Papers by Keyword: Extinction Ratio

Abstract: A second-order effective medium theory (second-order EMT) and thin film theory have been used to design a polarizing beam splitter (PBS) composed of one-dimensional sub-wavelength metal grating, considering the material of metal to be copper (Cu). It was analyzed by the finite difference time domain method for the wavelength of 1500nm. A high extinction ratio in transmission (>55.71dB) over abroad interval of angles of incidence ([-60o, 60o]) is achieved with the depth and the filling factor of the grating chosen to be 350nm and 0.3762, which are selected to transmit TM polarized light and reflect TE polarized light as much as possible at normal incident. The loss of the TE polarized light for the Cu structures is approximately less than 5.55% due to the absorption of Cu in a large angle range. The desired property will enable this type of polarizing beam splitter to be used in diverging beams. When the PBS needs to transmit approximately 25% of the TE polarized light and as much as possible the TM polarized light, it can be used in magneto-optical data storage head. But the depth of grating has been changed (approximately d=40nm) and TM transmission is only 94.7%. But it can be further improved (from 94.7% to 97.97%) by etching into the substrate.

Abstract: Cu-Al₂O₃ (Co-Al₂O₃) nano-array composite structures assemblies with Cu (Co) grown in the pores of an anodic alumina membrane (AAM) were obtained by alternating current electrode position. Their transmitted spectra and polarized spectra are systematically investigated. Experimental results indicate that the transmittance of Cu-Al₂O₃ is superior to that of Co-Al₂O₃ in visible and infrared waveband, but the extinction ratio of Co-Al₂O₃ is better than that of Cu-Al₂O₃ in near infrared waveband.

Abstract: During the measurement of a BOTDR system, it is significant to keep the extinction ratio of probe pulse uniform if constant sensing performance is desired. However the bias point of an electro-optic modulator (EOM) may slowly changes due to many external factors. Thus the variable bias point of the EOM must be stabilized. In this paper, a novel and simplified stabilization technique based on digital signal processor and step-by-step tracking algorithm is proposed. Contrast experiments with and without the stabilization are performed. The experimental results show that our method can lock the EOM’s bias point quite well and improve the sensing system’s performance obviously.

Abstract: Liquid crystal device (LCD) used as spatial gating apparatus has a lot of new using at low light detecting, imaging spectrum and so on. Since LCD's lattice characteristic, it can come true point gating, local field gating and whole surface gating. It can carry out point-by-point control and feedback of imaging cooperating with CCD detector. Some characteristics of we used LCD, LCX023CMT (SONY), have been detected in order to use conveniently, those include spectra transmittance and which’s changing with gating voltage. The results show that when incident wavelength more than 650nm, this LCD couldn't be used as spatial gating because of polaroid's extinction ratio becoming worse; LCD can modulate the incident light from 400 to 650nm, and the modulates of wavelength range, extent and linearity were related to the modulate voltage clearly. The results indicate that LCD modulates the incident light better and better at voltage more than 2.5V for 550nm; the action modulated become linear with voltage approximately; the modulate extent goes to saturation at voltage more than 5V, and the spectral range modulated is steady in 400-650nm. At voltage more than 5V, transmittance of spectrum is a horizontal beeline almost with incident wavelength range from 400 to 650nm. This indicates that transmittance of spectrum in this range is same, and liquid crystal has none selectivity in colored light. As a result, there is no chromatism between transmitted and incident light. However, because that there is lower transmittance, the reflected light can be used which can ensure not only effective using ratio of light, but also the consistency between reflected and incident light.