Dual-band infrared optical systems require complex designs to meet their optical and thermal requirements. This complexity involves an increase in the number of elements and, typically, a greater variety of substrate materials. Many of the elements are lenses, therefore requiring the maintenance of coating thickness uniformity and durability over curved surfaces. Coating thickness uniformity can be predicted using commercially available modeling software that takes into consideration the locations of sources, monitors, substrates and any motion of the parts during deposition. The coating chamber configuration can then be optimized for thickness uniformity. Coating environmental durability is more difficult to predict, however. It is commonly accepted that there is a correlation between the coating deposition angle, the porosity of the coating and its durability. The durability of a coating deposited on flat witnesses is not necessarily representative of that of the coating deposited over the surface of a curved lens. Therefore, the deposition angle distribution must also be taken into consideration when optimizing for coating uniformity. We discuss the optimization of a coating chamber configuration for the challenging geometry of a 6” diameter lens with a 6” radius of curvature. The configuration is optimized for both thickness uniformity and deposition angle distribution. Coating uniformity and durability are measured on a monolithic lens substrate as well as on witnesses arrayed in surrogate tooling simulating the lens surface. The coating durability on the witnesses and full lens are analyzed with respect to modelled uniformity and deposition angle distributions.
Bandpass filters transmitting the 3.5 to 5.0μm atmospheric window while simultaneously blocking the 4.3μm CO2
absorption band are in demand. However, realization of these dual bandpass filters is challenging from the standpoint of
coating design, material selection, and manufacturing process.
JDSU's Ucp-1 magnetron sputtering platform is ideally suited to the production of these types of filters. It enables the
use of coating materials with higher transmission and lower temperature shifts than conventional (i.e. thermally
evaporated) MWIR materials. Ucp-1 also has excellent layer thickness control, which allows complex designs to be
The performance of a dual bandpass filter manufactured for AFRL as part of their "Exploration of Novel Band-pass
Filter Designs" program is discussed. The filter achieved average transmission in the passbands of greater than 94% with
filter slopes of 1.1% or less. Blocking of the CO2 band was less than 1%, and the below and above band blocking was
less than 0.1%. All of the filter requirements were met over the temperature range of 77K to room ambient. We also
discuss the results achieved in extending the above approach to the design and manufacture of a quadruple bandpass
filter (with passbands centered at 1.23, 1.6, 2.2, and 3.75μm).
Narrow notch and multi-notch thin-film filters have applications in many fields. Raman spectroscopy and laser-based fluorescence instruments both desire filters that can remove one or more narrow spectral bands while maintaining high transmittance for light at adjacent wavelengths. Key figures of merit for notch filters include the width of the notch as a fraction of the blocked wavelength (narrower is better), the degree of suppression, and the overall transmittance of the filter.
Design approaches for narrowband notch and multi-notch filters are well-known, and include rugate or "quasi-rugate" designs. The manufacturing of these filters has proven to be challenging. The filters have to be very thick to achieve high suppression, and typically involve the deposition of gradient index layers or many very thin, discrete layers. Accurate spectral placement of the notches often requires extreme process control or post-deposition tuning of the filter.
JDSU has recently developed a design and manufacturing capability for single and multi-notch filters in the visible wavelength region where the notch width is less than 2% and the blocking levels are greater than OD 6. Designs for these types of filters can be 20 - 60 &mgr;m thick and consist of more than 1,000 layers. Our Ucp-1 high-rate magnetron sputtering platform with load-lock provides an inherently stable deposition process. This enables us to coat these challenging designs. In this paper, we present examples of both single and multi-notch filters that have 612 to 4410 layers and are 31 to 127 &mgr;m thick.
JDSU has developed a new family of optical retarders based on liquid crystal polymer (LCP) and form birefringent
dielectric thin film technologies. The manufacturing processes are wafer-based, allowing components up to 200mm
diameter to be produced. The component designs allow customization over a wide range of retardance values with
excellent accuracy, uniformity and low transmitted wavefront distortion. Form birefringent components are integrated
monolithically with an LCP-based retarder to create flat retardance response of ±2nm over an incident cone angle of
±30degrees. This paper will present an overview of the technology, measured performance attributes and provide
examples of product applications.
Due to high launch vehicle costs, space instrumentation designers are constantly pressured to decrease weight and increase reliability of flight hardware. To meet these needs in a spectrometer, the infrared products team at Optical Coating Laboratory, Inc. (OCLI) and the NASA Goddard Space Flight Center (GSFC) have developed an infrared logarithmically variable filter for use in NASA's Pluto Fast Fly-by instrument. The filter and diode array combination replaces the multiple optical elements in conventional spectrometers, resulting in lower instrumentation weight and complexity with no moving parts. The choice of logarithmic rather than linear profile yields constant resolving power on every pixel of the array. Filters were produced in which the center wavelength varied from 1.0-1.581 micrometers , and 1.581-2.5 micrometers over a distance of 1.024 cm. Bandwidth was 0.3% FWHM and overall transmittance ranged from 30% to 50%. This paper discusses the major issues and tradeoffs in the design, manufacture, and testing of the filters. Measurement techniques are presented and comparisons are made between theoretical and measured performance of bandwidth, transmittance, and spectral profile.