These compact glass aspheric lenses provide a convenient, high-quality alternative to microscope objectives. Unlike conventional spherical lenses, aspheric lenses can refract light at large angles without introducing any significant spherical aberration. This allows a single asphere to perform the same function as a compound lens system.
Perfect for use anywhere you might otherwise use a microscope objective, our aspheres are less lossy, less bulky, and have fewer components. They’re especially handy for low f number† applications like coupling light into and out of optical fibers or collimating diode lasers because the aspheric surface minimizes the aberrations experienced by rays traveling through the outer circumference of the lens.
Each asphere is made from laser-quality glass to provide optimum performance and has extremely low wavefront distortion over a wide wavelength range. (The lenses with plano second surfaces have the least aberration while those with convex second surfaces have the lowest f number.) The lenses come with your choice of broadband anti-reflection coatings and provide better than 97% transmission. Each lens is mounted in a threaded lens holder marked with the focal length and equivalent microscope-objective power.
The Model 5720 kit contains six lenses mounted in threaded holders and a Model 5709 RMS-threaded adapter for mounting the lenses as microscope objectives. The available Model 5708 1" adapter allows you to mount these lenses in our fiber aligner kits (Post-Mount Singlemode Fiber Aligners) and in other 1 inch mounts.
Choosing the Right Lens
A good way to estimate the best lens to use in your experiment is to choose the focal length of the lens using this formula:
f=dDπ/4l
where f is the lens focal length, d is the beam diameter at the focus, D is the 1/e2 diameter of the collimated beam, and l is the wavelength.
If you are collimating a beam, you also need to make sure the NA of the lens is larger than that of your fiber or diode so that you are capturing all the available light. If you are focusing into a fiber, be sure that the NA of the focused beam is smaller than the NA of the fiber to maximize coupling efficiency.
This analysis will give you a good estimate, but you may find that you need to try a few lenses to get optimum focusing.
AR Coating
For the “-A” coating, transmission is 97% from 375 to 650 nm. For the “-B” coating, transmission is 97% from 625 to 1050 nm. For the “-C” coating, transmission is 97% from 1000 to 1600 nm.
Focal Length
Except for the Model 5721, the focal length listed assumes the presence of a protective window, which is common in laser-diode packages. The lenses are also suitable for applications where there is no window over the laser diode. In this case, there will be a small change in the focal length (<1 mm).
Holder Length
The length of the lens holder, shown as “L” in the mechanical drawing.
NA
The numerical aperture of the lens.
Power
The approximate magnification of an equivalent microscope objective.
rms Wavefront Error
The root-mean-square wavefront distortion at the design wavelength.
Working Distance
The distance from the focal point to the surface of the lens. Lenses are recessed by 0.5 mm in each holder.
NOTE: Contact us for asphere coefficients and dispersion constants.
†f number (f/#)=focal length/lens diameter≈(2NA)–1
