Stories of Manufacturing#09
In Pursuit of the Quality and Potential of LightLaser Diode Development
The ‘Eye of Light’ that Captures the World
Invisible light is transforming the way we live
In restaurants and logistics warehouses, robots navigate spaces while avoiding obstacles to transport goods, and in offices and vehicle cabins, air purifiers and air quality monitors capable of detecting airborne pollen and PM2.5 concentrations are widely used.
Smartphone facial recognition systems project tens of thousands of infrared dots onto the face to calculate its 3D structure (depth information), enabling a highly secure form of authentication despite being remarkably easy to use.
These everyday technologies are powered by compact laser modules equipped with laser diodes.
With their small form factor, energy efficiency, and high-speed performance, these devices are being utilized across a broad spectrum of applications, from consumer mobile devices, medical, and healthcare equipment to industrial systems and automotive technologies, with further diversification of applications and significant market growth expected.
‘Precisely measuring spaces and objects with invisible light’
The evolution of sensing technology, from innovation to commercialization, societal integration, and expanding application fields, has been driven by over 40 years of continuous advancement in laser diode technology.
The Dawn of Laser Diodes
Chief Engineer
Product Development Section PMEG
Photonics Business Dept.
Module Business Div.
Since joining the company, he has been consistently involved in product planning and development related to laser diodes and LEDs.
He exudes the presence of someone who has skillfully navigated an unpredictable market with experience and resilience.
To achieve this, ROHM became one of the first companies in the industry to focus on MBE (Molecular Beam Epitaxy), a crystal growth technique at the forefront of semiconductor technology. Around the same time, the company adopted its current name, and after evaluating several next-generation product candidates, such as thin-film electroluminescence and liquid crystal displays, the laser diode was ultimately selected for development.
Captivated by the MBE system, which was prominently featured in academic journals, he convinced the company president to travel to Paris and acquire the equipment. Up to that point, everything had gone smoothly.
But what he couldn't have known then was just how long and challenging the road ahead would be.
Yoshida:
‘Simply put, we started with no manufacturing or evaluation equipment at all. MBE is a technology that allows atomic-level control of crystal thickness and composition by precisely regulating temperature in an ultra-high vacuum environment, but when we actually put it to use, its performance was wildly unstable, like trying to tame a bucking bronco.
As we struggled to get the system under the control, we would immediately evaluate each chip as soon as it was produced, feed the results back into the process that same day, and repeat the cycle again and again. And since there was no commercially available evaluation equipment at the time, our device engineers built everything from scratch.’
considered cutting-edge at the time, was adopted to enable crystal growth under ultra-high vacuum conditions. ROHM took the lead, establishing what would become the industry standard ahead of other manufacturers, both domestic and international.
Through persistent, in-house efforts to improve the MBE equipment itself, we finally succeeded in producing high-quality, stable crystal layers, culminating in 1984 with the establishment of mass production technology.
At the time, laser output was limited to just around 5mW. Achieving both stable laser output and high optical quality while also ensuring a precise structural design capable of accurately capturing reflected light required extensive trial and error. By working closely with manufacturers on product development, we reached the milestone of commercialization within just a few years of launching the project. These efforts quietly contributed to the evolution of electronics and the advancement of society, gradually influencing other manufacturers and setting new standards across the industry.
In Step with the Growth of the Electronics Industry
The demand for optical discs surged rapidly across the globe, reshaping the market landscape. Within a decade, the technology evolved from CD-ROMs to recordable CD-Rs and eventually DVDs, each step requiring continuous improvements in laser diode performance.
Yoshida:
‘The introduction of CD-Rs sparked a fierce race for faster write speeds. As manufacturers pushed to achieve 12x and 48x speeds, the focus of development shifted toward enabling even faster writing capabilities. Higher-speed writing meant spinning the disc at significantly greater speeds, which in turn required increasing laser output. On top of that, the laser had to maintain stable light emission at all times. It was a period of rapid innovation, where laser diode output and performance improved dramatically in response to escalating demands.
These technological innovations eventually moved beyond optical discs, expanding their reach across the rapidly evolving digital society and the broader electronics industry.
Yoshida:
‘When we achieve a great result, I believe it’s essential to thoroughly analyze why it worked. And when things don’t go as planned, we shouldn't view them as failures, but rather as opportunities to uncover insights that can guide the next step. That mindset, I believe, is a true measure of an engineer’s skill, and perhaps even a kind of talent.’
In Yoshida's view, nothing is ever wasted. It's this steady accumulation of trial and error that reflects ROHM’s deep-rooted commitment to craftsmanship and forms the foundation for cultivating the spirit of its engineers.
Over time, the technologies and expertise gained through these efforts have opened the door to entirely new fields of application, further expanding the possibilities of laser diodes.
Emerging Demands and the Push for Higher Output Power
As the 2010s began, product development for new applications such as printers and projectors ramped up significantly.
