Contents What constitutes the core significance of power and efficiency expansion in semiconductor lasers, and how will it influence future technology and society?
Power and efficiency scaling in semiconductor lasers represents a fundamental driver for next-generation photonic systems, with implications that extend far beyond simple performance metrics [1]. From a footprint perspective, scaling the output power of semiconductor lasers has significant implications for reducing the size and weight of both the laser devices themselves and the modules in which they are integrated. This compaction not only simplifies system architecture but also achieves power densities that previously required multiple laser devices operating in tandem. In applications such as LiDAR, optical communication, and biomedical imaging, higher power densities translate directly into enhanced performance metrics. For instance, in automotive LiDAR systems, output power densities greater than 2 kW/mm2, combined with beam divergence angles below 25°, have extended detection ranges beyond 200 m while maintaining sub-0.1° angular resolution. Similarly, in medical imaging, higher power enables deeper tissue penetration for non-invasive diagnostic procedures such as optical coherence tomography (OCT). In high-speed optical communication or optical wireless power transmission systems, increased power density enables long-distance data transmission with reduced signal degradation [2], [3].
Efficiency scaling further amplifies these benefits by reducing thermal dissipation. Efficient semiconductor lasers, with power conversion efficiencies greater than 60%, lower the cooling requirements, simplifying thermal management and enabling compact system designs, especially in mobile and wearable devices. Lower heat generation also enhances the operational lifetime of laser modules, reducing maintenance costs and increasing reliability.
Moreover, the societal impact of these advancements cannot be understated. The integration of efficient lasers in consumer electronics, such as SWIR cameras and AR/VR devices, offers lightweight, power-conscious solutions that enhance user experience [4], [5]. Additionally, the potential for semiconductor lasers in quantum sensing technologies promises to unlock entirely new markets, such as atomic clocks achieving stability better than 1×10−12 at one-second integration time.
What are the principal technical challenges faced in semiconductor lasers, and what strategies are typically adopted to overcome these impediments?
From a VCSEL (Vertical-Cavity Surface-Emitting Laser) perspective, several critical challenges emerge as the demand for higher power and efficiency increases. Among these, developing high junction-count VCSELs stands out as a technically complex yet crucial goal. Increasing the number of active junctions boosts output power and efficiency but introduces several technical obstacles:
Tunnel Junctions: Efficient, low-resistance (<5×10−5 Ω·cm2) tunnel junctions are integral to multijunction VCSELs, particularly for shorter wavelengths (<800nm). However, achieving low resistance without compromising optical transparency is challenging. Material systems such as highly-doped GaAs and related compositions of AlGaAs are under exploration to optimize performance at these wavelengths. Advances in epitaxial growth techniques, such as metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), play a pivotal role in overcoming these limitations.
Longitudinal Mode Stability: While single-junction VCSELs typically operate with a free spectral range exceeding 100nm due to their approximately one-wavelength cavity length, multijunction designs inherently have much longer cavities, scaling with the number of active junctions. This extension reduces the longitudinal mode spacing to 20-30 nm, significantly increasing the risk of longitudinal mode hopping. The challenge becomes particularly acute across automotive temperature ranges (-40 °C to 125 °C), where thermal effects can induce significant changes in the cavity's optical properties.
