"Closed field" magnetron (CFM) sputtering offers a flexible and high throughput deposition process for optical coatings and thin films required in display technologies. CFM sputtering uses two or more different metal targets to deposit multilayers comprising a wide range of dielectrics, metals and conductive oxides. Moreover, CFM provides a room temperature deposition process with high ion current density, low bias voltage and reactive oxidation in the entire volume around the rotating substrate drum carrier, thereby producing films over a large surface area at high deposition rate with excellent and reproducible optical properties. Machines based on the Closed Field are scaleable to meet a range of batch and in-line size requirements. Typically, thin film thickness control to < ±1% is accomplished simply using time, although optical monitoring can be used for more demanding applications. Fine layer thickness control and deposition of graded index layers is also assisted with a specially designed rotating shutter mechanism. This paper presents data on optical properties for CFM deposited optical coatings, including anti-reflection, IR blocker and colour control and thermal control filters, graded coatings, narrowband filters as well as conductive transparent oxides such as indium tin oxide. Benefits of the CFM sputter process are described.

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.

Using two or more materials to deposit a composite film has an advantage to get a film with desired refractive index. Besides, its optical property and mechanical property are better than a film deposited by a single material. In this study, (TiO₂)_X(Ta₂O₅)_1-X composite films have been prepared by a radio frequency ion beam sputtering deposition (RF-IBSD) where x was determined by the area ratio of titanium to tantalum targets. The optical constants of (TiO₂)_X(Ta₂O₅)_1-X composite films were calculated from their spectra by using envelope method. The refractive indices ranged from 2.481 to 2.165 at 550nm, and the extinction coefficients were lower than 1x10^-3 for wavelength in the ranges of 400nm to 600nm and lower than 1x10^-4 for wavelength longer than 600nm. The surface roughness of all composite films was about 0.1nm. The stress decreased from -520MPa for pure TiO₂ film to less than -280MPa for the composite films as measured by a phase-shift Twyman-Green interferometer. When the content of TiO₂ was less than 79.5%, the composite films were amorphous even post-baked to 400°C as measured by x-ray diffraction. The composite films mixed with TiO₂ and Ta₂O₅ can improve thermal stability and reduce extinction coefficient and stress. Composite films can replace the conventional high refractive index layer prepared by a single material to fabricate multilayer filters, and it is also suitable for high temperature applications, such as high reflection coating of projector lamps.

Metal oxide layers produced by plasma ion-assisted deposition are extensively used for complex optical coatings due to the availability of materials, the high packing density of films, and the smooth surfaces. Stringent optical surface figure specifications necessary for both laser optics and precision optics require film stress to be well controlled and surface deformation to be corrected or compensated. In this paper, SiO₂ based single cavity UV narrow bandpass filters were prepared by plasma ion-assisted deposition. The correlation between film stress, refractive index, deposition parameters, and post deposition annealing was established. The film stress was calculated based on interferometric surface deformation. The refractive index and film thickness were determined by means of variable angle spectroscopic ellipsometry. The center wavelength of the filters was obtained through spectral transmission measurement. The results suggest that the wavefront distortion of the multilayer coatings is dominated by the compressive stress of the SiO₂ layers, and can be controlled and corrected by the amount of plasma ion momentum transfer, substrate temperature, post deposition annealing, and stress compensation via backside SiO₂ coating. Based on the understanding of the mechanical and optical properties, the wavefront correction technique enables us to satisfy stringent surface figure specifications.

Ion beam sputtering enables high laser damage threshold mirrors to be manufactured. Oxygen partial pressure was found to have significant influence on the microstructure and optical properties of HfO₂ thin films deposited by ion beam sputtering (IBS). Atomic force microscopy studies have shown that the surface of single HfO₂ films is clearly characterized by deep holes. When oxygen is excessive, the RMS roughness of the surface increases with the presence of the holes, and the transmittance of the single HfO₂ layers reduces evidently in the shortwave spectral region. The laser-induced damage threshold (LIDT) of HfO₂/SiO₂ multilayer stacks was investigated with a diode pump laser at 1064 nm under a certain repetition frequency. The laser-induced damage morphology of DPL thin films were observed by the optical microscope. SiO₂ overcoats increase the damage threshold and modify the damage morphology of IBS coatings. The LIDT of the cavity mirrors is > 1 GW/cm² at 1064 nm (80 ns, 10 KHz).

