Glen R. Fox

PLANAR DEFECTS IN ZNO THIN FILMS DEPOSITED ON OPTICAL FIBERS AND FLAT SUBSTRATES

The microstructure and the defects of ZnO coatings deposited at room temperature by sputtering onto fibers and flat substrates were characterized using transmission electron microscopy (TEM), scanning electron microscopy, and x-ray diffraction (XRD). XRD shows that the films have a [0001] preferred orientation and a large angular width of the 0002 reflection. According to TEM observations, the film microstructure consists of columnar grains which contain large concentrations of basal planar defects and dislocations. High-resolution transmission electron microscopy analysis and the associated image simulation are in full agreement with the presence of single (type I) and double (type II) stacking faults. The relation between the observed defects and the 0002 peak broadening is discussed.

Efficient miniature fiber-optic tunable filter based on intracore Bragg grating and electrically resistive coating

An electrically tunable reflection filter based on a platinum-coated single-mode optical fiber that contains an intracore Bragg grating has been demonstrated. The device shows a dc tuning range of 2.15 nm with a corresponding electrical power of 0.54 W. Wavelength modulation (WM) has been observed at frequencies lower than 100 Hz. The wavelength shift depends linearly on the electrical input power. A maximum efficiency of 4.1 nm/W is obtained for dc tuning.

FABRICATION AND STRUCTURAL ANALYSIS OF ZNO COATED FIBER OPTIC PHASE MODULATORS

Fiber optic modulators were fabricated by coating optical fibers with electrode and piezoelectric ZnO layers. The techniques of piezoelectric fiber optic modulator (PFOM) fabrication are presented, and the microstructure and crystallographic texture of the coatings are analyzed, Ln order to produce thick (approximately 5 mu m) ZnO coatings, it was necessary to study the reactive de magnetron sputtering process in O-2/Ar gas mixtures under conditions close to the transition between an oxidized and nonoxidized Zn target surface. In situ quartz crystal microbalance measurements of the deposition rate revealed thee distinct regions in the deposition rate (R) vs oxygen partial pressure (P-o2) behavior, at constant total pressure, for sputtering under conditions that provided an oxidized Zn target surface. Additionally, a transition between oxygen and argon dominated sputtering as observed by varying the sputtering pressure while maintaining a constant P-o2. The transition between oxygen and argon dominated sputtering influences R to varying extents within the three R vs P-o2 regions for an oxidized target surface. Correlations among the cathode current and voltage, deposition rate, and gas flow rate are presented to give a better understanding of the reactive sputtering processes occurring at the oxidized Zn target surface. Sputtering conditions optimized for a high ZnO deposition rate were used to produce [001] radially oriented ZnO fiber coatings for PFOM devices that can produce optical phase shifts as large as 0.38 rad/V.

400 MHz-bandwidth all-fiber phase modulators with ZnO coating on standard telecommunication fiber

Miniature all-fiber phase modulators with a radially symmetrical piezoelectric ZnO jacket have been characterized over a wide frequency range up to 1 GHz. Multiple radial resonances with phase shift values as high as 0.82 rad were observed in the frequency region between 20-400 MHz. A linear dependence of the phase shift on the square root of the driving power is observed up to 125 mW with a phase shift efficiency of 0.21 and 0.175 rad//spl radic/mW per centimeter fiber length at 196.5 and 399.5 MHz, respectively. The dependence of the phase shift efficiency on the modulation length is demonstrated.

Optical performance of miniature all-fiber phase modulators with ZnO coating

Miniature all-fiber phase modulators with a radially symmetrical piezoelectric ZnO jacket have been characterized using a Mach-Zehnder interferometer over a wide frequency range from 50 Hz to 50 MHz. The frequency response of the modulators consists of two flat broad-band regions and various resonances. The maximum phase shifts measured in the broadband and resonance regions are 0.1 and 7.5 rad/V/meter of fiber, respectively. A linear dependence of the phase shift on the applied voltage up to 60 V (peak-to-peak) is observed in the broad-band region.

All-fibre acousto-optic modulator using ZnO piezoelectric actuators

Abstract Acousto-optic modulators on optical fibres have been realized using a coating of zinc oxide. The phase shift response of the modulators is 0.5 mrad V −1 from 10 kHz up to 10 MHz and as high as 0.3 rad V −1 on radial resonance modes of the fibre above 20 MHz. A phase-shift amplitude of π /2 has been realized with 60 mW of driving power.

High-performance optical phase modulation using piezoelectric ZnO-coated standard telecommunication fiber

Optical phase modulation in a standard telecommunication fiber coated with a piezoelectric ZnO jacket has been investigated both experimentally and theoretically. The frequency response of the modulator exhibits 18 peaks between 20 and 800 MHz, which correspond to radial resonances of the coated fiber composite. A theoretical model was developed to explain the experimental results. The model takes into account the geometry of the modulator, nonuniform strain distributions, and the structure of the ZnO film. The calculated positions of the resonances and cancellation of phase modulation at frequencies higher than 800 MHz agree well with the measured data. The analysis also demonstrates the capability of tuning the resonances positions by varying the thickness of the ZnO jacket or the metal electrodes.

Piezoelectric coatings for active optical fiber devices

A new class of active fiber devices based on piezoelectric coated optical fibers is currently being developed. The piezoelectric coating is used to produce acoustic waves within the optical fiber and these acoustic waves interfere with optical signals passing through the fiber waveguide. Optical phase modulation devices based on piezoelectric coated fibers have been demonstrated and the behavior of these devices will be reviewed. A second type of active optical fiber device has been fabricated by integrating a piezoelectric fiber coating with an intra-core Bragg grating, which acts as a reflection filter. The primary interest of this work is to produce a piezoelectric fiber optic tunable filter. These types of active all-fiber devices show promise for a variety of applications including telecommunications and sensing networks. The performance of active optical fiber devices that use piezoelectric coatings is dependent on the device structure and the piezoelectric properties of the fiber coating. Several important geometric parameters (e.g. coating thickness and device length) that influence device performance have been experimentally identified. Additionally, several relationships between the fiber coating sputter deposition process, microstructure, and properties have been observed for piezoelectric ZnO fiber coatings. Recent advances in the development of active all-fiber devices are presented.

Microstructure and defects of wurtzite structure thin films

ZnO and AlN, which exhibit the wurtzite structure, were deposited onto metal coated SiO2 substrates by sputtering. X-ray diffraction (XRD) indicated that the films contained no second phases and exhibited an [0001] texture. Transmission electron microscopy (TEM) observations confirmed the XRD results and revealed the columnar microstructure of the films. The width of the columnar grains were less than 30 nm for AIN and between 100 and 400 nm for ZnO. In the ZnO grains, a large concentration of defects were identified, which included dislocations and stacking faults that lie on the basal plane

Optical fibers with patterned ZnO/electrode coatings for flexural actuators

A fiber-based flexural actuator was developed using a patterned piezoelectric ZnO/electrode fiber coating on a standard telecommunications optical fiber. The actuator was composed of a concentric inner Cr/Au electrode, a thick sputtered ZnO coating, and an outer Cr/Au electrode. Using standard photolithography, 30-μm wide gaps in one of the electrodes were patterned along 2-cm lengths parallel with the fiber axis. This device can be driven in a bimorph mode. It was demonstrated that a split electrode actuator could be excited into electromechanical resonance to produce useful displacements at the end of the fiber. Such flexural fiber actuators could be used in scanning near field optical microscopes for fiber tip height adjustment. In addition, the actuator design can be extended to manufacture two-axis integrated fiber alignment devices.