Beam Divergence: The far-field beam profile of multijunction VCSELs typically exhibits a wider divergence angle compared to single-junction devices [6]. For example, single-junction VCSELs typically demonstrate far-field beam profile with full-width 1/e2 divergence angles between 15–20° depending on the operating current and temperature. On the other hand, multijunction VCSELs typically exhibit divergence angles greater than 30°. This increased beam divergence angle stems from complex interactions between multiple oxide apertures and their impact on lateral mode confinement. A divergence angle greater than 30° can limit resolution in sensing applications. Strategies to mitigate this include reducing the total number of oxide apertures used in the epitaxial structure, tapering the tip point of the oxide apertures, randomizing the profile of the oxide apertures relative to each other, optimizing their placement relative to the active region and the standing wave pattern, application of surface-relief mode filter, and employing ion implantation instead of the oxide layers to form lateral optical confinement [7], [8], [9]. Moreover, the use of anti-reflective mirrors in the n-DBR region that act as a passive cavity has shown to reduce the beam divergence angle in multijunction VCSELs. All these methods are used to reduce the optical transverse mode confinement in the cavity, which ultimately lead to a narrower far-field beam divergence angle. In addition to these epi-level solutions to control the beam divergence angle, integrating wafer-level metasurfaces offers a promising approach to dynamically modulate beam properties such as narrowing the divergence angle, collimation and controlling the polarization of the outcoupling beam.
Thermal Management: High-power VCSELs generate significant heat, which can degrade performance and reliability. Advanced packaging solutions, such as flip-chip bonding with integrated micro-thermal management systems, and innovations in thermal interface materials are critical in mitigating thermal effects.
Beyond VCSELs, edge-emitting lasers face their own set of distinct challenges. Facet engineering must achieve high catastrophic optical damage thresholds while maintaining precise control of facet reflectivity. Environmental stability at 85% relative humidity and 85 °C poses additional reliability challenges that require sophisticated passivation techniques. These challenges are being addressed through advanced epitaxial designs and novel waveguide architectures that optimize carrier transport and thermal management simultaneously.
What do you consider as the key to future breakthroughs in semiconductor laser technology? How will these breakthroughs affect the market and research orientation?
I believe that the next major breakthrough in semiconductor laser technology will likely emerge from further scaling the output optical power of semiconductor lasers while maintaining critical performance characteristics. From a VCSEL perspective, this translates to developing VCSELs with higher junction counts while preserving critical performance characteristics. Currently, multijunction 9xx nm VCSELs with up to eight active junctions have been demonstrated and produced at mass scale using 6-inch substrate platform [10]. However, the multi-mode output power density of these devices is <2 kW/mm2, which is insufficient for high-power LiDAR sensing applications. Similarly, single-mode, single-polarization power from these devices remains below 15 mW, which is inadequate for some quantum sensing and spectroscopic applications [11], [12], [13].
A significant breakthrough would be the development of VCSELs incorporating more than 12 active junctions while maintaining critical performance metrics. Such devices must achieve multi-mode output power densities greater than 2 kW/mm2 and single-mode output power greater than 15mW with side-mode suppression ratios exceeding 30 dB and polarization extinction ratios above 20 dB across the entire operating temperature range of −40 °C to +125 °C. These enhancements would enable higher-resolution sensing, greater detection range, and more robust quantum systems.
Such advancements will transform several industries:
Quantum Technologies: High single-mode single-polarization output power (>15 mW) with narrow-linewidth (<20 MHz) lasers are essential for quantum sensors, including atomic clocks, magnetometers, and Rydberg sensors. Enhanced laser performance will enable the chip-scale miniaturization and cost reduction of quantum devices, making them accessible for commercial deployment.
LiDAR and Autonomous Vehicles: Increasing the multi-mode output power density of VCSELs greater than 2 kW/mm2 while controlling divergence angle below 20° will improve the resolution and range of LiDAR systems. This combination would enable detection ranges beyond 200 m with high angular resolution, essential for Level 4 and 5 autonomous driving systems.
Biomedicine: In biomedical applications, these advanced VCSELs would enable deeper tissue penetration in optical coherence tomography (OCT) systems, potentially achieving imaging depths exceeding 3 mm with resolution better than 5 μm. The higher power density combined with precise spectral control would also enable new therapeutic applications, including targeted photodynamic therapy with unprecedented precision.
These breakthroughs will also shift research orientation towards multidisciplinary approaches, combining advancements in material science, photonic integration, and thermal management. Additionally, markets will increasingly prioritize customization, driving demand for application-specific laser designs.