Since 1990 thin film optical coatings have taken a prominent role in the development of highly efficient solar power concentrators for future space applications. During the initial development of this coating technology, the Boeing High Technology Center explored various ways of protecting ENTECH's DC93-500 silicone Fresnel lenses from the harsh space environment. ENTECH's mini-dome lenses focused solar energy onto small high-efficiency solar cells for generating electrical power. To protect the silicone lenses from solar UV darkening, one early approach involved a cerium-doped glass cover cemented over the lens. Unfortunately, during launch simulation shock testing the glass lens covers cracked. We next explored the deposition of a UV blocking thin film coating directly to the silicone lens surface. This was a problem of immense proportions analogous to pouring concrete on to the surface of a reservoir filled with "Jell-O." Differential in coefficient of thermal expansion between the DC93-500 silicone and the deposited dielectric optical coating had to be balanced with intrinsic stress of the optical coating materials. Ion Beam Optics' work has culminated, some fifteen years later, in the current coating technology that is being incorporated in the Stretched Lens Array SquareRigger (SLASR). SLASR is designed to replace classic flat panel solar arrays with a lighter, lower cost, and more efficient (30%) concentrator arrays for future space applications. This paper will describe the coating technology and show its performance and benefits for SLASR space power systems. Results from both ground tests and space flight tests will be presented.

The limit sensitivity of interferometric gravitational wave antennas is set by the thermal noise in the dielectric mirror coatings. These are currently made of alternating quarter-wavelength high/low index material layers with low mechanical losses. The quarter-wavelength design yields the maximum reflectivity for a fixed number of layers, but not the lowest noise for a prescribed reflectivity. This motivated our recent investigation of optimal thickness configurations, which guarantee the lowest thermal noise for a targeted reflectivity. This communication provides a compact overview of our results, involving nonperiodic genetically-engineered and truncated periodically-layered configurations. Possible implications for the advanced Laser Interferometer Gravitational wave Observatory (LIGO) are discussed.

When sampling a periodic image that includes high spatial frequencies with a digital image device, alias distortion is always produced. To reduce the distortion, an optical low-pass spatial filter (OLPF), which cuts off the high spatial frequency, can be applied. In this study thin-film phase grating optical low-pass filter (GOLF) with two-phase and three-phase of have been analyzed. By matching the period of the grating to the thickness of the thin film of two-phase GOLF, the cut-off bandwidth was twice of the pass bandwidth. By using the same technique, the cut-off bandwidth of three-phase GOLF was five times of the pass bandwidth. Two-phase GOLF was fabricated by using physical vapor deposition technology with a metal mesh as mask and showed advantages of being simple, cheap and good for mass-production as compared with the conventional methods. The surface profiles of the thin-film phase GOLF was measured by a white light interferometer. The optical property, the modulation transfer function (MTF) was measured by a MTF measurement system. Both results showed good agreement with the theoretical calculation. The image of a digital image device also showed the Moire pattern was suppressed successfully by the thin-film phase GOLF.

We developed coatable retarders for visible range of light. The Thin Birefringent Film (TBF) retarders are based on the newly developed family of water-soluble salts of aromatic polycyclic compounds, which absorb light in the ultra violet region of light spectra. TBF retarders are produced by coating and subsequent drying of an aqueous formulation on plastic or glass surface, thereby transforming the liquid coating material into molecularly oriented crystalline or amorphous nano-film. The TBF retarders are transparent in the whole visible spectral region and exhibit dichroic polarization characteristics in the UV region. We have produced films with thicknesses in the range of 100 nm to 1100 nm. Obtained TBF exhibit the negative A-plate birefringence characterized by Δn = n_e - n₀ = - 0.35 at 550nm. The thin form factor and the ability to coat on a variety of substrates give coatable retarders a great degree of design flexibility and advantages in LCD related applications. LCD applications of TBF retarders are also discussed.

