VCSEL Industry. Babu Dayal Padullaparthi
OCT
Using high performance VCSELs with sufficient output power, low‐loss optical fibers, and efficient high‐speed detectors, data can be transmitted at speeds of 25–100 Gb/s over 300 m at temperatures well over 85°C [56]. The details of multi‐mode VCSELs for data communications/data‐center applications are discussed in Chapter 4.
1.4.5.3 VCSELs in Optical Sensing
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.]
1.5 State of VCSEL Development
1.5.1 Published Papers
Figure 1.18 shows the number of published papers per year and accumulated statistics. Note that the total number of related papers has reached about 50,000 as of 2020. The yearly publications have skyrocketed over the last decade, indicating that commercialization is taking place.
1.5.2 Toward VCSEL Photonics
Ever since Honeywell started VCSEL commercialization and introduced the first reliable product in around 1996 [57], VCSEL technology has made a huge impact on several key industries with multiple growth windows. Thanks to several commercial epi‐houses, III‐V opto‐foundries, and other equipment vendors, researchers and engineers have overcome great challenges to make VCSEL‐based commercial products a practical reality since the beginning of 2021.
After 44 years of VCSEL invention [25] and the marathon industry efforts to realize volume manufacturing, it is not surprising that most people carry a VCSEL device along with them, if not a few! This means VCSELs have rapidly grown up, fully matured, and penetrated into commercial products that affect the daily lives of humans.
Four major industries dominate most of the VCSEL applications space (called core products), while few other neighboring fields are also emerging in the entire VCSEL application seabed. On core applications, the first is high‐speed VCSELs for data communications and data center applications. There is a steady demand for 100 to 300 m active optical cables in 100–400 Gb/s data center needs, HDMI AOC, USB‐3 (c‐type), and so on. The world’s fastest (as of 2019 and 2020) high‐performance computer, Fugaku, uses more than 6 400 000 chips of VCSELs for AOCs.
The second and biggest opportunity is high‐power VCSEL arrays for consumer electronics (3D sensing and imaging up to 10