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Optical Engineering

Extremely Low Switching Energy Optical Bistable Devices

M. Dagenais, Wayne F. Sharfin

Published Feb 1, 1986• 13 citations
Publisher

Abstract

An all-optical bistable device and an electro-optical bistable device, with performances approaching the fundamental statistical limits, are described. In the all-optical approach, the giant nonlinearities associated with bound excitons in CdS are exploited to demonstrate the lowest-switching-energy (< 4 pJ) all-optical bistable device. The device switches in less than 1 ns and fully recovers in less than 2 ns. These times are detector limited. A switching energy of less than 1 fJ is theoretically predicted for an optimized geometry. In the electro-optical approach, an InGaAsP/InP diode laser amplifier is used to demonstrate bistability with less than 6000 photons (< 8 X 10-16 J) incident on the device. The device switches in less than 1 ns and is cascadable since it has a gain of 100. It operates at room temperature and is compatible with diode laser sources.

DOI
10.1117/12.7973808

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Low-switching energy optical bistable devices

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We describe two approaches to low-energy switching and optical bistability. In one approach, which is a more fundamental approach, we use the nonlinearity associated with bound excitons in CdS to demonstrate the lowest total switching energy (4 pJ) of any optical device exhibiting two stable output states for the same input intensity.1 Bound excitons were chosen because they are known to have a very large oscillator strength (f = 7), a fast radiative decay (tspont = 500 ps), and they do not diffuse in the crystal, thus permitting a sharp focusing geometry. Furthermore, they are a good approximation to quantum dots. In a different experiment we have operated a standard diode laser structure below threshold and have demonstrated an efficient optical switch that can be used in thresholding and decision-making applications. The device switches with <400 aJ (4 × 10−16 J or <3000 photons) of optical energy incident on the device.2 During the switching operation, only 10 pJ of electrical power is dissipated. The switch operates at room temperature, is compatible with optical communication systems, and has a gain of the order of 15 dB, leading to the important properties of cascadability and large fan-out. The operation of a high contrast (5:1) AND gate was demonstrated.

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Fast All-Optical Switching at Extremely Low-Switching Energy in CdS Platelets

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Using a laser slightly detuned from the I2 bound exciton resonance in CdS, we report the observation of the lowest switching energy (< 4 pJ) for an all-optical bistable device. The deconvoluted switching-on and -off times are evaluated to be less than 1 and 2 ns respectively. Even shorter switching times are expected, and we are presently improving our time resolution. Forward, degenerate four-wave mixing experiments were also performed near the I2 bound exciton, an exciton bound to a neutral donor. A four-wave mixing signal was observed with less than 50 W/cm2 incident on the sample.

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Demonstration Of Cascadability And Spectral Bistability In Bistable Diode Laser Amplifiers

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We report the demonstration of cascadability in bistable diode laser amplifiers operated below threshold. A schematic of the experimental set-up is shown in Figure 1. There it is shown that the optical input to the first bistable diode laser amplifier is modulated by a mechanical chopper at frequency Ω1. The output from the first bistable diode laser amplifier is then modulated at Ω2= 2Ω1using a second mechanical chopper. The light is thereafter used as the input to the second bistable device. When the input intensity to the second device is higher than a certain threshold, the output switches. These results are shown in Figure 2. For these experiments, each of the bistable diode laser amplifiers were carefully studied. Detailed bistability measurements at different bias currents and different cavity detuning's were performed. It was found that both the bistability loop and the switching power gets larger as the detuning increases. The size of the hysteresis loop also increased as the laser was operated closer to threshold. In a two beam experiment, it was found that the switching power in the data beam can be as small as 25 nW. Gains larger than 1000 have been demonstrated, indicating the large fan-out capability of these devices. The turn-on and turn-off times in these bistable diode laser amplifiers was measured to be faster than 1 ns and detector limited. These bistable diode laser amplifiers are the most efficient optical devices that have yet been demonstrated and will find applications in photonic switching networks.

