Showing papers by "Martin M. Fejer published in 1992"

Quasi-phase-matched second harmonic generation: tuning and tolerances

Abstract: The theory of quasi-phase-matched second-harmonic generation is presented in both the space domain and the wave vector mismatch domain. Departures from ideal quasi-phase matching in periodicity, wavelength, angle of propagation, and temperature are examined to determine the tuning properties and acceptance bandwidths for second-harmonic generation in periodic structures. Numerical examples are tabulated for periodically poled lithium niobate. Various types of errors in the periodicity of these structures are then analyzed to find their effects on the conversion efficiency and on the shape of the tuning curve. This analysis is useful for establishing fabrication tolerances for practical quasi-phase-matched devices. A method of designing structures having desired phase-matching tuning curve shapes is also described. The method makes use of varying domain lengths to establish a varying effective nonlinear coefficient along the interaction length. >

Preparation and characterization of off-congruent lithium niobate crystals

Abstract: Vapor transport equilibration was used to prepare lithium niobate crystals of a variety of controlled off‐congruent compositions. Crystals were characterized through measurement of the ferroelectric Curie temperature Tc and measurement of the temperature for noncritical phase matching TPM of second‐harmonic generation from both 1.064‐ and 1.32‐μm laser sources. Across the majority of the single‐phase region, both Tc and TPM were observed to vary nearly linearly with Li/Nb ratio. The variation in TPM with Li/Nb ratio was observed to change direction within the single‐phase region at some small but finite compositional interval away from the Li‐rich phase boundary. Crystals equilibrated to the Li‐rich phase boundary had excellent optical homogeneity. Preparation of Li‐poor crystals was hampered by extremely slow lithium diffusivity and problems with second‐phase precipitation.

Composition dependence of lithium diffusivity in lithium niobate at high temperature

Abstract: An investigation was performed on the diffusivity of lithium in lithium niobate at 1100 °C in the crystallographic z direction over the composition range from 4838 to 4985 mol % Li2O A vapor transport technique was applied to produce a lithium niobate crystal with a widely varying diffusion‐limited lithium concentration profile The profile was measured through spatially resolved measurement of the phase‐match temperature for frequency doubling of a Nd:YAG laser A Boltzmann–Matano analysis was applied to the profile to estimate diffusivity as a function of composition The validity of the Boltzmann–Matano results was examined through numerical simulation, taking into account finite interfacial mass transport A dramatic increase of lithium diffusivity with Li/Nb ratio was observed, ranging from roughly 3×10−9 cm2/s at the 4838 mol % Li2O congruent composition to roughly 50×10−9 cm2/s at 4985 mol % Li2O

Fused-silica monolithic total-internal-reflection resonator.

Abstract: We have characterized a miniature fused-silica monolithic optical ring resonator in which the Gaussian mode is confined by total internal reflection. Laser light is coupled into and out of the resonator by frustrating one of the total internal reflections by means of a prism. The resonator can be overcoupled and undercoupled by varying the resonator–prism distance. The minimum measured resonator linewidth was less than 3 MHz. This type of broadband, stable, low-loss resonator has applications in linear and nonlinear optics.

Fabrication, characterization and index profile modeling of high-damage resistance Zn-diffused waveguides in congruent and MgO:lithium niobate

Abstract: A study of the fabrication and optical properties of planar waveguides fabricated in MgO:LiNbO/sub 3/ and LiNbO/sub 3/ substrates by diffusion of a ZnO film is presented. Transmission electron microscopy was used to show that using ZnO instead of metallic zinc as a source, and maintaining the ZnO film thickness below a prescribed value, greatly reduces second phase precipitation and produces usable waveguides. Dopant and refractive index profiles were characterized by electron microprobe analysis and interference microscopy, respectively. The dependence of the Zn diffusion coefficient on temperature and the dependence of the refractive-index change on Zn concentration are inferred from these measurements. A simple model is also reported which predicts the index profile of the waveguide given the film thickness, diffusion time and temperature. The validity of the model is demonstrated by comparison between calculated profiles and profiles measured by prism coupling and IWKB analysis. >

Measurement of the spontaneous polar Kerr effect in YBa2Cu3O7 and Bi2Sr2CaCu2O8.

Abstract: The existence of spontaneous polar Kerr rotation in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ single crystals and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{7}$ thin films was tested using a Sagnac interferometer. Observation of this effect would be strong evidence that the superconductivity in the cuprates is described by a theory that predicts broken time-reversal symmetry. The Kerr effect was analyzed for both a spatially fluctuating component (anticipating domains) and absolute offset. Neither effect was observed within the sensitivity of the apparatus. The drift of the apparatus sets an upper limit for the offset component at 10 \ensuremath{\mu}rad. The noise places an upper limit of 3 \ensuremath{\mu}rad on the standard deviation of the spatial fluctuation of the effect.

Measurement of the second-order nonlinear susceptibility of proton-exchanged LiNbO 3

Abstract: We have measured the d33 nonlinear coefficient in proton-exchanged LiNbO3 by using angle-dependent reflected second-harmonic generation and observed a reduction to ≤1% of the bulk LiNbO3 value.

Nonlinear Frequency Conversion in Periodically-Poled Ferroelectric Waveguides

Abstract: By patterning the domains in ferroelectric crystals, it is possible to introduce periodic changes in the sign of the nonlinear susceptibility in waveguide frequency conversion devices. Appropriate choice of the spatial frequency of the modulation allows quasi-phasematching of any nonlinear interaction involving radiation in the transparency range of the crystal. Room temperature second harmonic generation of visible radiation and difference frequency generation of infrared radiation have been demonstrated.

Monolithic total internal reflection optical resonator

Abstract: The combination of a resonator having total internal reflection with a coupler providing coupling via frustrated total internal reflection. Both linear and non-linear embodiments are described. The linear embodiment is a spectrum analyzer. The non-linear embodiment is a second harmonic generator, although modifications are described for turning the same into an optical parametric oscillator.