What Is a Ball Lens?
A ball lens is a spherical lens with an extremely short focal length and high light-collecting ability compared to a normal convex lens.
Because of their short focal length, ball lenses are used as coupling elements for various sensors and optical fibers to focus a wide range of light to a single point or for collimating (converging light into a parallel state).
Generally, ball lenses with diameters ranging from 0.5 mm to 10 mm are produced as products, and extremely small focal lengths of 0.3 mm to 7.3 mm are realized.
Uses of Ball Lenses
Ball lenses are used as light-collecting elements in optical sensors such as bar code scanners and endoscopes. Since these sensors require a smaller size and the ability to detect a wide range of optical information, the short focal length is directly related to the sensor’s capability.
Ball lenses are also used to couple the light from the laser source to the optical fiber. By using a ball lens with an appropriate aperture for the beam diameter and numerical aperture (NA) of the laser beam, light diffused from the laser beam is aligned in a straight line and enters the optical fiber.
Principle of Ball Lenses
Since ball lenses are optical elements used in precision instruments, they cannot be shipped as products if they have a scratch or dust as small as 0.1 mm.
For the same reason as above, it is also difficult to automate the production process, and in many cases, transportation, inspection, and sorting are done manually. For this reason, the selling price tends to be high, ranging from several hundred dollars for a single ball lens.
The scope of quality assurance is also defined in detail for each product, and in addition to diameter and focal length, design wavelength, sphericity, surface quality, and eccentricity variation are also specified.
Single-glass (optical glass) materials, such as N-BK7 and N-SF15, are used for ball lenses. Ball lenses made of sapphire can be used in a wide range of wavelengths, from infrared to ultraviolet (wavelengths from 0.17 to 5.5 micrometers).
Products with anti-reflective coating surface treatment have markings for checking the optical axis printed on them so that the coated surface can be identified, and the markings must be wiped off with alcohol or the like when the product is used.