Directional couplers model

In this section, the interaction length of a directional coupler is determined by substituting the refractive index of the NLO polymer into several dielectric strip waveguide directional coupler models. Driving the separation between the waveguides to zero allows us to determine the interaction length of the zero-gap directional coupler. 

The forward and reflected electric power is measured in continuous wave (CW) mode before the exposures using a digital power meter (HP Model) and a dual directional coupler (Werlatone Model C1373). 

The subscript C/ in (4.1.45) stands for unitary since the system Hamiltonian is invariant under general unitary transformations in case all antiunitary symmetries are broken. The effects of time reversal symmetry breaking on the level statistics were recently investigated experimentally by So et al. (1995) and Stoffregen et al. (1995) by measuring the resonance spectrum of quasi-two-dimensional microwave cavities in the presence of time reversal breaking elements such as ferrites and directional couplers. These experiments are of considerable relevance for quantum mechanics since quasi-two-dimensional microwave cavities are generally considered to be excellent models for two-dimensional quantum billiards. 

Extensive treatment of optical waveguide and directional coupler theory has been addressed by many researchers for both continuous two-dimensional film waveguides and dielectric strip waveguides. Various methods, such as dielectric waveguide, coupled-mode theory, effective index, the beam propagation method, and finite-element analysis, have been used [15,24,25,75,77,78,83,89-114]. Analysis of these methods shows good agreement between all of the different models. 

Electro-optic modulators and directional couplers using NLO polymers have been modeled, fabricated, and/or analyzed extensively over the years by many researchers [4,7,8,21,22,35,36,39-43,45-70]. The EO coefficients for various NLO polymers have been measured by several researchers as well [3,4,21,22,41-43,45-70,124]. 

FIGURE 16 Beam propagation model of passive zero-gap directional coupler using NLO and passive polymers with matching indices. 

We now describe an instrument using monomode fibre and an integrated fibre coupler, that therefore has no breaks in the transmission path due to the insertion of bulk optical components. Back reflection of a portion of the incident beam from the output port means that we detect a mixture of scattered light and a "reference beam", the so-called heterodyne detection scheme in which the first order correlation coefficient g( )(T) is measured directly. The signal is detected by a photomultiplier and processed by a multibit correlator. The fibre end is available to use directly as a probe into a dispersion or may be,mounted in a thermostatted flow cell. Results will be presented showing the performance on model systems as a function of concentration. The use of such an instrument for remote sensing in a variety of applications will be discussed. 

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