[Abstract] This white paper provides an essential guide for research and development engineers, designers, buyers, end-users, and anyone involved in the manufacture of LiDAR devices on the best practice when it comes to coating specialist optics such as cylinder windows and metal spinners.
Anti-reflection (AR) coatings are applied to the surface of optical elements to reduce reflection. They are used in a variety of applications in which light passes through an optical surface, and reduced reflection is needed, for example on camera lenses or optics used in defense applications and high laser damage threshold tests (LDT).
In more recent years AR coatings have found uses in new applications such as augmented and virtual reality and LiDAR applications. In terms of the latter, it is important that the optics, such as cylinder windows, are correctly coated. Likewise the metal spinners used in the sensors must have the correct metal coating applied.
This is important because the coating can impact the sensitivity that is vital to the accuracy and ability to see low-reflectivity objects. Likewise, the types of conditions in which LiDAR devices operate require very durable windows and optics with high transmission at the operational wavelength. Therefore, research and development engineers, designers, buyers, end-users and anyone else involved in the manufacture and use of these devices must make sure that this is designed in at the early stage, and the coating partner is up to the challenge.
One of the biggest challenges for this demographic is that, while they have a wealth of expertise when it comes to the technology behind these optics, there is less knowledge available as to how a coating will play into it and which type will work best for a particular substrate and application.
This has been exacerbated by the current labor shortage across a wide variety of areas in the market. Great salespeople, engineers, and people that understand optics and coatings are hard to find. This in-turn means that there is less awareness of the challenges associated with uniformly coating the multiple facets of these specific components.
A lack of expertise in this niche area is challenging because, to get the coating absolutely correct, there is a lot to consider from the early stages, and the right partner will insist on being involved from the early stages, asking the right questions to ensure the right results.
Alan says: “Buyers and engineers will, on occasion say, ‘you make my job so much easier because you will remind me if something is missing’” – Alan Parsons, Sales Manager, AccuCoat
Likewise, the essential field testing and prototyping can be more challenging, with a lack of experts available to perform these vital tasks. The ever-present supply chain crisis has also presented more than its share of challenges, with quality and shipping issues meaning that this audience is looking for a more viable solution for these specific optics closer to home.
Established in New York as a highly-accomplished manufacturer of stock and custom-designed thin-film coatings since 1998, AccuCoat has developed coatings for optics requiring wide-angle AR coatings or AR/VR beam splitters with a range of standard or custom options for various substrates. We pride ourselves on acting as an extension of your business, assisting you from the earliest stages of a project, and asking all of the right questions to guarantee the best result. Accucoat’s thin-film design software programs allows for creation of the best coating solution for your needs, while our prototyping service gives you the confidence that the coatings will be the ideal option for your requirements.
The coating process
The very start of the process should include a consultation with your coating partner during which they should ask for all of the relevant information to ensure the right coating is applied for the particular scenario. Things to consider include the size, curvature and form factor that requires coating. If a photo or drawing can be provided at this stage, so much the better. What is the substrate material and what coating type might it need? What are the wavelength and efficiency specs? What angle is the light likely to hit the object? Also think about the clear aperture, surface quality and durability of the optic.
Alan says: “If your coating partner is asking an almost annoying amount of questions, you’ve probably found the right one! They will want to get it right, give you what’s going to work and what’s going to last. Communication is key at every stage”
The coating of windows and metal spinners requires a specialist setup, where the materials are at the bottom of the machines shooting upward and the optics are hung above with the surface for coating faced downward. The machines have a simple rotation that can be likened to an umbrella, with the materials at the end of the handle and the optics sitting in holes within the umbrella, which slowly rotates over the coating source.
In order to coat the outside of windows or the facets of a polygon, the optic faces need to be turned so those now face downward. This involves mounting these optics on custom-designed spindles. The optics are stacked along a rotating spindle, designed to sit within the umbrella so that the optical surfaces are in the correct position to the coating source. The challenge here is that, without spinning it, you end up coating just one section of the cylinder, so some quite intricate rotation is required.
Not a lot of companies can boast such a setup, but AccuCoat offers exactly this at its 11,000 square feet facility in Rochester, New York. It is also from here that our helpful and friendly sales and customer service team will be in touch to ask all of the questions required to understand your application and your optics.
Alan says: “Your coating partner should have the experience and confidence to talk you through all of the different steps, looking at the pros and cons of your initial idea to guide you down the right path and be honest about what is achievable”
In many cases the research and development engineers, designers, buyers, end-users and others involved in making these devices won’t require volume production for their project, for example in aerospace or industrial applications, instead a smaller volume would be all that is required. The challenge here for this demographic is that it will not be in the interest of all coating houses to take on something lower-volume.
Luckily, AccuCoat is able to offer just this solution for those cases. Even if there is just, for example, a single, large window comprising the entire project, we have the expertise and equipment to custom coat, test and ship just that one part to you. This includes options from metal, glass or polymer materials.
Alan says: “Prototyping can be challenging for people making these devices because assistance and guidance is essential throughout the process, and customer service is incredibly important”
Again, it is really important in this case to understand exactly what you need at the earliest stage of the process in order to develop a coating solution to efficiently bring you through prototyping but which could also transition easily to volume. This means that volume production details are taken into account such as tolerancing, clear aperture, handling, yield, and packaging when designing your prototypes. So you can have the confidence that the quality and performance you receive at lower volumes can be replicated in the thousands and within your cost target.
Applications and business benefits
Coating aluminum optic spinners for an NIR application:
A diamond-turned aluminum optic with a NIR coating project required very high reflectivity with stringent specifications for environmental testing and durability factors. The challenge was to coat the multiple facets of each part uniformly.
In order to successfully perform this, AccuCoat used its custom fabricated spacers to allow the stacking of the components on rotating spindles to stabilize the parts as they orbited the coating chamber. This allowed for the uniform deposition of the coating on all of the facets, while protecting any perpendicular surfaces from overspray. In order to enhance the NIR performance and stability over the life of the product, AccuCoat added a dielectric protection layer to the gold metal layer.
This attention to detail allowed for very high yield as well as high run-to-run consistency for delivered, measured performance: a reflectivity > 98% @1550nm across wide-angle was consistently achieved.
Spinners and polygons:
As well as LiDAR technology, optical coatings for spinners are used in critical laser guidance systems, bar code readers and land surveying. AccuCoat coats these multifaceted polygons and cylinders using a sophisticated system that enables rotation of parts around multiple axes simultaneously.
This ensures uniform high reflectivity and AR coatings, whether on injection molded plastic parts or high precision spinners for premium laser market applications.
With the LiDAR market widely predicted to grow by billions over the next few years, there is certainly opportunity for research and development engineers, designers, buyers, end-users and anyone involved in device manufacture in this area. The right products and technology within the right lead times will be essential considerations in the success of any project, and the coating is a crucial part of this to ensure high-performance and durability.
It is really important to work with an experienced coating partner that has all of the tools and expertise to ensure a perfect solution, whatever your project or volume. AccuCoat will act as an extension of your business, asking all the right questions from the start, and offering fast prototyping and unrivaled experience and capabilities to deliver the right product the first time for the fast-paced LiDAR market.
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