| 摘要 |
Apparatus for filtering optical radiation, which apparatus comprises a waveguide (50), and which waveguide (50) comprises a grating (51) having a first reflection wavelength band (52) having a first average wavelength (53) and a first group delay (54), and a second reflection wavelength band (55) having a second average wavelength (56) and a second group delay (57), wherein the first group delay (54) and the second gorup delay (57) are different in at least a portion of the second reflection wavelength band (55).
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