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Chip scale emission of blue quantum light at elevated temperatures from photonic circuit integrated with Rubidium vapor

Arieh Grosman, Ilan Sher, Roy Zektzer, Noa Mazurski, Uriel Levy

Published Jan 1, 2026• 0 citations
Publisher

Abstract

We generate 420nm blue light by four wave mixing in Rubidium vapor interacting with nano-photonic waveguides. Light emission is characterized at elevated temperatures and as a function of device length. Quantum applications are discussed.
DOI
10.1364/cleo_fs.2026.fm2g.5

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ABSTRACT Blue light emission from Rubidium (Rb) vapor cells is attractive for a myriad of applications, from quantum sensing and metrology to communication, quantum memories, and more. Typically, such emissions are observed from bulky free‐space glass cells. Here we experimentally demonstrate the generation of blue light from a chip‐scale optical waveguide integrated with rubidium vapor. The atomic ladder excitation using a combination of 780 and 776 nm light propagates through the Atomic Clad Waveguide (ACWG), directly interacting with Rubidium, emitting a photon at 420 nm and a matching photon at 5233 nm. The blue light emission is characterized and measured at elevated temperatures, up to 240°C. The results show a peculiar dependency of emission intensity as a function of temperature, wherein the emission intensity monotonically increases up to 200°C, followed by a pronounced roll‐off at higher temperatures. This is explained by a model that considers the reabsorption of emitted blue photons propagating along the optically thick Rubidium vapor. These results demonstrate a viable pathway for integrating nonlinear atomic vapor processes into chip‐scale quantum devices.
This work introduces an approach to generate coherent 420 nm (blue) light utilizing narrowband, CW pump beams at 795 nm, 532 nm and 1320 nm in a rubidium vapor cell. The frequencies giving the strongest signal intensity are found. The method is compared to other transition pathways that generate 420 nm light in rubidium vapor, namely using the 776 nm and 780 nm absorption lines. The approach discussed in this work has the potential to be used in a diagnostic measurement capability as a means to spectrally filter a component of a scattered signal.
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 μμμW 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.
This work experimentally demonstrates the conversion of coherent and incoherent green 532 nm light to collimated blue 420 nm light through resonant four-wave mixing in rubidium vapor. The 532 nm light co-propagates with 795 nm and 1320 nm CW pump beams, simultaneously taking advantage of resonances between the 5 P, 10 S, 6 P and 5 S ground states of rubidium. Using a coherent green beam, the intensity of the collimated 420 nm signal is characterized under varying polarizations, cell temperatures, frequency detunings and pump intensities. A 2 d image is up-converted from green to blue light to extend the technique to spatially incoherent light. This excitation pathway has the potential to be used as a narrow linewidth ( < 1 GHz), tunable bandpass filter for lidar or other remote sensing applications. • Narrow linewidth of 532 nm signal up-converted to blue light using four wave mixing. • Demonstration of image up-conversion using hot Rb vapor. • A third applied IR pump beam increases conversion efficiency.
Quantum light generated through spontaneous four-wave mixing (SFWM) process in nonlinear materials, such as entangled photon pairs and single photons, is an important resource for various emerging quantum applications. Integrated quantum photonics has enabled the generation, manipulation, and detection of quantum states of light with steadily increasing scale and complexity levels. Importantly, the exploration of on-chip integration has accumulated substantial progresses in recent years toward the realization of low-cost, large-scale quantum photonic circuits. Here, we review the underlying mechanism and discuss state-of-the-art SFWM on-chip quantum light sources fabricated with various structures and materials on chip. Furthermore, we enumerate the most appealing applications of on-chip SFWM such as heralding single-photon source, entangled photon source, and system-level integration.