N. F. Hartman

Holographic formation of gratings in optical waveguiding layers

Thick phase gratings were formed photorefractively (through optically induced refractive index changes) in planar optical waveguides by intersecting short−wavelength coherent guided beams. In multimode guides formed by effusing Li from LiNbO3, maximum diffraction efficiencies were 52% at the 0.488−μm write wavelength and 3.1% at 0.633 μm. In a two−mode LiTa1−xNbxO3 guide formed by diffusing Nb into LiTaO3 at 1100 °C, diffraction efficiencies were 65% and 28% at the same two wavelengths, respectively.

Large-angle optical switching in waveguides in LiNbO3

Abstract Optical waveguiding layers displaying great photorefractive sensitivity have been formed by diffusion of iron into LiNbO3. Thick phase gratings of greater than 50% diffraction efficiency have been formed within such waveguiding layers by intersecting guided beams of red light from a He-Ne laser. By writing the gratings in a sample heated to 160°C, fixed gratings of about 1% diffraction efficiency have been produced. Modulation of the diffracted beam by electro-optic deflection of the input beam has been demonstrated.

Stoichiometry dependence of lithium outdiffusion in LiNbO3

Measurements by Mach‐Zehnder interferometry of the refractive‐index changes near the surface of outdiffused LiNbO3 crystals indicate that, in agreement with recent results of Noda et al. [J. Appl. Phys. 51, 1379 (1980)], the rate of lithium outdiffusion is greater for more nearly stoichiometric crystals. The activation energy for diffusion of Li does not vary significantly with stoichiometry. The Li diffusion coefficient is also higher in the relatively Li‐depleted regions near the surface.

Integrated Optics Devices Utilizing Thick Phase Gratings

Thick phase gratings have a variety of possible uses as device components in integrated optical systems. The applications make use of one or more of the unique properties of these gratings: high diffraction efficiency, good angular selectivity, and straightforward fabrication. In planar waveguides, the diffraction efficiency and angular selectivity desired for a particular application determine the length of the grating along the waveguide surface. We have holographically recorded 2 mm gratings having peak diffraction efficiencies in excess of 50% and angular selectivities less than 2 mrad by intersecting guided waves in a sample of photorefractive LiNbO3. Such gratings provide the central element in a number of actual and contemplated waveguide devices, including mirrors, beam splitters, lenses, switches, modulators, and interferometers.

Two-photon photorefractivity in pure and doped LiNbO3

Abstract Measurements at 5 wavelengths between 0.53 and 0.725 μm, and at moderate power levels in the 1–10 MW/cm2 range, indicate that two-photon photorefractive sensitivity in 0.1% iron-doped LiNbO3 is considerably greater than that in undoped crystals.

Characteristics of effused slab waveguides in LiNbO3

Concentration profiles for LiNbO3 surface optical‐waveguiding layers formed by diffusion‐controlled evaporation of Li2O are calculated on the assumption that the evaporant flux is small and proportional to the available lithium ion concentration at the surface. The calculated profiles are found to agree reasonably well with the index‐of‐refraction changes observed by Kaminow and Carruthers. The apparent concentration dependence of the diffusion coefficient is discussed qualitatively. Approaches to design of waveguiding layers of specified characteristic are described.

Fabrication of a 16-Channel Integrated Optical Data Preprocessor

A 16-channel integrated optical data preprocessor based on a Mach-Zhender interferometer configuration has been fabricated on a LiNbO3 substrate. The fabrication procedure is reviewed and a detailed discussion of the steps utilized to integrate the individual components is presented. The results of the device testing experiments are also discussed.

Optical erasure of one- and two-photon holograms in fe-doped linbo3

Abstract The dynamics of erasure of holographic gratings formed by one-photon and two-photon photorefractive processes in iron-doped (150 ppm) LiNbO3 have been studied as a function of wavelength of the erasing light. For a given wavelength and intensity of this light, the time constant for erasure of holograms recorded at 0.61 μm by a two-photon process is similar to that for erasure of one-photon holograms of the same grating spacing recorded at 0.488 μm. Thus the same ultimate traps appear to be involved in both recording processes. The minimum photon energy required to empty these traps is not greater than 1.9 eV. Rapid erasure occurs when the photon energy is above 2.35 eV.

Optical erasure of one- and two-photon holograms in lithium niobate

Abstract The dynamics of optical erasure of holographic gratings formed by one-photon and two-photon photorefractive processes in iron-doped (150 ppm) LiNbO3 have been studied as a function of wavelength of the erasing light. At a given erasing wavelength and intensity, the time constant for erasure of holograms recorded at 0.61 μm by a two-photon process is similar to that for erasure of one-photon holograms of the same grating spacing recorded at 0.488 μm; thus the same ultimate traps appear to be involved in both recording processes. The minimum photon energy required to empty these traps is not greater than 1.9 eV. Rapid erasure occurs when the photon energy is above 2.35 eV. These results will be compared with erasure dynamics in nominally undoped LiNbO3, and with the recording dynamics in the doped and undoped materials; and the implications for photorefractive recording mechanisms will be discussed.