Читать книгу VCSEL Industry - Babu Dayal Padullaparthi - Страница 47

Referring to the optical sensing system in Figure 1.16(b), short‐range (<10 m) image sensing in consumer electronics use 2D VCSEL arrays as light source with two different schemes. In the first scheme, intense uniform light from 2D VCSEL arrays illuminates on an 2D/3D object, is reflected back to image sensors, and the distance of the object is measured by a method called time of flight (ToF).

Figure 1.17 VCSEL‐based optical communication and sensing systems.

Source: Figure by K. Iga [copyright reserved by author].

Besides, a simple 3–6‐emitter VCSEL array is also used for proximity sensing in smart phones using the ToF technique.

In the second scheme, intense distributed light from a 2D VCSEL array illuminated on a 3D object is reflected back to the image sensors, and the depth of the object is measured by a method called structured light. This is the mechanism of face unlocking in smart phones. There are a host of emerging applications from VCSEL arrays as sensors in AR, robotics, smart‐home appliances, and so on. Details are discussed in Chapter 5.

Long‐distance ranging or object detection (~250 m or longer) can also be done using the sensing concept shown in Figure 1.16 for automobile by using LiDARs. This is sometimes known as vehicle‐to‐everything (V2X). LiDARs use individually or row/column addressable arrays of VCSELs or edge‐emitting laser arrays to illuminate the scene either through a single flash, sequential flashes by selectively addressing the emitters, or scan functions, and the object image is created through powerful signal processing and artificial intelligence (AI).

Besides ToF, more precise object measurement techniques such as optical phased arrays (OPA) or frequency modulations (FMCW) are also used for advanced driver‐assistance systems (ADAS). Details of other applications are discussed in Chapters 6–9.

To facilitate comprehension, supplementary information is given as appendices on generic VCSEL design (Appendix A), epitaxial growth (Appendix B), wafer processing (Appendix C), testing (Appendix D), reliability and qualification (Appendix E), and eye‐safety issues (Appendix F). Special notes on display (Appendix G), red VCSELs (Appendix H), photodetectors (Appendix J), and GaN VCSELs (Appendix I) and are also provided.

Figure 1.18 Published papers on VCSEL.

Source: Data taken from Google Scholar on November 2, 2020. (Searching key words: “VCSEL” OR “vertical‐cavity surface‐emitting laser” OR “surface emitting laser” in the text or title.) [Image courtesy of Tomoyuki Miyamoto, Tokyo Institute of Technology.]