Reynard Corporation works with customers in evolving advanced technologies to meet their stringent demands.
The following technologies are some of the more interesting capabilities that we have driven. Reynard Corporation is dedicated to advancing the field of optics globally.
Optical Power Limiters (OPL):
Optical Power Limiters are essential for protecting sensitive electronic or photonic sensors and detectors from damage due abnormally high radiation exposure, accidental or deliberate. The optic limits the amount of power transmitted through the optical component even as the input power continues to increase, as shown in example below:
Reynard has developed a broadband, thin film optical limiter that can be tuned to react at specified power levels. The design is indium based, with performance enhancements to improve pre-exposed optical transmission. Reaction response time is in the millisecond range, as validated by laboratory testing at 532nm. The design is non-reversible, meaning that once the limiter goes into the reactive protection state, the radiated area of the limiter does not revert back to pre-exposed transparency levels. Anti-reflection, or other types of metal or dielectric coatings can be applied to the optic for application specific requirements.
There are several types of metalization that are of interest to systems designers. Optics can be metalized for their optical properties (eg. mirrors), for their electrical properties (buss-bars, traces and EMI gridding) or for their mechanical properties (solderability and sealing). Reynard's metalized coatings have excellent adhesion to the optical surface and have properties that can be tuned to your application.
For solderability, Reynard has two proven, high-performing metallization designs; one based on a nickel (Ni) barrier layer and the other on a platinum (Pt) barrier layer. The barrier layer performance is critical to achieve a good soldering performance, to protect the substrate against high-temperature during soldering, and to eliminate the collection of moisture during the soldering process. The selection of the barrier level depends on the environmental conditions, performance needs, and cost. These coatings are compatible with a gettering process. With our proprietary surface implantation process, we have shown to exceed well over 8000psi tensile strength on several glass and crystal substrates. For some substrate materials binding layers are used to enhance the substrate-to-metallization performance. The design of this binding layer is tuned based on the substrate material.
With innovative thin film design and precision deposition process control, Reynard has produced a variety of very high reflection coatings. High reflection coatings can be implemented across any wavelength band from the UV to the Far IR. Narrow band designs typically perform better than wide-band, and can be tuned for an optimal performance band. Reynard’s high-reflection (HR) coatings have been validated to achieve over 99.9% reflection. Measurement of these high reflectors becomes very difficult at higher performance values, as they are typically comparisons against a known reflectance standard, such as an unprotected gold or silver reflector. Known standards can degrade over time due to oxidation, environmental changes, or even handling, among other possibilities, changing the reflective performance. This degradation of the standard affects the validity of all future product measurements. For that reasons, an indirect measurement can also be used. For example, Reynard has measured transmission through a reflective device to be less than 0.1%, indicating a better than 99.9% reflection value. However, this indirect measurement does not account for material absorption or surface scattering, which can affect the true reflection value. Careful substrate design and coating material specification can help to minimize these concerns. High reflection coatings are used in applications such as reflecting telescopes, such as in a Cassegrain design, galvo mirrors, and space applications.
Every transmission optic that Reynard designs and builds has aspects of anti-reflection design in order to maximize transmission. This experience has led to fundamental understandings of many substrate materials and how to maximize light through these optical components. We have taken this knowledge and formulated very high-performing, broadband anti-reflection (AR) coatings for the visible and NIR. A standard visible design was measured with R(avg) to be less than 0.5% from 0.45um through 0.65um. The more extended Vis-NIR design, with the wavelength band from 0.4um to 1.0um, was measured with R(avg)<0.75%.
Custom broadband AR coatings have also been developed for single and multiple IR bands covering the mid-wave (3-5um band) and the long wave (8-12um band). Performance varies greatly for the many IR material types.
IR Dual Band:
IR coatings have been a specialty of Reynard for many years through direct and indirect government programs. As third generation infrared imaging matures, the demand for dual band IR coatings is growing. Reynard has taken their experience in working with IR material sets and specialized IR substrate materials and has successfully developed a variety of dual band coatings. The most common request is a mid-wave infrared (MWIR, 3-5 µm) and long-wave infrared (LWIR, 8-12 µm) dual bandpass coating, in which we have achieved above an average transmission of 95% in each band. Reynard coatings offer fast transitions between the in-band and out-of-band wavelength regions, while providing high average transmission. Out-of-band blocking can reach levels of several OD.
Other variation of multi-band requests include pairing the LWIR band with the near IR (NIR), shortwave IR (SWIR, 0.9-1.7µm), or even the visible band (0.4-0.7µm). One of the factors that limit multi-band functionality is the selection of the substrate materials. Careful selection must be made to choose a material that does not cut-off in the band of interested transmission.
Fabrication of Exotic Materials:
The optical fabrication department at Reynard Corporation has developed an expertise in working with exotic materials in addition to a full line of visible and infrared glass and crystals. One such example is our ability to work with semiconductor-type materials.
