| 摘要 |
<p>An optical filter comprises a volume diffraction grating (1) provided within a waveguide. The grating (1) 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, whilst 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.</p> |
