Reverse saturable absorption (RSA) occurs in nonlinear materials where the excited state exhibits higher absorption than the ground state. This study presents a full-wave spatio-temporal numerical model that accurately simulates coherent RSA by coupling quantum systems with Maxwell’s equations. The model enables the design of complex photonic metamaterials and metasurfaces beyond the capabilities of conventional absorption models. To demonstrate its effectiveness, we analyze a metasurface-enhanced optical absorber, achieving over twice the absorption enhancement compare to the bare layer. This approach paves the way for highly efficient low-power optical absorption devices, with applications in protective optics and photonic elements.
Reverse saturable absorption (RSA) occurs in nonlinear materials where the excited state exhibits higher absorption than the ground state. This study presents a full-wave spatio-temporal numerical model that accurately simulates coherent RSA by coupling quantum systems with Maxwell’s equations. The model enables the design of complex photonic metamaterials and metasurfaces beyond the capabilities of conventional absorption models. To demonstrate its effectiveness, we analyze a metasurface-enhanced optical absorber, achieving over twice the absorption enhancement compare to the bare layer. This approach paves the way for highly efficient low-power optical absorption devices, with applications in protective optics and photonic elements.
Abstract Nonlinear optics plays a crucial role in science and technology, with applications ranging from spectroscopy to quantum information processing. Therefore, precise estimation of their nonlinear optical parameters is of fundamental importance. Here, we investigate quantum-enhanced sensitivity in the estimation of nonlinear absorption parameters, including saturable absorption (SA) and reverse saturable absorption (RSA). By employing the quantum Fisher information, we quantify the enhancement in sensitivity for estimating transmission ( T ), linear absorption coefficient ( α0 ), saturable intensity ( Is ), and two-photon absorption coefficient ( β ) using bright two-mode squeezed states (bTMSS) and applied it to analyze the nonlinear parameters of Pt nanoparticle samples as an example. In addition, we propose an experimental scheme based on an open-aperture Z-scan with bTMSS to realize quantum-enhanced sensitivity. Our findings establish a pathway toward quantum-enhanced estimation of nonlinear optical parameters.
Multiple photon absorption processes typically have a nonlinear dependence on the amplitude of the incident optical field. On the other hand, quantum technologies rely on single photon events. It has therefore been of great technical difficulty to achieve nonlinear devices using single photons. This is due to the small cross-section of absorption in room temperature devices, with multi-photon absorption events occurring with extremely low probability. The lack of access to nonlinear processes severely inhibits the use of optics for a large number of applications surrounding quantum technologies. We demonstrate experimentally that by exploiting a coherent absorption mechanism for N=2 N00N states, outlined theoretically by Jeffers in 2000 [1] and experimentally explored by Roger et. al. in 2016 [2], that it is possible to determine and enhance the number of two photon states that are absorbed. Here a 50% absorbing metasurface is placed inside a Sagnac interferometer into which we inject a N00N state. We show that by tuning the phase φ of the input state, |2,0〉 + exp(-ί2φ) |0,2〉, we can selectively tune the output state. For an input phase of φ = π/2 or 3π/2 we find that a single photon is absorbed with 100% probability. However, when we tune the input phase to φ = 0 or π we see that either 0 or 2 photons are absorbed with equal probability. We have developed a theoretical model that, with no free parameters, fits the experimentally measured two-photon contribution and finds the maximum contribution of |0,0) (0,0| to the output state to be 40.5%.