Reynard has a specialized III-V material processing facility dedicated for working with semiconductor materials that include InAs, InP, InGaAs, GaAs, MCT, and others. Working with these materials requires intimate knowledge about crystal growth formation within the material. Crystalline grain boundaries cannot be eliminated from a cut wafer; however, surface finishing can greatly reduce their effects on a transmitted signal. Dedicated grinding and polishing machines allow a Master Optician to produce finished product with very low surface defects and excellent optical quality surfaces. Further, Reynard is able to utilize their proven edge polishing technique to eliminate edge defects that could result in a fractured part. Optical coatings, such as anti-reflection or filtering, can be applied after the product is fabricated to increase performance for its intended application. Most commonly, these finished products are stand-alone optics used as part of an optical system, although, Reynard has also successfully coated directly on a detector as well.
In addition to producing plano windows with these exotic materials, spherical off-axis lenses have been produced. These hand-crafted lenses utilize the same surface and edge polishing techniques developed for plano optics to create a high precision finished optical element.
Crystal bases substrate materials tend to be brittle and can fracture easily if handled improperly. Chips or cracks appearing on the edge of the substrate after polishing create a stress point that can propagate across the entire surface of the part, resulting in a fractured product. Reynard has developed an edge polishing process that resolves these edge fractures to create a more robust substrate. Since the hardness of crystalline materials varies greatly, the polishing process is tuned to a specific material type and, typically, involves a multi-stage polish. This process has been shown to resolve fracture points that exist on the surface of the substrate, as well as resolving potential defects inside of large area edge chips.
Filter stacks (or "Laminated Filters") consist of two or more substrate materials that are bonded together. The thickness of the layers and chosen materials can be varied to affect virtually any transmission function. These structures are an excellent alternative to interference coatings for some applications.
- No "angle shift" - normalized internal transmission remains constant at any angle
- Durable and Cleanable - Even the hardest coatings can be damaged by abrasives and solvents. Filter stacks are as durable as a piece of glass.
- Lower cost
These structures can even be coated for an additional performance boost. Our advanced design tools will make quick work of determining the ideal structure for your application.
Coating on Chalcogenide Materials:
Chalcogenide materials have a known reputation of having adhesion issues after thin film deposition layers are applied. Through innovative deposition techniques, Reynard has developed a durable thin film coating process on materials such as Amorphous AMTIR (-1, -2, -3, -4, and -5), Schott IG (-3, -4, and -6), and Lightpath BD-2. Many variants of anti-reflection and filter coatings have been validated on these materials for spectral and durability compliance directly by customer third-party testing. Coatings can be applied to plano (flat), concave, and convex surfaces. In-house testing includes Mil-Spec thermal cycling, humidity testing, adhesion, and abrasion. Additional custom testing programs can be defined and implemented, as well.
LN2 Cold Testing:
Windows or filters used in photovoltaic infrared cameras may have a requirement to operate at the same low temperature as the cooled detector. Reynard has manufactured many variants of these infrared windows and filters. To validate durability at low temperature, one-inch witness samples are placed on a cold shield in a liquid nitrogen (LN2) Dewar, and brought down to the operational temperature of 77°K. The Dewar is used in conjunction with a spectrometer in a customized fixture to perform spectral measurements. Spectral transmission of the witness sample can be measured across any visible or infrared spectral band out to 20µm.
Radiation Hardened Mirror Coatings:
Reynard has developed three mirror coatings that have been hardened against increased x-ray radiation. The three designs include a visible band design, a long-wave infrared design, and a dual band design covering both the visible and the long wave IR spectrum. The designs have been tested at three different test facilities, including the newest National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory. Radiation performance enhancements have been measured from 2x to 5x better than the current gold standard design. In addition to x-ray radiation enhancements, the mirrors have also been tested successfully to perform against other types of radiation including electron, proton, and gamma in laboratory environments.
Spectrally, the designs perform very well in their intended wavelength bands, showing reflection above 99.5% in some cases. The designs can be tuned to function in shifted wavelength bands if the application warrants a change, and computer simulated to predict performance.
Currently, the dual-band and the LWIR designs are part of the MISSE-8 program aboard the International Space Station (ISS).
Transparent conductive optical coatings are utilized in markets that require efficient optical transmission along with the need to conduct electricity or dissipate charge. Indium Tin Oxide (ITO) is the most widely known transparent conductive material. It offers good optical performance across the visible band, while providing an impedance range from below 10 Ohms per square to well over 10,000 Ohms per square. There is a direct correlation with the film deposition thickness between optical transmission and impedance targets. Reynard has a long history of balancing the impedance and transmission characteristics of ITO, participating in market needs for heated windows, flat-panel displays, EMI grids, and photovoltaic development. Very high transmission can be achieved with impedance downs to 2K Ohms per square. Low resistance designs of 10 Ohms per square have also been developed that achieves transmission in the 80%-85% range. When combined with an AR coating, the ITO can be index matched to the substrate material on which it is being deposited.
