The invention relates to a photonic circuit for attenuating the amplitude of an optical signal, comprising a Mach-Zehnder interferometer for coupling an input waveguide (14) and an output waveguide (15), said interferometer comprising a modulation section (SM1) which includes a first waveguide (11), a second waveguide (12) and a phase shifter (13) configured to introduce a phase difference between a first optical signal circulating on the first waveguide and a second optical signal circulating on the second waveguide.
The first and second waveguides are arranged in two distinct parallel layers and the phase shifter is a thermo-optical phase shifter arranged to preferentially act on one of the first and second waveguides.