Optical filters
AssigneeBritish Telecommunications public limited company
InventorsGiles R. Chamberlin, David B. Payne, David J. McCartney
Life of this patent
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Abstract
An optical filter includes a volume diffraction grating provided within a waveguide. The grating has a thickness T sufficient such that when an optical beam R is incident on the grating from outside the waveguide, wavelengths at or near the Bragg wavelength for the grating are diffracted and coupled into the waveguide, all but the first order interferences being substantially eliminated, while wavelengths away from the Bragg wavelength pass through the waveguide substantially undiffracted. The grating pitch L may be varied to permit tuning of the filter response.
Claims9
An optical filter comprising:
- an optical waveguide within which is provided a volume diffraction grating of refractive index modulations,
- the grating having a thickness sufficient such that when an optical beam is incident on the grating from outside the waveguide, wavelengths at or near a predetermined Bragg wavelength for the grating are diffracted and coupled into the waveguide, all but the first order diffraction being substantially eliminated, while wavelengths away from the Bragg wavelength pass through the waveguide substantially undiffracted.
Apparatus for selectively diffracting optical signals of predetermined wavelength, said apparatus comprising:
- a volume diffraction grating disposed within an optical waveguide having a longitudinal axis along which said diffraction grating is also disposed;
- and
- optical input means for directing input optical signals including signals over a range of different wavelengths, into said waveguide at an acute, non-zero, angle with respect to a normal to said longitudinal axis;
- said diffraction grating having a sufficient thickness dimension transverse to said longitudinal axis to cause input optical signals of the said predetermined wavelength to be diffracted and to pass along said longitudinal axis within the waveguide while other input optical signals having other wavelengths are not so diffracted.
Method for selectively diffracting optical signals of predetermined wavelength, said method comprising:
- disposing a volume diffraction grating within an optical waveguide having a longitudinal axis along which said diffraction grating is also disposed;
- and
- directing optical input signals including signals over a range of different wavelengths, into said waveguide at an acute, non-zero, angle with respect to a normal to said longitudinal axis;
- providing a sufficient thickness of said diffraction grating transverse to said longitudinal axis to cause input optical signals of said predetermined wavelength to be diffracted and to pass along said longitudinal axis within the waveguide while other input optical signals having other wavelengths are not so diffracted.
Dependencies are inferred from the claim text.