Birefringence control

W.N. Ye, D.-X. Xu, S. Janz, P. Cheben, M.-J. Picard, B. Lamontagne, and N.G.T. Tarr, "Birefringence control using stress engineering in sihcon-on-insulator (SOI) waveguides," IEEE J. Lightwave Technol. (in press, 2005). 

The refractive index must be precisely controlled because it is essential for optical components such as single-mode optical waveguides. This control can be achieved by copolymerization of low- and high-refractive-index polyimides. Birefringence control can be achieved by a film elongation technique using a particular polyimide. 

Yamaguchi, M., and Masuzawa, K. (2007). Birefringence control for binary blends of cellulose acetate propionate and poly(vinyl acetate), Eur. Polvm. L 43. 3277-32R2. 

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. 

Linearly polarized, near-diffraction-hmited, mode-locked 1319 and 1064 nm pulse trains are generated in separate dual-head, diode-pumped resonators. Each 2-rod resonator incorporates fiber-coupled diode lasers to end-pump the rods, and features intracavity birefringence compensation. The pulses are stabilized to a 1 GHz bandwidth. Timing jitter is actively controlled to < 150 ps. Models indicate that for the mode-locked pulses, relative timing jitter of 200 ps between the lasers causes <5% reduction in SFG conversion efficiency. 

As observed on a Mettler Hot Stage FP 52 with FP5 controller, the sample appeared as birefringent needle-like crystals which melted from 115-117°C. The sample did not recrystallize from the melt (5). 

Figure 13.5 Birefringence as a function of wind-up speed (a) A, PET control (b) A, PET containing 3% copolyester of 1,4-phenyleneterephthalate and p-oxybenzoate (c) O, PET containing 3% copolymer of 6-oxy-2-naphthalene and p-oxybenzoate [17]. From Orientation suppression in fibers spun from melt blends, Brody, H., J. Appl. Polym. Sci., 31, 2753 (1986), copyright (1986 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

Switchable birefringence film Supertwisted nematic (STN), ferroelectric (FLC), electrically controlled birefringence (ECB) displays... 

Accuracy in determining the melting temperature, Tm, is difficult to specify as the melting point of any sample depends on its thermal history. The accuracy of the birefringence experiment in determining the sample thickness is probably no better than 5% due to the limited control over the variables of the experiment. 

TF Systems A TF is a device whose spectral transmission can be controlled by applying a voltage or acoustic signal. There are two main TF devices acousto-optical TF (AOTF), based on diffraction, and liquid crystal TF (LCTF), based on birefringence. An AOTF is a transparent crystal in which an ultrasonic wave field is created,... 

Retardation matching Control of birefringence Film elongation... 

It is also possible for these copolyimides to control the refractive index because 6FDA/TFDB and PMDA/TFDB have largely different values. The refractive index and birefringence of the fluorinated copolyimides are described in detail in the next section. 

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]...

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