Digest on Nonlinear Optics: Materials, Phenomena and Devices•Jan 1, 1990•0 citations
An all-optical bistable device and an electro-optical bistable device, with performances approaching the fundamental statistical limits, are described. In the all-optical approach, the giant nonlinearities associated with bound excitons in CdS are exploited to demonstrate the lowest-switching-energy (< 4 pJ) all-optical bistable device. The device switches in less than 1 ns and fully recovers in less than 2 ns. These times are detector limited. A switching energy of less than 1 fJ is theoretically predicted for an optimized geometry. In the electro-optical approach, an InGaAsP/InP diode laser amplifier is used to demonstrate bistability with less than 6000 photons (< 8 X 10-16 J) incident on the device. The device switches in less than 1 ns and is cascadable since it has a gain of 100. It operates at room temperature and is compatible with diode laser sources.
We describe two approaches to low-energy switching and optical bistability. In one approach, which is a more fundamental approach, we use the nonlinearity associated with bound excitons in CdS to demonstrate the lowest total switching energy (4 pJ) of any optical device exhibiting two stable output states for the same input intensity.1 Bound excitons were chosen because they are known to have a very large oscillator strength (f = 7), a fast radiative decay (tspont = 500 ps), and they do not diffuse in the crystal, thus permitting a sharp focusing geometry. Furthermore, they are a good approximation to quantum dots. In a different experiment we have operated a standard diode laser structure below threshold and have demonstrated an efficient optical switch that can be used in thresholding and decision-making applications. The device switches with <400 aJ (4 × 10−16 J or <3000 photons) of optical energy incident on the device.2 During the switching operation, only 10 pJ of electrical power is dissipated. The switch operates at room temperature, is compatible with optical communication systems, and has a gain of the order of 15 dB, leading to the important properties of cascadability and large fan-out. The operation of a high contrast (5:1) AND gate was demonstrated.
A general discussion of the linear-optical properties of free and bound excitons in direct-gap semiconductors at low temperature is presented. This discussion then specializes to CdS. The nonlinear-optical response of CdS is introduced by first discussing the saturation behavior of bound excitons. A new type of cavityless optical bistability based on induced absorption near the free and bound excitons is described. Finally, fast all-optical switching (<1 nsec) at very low switching energies (<8 pJ) is demonstrated, using the giant nonlinearity associated with bound excitons.
Using a laser slightly detuned from the I2 bound exciton resonance in CdS, we report the observation of the lowest switching energy (< 4 pJ) for an all-optical bistable device. The deconvoluted switching-on and -off times are evaluated to be less than 1 and 2 ns respectively. Even shorter switching times are expected, and we are presently improving our time resolution. Forward, degenerate four-wave mixing experiments were also performed near the I2 bound exciton, an exciton bound to a neutral donor. A four-wave mixing signal was observed with less than 50 W/cm2 incident on the sample.
We report the demonstration of cascadability in bistable diode laser amplifiers operated below threshold. A schematic of the experimental set-up is shown in Figure 1. There it is shown that the optical input to the first bistable diode laser amplifier is modulated by a mechanical chopper at frequency Ω1. The output from the first bistable diode laser amplifier is then modulated at Ω2= 2Ω1using a second mechanical chopper. The light is thereafter used as the input to the second bistable device. When the input intensity to the second device is higher than a certain threshold, the output switches. These results are shown in Figure 2. For these experiments, each of the bistable diode laser amplifiers were carefully studied. Detailed bistability measurements at different bias currents and different cavity detuning's were performed. It was found that both the bistability loop and the switching power gets larger as the detuning increases. The size of the hysteresis loop also increased as the laser was operated closer to threshold. In a two beam experiment, it was found that the switching power in the data beam can be as small as 25 nW. Gains larger than 1000 have been demonstrated, indicating the large fan-out capability of these devices. The turn-on and turn-off times in these bistable diode laser amplifiers was measured to be faster than 1 ns and detector limited. These bistable diode laser amplifiers are the most efficient optical devices that have yet been demonstrated and will find applications in photonic switching networks.