Another solution that Reynard has had much success is with thin metals. For example, gold (Au), can achieve fewer Ohms per square while achieving high optical transmission - even in the IR! However, due to the high cost of Au, it is an unpopular selection when ITO can achieve the required results. Reynard has also successfully deposited materials with silver nanoparticles to achieve conductive coatings. This solution is typically used in hybrid thin film designs where additional optical filtering is required.
ITO and thin metals can be deposited at low-temperature, allowing for deposition on substrate materials such as plastics. These transparent conductive materials can also be patterned using an in-house photolithography process to create patterns from simple match length lines to complex custom grids.
Fiber Ends, or Fiber Barrels/Micro Lenses:
For both enhancing fiber communications and for high-power fiber applications there has been a need to have the ends of fibers coated with special thin film coatings that enhance performance. Reynard has been able to serve the needs of both markets. Advancing telecommunication technologies is requiring the use of specialty fibers that couple with existing fiber networks. The index of refraction mismatch between fiber types causes loss of signal that could be detrimental to the communication channel. Reynard has worked with customers to coat the ends of fibers with index matched anti-reflection coatings, as well as coatings for special filtering of the signal. These coatings greatly reduce surface reflections to maintain a homogeneous signaling channel. Coatings have been developed that cover both the visible spectrum as well as the infrared spectrum.
Coupling the output of high power lasers into a fiber is a need for many industries, as it allows the laser to be directed to non-line-of-site areas or areas that are in constant motion. However, when the laser hits the end of the fiber, the index match between the fiber and the next medium, typically air, can damage the end of the fiber. Reynard has coated the ends of fiber optics with coatings that minimize the chance of damage to the fiber end interface.
When working with fiber, typically there is a protective coating or cladding around the fiber. To be compatible with a deposition process, this cladding must be vacuum compatible, in that it will not outgas when used in a vacuum environment. Reynard has experience coating bare fibers as well as fibers with vacuum compatible claddings.
Reynard is capable of supporting development from prototype through production. For thin film coatings we can move jobs from small development vacuum coating chambers into large chambers that can support larger volumes of product, thus lowering the individual piece part cost. Having large coating chambers, up to our 54” (1.3m) box coaters, we are also deeply experienced in coating large optics up to 50” in diameter with single rotation. The ability to achieve excellent uniformity across a surface this size lies in our experience and design tools for modelling and optimizing uniformity masks. For larger optics, we have achieved a non-uniformity of less than 1% P-V across the surface of the optic.
Our fabrication capabilities include polishing plano optics up to 36” diameter on any of our large 96” continuous polishers.
As optics become more complex by either using exotic substrate materials or by very high precision thin film coatings, it is best to minimize the handling to avoid any incidental damage to a completed optic. Reynard has been assisting its customers in this regard by offering first level assembly of the optical component into a higher level assembly.
Assembly of optical components can be at several levels. One such basic level is the mounting of the optical component into a frame or fixture. These configurations require several cementing zones to hold the optic into place. Once cured, the cemented zones are durable the entire assembly is delivered to the customer
More complex assemblies require RTV Potting and/or soldering. In these configurations RTV holds the optic into place inside of a fixture, as shown below. For some cases, it is necessary to add electrical components, such as thermisters while mounting the optic. Reynard can also attached soldered leads to the surface of the optics, where solder pads have been created. Electrical tests can be performed to ensure proper connectivity
In all cases, the optic is first tested so that it meets all necessary environmental and durability requirements set forth by the customer drawing, as well as for the spectral performance of the optic.
Reynard has developed a proprietary photolithography deposition technique that allows the placement of multiple filters on a substrate without a gap or overlap between filters. Removing the gap allows for more surface area for the filter and minimizes diffraction edge effects when filtering light. Overlapping filters has been the most common approach to exclude a gap; however, the overlap again reduces the filter surface area and can still cause unwanted edge effects. An example of use is in the 3-color Bayer filter, or similar, shown below, where color filters are placed just above detector pixels. Any diffraction patterns or stray light can affect the signal reaching the detector. A gapless deposition technique eliminates these anomalies.
This technology is best utilized when creating sensor windows at the wafer level. Many gapless multiple-window arrays can be deposited on a wafer substrate. After the wafer is tested for compliance, it is diced to produce the individual sensor windows. Any deposition material or filter design can be implemented in conjunction with this photolithography processing technique. An example of a gapless 3-band color filter is shown below.
3-band gapless filter
The same gapless photolithography technique can be applied to a wafer level packaging window for sensors. In this configuration, multiple multi-element filters are created on a single substrate. Each filter can then be diced and applied to a sensor, dramatically reducing the per filter cost to manufacture in high volume. As shown in the image below, large filter test areas can be defined that spatially represent the smaller sensor filters. Testing prior to dicing allows the customer to have confidence that the smaller filters meet their specifications.