Enhanced diffraction of light in GaAs microcavities

Abstract

We analyze theoretically the diffraction of light by gratings that are photogenerated in Fabry-Pérot microcavities. The coupled wave theory of volume gratings is combined with appropriate boundary conditions to yield expressions for the diffraction efficiency. Multiple round trips within the cavity are seen to increase the effective grating thickness, and therefore the efficiency. Numerical calculations specific to GaAs microcavities show that the diffraction efficiency can be enhanced by more than two orders of magnitude at the resonant wavelengths.

Photodiffraction in InGaAs/InGaAsP multiple quantum wells enclosed in a microcavity

“…2 are the results of a model based on Kogelnik's coupled wave theory [4] and extended to gratings in a resonant structure by Collet et al [1]. The index of refraction, n, and the amplitude of the index variation, n, are parameters which are adjusted for each fringe in order to fit the data.…”

“…This is accurate when the following conditions are met: (i) both inter-and intraband transitions are taken into account; (ii) the valence and conduction bands are parabolic; (iii) thermal equilibrium between the carriers; and (iv) the variations in the densities of electrons and holes are equal. The diffraction efficiency in the reflection geometry of a grating in a cavity depends on n and α as follows [1]:…”

“…A MQW structure was chosen for the active medium because of its enhanced nonlinear optical properties compared to the bulk material. The idea of using a microcavity is to increase the diffraction efficiency [1]. When a resonant wavelength is used during readout, multiple reflections increase the effective thickness; thus the diffraction efficiency increases.…”

Bragg thickness criterion for intracavity diffraction gratings

“…The lowest-order development of I Ϫ1 FP can also be related to the sample length at Fabry-Perot resonance l m and compared to the development of the transmitted intensity diffracted by a sample with no mirror at all, I Ϫ1 nomir , to introduce an effective interaction length 10 that is due to the Fabry-Perot cavity:…”

“…It has been shown [9][10][11][12] that one can overcome these limitations by putting the grating into a Fabry-Perot resonator. Strong improvement results when it is assumed that all the diffracted energy is concentrated into the main diffraction order.…”