Optical filter with harmonic elements
AssigneeCorning Incorporated
InventorDaniel A. Nolan
Life of this patent
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Abstract
Optical interference filters are designed with harmonic elements that can be related to Fourier series approximations of desired filter responses. The harmonic elements can be fashioned as individual waveguides of an array arranged in various formats including planar or concentric geometries. The expansion coefficients of the Fourier series correspond to normalized power distributions among the waveguides, and the harmonic components of the series correspond to incremental optical path length differences between the waveguides.
Claims22
A phased-array interference filter for relatively attenuating selected spectral portions of a beam of light comprising:
- a single optical input and a single optical output joined by a plurality of individual optical pathways formed in a common planar optical waveguide;
- said optical pathways within the planar optical waveguide being arranged for conveying unequal portions of the beam's power;
- said optical pathways having unequal optical path lengths differing from one another as multiples of a common number for relatively shifting phases of the unequal beam portions;
- an input optical coupler that connects the single input to the plurality of pathways in the planar optical waveguide for dividing the beam into the unequal beam portions;
- and
- an output optical coupler that connects the plurality of pathways in the planar optical waveguide to the single output for recombining the phase-shifted beam portions to attenuate selected spectral portions of the beam by interference.
A coaxial interference filtering system that divides a beam of light into concentric beam portions that transverse different optical path lengths and recombines the concentric beam portions to interfere with each other to approximate a predetermined spectral response in which (a) single input and output optical pathways are coupled to opposite ends of a coaxial array of waveguide rings that are arranged for apportioning optical energy between the beam portions in accordance with relative magnitudes of a series of harmonic functions and (b) the waveguide rings have different optical path lengths equated to periods of the harmonic functions.
A method of designing an optical interference filter to approximate a predetermined spectral response comprising the steps of:
- representing the predetermined spectral response with a Fourier series of harmonic functions having a form of:
- F out = α 0 + ∑ m = 1 n α m exp [ m j β Δ z ]
- where “Fout” is the spectral response of the filter, “α0” and “αm” are the Fourier coefficients corresponding to the magnitudes of each of “m” numbered harmonic functions, “j” is an imaginary number, and “β Δz” is a period of the harmonic functions;
- converting the magnitudes “α0” and “αm” of the harmonic functions into relative amounts of power in each of “m” numbered optical pathways through the filter;
- and
- converting the periods “β Δz” of the harmonic functions into an incremental difference in optical path length between the optical pathways for producing a filter with a spectral response that at least approximates the predetermined spectral response.
A phased-array interference filter for modifying spectral characteristics of a multi-wavelength beam of light comprising:
- a waveguide array including a plurality of individual optical waveguides formed in a common planar waveguide having different optical path lengths;
- at least one optical coupler connecting the waveguide array between a single input waveguide and a single output waveguide;
- the waveguides of the array being sized and positioned in relation to each other for conveying unequal portions of a total optical power of the beam;
- the waveguides of the array having optical path lengths that differ from one another by a multiple of a given optical path length difference;
- and
- the at least one optical coupler recombines the unequal beam portions at the single output waveguide to attenuate selected spectral portions of the multi-wavelength beam by interference.
Dependencies are inferred from the claim text.