The health risks associated with the inhalation or ingestion of cadmium are well documented. During the past 18 years, EU legislation has steadily been introduced to restrict its use, leaving a requirement for the development of replacement materials. This paper looks at possible alternatives to various cadmium II-VI dielectric compounds used in the deposition of optical thin-films for various opto-electronic devices. Application areas of particular interest are for infrared multilayer interference filter fabrication and solar cell industries, where cadmium-based coatings currently find widespread use. The results of single and multilayer designs comprising CdTe, CdS, CdSe and PbTe deposited onto group IV and II-VI materials as interference filters for the mid-IR region are presented. Thin films of SnN, SnO₂, SnS and SnSe are fabricated by plasma assisted CVD, reactive RF sputtering and thermal evaporation. Examination of these films using FTIR spectroscopy, SEM, EDX analysis and optical characterisation methods provide details of material dispersion, absorption, composition, refractive index, energy band gap and layer thicknesses. The optimisation of deposition parameters in order to synthesise coatings with similar optical and semiconductor properties as those containing cadmium has been investigated. Results of environmental, durability and stability trials are also presented.

Zinc oxide (ZnO) thin films were deposited on quartz, silicon, and polymer substrates by pulsed laser deposition (PLD) technique at different oxygen partial pressures (0.007 mbar to 0.003 mbar). Polycrystalline ZnO films were obtained at room temperature when the oxygen pressure was between 0.003 mbar and .007 mbar, above and below this pressure the films were amorphous as indicated by the X-ray diffraction (XRD). ZnO films were deposited on Al₂O₃ (0001) at different substrate temperatures varying from 400°C to 600°C and full width half maximum (FWHM) of XRD peak is observed to decrease as substrate temperature increases. The optical band gaps of these films were nearly 3.3 eV. A cylindrical Langmuir probe is used for the investigation of plasma plume arising from the ZnO target. The spatial and temporal variations in electron density and electron temperature are studied. Optical emission spectroscopy is used to identify the different ionic species in the plume. Strong emission lines of neutral Zn, Zn⁺ and neutral oxygen are observed. No electronically excited O⁺ cations are identified, which is in agreement with previous studies of ZnO plasma plume.

Dense Wavelength Division Multiplexers (DWDM), a kind of narrow band-pass filter, are extremely sensitive to the optical thickness error in each composite layer. Therefore to have a large useful coating area is extreme difficult because of the uniformity problem. To enlarge the useful coating area it is necessary to improve their design and their fabrication. In this study, we discuss how the tooling factors at different positions and for different materials are related to the optical performance of the design. 100GHz DWDM filters were fabricated by E-gun evaporation with ion-assisted deposition (IAD). To improve the coating uniformity, an analysis technique called shaping tooling factor (STF) was used to analyze the deviation of the optical thickness in different materials so as to enlarge the useful coating area. Also a technique of etching the deposited layers with oxygen ions was introduced. When the above techniques were applied in the fabrication of 100 GHz DWDM filters, the uniformity was better than +/-0.002% over an area of 72 mm in diameter and better than +/-0.0006% over 20mm in diameter.

Optical transmission systems have evolved rapidly in recent years with the emergence of new technologies for gain management, wavelength multiplexing, tunability, and switching. WDM networks are increasingly expected to be agile, flexible, and reconfigurable which in turn has led to a need for monitoring to be more widely distributed within the network. Automation of many actions performed on these networks, such as channel provisioning and power balancing, can only be realized by the addition of optical channel monitors (OCMs). These devices provide information about the optical transmission system including the number of optical channels, channel identification, wavelength, power, and in some cases optical signal-to-noise ratio (OSNR). Until recently OCMs were costly and bulky and thus the number of OCMs used in optical networks was often kept to a minimum. We describe a family of tunable thin film filters which have greatly reduced the cost and physical footprint of channel monitors, making possible 'monitoring everywhere' for intelligent optical networks which can serve long haul, metro and access requirements from a single technology platform. As examples of specific applications we discuss network issues such as auto provisioning, wavelength collision avoidance, power balancing, OSNR balancing, gain equalization, alien wavelength recognition, interoperability, and other requirements assigned to the emerging concept of an Optical Control Plane.

A polynomial inversion for the substrate optical constant of a transparent-film transparent-substrate system is analytically derived and presented. The reader is spared the derivation procedure which includes involved numerous transformations and algebraic manipulations. Also, closed-form formulae are given to calculate the film thickness of the system. The closed-form formulae are algebraically accurate and introduce no errors. A study of the effects of the experimental random and systematic errors of modern-day ellipsometers is presented which proves the very high accuracy of the method. The method does not need a guessed starting solution and it always provides the correct answer with no divergence. Those are important advantages over the widely used, manufacturer supplied, fitting routines.