The potential of laser diodes had long been recognized, and one of the most persistent needs in the market was the ability to ‘project lasers over longer distances.’ In response, the demand for higher output has steadily intensified year after year.
Around that time, robot vacuum cleaners surged in popularity, sparking interest in laser diodes for sensing applications.
Then in 2019, mass production began for devices that made a significant leap in output, shifting from the conventional few hundred milliwatts to the 25W-class. With that, the performance expectations of the market had entered a new phase.
General Manager
Photonics Business Dept.
Module Business Div.
Within ROHM, a comprehensive semiconductor manufacturer, the Photonic Device Division is dedicated to advancing optical technologies. Leading this highly specialized division is the general manager, who oversees a team of 65 engineers.
Yamamoto:
‘Our goal is to enable vehicles traveling at highway speeds to accurately detect obstacles 500 meters ahead.’
These were the words of Mr. Yamamoto from ROHM's Photonics Division.
In recent years, LiDAR (Light Detection and Ranging) has emerged as a critical technology in the push toward practical autonomous driving. Particularly in Europe, where efforts to establish international standards for driver assistance systems are accelerating, automakers are demanding ever-higher levels of performance.
Yamamoto:
‘On the Autobahn, where long straight stretches are common, it’s not unusual for vehicles to travel at speeds exceeding 150km/h. Even on one-way roads, when factoring braking distances at those speeds, a detection range of 500m is entirely reasonable. The key to making that possible lies in technology capable of projecting the laser both accurately and over long distances.
From mW to the kW Class
The most effective way to achieve long-range performance in LiDAR systems is by increasing the output power of the laser diode itself.
ROHM's RLD90QZWx series addresses this need with a maximum pulse output of 145W, made possible through a multi-stack structure, where laser elements are vertically layered, and a multi-channel configuration that arranges multiple elements horizontally.
High output is achieved through ROHM’s proprietary technology that combines a multi-stack structure with multi-channel configuration
Yamamoto:
‘Just before the 2020s, we made a significant leap in output power from several hundred milliwatts to the watt-class. And now, just five years later, are already advancing development targeting the kilowatt class. But can LiDAR range be extended by simply increasing the laser output alone? The answer is definitely not.’
Mr. Yamamoto has always approached his work with a strong sense of purpose, placing a strong emphasis on the core concept of ‘light quality.’
Light Quality - Higher Resolution
A key feature of ROHM's laser diodes is their exceptional resolution, enabling high-precision 3D scanning.
By increasing the light density in a narrow emission width and ensuring uniform emission from edge to edge, the system can produce high-definition images.
This ability to clearly render distant people and objects in high sharp detail significantly enhances detection accuracy.
Compared to scanning images from conventional laser diodes, the boundaries of detected objects are noticeably sharper and more clearly defined
Tanaka:
‘In the early stages of development, the focus on LiDAR was mainly on light quantity, or how to achieve higher output, rather than the quality of light, in order to measure longer distances. But as we gained a deeper understanding of LiDAR systems, it became increasingly clear that projecting light precisely and cleanly onto a target area is essential for achieving the resolution the market expects.’
These insights come from Mr. Tanaka, who has been deeply involved in laser diode development throughout his career, from his time in the R&D division to his current role.
Chief Engineer
Production Development Section PMEG
Photonics Business Dept.
Module Business Div.
During the development process, results sometimes align with expectation, but just as often they don't. In those moments, he stresses the importance of going back to the fundamental principles.
Tanaka:
‘After gathering feedback from numerous customers, one common observation was that the variations in laser intensity between the center and edges of the beam when projected onto a target were negatively impacting detection accuracy. In response, we began exploring ways to improve emission uniformity, which led us to focus on controlling both the current flow within the laser diode and the shape of the emitted light.’
He notes that the need for deep expertise in optical design in addition to electrical characteristics is one of the a major differences from conventional semiconductor manufacturing.
Tanaka:
‘That's why structural design - especially the layout - is absolutely critical in product development. It's a painstaking process where even slight changes in positioning or wiring can have a significant impact on performance. One of the biggest challenges is that, unlike IC design, simulation technology in this field is still underdeveloped.
Particularly for high-power laser diodes used in LiDAR, there are no standardized evaluation systems available, which is why I've always felt a strong need to build our own testing environments.
To find the optimal, trade-off-free combination from among dozens of design parameters, there's no shortcut, just patient, consistent work. It requires going back and forth between layout design on the screen and a broad range of validation experiments. This steady accumulation of effort is the only sure path to achieving the desired outcome.
The development process is often marked by continuous trial and error. Within that journey, the combination of hands-on validation and accumulated experience proves to be the most critical factor for success.
Light Quality - Wavelength Temperature Dependence
Another significant achievement has been our ability to greatly reduce wavelength temperature dependence.
