All-optical information conversion, conveying optical signals without electro-optical transformation, plays a vital role in the all-optical devices and optical communication. We achieve the all-optical information conversion in Rb vapor by utilizing the spatial cross-phase modulation. The refractive index of atomic medium is spatially modulated by the strong switch laser beam, which makes it as a nonlinear focusing lens for the weak signal laser beam. As a result, the far-field diffraction ring patterns of the signal laser beam interacted with atoms can effectively carry the nonlinear phase shift information of the switch laser beam. The channel numbers, channel capacities and channel storage densities of information transmission from switch laser beam to signal laser beam are investigated in the terms of switch laser intensity and vapor temperature. Finally, a special "sxu" alphabetic string, encoded by ASCII code, is introduced to verify this all-optical information conversion scheme. This work paves the way for studying optical information processing and all-optical networking with atomic ensembles.
All-optical information conversion, conveying optical signals without electro-optical transformation, plays a vital role in the all-optical devices and optical communication. We achieve the all-optical information conversion in Rb vapor by utilizing the spatial cross-phase modulation. The refractive index of atomic medium is spatially modulated by the strong switch laser beam, which makes it as a nonlinear focusing lens for the weak signal laser beam. As a result, the far-field diffraction ring patterns of the signal laser beam interacted with atoms can effectively carry the nonlinear phase shift information of the switch laser beam. The channel numbers, channel capacities and channel storage densities of information transmission from switch laser beam to signal laser beam are investigated in the terms of switch laser intensity and vapor temperature. Finally, a special "sxu" alphabetic string, encoded by ASCII code, is introduced to verify this all-optical information conversion scheme. This work paves the way for studying optical information processing and all-optical networking with atomic ensembles.
All-optical devices used to process optical signals without electro-optical conversion plays a vital role in the next generation of optical information processing systems. We demonstrate an efficient all-optical modulator that utilizes a periodic dielectric atomic lattice produced in a gas of 85 Rb vapor. Four orders of diffraction patterns are observed when a probe laser is passed through the lattice. The frequency shift of the peak of each diffraction order can be tuned by adjusting the control laser power and two-photon detuning, enabling this device to be used as a multi-channel all-optical modulator. Both theoretical simulations and experimental results demonstrate that this modulator can operate over a frequency band extending from about 0 to 60 MHz. This work may pave the way for studying quantum information processing and quantum networking proposed in atomic ensembles.
High-dimensional all-optical information transfer facilitates large-capacity, high-speed, and energy-efficient optical communication, playing a pivotal role in advancing modern photonic technologies. Here, we demonstrate the all-optical transfer of structured information between two beams with different frequencies via spatial cross-phase modulation in a hot 85Rb vapor. A high-power pump beam, characterized by a structured light, induces a refractive index change in the rubidium vapor. A low-power, initially Gaussian probe beam counter-propagates through the rubidium vapor cell, undergoing a nonlinear phase shift induced by the pump beam. This enables the transfer of the spatial characteristics imprinted by the pump beam onto the probe beam with maximum structural integrity and similarity. The spatial evolution of the transverse intensity of the probe beam vs frequency detunings of the pump and probe beams, pump beam power, and cell temperature is studied. We have further shown that the structural similarity can be manipulated by changing the pump beam power and temperature of the vapor cell. Our findings may reveal a way to manipulate light fields, offering potential applications in optical communication, all-optical data processing, and advanced photonic devices.
Nonlinear atomic media are promising substitutes for spatial light modulators (SLMs) owing to the high tunability and fast response. We demonstrate the generation of high-order Bessel-like beam based on cross-phase modulation in 85 Rb atoms. The atomic medium, whose refractive index is spatially modulated by the focused Gaussian pump beam, acts as a nonlinear focusing lens for the Laguerre-Gaussian probe beam. As a result, the probe beam carries the nonlinear phase shift and is converted into a Bessel-like mode in far-field diffraction. The superior self-healing ability of the generated high-order Bessel-like beam is verified by inserting an obstruction in the beam path, and its high tunability is investigated in terms of the pump beam power and vapor temperature. Furthermore, this novel beam is used in an obstruction-immune rotation sensor to measure the angular velocity. Nonlinear atomic medium as a novel SLM promises considerable application prospects in modulating the light field structure.
