A polarization independent Fabry–Perot liquid crystal tunable filter coupled to an optical fiber is demonstrated using polarization diversity. Using a Wollaston prism, the beam splits into two orthogonal beams, while the polarization of one of the beams is rotated by 90 deg using a variable half wave plate. The two beams are then combined into an optical fiber. Tuning of unpolarized light over the range 720 to 800 nm is demonstrated.
A critical feature of one-dimensional photonic crystals (omnidirectional reflectors) is an existence of bandgaps
where both transverse electric (electric field perpendicular to the plane of incidence) and transverse magnetic
(magnetic field perpendicular to the plane of incidence) polarizations of impinging light are totally reflected for
any incident angle. In this paper it is shown that omnidirectional bandgaps of binary (two layers in the unit
cell) crystals might be increased when each cell is modified by a third layer with the refractive index value in
between of the refractive indices of two layers constituting the original cell.
This paper describes optical, durablility and environmental performance of a germanium carbide based durable antireflection
coating. The coating has been demonstrated on germanium and zinc selenide infra-red material however is
applicable to other materials such as zinc sulphide.
The material is deposited using a novel reactive closed field magnetron sputtering technique, offering significant
advantages over conventional evaporation processes for germanium carbide such as plasma enhanced chemical vapour
deposition. The sputtering process is "cold", making it suitable for use on a wide range of substrates. Moreover, the
drum format provide more efficient loading for high throughput production.
The use of the closed field and unbalanced magnetrons creates a magnetic confinement that extends the electron mean
free path leading to high ion current densities. The combination of high current densities with ion energies in the range
~30eV creates optimum thin film growth conditions. As a result the films are dense, spectrally stable, supersmooth and
low stress. Films incorporate low hydrogen content resulting in minimal C-H absorption bands within critical infra-red
passbands such as 3 to 5um and 8 to 12um.
Tuning of germanium carbide (Ge(1-x)Cx) film refractive index from pure germanium (refractive index 4) to pure
germanium carbide (refractive index 1.8) will be demonstrated. Use of film grading to achieve single and dual band
anti-reflection performance will be shown. Environmental and durability levels are shown to be suitable for use in harsh
external environments.
Single wavelength (670 nm laser diode) optical monitoring of reflectance at 1 second intervals was used to observe the
surface oxidation of Ni and Hafnium metal films in-situ in a low pressure oxygen atmosphere and also in a microwave
plasma oxygen environment.
After depositing thin metal films by sputtering in an oxygen-free environment, the observed reflectance quickly
decreased when low pressure oxygen gas was introduced into the vacuum chamber and reached a stable value within a
few seconds, after formation of a thin oxide layer. An additional rapid fall in reflectance and increase in oxide thickness
was observed when a microwave plasma generator was used to produce an oxygen plasma containing atomic oxygen.
Based on pre-determined optical properties of the metal and metal oxide films, the optical monitoring data was fitted to
obtain the thickness of the metal oxide as a function of time. The fitting results showed that the exposure to low pressure
oxygen forms an equilibrium thickness of less than 0.5 nm of NiOx and 0.78 nm of HfOx, while the oxygen microwave
plasma treatment produces an equilibrium thickness of 1.5 nm for both NiOx and HfOx.
Two complex multilayer thin-film filters have been produced by reactive e-beam evaporation. The filter specifications were challenging with respect to design and manufacturing. The optimized design configurations of 29- and 44-layer structures for the two filters, based on TiO2 and SiO2 as high- and low-index materials, have been finalized. The total thickness for the 29-layer filter is 2.1 µm and for the 44-layer filter is 4.1 µm. The deposition conditions and optical parameters of the material used were optimized and the films were characterized using spectrophotometry, atomic force microscopy, x-ray diffraction, and scanning electron microscopy, prior to manufacturing of multilayer structures. The multilayer structures are also characterized using the same techniques. Extremely good spectral performance, matching design specifications, has been achieved for the two filters, with compact and smooth film surfaces and dense structure. Both filters have been subjected to optical and structural characterization, and the results are discussed. The multilayer filters also passed the standard tape test to show good adhesion of the films to the substrate. The performance of the prepared filter samples are comparable with similar characteristic samples prepared by more energetic techniques like sputtering.
Optical thin films deposited using plasma ion assisted deposition (PAD) are characterized by ellipsometry, spectrophotometry and nano-indentation. PAD utilizes a dc voltage between an anode and a hot cathode, creating a high-density plasma that is extracted by an electromagnetic field. The assisted source allows denser, more stable films with higher refractive indices to be deposited without additional heating of the substrates. The primary advantage of the plasma compared to the ion source approach is that the plasma fills the vacuum chamber and couples into the evaporant, inducing partial ionization.
TiO2 thin films were deposited on the glass substrates by dc reactive magnetron sputtering technique at different sputtering pressures. The films prepared at low pressures have an anatase phase, and the films prepared at high pressures have an amorphous phase. The optical properties were studied by measuring the transmittance and the ellipsometric spectra. The optical constants of the films in the visible range were obtained by fitting the transmittance combined with the ellipsometry measurements using the classical model with one oscillator. The films prepared at the pressure higher than 6 x 10-3 mbar show a volume inhomogeneity. This volume inhomogeneity has been calculated by fitting the transmittance and the ellipsometric spectra.
