China
Africa
Explore chapters and articles related to this topic
Laser Beams, Polarization, and Interference
Published in Walter Fox Smith, Experimental Physics, 2020
We now consider two types of devices that can manipulate polarization: a polarizer and a wave plate. A linear polarizer, commonly just called a polarizer, absorbs the vector component of the electric field that is perpendicular to the transmission axis so that the transmitted light is linearly polarized, as shown in Figure 11.1. A wave plate is made from a birefringent crystal wherein the index of refraction that light experiences depends on the orientation of its polarization. Wave plates have the appearance of thin windows and do not absorb light. Rather, a wave plate introduces a relative phase delay between field components oriented along the slow axis and the fast axis, as shown in Figure 11.2. These two axes are associated with higher and lower refractive indices, respectively.
Vibrational Spectroscopy
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Peter Fredericks, Llewellyn Rintoul, John Coates
LIQUID CRYSTAL TUNABLE FILTERS. An LCTF also functions as an electronically tunable filter, but with considerably less wavefront distortion than the AOTF. LCTFs are polarization devices based on the principles of the Lyot filter. A three-stage Lyot filter is shown in Figure 7.23. Each stage consists of a birefringent waveplate oriented at 45° to, and sandwiched between, two parallel linear polarizers. The polarizers convert incoming light into plane-polarized light aligned at 45° to the fast axis of the waveplate, wherein it is decomposed equally into an ordinary wave and an extraordinary wave. The two waves travel with different velocities in the waveplate and recombine upon exit to produce a beam with modified polarization characteristics. The accumulated phase separation of the two beams is called the retardance, and is a product of the birefringence, Δn, and the thickness of the waveplate. Transmittance through the second polarizer only occurs when the retardance of the waveplate is a multiple of the wavelength. When this condition is met, the two beams will be in phase to combine to form plane-polarized light parallel to the exit polarizer.
Uniaxial Materials and Components
Published in Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young, Polarized Light and Optical Systems, 2018
Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young
Awaveplate is a common type of retarder formed from a plane parallel plate of birefringent material. Its function is to introduce retardance between its two orthogonal eigenmodes in the transmitted light. They are utilized to control polarized light, adjust ellipticity, rotate polarization, and even fine-tune laser wavelengths when used inside laser cavities. They are widely used in polarimetry, medical imaging, microscopy, telecom, and the laser cutting industry. Simple isotropic plane parallel plates cause focus shift and spherical aberration on-axis and add coma and astigmatism off-axis due to the variation of the optical path length with angle.17The aberrations of the retarder’s ordinary wave are the same as for the isotropic plate. The aberrations of the extraordinary wave are more complicated because they include all the isotropic aberrations as well as additional aberrations arising from the variation of refractive index with direction. These aberrations and their effect on image formation will be calculated from polarization ray tracing.
Accurate optical fiber current transducer for high-voltage direct current (HVDC) transmission
Published in Instrumentation Science & Technology, 2022
Haifeng Liu, Hongjie Guo, Manqing Tan, Qin Li, Xiangqiang Meng, Xu Yang
The optical fiber current sensing system is shown in Figure 2. A broadband light source such as a super-luminescent diode (SLD) emits a low polarized light wave. The light wave propagates through the single-mode coupler and the polarizer and is converted to a highly polarized light wave. The light wave is changed to two orthogonal linearly polarized light waves when propagating through the 45° spliced point. The two light waves are modulated by the electro-optic modulator and propagate through the delay fiber coil. The phase modulator is used to make the phase difference between the two polarized lights. It is necessary to convert linearly polarized light into circularly polarized light and back in order to suppress the amplitude polarization error and intensity polarization error of light wave in reflective optical fiber current transformer. The delay fiber coil provides sufficient time for the modulating cycle. The quarter wave plate converts two orthogonal linearly polarized light into left and right circularly polarized light. The phase angle of the two circularly polarized light shifts under the influence of the magnetic field generated by the current.[16,17] The two lights are reflected by the mirror and again propagate to the quarter wave-plate. The two circular lights with phase shifts are converted to two linearly polarized light waves by the quarter wave-plate and the two circular beams are converted to a linearly polarized light wave with a polarized rotation angle in the 45° spliced point. The linearly polarized light of the two orthogonal modes interferes at the polarizer. The light carrying the phase information is converted into an electrical signal by the photodetector and sent to the signal processor to realize the current detection.[18] A field programmable gate array (FPGA) collects the digital signals of the light intensity change with the analog-to-digital (AD) converter and demodulates the desired current. The output is described by