An Introduction to Polarization Directed Flat Lenses Contents 2

AN INTRODUCTION TO POLARIZATION DIRECTED FLAT LENSES CONTENTS 2

• Background/Technology • Product Info • FAQ’s

Technology Basics

Using Liquid Crystal Polymers (LCP), Linear Photo Polymerizaon (LPP) and a variety of dopants, three-dimensional paerns of liquid crystals are created and captured within a thin ﬁlm.

Dynamic Phase

• The “normal” phase delay • For example, – Prisms – Lenses – Phase Gratings – Spatial Light Modulators (computer generated holograms) • All optical path length difference

(Reference, wave in vacuum)

2π (Isotropic media) δ = n d “normal” phase delay λ n, d called dynamic phase due to opcal path length diﬀerence Dynamic phase

⎛ ne + no ⎞ 2π (Anisotropic media) δ = ⎜ ⎟ d ± 2φ “extra” phase delay ⎝ 2 ⎠ λ n , n , d,φ called geometric phase e o Geometric Phase

Principle:

Ø Structure is nonlinear orientaon angle

Ø Phase =

Ø Phase can be aspheric, oﬀ-axis, or any funcon

Ø Polarizaon selects ± focal length

Principle:

Ø Structure is nonlinear orientaon angle

Ø Phase =

Ø Phase can be aspheric, oﬀ-axis, or any funcon

Ø Polarizaon selects ± focal length

Dimensions 25 x 25mm Dimensional Tolerance ±0.25mm Thickness 0.45mm Thickness Tolerance ±0.25mm Lens Aperture 24.5mm Diameter

Coang Speciﬁcaon Rabs <0.5% @ 450 - 650nm Surface Quality 60-40 Design Wavelength 550nm Substrate D263

Size Eﬀecve Focal Length f/# Stock Number 25 x 25mm 45mm 1.8 #33-463 25 x 25mm 50mm 2 #33-464 25 x 25mm 75mm 3 #33-465 25 x 25mm 100mm 4 #33-466

Q: What is a Polarization Directed Flat Lens? A: A Polarization Directed Flat Lens is a thin (0.45mm) flat window with a complex photo-aligned liquid crystal polymer (LCP) film deposited on the surface. By varying the geometrical phase shift spatially, the LCP achieves near perfect diffraction efficiency of the holographically recorded lens wavefront. Essentially, a Polarization Directed Flat lens is a thin film equivalent of a geometric optic with very little volume, yielding significant reductions in weight and thickness.

Q: How does polarization affect the performance? A: The Polarization Directed Flat Lenses are sensitive to circular polarization. The lenses have the unique property that one circular polarization will focus or converge through the lens (positive focal length) and the orthogonal circular polarization will defocus or diverge (negative focal length).

• When the lens is oriented with the LCP surface facing the light source: Left-Hand Circular Polarization (LHCP) light will focus with the stated positive focal length of the lens. Right-Hand Circular Polarization (RHCP) light will diverge with the negative stated focal length of the lens.

• When the lens is oriented with the LCP surface away from the light source: RHCP light will focus with the stated positive focal length of the lens. LHCP light will diverge with the negative stated focal length of the lens.

Q: Will the lens focus unpolarized light? A: With unpolarized light, the Polarization Directed Flat Lens will act as a positive lens for 50% of the light (one of the circular polarizations) and it will act as a negative lens for the other 50% of the light (the orthogonal polarization).

Q: What happens with linear polarized light? A: Linear polarized light will act the same as unpolarized – 50% of the light will be focused, and 50% of the light will be diverged with a negative focal length.

Q: What are the advantages of Polarization Directed Flat Lenses? A: Polarization Directed Flat Lenses are a thin film equivalent of a geometric optic. Thus, they have significantly less volume than an equivalent spherical optic, yielding significant reduction in weight and thickness. The technology used to create them is also well suited to create gratings and other polarization optics, allowing for multiple optical technologies to be designed into a single optical component.

Q: Are there any disadvantages to Polarization Directed Flat Lenses? A: To operate as efficiently as possible, the lenses require the incoming light to be circularly polarized. This requires extra care in the setup, and potentially additional polarization optics in the optical design. Also, the lenses function as a grating, and thus have significant chromatic aberration when used with broadband illumination. Care should be taken to limit the spectral bandwidth of the illumination for optimum results.

Q: How can I specify a custom Polarization Directed Flat Lens? A: To create a custom Polarization Directed Flat Lens, the following information is required: • Lens Size (Diameter, Square, etc) • Clear Aperture • Maximum Thickness • Desired Focal Length • Operating Wavelength Range • Wavefront Characteristics (aspheric, etc) • AR Coating Specs (wavelength, reflectance, etc.) • Wavefront Accuracy

Q: How should I clean my Polarization Directed Flat Lens? A: Polarization Directed Flat Lenses can be cleaned with the same methods used for other anti-reflection coated optics. Visit our application note on Cleaning Optics for more information.

Q: How can I mount my Polarization Directed Flat Lens? A: All of our standard Polarization Directed Flat Lenses are 25 x 25mm. Our 25mm Square Rectangular Bar Clamp, #54-994, is a good choice for bench mounted applications.