Most consumers are familiar with gesture recognition as part of a user interface that senses touch or finger motion, such as is used in portable devices with touchscreens like tablets. The full range of applications possible with 3D sensing, however, is much wider.
By passing an infrared light source through an optical element to spread the light either into a structured pattern or a sheet of light, systems are able to capture depth information across an entire room by measuring the light reflected off of objects. This enables, for example, consumers to control games or their entire entertainment center with gestures without getting up from the couch or having to locate the remote control. Gesture recognition can also enhance touchscreen capabilities by allowing users to make gestures a foot or more away from the device without having to touch or block the screen. In future mobile devices, 3D sensing will augment camera capabilities to enable object recognition, depth data, greater precision, and object placement.
To be able to detect movement across a living room, however, the detection system needs high power and precision: it’s one thing to track a finger on a touchscreen and altogether another to detect a slight finger movement at six feet. “Time of flight” tracking techniques, for example, flash a light pulse and track depth and motion by measuring the travel time of the light pulse from an object to an individual pixel on an image sensor. In some cases, phase differences are used to calculate depth and motion. Wavelength stability over the entire operating temperature range of the optical source is critical to maintaining tracking precision as filters are typically applied in the receive path to minimize noise in the received signal. Electrical efficiency may further be improved by optimizing the pulse width and duty cycle at which the system must flash to achieve sufficient resolution. This directly impacts battery life in portable systems and minimizes how much heat the system will need to dissipate.
Distributed Feedback Laser (DFB) are a type of edge emitter laser (EEL) also being considered for gesture recognition. However, DFBs are limited in that they tend to be fixed in their output power. Thus, to scale power, multiple DFBs are required. Additionally, power scales in large steps.
Light Emitting Diode (LED) technology, while low cost, emits light in 180 degrees and so must output more power to overcome losses. In addition, LEDs cannot be modulated quickly, limiting resolution and increasing power consumption through increased flash duration.
VCSELs bring together the advantages of low cost and optical efficiency within a small footprint. They further have the advantage of wavelength stability over temperature and are directionally focused to maximize output efficiency. In addition, because VCSELs are top-side emitting, they may be integrated with simpler optics and can be mounted as dies on printed circuit boards or integrated with a laser, driver, and control logic all within the same package.
Gesture recognition and 3D sensing technology are still in the early stages of development. To establish leadership and market share in emerging markets, many OEMs are investing in their own proprietary IP. To meet the needs of these OEMs, VCSEL manufacturers offer solutions that can be highly customized to meet the specific precision, power, size, packaging, and cost constraints for each application.