Modulation optical polarization

Fig. 1. Representative device configurations exploiting electrooptic second-order nonlinear optical materials are shown. Schematic representations are given for (a) a Mach-Zehnder interferometer, (b) a birefringent modulator, and (c) a directional coupler. In (b) the optical input to the birefringent modulator is polarized at 45 degrees and excites both transverse electric (TE) and transverse magnetic (TM) modes. The appHed voltage modulates the output polarization. Intensity modulation is achieved using polarizing components at the output.

As described above, there are two forms of vibrational optical activity, one derived from infrared absorption and the other from Raman scattering. Both forms involve the differential response of a molecule to the modulation of polarization of the interacting radiation between right and left circularly polarized states. In the case of infrared absorption, VCD is defined as die differential absorbance for left minus that for right circularly polarized infrared radiation. This is expressed by the relation ... 

The basic optical setup was shown in Fig. 12 [90]. The spectra were recorded on a commercially available spectrometer equipped with an external PM setup. The photoelastic modulator modulated the polarization of the IR light at a fixed frequency. Demodulation was performed with a lock-in amplifier and a low-pass filter. After the IR beam passes through the polarizer and modulator, it is focused on the sample, then focused on an mercury-cadmium-telluride (MCT) detector cooled by liquid nitrogen. 

Plastics doped by atomic clusters of ferromagnetic metals show magnetooptical properties (i.e., when subject to a strong magnetic field, they can rotate the vibration plane of a plane-polarized light), and therefore they can be used as Faraday rotators. These devices have a number of important optical applications (e.g., magnetooptic modulators, optical isolators, optical shutters, etc.). 

The photoelastic modulator is an optical element, which periodically modulates the polarization of the fight. It has to be aligned carefully, so that one of its optical axis is parallel to the direction of s polarization. To demonstrate... 

Cylindrically symmetric optical fibers are theoretically not birefringent, however, in practice bends and twists induce birefringence in optical fibers, which can modify the state of polarization of light in an unpredictable way as it propagates through the fiber. The performance of many devices used in optical fiber lasers (e.g., electro-optic modulators) is polarization-dependent, so it is often necessary to control the polarization state of light at some point in the fiber and/or compensate for unwanted birefringence. 

Chen, J. et al. (2004). Multi-port polarization-independent optical circulators by using a pair of holographic spatial- and polarization- modules. Optics Express, Vol. 12, pp. 601-608... 

Fig. 4 (a) The D1 transitions coupled by a fiequency modulated coupling field and two probe fields (one as the signal Qs and another as the control Qc) behaves as the coherently coupled three-level A-type system. The spontaneous decay rate of the excited state 3> is 73 (=271x5.4x10 s for the 5Pi/2 F =3 state), (b) Simplified diagram of the experimental set up. AOM acousto-optic modulator EOM electro-optic modulator, PMF polarization maintaining fiber X/4 quarter-wave plate DL extended-cavity diode laser, M mirror, D photodetector. 

Other demonstrated prototype devices include optical gyroscopes (144), broadband acoustic spectrum analyzers (145), 1x2 Y-fed directional couplers (146) and polarization-insensitive electrooptic modulators (147,148). For long-haul telecommimication applications, it is difficult to maintain polarization control thus, a need exists for polarization-insensitive modulators. Indeed, polarization insensitivity was one of the advantages claimed for gallium arsenide elec-troabsorptive modulators. By using different poling schemes, overall polarization insensitivity has been achieved for polymeric modulators (147,148). 

FIG. 1. The experimental arrangement BS, beam splitter VA, variable attenuator BSC, Babinet-Soleil compensator LC, liquid crystal AOM, acousto-optic modulator PR, polarization rotator P, Gian prism polarizer. 

The resulting films were characterized by FllK and UV-VIS spectroscopies before and after imidization. It was studied kinetics imidization at different temperatures. The results show that optimal conditions for imidization are temperature 300 °C for 1 h. It is known that azobenzene derivatives possess optical properties associated with optical anisotropy due to photoisomerisation photoorientation of azochromophore, perpendicular to the direction of the polarized beam. These properties of azobenzene derivatives are important for their application in nonlinear optics and nanotechnology, optical modulators, optical recording media and other devices [16,17,18,19]. 

Figure 1 Optical components of a typical MCD/CD Instrument. The modulator, now most commonly a piezoelectrically driven photoelastic device, converts linearly polarized light to a.c. modulated circularly polarized light.

The arrival of practical fiber optic communication networks has strengthened the need for more-efficient devices which are capable of routing or modulating optical signals. Such devices often rely on nonlinear optical effects such as the Pockels and Kerr effects which are second- and third-order phenomena, respectively. These effects arise as a result of the electric-field expansion for the electric polarization in a nonlinear medium ... 

In a motor-driven self-nuUing ellipsometer, the dc feedback currents are used to drive servomotors instead of being passed through the Faraday cell. As an alternative to the polarizer modulation described above, crystals with electro-optic effect (e.g., Pockels effect) can be used to modulate the relative phase retardation by an electric ac field. Independent modulations of polarizer... 

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