How significant is interdisciplinary collaboration in the development of semiconductor laser technology? Which areas of collaboration are most crucial for accelerating technological progress?
Interdisciplinary collaboration has proven to be instrumental in advancing high-efficiency VCSELs tailored for specific applications. At Mesa Quantum, our primary focus is the development of next-generation low-SWaP (size, weight, and power) chip-scale atomic clocks (CSACs). While CSACs have been commercialized since the early 2010s by companies like Microchip (formerly Symmetricom) and Teledyne, the laser light source—a critical component in any quantum sensor—remains a critical technical bottleneck. These lasers must adhere to stringent performance specifications, including precise emission wavelengths (depending on alkali atom transitions), narrow linewidths (<20 MHz), and single-mode, single-polarization outputs [14].
Traditional VCSEL foundries often produce devices optimized for broader markets, which may not meet the precision required for quantum sensors. For instance, their standard processes both on the epi side and also the device fabrication side, result in linewidths exceeding 50MHz and unstable polarization, all of which lead to yield losses exceeding 90% across a 6-inch wafer. All these factors eventually drive-up costs and lead times (>20 weeks) for CSAC manufacturers. At Mesa Quantum, we tackled these issues through close collaboration between atomic physicists and VCSEL designers. By leveraging this synergy, we develop customized VCSELs optimized for quantum applications, significantly reducing yield losses and turnaround times.
Key areas of interdisciplinary collaboration include:
Epitaxial Growth and Fabrication: Collaboration with foundries enables the refinement of growth techniques, reducing variability and improving device uniformity.
Targeted Device Design: Atomic physicists, VCSEL designers, and process integration engineers work closely to define exact specifications, ensuring that laser designs align perfectly with application demands.
Process Optimization: By integrating atomic physics insights into epitaxial growth and fabrication processes, we achieve performance metrics well beyond what traditional VCSELs can achieve.
Our collaborative model not only enhances VCSEL performance but also reduces the costs and lead times of CSAC production by more than half. This highlights the broader importance of interdisciplinary collaboration in achieving tailored, high-performance semiconductor lasers for diverse applications.
In which fields do you believe semiconductor laser technology will be given priority in application, such as communication, sensing, medicine, and emerging applications in quantum, VR/AR, LiDAR, and LIFI?
In my opinion, semiconductor laser technology will be prioritized in two key areas: LiDAR and quantum sensing.
LiDAR: Automotive LiDAR systems rely on high-power semiconductor lasers with output power densities exceeding 2kW/mm2. These lasers must deliver stable performance and narrow divergence angles (<20°) to enable precise detection and high-resolution mapping. The automotive sector is driving rapid adoption of this technology, especially for short- and medium-range LiDAR modules in self-driving vehicles, where high-resolution mapping demands signal-to-noise ratios exceeding 20 dB at the maximum range. Advances in multijunction VCSELs further enhance power output and efficiency, satisfying the growing requirements of this field.
Quantum Sensing: Quantum sensors demand lasers with exceptional spectral stability and precision, including narrow linewidths (<20 MHz), single-mode single-polarization operation (SMSR>30 dB & PER>20 dB), and highly specific emission wavelengths. These sensors play a vital role in PNT (positioning, navigation, and timing) systems and are expanding into emerging biomedical markets, enabling non-invasive biosensing technologies. The recent progress in multijunction VCSELs, with improved power conversion efficiencies (60% vs. 40% in single-junction devices), directly supports these stringent requirements. Additionally, wafer-level integration of metasurfaces into VCSELs enhances beam shaping, collimation, and polarization control, further optimizing these lasers for quantum applications.
I believe that LiDAR and quantum sensing represent the forefront of innovation for semiconductor laser technology, driving advancements that will shape the future of autonomous systems, telecommunications, and biomedical diagnostics.
How is the global push for emerging applications in quantum, VR/AR, LiDAR, and LIFI development influencing the demand for tunable and high-power semiconductor lasers?