Optical vortex orbital angular momentum modes, namely the twists number of the light does in one wavelength, play a critical role in quantum-information coding, super-resolution imaging, and high-precision optical measurement. Here, we present the identification of the orbital angular momentum modes based on spatial self-phase modulation in rubidium atomic vapor. The refractive index of atomic medium is spatially modulated by the focused vortex laser beam, and the resulted nonlinear phase shift of beam directly related to the orbital angular momentum modes. The output diffraction pattern carries clearly distinguishable tails, whose number and rotation direction correspond to the magnitude and sign of the input beam orbital angular momentum, respectively. Furthermore, the visualization degree of orbital angular momentums identification is adjusted on-demand in the terms of incident power and frequency detuning. These results show that the spatial self-phase modulation of atomic vapor can provide a feasible and effective way to rapidly readout the orbital angular momentum modes of vortex beam.
We report a tunable ring-shaped diffraction pattern via either nonlinear spatial self- or cross-phase modulation caused by the EIT-like effect in rubidium atomic vapor. During the propagation of an input Gaussian-profile beam, its output wavefront exhibits a ring-shaped diffraction pattern. Furthermore, the spot center can be tuned from dark to bright by varying individual experimental parameters, such as power, frequency detuning, the polarization state of the incident beams and atomic temperature, which makes the nonlinear phase shift evolve beyond 2π. In particular, the input intensity can be as low as 500 W m-2.
All-optical devices allow improvements in the speed of optical communication and computation systems by avoiding the conversion between the optical and electronic domains. The focus of this thesis is the experimental investigation of a new type of all-optical switch that is based on the control of optical patterns formed by nonlinear interactions between light and matter.\nThe all-optical switch consists of a pair of light beams that counterpropagate through warm rubidium vapor. These beams induce a nonlinear optical instability that gives rise to mirrorless parametric self-oscillation and generates light in the state of polarization that is orthogonal to that of the pump beams. In the far-field, the generated light forms patterns consisting of two or more spots. To characterize this instability, I observe experimentally the amount of generated power and the properties of the generated patterns as a function of pump beam intensity, frequency, and size. Near an atomic resonance, the instability has a very low threshold: with less than 1 mW of total pump power, >3 μW of power is generated.\nTo apply this system to all-optical switching, I observe that the orientation of the generated patterns can be controlled by introducing a symmetry-breaking perturbation to the system. A perturbation in the form of a weak switch beam injected into the nonlinear medium is suitable for controlling the orientation of the generated patterns. The device operates as a switch where each state of the pattern orientation corresponds to a state of the switch, and spatial filtering of the generated pattern defines the output ports of the device. Measurements of the switch response show that it can be actuated by as few as 600 ±40 photons. For a switch beam with 1/e field radius w0 = 185 ± 5μm, 600 ±40 photons correspond to an energy density of 5.4±0.7×10−4 photons/λ2/(2π) which is comparable to the best reported results from all-optical switches. The approach to all-optical switching I report here operates at very low light levels and exhibits cascadability and transistor-like response. Furthermore, the sensitivity is comparable to switches using cold-atom electromagnetically-induced transparency or cavity quantum-electrodynamics techniques, but is achieved with a simpler system, requiring only one optical frequency and occurring in warm atomic vapor.\nI develop a numerical model for the switch that exhibits patterns that rotate in the presence of a weak applied optical field. Results from this model, and from my experiment, show that the switch response time increases as the input power decreases. I propose that this increase is due to critical slowing down. Mapping the pattern orientation to a simple one-dimensional system shows that critical slowing down may account for the observed increase in response time at low input power. The ultimate performance of the device is likely limited by critical slowing down and I conclude that the minimum number of photons capable of actuating the switch is between 400 and 600 photons.\nMy approach to all-optical switching is simple, extremely sensitive and exhibits many of the properties necessary for use as an optical logic element. Additionally, this work has implications for a wide range of pattern forming systems, both in the field of optics and beyond, that may be applicable as novel devices for sensitive measurement and detection.