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CUSTOMIZING A 1650NM FRESNEL LENS: AN INFRARED OPTICS CASE STUDY

In this article, we share how Aubor Optical developed a custom 1650nm Fresnel lens for an industrial customer—focusing on material selection, optical design, and practical molding considerations.

CUSTOMIZING A 1650NM FRESNEL LENS: AN INFRARED OPTICS CASE STUDY

Introduction: One Wavelength Changes Everything

Most polymer Fresnel lenses in sensing applications are designed for the far-infrared (8–14 µm) spectrum, targeting thermal motion detection. But when your system works at 1650nm, a near-infrared (NIR) wavelength used in laser ranging or gas detection, the rules of design, material, and optics change dramatically.

In this article, we share how Aubor Optical developed a custom 1650nm Fresnel lens for an industrial customer—focusing on material selection, optical design, and practical molding considerations.



The Problem: A Lens That Blocked the Signal

A Turkish client approached us in 2024 with a challenge. Their laser-based NIR sensor operated at 1650nm and needed a compact Fresnel lens to collect reflected IR signals. Off-the-shelf PIR lenses didn’t work:

  • Transmission was too low at 1650nm.

  • Focal geometry didn’t match the tight beam angle required.

  • Ghosting and scattering introduced false signals.

They needed a custom lens that could pass more than 85% of light at 1650nm, focus within a 12mm range, and fit within a 2mm thickness envelope.



Step 1: Choosing the Right Material for 1650nm

Most PIR lenses use HDPE or PMMA, which perform poorly at 1650nm. After FTIR testing, we considered:

  • COC (Cyclic Olefin Copolymer): High NIR transparency, excellent moldability.

  • NIR-grade PMMA: Cost-effective but slightly lower transmission.

  • ZEONEX® E48R: Best performance, but more expensive.

We selected COC, offering over 85% transmittance at 1650nm with manageable molding conditions.



Step 2: Optical Design for Narrowband NIR

Using Zemax OpticStudio, we designed a 20mm diameter Fresnel lens with:

  • Focal length: 12mm

  • Groove pitch: 150–200 µm

  • Optimized for 1650nm narrowband source

Simulation showed tight energy convergence with <2mm beam diameter on the detector, minimal aberration, and over 90% effective beam efficiency across ±10°.



Step 3: Mold Fabrication and Molding

We manufactured the mold using single-point diamond turning (SPDT) for ultra-fine groove replication. Molding was done using:

  • 50T electric injection press

  • Controlled mold temperature (90–110°C)

  • Resin drying for COC (6h at 80°C)

Output: 500 lenses, thickness 1.8mm, optical surface Ra < 100nm



Final Results

Customer testing confirmed:

  • Transmission at 1650nm: 87% average

  • Focal accuracy: Spot size <1.5mm at 12mm

  • No ghosting or internal reflection

  • Detection range improved 35% compared to off-the-shelf alternatives



Conclusion: When Customization Unlocks Performance

This project reinforced a core belief: materials and wavelength-specific design matter in optics.

At Aubor Optical, we specialize in:

  • Infrared polymer optics: From 850nm to 10µm

  • Simulation-based design: Co-developed in Zemax

  • In-house tooling and molding: For fast iteration

  • Support for small and mid-scale production

Optical performance is never one-size-fits-all. Especially in the infrared.




For more product information, please contact us.