Nonlinear Frequency Translation in Micromachined Rb Vapor Cells

TL;DR

This paper demonstrates efficient nonlinear frequency translation in a chip-scale rubidium vapor cell, generating coherent blue and mid-IR light with high efficiency and stability, suitable for advanced optical applications.

Contribution

It introduces a compact, micromachined Rb vapor platform capable of efficient four-wave mixing for coherent light generation at multiple wavelengths.

Findings

Achieved ~20 μW blue light with ~1 MHz linewidth in a short vapor cell.

Higher efficiency in micromachined cell compared to conventional glass cells.

Detected ~50 nW mid-IR emission, confirming nonlinear conversion.

Abstract

The exceptional nonlinearity of alkali-metal vapors enables highly efficient nonlinear optical processes even at relatively low optical intensities. However, such processes have traditionally relied on centimeter-scale vapor cells. Here, we utilize a versatile chip-scale Rb vapor platform to generate coherent blue and mid-IR light in continuous-wave mode by means of resonant four-wave mixing. Optimized optical overlap with the atomic medium enables blue light generation of $\sim$20 $\mu$W over a very short interaction length, while maintaining a directly measured linewidth of $\sim$1 MHz, which is presently limited by the measurement apparatus. Comparison with a conventional glassblown vapor cell further shows that the micromachined platform can achieve higher coherent blue-light generation efficiency despite its substantially shorter interaction length. Moreover, an anodically bonded Si window enables to detect coherent mid-IR emission with collected powers of $\sim$50 nW. We further characterize the temperature dependence and input-power scaling of the blue emission, confirming efficient nonlinear conversion within these compact vapor cells. This chip-scale platform provides a versatile foundation for a range of nonlinear optical functions, from precise wavelength references and quantum light sources to next-generation quantum sensors.