Lenses: Overview

Engineering Fundamentals

Introduction

This sheet offers a short overview of the most used lens types, their properties, and typical applications. The main properties, cost and typical outer dimensions of the different lenses give a direct indication whether a lens type can be useful or not.

Lens dimensions

The basic dimensions are the Effective Focal Length (EFL), the Center Thickness (CT) and the Outer Diameter (OD) of the lens. In the table below, the EFL and the CT are expressed in relation to the outer diameter OD. The EFL is the distance from the focal points to the respective principal planes and determines the magnification of the lens. The principal planes are usually inside the lens.

Lenses overview: Lens Dimensions

Points of attention when choosing a lens

  • AR or Anti-Reflective coating: To ensure high power transmission, equip your lens with an AR coating suitable for the wavelength of usage. This reduces the back reflection.
  • Design Wavelength: If the design wavelength differs from the used wavelength, the EFL is altered. This shift can be 5-10% of the EFL.
  • Edge-blackening: Lens edges cause more aberrations than the areas near the lens central axis. Edge blackening avoids this image distortion.
  • Material: Polymer lenses are less costly than glass lenses. Low quality glass (example N-BK7) is less costly than higher quality glass (example fused Silica)
  • Clear Aperture: In many cases, not the whole outer diameter is suitable as optical surface (for instance if the edge should be used for mechanical integration). The clear aperture indicates the ‘optical’ lens diameter.
  • Lens shape: Besides the type, lenses can have different shapes. For example one (plano-) or two (bi-) curved surfaces, with positive EFL (-convex) or negative EFL (-concave) surface radii.
Lens typePhysical principlePro’s & con’sCostEFL [xOD]OD [mm]CT [xOD]Typical applications
Spherical lensesLenses overviewCurved surface Low cost
(Spherical) aberration
0.6-101-500.2-0.8Low cost simple systems
AspheresLenses overviewCurved surface No (spherical) aberration0.3-31.5-500.3-0.6High performance (monochromatic) systems
AchromatsLenses overviewChromatic balanced index of refraction Less (achromatic) aberration
Size
1-101-1500.4-1Imaging
Ball/drum lensesLenses overviewCurved surface Short positive EFL
Easy integration
(Spherical) aberration
0.5-10.3-100.5-1Fiber coupling, pre-forms for aspheres
MeniscusLenses overviewCurved surface Small CT
High EFL
1-4010-500.1-0.5Decrease EFL of other lens with constant NA
AxiconLenses overviewConical surface/≈250.15-0.6Ring-shaped beam
Multi-lens arraysLenses overviewMultiple small identical curved surfaces Non-Gaussian uniformity0.1-2010-50 (total array)0.1-0.2Beam homogenation
Fresnell lensesLenses overviewConcentric grooves Low CT
Large distortion
0.3-210-2500.01-0.03Light gathering
Gradium lensesLenses overviewVarying index of refraction Less (spherical) aberration2.5-3.35-300.2-0.4High performance systems
GRIN rod lensesLenses overviewVarying index of refraction Easy integration
Short/zero WD
Size coupled to performance
≈10.5-2≈2Fiber coupling, laser beam shaping
Toroidal Lenses overviewNon-radially uniform curvature Non-radial uniform beam1-105-500.15-0.5Create line profile from circular beam

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