Chiral light–matter interactions in hot vapor-cladded waveguides

Abstract

Recently, there has been growing interest in integrating alkali vapors with nanoscale photonic structures, such as nanowaveguides, resonators, and nanoantennas. Nanoscale confinement of electromagnetic fields may introduce a longitudinal electric field component, giving rise to circularly polarized modes that are essential for diverse applications involving vapor and light, such as chirality and nonreciprocity. Hereby, we have designed, fabricated, and characterized a miniaturized vapor cell that is integrated with optical waveguides that are designed to generate a peculiar circular-like polarization. Taking advantage of this phenomenon, we demonstrate a spectral shift in the atomic absorption signatures at varying magnetic fields, and significant isolation between forward-and backward-propagating waves in our atomiccladded waveguide. Our results pave the way for the utilization of chip-scale integrated atomic devices in applications such as optical isolation and high spatial resolution magnetometry.Alkali vapors such as rubidium are being used in various research fields such as quantum information [1-3], nonlinear optics [4-6], magnetometry [7][8][9], and atomic clocks [10,11]. In the last few years, there has been a growing interest in miniaturizing rubidium cells from centimeter scale to micro-and nanoscale. On top of the obvious advantages of such integration in reducing footprint and cost, many other great qualities result from such an approach. For example, the high confinement allows one to observe significant nonlinear effects under very low optical power levels (nanowatts) [12][13][14][15]. Several miniaturized rubidium systems have been demonstrated over the last few years, e.g., the atomic-cladded waveguide (ACWG) [15,16], hollow core waveguide [17] and coupled atomic-plasmonic systems [14,18]. The combination of strong nonlinear effects and high confinement pave the way for applications such as few-photons communication systems by alloptical switching [15].Rubidium is a highly dichroic medium due to its strong Zeeman effect, and thus has been used to realize a variety of polarization-selective and unidirectional devices such as optical isolators [19]. Basically, the Zeeman effect generates circular dichroism, i.e., two orthogonal circular polarizations are experiencing a large difference in their absorption spectrum. This effect has also been used for applications such as frequency stabilization [20], memories [2], and magnetometers [7][8][9]. While a rectangular waveguide supports quasi-linear polarized modes, it has been shown in systems combining waveguides and cold atoms that a strong longitudinal electric field is generated due to the strong field confinement. Thus, one can define the quantization axis by applying a magnetic field perpendicular to the propagation direction such that an atom will experience circular polarization interrogation [3]. The absorption lines of such an atom could be controlled by the strength of the magnetic field. This effect has been used for fabricating single-photon ...

Demonstration of an integrated nanophotonic chip-scale alkali vapor magnetometer using inverse design

“…The graph also presents the theoretical curves obtained by solving the optical Bloch equations. The difference in the observed spectrum for each circular polarization is expected due to the different coefficient strengths for each transition 12 , 30 .

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“…This extreme confinement allows observation of significant nonlinear effects at very low optical powers (nanowatts), paving the way for applications like few-photon communication systems based on all-optical switching 8 . Another example showing the advantages provided by integrated systems is the recent demonstration of an efficient optical isolator based on transverse photon spin and linear momentum locking of the evanescent field interacting with rubidium (Rb) vapor 12 .…”

Noiseless photonic non-reciprocity via optically-induced magnetization

“…The demonstrated noiseless non-reciprocity only requires an atomic ensemble with the degenerate Zeeman energy levels, thus the mechanism is applicable to many atoms or atom-like emitters, including hot and cold atoms, molecules, as well as emitters in solids (such as NV centers and rare-earth atoms). There are several potential approaches to integrate these emitters with the waveguides, including the fabrication of hot-atom-cladding waveguide by bonding atomic vapor cell to photonic integrated circuits 37 – 40 , trapping cold atoms in the evanescent field of the waveguide 41 , 42 , transferring molecules and nanocrystals on the surface of waveguides 43 , 44 , as well as implanting and doping ions in the waveguide or the cladding layer 45 , 46 . However, the optical waveguide modes on photonic chips are distinct from the laser beam in free space, and the configuration in Fig.…”

“…1 could not be directly applied because the conventional circularly-polarized optical field is only applicable for integrated photonic waveguides with a circular cross-section. Luckily, there is a mechanism of optical spin-orbit coupling in photonic waveguides 33 , 47 , 48 , which enables the realization of the OIM by harnessing transverse circularly-polarized optical fields that are perpendicular to the light propagation direction 40 . For instance, the field distributions of co-propagating drive and signal lasers in fundamental mode are almost the same, thus each individual atom couples with σ + -polarized (or σ − -polarized, the polarization is spatially dependent 33 , 47 , 48 ) field of both drive and signal lights simultaneously, then realizing the circular birefringence and dichroism in Fig.…”

Photonic bands, superchirality, and inverse design of a chiral minimal metasurface

“…To date, the most common technique to prepare and analyze chiral light is to employ birefringent plates and linear polarizers that convert light to and from linear polarization, as the technology of direct sources and detectors of chiral light is still in its infancy [2][3][4][5]. Last advances in nanotechnology are however revolutionizing chiral optical devices [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Far-and near-field chiral electromagnetic responses have been indeed observed in a variety of artificially structured systems, where the shape of the machined elements must have a three-dimensional character if geometric and electromagnetic chirality has to be attained in its most rigorous form, because of the requirement of the absence of any mirror symmetry plane [22][23][24].…”