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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Nonlinear switching mechanism in nanostructures doped in photonic crystals

Mahi R. Singh

Published Jun 21, 2007• 0 citations
Publisher

Abstract

We have investigated the nonlinear switching mechanism in nanostructures doped in photonic crystals. The nonlinear phenomenon studied in this paper is the two-photon absorption process. A probe laser field is applied between the ground state and the next excited state of the nanoparticles to measure the two-photon absorption spectrum. A coupling field is applied between the two excited states of nanoparticles to control the two-photon process. It is found that when the decay resonance energy lies away from the photonic band edge the inhibition of two-photon absorption is observed. However, when the probe field is not resonance, the inhibition of two photons absorption is not observed. An interesting result is observed when the decay resonance energy lies near the band edge. It is found that the inhibition of the two-photon absorption disappears. It means that the phenomenon of two-photon absorption can be switched on and off by tuning the resonance energy within the lower band of the crystal. This mechanism can be used to make a new type of photonic switching devices using photonic crystals.

DOI
10.1117/12.778766

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We have investigated the nonlinear switching mechanism in nanostructures doped in photonic crystals. The nonlinear phenomenon studied in this paper is the two-photon absorption process. A probe laser field is applied between the ground state and the next excited state of the nanoparticles to measure the two-photon absorption spectrum. A coupling field is applied between the two excited states of nanoparticles to control the two-photon process. It is found that when the decay resonance energy lies away from the photonic band edge the inhibition of two-photon absorption is observed. However, when the probe field is not resonance, the inhibition of two photons absorption is not observed. An interesting result is observed when the decay resonance energy lies near the band edge. It is found that the inhibition of the two-photon absorption disappears. It means that the phenomenon of two-photon absorption can be switched on and off by tuning the resonance energy within the lower band of the crystal. This mechanism can be used to make a new type of photonic switching devices using photonic crystals.
A possible switching mechanism has been investigated for nonlinear photonic crystals doped with an ensemble of non-interacting three-level nanoparticles. In this scheme, an intense pump laser field is used to change the refractive index of the nonlinear photonic crystal while a weaker probe field monitors an absorption transition in the nanoparticles. In the absence of the strong laser field the system transmits the probe field when the resonance energy of the nanoparticles lies near the edge of the photonic band gap due to strong coupling between the photonic crystal and the nanoparticles. However, upon application of an intense pump laser field the system becomes absorbing due to a band edge frequency shift that arises due to a nonlinear Kerr effect which changes the refractive index of the crystal. It is anticipated that the optical switching mechanism described in this work can be used to make new types of photonic devices.
A theory of the nonlinear two-photon absorption has been developed in a photonic crystal doped with an ensemble of four-level nanoparticles. We have considered that the nanoparticles are interacting with the photonic crystal. An expression of two-photon absorption has been obtained by using the density matrix method. The effect of the dipole–dipole interaction has also been included in the formulation. Interesting new phenomena have been predicted. For example, it is found that the inhibition of two-photon absorption can be turned on and off when the decay resonance energies of the four-level nanoparticles are moved within the energy band.
A theory of nonlinear phenomena has been developed for a photonic crystal in the presence of a pump and a coupling laser field. The crystal is doped with an ensemble of four-level nanoparticle impurities. It is considered that the impurity particles are not only interacting with the photonic crystal but also with each other via dipole-dipole interaction. An expression for the susceptibility has been obtained using the density matrix method. The nonlinear effects due to the coupling and the pump fields have been included in the formulation. The absorption spectrum has been calculated in the presence of the strong coupling and pump fields for an isotropic photonic crystal made from dielectric spheres. The photonic crystal has a gap to midgap ratio of about 21%. It is predicted that the absorption spectrum in the photonic crystal can have zero, one, two or three absorptionless states by tuning one of the transition energies within the bands. This is an interesting phenomenon which can be used to make photonic switching devices. We have also calculated the absorption spectrum in the presence of the dipole-dipole interaction. It is found that a symmetric absorption spectrum changes to an asymmetric one due to this interaction. It is also found that there is a large enhancement in the absorption and the dispersion simultaneously for certain values of the detuning and concentration.
We study the two-photon switching mechanism in photonic crystal nanowires doped with an ensemble of nanoparticles. Nanowires are made from embedding one crystal into another. The energy spectrum of the embedded crystal is higher than that of the outer photonic crystal. The nanoparticles are interacting with bound states and with each other. The photon absorption coefficients have been calculated in the presence of a probe and a pump laser fields. Two transparent and absorption states are found. We anticipate that the present research can be used to make new types of all-photonic devices.
In this work, the absorption coefficient of a metallic photonic crystal doped with nanoparticles has been obtained using numerical simulation techniques. The effects of quantum interference and the concentration of doped particles on the absorption coefficient of the system have been investigated. The nanoparticles have been considered as semiconductor quantum dots which behave as a four-level quantum system and are driven by a single coherent laser field. The results show that changing the position of the photonic band gap about the resonant energy of the two lower levels directly affects the decay rate, and the system can be switched between transparent and opaque states if the probe laser field is tuned to the resonance frequency. These results provide an application for metallic nanostructures in the fabrication of new optical switches and photonic devices.
We study a dielectric catastrophe in a new class of materials called nanophotonic quantum wires. They are made from two types of photonic crystals where one is embedded in the other. It is considered that the embedded crystal is made from nonlinear dielectric spheres. The wire is doped with an ensemble of nanoparticles which are interacting with each other via the dipole‐dipole interaction. The absorption coefficient of the wire has been investigated in the presence a weak probe laser and a strong pump laser. The probe field measures the absorption spectrum and the pump field changes the refractive index of nonlinear photonic crystals due to the Kerr effect. The density matrix method is used to calculate the absorption coefficient. Numerical simulations have been performed for the dielectric constant and the photon bound states. It is found that the dielectric constant of the system has a singularity when the resonance energy of a nanoparticle lies near the bound photon states of the wire. This is known as the dielectric catastrophe. This phenomenon can be used to make all‐optical switching devices.