These compact glass aspheric lenses provide a convenient, high-quality, compact alternative to microscope objectives for applications including fiber coupling and spatial filtering.
- Replace bulky microscope objectives
- Coupling, collimation & manipulation of diode laser beams
- Convenient kit contains 0.16 to 0.65 range of NAs
- Low wavefront distortion over wide wavelength range
Replace Bulky Microscope Objectives
For simple applications such as laser diode collimation, or coupling to optical fibers, compact aspheric lenses offer the same magnification and on-axis performance as microscope objectives in a lighter and more compact package. The aspheres are compatible with the same RMS threads as microscope objectives.
A good way to select the correct lens for your beam collimation (or focusing) application is to start by finding the appropriate focal length using this formula: f = D( πω/4λ) where f is the lens focal length, D is the 1/e2 diameter of the collimated beam, ω is the beam diameter at the focus, and λ is the wavelength.
If you are collimating light, you must then find a lens with NA larger than that of your fiber or diode in order to capture 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 multimode fiber to maximize coupling efficiency (this may alternatively be done by using less than the full aperture on a higher NA lens). This analysis will give you a good estimate, but you may find that you need to try a few lenses to get optimum focusing.
Advantage of Aspheric Lenses
In applications that require large acceptance angles, such as light gathering for illumination, spherical lenses are unsuitable due to spherical aberration, or the effect of refractive power of a spherical surface becoming greater with increasing aperture. Aspheric lenses maintain constant focal length or very high NA, avoiding the need for multiple elements to correct spherical aberration. This simplifies system design by reducing weight and component count. It also results in less transmission loss, and less ghosting due to having fewer surfaces. The primary drawback of aspheric lenses is off-axis performance is poor. This is not a problem for coupling to and from optical fibers or collimating light sources, but aspheric lenses are not usable over a wide field of view.
Aspheric Lens Construction
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.
Focal Length and Working Distance
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). The working distance is defined as the distance from the focal point to the surface of the lens. Lenses are recessed by 0.5 mm in each holder.
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.