Appliance Design - February 2008 - (Page 32) CONTROLS & SENSORS Leveraging Lasers V VCSEL sensors. Laser-based optoelectronic sensors can provide more information than traditional LED-based components. by jim tatum and andre lalonde Jim Tatum is the director of strategic marketing, and Andre Lalonde is the applications manager, Advanced Optical Components Div., Finisar, Allen, Texas. ertical Cavity Surface Emitting Lasers (VCSELs) were commercialized in 1996 primarily for use in data communication networks using fiber optic cables. Since then, many millions of devices have been deployed with arguably the highest reliability of any optoelectronic component ever produced. Other applications for VCSELs have since emerged, principally as the light source replacement for Light Emitting Diodes (LEDs) in optical mice. Further expansion of VCSELs into other optical components is just beginning as more OEMs realize the inherent benefits of using a VCSEL-based optoelectronic component. VCSELs can be thought of as a marriage of two key optoelectronic devices, the LED and the Edge Emitting Laser (EEL). They combine into one device many of the advantages of the LED, such as surface emission, wafer-level testing and diverse packaging options, with the advantages of EELs, such as coherence, beam quality, and efficiency [1]. Some of the key physical properties of VCSELs, EELs, and LEDs are summarized in Table 1. The performance and packaging advantages of VCSELs has enabled them to be used in applications where LEDs were not the optimal choice and where the EELs could not penetrate because of packaging limitations. A prime example of this situation is the optical mouse. The use of optoelectronic components in consumer appliances is now mainstream, with sensors for proximity, turbidity, velocity, and ambient light among some of the more commonly deployed [2]. To date, these sensors have generally utilized LEDs as the light source primarily because of the low cost of deployment. With the advent of ever more “green” initiatives, the usefulness of these sensors is being challenged. One reason regards total power consumption. For an equivalent amount of useful optical power, the VCSEL will provide about a 10x reduction of required electrical power. Another reason is the examination of how to better utilize sensors to improve the entire system. To understand this point more clearly, it is instructive to examine more closely the function of a turbidity sensor. In its simplest form, a turbidity sensor is comprised of a light source impinging on a medium, and a detector placed normal to the incoming light beam. Other detectors can be used to normalize the optical power as shown in Fig. 1. This type of turbidity sensor has been used in a large number of 32 applianceDESIGN February 2008 www.applianceDESIGN.com http://www.appliancedesign.com
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