In recent years, the demand for precise and efficient sensing technologies has grown exponentially across various industries. From quantum science, aerospace, and autonomous vehicles to biomedical imaging, the need for cutting-edge solutions that address the limitations of existing sensing technologies has never been more pressing.
At the heart of this evolution in sensing technologies is Mesa Quantum’s mission to develop cutting-edge quantum sensors, particularly chip-scale atomic clocks, with the support of its advanced vertical-cavity surface-emitting lasers (VCSELs) that are custom designed with features that would meet specific challenges posed by these groundbreaking technologies.
Quantum sensors—transformative tools offering unprecedented accuracy and reliability in applications such as positioning, navigation, and timing (PNT) systems, atomic clocks, and magnetometers—represent a key area where these advancements hold immense promise as the primary or backup timing source. However, their full potential remains constrained partly by the limitations of VCSELs based on the current technology, which lacks the precision and stability in their optical output performance required for quantum applications, resulting in significant performance bottlenecks.
Among the most pressing challenges in the development of VCSELs used in quantum sensors are narrow linewidth requirements, higher single-mode output power, single-polarization performance, and emission wavelength tunability. Quantum sensors demand lasers with extremely narrow linewidths, often less than 20 MHz, to ensure spectral stability. Current VCSELs, especially those manufactured at high volumes, struggle to meet these stringent requirements mainly due to epi wafers’ nonuniformity across a six-inch substrate platform, and also due to the variations during the chip processing at the fab foundry. Currently, such VCSELs exhibit emission linewidths greater than 50 MHz, which can significantly degrade the signal in atomic clocks, reducing timing precision. Most quantum-sensing applications, such as magnetometers and optical clocks, would significantly benefit from VCSELs that can exhibit narrower emission linewidths, in addition to being spectrally single-mode with stable single-polarization output optical power. Moreover, a stable optical output power across the temperature range from 25 degrees Celsius to 95 degrees Celsius guarantees optimized performance of the quantum sensor with minimal noise levels.
Microscope image of a single-aperture VCSEL. Photo credit: A.Ghods et al., SPIE VCSELs XXVII 12439, 130-138 (2023).
Adding to these challenges is the critical need for emission wavelength tunability, as any deviation from the target emission wavelength can compromise the optimal performance of the quantum sensor. Such VCSELs must emit at specific wavelengths tailored to their applications. For example, lasers used in rubidium atomic clocks are required to emit precisely at 794.9 nm to resonate with the specific atomic transitions. However, this is often not achieved, where VCSELs emit either as shorter or longer wavelengths, and this adds to the total yield loss of VCSELs that can be used for these atomic clocks.
Traditionally, emission wavelength tunability is achieved by changing the bias current or operating temperature of the VCSELs, but such methods often affect the optical output power, which ideally should remain consistent throughout the sensor’s operational lifetime.
By redesigning the VCSEL chip layout, Mesa Quantum’s VCSELs achieve high single-mode output power levels with a high degree of spectral purity. Wafer-level metasurface and other epi-integrated solutions further enhance the performance of these devices, achieving linearly polarized output power that remains stable at elevated temperatures up to 95 degrees Celsius. The integration of multijunction epitaxial structure further enhances the single-mode output power of these VCSELs. In these multijunction VCSELs, several active light-emitting junctions are integrated into the epitaxial structure, which leads to scaling of the output power. Multijunction VCSELs can support the integration of up to 10 active junctions, significantly enhancing the maximum available output power levels. Furthermore, novel epi-level techniques reduce the emission linewidth to less than 20 MHz while enabling independent wavelength tuning without affecting optical output power. Similarly, emission wavelength tunability is achieved by integrating the passive cavities within the epitaxial structure of such VCSELs.
The benefits of multijunction VCSELs extend beyond quantum sensing. In lidar systems, these VCSELs achieve higher multimode output power densities, exceeding 2 kW/mm², significantly enhancing detection range and resolution. For automotive lidar systems, VCSEL technology that results in narrow beam divergence angles (full-width 1/e2<20°) and high power density, enable longer detection ranges and greater angular resolution, driving advancements in autonomous vehicle technologies. By utilizing innovative epi-design solutions, it is possible to improve the temperature performance of the VCSELs, meaning an operational temperature range anywhere from –40 degrees Celsius to 125 degrees Celsius with negligible drop in electro-optical characteristics.
Similarly, in biomedical imaging applications like optical coherence tomography (OCT), the precision and power of multijunction VCSELs enable deeper tissue penetration and higher resolution, revolutionizing diagnostic capabilities. In consumer electronics, the miniaturization and cost- effectiveness of these lasers open new possibilities in AR/VR devices and SWIR cameras, providing lightweight and power-conscious solutions.
Mesa Quantum’s mission to develop the next generation of low-SWaP (size, weight, and power) atomic clocks at the chip scale exemplifies the potential of its VCSEL technology. The current market for chip-scale atomic clocks is constrained to a few suppliers with long delivery times and high unit costs. This is partly caused by significant yield losses of more than 90% during VCSEL production due to the strict performance characteristics required. Mesa Quantum’s advanced VCSEL technology not only addresses these technological bottlenecks but also improves production yields by more than double, which ultimately results in reduction in both unit costs and lead times, thus making high-performance quantum-sensing devices more accessible.
Collaboration has been instrumental in realizing these advancements to VCSEL technology. Mesa Quantum’s interdisciplinary approach brings together atomic physicists, photonic designers, and material scientists to refine every aspect of laser design, from epitaxial growth to device-level packaging. This synergy ensures that the devices meet the exacting requirements of quantum and biomedical applications while remaining scalable for commercial production.
Mesa Quantum’s innovations in VCSEL technology are not just about overcoming current limitations; they are about redefining what is possible. By addressing the unmet needs of quantum sensing and extending these advancements to broader applications, Mesa Quantum is paving the way for a new era of precision sensing. With their multijunction VCSEL technology, the future of photonics is brighter, more efficient, and more impactful than ever before.
Amirhossein Ghods is vice president of photonics at Mesa Quantum Systems where he leads development of photonic devices, including high-efficiency semiconductor lasers designed for quantum sensors. mesaquantum.com/vcsel/
