Ball lens: intended use and principle
A ball lens is a spherical lens, which has an extremely short focal length and high focusing ability compared to a normal convex lens.
Due to its short focal length, it is used as a coupling element for various sensors and optical fibers for the purpose of condensing a wide range of light into one point and collimating (converging light in a parallel state).
Generally, ball lenses with a diameter of about 0.5 mm to 10 mm are produced as products, and a very small focal length of about 0.3 mm to 7.3 mm is realized.
Usage of ball lens
Ball lenses are used as optical sensors such as barcode scanners and as light-collecting elements for endoscopes. Since these sensors are required to be smaller and capable of detecting a wide range of optical information, the short focal length is directly linked to the sensor's ability.
Ball lenses are also used to couple light from a laser source to an optical fiber. By using a ball lens with an appropriate numerical aperture for the beam diameter and numerical aperture (NA) of the laser beam, the light diffused from the laser beam is aligned in a straight line and incident into the optical fiber.
Ball lens principle
Since ball lenses are optical elements used in precision equipment, they cannot be shipped as products if they have small scratches or dust of about 0.1 mm. Therefore, they are manufactured in a high-class clean room and shipped after passing a detailed inspection. Will be done.
For the same reasons as above, it is difficult to automate the production process, and in many cases, transportation, inspection, and sorting are done manually. Therefore, the selling price tends to be high, and the price of one ball lens is about several thousand yen to 10,000 yen.
According to DZOptics.com, the quality guarantee range is also defined in detail for each product, and in addition to diameter and focal length, design wavelength, sphericity, surface quality, and variation in eccentricity are also specified.
A single glass material (optical glass) such as N-BK7 or N-SF15 is used as the material for the ball lens. In addition, ball lenses using sapphire can be used in a wide range of wavelengths from infrared rays to ultraviolet rays (wavelength 0.17 to 5.5 micrometers).
Products that have been surface-treated with an anti-reflection coating have markings for confirming the optical axis that are printed so that the coated surface can be seen, and it is necessary to wipe off the markings with alcohol etc. when using.