Kyuman Cho
Sogang University, South Korea
Title: A high performance I/Q-interferometer using a polarizing beam displace and its application to resolution refractive index sensor
Biography
Biography: Kyuman Cho
Abstract
It has been shown that an I/Q-interferometer can be used for measuring refractive index of a liquid or liquid mixture flowing through fluidic channels. We recently developed a new I/Q-interferometer which may be ideal for fluidic channel measurements because of its simple optical arrangement and capability of adjusting beam separation. A schematic of optical arrangement is shown in the image. The polarizing beam displace (PBD) is a modified polarizing beam splitter for which the two output faces are angle polished to make two orthogonally polarized output beams from the polarizing beam splitter parallel to each other. The output beams are circularly polarized with opposite handedness are making double pass through the corresponding liquids in the fluidic channels by use of the mirror coated on the backside of the fluidic channel. The phase difference and amplitude difference between the returning two beams are induced by the corresponding liquids in the fluidic channels. After making double pass in the quarter-wave plate, the plane of polarization of the two beams are rotated by 90o and combined at the PBD. The combined beam is output through the remaining port of the PBD and sent to the I/Q-demodulator. The phase difference and amplitude difference are measured simultaneously by using either a homodyne or a heterodyne I/Q-demodulator. We had shown that a heterodyne I/Q-interferometer with more complicated optical arrangement can measure 1´10-8 refractive index difference between liquids in the reference and probe channel. Our new arrangement can provide a better sensitivity because not only it has a fewer number of optical components but also the system can be integrated into a small size device. In the sample channel, reference fluid and sample fluids can be flown through an alternating way. Phase measurements across consecutive liquid flow and unwrapping measured phases allow a precision measurement of refractive index difference between two liquids.