image: Figure | Device architecture and optoelectronic characteristics. a, Schematic illustration and corresponding cross-sectional SEM image of the device, comprising n-type DBRs, a passive cavity, multiple quantum wells, an oxide layer, and p-type DBRs. Scale bar: 5 μm, 500 nm, 200 nm. b, Emission spectra measured at different temperatures (25 °C to 95 °C) under a fixed injection current of 1.4 mA. c, Single-side frequency noise PSD of the proposed VCSEL, compared with state-of-the-art free-running laser sources. The inset shows the corresponding Lorentzian linewidth derived from the PSD, with the dashed line indicating the β-separation line that delineates coherence-dominant noise.
Credit: Aobo Ren et al.
Narrow-linewidth vertical-cavity surface-emitting lasers (VCSELs) are critical for quantum sensors and chip-scale atomic clocks. However, conventional designs typically suffer from broad linewidths due to short cavity lengths and excess spontaneous emission. A team from the University of Electronic Science and Technology of China, in collaboration with other research institutions, has overcome these challenges by embedding a passive cavity adjacent to the active region of a VCSEL, achieving a linewidth compression to ~1 MHz.
In a new paper published in Light: Science & Applications, a team of scientists, led by Prof. Jiang Wu from the University of Electronic Science and Technology of China (UESTC), and co-authors have developed a monolithically integrated VCSEL technology. This device achieves linewidth compression to approximately 1 MHz, a breakthrough for quantum sensing and chip-scale atomic clocks.
The team integrated a passive cavity within the VCSEL, extending photon lifetime and minimizing spontaneous emission, without requiring external optical feedback. This design ensures stable single-mode operation across a wide range of temperatures and currents, delivering robust performance for precision applications. The device demonstrated impressive performance, including a side-mode suppression ratio (SMSR) exceeding 35 dB, an orthogonal polarization suppression ratio (OPSR) greater than 25 dB, and frequency stability of 1.89×10-12 τ-1/2 when incorporated into a cesium vapor-cell atomic clock.
These scientists summarize the operational principle of their VCSEL:
“We design a monolithic VCSEL with an integrated passive cavity for three primary purposes: (1) to achieve linewidth compression to ~1 MHz without external optical feedback; (2) to extend photon lifetime and suppress higher-order transverse modes for improved stability; and (3) to maintain stable single-mode operation over a wide temperature and current range, ensuring robustness even under varying environmental conditions.”
“By reducing frequency noise and enhancing coherence, this technology is ideal for next-generation quantum sensors and timing systems,” they added.
“The breakthrough opens new possibilities for quantum sensing, precision timing, and other applications requiring stable, compact light sources,” the scientists forecast.
Journal
Light Science & Applications
Article Title
1-MHz Linewidth VCSEL Enabled by Monolithically Integrated Passive Cavity for High-Stability Chip-Scale Atomic Clocks