Interference (wave propagation)

About: Interference (wave propagation) is a research topic. Over the lifetime, 26086 publications have been published within this topic receiving 321110 citations.

Simultaneous measurement of RI and temperature based on the combination of Sagnac loop mirror and balloon-like interferometer

Abstract: A novel composite interference structure constructed with the combination of Sagnac loop mirror and balloon-like interferometer for simultaneous measurement of refractive index (RI) and temperature is proposed and experimentally demonstrated. A polarization maintaining fiber (PMF) is embedded into the Sagnac loop structure to form a Sagnac loop interferometer, which is highly sensitive to external temperature variations. The balloon-like structure is built with a bend single mode fiber (SMF) to form a modal interferometer, which is sensitive to both external RI and temperature variations. As the two sensing structures are based different interference principles, the two interference spectra do not interfere with each other. By optimizing the bending diameter of the balloon-like interferometer and the length of PMF in the Sagnac loop mirror, separate different resonance wavelengths can be well formed. Hence, the simultaneous measurement of RI and temperature can be realized by monitoring the shift of different resonance wavelengths. Experimental results show that the optimal sensitivities of the RI and temperature can reach up to 218.56 nm/RIU and 1.7 nm/°C, respectively.

An extrinsic Fabry?Perot interferometer-based large strain sensor with high resolution

Abstract: A three-layer packaged structure is proposed for an extrinsic Fabry?Perot interferometer-based optical fiber sensor in order to produce high resolution for large strains. The resolutions of three data processing algorithms including interference frequency tracking, period tracking and phase tracking are investigated and compared. Laboratory tests indicate that the proposed sensor structure can measure a strain of up to ?120?000 ?? (?12%) with resolution as high as 10 ??. The sensor prototype is insensitive to fiber misalignment, enabling the study of progressive structural failures with an integrated use of the three algorithms.

Parallel Data Transmission in Indoor Visible Light Communication Systems

Abstract: This paper presents an indoor visible light communication (VLC) system in conjunction with an imaging receiver with parallel data transmission (spatial multiplexing) to reduce the effects of the inter-symbol interference (ISI). To distinguish between light units (transmitters) and to match the light units used to convey the data with the pixels of the imaging receiver, we propose the use of subcarrier multiplexing (SCM) tones. Each light unit transmission is multiplexed with a unique tone. At the receiver, a SCM tone decision system is utilized to measure the power level of each SCM tone and consequently associate each pixel with a light unit. In addition, the level of co-channel interference (CCI) between light units is estimated using the SCM tones. Our proposed system is examined in two indoor environments taking into account reflective components (first and second order reflections). The results show that this system has the potential to achieve an aggregate data rate of 8 Gb/s with a bit error rate of 10–6 for each light unit, using simple on-off-keying (OOK).

Optical gap measuring apparatus and method using two-dimensional grating mark with chirp in one direction

Abstract: An apparatus and method of measuring the gap between one substantially planar object, such as a mask, and a second planar object, such as a substrate. The invention achieves a high degree of sensitivity, accuracy, capture range, and reliability, through a novel design of a mark located only on the mask-plate. The light is inclined to the surfaces so associated optical components do not interrupt the exposing beam used in lithography. The same optics are used as for aligning overlay. Each gapping mark on the mask-plate includes one or more two-dimensional gratings (1441, 1442), each with period constant in the incident plane, but varying in the transverse plane as shown in the enlargements (1443, 1444). When illuminated, two images are formed of each of the two-dimensional gratings, with fringes resulting from interference between paths having traveled different distances through the gap and the mask-plate as a result of successive diffractions and reflections. Phase and geometric measurements from these images yield accurate measurement of the gap between the plates. Direct calibration, referenced to the light-wavelength, is obtained from a diffractive Michelson technique that uses a linear grating also included within the gapping mark.

Cyclostationarity-based filtering for narrowband interference suppression in direct-sequence spread-spectrum systems

Abstract: This paper addresses the problem of narrowband interference suppression in direct-sequence spread-spectrum (DS/SS) techniques, which have been adopted to implement code division multiple access (CDMA) systems for wireless mobile communications. The theory of cyclic Wiener filtering, based on the cyclostationarity assumption for the signals involved in the reception problem, is applied to design single-channel adaptive frequency-shift filters which exploit both temporal and spectral correlation properties, i.e., the correlation between time- and frequency-shifted versions of the received signal. The numerical results show that receiving structures based on the proposed cyclostationarity-based interference suppression schemes largely outperform receivers that utilize conventional linear time-invariant suppressors, when they operate in highly contaminated interference environments.