Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-07-28
2001-10-23
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
Reexamination Certificate
active
06307991
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of optical communications, and more particularly to devices and methods employing optical interference phenomena for differentially attenuating selected wavelengths of light to provide filtering for, e.g., gain flattening, as well as dispersion compensation and for other wavelength management purposes.
BACKGROUND
Interference filters rely on constructive and destructive interference to provide and shape filter responses. The interference is created by overlapping different phase-shifted portions of the same beam. The beam divisions are generally overlapping portions separated only by time (i.e., phase delay). However, the beams can also be divided spatially into transverse sections subject to different phase delays, which must be recombined to produce the required overlap.
Examples of interference filters with temporally separated beam portions include dielectric filters, Fabry-Perot etalons, Bragg gratings, long period gratings, and micro-optic devices. Most of these filters, particularly Fabry-Perot etalons and long period gratings, have limited response profiles and must be concatenated to produce more complex response profiles. For example, simple response profiles, such as Gaussian profiles, can be combined by conventional curve fitting techniques to approximate the desired response profiles, however, the multiple filter components can be cumbersome to assemble and are subject to both fabrication and assembly errors.
Co-assigned U.S. Pat. No. 5,841,583 to Bhagavatula entitled “Multi-path Interference Filter” discloses examples of interference filters with spatially separated beam portions. Complex response profiles can be supported by the multi-path filters, but fitting the filters' performances to desired response profiles is more difficult.
SUMMARY OF THE INVENTION
The present invention is directed to optical interference filters and filtering methods. It promotes a simplified design of optical interference filters for approximating a wide range of spectral responses. The filters include a series of harmonically related elements that can be combined to produce more complex periodic spectral responses. The harmonically related elements correspond to beam divisions distinguished by phase angles and optical power.
Many desired spectral response functions can be approximated by a series of harmonic functions (such as a Fourier series), and such a representation can be directly related to the physical design of an interference filter. According to an embodiment of the invention, the filter divides a beam of light into beam portions that traverse different optical paths lengths and that subsequently interfere with each other. Optical energy of the beam is apportioned between the beam portions in accordance with relative magnitudes of the series of harmonic functions, and the different optical path lengths are equated to periods of the harmonic functions.
In a preferred aspect of the invention, the filter has an array format composed of a series of individual waveguides, but other formats for dividing beams either spatially or temporally can also be directly related to such harmonic series. A Fourier series analysis of the desired response function, for example, can be converted directly into the physical characteristics of the filter array required to achieve the Fourier series approximation. The coefficients of the Fourier series convert directly into divisions of optical power among the waveguides, which can be accomplished by adjusting the position or the relative size of the waveguides in the beam field. The phase angle terms of the Fourier series representing integer multiples of a fundamental frequency convert directly into relative differences in the optical path lengths of the waveguides, which can be accomplished by adjusting the physical path lengths or the propagation constants of the waveguides.
In another embodiment, an interference filtering system provides a desired spectral response through beam division and apportionment and subsequent selective interference.
A further embodiment describes a phased-array interference filter for modifying the spectral characteristics of a multi-wavelength light beam, and includes a waveguide array having a plurality of optical waveguides with different optical path lengths, at least one optical coupler connecting the waveguide array to input and output waveguides wherein the waveguides of the array are sized and positioned in relation to each other for conveying unequal portions of the total optical power of the beam, and further wherein the waveguides of the array have optical path lengths that differ from one another by a multiple of a given optical path length difference.
Another embodiment of the invention describes a method of designing an optical interference filter to approximate a desired spectral response. An aspect of this embodiment involves representing the desired spectral response by a series of harmonic functions, converting magnitudes of the harmonic functions into apportionments of power among optical pathways through the filter, and converting periods of the harmonic functions into optical path length differences among the optical pathways.
REFERENCES:
patent: 5926298 (1999-07-01), Li
patent: 5930441 (1999-07-01), Betts et al.
patent: 6094513 (2000-07-01), Rigny et al.
patent: 6137939 (2000-10-01), Henry et al.
patent: 6141467 (2000-10-01), Doerr
patent: 6144783 (2000-11-01), Epworth et al.
patent: 0 724 173 A1 (1996-07-01), None
K. Okamoto et al., “Arrayed-Waveguide Grating Multiplexer With Flat Spectral Response”, Optics Letters vol. 20, No. 1, Jan. 1. 1995, pp. 43-45.
“Synthesis of Coherent Two-port Lattice-form Optical Delay-line Circuit”, K. Jinguji and M. Kawachi, Journal of Lightwave Technology, vol. 13, No. 1, Jan. 1995, pp. 73-78.
Agon Juliana
Corning Incorporated
Greener William
Ryan Thomas
Ullah Akm E.
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