We report on an all-optical switch that operates at low light levels. It consists of laser beams counterpropagating through a warm rubidium vapor that induce an off-axis optical pattern. A switching laser beam causes this pattern to rotate even when the power in the switching beam is much lower than the power in the pattern. The observed switching energy density is very low, suggesting that the switch might operate at the single-photon level with system optimization. This approach opens the possibility of realizing a single-photon switch for quantum information networks and for improving transparent optical telecommunication networks.
We report on an all-optical switch that operates at low light levels. It consists of laser beams counterpropagating through a warm rubidium vapor that induce an off-axis optical pattern. A switching laser beam causes this pattern to rotate even when the power in the switching beam is much lower than the power in the pattern. The observed switching energy density is very low, suggesting that the switch might operate at the single-photon level with system optimization. This approach opens the possibility of realizing a single-photon switch for quantum information networks and for improving transparent optical telecommunication networks.
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.
We demonstrate an all-optical switch that operates at ultra-low-light levels and exhibits several features necessary for use in optical switching networks. An input switching beam, wavelength $\ensuremath{\lambda}$, with an energy density of ${10}^{\ensuremath{-}2}$ photons per optical cross section $[\ensuremath{\sigma}={\ensuremath{\lambda}}^{2}∕(2\ensuremath{\pi})]$ changes the orientation of a two-spot pattern generated via parametric instability in warm rubidium vapor. The instability is induced with less than 1mW of total pump power and generates several $\ensuremath{\mu}\mathrm{Ws}$ of output light. The switch is cascadable: the device output is capable of driving multiple inputs, and exhibits transistor-like signal-level restoration with both saturated and intermediate response regimes. Additionally, the system requires an input power proportional to the inverse of the response time, which suggests thermal dissipation does not necessarily limit the practicality of optical logic devices.
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.\n\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~muW of power is generated.\n\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~photons. For a switch beam with 1/e field radius w0=185,mum, 600 photons correspond to 5.4times10−4 photons/\\lambdasquared which is comparable to the best reported results from all-optical switches based on electromagnetically-induced transparentcy (EIT). This approach to all-optical switching operates at very low light levels and exhibits cascadability and transistorlike response. Furthermore, the sensitivity is comparable to switches using cold-atom EIT or cavity quantum-electrodynamics techniques but is achieved with a simpler system, requiring only one optical frequency and occurring in warm atomic vapor.\n\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 (CSD). Mapping the pattern orientation to a simple one-dimensional system shows that CSD can account for the observed increase in response time at low input power. The ultimate performance of the device is likely limited by CSD and I conclude that the minimum number of photons capable of actuating the switch is between 400 and 600 photons.
Abstract We review recent theoretical and experimental efforts toward developing an all‐optical switch based on transverse optical patterns. Transverse optical patterns are formed when counterpropagating laser beams interact with a nonlinear medium. A perturbation, in the form of a weak switch beam injected into the nonlinear medium, controls the orientation of the generated patterns. Each state of the pattern orientation is associated with a state of the switch. That is, information is stored in the orientation state. A realization of this switch using a warm rubidium vapor shows that it can be actuated by as few as 600 ± 40 photons with a response time of 5 µs. Models of nonlinear optical interactions in semiconductor quantum wells and microresonators suggest these systems are also suitable for use as fast all‐optical switches using this same conceptual design, albeit at higher switching powers.
We report an experimental demonstration of single-photon switching in laser-cooled 87Rb atoms. A resonant probe pulse with an energy per unit area of one photon per λ2/2π propagates through the optically thick atoms. Its energy transmittance is greater than 63% or loss is less than e−1 due to the effect of electromagnetically induced transparency. In the presence of a switching pulse with an energy per unit area of 1.4 photons per λ2/2π, the energy transmittance of the same probe pulse becomes less than 37% or e−1. This substantial reduction of the probe transmittance caused by single switching photons has potential applications in single-photon-level nonlinear optics and the manipulation of quantum information.
We investigated the optical transverse pattern produced by counterpropagating two waves through a rubidium vapor cell in presence of a longitudinal magnetic field. A bistable behavior is observed. The optical switching process between two of these patterns is carried out using three different mechanisms: mechanical closing of a pump beam, modulation of a pump beam intensity and modulation of additional beam intensity. A rapid switching of less than 10 μs between patterns can be carried out with a 2 μw power beam.