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.

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.