There are several types of wide or divergent light sources, such as LEDs or fiber optic illuminators, that can be measured with the Wide Beam Imager, but its main application is the far field measurement of VCSELs. Vertical Cavity Surface Emitting Lasers (VCSELs) are a type of semiconductor laser diode. Unlike edge emitting laser diodes, VCSELs emit upwards and thus can be easily packaged as emitter arrays containing hundreds of emitters on a single chip.
Low power VCSELs are used for high speed data communication, 3D sensing (like gesture and facial recognition), and proximity sensors, while high power VCSELs are designated for LIDARs and other remote sensing applications. Many of these applications run on batteries, thus power consumption needs to be minimized. To ensure the proper operation of the VCSEL devices, it is essential to measure and analyze VCSEL power, beam profile, and noise. While there are many methods for measuring the radiant power of VCSELs, profiling their output beam usually requires bulky laboratory equipment that does not fit into production lines and is inconvenient for "in situ" tests.
The second challenge revolves around the angle of incidence: The quantum efficiency of standard detectors (such as silicon-based photodiodes or CCD sensors) highly depends on the angle of incidence - by as much as 10 % for every 15-degrees. Thus, they cannot accurately measure diverging beams. WB-I captures the beam and images its power distribution onto the camera with an accuracy of better than 5%. Let's look at how that precision be achieved.
The WB-I device captures wide beams on a diffusive screen and re-images them to produce a complete and accurate mapping of the light's intensity distribution. The compact optical system is designed for use with camera-based beam profiling systems together with the Ophir BeamGage measurement software. WB-I is a ruggedized, compact, dust-proof, "ready to use" accessory intended for both production environments and service at a customer site. With its 45 mm diameter aperture and an angle of incidence of 140 degrees, beams of any beam shape (round, line, or square) that are too divergent and too large for a camera sensor can be imaged (Fig 2) by a defined scaling factor. The measurement itself is instant and requires minimal settings to be optimized for various illumination intensities. The distance between the light source being measured and the WB-I diffuser varies between single mm to a few tens of mm, depending on test type and application.