Boron phosphide films prepared by PECVD have been characterised as a function of phosphine flow rate during deposition. The films were characterised by x-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), Nano-indentation and Scanning electron microscopy. The effect of phosphine flow rate during deposition on the dispersive, polar and acid-base components of the surface energy of the films was investigated. The components of the surface energy were determined by the Owens-Wendt (OW) and the Van-Oss-Chaudhry-Good (VOCG) methods. Both the Lifshitz-Van der Waaals dispersive interaction and the electron donor/electron acceptor acid-base components were found to depend on the phosphine flow rate during film preparation. Our results indicate the potential of Boron Phosphide films for tribological and engineering applications beyond their current application as protective coatings for soft infra-red transmitting substrates.
The corrosion susceptibility of Boron phosphide films prepared by PECVD, was studied in saturated saline solution as a function of phosphine flow rate during deposition. The chemical composition of the Boron phosphide films was determined by x-ray photoelectron spectroscopy (XPS) analysis. The investigation involved open circuit potential measurements (OCP) over several hours, potentiodynamic polarisation and electrochemical impedance Spectroscopy (EIS) measurements. The corrosion rate of the Boron Phosphide films was found to vary with changes in the phosphine flow rate during deposition. The results of our investigation also showed that Boron phosphide coated stainless steel plates had superior corrosion resistance, when compared to bare uncoated stainless steel plates. This opens up the potential for the application of Boron Phosphide films as a protective coating to improve the corrosion resistance of metals and alloys for various engineering applications.
The anode characteristic differences of n- and p- type germanium in aqueous solutions has been investigated in the early 1950's. n-type electrodes were always pitted after being made anode above the breakdown potential, whereas p-type electrodes exhibited an electro-polished surface finish.
Diamond Like Carbon (DLC) coated germanium has been used extensively as the material of choice in harsh sub-surface and surface seawater environments. It has been widely demonstrated that DLC coated germanium provides limited protection and that electrolytic etching of the germanium still occurs.
This paper investigates the corrosion resistance properties of Boron Phosphide on germanium in a naval environment by presenting measured, comparative data from tests and field trials.
KEYWORDS: Signal to noise ratio, Modulation, Sensors, Position sensors, Light sources, Electrodes, Amplifiers, Optical amplifiers, Inspection, Time metrology
Aluminium oxynitride thin films have been produced by using a reactive dc magnetron sputtering system incorporating a microwave plasma to improve the ionization of the reactive gases. This allows films of high optical quality to be deposited at commercially acceptable deposition rates. A series of homogeneous films of aluminium oxynitride films covering the range of compositions from aluminium oxide to aluminium nitride have been prepared and their optical constants characterized over the wavelength range 300 nm to 1500 nm. As a demonstration of the stability and reproducibility of the system, some complex graded-index optical filters have been designed and fabricated using a simple control program based only on setting the gas flows and times for each layer. The experimental results are shown to agree very well with theoretical results based on the dispersive optical constants of the individual layers.
Aluminium oxynitride of graded-index films in which the refractive index changes continuously with thickness over the range 1.56 - 1.97 have been produced by reactive RF sputtering. Optical properties and other characteristics with deposition parameters have been investigated by Fractional Factorial Designs. We showed that the optical density of laser rejection filters can be made close to 5 and rejection wavelength can be chosen from 300 nm to infrared, coupled with good optical properties, hardness and adherence of these films. This work also showed that Factorial Design is a very efficient way to investigate or optimize the sputtering conditions.
Diamond is an ultra-durable material with high thermal conductivity and good transmission in the visible, near IR and far IR wavebands. Advances in the performance of synthetic diamond made by chemical vapor deposition promise an expanding range of applications for the material. An example is in advanced airborne windows and domes for high- speed flight, either as a window or as a protective coating for other IR window materials. Diamond has sufficient durability to withstand high-speed impact by solid particles and raindrops and a high level of thermal conductivity to minimize the effect of thermal shock due to aerodynamic heating. However, diamond is subject to oxidation in air at temperatures greater than 750 degrees C. After only a few seconds exposure at such temperatures the diamond surface becomes severely etched, and the optical transmission is degraded. Very high-speed flight can lead to temperatures in excess of 800 degrees C. This means that, in high temperature applications, a coating is required which can protect the diamond surface from exposure to air. In addition the coating must have excellent adhesion and mechanical durability, and itself be resistant to impact. Using sputtered coatings based on aluminium nitride, we have demonstrated complete protection for extended exposures at temperatures up to 1000 degrees C. The coatings also have excellent mechanical durability as demonstrated by particle erosion test.
High quality coatings of aluminium oxynitrides have been deposited by reactive RF sputtering of aluminium in argon/oxygen/nitrogen atmospheres. Graded-index films in which the refractive index changes continuously with thickness over the range 1.6-2.0 have been produced by varying the oxygen and nitrogen content of the growing film. Computer control of the gas flow rates has allowed the reproducible production of laser rejection filters having optical densities greater than 4 and rejection wavelengths which can be chosen from < 300 to > 1100 nm. Scanning electron microscopy has shown that films when broken, tend to fracture preferentially at one particular composition. Depth profiling chemical analysis of the films has been carried our using x-ray photoelectron spectroscopy, showing clearly that the desired sinusoidal composition variations with depth has been achieved in these films.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.