The recent advent of optical metasurfaces, ultra-thin structures composed of nanoresonators facilitating strong light concentration [1–3], opens the path towards efficient \nfrequency conversion [4–7] in a material thousand times thinner than a human hair [8]. \nThere is a remarkable capacity to individually shape each nanoresonator of the metasurface to spatially and spectrally control the conversion process with unprecedented \nnanoscale resolution, facilitating an ultimate flexibility to selectively convert, focus, \nand image different colours with a single metasurface. The strong enhancement of the \nnonlinear processes in dielectric nanoresonators is largely due to the absence of material \nabsorption and the excitation of Mie-type bulk resonances [2]. The highest conversion \nefficiency to date has been achieved employing III-V semiconductor nanostructures, \nsuch as AlGaAs which is a non-centrosymmetric material with high quadratic nonlinear \nsusceptibility. In particular, second-harmonic generation efficiencies up to 10−4 have \nbeen recently demonstrated [8–12], six orders of magnitude higher than in plasmonics. \nSuch capabilities can make an immense fundamental and practical impact, including \nthe quantum state generation in nonlinear metasurfaces as we discuss in this chapter. \nThe quantum state of correlated photon-pairs is the essential building block for photon entanglement [13, 14], which underpins many quantum applications, including secure networks, enhanced measurement and lithography, and quantum information processing [15]. One of the most versatile techniques for the generation of correlated photons is the process of spontaneous parametric down-conversion (SPDC) [16, 17], see \nFig. 1. It allows for an arbitrary choice of energy and momentum correlations between \nthe generated photons, robust operation at room temperature, as well as for spatial and \ntemporal coherence between simultaneously pumped multiple SPDC sources. Alternative approaches based on atom-like single photon emitters, such as solid-state fluorescent atomic defects [18], quantum dots [19, 20], and 2D host materials [21, 22], have \nreached a high degree of frequency indistinguishability, purity and brightness [19, 20]. \nHowever, this comes with the expense of operation at cryogenic temperatures and lack \nof spatial coherence between multiple quantum emitters. These features might limit \npossible applications and reduce the potential for device scalability. Furthermore, the \nsmall size of the atomic sources often requires complex schemes aimed at coupling to \noptical nanoantennas and improving the photon extraction efficiency [21]. \nThe miniaturization of SPDC quantum-light sources to micro and nanoscale dimensions is a continuing quest, as it enables denser integration of functional quantum \ndevices. Traditionally, bulky cm-sized crystals were utilized for SPDC, entailing the \ndifficulty of aligning multiple optical elements after the SPDC crystal, while offering \nrelatively low photon-pair rates [17]. As a first step of miniaturization, SPDC was \nrealized in low-index-contrast waveguides, which allowed confining light down to several square micrometers transversely to the propagation direction, significantly enhancing the conversion efficiency [23]. However, this approach still requires centimetres \nof propagation length, which makes the on-chip integration with other elements challenging [24]. The introduction of high-index contrast waveguides and ring resonators \nallowed for shrinking the sizes necessary for SPDC to millimetres [25], and to tens \nof micrometers [26]. However, further miniaturisation down to the metasurfaces composed of nanoresonators requires conceptually different approaches.
From metamaterials to metasurfaces, optical nano-structure has been widely investigated for novel and high efficiency functionalities. Apart from the intrisinsic properties of composite material, rich capabilities can be derived from the judicious design of metasurfaces, which enable more excellent and highly integrated optical devices than traditional bulk optical elements. In the meantime, the abundant manipulation abilites of light in the classical domain can be carried over into quantum domain. In this review, we highlight recent development of quantum optics based on metasurfaces, ranging from quantum plasmonics, generation, manipulation and appplication of quantum light to quantum vaccum engineering etc. Finally, some promising avenues for quantum optics with the help of optical metasurface are presented.
Multiphoton absorption processes have a nonlinear dependence on the amplitude of the incident optical field, i.e., the number of photons. However, multiphoton absorption is generally weak and multiphoton events occur with extremely low probability. Consequently, it is extremely challenging to engineer quantum nonlinear devices that operate at the single photon level and the majority of quantum technologies have to rely on single photon interactions. Here we demonstrate experimentally and theoretically that exploiting coherent absorption of N=2 NOON states makes it possible to enhance the number of two-photon states that are absorbed by at most a factor of 2 with respect to a linear absorption process. An absorbing metasurface placed inside a Sagnac-style interferometer into which we inject an N=2 NOON state, exhibits two-photon absorption with 40.5 efficiency, close to the theoretical maximum. This high probability of simultaneous absorption of two photons holds the promise for applications in fields that require multiphoton upconversion but are hindered by high peak intensities.
Generation and control of the reverse saturable absorption (RSA) and optical limiting (OL) are investigated in a four-level Y-type quantum system. It is demonstrated that the applied laser fields induce the RSA and it can be coherently controlled by either intensity or frequency of the applied laser fields. The effect of the static magnetic field on the induced RSA is studied and we obtain that it has a constructive role in determining the intensity range in which the OL is established in the system. In addition, we find that the transmission of the suggested optical limiter can be decreased either by increasing the length of the medium or by getting the atomic system denser. Finally, the Z-scan technique is presented to confirm our theoretical results. The proposed scheme can be used in designing the coherent optical limiters with controllable threshold and intensity range of the OL.