A peek behind the VCSEL curtain – The Chronicles by Yole SystemPlus

According to Yole Intelligence’s report, VCSEL 2023, the VCSEL (Vertical-Cavity Surface-Emitting Laser) market is expected to reach US$1.4 billion by 2028, exhibiting a compound annual growth rate (CAGR) of 6% from 2022 to 2028. While the consumer and telecom sectors are still expected to be well ahead of the pack at this time, the automotive market is expected to capture an 8% share, experiencing a noteworthy CAGR of 71% from 2022 to 2028.

Depending on the application, manufacturers are adopting strategies to either reduce system costs by substituting expensive EELs (Edge-Emitting Lasers) with this decade-old technology or enhance sensing performance by integrating VCSELs instead of LEDs in in-cabin automotive cameras. In its report (VCSEL Comparison 2023), Yole Group analyzes various target applications for VCSELs in particularly the smartphone, telecom, industrial, automotive, and defense sectors. The analysis covered one or multiple systems within each application sector, with a total of ten systems being torn down. VCSEL dies from six major players (Coherent, Lumentum, ams OSRAM, Trumpf, Solidlite, and Vertilite) are analyzed on both technological and cost aspects.

Let us take a more in-depth look at two flagship device categories, namely smartphones and automotive LiDARs.

Since Apple’s entry into the scene in 2017 with the launch of the iPhone X featuring VCSELs for facial recognition, the mobile and consumer market has witnessed a significant transformation, surging to a US$440 million valuation a year later. Over time, the cavity diameter, the pitch between the cavities, and the number of pairs in the top and bottom distributed Bragg reflector layers have been optimized. In the case of DOE (diffractive optical elements) and flood illuminator functions, an impressive die area reduction of 40% or more is observed when comparing newer and older VCSEL generations from Lumentum, Trumpf, and ams OSRAM.

In a bid to minimize the notch size, Apple has taken a step forward with the iPhone 13 Pro Max by integrating the dot projector and the flood illuminator into a single module. In this case, according to the VCSEL Comparison 2023 report, two generations of VCSELs supplied by Lumentum (2017 and 2020) have been combined. Light beams from both VCSELs are detected and processed by the same global shutter CIS (CMOS Image Sensor).

Traditionally confined to a limited range of a few tens of centimeters, VCSELs are typically utilized for in-cabin cameras within the automotive sector. Velodyne breaks new ground by incorporating VCSELs into an automotive LiDAR, marking the first instance of such integration noted by Yole SystemPlus, in the Velodyne Short- and Long-Range LiDAR with VCSEL and EEL report. The Velarray H800 system integrates two illumination modules: the first manages mid- and far-field measurements (up to 200 m) and relies on eight 905 nm EELs provided by ams OSRAM. These EELs are assembled with eight photodiodes and optical elements on the same substrate, forming an MLA (Micro-Lidar Array). For the near-field illumination (from 10 cm up to a few meters), Velodyne opted for four multi-junction VCSEL dies from Vixar (a subsidiary of ams OSRAM) placed side by side. The eight photodiodes serve as reception systems and time of flight measurements for both illumination systems (EEL and VCSEL) to draw the distance map of the objects in the vehicle’s environment.

Typically designed with a single active layer, the Vixar VCSEL architecture comprises five stacked layers, significantly boosting the power of the light pulses and allowing the integration of these lasers in new applications such as the near-range automotive LiDAR. Although in development for an extended period, the unique structure poses manufacturing challenges, primarily attributable to a more intricate epitaxy process. This process requires extensive technological expertise in VCSELs, a skillset that ams OSRAM gained through its acquisition of Vixar in 2018.

In addition to achieving longer ranges, the multi-junction VCSEL can produce a narrower light beam requiring smaller optics for adequate performance this allow to reduce volume and cost of the system. The twin positive effects of this are greater device compacity and reduced costs. It is likely that other laser manufacturers will be enticed by this VCSEL architecture, leading to an increasing number of applications. This could be particularly significant for the mobile market, driven by the continual pursuit of miniaturization. In the longer term, datacom may also embrace this technology with the goal of improving range performance at a reduced cost. Nevertheless, additional development would be necessary to meet the compatibility requirements of high-frequency systems.

Another noteworthy evolution in smartphone VCSELs has been observed. Yole SystemPlus recently examined a VCSEL structure with the cathode and the anode positioned on the same side of the die. This innovative architecture enables a flip-chip assembly on an ASIC (Application-Specific Integrated Circuit), providing the advantage of independent and more precise control over each VCSEL. This additional benefit extends the sphere of possible applications.

Sylvain Hallereau is Principal Technology & Cost Analyst at Yole SystemPlus, part of Yole Group (Yole). Working in close collaboration with the laboratory teams, Sylvain produces reverse engineering & costing reports while also contributing to custom projects, especially focused on solid-state lighting components, sensors, biotechnology devices, and ICs. Together, they define the objectives of the analysis and the most relevant methodology to gain a detailed understanding of the structure of the device. Sylvain then analyzes the results to describe the technology choices made by the leading semiconductor companies and the related process flows and also calculates the cost structure. In parallel, based on his significant technical and industrial knowledge, Sylvain supports the development of the semiconductor device activities and the related team at Yole SystemPlus and contributes to the strategy of this department. Sylvain runs a daily strategic watch within the semiconductor community. Through his investigations, his aim is to identify innovative components and new manufacturing processes. In this way, Sylvain supports Yole SystemPlus by setting up new methodologies for analysis and updating advanced simulation tools, especially those developed internally by Yole SystemPlus’s experts.
Sylvain regularly contributes to numerous media articles, using his technology and industry expertise to analyze and comment on the latest innovations. He holds a master’s degree in Microelectronics from the University of Nantes (France).