| CPC G02B 27/4244 (2013.01) [G02B 26/0833 (2013.01)] | 10 Claims |
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1. A tunable filter, comprising:
an optical input/output unit;
a first mirror having a first reflective surface disposed to reflect input light from the optical input/output unit;
a transmissive diffraction grating disposed on a propagation path of the input light reflected by the first mirror;
a second mirror having a second reflective surface disposed to reflect transmitted diffracted light from the transmissive diffraction grating corresponding to the input light, and
an optical element disposed between the first mirror and the transmissive diffraction grating, that suppresses wavelength dependency of a full width at half maximum of the tunable filter and has an apex angle optimized by simulation,
wherein
the first reflective surface is a variable-angle reflective surface,
the second reflective surface has a fixed orientation relative to the transmissive diffraction grating,
the angle of the first reflective surface determines an incidence angle of the input light reflected by the first mirror on to the transmissive diffraction grating,
the incidence angle determines light of a defined wavelength band, among the transmitted diffracted light, that is reflected at the second reflective surface so as to be propagated down a regular path, and
the light of the defined wavelength band reflected at the second reflective surface is propagated on a path heading toward the optical input/output unit as the regular path and output from the optical input/output unit.
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