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Knight Optical supplies high quality silicon optics and associated components, including silicon windows, silicon lenses and silicon prisms, made to your custom specification. We can offer uncoated and coated silicon optics, including broadband antireflective (BBAR) and diamond-like carbon (DLC) coatings operating at 3 to 5µm (MWIR) wavebands.
Monocrystalline silicon (Si) stands as one of the most robust optical materials that transmits in the infrared spectrum. Not only is it hard-wearing, but it’s also relatively lightweight, weighing in at just half the density of germanium. This makes it an excellent choice for weight-sensitive optical systems. This material offers an advantageous silicon lens price and the option for silicon aspheric lens designs.
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Optical Properties of Silicon
Silicon offers a multitude of advantages that make it a top choice for optical applications. Among its benefits are its low dispersion and low density, making it ideal for lightweight, high-performance optics systems. Additionally, its excellent thermal stability ensures reliable performance even under varying temperature conditions. To top it off, silicon’s high thermal conductivity further elevates its suitability for applications requiring heat dissipation. Whether you’re considering a standard silicon lens or a more specialised silicon carbide lens, these benefits make for an attractive price and further open the door for silicon aspheric lens designs.
Our typical manufacturing specifications are listed below, however, we are always expanding our capabilities so if your requirements are not mentioned below, please contact our technical sales team who will guide you through your enquiry. A full data sheet of silicon’s optical properties is available here.
| Transmission range | 1.2 to 15µm |
|---|---|
| Refractive Index | 3.4223 @ 5µm |
| Density | 2.33 g/cm3 |
| Melting Point | 1420°C |
| Hardness | Knoop 1150 |
| Diameter | < 5mm to 300mm + |
|---|---|
| Form error (@633nm) | < 0.25 waves |
| Centration /parallelism | < 1 arc minute |
| Scratch/dig | < 60/40 |
| Typical coatings | BBAR @ 3-5µm, DLC @ 3-5µm |
Frequently Asked Questions
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What are Silicon Lenses and Where Are They Commonly Used?
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Silicon lenses are optical components manufactured from monocrystalline silicon, a semiconducting material which is transparent in the infrared region, between 1.2µm to 15µm. It also transmits again above 50µm. Due to silicon’s low density and low dispersion, it is often used in weight-sensitive and more compact optical systems, especially in thermal imaging systems and infrared cameras working in the NIR and MWIR regions.
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How Does Monocrystalline Silicon Differ from Other Forms of Silicon?
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Monocrystalline silicon is composed of one continuous crystal structure of silicon grown from a seed crystal. This gives optical monocrystalline silicon a high purity. The key difference between monocrystalline silicon and other forms, mainly polycrystalline and amorphous silicon, is their crystal structure and purity.
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What Are Silicon Optics and What Makes Them Special?
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Silicon optics are components manufactured from monocrystalline silicon (Si). Silicon optics have some key properties that make them ideal in certain optical applications and systems. This includes transmission in the infrared region, a high refractive index allowing for more compact design, low dispersion which minimises chromatic aberration, and thermal stability.
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Is Optical Silicon Different from Regular Silicon?
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Yes, optical grade silicon has a higher purity than regular silicon as it is manufactured to have minimal impurities and defects that could affect the optical performance, especially its transmission. Regular silicon, which is often used in electronics and the semiconductor industry, will not have the same level of purity as it is not a critical requirement.
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How Does the Price of a Silicon Lens Compare to Other Materials?
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This is dependent on the requirements, but typically lens manufactured from silicon, versus the same specification lens made from germanium, would be more cost-effective. This is due to the abundance of silicon available.
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Additional Information
Fabrication methods
Silicon can be fabricated using various methods, notably the Czochralski (Cz) and Float-Zone (Fz) techniques. Using the Czochralski pulling method results in an absorption peak at 9µm due to oxygen presence. However, this is significantly minimised when the Float-Zone technique is employed. Both methods have their own merits and drawbacks, affecting factors such as silicon’s lens price and its quality for silicon optics applications.
Semiconducting nature
Similar to germanium, silicon is a semiconducting material featuring an indirect bandgap of 1.1µm at room temperature. This characteristic can influence its performance in optical systems.
Coating recommendations
Silicon’s transmission hovers at about 50% between 1-6µm, and again above 50µm. For improved performance in silicon optics, an AR coating is advised to enhance transmission. Additionally, a DLC coating can be applied to exposed surfaces for increased durability.
Typical Applications
Thermal Imaging
Silicon windows and lenses are frequently employed in NIR and MWIR thermal imaging applications. While they may not offer image quality on par with germanium or zinc selenide, silicon stands as a more lightweight and cost-effective alternative. In terms of optics, this material offers a competitive price, making it a viable choice for those looking to balance performance and cost in their optical components.
Laser Cutters
Due to its high thermal capacity, silicon serves as an ideal substrate for reflectors, particularly in applications like CO2 laser cutters. This thermal advantage further solidifies its role in silicon optics, offering a blend of performance and affordability.
Infrared Filter Substrate
Silicon is commonly used as the substrate for infrared optical filters, which are integral components in FTIR spectrometers. This frequent usage in such advanced applications underscores its importance in the realm of optics and adds value to the overall optical silicon market, while maintaining a reasonable price.
Detector Versatility
Silicon optics are frequently employed in NIR and MWIR detectors, owing to their transmission range from 1 to 6µm. Silicon-based detectors find applications in fields like LiDAR and muzzle flash detection. This versatility in application further cements silicon’s role in the optical silicon sector.
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With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet your requirements. You can find out more about our testing facilities here.
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Operating for over 30 years
Knight Optical has been operating for over 30 years, with our managing director Colin Overton at the helm. Over this time, we have become a global leader in the production and distribution of scientific optical components and bringing quality into focus for all of our products and services that we provide.
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