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IEEE Journal of Quantum Electronics

Tunable optical bistability of bichromatic fields interacting with four-level systems

D. Kagan, Harry Friedmann

Published Jun 1, 1989• 3 citations
Publisher

Abstract

A simple four-level model is used to describe two-band systems such as dyes and semiconductors. The system is irradiated by a bichromatic input in an optical cavity and both fields exhibit optical multistability. The calculations take into account the possibility of noncoherent (electrical) pumping of the system, thus generalizing the model to include semiconductor laser amplifiers. Since both fields are allowed to resonate in the cavity, a low-intensity control beam and/or the noncoherent pumping intensity can 'tune' and adapt the response of the second input. Some applications of this tunability are outlined.>

DOI
10.1109/3.29245

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Journal of the Optical Society of America B•Feb 15, 2013•45 citations
A simple four-level model is used to describe two-band systems such as dyes and semiconductors. The system is irradiated by a bichromatic input in an optical cavity and both fields exhibit optical multistability. The calculations take into account the possibility of noncoherent (electrical) pumping of the system, thus generalizing the model to include semiconductor laser amplifiers. Since both fields are allowed to resonate in the cavity, a low-intensity control beam and/or the noncoherent pumping intensity can 'tune' and adapt the response of the second input. Some applications of this tunability are outlined.>
We have studied the case of optical multistability in a four-level system interacting with two coherent fields. The system, shown in fig. 1, consists of two pairs of energy levels, 1, 2, and 3, 4, absorption occurs between levels 1- 4 and emission takes place from 3-2. The 'intra-band' transitions, 4-3 and 2- 1 are assumed non-radiative and extremely fast. The system is irradiated by two beams, one tuned to the absorption spectrum, the other to the emission spectrum, in a Fabry-Perot cavity. Solution of the optical Bloch equations following [1] enables us to write the input-output equations, la and lb, in the form where Yi, Xi, are the appropriately scaled input and output fields, Ci the 'bistability' parameter, and Δi, ϕi, the atomic and cavity detuning respectively, of field i.
During the last few years we have suggested1−2 the use of a four-level system irradiated by a bichromatic beam to obtain a tunable optical bistable device. By tunable we mean that the switching threshold can be altered without changing the hardware characteristics, the operating temperature, or the frequencies of the inputs to the device. The basic principle of our suggestion is that by irradiating the non-linear optical material by two beams of appropriately chosen frequencies in an optical cavity, one can act as a signal and the other as tuning control beam. The advantage of the four level system lay in the possibility of using low power control beams which could tune the characteristic optically bistable output curves.
The optical behavior of a four-level system in a ring cavity driven by two coherent laser fields is studied. One laser field is treated as the incident field and the other the control field, respectively. It is found that there is optical transparency when the difference between the two frequency detunings of the incident and control fields from the corresponding atomic transition frequencies is zero. Optical bistability can be produced and controlled by increasing the magnitude of the frequency difference. The bistable hysteresis becomes larger when the frequency difference is increased. Further increase of the latter can lead to onset of multistability.
The optical properties of a four-level atomic system via coherent and incoherent pumping fields are investigated. The giant Kerr nonlinearity with reduced linear and nonlinear absorption, which has a major role in decreasing the threshold of optical bistability (OB), can be obtained with subluminal light propagation via adjusting the intensities of coupling fields. An incoherent pumping field is noticed to be an extra parameter to reduce the threshold of OB and multistability, and it can be used as an effective parameter in producing lasing with or without population inversion. In this model, optical multistability is achieved simply by tuning the intensity of coupling laser fields. Furthermore, it is shown that the subluminal and the superluminal light propagation can be obtained by appropriate values of the incoherent pumping rate.