Widely tunable and narrow-linewidth violet lasers enabled by UV-transparent materials

This article presents the first integrated extended cavity diode laser using UV-transparent materials, specifically aluminum oxide (Al₂O₃) as the core material for the waveguide, paired with silicon dioxide (SiO₂) cladding. This design enables the generation of violet light at wavelengths around 405 nm, critical for applications such as ion traps in quantum computing and optical clocks.

Key Contributions:

1. Waveguide Platform:

• The laser is based on a UV-transparent platform using aluminum oxide (Al₂O₃) with silicon dioxide cladding, which allows the light to propagate efficiently in the UV range. Aluminum oxide's wide transparency range (spanning from 165 nm to visible wavelengths) makes it a suitable material for such applications, offering much lower propagation losses than typical materials for UV waveguides.

2. Laser Design and Tuning:

• The laser design uses micro-ring resonators in a Vernier filter configuration, providing narrowband optical filtering and precise wavelength tuning. The tunable wavelength output was demonstrated with a tuning range of 4.4 nm (8 THz), allowing for mode-hop-free tuning across a wide spectral range.

• The laser is tunable from 408.1 nm to 403.7 nm using three heaters, which adjust the laser cavity length and phase. Mode-hop-free tuning was achieved over a 16 GHz span, enabling precise wavelength control critical for applications like Sr⁺ ion traps.

3. Performance Metrics:

• Fiber-coupled output was measured at 0.74 mW at 405.5 nm with a side-mode suppression ratio (SMSR) of 43 dB, indicating excellent single-wavelength operation. The laser demonstrated low intrinsic linewidth of 300 kHz, at least an order of magnitude lower than previous work in this wavelength range.

• Frequency noise measurements showed that the laser frequency noise was dominated by quantum-limited noise (Schawlow-Townes limit), with a measured linewidth of 313 ± 25 kHz, one of the lowest reported for integrated lasers at this wavelength.

4. Long-Term Stability:

• The laser exhibited high long-term frequency stability, maintaining mode-hop-free operation for over 70 minutes. The drift in frequency was measured to be about 1 MHz/min, demonstrating that the laser remains highly stable over extended periods, which is crucial for precision applications in quantum computing and optical clocks.

5. Applications in Quantum Technologies:

• The laser's narrow linewidth and high stability make it ideal for ion trap-based quantum computing applications, where precise wavelength control is necessary for cooling and state preparation of ions like Sr⁺. The laser can also be used for miniaturizing optical clocks and scalable quantum computing.

Conclusion:

This work demonstrates the first UV-integrated laser based on aluminum oxide waveguides and provides a highly tunable, narrow-linewidth light source suitable for quantum technologies. With the ability to achieve mode-hop-free tuning and long-term frequency stability, this integrated laser sets the stage for advances in miniaturized ion traps, optical clocks, and quantum computing applications. The development of these UV-transparent waveguides and integrated lasers opens new avenues for multi-wavelength light generation and precise frequency control in integrated photonics.