Todo:
‘Automotive LiDAR is intended for outdoor use, and during daytime driving in particular, it's highly susceptible to interference from strong sunlight.
Sunlight has a very broad wavelength spectrum that overlaps with the operational range of LiDAR, making it easy for this light to register as noise on the photodetector. To mitigate this, filters are used to block out all but specific wavelengths, but even these can't fully eliminate sunlight interference, which can result in reduced detection accuracy.
Another major challenge is the shift in laser wavelength due to temperature changes. Laser diodes tend to redshift - their emission wavelength varies - as temperature rises.
This means fluctuations in ambient temperature can affect both the wavelength and output, potentially causing measurement errors.’
Engineer
Production Development Section 1G
Photonics Business Dept.
Module Business Div.
Mr. Todo also emphasized that one of a developer's core responsibilities is to pursue *practical usability*—a quality that can't be fully measured by product evaluation data alone.
ROHM's RLD90QZW8 represents a breakthrough solution that addresses both challenges simultaneously.
By combining proprietary device development technology with a unique structural design and advanced packaging optimized for heat dissipation, we successfully reduced the temperature dependence of the laser wavelength by 66% compared to standard products.
This improved thermal stability enables the use of narrower-band sunlight cut filters that more effectively minimize solar noise. As a result, we achieved longer LiDAR detection ranges with greater accuracy while decreasing overall system size.
Even with narrower-band sunlight cut filters, the wavelength is less likely to shift, improving light-receiving efficiency and distance measurement accuracy
ROHM's front-end manufacturing equipment has been developed through years of accumulated expertise in mass production technologies unique to laser diodes.
In reality, few manufacturers possess the technical capability to mass-produce laser diodes.
A major barrier to market entry is the high degree of specialization and the many years of experience needed at every stage, from structural design and crystal growth to fine processing and assembly. As mentioned earlier, ROHM has steadily built a foundation of expertise over more than 40 years, covering the entire process from front-end manufacturing to final packaging.
It’s no exaggeration to say that breakthroughs in highly sensitive and complex issues, such as suppressing wavelength temperature dependence, have only been possible only due to the long-term, methodical accumulation of knowledge.
Looking Ahead to Future Innovations and Applications
ROHM's laser diode technology is entering a new phase, going beyond traditional distance measurement and sensing applications.
One highlight not fully covered in this video is the 2024 introduction of a completely new infrared light source, VCSELED™ (pronounced vixel-led). This launch marked the 40th anniversary of ROHM’s entry into the laser diode business.
Developed using ROHM's proprietary technology that combines the strengths of VCSELs (Vertical Cavity Surface Emitting Lasers) and LEDs, VCSELED™ stands out for its exceptionally narrow wavelength spectrum that enables the emission of low-visibility, ‘invisible red’ light.
Yamamoto:
‘VCSELED™ is a groundbreaking product that redefines the concept of light, introducing something entirely new that hasn't existed before.
We initially planned to begin sample shipments for consumer use in October 2024, followed by automotive applications in 2025, but due to the overwhelmingly positive response following the announcement, we're now accelerating our development timeline.’
The unexpectedly strong market reaction is clearly reflected in Mr. Yamamoto's confident tone.
Yamamoto:
‘Automotive customers in particular are showing strong interest in VCSELED as a light source for Driver Monitoring Systems (DMS). Traditional LED light sources have a broad emission spectrum that often results in visible red light being projected onto the driver, a phenomenon known as ‘red visibility.’ VCSEL technology fundamentally resolves this problem by offering a much narrower spectral width at half the peak intensity.
On top of that, with a package thickness of just 0.55mm, this device is ideally suited not only for automotive use but also for a wide range of applications, including mobile devices and medical equipment.
Mr. Yamamoto remains steadfast in his vision for the future, looking beyond the anticipated surge in automotive LiDAR demand to also focus on advancing the research and development of optical data transmission technologies for data centers and other emerging fields.
Development and mass production are already gaining momentum, with full-scale deployment for automotive applications anticipated as early as 2025.
In the fast-evolving world of electronics, the possibilities enabled by light continue to grow and diversify. What lies beyond this challenge lies an ‘invisible yet unmistakable light’ quietly woven into the fabric of our daily lives.
With a vision set on the next 40 years, a new chapter in ROHM's story is now beginning to unfold.
Yoshida:
‘ROHM began mass-producing laser diodes in 1984, so the development project likely kicked off 3 to 4 years earlier, probably in the early 1980s, just as the decade began. Since that was 40 years ago, most of what I know about that period comes from those who were directly involved at the time (laughs). The initial focus was on developing optical pickups for audio equipment, specifically CD players. This technology used an infrared laser at a wavelength of 780nm to irradiate the disc, then read the intensity of the reflected light to extract the digital signal. Back then, analog records and cassette tapes were the standard, so the ability to read data without physical contact was truly groundbreaking.’