Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1990-08-10
1992-06-09
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356345, 356361, 385 12, G01B 902
Patent
active
051201313
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an integrated optical interference method according to the preamble of claim 1.
Optical film waveguides consist of a thin waveguiding film of higher refractive index on a substrate of lower refractive index. Strip waveguides consist of a strip of higher refractive index on a substrate of lower refractive index or inlaid into the surface of said substrate. Also the superstrate with which the film or strip waveguide is covered has to have a lower refractive index than the film or strip waveguide. According to geometrical optics the optical waves are guided in film waveguides by total internal reflection in the plane of the film; in strip waveguides they are additionally also guided transversally. An important special case of the film waveguide is the planar waveguide where the substrate is planar.
According to wave optical or electrodynamical theory, optical waves propagate in waveguides in the form of guided modes which are characterized by their frequency .nu. or their vacuum-wavelength .lambda.=c/.nu.,their polarization, their transverse field distribution, and their phase velocity v.sub.p =c/N. Here c is the velocity of light in vacuum and N the effective refractive index of the mode. In planar waveguides the modes are designated according to their polarization as TE.sub.m -(transverse electric) and TM.sub.m -(transverse magnetic) modes. The mode number m=0,1,2, . . . denotes modes with different transverse field distributions. Also in strip waveguides, modes with different polarizations and transverse field distributions can propagate. The effective refractive indices N depend on the frequency .nu., the polarization, the mode number, and the properties of the waveguide, such as the refractive indices of the substrate, the superstrate, and the waveguiding film or strip, and the latters thickness and thickness and width, respectively. Light of the same frequency .nu. can propagate in a waveguide simultaneously in the form of modes of different polarization, for example, in a planar waveguide as TE.sub.m - and as TM.sub.M -modes with the same mode number m=0,1, . . . . The effective refractive indices N(TE.sub.m) and N(TM.sub.M) differ from each other.
In integrated optical two beam interferometers according to the prior state of the art, as the Michelson- or Mach-Zehnder-interferometer, a guided wave or mode is with a beam splitter divided up into two partial waves 1 and 2, which propagate along different paths and are superimposed by a beam recombiner. Beam splitter and recombiner can in planar waveguides be realized, for example, by gratings, and in the case of strip waveguides by 3dB-couplers. The partial waves 1 and 2 interfere with the phase difference .phi..sub.1 -.phi..sub.2 =(2.pi./.lambda.)[.sub.1 N ds-.sub.2 N ds], where the integral .sub.j N ds with the incremental path element ds is the path integral over the effective refractive index N on the path of the partial wave j=1,2 and the expression in the bracket is the optical path difference. The intensity at the output port of the interferometer is -.phi..sub.2). (1) interference fringes, i.e., the maxima and minima of the intensity I, the values of the phase difference .phi..sub.1 -.phi..sub.2 can be determined as integers of 2.pi. and of .pi., respectively.
With an integrated optical interferometer according to the prior state of the art changes of the effective refractive index N can be measured, if either the geometrical path lengths in the two legs of the interferometer are chosen to be of different lengths, or if N is changed in one leg only but remains constant in the other leg. Integrated optical interferometers according to the prior state of the art have the disadvantage of being expensive; their fabrication is complicated since microstructures have to be very precisely produced.
The object of the present invention is to provide an integrated optical interference method for the selective detection of substances in liquid or gaseous samples, and/or for the measurement of chan
REFERENCES:
patent: 4932783 (1990-06-01), Kersey et al.
patent: 4940328 (1990-07-01), Hartman
patent: 4950074 (1990-08-01), Fabricius
"Polarization Fluctuations in Optical Fibers Based on Probability", Imai et al., Optics Letters, Sep. 1987, pp. 723-725.
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