J. L. Jackel

Proton exchange for high‐index waveguides in LiNbO3

We describe the fabrication and characterization of optical waveguides formed in LiNbO3 by proton exchange in benzoic acid melts at 200–250 °C. Proton exchange, in LiNbO3 the replacement of lithium ions with protons, takes place when the substrate is immersed in the molten acid. We observe a surface increase in the refractive index of 0.12, for the extraordinary polarization only, with a step function index profile. This is the highest index increase obtainable to date for LiNbO3. Measured diffusion rates for x‐cut crystals are 1.37 μm2/h at T = 249 °C and 0.37 μm2/h at T = 217 °C, so that very deep guides can be formed in short times. Diffusion is somewhat slower in the z direction. The process as described is not useful for y‐cut crystals, since it damgaes this surface. Losses, measured on x‐cut samples, were <0.5 dB/cm. All measurements were made at 0.633 μm.

Elimination of out‐diffused surface guiding in titanium‐diffused LiNbO3

We describe a means of eliminating undesired surface guiding in titanium‐diffused strip waveguides on LiNbO3. Surface guiding for light of the extraordinary polarization, normally produced when the crystal is diffused in dry argon or oxygen, can be eliminated entirely by adding water vapor to the diffusion gases. Infrared absorption measurements show that hydrogen enters crystals diffused in a wet atmosphere. Although the mechanism for the prevention of surface guiding is not fully understood, we suggest that the presence of excess hydrogen reduces lithium mobility.

Continuous electrowetting effect

We introduce a new electrowetting effect, continuous electrowetting (CEW), and show its advantages for applications to displays and other electro‐optic devices. We demonstrate experimentally, by using CEW, fast and reversible electrowetting flow on the theoretically predicted scale of ∼10 cm/s for ∼1‐V driving voltage.

Electrowetting switch for multimode optical fibers

Construction and characterization of an optical switch, based on electrowetting and suitable for use with multimode fibers are described. With a 50-μm core, 0.23-N.A. input and output fibers, the measured fiber-to-fiber insertion loss at λ = 0.633 μm was 0.5 ± 0.1 dB for one channel and 2.0 ± 0.2 dB for the other, with cross talk of −22.8 ± 0.5 and <−51 dB, respectively. Response time is ≈20 msec with driving power of ≈25 μW and a voltage requirement of ≤1.0 V. The switch has been tested for over 107 cycles with no observable degradation.

Reactive ion etching of LiNbO3

We describe the reactive ion etching of LiNbO3 in gas mixtures containing CCl2F2, CF4, O2, and Ar. The effects of gas composition and pressure, in the range 1–10‐μm total pressure are discussed. Because it is possible to replicate fine features (∼2000 A) with control of etch profiles, we expect the process to be used for three‐dimensional patterning of LiNbO3 for electro‐optic and acoustic‐optic devices.

Short-And Long -Term Stability In Proton Exchanged Lithium Niobate Waveguides

We describe fabrication conditions which produce proton exchanged waveguides with long and short term index stability. We present also the surface index change and effective diffusion coefficients associated with exchange in melts of varying concentration, from pure benzoic acid to mixtures containing up to 4 Mole % lithium benzoate. Infrared absorption measurements supporting our explanation for the causes of index instability are presented.

Proton exchange in LiNbO3

Abstract This paper reviews the recently described process of proton exchange in LiNbO3 and reports some current results. Only results directly applicable to integrated optics will be described, although other applications are possible, and much of the work is interesting from a more fundamental point of view.

Dynamic Sensing for Robots: An Analysis and Implementation

Dynamic sensing is discussed in detail. We have initiated a systematics of robotic sensor design by formulating the general problems and addressing the specific question of how to arrange the sensing elements. We have derived a general relationship between the number and speed of the sensing elements as a function of their response and processing times. We have thus constructed afiber-optic sensor for the fingers of a Unimation Puma 500 robot. The sensor consists of three linear arrays ( each with 12 sensing elements), attached to the edges of the robot fingers in a U shape. The elements are composed of parallel, equally spaced, collimated light beams that pass from finger to finger. Each linear array can be scanned dynamically to provide a 12 X 18 = 256-pixel cov erage of a 2 X 3-cm area.

High‐Δn optical waveguides in LiNbO3: Thallium‐lithium ion exchange

Waveguides with large Δne have been fabricated in x‐cut LiNbO3 using ion exchange in a TlNO3 melt. The exchange was carried out at ∼240 °C, producing surface index increases of Δne ≅0.12–0.13. No increase in Δn0 was seen. A simple index profile resulting in the best fit to the observed mode structure is a step‐index profile. Analysis of the diffusion process shows that such a profile can be produced by ion exchange in which self‐diffusion coefficients of the two counterdiffusing species are concentration dependent. This provides the first direct evidence that ion exchange occurs in LiNbO3.

Variation in waveguides fabricated by immersion of LiNbO3 in AgNO3 and TlNO3: The role of hydrogen

Optical waveguides fabricated in LiNbO3 by what has previously been described as silver‐lithium or thallium‐lithium ion exchange in the molten nitrates AgNO3 or TlNO3 have not generally been reproducible. We show that the large increases of the extraordinary index (Δne = 0.12), which are observed intermittently, result not from introduction of the heavy ions, Ag+ or Tl+, but from hydrogen‐lithium exchange, which occurs when hydrogen is present as an impurity in the melts.