmetric waveguide into the hyperbolic secant or symmetric Epstein profile by exploring the dispersion relation and the fundamental mode field. As a test, these approximations are compared with the series solution of the cladded-parabolic profile.     

Theoretical study of Ti:LiNbO3 strip waveguides in the Mid-infrared

Abstract

The transverse magnetic and transverse electric mode size and effective refractive index as functions of the Ti-strip initial width W, diffusion temperature T and Ti-strip initial thickness H in c-cut Ti-diffused LiNbO₃ waveguides have been theoretically studied at wavelengths of 3.0 and 3.39 μm on the basis of modified expressions for the waveguide surface index increment. The single-mode, multiple-mode and cut-off conditions have been identified from those effective refractive index plots. These mid-infrared numerical results are discussed comparatively with near-infrared data reported earlier.     

Transverse electric modes in planar slot waveguides

Transverse electric (TE) modes in symmetrical planar slot waveguides are analytically solved, and a comprehensive knowledge about them is provided. It has been shown that there are four types of TE modes in planar slot waveguides just as the TM modes. Their field solutions, characteristic equations and cut-off conditions are derived. The cut-off conditions and the power confinement factors of the TE and TM modes are compared. It is demonstrated that there may be degeneration points between TE and TM modes. Because a three-dimensional waveguide has similar modal characteristics as its planar counterpart, our work presents a foundation of recognizing and utilizing the three-dimensional slot waveguides.     

Lithium iodate planar waveguides by proton implantation

Permanent optical waveguides have been produced by proton implantation in LiIO₃ single crystals by using a Van De Graaff accelerator. The effects of the crystal cut and of the implantation paramaters on the optical waveguides properties, investigated by dark line mode spectroscopy, are presented. The profiles of the ordinary and extraordinary refractive indices are reconstructed by an inverse WKB method. Optical barriers with depths of few hundredths (Δn < 0) are currently obtained and their location can be accurately adjusted from 4 to 17 μm.     

Free-electron masers based on planar Bragg waveguides

A new scheme of the free-electron maser (FEM) with a ribbon electron beam is proposed in which the radiation is channeled in an open planar Bragg waveguide structure of two parallel plates with corrugated inner surfaces. The direction of corrugation is parallel to the radiation group velocity vector. The electron beam propagates in the waveguide at a large angle to its axis. The electron translation velocity is parallel to the direction of propagation of one of the partial waves that form the waveguide mode, which makes the maximum Doppler up-shift of the radiation frequency possible. A nonlinear analysis shows that the proposed FEM scheme provides a high gain (up to 30 dB). Using the Bragg waveguide, it is possible to ensure effective mode filtration, thus controlling the spatial structure of the output radiation.     

Sol-gel planar waveguides for improved fluorescence microarrays

The real-time monitoring of the hybridization signal, giving access to the reaction kinetics, can widen the results of a microarray experiment. Nevertheless, the presence of a strong fluorescent mix often degrade the experimental sensitivity, limiting the interest of this technique: the implementation of an evanescent wave excitation scheme can represent in this case a real advantage. In this paper, we propose high refractive index waveguides fabricated by sol-gel process for evanescent wave microarray applications. The influence of the sol composition and annealing parameters on materials microstructure are carefully studied to obtain good optical properties and high refractive index (n = 1.8-2.1) using thermal treatments below 250 °C. Monomode TiO₂ planar waveguides chelated by acetic acid are used as substrates for waveguide-based microarray in real-time experiments, demonstrating a significant increase of the signal to noise ratio.