The global semiconductor laser market is experiencing significant regional differentiation in terms of technological focus and application demands. In the LiDAR sector, there is intense development activity centered on high junction-count multijunction VCSELs, with particularly strong demand emerging from automotive OEMs in both China and the United States. These manufacturers are driving specifications toward increasingly stringent automotive-grade requirements. A notable trend is the emerging demand for polarization-stable multijunction VCSELs, targeting both in-cabin sensing and external LiDAR applications. The specifications for these devices typically include power densities exceeding 2 kW/mm2, operating temperature ranges from -40 °C to +125 °C, and beam divergence angles below 20° for precise detection capabilities. As the push for electric vehicles (EVs) and autonomous vehicles grows, I believe the demand for these advanced VCSELs will only continue to increase.
When it comes to quantum sensing, the greatest drive is currently in the U.S., with some emerging efforts in Europe. In my opinion, the biggest demand with regards to light source in this sector lies in developing customized lasers that meet specific performance criteria for quantum applications. These requirements include narrow linewidths (<20 MHz), polarization stability, and single-mode operation, with output power levels ranging from 1 mW to around 20 mW. A significant manufacturing challenge exists in the current ecosystem, as much of the specialized VCSEL production for quantum applications is concentrated in foundries located in Taiwan and South Korea. This geographic distribution of manufacturing capabilities highlights a critical need for localized research, development, and production facilities, particularly in regions where quantum technology development is most active. The situation is complicated by the necessity for highly specialized epi growth and fabrication processes that differ from standard high-volume VCSEL production.
Overall, I believe the global push for advanced semiconductor lasers is reshaping the landscape of both LiDAR and quantum sensing technologies, fostering innovation and driving new opportunities in these critical fields.
Specifically, VCSEL has attained significant attention and progress over the past years. How do you think this progress will change the technological competition landscape between VCSELs and edge-emitting lasers, and what profound impacts will it have on emerging applications such as quantum, VR/AR, LiDAR, and LIFI?
VCSELs have several distinct advantages over edge-emitting lasers, including superior temperature stability, operation in a single-longitudinal mode, circular beam profiles, and the ability for wafer-level testing which eliminates the need for dicing and reduces the unit cost of devices. These characteristics have historically positioned VCSELs as a promising alternative for applications requiring compact, cost-effective solutions. However, traditional VCSELs have faced challenges such as lower output power, unstable single-mode and single-polarization performance, and broad linewidths (>50 MHz).
Recent breakthroughs in multijunction VCSEL technology have substantially expanded their capabilities. It is now possible to design and manufacture VCSELs with up to eight active junctions, achieving output power densities around 1.5kW/mm2 and single-mode, single-polarization power around 13mW. Additionally, breakthroughs in MOCVD epitaxial growth techniques have enabled the production of VCSELs with narrow emission linewidths (<20 MHz) and tunable electro-optical performance to meet specific application requirements.
These advancements make VCSELs a compelling alternative to edge-emitting lasers, particularly in high-demand fields such as LiDAR and quantum sensing. In LiDAR, the high-power density is desired to remain stable across the −40 °C to 125 °C temperature range, and precise beam shaping capabilities of advanced VCSELs are critical for achieving superior resolution and range. In quantum sensing, the ability to produce narrow-linewidth, single-mode polarization-stable VCSELs enhances the performance of systems such as atomic clocks and magnetometers, where precision and stability are paramount.
Furthermore, the integration of metasurfaces at the wafer level allows for tailored beam properties, such as collimation, divergence control, and polarization tuning, providing VCSELs with additional flexibility to address diverse technical requirements. These innovations are not only reducing costs but also expanding the scope of applications where VCSELs can outperform edge-emitting lasers. As a result, I believe VCSELs are reshaping the technological competition landscape, establishing themselves as a highly versatile and efficient solution for emerging applications, including quantum sensing technologies, LiDAR, AR/VR, and advanced communication systems like LIFI.