Multilevel diffractive lens in the MWIR with extended depth-of-focus and wide field-of-view

Area of Science:

• Optics and Photonics
• Infrared Technology
• Materials Science

Background:

• Mid-wave-infrared (MWIR) optics are typically bulky, heavy, and costly.
• Conventional refractive lenses present limitations in size and weight for certain applications.

Purpose of the Study:

• To demonstrate novel, compact diffractive lenses for MWIR applications.
• To compare the performance of inverse-designed multi-level diffractive lenses (MDLs) with conventional Fresnel zone plates (FZPs).

Main Methods:

• Fabrication of multi-level diffractive lenses using optical lithography.
• Design of one lens using inverse design principles and another using the conventional propagation phase (FZP).
• Characterization of lens performance at a wavelength of 4 μm with a diameter of 25 mm and focal length of 25 mm.

Main Results:

• Both fabricated lenses are flat (thickness ≤0.5 mm) and lightweight (weight ≤3.63 g).
• The inverse-designed MDL exhibited a larger depth-of-focus and superior off-axis performance.
• The FZP showed a smaller spot size and higher focusing efficiency compared to the inverse-designed MDL.

Conclusions:

• Multi-level diffractive lenses offer a significant size and weight reduction compared to traditional refractive optics.
• Inverse design provides advantages in depth-of-focus and off-axis performance for MWIR diffractive lenses, albeit with trade-offs in efficiency and spot size.