Topic
Diffraction grating
About: Diffraction grating is a research topic. Over the lifetime, 24884 publications have been published within this topic receiving 372437 citations. The topic is also known as: grating.
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TL;DR: A novel method that realizes simultaneous and completely discriminative measurement of strain and temperature using one piece of Panda-type polarization-maintaining fibre is presented and it is found that the Brillouin frequency shift and the birefringence have the same signs for strain-dependence but opposite signs for temperature-Dependence.
Abstract: This paper presents a novel method that realizes simultaneous and completely discriminative measurement of strain and temperature using one piece of Panda-type polarization-maintaining fibre. Two independent optical parameters in the fiber, the Brillouin frequency shift and the birefringence, are measured by evaluating the spectrum of stimulated Brillouin scattering (SBS) and that of the dynamic acoustic grating generated in SBS to get two independent responses to strain and temperature. We found that the Brillouin frequency shift and the birefringence have the same signs for strain-dependence but opposite signs for temperature-dependence. In experiment, the birefringence in the PMF is characterized with a precision of approximately 10(-8) by detecting the diffraction spectrum of the dynamic acoustic grating. A reproducible accuracy of discriminating strain and temperature as fine as 3 micro-strains and 0.08 degrees Celsius is demonstrated.
274 citations
TL;DR: In this article, a novel approach to grating writing in optical fibres is described, which involves writing the grating point by point through the side of the fiber using a UV laser source.
Abstract: A novel approach to grating writing in optical fibres is described. This method involves writing the grating point by point through the side of the fibre using a UV laser source. Efficient mode conversion between forward propagating modes is demonstrated. The wavelength at which conversion occurs is determined by the periodicity of the grating. The grating can be designed to couple light at any wavelength of interest.
274 citations
Patent•
12 Feb 2002
TL;DR: In this article, an alignment accuracy between two or more patterned layers is measured using a metrology target comprising substantially overlapping diffraction gratings formed in a test area of the layers being tested.
Abstract: Alignment accuracy between two or more patterned layers is measured using a metrology target comprising substantially overlapping diffraction gratings formed in a test area of the layers being tested. An optical instrument illuminates all or part of the target area and measures the optical response. The instrument can measure transmission, reflectance, and/or ellipsometric parameters as a function of wavelength, polar angle of incidence, azimuthal angle of incidence, and/or polarization of the illumination and detected light. Overlay error or offset between those layers containing the test gratings is determined by a processor programmed to calculate an optical response for a set of parameters that include overlay error, using a model that accounts for diffraction by the gratings and interaction of the gratings with each others' diffracted field. The model parameters might also take account of manufactured asymmetries. The calculation may involve interpolation of pre-computed entries from a database accessible to the processor. The calculated and measured responses are iteratively compared and the model parameters changed to minimize the difference.
265 citations
TL;DR: In this paper, the authors describe a phenomenon in which a gratinng with very shallow grooves absorbs virtually all of the light of a given wavelength which is incident upon it.
265 citations
TL;DR: The coupler principle is based on gradual modification of the waveguide mode effective index by the SWG effect that at the same time frustrates diffraction and minimizes reflection loss and advantages of the proposed coupling principle for fabricating 3D coupling structures are discussed.
Abstract: We propose a new method for mode conversion and coupling between an optical fiber and a sub-micrometer waveguide using a subwavelength grating (SWG) with a period less than the 1st order Bragg period. The coupler principle is based on gradual modification of the waveguide mode effective index by the SWG effect that at the same time frustrates diffraction and minimizes reflection loss. We demonstrate the proposed principle by two-dimensional Finite Difference Time Domain (FDTD) calculations of various SWG structures designed for the silicon-on-insulator (SOI) platform with a Si core thickness of 0.3 microm. We found a coupling loss as small as 0.9 dB for a 50 microm-long SWG device and low excess loss due to fiber misalignment, namely 0.07 dB for a transverse misalignment of +/-1 microm, and 0.24 dB for an angular misalignment of +/-2 degrees. Scaling of the SWG coupler length down to 10 microm is also reported on an example of a 2D slab waveguide coupling structure including aspect ratio dependent etching and micro-loading effects. Finally, advantages of the proposed coupling principle for fabricating 3D coupling structures are discussed.
264 citations