Modulators birefringent

Schematic diagram showing the integration of a polarization modulated birefringence apparatus within a laser Doppler velocimeter. This shows the side view. L light source (a diode laser was used) PSG rotating half-wave plate design LS lens FC flow cell (flow is into the plane of the figure) CP circular polarizer D detector 2D-T two dimensional translation stage 3D-T three dimensional translation stage LDVP laser Doppler velocimeter probe.

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.

The birefringent (BR) modulator makes use of polarized light and tensorial nature of the electrooptic coefficient. For example, poled organic polymer films are characterized by two nonzero components for the electrooptic tensor and parallel and orthogonal to the poling direction,... 

Compared to the Mach-Zehnder modulator, the modulation efficiency of the birefringent modulator is lower because is 1.5 times higher, ie,... 

In an electrooptic material the phase retardation angle is controlled by altering birefringence, which is in turn controlled by the potential of an apphed electric field. An electrooptic device thus acts as a variable phase optical retardation plate, and can be used to modulate the wavelength or intensity of an incident beam. 

The above description refers to a Lagrangian frame of reference in which the movement of the particle is followed along its trajectory. Instead of having a steady flow, it is possible to modulate the flow, for example sinusoidally as a function of time. At sufficiently high frequency, the molecular coil deformation will be dephased from the strain rate and the flow becomes transient even with a stagnant flow geometry. Oscillatory flow birefringence has been measured in simple shear and corresponds to some kind of frequency analysis of the flow... 

Birefringent (BR) LCDs, 15 115 Birefringent modulator, 17 446 Birkeland-Eyde process, 17 291-292... 

Sensitized for blue-green or red light, photoconductive polyimides and liquid crystal mixtures of cyanobiphenyls and azoxybenzene have been used in spatial light modulators [255-261]. Modulation procedure was achieved by means of the electrically controlled birefringence, optical activity, cholesteric-nematic phase transition, dynamic scattering and light scattering in polymer-dispersed liquid crystals. 

Fig. 33. Diffraction efficiency versus voltages for spatial frequencies in mm-1 10 (/), 28 (2), 51 (i). Switch on time versus voltages at spatial frequencies in mm"110 (/ ), 36 (2 ), 60 (S ). Commutational regime for polyimide-liquid crystal modulator with controlled birefringence [256]...

It is worth pointing out that in low-7(, PR materials with molecular birefringence as the dominant contribution to the index modulation, the real response time and the PR sensitivity can also be limited by the diffusion time of angular rotation of the chromophores under the drive of the space-charge field, and even the time constant xe for the formation of the space-charge field may be smaller [27],... 

The last requirement for a PR effect is the mechanism for index modulation in the response of the space-charge field. Two mechanisms have been found to lead to index change EO response and birefringence. 

Note that the index modulation from the EO effect in a low-7], material [Eq. 39] is about twice as large as that in a high-7 material [Eqs. (17) and (36)]. The total index modulation in a low-7], material is given by the sum of those from both birefringent and EO effects as in Eqs. (38) and (39). On a microscopic level, a new figure of merit for a PR chromophore is defined [38 10] ... 

Some of the most useful polarization-dependent NSOM methods, however, involve modulation of the polarization from the probe (see Figure 3.20),224 coupled with synchronous detection of the near-field signals. Such methods allow for multiple imaging modalities so that topography, absorption dichroism, and/or birefringence information can all be readily obtained. 

---