This paper presents a review of the various applications of feedback in optical systems. There are two general areas, optical image processing and bistability. In optical image processing both coherent (optical spatial feedback network internal to an optical resonator) and hybrid (TV) systems are discussed. In the area of bistability there are molecular systems (atoms in an optical resonator), both absorptive and dispersive; hybrid (employing electronic feedback) single-beam and many-element (TV and spatial light modulator-based) systems. All the systems are discussed. A detailed model showing the many facets of molecular bistability is presented along with a discussion of catastrophe theory applied to optical bistability.
This paper presents a review of the various applications of feedback in optical systems. There are two general areas, optical image processing and bistability. In optical image processing both coherent (optical spatial feedback network internal to an optical resonator) and hybrid (TV) systems are discussed. In the area of bistability there are molecular systems (atoms in an optical resonator), both absorptive and dispersive; hybrid (employing electronic feedback) single-beam and many-element (TV and spatial light modulator-based) systems. All the systems are discussed. A detailed model showing the many facets of molecular bistability is presented along with a discussion of catastrophe theory applied to optical bistability.
The nonlinear phenomenon known as optical bistability, which enables optical systems to maintain two stable output states for a single input, is thoroughly examined in this review article. Through a detailed analysis of two important devices—the Simple Fiber Ring (SFR) resonator and the Nonlinear Optical Loop Mirror (NOLM)—it investigates the basic concepts of optical bistability, namely nonlinearity and feedback. Numerical simulations demonstrating dynamic dynamics and stability conditions bolster a strong theoretical framework. Recent advancements in bistable optical technologies, including developments in epsilon-near-zero materials, silicon photonics, hybrid plasmonic structures, neuromorphic photonics, and AI-driven photonic processors are also discussed. Furthermore, this review highlights emerging applications of optical bistability in optical logic circuits, high-speed communication, and quantum information processing. This review work is a useful tool for researchers and engineers creating next-generation optical systems because it connects theoretical insights with cutting-edge technological developments.
In the last chapter, we examined the effect of cubic nonlinearity on selfrefraction of an optical beam. We have also seen that the presence of a quadratic nonlinearity can also contribute to change in the profile of a Gaussian beam in a crystal. In this chapter we will see how the effect of nonlinearity, alongwith the proper feedback, can give rise to optical bistability and hysteresis. This is not unexpected as hysteresis and bistability are also observed in nonlinear electronic circuits with feedback, such as in the Schmitt trigger, as well as in hybrid optical devices, such as an acoustooptic device with feedback (Banerjee and Poon, 1991). In what follows, we will examine two different types of optically bistable devices based on optical nonlinearities. The first is a nonlinear ring resonator comprising a two-level gain medium as the nonlinear element. We will treat both absorptive and dispersive bistability. Absorptive bistability is the case when the incident optical frequency is close to or equal to the transition frequency of the atoms from one level to another. In this case, the absorption coefficient becomes a nonlinear function of the incident intensity. On the other hand, if the frequencies are far apart, the medium behaves like a Kerr-type material and the system exhibits what is called dispersive bistability. In this case the material can be modeled by an effective n2 or v (3), meaning that the refractive index becomes a nonlinear function of the optical intensity. The second configurationwewill examine is a linear-nonlinear interface. In this case, the interface provides the feedback due to refractive index mismatch. In fact, the reflection coefficient (as well as the transmission coefficient) is modified due to the nonlinearity, which, as we shall see later, is responsible for demonstrating optical switching and bistability.
A possible new way to drive hybrid optical devices based on a differential two-channel feedback configuration is presented. To verify the feasibility and characteristics of this approach, comparisons between two-channel and single-channel arrangements are reported. Several analogies and differences in operating conditions are also proved. From the point of view of application possibilities, the optical image obtained of an optical pulse exhibits time-discrimination characteristics, whereas in the single-channel case it shows discriminated intensity levels. This fact can be profitably used in parallel image processing systems.
Gives a broad description of optical bistability: from practical applications, as an optical transistor or optical memory element, to its phase transition interpretation. The theory is divided into three parts. The first is a simple discussion that covers most of the basic experimental effects and concepts of practical importance. The second part applies to atomic system where a semiclassical as well as a quantum-mechanical approach is possible. The third one discusses the mechanisms compatible with large nonlinearities observed in InSb and GaAs as semiconductors constitute the most promising materials for applications. Current experimental progress in all-optical and hybrid devices is also discussed and scaling example is presented to indicate the possibilities in high-speed all-optical signal processing.
In Chapter 9 we discussed the case of a nonlinear cavity containing an active medium. In this framework, the outstanding phenomenon which arises is laser emission, and we calculated the stationary solutions for the ring laser. In this chapter, instead, we turn our attention to the passive nonlinear cavity and in this framework the outstanding phenomenon is optical bistability , i.e. the existence of two distinct stable stationary states that coexist for the same fixed values of the parameters in play. This phenomenon can arise also in the case of an active system contained in a cavity, as we have already noted in Section 9.1 and as we will discuss further in connection with the laser with injected signal, but it became popular from the studies of nonlinear passive optical cavities in the 1970s and 1980s. In contrast to the laser case, in the passive configuration we use an input coherent field, which is injected into the cavity. We discussed this case in Chapter 8 and derived a general equation for the transmission of the cavity (Eq. (8.23)), which we used for an empty cavity and for a linear cavity in Sections 8.4 and 8.5, respectively. In this chapter we will discuss the full nonlinear configuration. It is customary to identify two extreme cases of optical bistability called absorptive optical bistability and dispersive or refractive optical bistability . In both cases an essential ingredient to obtain the bistable behavior is the feedback action exerted by the mirrors of the cavity. In the purely absorptive configuration, in which there is exact resonance among the frequencies of the input field, of the atoms and of the cavity, the other essential ingredient is the saturable nonlinearity of the absorption. In the dispersive case, instead, the main feature is the nonlinearity of the refractive index. These two cases will be illustrated in Sections 11.1 and 11.2, respectively, both “exactly” and in the low-transmission limit.