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Foreword

“A conventional stripe semiconductor laser consists of two end mirrors perpendicular to the active layer so that the light output is parallel to the wafer surface. If a semiconductor laser with the light output perpendicular to the wafer surface could be obtained, it would be very easy to fabricate a 2‐dimensional laser array…” This was proposed by Kenichi Iga in 1977, and the first paper on its realization, written by Haruhisa Soda, Kenichi Iga, Chiyuki Kitahara, and Yasuharu Suematsu, came out in 1979 [1]. This paper was a key milestone for the birth of the vertical‐cavity surface‐emitting laser, or VCSEL, as we now call it. As a longtime worker in fiber optics communications, I realize that the geometry of “the conventional laser” was deeply ingrained in the mindset of system engineers. The design, alignment, and packaging of an end‐to‐end fiber optics system were by and large catered to the concept that the laser light output is parallel to the wafer surface.

Following breakthroughs of the first room‐temperature CW operation of VCSELs [2] and the first experimental demonstration of a 2D VCSEL array [3], worldwide VCSEL R&D was kick‐started in the early 1990s. In 2000, DARPA managers Elias Towe, Robert F. Leheny, and Andrew Yang wrote the following about VCSEL in their review paper [4]: “Its size, manufacturability, and potential ease of heterogeneous integration of electronics promise a range of applications that have yet to be explored.” This was the time DARPA invested considerable human and monetary resources in the R&D of VCSELs, in particular the massive integration of VCSELs, detectors, micro‐optics, and driving electronics for optical backplanes, free‐space optical interconnections, and all optical switching. While these applications did not emerge immediately, the DARPA funding impetus did drive widespread commercialization efforts.

The first commercial VCSELs, offered by Honeywell in 1996, were driven by the emerging demand for global bandwidth [5] that is now fueled by the need for low‐cost data center communications with the worldwide construction of giant data centers by cloud computing companies such as Google, Amazon AWS, Facebook, and Alibaba. First generation VCSELs operated at 1 Gbps and have since evolved to datalink or active optical cables operating at 25 Gb/s NRZ modulation and 50 Gb/s PAM4 modulation for a single channel. Spectral and spatial multiplexing results in bandwidth expansions from 25 Gb/s to more than 400 Gb/s optical networks using multiple channels over a distance of several hundred meters. Another application in optical communications is in the widespread deployment of radio access network (RAN) in 4G and 5G LTE wireless fronthaul networks.

Yet another impetus for VCSEL applications is the progress in optical sensing and imaging in the fields of consumer electronics (mobile/smartphones) and automotive transport (autonomous vehicles through LiDARs). The property of optical signal processing perpendicular, rather than parallel, to the wafer surface makes VCSEL an ideal light source for many applications in computer vision and sensing. In 2017, Apple Inc. began to incorporate several kinds of VCSELs into its latest products starting with a structured light source for 3D depth sensing application (face ID) and now includes a LiDAR with 5 m range. We also witnessed the introduction of massively integrated VCSELs in other commercial LiDARs that has the potential to address the question of scalability in increasing the number of laser scanning lines beyond 16 and 32 to 64, 128, or even higher. The ability to integrate a large number of parallel beams perpendicular to the surface of the wafer also makes a VCSEL structure ideal for high‐power (kW level) applications such as laser heating and laser cutting, among others. Other multi‐mode and single‐mode applications for VCSELs include atomic clocks, computer mice, laser printers, biometrics (Optical Coherence Tomography OCT), defense (drones), gas sensing, and polarization‐controlled light sources for future quantum communication. Over the past 40 years, VCSELs have moved from a research curiosity to more than one billion devices in use today in a diverse range of applications. This commercial ramp‐up has attracted a large commercial base that has heavily invested in high‐volume manufacturing infrastructure [6].

With VCSELs now representing a multibillion‐dollar global industry and worldwide interest in VCSEL’s commercial usage, it is timely to write a book covering these wide range of applications and help to stimulate other novel applications. We are very fortunate and deeply honored to have Dr. Babu Dayal Padullaparthi, Dr. Jim Tatum, and Professor Kenichi Iga, a team of VCSEL experts who kindly agreed to write the book for Wiley‐IEEE Press. Professor Iga is none other than the original VCSEL pioneer and author of the 1979 paper mentioned earlier. These three outstanding researchers have a collective amount of experience in academic and industrial research as well as commercial productization of VCSEL spanning the past four decades. They will provide the readers with a historical perspective and current state‐of‐the‐art technology and product status of the field. Through the authors’ extensive contacts with leading VCSEL manufacturers worldwide, the book will also present an up‐to‐date picture of R&D and product trends for both researchers and practicing engineers. I am confident that the readers will find this book an enjoyable tutorial and product reference covering the long and exciting journey of VCSELs.

Nim Cheung

Series Editor, Wiley‐IEEE Press

November 23, 2020

References

1 1 H. Soda, K. Iga, C. Kitahara, and Y. Suematsu, ‘GaInAsP/InP surface emitting injection lasers’, Jpn. J. App. Phys., Vol. 18, No. 12, Pages 2329–2330 (1979)

2 2 F. Koyama, S. Kinoshita and K. Iga, ‘Room temperature CW operation of GaAs vertical cavity surface emitting laser’, IEICE Trans., E71, 1089–1090 (1988)

3 3 Y. H. Lee, J. L. Jewell, A. Scherer et al., ‘Room‐Tempreature, Continuous‐Wave Vertical‐Cavity Single‐Quantum‐Well Microlaser Diodes’, Electronics Letters 25, No. 20 Pages 1377–1378 (1989)

4 4 E. Towe, R. F. Leheny, and A. Yang, ‘A historical perspective of the development of the vertical‐cavity surface‐emitting laser’, IEEE J. Sel. Top Quantum Electron., Vol. 6, No. 6, Pages 1458–1464 (2000)

5 5 J. A. Tatum, A. Clark, J. K. Guenter, R. A. Hawthorne, and R. H. Johnson, ‘Commercialization of Honeywell's VCSEL technology,’ Proc. SPIE3946 2–13 (2000)

6 6 B. D. Padullaparthi, R. Chen, A. Tan et al. ‘High Volume Manufacturing of VCSELs for Datacom & Sensing’, Industry Panel Discussions, Th4, pp: 51, International Nano‐Optoelectronics Workshop (i‐NOW) 2018, UC Berkeley, USA.