Many applications of Laser diode require antireflection coatings either on one or both the facets of the diode. These include, for example, semiconductor optical amplifiers, optical pumping for solid state lasers and creation of broad band source for tunable external cavity. We have used single layer antireflection coating on the front facet of the laser diode using electron beam evaporation technique to enhance optical power output from the facet. To optimize the coating conditions with precise control over facet reflectance of the laser diode, we have carried out experiment for In-Situ reflectivity measurement. We have used MgF₂ as a low refractive index dielectric material for antireflection coating. The actual single layer AR coating consists of λ/4 thick MgF₂ film. The reflectivity of the film being deposited is measured on GaAs test substrate, kept in close vicinity of the laser diode bar, with the help of a 657 nm (red) laser diode and a photo detector. A LabVIEW programme, called Virtual Instrument (VI), has been prepared to automate the whole experiment. We have also carried out simulation of facet reflectivity subject to the film thickness being deposited.

Experimental results of reflection and light scattering measurements using the technique of attenuated total reflection (ATR) in the Kretschmann configuration of a system when it is excited an electromagnetic guided mode are reported. The system used is BK7 glass-prism/Dielectric1/Dielectric2/Dielectric1/air, where the refractive index of dielectric1 is less than the refractive index of the dielectric2. It was found a dip in the specular reflection as a function of the incident angle due to the excitation of a guided mode in the dielectric2 film. The guided mode was found for s polarization of the incident light. The angular dependence of the scattered light displays a peak caused by single-scattering and located approximately at the angles of excitation of the guided modes whose normalized wave numbers are less than the refractive index of the glass. Values of thickness, refractive index and absorption index obtained from Lorentz dispersion model of the film are reported.

We report about properties of Gallium Nitride layers doped by Erbium and Erbium/Ytterbium ions. The GaN layers were fabricated by Metal Organic Chemical Vapor Deposition on sapphire substrate, and Er³⁺ and Yb³⁺ ions were incorporated into the deposited layers by using ion implantation. After the implantation the samples were annealed in nitrogen atmosphere. The structures of the GaN samples were examined by the X-Ray Diffraction analysis; composition of the samples was measured by Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis. The GaN layers had single crystalline hexagonal wurtzite structure and content of Er³⁺ and Er³⁺\Yb³⁺ ranged from 0.05 to 3.38 at. %. The photoluminescence measurement was carried out at excitation of λ_ex = 632.8 nm (temperature 4 K) and λ_ex = 980 nm (room temperature). Photoluminescence spectra taken at 4 K showed typical erbium ⁴I_13/2→⁴I_15/2 emission bands. Some of our samples exhibited the desired emission even at the room temperature, which indicated that the samples were of a good quality what concerned their crystallographic homogeneity, as well as distribution and appropriate concentration of the Er³⁺ and Yb³⁺.

We report about theoretical results and experiments, which led to the demonstration of optical bistability on the specially modified laser diode (LD) created on the double heterostructure Ga_1-xAl_xAl/GaAs with saturable absorption section. To prove the bistability, the time method for bistability impulse verification (BIV) by bistable laser diode (BLD) was proposed. With the use of the BIV method, basic parameters of the hysterisis loop of the W-A characteristic samples of realized BLD were determined. Also the mathematic model of the W-A characteristic was derived, used for the simulation of the characteristic for the realized BLD. Element values of the electrical equivalent circuit of the BLD for small changes of signal were calculated for selected operating points of the simulated W-A characteristics. The dependency of bistability on the temperature is monitored by measuring the BLD W-A characteristic.

We discuss the X-measuring ellipsometer which measures the film-thickness exponential function of a film-substrate system: detecting two conditions on X. It works for all types of film-substrate systems: negative, zero, and positive. Only the transparent zero film-substrate system is discussed in detail. We present more than one ellipsometric configuration to implement the technique. We also present the inversion procedure to obtain the optical constants of the film and the substrate, in addition to the film thickness. Closed-form formulas to obtain the film thickness; the film thickness and its multiplicity; or the film thickness, its multiplicity, and the film and substrate optical constants using one, two, or three measurements, respectively. The instrument is versatile, accurate, fast, and is easily automated. The measurement multiplicity as related to the film thickness, and the permissible-thickness bands and forbidden-thickness gaps are briefly presented and discussed.