Analysis of bistability at the coupling between waveguide and whispering gallery modes of a nonlinear hemicylinder

The optical bistability caused by the coupling between modes of the parallel-plate waveguide and a nonlinear hemicylindrical crystal is studied using theoretical and numerical analysis. In such a system a waveguide channel is parallelly coupled to whispering gallery modes of a hemicylindrical microresonator ensuring bistable behaviour at input intensities of the order of a few MW/cm2. The characteristic minimum switching time of the system (around 30 ps) can be controlled by varying the thickness of the metal layer which couples the waveguide and whispering gallery modes. This is conditioned by the change of the quality Q-factor, as well as the coupling coefficient of the resonator. The main advantages of the system are fabrication simplicity, small sizes of the order of 3 µm and the possibility of adjusting the processes by making use of the electro-optical effect.

Tailoring Optical Bistability In Nonlinear Photonic Crystals Based on Metallic Nanoparticles And Graphene

In this work, we revisit the optical response of a one-dimensional photonic crystal consisting of graphene monolayers and a plasmonic nanocomposite as a defect layer in the structure. By taking advantage of the modified transfer matrix approach, the analytical solution of the light transmission and field distribution of the photonic crystal are evaluated. Besides, by considering one of the layers as a Kerr-nonlinear medium, we delve into optical bistability phenomenon in the model for two different cases. Our numerical results reveal that the proposed photonic crystal can enhance the field distribution and reduce the optical bistability’s threshold in comparison to the conventional photonic crystals. Furthermore, the optical bistable switch-up and switch-down thresholds of the proposed resonator can be tailored flexibly by plasmon-plasmon interactions in the defect layer. Finally, the electric field distribution amelioration and optical bistability by means of graphene layers in the structure are attainable. The influences of the parameters such as the graphene and the nanocomposite on the performance of OB are analyzed and compared in the two different cases. Therefore, present approach can lay the groundwork for designing highly sensitive surface plasmon resonance biosensors and switches where the proposed technique may find unprecedented capabilities.

Saturable absorption and its consequent effects in bistable erbium‐doped fiber ring laser

The linear absorption in erbium-doped fiber contributes to its excellent role in erbium-doped fiber amplifiers and lasers. A nonlinear optical contribution in the absorption of erbium-doped fiber is responsible for optical bistable action when it is present in a laser cavity. To quantify this effect, the variation of absorption coefficient is measured at different signal powers at multiple wavelengths in the C-band for different EDF lengths, and saturable absorption parameters such as the saturation power are extracted. Then the modification in the output characteristics of erbium-doped fiber ring laser with change in fiber length and in the presence of self-induced saturable absorption effect within the gain medium which leads to optical bistability is measured. By comparing the measured parameters obtained from saturable absorption in erbium-doped fiber and optical bistability in erbium-doped fiber ring laser, we estimated the length of the gain medium which acts as the saturable absorber inside the cavity of the laser. This is useful in constructing bistable lasers with optimized conditions. The temporal evolution of cavity loss and gain with the intra-cavity power and up- and down-thresholds helps in understanding why the down-threshold will be lesser than the up-threshold in bistable laser systems.

Controllable optical bistability based on rotation in semiconductor micro-cavity

In this paper, we discuss a possibility to realize the optical bistability in a rotating semiconductor micro-cavity system. To study the mean cavity photon number profile, we have obtained stationary solution by solving Heisenberg–Langevin equations of motion. In a rotating semiconductor micro-cavity system, bistability is observed when the cavity is driven externally in one direction but not the other direction. The bistable behavior is possible for strong coupling regime, and this can be controlled by hopping strength, decay rates and pump power. The photon profile also shows tunable zero intensity window. The system may be useful to design all-optical switch and optical flip–flop i.e., optical memory element, which would be faster in applications and compact in size.

OPTICAL BISTABILITY IN A DEGENERATE TWO-LEVEL EIT MEDIUM UNDER THE INFLUENCE OF AN EXTERNAL MAGNETIC FIELD: AN ANALYTICAL APPROACH

We investigate the behavior of optical bistability in a degenerate two-level atomic medium using an external magnetic field to separate the lower level into two distinct levels that both connect to an upper level by the probe and coupling laser fields. Based on analytical solutions, the absorption spectrum and behavior of optical bistability in an electromagnetically induced transparency regime under an external magnetic field are investigated. By controlling the external magnetic field, we find that the appearance and disappearance of the optical bistability can be easily controlled according to the strength of the magnetic field in the transparent window domain. Furthermore, the effects of the intensity of the coupling laser field and the parameters of the system on the behavior of optical bistability are also considered. The proposed model is useful for applications in all-optical switches and magneto-optic storage devices.