Mach-Zender-interferometer

Electro-optic modulation (Pockels effect) using a poled polymer is shown schematically in Figure 5.33, where an optical signal confined in a wave-guide is modulated by the application of an external voltage, known as a Mach-Zender Interferometer. 

Modulators are needed to convert electrical signals into optical amplitudes or phase modulations. Polymeric waveguides may be more compatible with integrated optics owing to processing considerations, and will be much cheaper to manufacture. Routing switches, electrooptic shutters, and amplitude modulators are imponant components for optical communications networks. Directional couplers, mode sorters, and Mach-Zender interferometers (Figure 2) are representative of the specific device mechanisms. These devices can op-... 

Figure 2 Mach-Zender interferometer. The input light source (from the left) is split into two beams, A and B. An external voltage is applied across the bath for beam B, which changes the index of refraction of the medium. This alters the speed of the light in path B such that when the two beams are recombined, a phase mismatch is introduced. The voltage thus introduces a modulation signal into the light beam.

Figure 19. Bragg-Grating-based tap/combiner (add/drop filter). Input signals (X4-X8) are coupled to Mach-Zender interferometers with Bragg grating. X4 is reflected to tap 2. All others exit through port 4.

A neutron reflectometer utilizes the optical phenomenon that neutrons incident on the material surface undergo refraction and reflection if the refractive indices on each side of the surface interface are different. A neutron interferometer using a perfect silicon crystal is analogous to the Mach-Zender interferometer of classical optics. The neutron wave amplitude coherently split by the Bragg reflection is superposed again at the second beam splitter and... 

Fig. 3.11 (A) Single-photon interference in a Mach-Zender interferometer with equal arms. BSl and BS2 are beam-splitters with coefficients Ct and for transmission and reflectirai, respectively (ICrl = Cr = 1/2) Ml and M2 are mirrors (100% reflecting) and D and D2 are photoncounting detectors. The dependence of photon wavefunction If on time and the distance along the optical path is not indicated explicitly. If BS2 is removed, or if either path is blocked before BS2, photons are detected at D1 and D2 with equal probability but when BS2 is presem and both paths are open, photons are detected only at Dl. (B) Two-photon quantum interference. Short pulses of light with frequency v are focused into a crystal with nonlinear optical properties (XTL). This...

It is found by studying thin slices on the Mach-Zender interferometer by the method from ref. [30] that providing for high jump of RI and elimination of RID profile deformation demand combination of profile diffusional formation with its fixing. 

Refractive indices of initial polymers were measured according to ref [136], Variation of the refractive index was measured on the Mach-Zender interferometer with... 

Fig. 7 Equivalent Mach-Zender arrangement of an intermodal interferometer or two cascaded LPGs...

Spectral characteristics of intermodal interferometers. An intermodal interferometer has a cosine response. In the case of cascaded LPGs, the spectrum of a single LPG is periodically modulated by the intermodal sine response. So, instead of a broad spectral dip, we have several spikes which are narrower and, thus, wavelength shifts can be detected with greater precision. There are two schemes for intermodal interferometers the Mach-Zender arrangement and the Michelson arrangement. In the latter, only one splice or LPG is used in combination with a mirror, as shown in Fig. 7b. The light thus traverses the two-mode area twice. 

The other interrogation schemes are based on the use of linear filters, matched gratings, interferometers (Michelson, Mach-Zender, Fabry-Perot), and CCD arrays in combination with diffraction gratings. The best resolution attainable after averaging is about 1 pm. LPGs, however, have a wider spectrum and their wavelength shifts are detected with smaller resolution. 

For immersion into liquids, however, a Michelson arrangement is more suitable. The response of a LPG-based Michelson interferometer to concentration changes of glycerol in water (corresponding to SRI changes fi om 1.33 to 1.45) has been reported by Brakel [3] (Fig. 18) and is similar to that of the Mach-Zender arrangement studied by Allsop et al., but the accumulated phase is twice smaller. 

LPGs based intermodal interferometers in Michelson and Mach-Zender arrangement have been shown to offer even greater sensitivities, but for the moment, their full potential appears to be underexploited. 

Among these methods, the most applicable is the method 1, because of its accuracy, universality, obviousness, ease of mathematical processing of experimental data obtained, and ability for reproduction. Most often applied to measurements is the method of a fine slice using the Mach-Zender mirror (double-beam) interferometer (Figure 1) [14, 27]. 

The physical model for studying formation of the refractive index distribution of selfocs may be described in the following manner. In the initial stage, in order to obtain a gel-matrix, polymerization is performed not in a tube, but between two glass plates with a thin (100 - 200 pm) polyethylene layering between them. A round hole is cut off in the layer, in which the component A is installed. When the initial stage is finished, the polyethylene layer is removed, and the plate together with clamped gel-polymeric tablet is placed in a cuvette with the component B. The whole system is thermostatically controlled and placed into one of the shoulders of the Mach - Zender laser interferometer [27]. 

---