# Si Photonics for Practical LiDAR Solutions
## 1 Introduction  
Silicon (Si) photonics have emerged as one of the so-called \"more-than-Moore\" technologies that are based upon or derived from Si complementary metal-oxide-semiconductor (CMOS) and are focused on application and diversity rather than transistor scaling. Many integrated circuit (IC) and communication companies have been heavily invested in Si photonics for over a decade, not long after the academic world put it under the spotlight. Thanks to extensive research and development on SiGe epitaxy for bipolar CMOS (BiCMOS) and silicon-on-insulator (SOI) wafers for radio frequency IC (RFIC) and partially or fully depleted CMOS, most Si photonics components can be fabricated using slightly modified SOI processes with the addition of pure Ge epitaxy and associated metallization processes. High compatibility with CMOS helps Si photonics to create a fast growing fabless-foundry ecosystem that has been repeatedly proven a key to success by the cases like image sensors. Si photonics has achieved its early success in commercialization by enabling high-volume optical transceiver modules for both data center and long-haul optical networks.  
While people realize that Si photonics has its limitations and may co-exist with its fierce InP competitors for many years to come, many IC, optics and communication companies are embracing this technology and many released products in recent years. On the foundry side, starting with a couple of research or pilot fabrication lines in imec (Belgium), Institute of Microelectronics (IME) (Singapore), American Institute of Manufacturing (AIM) Photonics (US), Chinese Academy of Sciences--Institute of Microelectronics (CAS-IME) (China), etc., many semiconductor foundries have released their Si photonics commercial offerings, including GlobalFoundries (Santa Clara, CA, USA), STMicroelectronics (Geneva, Switzerland), TowerJazz (Migdal HaEmek, Israel), Taiwan Semiconductor Manufacturing Company (TSMC) (Hsinchu, Taiwan), Advanced Micro Foundry (AMF) (Singapore), etc.  
As Si photonics has made its entry into the optical communications market and grasps sizable shares, the designs and processes are maturing and standardizing and the optical transceiver products it enables are increasingly competing on manufacturability, cost, yield, and supply chain instead of technological novelty. Many Si photonics researchers and start-ups are looking into other applications such as optical sensing, among which, light detection and ranging (LiDAR) sensors have enjoyed a lot attention in recent years thanks to the burgeoning autonomous driving market. While there have been many review articles on Si photonics for optical communication applications [1; 2; 3; 4; 5], there are fewer forLiDAR [6], in particular, with the focus on practical implementation. The authors attempt to capture the published results of this rapidly developing field in last decade with an emphasis on practical aspects for commercialization than scientific novelty. The authors understand that it is very challenging, if not impossible, to accomplish a complete survey of such an actively developing field and we apologize in advance to those researchers and institutions whose work we have inadvertently overlooked.