We investigate an integrated optical chip immersed in atomic vapor providing several waveguide geometries for spectroscopy applications. The narrow-band transmission through a silicon nitride waveguide and interferometer is altered when the guided light is coupled to a vapor of rubidium atoms via the evanescent tail of the waveguide mode. We use grating couplers to couple between the waveguide mode and the radiating wave, which allow for addressing arbitrary coupling positions on the chip surface. The evanescent atom-light interaction can be numerically simulated and shows excellent agreement with our experimental data. This work demonstrates a next step towards miniaturization and integration of alkali atom spectroscopy and provides a platform for further fundamental studies of complex waveguide structures.
We investigate an integrated optical chip immersed in atomic vapor providing several waveguide geometries for spectroscopy applications. The narrow-band transmission through a silicon nitride waveguide and interferometer is altered when the guided light is coupled to a vapor of rubidium atoms via the evanescent tail of the waveguide mode. We use grating couplers to couple between the waveguide mode and the radiating wave, which allow for addressing arbitrary coupling positions on the chip surface. The evanescent atom-light interaction can be numerically simulated and shows excellent agreement with our experimental data. This work demonstrates a next step towards miniaturization and integration of alkali atom spectroscopy and provides a platform for further fundamental studies of complex waveguide structures.
We investigate an integrated optical chip immersed in atomic vapor providing several waveguide geometries for spectroscopy applications. The narrow-band transmission through a silicon nitride waveguide and interferometer is altered when the guided light is coupled to a vapor of rubidium atoms via the evanescent tail of the waveguide mode. We use grating couplers to couple between the waveguide mode and the radiating wave, which allow for addressing arbitrary coupling positions on the chip surface. The evanescent atom-light interaction can be numerically simulated and shows excellent agreement with our experimental data. This work demonstrates a next step towards miniaturization and integration of alkali atom spectroscopy and provides a platform for further fundamental studies of complex waveguide structures.
We study an integrated silicon photonic chip, composed of several sub-wavelength ridge waveguides, and immersed in a micro-cell with rubidium vapor. Employing two-photon excitation, including a telecom wavelength, we observe that the waveguide transmission spectrum gets modified when the photonic mode is coupled to rubidium atoms through its evanescent tail. Due to the enhanced electric field in the waveguide cladding, the atomic transition can be saturated at a photon number ≈80 times less than a free-propagating beam case. The non-linearity of the atom-clad Si-waveguide is about 4 orders of magnitude larger than the maximum achievable value in doped Si photonics. The measured spectra corroborate well with a generalized effective susceptibility model that includes the Casimir-Polder potentials, due to the dielectric surface, and the transient interaction between flying atoms and the evanescent waveguide mode. This work paves the way towards a miniaturized, low-power, and integrated hybrid atomic-photonic system compatible with CMOS technologies.
Devices based on spectroscopy of atomic vapors can measure physical quantities such as magnetic fields, RF electric fields, time and length, and rotation and have applications in a broad range of fields including communications, medicine, and navigation. We present a type of photonic device that interfaces single-mode silicon nitride optical waveguides with warm atomic vapors, enabling precision spectroscopy in an extremely compact (<1 cm3) package. We perform precision spectroscopy of rubidium confined in a micro-machined, 27 mm3 volume, vapor cell using a collimated free-space 120 μm diameter laser beam derived directly from a single-mode silicon nitride waveguide. With this optical-fiber integrated photonic spectrometer, we demonstrate an optical frequency reference at 780 nm with a stability of 10−11 from 1 to 104 s. This device harnesses the benefits of both photonic integration and precision spectroscopy for the next generation of quantum sensors and devices based on atomic vapors.
Alkali vapours, such as rubidium, are being used extensively in several important fields of research such as slow and stored light nonlinear optics quantum computation, atomic clocks and magnetometers. Recently, there is a growing effort towards miniaturizing traditional centimetre-size vapour cells. Owing to the significant reduction in device dimensions, light–matter interactions are greatly enhanced, enabling new functionalities due to the low power threshold needed for nonlinear interactions. Here, taking advantage of the mature platform of silicon photonics, we construct an efficient and flexible platform for tailored light–vapour interactions on a chip. Specifically, we demonstrate light–matter interactions in an atomic cladding waveguide, consisting of a silicon nitride nano-waveguide core with a rubidium vapour cladding. We observe the efficient interaction of the electromagnetic guided mode with the rubidium cladding and show that due to the high confinement of the optical mode, the rubidium absorption saturates at powers in the nanowatt regime. Alkali vapours are increasingly useful in photonic research and metrology applications, and they provide a useful test bed for investigating light–matter interaction. Stern et al. integrate silicon nitride waveguides with alkali vapours to study light–matter interactions on a chip-scale platform.
Atomic spectroscopy relies on photons to probe the energy states of atoms, typically in a gas state. In addition to providing fundamental scientific information, this technique can be applied to a number of photonic devices including atomic clocks, laser stabilization references, slow light elements, and eventually quantum communications components. Atomic spectroscopy has classically been done using bulk optics and evacuated transparent vapor cells. Recently, a number of methods have been introduced to dramatically decrease the size of atomic spectroscopy systems by integrating optical functionality. We review three of these techniques including: 1) photonic crystal fiber based experiments, 2) wafer bonded mini-cells containing atomic vapors and integrated with lasers and detectors, and 3) hollow waveguides containing atomic vapors fabricated on silicon substrates. In the context of silicon photonics, we will emphasize the hollow waveguide platform. At the heart of these devices is the anti-resonant reflecting optical waveguide (ARROW). ARROW fabrication techniques will be described for both hollow and solid core designs. Solid-core waveguides are necessary to direct light on and off the silicon chip while confining atomic vapors to hollow-core waveguides. We will also discuss the methods and challenges of attaching rubidium vapor reservoirs to the chip. Experimental results for optical spectroscopy of rubidium atoms on a chip will be presented.
We demonstrate chip-scale sub-Doppler spectroscopy in an integrated and fiber-coupled photonic-metasurface device. The device is a stack of three planar components: a photonic mode expanding grating emitter circuit with a monolithically integrated tilt-compensating dielectric metasurface, a microfabricated atomic vapor cell, and a mirror. The metasurface photonic circuit efficiently emits a 130 μm wide (1/e2 diameter) collimated surface-normal beam with only −6.3 dB loss and couples the reflected beam back into the waveguide and connecting fiber, requiring no alignment between the stacked components. We develop a simple model based on light propagation through the photonic device to interpret the atomic spectroscopy signals and explain spectral features covering the full Rb hyperfine state manifold. The demonstration of waveguide-to-waveguide coupling through the vapor cell paves the way for atomic ensembles to be used as components in complex photonic integrated circuits, allowing the unique properties of atomic systems to be available for future highly miniaturized optical devices and systems.